Unconventional Yeast in the Bakery Industry: A Review

Abstract

The shift toward future-forward foods begins with subtle yet innovative alternatives—yeast among them, playing a surprising role in this transformation. Traditionally, Saccharomyces cerevisiae has dominated the bakery industry due to its reliable fermentation and predictable performance. However, rising demand for artisanal, nutritious, and eco-friendly baked goods has sparked interest in unconventional yeast species. This review highlights the potential of alternative yeasts such as Torulaspora delbrueckii, Candida milleri, Pichia anomala, and Yarrowia lipolytica to enhance bakery processes. These species possess distinctive metabolic traits, enabling the formation of complex aroma and flavour compounds—like esters, higher alcohols, and organic acids—that enrich bread’s taste and texture. Moreover, some strains offer nutritional benefits by synthesizing essential micronutrients, breaking down anti-nutritional phytates, and improving mineral and vitamin bioavailability. Their robustness under stress conditions, such as high sugar, salt, or temperature, and their ability to ferment diverse substrates further support their industrial appeal. Still, challenges persist: unconventional yeasts often exhibit weaker leavening capacity, greater sensitivity to processing, and loss of volatiles during baking. Even so, hybrid fermentations that blend conventional and unconventional yeasts show promise in enhancing both dough performance and end-product quality. Overall, the integration of these alternative yeasts represents a forward-looking approach in bakery, aligning with consumer preferences for health-conscious and sustainable options while offering opportunities for innovation and product differentiation.

1. Introduction

The bakery industry holds a significant position in the European economy, reflecting strong economic importance and high market demand. In 2020 alone, the European bakery sector generated an estimated revenue of €80 billion, highlighting its prominence within the food industry [1]. This economic footprint is driven by the enduring popularity of bread and other bakery products, which have long been staples in diets across various cultures and demographics [2]. Notably, the industry’s resilience has been tested by evolving consumer preferences for healthier and more innovative product offerings, contributing to steady growth in new product development strategies [3]. Studies indicate that the surge in home baking during health crises has revitalized interest in traditional baking techniques, influencing consumer behaviour [4]. Furthermore, small bakeries, which historically faced challenges in competing with larger industrial entities, are now leveraging niche markets by offering unique and locally-sourced products [5]. This shift enhances competition and fosters economic resilience among small-scale bakers [6].

Yeast, a microorganism classified under the fungi kingdom, ferments the sugars in dough to produce carbon dioxide (CO₂) and ethanol. This fermentation process not only helps the dough rise but also enhances the texture and flavour of the finished bakery products. The overall fermentation process involves mixing the ingredients—flour, water, sugars, and salt—creating a dough that serves as a medium for yeast activity [7]. Yeast also produces many other metabolites, such as organic acids, ethanol, hydrogen peroxide, glutathione, flavour compounds, and enzymes, which can also strongly affect the rheological properties of dough and product quality [8]. During fermentation, CO₂ produced by yeast creates bubbles within the dough, resulting in an increase in volume and porosity. Moreover, the ethanol evaporates during baking, enhancing the aroma of the bread [9]. Within the bakery industry, Saccharomyces cerevisiae is the predominant yeast species employed. Its ability to ferment quickly is essential for the efficient production of many types of bread.

Non-traditional yeast strains, encompassing atypical species and newly discovered variants, can provide distinctive characteristics that are absent in conventional baker’s yeast. Research indicates that using atypical yeast strains can enhance the sensory attributes of products, promoting artisanal qualities that consumers increasingly appreciate [10,11]. Such yeast might also provide additional health benefits through their diverse biochemical pathways, positively affecting nutritional profiles [12]. Nevertheless, the innovative use of unconventional yeast poses certain challenges. Many atypical yeast strains have lower leavening capacity and are harder to control compared to commercial yeast, with limitations such as poor resistance to freezing and drying that restrict their use in baking applications.

Recent research illustrates a growing interest in unconventional yeasts, which are being explored for their diverse functional properties that can enhance the baking process [13,14]. Studies on unconventional yeast have proliferated but are still comparatively less numerous than studies on traditional yeast. These non-Saccharomyces yeasts have been found to contribute positively to flavour and aroma compounds, indicating unexplored potential for their use in the bakery industry [13].

The increased interest in unconventional yeast can be attributed to several factors. There is a growing consumer demand for artisanal and naturally leavened breads that emphasise unique flavour profiles derived from varied microbial populations [15]. Additionally, the exploration of non-Saccharomyces yeast has been spurred by the recognition that these microorganisms can impart desirable sensory properties that traditional yeast may not achieve alone [14,16]. Goals of studies on unconventional yeast primarily include enhancing the complexity and quality of baked goods while also addressing the nutritional, sensory, and functional aspects of bread. Researchers aim to establish these yeasts as viable alternatives to conventional yeast by investigating their potential to improve dough performance, bread texture, and shelf life [14,17].

In summary, the growing focus on unconventional yeast in the bakery field reflects a notable trend shaped by changing consumer demands and the increasing sophistication of baking science. Although research on Saccharomyces cerevisiae remains predominant, there is a rising acknowledgement of the varied advantages provided by unconventional yeast. This evolving perspective expands the scope of yeast applications and supports the industry’s goals of improving quality and promoting sustainability in bakery products.

This review emphasizes the importance of research conducted for the identification, selection, and use of new unconventional yeast strains in the bakery industry, synthesizes studies in the field conducted to date, and highlights the prospects of new research directions.

2. The Main Advantages of Using Unconventional Yeasts in the Bakery Industry

The application of these yeasts in the baking industry aligns with the trends towards natural fermentation processes, where slow fermentation techniques can lead to products that are not only healthier but also more flavourful, further resonating with contemporary consumer preferences [18]. An overview of the main advantages associated with unconventional yeast is presented in Figure 1.

The incorporation of unconventional yeast into baking processes offers several compelling advantages:

Flavour and aroma enhancement

A major advantage of using unconventional yeast in baking is its capacity to elevate the flavour and aroma of baked products. The fermentation by-products produced by this unconventional yeast promote the creation of volatile compounds that enrich the bread’s overall flavour profile such as 2-phenylethanol and phenolic compounds, ethyl hexanoate and 2-phenyl ethyl acetate, sulfur-containing compounds and pyrazines. Studies indicate that yeast strains such as Torulaspora delbrueckii can increase the aromatic complexity of bread, leading to improved sensory characteristics [13]. This signature complexity appeals to contemporary consumers seeking artisanal and gourmet baked products.

Nutritional benefits

Unconventional yeast is known to improve the nutritional quality of bread. For example, certain species, such as Kluyveromyces marxianus, can effectively metabolize lactose in bakery products containing milk or dairy products, which is not possible for Saccharomyces cerevisiae [19]. This characteristic can enhance the nutritional profile of products, particularly for lactose-intolerant populations. Additionally, unconventional yeast can produce essential vitamins and bioactive compounds during fermentation, enhancing the overall health benefits of baked goods [20].

Tolerance to environmental stressors

Unconventional yeasts have been shown to exhibit exceptional tolerance to various stress conditions, such as elevated osmotic pressure and temperature fluctuations [20]. This trait is especially important in baking, as dough formulations may be exposed to elevated sugar levels and fluctuating temperatures throughout fermentation and bakery processes. For instance, Yarrowia lipolytica has been extensively studied for its metabolic flexibility and resiliency to environmental stressors, making it a potent candidate for fermentation in diverse bread formulations [21,22]. This robustness helps maintain stable fermentation quality despite changing external conditions.

Improvement of fermentation processes

Unconventional yeast can also influence fermentation kinetics. The use of species like Schizosaccharomyces pombe has been shown to result in a different fermentation dynamic than Saccharomyces cerevisiae, potentially leading to the production of products with desirable attributes, such as improved volatile organic compounds (VOCs) profiles [23]. This effect can also be applied to baking, where the distinct fermentation patterns of unconventional yeast enhance dough performance and overall bread quality.

The importance of unconventional yeast in the bakery industry is multifaceted, encompassing flavour enhancement, nutritional benefits, stress tolerance, and improved fermentation processes. As consumer preferences continue to evolve towards more artisanal, healthier, and sustainably produced food products, the incorporation of these unconventional strains may provide bakers with the innovative edge required to meet market demands.

3. Comparative Study Between Conventional and Unconventional Yeasts Used in the Bakery Industry

In baking, yeast plays an essential role as a leavening agent, greatly impacting the texture, flavour, and overall quality of bakery products. The emergence of unconventional yeast in this field introduces both promising prospects and notable challenges, leading to comparative evaluations with conventional yeast. Among these, Saccharomyces cerevisiae is especially well known for its efficient carbon dioxide production, which drives dough leavening and contributes to the light, airy structure of bread. They are highly favoured for their consistent performance in various baking environments, enabling bakers to achieve predictable product qualities [24]. Nevertheless, these yeasts exhibit limitations, particularly when subjected to stress conditions such as heat or high-sugar environments, which can hinder their fermentation efficiency and the shelf life of the products [25,26]. To eliminate these disadvantages, specialists have focused on identifying, selecting, and using unconventional yeasts that can be used singly or in combination with conventional ones in the bakery industry. Figure 2 illustrates the beneficial effects of combining the conventional yeast Saccharomyces cerevisiae with various unconventional yeasts. These synergistic interactions improve fermentation performance, product quality, and stress tolerance in baking and dough-based processes.

Notably, several studies have explored innovative approaches involving the co-fermentation of conventional and unconventional yeasts. This hybrid fermentation strategy aims to capitalise on the benefits of both yeast types. Implementations combine traditional baker’s yeast with non-Saccharomyces strains to facilitate enhanced flavour complexity and improved dough rheology [16,27]. The cooperative interactions between conventional and unconventional yeast can result in well-leavened products with enhanced flavour complexity and greater resistance to spoilage. Comparative analyses highlight clear distinctions in their roles within baking, emphasising the strengths of unconventional strains—such as superior stress tolerance, richer flavour profiles, and potential nutritional enhancements. Investigating hybrid fermentation methods points to a promising path forward for the bakery industry, offering opportunities to develop novel products aligned with shifting consumer preferences.

3.1. Flavour Components

Unconventional yeast produces a wide range of aromatic compounds that impart unique flavours to bakery products, clearly distinguishing them from those generated by traditional yeast strains. These unconventional yeasts exhibit diverse metabolic pathways that enhance flavour profiles and potentially improve the nutritional quality of bakery products [28]. The following

Table 1. Production mechanism of flavour components of unconventional yeast in dough.

Flavour Type	Unconventional Yeast	Production Mechanism	Reference
Floral	Debaryomyces hansenii	Produces aromatic volatiles such as 2-phenylethanol and phenolic compounds during fermentation.	[11]
	Candida tropicalis	This yeast produces sulfur-containing compounds, which contribute to savoury flavour profiles.	[29]
Earthy	Cryptococcus species	Generates earthy flavours through the production of volatile phenols and terpenes.	[30]
	Wickerhamomyces anomalus	Creates herbal scents through the generation of terpenes during fermentation.	[13]
Butter-like	Yarrowia lipolytica	Produces diacetyl via the metabolism of fatty acids during fermentation.	[28]
Fruity	Hanseniaspora uvarum	Produces esters such as ethyl hexanoate and 2-phenyl ethyl acetate.	[31]
	Torulaspora delbrueckii	Produces esters like isoamyl acetate, resulting in a banana aroma.	[13]
	Pichia kudriavzevii	Generates aromatic compounds that yield a sweet and fruity note.	[32]
Nutty	Candida milleri	Characterized by the production of pyrazines, developed through Maillard reactions during baking.	[33]
	Hanseniaspora guilliermondii	Synthesizes pyrazines, which contribute to nutty flavours through reactions during baking.	[16]
Spicy	Zygosaccharomyces bailii	Develops spicy notes via the synthesis of volatile aromatic compounds and organic acids.	[34]
	Kazachstania slooffiae	Produces various volatile organic compounds (VOCs) that bring out spicy notes during fermentation.	[16]
Sweet	Pichia pastoris	Produces sweet aromatic volatiles, including ethyl esters, through fermentation processes.	[35]
	Debaryomyces hansenii	Generates caramel-like aromas primarily through sugar metabolism and Maillard reaction products	[13]

summarizes various flavour types associated with unconventional yeast, specifying the yeast species responsible and the mechanisms behind the production of these flavour compounds.

Comparative studies show that unconventional yeast not only supports fermentation processes but also plays a key role in enriching the flavour profiles of bakery products. With consumer interest increasingly leaning toward novel and distinctive tastes, these yeast strains are expected to become important assets in the future advancement of the bakery industry.

3.2. Nutritional Benefits

The baking industry has increasingly adopted unconventional yeast strains in addition to the conventional Saccharomyces cerevisiae, aiming to improve not only dough leavening but also the nutritional value and sensory characteristics of bakery products. Among these non-traditional yeasts, species like Kazachstania gamospora, Wickerhamomyces subpelliculosus, and Brettanomyces have attracted interest due to their promising contributions to nutrition and flavour. The following

Table 2. Production mechanism of nutritional benefits of unconventional yeast in dough.

Unconventional Yeast	Nutritional Benefit	Production Mechanism	Reference
Kazachstania gamospora	Increased bioavailability of minerals	Produces phytase, degrading phytic acid and increasing the absorption of minerals like iron and zinc.	[36]
Wickerhamomyces subpelliculosus	Enhanced protein content	Exhibits high proteolytic activity during fermentation, increasing amino acid availability in the final bakery products.	[37]
Yarrowia lipolytica	Production of essential fatty acids	Biosynthesizes polyunsaturated fatty acids from various substrates during fermentation.	[38]
Brettanomyces	Enhanced antioxidant properties	Produces phenolic and flavonoid compounds that contribute to the antioxidant capacity of bakery products.	[39]
Candida milleri	Higher dietary fiber content	Ferments non-digestible oligosaccharides, increasing soluble fiber content beneficial for gastrointestinal health.	[40]

summarizes key nutritional benefits offered by unconventional yeast in the bakery industry, including the mechanisms by which these benefits are produced.

3.3. Stress Resistance Mechanisms

The following

Table 3. Production mechanism of stress resistance of unconventional yeast in dough.

Type of Stress	Unconventional Yeast	Production Mechanism	References
Osmotolerance	Yarrowia lipolytica	Synthesizing compatible solutes, like glycerol, stabilizes cell structures.	[41]
	Hanseniaspora uvarum	Similarly, utilizes glycerol accumulation as an osmoprotectant.	[16]
	Zygosaccharomyces bailii	Accumulating trehalose and other protective sugars that stabilize cellular structures.	[16]
Temperature stress tolerance	Ogataea polymorpha	Heat shock proteins that stabilize other proteins and membranes during thermal stress allow it to maintain cellular function.	[42]
	Candida krusei	Enzyme stability and increasing chaperone protein production.	[43]
	Debaryomyces hansenii	Ensures membrane fluidity adaptability to temperature changes.	[43]
Alcohol tolerance	Candida tropicalis	Enhanced membrane composition that integrates unique lipids, reducing fluidity and improving integrity, helps to prevent leakage of essential metabolites.	[44]
	Kluyveromyces marxianus	Increasing expression of alcohol dehydrogenases that facilitate ethanol metabolism, thus reducing toxicity.	[45]
Oxidative stress resistance	Yarrowia lipolytica	Produce more glutathione and reactive oxygen species (ROS)-scavenging enzymes.	[41]
	Wickerhamomyces anomalus, Pichia pastoris	Production of antioxidant compounds like superoxide dismutase (SOD) and catalase, which mitigate oxidative damage.	[46]
Salt tolerance	Yarrowia lipolytica	Up regulation of specific regulatory pathways that enhance sodium expulsion, coupled with adaptive osmotic adjustment mechanisms using compatible solutes that safeguard intracellular processes.	[47]
	Torulaspora delbrueckii, Hanseniaspora vineae	Employing sodium ion expulsion mechanisms and osmotic adjustment strategies allows them to maintain cellular homeostasis and metabolic functions.	[43]
Acid tolerance	Yarrowia lipolytica, Candida tropicalis	Promote proton efflux and synthesis of pH-responsive proteins to maintain enzymatic activity and cellular stability.	[48]
	Candida utilis, Hanseniaspora vineae	Similarly, possesses effective proton pumps that extrude excess protons from the cell.	[16]

summarizes the types of resistance to specific stress conditions, alongside examples of yeast, highlighting those that have shown superior performance in each category.

Current research on unconventional yeasts highlights their diverse stress resistance mechanisms, underscoring their potential to drive innovation in baking technology. By studying these unique traits, researchers can develop customized yeast strains to optimize fermentation and improve product quality in various baking applications.

3.4. Improvement of Fermentation Processes

Table 4. Production mechanism of stress resistance of unconventional yeast in dough.

Improved Dough Characteristic	Unconventional Yeast	Production Mechanism	Reference
Gas retention capacity	Yarrowia lipolytica	Produces glycerol, enhancing the formation of a more stable gluten network that significantly contributes to gas retention during fermentation.	[49]
Rheological properties	Kluyveromyces marxianus	Modifies protein interactions through enzymatic activities, improving the dough’s cohesiveness and viscoelastic properties, contributing positively to rheology.	[50]
Elasticity	Debaryomyces hansenii	Produces glycoproteins that enhance the gluten network’s resilience, improving the dough’s ability to stretch without breaking during fermentation.	[51]
Gas formation	Torulaspora delbrueckii	Utilizes alternative fermentation pathways, notably enhancing CO2 production and thus increasing dough volume and lightness.	[52]
Plasticity	Pichia pastoris	Improves dough plasticity through the secretion of specific enzymes that promote better hydration interactions between gluten and starch.	[53]

illustrates how different unconventional yeasts can enhance important dough characteristics. Through distinct biochemical mechanisms, this yeast enhances properties such as gas retention, elasticity, and rheology, contributing to better dough performance during fermentation.

4. Types of Unconventional Yeast Used in the Bakery Industry

Conventional yeasts are highly domesticated and standardized strains like Saccharomyces cerevisiae, optimized for performance in baking. In contrast, unconventional yeast, such as those from genera like Candida, Pichia, Torulaspora, and others, exhibit varied fermentation profiles, tolerate different environmental conditions, and can contribute unique flavour compounds, thus offering a broader spectrum of fermentation characteristics beneficial for specialty breads [18,54]. The taxonomy of unconventional yeast can be broadly classified based on their industrial utility, fermentation capabilities, and ecological niches they occupy. The importance of diverse yeast strains stems from their unique enzymatic profiles, which can affect the dough’s rheological properties and the nutritional content of bakery products, enhancing not just consumer acceptance but also health benefits attributed to such products [54]. A detailed exploration reveals several species of unconventional yeast, organized by genera, along with their characteristics and relevance to the bakery process. The key characteristics of unconventional yeast species are summarized in

Table 5. Key characteristics of using unconventional yeast in the bakery industry.

Genus	Species	Key Characteristics	Reference
Candida	Candida milleri	Commonly associated with sourdough fermentation, known for its ability to enhance flavour and aroma	[55]
	Candida humilis	Another important sourdough yeast, recognized for its contributions to the fermentation process and flavour development	[55]
	Candida krusei	Exhibits good fermentation properties and is often found in sourdough ecosystems	[56]
Pichia	Pichia anomala (formerly Wickerhamomyces anomalus)	Known for its ability to ferment a variety of sugars and enhance bread texture and flavour profiles	[56]
	Pichia norvegensis	Explored in sourdough production for its unique sensory contributions and fermentation capabilities	[56]
Torulaspora	Torulaspora delbrueckii	Valued for its potential to improve the sensory aspects of breads, including aroma and texture	[57]
Kazachstania	Kazachstania exigua	Found in a variety of sourdoughs, contributing to the complex microbial interactions within the dough	[56]
Rhodosporidium	Rhodosporidium mucilaginosa	Occasionally found in fermented products, this yeast shows promise for flavour enhancement	[55]
Zygosaccharomyces	Zygosaccharomyces rouxii	Known for thriving in high-sugar environments and used in specific fermentation processes	[56]
Hanseniaspora	Hanseniaspora uvarum	Commonly encountered in wine and beer production, it exhibits interesting fermentation properties that could be applied in specialized baking contexts	[58]
Brettanomyces	Brettanomyces bruxellensis	while primarily associated with barrel-aged beverages, it has been recognized for introducing unique flavours and aromas that may benefit artisan bakers	[58]
Debaryomyces	Debaryomyces hansenii	Known for its osmotolerance, it is used in specialty breads that require fermentation in high sugar concentrations	[58]

.

4.1. Candida milleri

Candida milleri is predominantly found in sourdough cultures and has been isolated from various traditional bread environments, such as those common in Europe and Ethiopia. This yeast is commonly associated with artisanal baking methods, contributing unique flavours and leavening characteristics that distinguish sourdough from breads made with standard baker’s yeast [59].

Flavour components

Candida milleri produces volatile compounds including acetic acid, lactic acid, and various esters like ethyl acetate and isoamyl acetate, as well as alcohols and aldehydes, which collectively contribute to the complex tangy flavour characteristic of artisanal breads [60,61]. The conversion of carbohydrates during fermentation results in these flavour compounds through enzymatic activities and metabolic processes involving both yeast and accompanying lactic acid bacteria [62].

Improvement of leavening

Candida milleri significantly contributes to the leavening process by producing carbon dioxide through fermentation. This yeast has an effective synergistic relationship with lactic acid bacteria, allowing it to thrive in acidic environments. This co-culture mechanism not only increases gas production but also improves aeration in the dough, achieving higher loaf volumes [60].

Nutritional benefits

Incorporating Candida milleri into baking processes has been associated with enhanced nutritional content, particularly regarding B vitamins. This yeast facilitates the bioavailability of nutrients within the bread, making essential vitamins such as riboflavin available to the consumer [63]. This increased B vitamin content in bakery products is attributed to the metabolic processes during fermentation [62].

Resistance to stress conditions

Candida milleri exhibits notable resilience to various stress conditions that can affect yeast performance, such as low pH, high salt concentrations, and temperature fluctuations. This adaptability is vital in maintaining consistent fermentation quality in sourdough. The yeast’s ability to withstand these stressors comes from its inherent metabolic adjustments, allowing it to support fermentation effectively, which helps suppress the growth of spoilage microorganisms [64].

4.2. Candida humilis

Candida humilis is a yeast species commonly found in sourdough fermentation systems, predominantly in rye-based sourdoughs. It is recognized for its prevalence in the microbial community associated with sourdough, alongside other yeast species such as Saccharomyces cerevisiae and Kazachstania exigua. Studies suggest its significant presence in various regional sourdoughs, especially across Europe, notably Belgium and Italy [65,66,67]. The use of Candida humilis in baking is becoming increasingly popular owing to its multiple advantages in sourdough fermentation. Notably, this yeast contributes to richer flavour profiles, better dough rheology, prolonged shelf life, and enhanced nutritional value–each of which will be explored in detail in the following sections.

Flavour components

Candida humilis is known for its ability to produce a range of flavour compounds crucial for enhancing the overall sensory profile of baked products. It can synthesize esters such as ethyl acetate and isoamyl acetate, along with higher alcohols, which contribute fruity and floral notes to the bread. The fermentation by this yeast utilizes the Ehrlich pathway, where branched-chain amino acids are converted into these volatile compounds, resulting in a more complex flavour profile that is highly appreciated in artisan breads [68].

Improvement of leavening

Candida humilis promotes beneficial changes in the rheological properties of dough through its metabolic activities. It produces organic acids, notably lactic acid, which acidifies the dough and enhances gluten network development, thereby improving gas retention during fermentation. This leads to a more elastic and extensible dough, which is essential for achieving the desired texture in bakery products [69].

Nutritional benefits

The fermentation process involving Candida humilis also enhances the nutritional profile of bakery products. Sourdough fermentation can increase the bioavailability of minerals like calcium, magnesium, and iron by degrading phytates that inhibit their absorption. Additionally, studies show that the presence of Candida humilis and other sourdough yeasts stimulates the production of B vitamins, particularly folate and riboflavin, during fermentation [70]. Furthermore, beneficial metabolites resulting from the yeast’s activity contribute to improved digestibility of proteins, enhancing the nutritional value for consumers [68].

Resistance to stress conditions

Candida humilis is recognized as an acid-tolerant yeast, closely related to Saccharomyces cerevisiae. Its survival in the low pH environment typical of sourdough is attributed to its sophisticated regulatory mechanisms that allow it to maintain intracellular pH homeostasis, thereby facilitating metabolic activity despite external acidity [71]. Candida humilis also demonstrates mechanisms that enable it to cope with oxidative stress, which is critical during fermentation, as reactive oxygen species (ROS) can impair cellular functions. The yeast expresses antioxidant enzymes such as superoxide dismutase (SOD) and catalase, which mitigate oxidative damage to cellular components. Furthermore, the increased expression of glyceraldehyde-3-phosphate dehydrogenase (GAPDH) has been correlated with its response to oxidative stress, suggesting a metabolic reconfiguration that enhances its resilience [72,73].

4.3. Candida krusei

Candida krusei is primarily associated with diverse environments, including soil, decaying plant matter, and as a spoilage organism on various foods, particularly fermented products. While Candida krusei has been studied for its fermentation qualities, its use in the bakery industry, specifically for enhancing processes in gluten-free and artisanal bread, is still under investigation in scholarly research [74].

Flavour components

Candida krusei is noted for its capability to produce various flavour-active compounds during fermentation. It generates esters, phenols, and organic acids, enriching the aroma and flavour of bakery products. This characteristic could be advantageous in the production of specialized breads with unique sensory properties, thereby enhancing consumer satisfaction and differentiating products in the competitive market [75].

Nutritional benefits

Recent studies have suggested that some strains of Candida krusei may exhibit properties beneficial for gut health, potentially serving as a probiotic. Incorporating this yeast into bakery products could not only provide leavening but also contribute to health benefits associated with probiotics, appealing to health-conscious consumers [76]. Candida krusei is a non-gluten-forming yeast, making it an ideal candidate for gluten-free baking applications. It can contribute to desired texture and moisture retention in gluten-free products, addressing challenges faced with traditional yeast strains. Its inclusion in gluten-free formulations can lead to improved product quality, texture, and consumer acceptance, responding to the growing demand for gluten-free options in the market [74,76].

Resistance to stress conditions

One notable advantage of Candida krusei is its ability to thrive in high-sugar environments, which are essential in various baking contexts. This yeast is capable of fermenting higher sugar concentrations than common strains like Saccharomyces cerevisiae, making it especially beneficial for sweet bread and high-sugar dough formulations ([75,76]. The significant sugar tolerance of Candida krusei can lead to improved fermentation rates and enhance product sweetness, contributing to the flavour profile of bakery products. Interestingly, Candida krusei has been reported to exhibit intrinsic resistance to several antifungal agents commonly used in the food industry, particularly azoles [77,78]. This property allows it to survive in antifungal-rich environments where other yeast might struggle. Such resistance may make Candida krusei a resilient choice where traditional baking yeast could be inhibited, leading to consistent fermentation with minimal batch variability [77,78].

4.4. Pichia anomala

Pichia anomala, also known as Wickerhamomyces anomalus, has emerged as a significant player in the bakery industry, thriving in diverse environments such as fruits, grains, silage, and traditional fermentation processes. This yeast is frequently isolated in sourdough systems, particularly in Europe, where it coexists with more traditional yeast species like Saccharomyces cerevisiae. It is known for contributing beneficial characteristics to fermentation processes in both baking and brewing contexts [66,79].

Flavour components

In the baking industry, Pichia anomala is celebrated for its unique fermentation properties and its impact on the sensory qualities of bakery products. A major advantage of Pichia anomala is its ability to produce volatile organic compounds (VOCs) during fermentation, which enhance the aroma and flavour profile of bakery products. These aromas contribute to a more complex sensory experience than that achieved with conventional baker’s yeast. VOCs from Pichia anomala include ethyl acetate and phenethyl alcohol, which are recognized for imparting desirable fruity and floral notes to breads and pastries [80]. Moreover, the diverse metabolic capabilities of Pichia anomala allow for manipulation of the fermentation process to tailor specific characteristics of the finished product. This capability opens avenues for the development of artisanal bread with distinct flavour profiles that cater to changing consumer preferences towards gourmet and health-conscious products [79].

Nutritional benefits

In addition to its functional characteristics, Pichia anomala can hydrolyze complex carbohydrates and proteins within flour. This enzymatic activity facilitates the breakdown of gliadin proteins into more digestible components, potentially improving the nutritional profile of the finished bakery product [79]. Such functionality makes it a valuable addition to the formulation of gluten-free and specialty breads, where ingredient composition and processing conditions often require innovative fermentation solutions.

Resistance to stress conditions

Another notable advantage of Pichia anomala is its tolerance to various fermentation stresses. This yeast exhibits resilience against high sugar concentrations and low pH environments, making it suitable for use in the production of sourdough and other yeast-leavened products. The adaptability of Pichia anomala allows for consistent fermentation performance under varying production conditions, which is crucial for maintaining product quality [81]. One of the distinguishing features of Pichia anomala is its remarkable osmotolerance, which allows it to thrive in environments with high sugar concentrations. This quality is vital in bakery settings where dough often contains significant amounts of sugar and where osmotic stress can inhibit fermentation. Studies have shown that Pichia anomala can sustain its metabolic activity and fermentation capacity even in high osmotic conditions [82,83]. Furthermore, Pichia anomala exhibits thermotolerance, permitting it to remain viable and effective under elevated temperature conditions typical during bread baking processes [84]. Pichia anomala is also known for its high alcohol tolerance, which is crucial in fermentation processes where ethanol accumulation can inhibit yeast activity. This strain has been shown to persist and mitigate the effects of ethanol during fermentation, enhancing its utility in producing various alcoholic beverages and potentially in specific baking applications where alcohol production is desired [85]. Additionally, studies indicate that Pichia anomala can tolerate oxidative stress, which can improve its performance in environments where oxygen levels fluctuate, such as in open fermentation systems [86].

4.5. Pichia norvegensis

Pichia norvegensis is an unconventional yeast predominantly found in association with rotting fruits and plant matter, particularly cacti like Opuntia, as well as in clinical environments [87,88]. This species belongs to the Pichia genus and is part of the Pichia cactophila clade, indicating its evolutionary link to other yeasts that are often isolated from similar environments [89]. While its traditional applications in baking have not been extensively documented, its unique properties position it as a potentially advantageous agent in this sector.

Flavour components

Pichia norvegensis exhibits a distinct metabolic profile that allows for the production of various volatile compounds during fermentation, which can enhance flavour complexity in bakery products. The presence of Pichia has been noted in several traditional fermentation contexts, which indicates its ability to contribute to the unique sensory attributes of the finished product [90,91]. The production of these compounds can lead to the development of novel flavours that improve consumer appeal.

Improvement of leavening

This yeast species is recognized for its ability to grow at elevated temperatures, which can be beneficial for fermentation processes that occur at higher than typical yeast culture temperatures. Research suggests that Pichia norvegensis can thrive at temperatures around 37 °C, potentially improving process stability and product consistency [92].

Nutritional benefits

Preliminary studies suggest that yeasts like Pichia norvegensis may possess probiotic characteristics, contributing to gut health. Incorporating Pichia into bread formulations could lead to health benefits beyond basic nutrition, potentially improving the functional food value of baked products [93]. This probiotic aspect could cater to a growing consumer demand for health-promoting foods.

Resistance to stress conditions

Fermentation by Pichia norvegensis has shown some resistance to common contaminants that may affect dough fermentation, such as certain molds and bacteria. This resistance enhances the hygienic quality and safety of the final product [94] Pichia norvegensis’s inherent antifungal properties, including the secretion of β-glucans, can also act as a protective mechanism during the fermentation stages, which assists in maintaining the integrity of the dough [95].

4.6. Torulaspora delbrueckii

Torulaspora delbrueckii is a conventional yeast frequently identified in various fermentative environments, notably in sourdough, where it coexists with other yeast such as Saccharomyces cerevisiae, Candida humilis, and Kazachstania exigua [65]. It is prevalent in traditional baking processes and home-made corn and sourdough products, highlighting its adaptability and significance in artisanal bread-making [96]. Torulaspora delbrueckii has attracted interest in recent years due to its properties, ranging from its ability to produce flavour- and aroma-enhanced wine to its ability to survive longer in frozen dough [97].

Flavour components

One of the primary advantages of incorporating Torulospora delbrueckii in baking is its ability to produce a diverse array of volatile compounds, which contribute to the aroma and flavour of the finished product. The yeast is known for generating higher levels of esters and phenolic compounds, resulting in unique fruity and floral notes in the bread [98]. This characteristic is particularly useful in artisanal and specialty bread production, where sensory attributes significantly influence consumer preference [99]. Sensory evaluations indicate a consumer preference for bread fermented with Torulospora delbrueckii, highlighting the potential market acceptance of products made with this alternative yeast. The broader range of volatile compounds produced by Torulospora delbrueckii, contributes to more complex and desirable bread aromas, as confirmed by GC–MS analysis. Their data show that this strain adds more complexity to the sensory profile of bread, adding specific nutty and fruity tones [13].

Improvement of leavening

As a natural component of sourdough microbiota, Torulospora delbrueckii plays a pivotal role in the fermentation process, significantly influencing the overall microbial balance and the metabolic activities associated with dough fermentation. Its ability to coexist with lactic acid bacteria and other yeasts allows it to contribute positively to sourdough dynamics, improving rise, flavour complexity, and shelf-life extension [100]. This interplay not only enhances the sensory qualities of bread but also endows it with health benefits due to the production of organic acids and enzymes that enhance digestibility and nutritional profiles [101]. The yeast demonstrates superior water absorption capabilities, which can improve dough consistency and overall bread quality during baking [102]. This property is particularly advantageous because higher water absorption can lead to softer and moister bread, a desirable trait for consumers. The ability of Torulospora delbrueckii to effectively utilize a broad range of carbon sources during fermentation contributes to its versatility in various dough formulations [103]. Moreover, this yeast may further improve dough elasticity and extensibility, which are crucial parameters affecting the final structure of bakery products. Improved elasticity allows the dough to withstand the mechanical stresses during fermentation and baking, thereby fostering better gas retention and enhancing the bread’s overall volume. Recent studies have shown that Torulospora delbrueckii fermentation leads to improved handling qualities of dough, making it a superior choice in artisanal and bakery applications [104]. Such shifts in volatile composition enhance the sensory appeal of the finished bakery product and offer opportunities for product differentiation in competitive markets. Moreover, Torulospora delbrueckii’s ability to ferment a range of carbohydrates—including fructose, glucose, maltose, and sucrose—provides additional versatility in its application, ensuring that it meets the metabolic demands of diverse dough formulations [105]. Torulospora delbrueckii exhibits favourable dough fermentation capacity and gas production, essential features for achieving well-risen bakery products. Comparative studies involving model dough have pointed out that Torulospora delbrueckii, either as a monoculture or in mixed fermentations, can deliver satisfactory CO₂ production, thus ensuring adequate leavening [13,16]. Although Saccharomyces cerevisiae is renowned for its rapid and vigorous gas production, Torulospora delbrueckii has been shown to generate a comparable and, in some cases, more balanced fermentation profile, which may result in improved textural and sensory characteristics [105,106].

Nutritional benefits

One of the significant advantages of utilizing Torulospora delbrueckii in bread making lies in its ability to enhance the nutritional value of the finished product. The fermentation process facilitated by this yeast produces bioactive compounds, including vitamins and antioxidants, which contribute positively to the bread’s overall nutritional profile [13]. Furthermore, sourdough fermented with Torulospora delbrueckii shows indications of improving the bioavailability of minerals, an important factor for consumers increasingly concerned about the nutritional aspects of their diets. The fermentation process can lead to the breakdown of phytic acid, a known antinutrient that binds minerals, thus potentially increasing the bioavailability of critical nutrients such as iron and zinc [107]. Furthermore, the mixed inocula of Saccharomyces cerevisiae and Torulospora delbrueckii enhanced the production of succinic acid, acetic acid, and essential amino acids in the fermented dough [108].

Resistance to stress conditions

Torulospora delbrueckii exhibits osmotolerance, enabling it to thrive in high-sugar dough formulations that can pose challenges for traditional baker’s yeast. This trait allows it to maintain fermentation vigour even under osmotic stress, leading to better dough performance and improved gas retention during baking [11]. Consequently, breads produced with Torulospora delbrueckii can exhibit enhanced crumb structure and superior texture, appealing to a segment of consumers seeking high-quality, artisanal bread [109]. Although specific thermo tolerance studies in the context of bakery applications remain limited, investigations in related matrices such as scalded dough have shown that co-cultures incorporating Torulospora delbrueckii can withstand elevated temperatures and contribute positively to fermentation kinetics [110]. In addition, the yeast’s moderate alcohol tolerance has been observed during fermentations where ethanol production is lower than that achieved by Saccharomyces cerevisiae [111]. Oxidative stress during fermentation, which can negatively affect yeast viability and dough leavening, is addressed by Torulospora delbrueckii’s adaptive stress responses, as revealed in early transcriptional studies. These responses may include the induction of protective proteins that mitigate oxidative damage [112].

4.7. Kazachstania exigua

Kazachstania exigua, also known historically as Saccharomyces exiguus, is an unconventional yeast predominantly isolated from various environments, including fermented foods and beverages, particularly kefir and sourdough. This yeast species has been detected in traditional and artisanal fermentations across several regions, contributing to the rich microbial diversity essential for fermentation processes in the bakery industry [113,114]. Its ability to thrive in diverse environmental conditions has made it an attractive candidate for various applications in food production.

Flavour components

In the bakery industry, Kazachstania exigua offers several advantages that enhance the quality and characteristics of bakery products. The metabolic pathways employed by Kazachstania exigua lead to the production of various volatile compounds, which are critical for the aroma and taste of breads and pastries [115,116]. One of the primary groups of volatile compounds produced by Kazachstania exigua is esters, which are recognized for their fruity and floral notes. Esters are typically generated during the metabolism of sugars and alcohols, which occur during fermentation. Specific esters synthesized include ethyl acetate and isoamyl acetate, which are known to impart pineapple and banana-like flavours, respectively. These flavour notes are highly desirable in many bakery products as they add complexity and depth [117,118]. Moreover, the production of such esters can vary depending on the fermentation conditions, such as temperature and pH [119,120]. In addition to esters, Kazachstania exigua is capable of producing higher alcohols, which also contribute significantly to the flavour profile of products. These include fusel alcohols such as isoamyl alcohol and 1-butanol, which can lend a warming, malty flavour to bread and other fermented products [121,122].

Nutritional benefits

Secondly, the use of Kazachstania exigua in sourdough fermentation is linked to increased nutritional benefits. This yeast has demonstrated the ability to improve the bioavailability of essential nutrients, particularly minerals such as calcium and iron, by degrading antinutritional factors like phytate present in wholegrain flours [68]. This characteristic is particularly important in producing artisanal and wholemeal breads, where the presence of Kazachstania exigua can optimize nutrient absorption, making the finished product not only tastier but also healthier for consumers [68]. Another key advantage of employing Kazachstania exigua in baking is its potential probiotic properties, which may confer health benefits to consumers. Research has indicated that Kazachstania exigua exhibits antimicrobial activity against various pathogens, thus potentially improving the safety and shelf-life of bakery products [123]. The yeast has also shown probiotic traits that can positively influence gut health, making products containing this yeast more appealing to health-conscious consumers [124].

Resistance to stress conditions

Moreover, Kazachstania exigua’s resilience under varying fermentation conditions ensures its utilization regardless of external factors such as temperature fluctuations in bakeries. Its ability to co-exist with other microorganisms, particularly lactic acid bacteria, allows for complex fermentation dynamics that can be harnessed to optimize the texture and shelf-life of baked products [27,125]. This synergistic relationship can lead to better dough stability and fermentation efficiency, essential factors in large-scale baking operations [125].

4.8. Rhodosporidium mucilaginosa

Rhodosporidium mucilaginosa, a member of the Basidiomycota phylum, is widely distributed in various habitats, including soil, water bodies, and plant surfaces. Its presence is notably recorded in environments with rich organic matter, particularly in molasses, which serves as a substrate for its growth [126,127]. This yeast thrives in sugar-rich media, making it particularly relevant in fermentation processes related to baking and other food applications where sugar is a primary component [127]. The incorporation of Rhodosporidium mucilaginosa in the bakery industry has attracted attention due to its unique benefits compared to traditional baker’s yeast, such as Saccharomyces cerevisiae. It provides advantages including enhanced flavour development, improved dough characteristics, and potential health benefits due to its metabolic by-products.

Flavour components

Rhodosporidium mucilaginosa is known for its ability to produce distinctive metabolites during fermentation. These metabolites include various volatile compounds that contribute to the overall flavour profile of bakery products. Research indicates that the presence of unconventional yeast can enhance the complexity and depth of flavours in bread, thereby providing consumers with a more diverse sensory experience [128,129]. Notably, the production of carotenoids, which impart unique colours and flavour nuances, further underscores its potential as a flavour enhancer in bread making [130].

Improvement of leavening

The incorporation of Rhodosporidium mucilaginosa can significantly affect the rheological properties of dough. This yeast has been associated with improved stress tolerance and elasticity, critical parameters for quality bread production. Studies indicate that the addition of Rhodosporidium mucilaginosa leads to better dough fermentation and gas retention, resulting in superior volume and texture of the finished product [126,131]. These improvements can enhance consumer acceptability and market competitiveness.

Nutritional benefits

Rhodosporidium mucilaginosa has garnered interest for its potential health benefits attributed to its ability to produce bioactive compounds such as indole-3-acetic acid (IAA). This compound is associated with various health-promoting effects in the human gut and can contribute to improved digestive health when included in bakery products [131]. Furthermore, certain strains have been noted for their lipid production, which can lead to the creation of healthier fat profiles in bakery products, offering a more nutritious alternative to products high in saturated fats [129,130].

4.9. Zygosaccharomyces rouxii

Zygosaccharomyces rouxii is a notable member of the unconventional yeast family, predominantly found in environments characterized by high osmotic pressure, such as concentrated brines and sugar-rich substrates. It plays a significant role in various fermentation processes, contributing notably to traditional products like soy sauce, miso, and various fermented beverages [132,133]. This yeast is often regarded as a spoilage microorganism in the bakery industry due to its resilience against osmotic stress and high concentrations of sugars, leading to its dual role as a beneficial fermenter and a potential spoilage agent [133].

Flavour components

In the baking industry, the advantages of Zygosaccharomyces rouxii are noteworthy. Its remarkable osmotolerance enables it to thrive in high-sugar environments, which is critical in many baking scenarios where sugar concentrations can be elevated [134].This property not only supports effective fermentation but also promotes the production of unique flavour compounds, such as furanones, which impart a desirable caramel-like aroma to baked goods [134]. Moreover, the presence of Zygosaccharomyces rouxii can enhance the overall flavour profile of bread and other products through the generation of volatile aromatic compounds [134].

Resistance to stress conditions

Another significant benefit of Zygosaccharomyces rouxii is its adaptability to various fermentation conditions. Its capability to adjust to different osmotic pressures allows it to be utilized effectively across diverse baking formulations [133]. Furthermore, the yeast’s genetic versatility facilitates its use in developing strains with specific functional traits tailored for the bakery industry, such as increased flavour production or enhanced preservation abilities.

4.10. Hanseniaspora uvarum

Hanseniaspora uvarum, a type of unconventional yeast, plays a significant role in the production of various fermented products, particularly in the winemaking and baking industries. This yeast can predominantly be found on grape skins and is often isolated from fermenting grape must, with a notable presence also reported in diverse food products [135,136]. Its unique properties make it a subject of interest for food scientists and bakers alike.

Flavour components

In the bakery industry, Hanseniaspora uvarum is recognized for its beneficial attributes which can enhance the flavour profile and overall quality of bakery products. The yeast not only contributes to fermentation but also brings unique sensory properties to the finished product, such as improved flavour complexity. One of the primary advantages is its ability to produce various aroma compounds, which enrich the sensory characteristics of dough products. Research shows that the metabolic activity of Hanseniaspora uvarum results in the production of esters and higher alcohols, which can enhance the aroma and flavour complexity in bread making [137,138].

Improvement of leavening

Another significant advantage of using Hanseniaspora uvarum in baking is its impact on dough fermentation. This yeast has been identified as having efficient sugar fermentation capabilities, which can result in desirable texture and moisture retention in baked products [136,139]. Its robust metabolic pathways allow for effective sugar utilization, which can aid in the development of a better crumb structure and volume.

Nutritional benefits

Furthermore, Hanseniaspora uvarum presents certain ecological benefits when involved in mixed fermentations. Its co-culture with other yeast species can create a balanced fermentation environment that promotes biodiversity and prevents the dominance of undesirable microorganisms [140]. The interactions during co-fermentation may also lead to a broader spectrum of flavours, ultimately benefiting the quality of the finished bakery product.

4.11. Brettanomyces bruxellensis

Brettanomyces bruxellensis is commonly found in various fermentation environments, including beer, wine, and kombucha production, where its contribution to flavour profiles can be both beneficial and problematic. This unconventional yeast is characterized by its ability to thrive in conditions that are not conducive to traditional yeast such as Saccharomyces cerevisiae, often surfacing in products prone to spoilage due to its resilience and metabolic adaptability [141,142,143]. While predominantly noted for its roles in the alcoholic beverage industry, its relevance in the baking sector warrants exploration, particularly for artisan bread production and niche bakery products.

Flavour components

The unique metabolic pathways of Brettanomyces bruxellensis allow it to produce a plethora of volatile compounds that can significantly enhance the flavour complexity of bakery products. The presence of this yeast results in the synthesis of compounds such as esters and phenols, contributing flavours that range from fruity to spicy, which are appealing in artisan bread products [144,145]. The ability of Brettanomyces bruxellensis to produce distinct 4-ethyl phenol and 4-ethyl guaiacol provides a unique aromatic profile, often experienced in sourdough breads and other similar products, thereby elevating their gustatory experiences [146].

Improvement of leavening

The metabolic activities of Brettanomyces bruxellensis can impart valuable qualities such as increased gluten strength and dough stability. By interacting with the gluten matrix, this yeast promotes a network that improves the elasticity and extensibility of the dough, critical for achieving desirable bread textures [141,142]. Its robust fermentation process can lead to improved gas retention, resulting in loaves with a lighter crumb structure and enhanced volume, which are desirable characteristics in high-quality bakery products.

Resistance to stress conditions

In comparison to conventional yeast, Brettanomyces bruxellensis demonstrates enhanced fermentation capabilities, particularly in challenging environments with high osmotic pressure or low nutrient availability. This species can often continue fermentation despite adverse conditions where others fail, which may be beneficial for producing specific styles of bread that require longer fermentation times [142,146]. Additionally, its enzymatic activity can promote the breakdown of complex carbohydrates within the dough, which may enhance the loaf structure and texture of the finished product.

4.12. Debaryomyces hansenii

Debaryomyces hansenii is an unconventional yeast species predominantly found in various environmental niches such as soil, water, and decaying plant material. It has often been isolated from fermented foods, particularly cheeses and cured meats, where it is recognized for its salt tolerance and ability to thrive in high microbial diversity environments [147]. In addition to its traditional habitats, recent studies have demonstrated its emerging significance in industrial applications, particularly in the bakery industry. In the baking sector, Debaryomyces hansenii offers several advantages that contribute to improved product quality and shelf life.

Flavour components

Debaryomyces hansenii is also known for its role in flavour development during the fermentation process. The yeast is capable of producing a range of volatile compounds, including esters and other aromatic compounds that can enhance the sensory profile of bakery products. This flavour enhancement is particularly valued in artisanal and specialty bread production, where consumer preference leans towards products with diverse and complex flavours. Additionally, its historical isolation from traditional fermented foods underscores its potential to impart specific regional flavours [148].

Nutritional benefits

The emergence of gluten-free diets has fuelled interest in alternative baking agents, making Debaryomyces hansenii particularly relevant. Strains of Debaryomyces hansenii have shown promise in gluten-free formulations, offering improved fermentation characteristics necessary for producing gluten-free bread. Its adaptability allows for effective fermentation of various substrates, enhancing the texture and sensory properties of gluten-free bakery products [149]. This capability not only meets the growing consumer demand for gluten-free options but also diversifies the applications of Debaryomyces hansenii within the bakery industry.

5. Perspectives, Limits, Challenges

5.1. Perspectives

Unconventional yeast, often overlooked in the bakery industry compared to their mainstream counterparts like Saccharomyces cerevisiae, has begun to emerge as vital components of novel baking technologies. The identification of new yeast species and the use of yeast mixtures offer promising avenues for improving bread characteristics. These yeast, including Torulaspora delbrueckii and various non-Saccharomyces strains, are being increasingly studied for their unique flavour profiles and fermentation characteristics, predominantly in the wine and brewing sectors. However, their potential applications in baking remain less explored despite promising attributes that could enhance the sensory qualities of bread products [13,16].

The perspectives for utilizing unconventional yeast in the bakery industry are significant. The integration of these yeast could lead to a wider array of flavours, improved bread textures, and enhanced nutritional benefits. For instance, unconventional strains may exhibit unique fermentative properties, such as the ability to metabolize complex sugars and produce distinct aroma compounds. Furthermore, studies indicate a positive correlation between yeast-derived compounds and the overall flavour complexity of bread, which could appeal to a market increasingly interested in artisanal and gourmet bakery products [13,16]. Should the sector adopt these yeast more broadly, it could result in a transformation of consumer preferences towards more diverse and flavourful bread products.

Moreover, the exploration of residual or dead yeast application in dough formulations has gained traction. Utilizing residual yeast could not only be a cost-effective measure for bakers but may also improve the nutritional benefits and textural qualities of the finished product. For example, the addition of residual yeast from brewing or fermentation processes contains significant levels of beneficial compounds, such as beta-glucans and proteins, which may enhance the bread’s overall nutritional profile and functional properties. Recent studies of [150,151,152] indicate that incorporating such residual microorganisms into the baking process can interact synergistically with traditional baking yeasts, resulting in dough that not only rises well but also possesses enhanced flavours and shelf life. In addition to these advancements, the potential for mixed starter cultures, combining various yeast and lactic acid bacteria (LAB), has demonstrated significant benefits in bread production. These mixed cultures can contribute to improved fermentation dynamics, better control over the dough’s fermentation rates, and enhanced flavour development through the synergistic production of volatile compounds during fermentation [39,43,152]. By harnessing the metabolic diversity of unconventional yeast, it is possible to create a broader spectrum of flavour profiles and textures in bakery products, aligning with modern consumer preferences for artisan-quality products.

5.2. Limits in the Use of Unconventional Yeast

The investigation of unconventional yeast in the bakery industry faces several limitations, primarily due to the complex nature of baking processes and the volatile characteristics of flavour compounds. One significant constraint is the evaporation of various flavouring substances during the baking process. Yeast, including non-Saccharomyces species, produces a variety of aromatic compounds through fermentation, such as esters, organic acids, and aromatic alcohols. However, many of these compounds have low boiling points and are prone to evaporation at the high temperatures used in baking, thus reducing their presence in the finished product [153]. Zotta et al. (2022) have highlighted that while some unconventional yeast strains show promise in mimicking the fermentation characteristics traditionally attributed to Saccharomyces cerevisiae, the retention of flavour compounds produced during fermentation remains a challenge due to their volatility [16].

Moreover, Aslankoohi et al. (2016) emphasize that although the presence of these unconventional yeasts can enhance the aroma complexity in the bread due to diverse metabolic profiles, the myriad of volatile compounds they produce can be lost during baking, leading to unintended flavour dilution [13]. This indicates that the full potential of unconventional yeasts in flavour enhancement might not be fully realized in practical baking scenarios. Additionally, the inherent variability in the performances of unconventional yeast adds another layer of complexity to their study. Variability can arise from differences in yeast strain genetics, fermentation conditions, and the baking environment, all of which can significantly influence the flavour output and consistency [60,154]. Therefore, understanding the specific interactions between yeast metabolisms, potential flavour production, and baking conditions is crucial for optimizing the use of unconventional yeast in industrial baking. Finally, other limitations encompass the need for more comprehensive research into the interactions between yeast species, enzymes, and flour components during fermentation and baking [61]. This knowledge is paramount as it can help mitigate the negative effects caused by the loss of flavour compounds while maximizing the benefits gained from alternative yeast strains.

5.3. Challenges

The study of unconventional yeast in the bakery industry presents several hurdles that affect both research and practical applications. One significant challenge is the genetic complexity of unconventional yeast species. Unlike the extensively studied Saccharomyces cerevisiae, unconventional yeasts such as Yarrowia lipolytica exhibit variable metabolic pathways that complicate analysis and characterization [51]. This metabolic diversity results in inconsistent fermentation patterns, which poses challenges in predicting baking performance [155]. Moreover, many of these unconventional species are less amenable to genetic manipulation, making it harder to improve desirable traits through traditional biotechnological approaches [156].

Additionally, the application of unconventional yeast in baking involves navigating regulatory frameworks. Some unconventional yeasts have not been recognized as Generally Recognized As Safe (GRAS) by regulatory bodies, which can hinder their commercial deployment; however, certain strains of Yarrowia lipolytica have been assessed in this context [156]. This lack of regulatory acceptance can limit innovations within the bakery industry, as the incorporation of these yeasts may require extensive safety assessments that do not affect more documented species like Saccharomyces cerevisiae. This remains an important consideration but lacks a specific reference supporting a claim around GRAS status [157]. Interest in overcoming these challenges stems from the potential benefits associated with unconventional yeast. These species may contribute unique flavour profiles, enhanced nutritional qualities, and improved dough characteristics that are increasingly in demand in artisan and health-oriented baking sectors [54].

For instance, the utilization of unconventional yeast can lead to the production of breads with lower fermentable oligosaccharides, disaccharides, monosaccharides, and polyols (FODMAP) content, making them more suitable for individuals with digestive sensitivities [158]. Furthermore, the successful integration of these yeasts can expand the range of functional properties available in commercial baking applications, indicating a pressing need for ongoing research and innovation within this domain [159]. If the challenges associated with studying unconventional yeast are addressed, significant advancements can be made in the bakery industry. This includes the development of novel products that cater to emerging consumer preferences for health-oriented choices and options that leverage unique organoleptic properties associated with specific yeast strains [160]. By overcoming these scientific and regulatory barriers, the bakery industry can not only boost its product offerings but also enhance its competitive advantage in a crowded marketplace responsive to new trends and technologies.

6. Conclusions

The integration of unconventional yeast species into modern baking practices marks a significant evolution in the industry’s approach to fermentation science. While Saccharomyces cerevisiae has long dominated commercial baking due to its reliable leavening properties, emerging research demonstrates that alternative yeast strains offer multidimensional benefits that extend far beyond simple dough rising. These microorganisms, including Torulaspora delbrueckii, Candida milleri, Candida humilis, Pichia anomala, and Kazachstania exigua, possess unique metabolic pathways that fundamentally transform both the technical and qualitative aspects of bakery products. Unconventional yeast contributes substantially to dough rheology and fermentation dynamics. Species like Torulaspora delbrueckii improve gas retention and gluten network development, while Candida milleri enhances water absorption capacity—critical parameters for achieving optimal crumb structure and loaf volume. Furthermore, their enzymatic activities, particularly in phytate degradation and protein hydrolysis, increase mineral bioavailability and protein digestibility, addressing nutritional deficiencies in grain-based products. The stress tolerance of many strains (osmotic, thermal, and oxidative) ensures fermentation consistency under variable industrial conditions, reducing batch failures and improving process reliability.

The flavour-enhancing capabilities of non-Saccharomyces yeast represent perhaps their most commercially valuable attribute. Through the production of diverse volatile compounds (esters, higher alcohols, and organic acids), these microorganisms create complex aromatic profiles ranging from fruity and floral to nutty and spicy. This biochemical diversity enables bakers to develop signature products with distinctive sensory characteristics that cater to growing consumer demand for artisanal and premium bakery products. Particularly noteworthy is the ability of certain strains to maintain these flavour compounds through the baking process, overcoming a historical challenge in unconventional yeast applications. Beyond sensory improvements, these yeast strains offer measurable health benefits. Several species demonstrate probiotic potential, while others reduce gluten content or mitigate allergenic compounds through enzymatic action. The increased bioavailability of iron, zinc, and B-vitamins through their phytase activity presents opportunities to address micronutrient deficiencies in staple foods. Additionally, some strains synthesize functional compounds like antioxidants and polyunsaturated fatty acids, potentially transforming ordinary bread into a functional food product.

The environmental advantages of unconventional yeast adoption merit special attention. Many strains thrive on alternative substrates, including agricultural by-products (whey, molasses, lignocellulosic materials), offering opportunities for waste valorization. Their frequently observed antifungal properties can naturally extend product shelf life, reducing food waste. Moreover, their metabolic efficiency in mixed-culture fermentations may lower overall energy requirements in production facilities. Looking forward, the baking industry stands at the threshold of a microbial revolution. By moving beyond the monoculture of Saccharomyces cerevisiae and embracing yeast biodiversity, bakers can unlock new dimensions of quality, nutrition, and sustainability. This paradigm shift will require collaboration between microbiologists, food technologists, and bakers to overcome technical barriers and fully realize the potential of these remarkable microorganisms. The future of baking may well depend on our ability to harness the untapped potential of the microbial world, transforming an ancient practice through modern science.