Dairy Fermentation 2.0

The manufacture of fermented dairy products has a long history, and such products are produced globally, following artisanal or industrial fermentation processes, satisfying consumers’ need for healthy, nutritious, delicious and safe foods [1]. Milk from cows, as well as other mammals, including sheep, goats, camels, mares, buffalo and yaks, is used for their production. Milk from different species shows differences in microbiota and chemical composition and certain components vital for fermentation [2]. The diversity of fermented milk products is further influenced by the wide variety of manufacturing practices [1]. Throughout the evolution of fermented milk products, functional and therapeutic properties have been attributed to certain components, and thus, these products have gained a significant market share [3,4]. The exploitation of microbiological methods based on DNA (or RNA) extraction and, more recently, high-throughput techniques has revealed the significance of the properties of autochthonous microbes and provided novel insights into the role of the microbiota in the functional and organoleptic properties of many fermented milk products.

The fermentation of milk is carried out by complex microbial communities [1,5,6]; their biochemical activities are key steps in the formation of the special characteristics and the safety of the fermented dairy products. Lactic acid bacteria (LAB) constitute the most important member of microbial communities [1,7]. LAB are naturally present in milk, as part of the autochthonous microbiota, as well as contaminants during milking and/or throughout the manufacturing process from the dairy factory environment and storage surfaces [8]. Cheese is the most complex fermented dairy food product, and the diversity in herd management, cheese making and cheese ripening practices, often in small-scale production, has generated a great diversity of cheese characteristics, especially for the matured cheeses [6].

The present Special Issue (SI) is focused on the latest research on dairy fermentation and fermented dairy products. This SI comprises six papers, two review articles and four research articles, studying aspects of the technology and microbiology of dairy products such as cheese, fermented milk and probiotic yogurts. These articles show some interesting approaches to dairy fermentation.

Industrial production has an impact on the loss of biodiversity, and researchers are searching for innovative ways to restore some of the autochthonous milk microbiota. The use of autochthonous LAB isolated from the traditional “Paški sir” was investigated by Kiš et al. (2023) (Contribution 1). The authors added the cultures as a microencapsulated form, and the number of Lactiplantibacillus plantarum remained stable throughout the ripening process and produced cheese with the same characteristics as the traditional product.

Samelis et al. (2023) investigated the addition of adjunct cultures of a mixed thermophilic and mesophilic starter culture consisting of Streptococcus thermophilus ST1, Lactococcus lactis subsp. cremoris M78 and L. plantarum H25 for the manufacture of traditional Galotyri Protected Designation of Origin cheese (Contribution 2). The addition of the L. plantarum H25 adjunct strain showed minor effects on the cheese’s pH, gross composition and proteolysis but improved the texture, flavor and bacteriological quality of the cheese during processing. Due to its antifungal activity, it is suggested that the adjunct culture be used as a protective culture.

The health benefits of probiotics (Lactobacillus acidophilus and Bifidobacteria) and/or prebiotics (1 and 3% inulin and fructo-oligosaccharides) on the content of butyric acid and pyroglutamic acid in yogurt during its shelf-life was evaluated (Contribution 3). The symbiotic yogurt showed increased contents of both acids.

Gizachew et al. (2023) tested 43 LAB, isolated from Ethiopian traditional cheese and yogurt, and evaluated them for their functional and safety properties as candidate probiotics (Contribution 4). The authors suggested five isolates, namely L. plantarum 54B, 54C and 55A, Lactiplantibacillus pentosus 55B and Pediococcus pentosaceus 95E, as potential novel probiotic candidates of interest for clinical trial follow-up.

The application of protective cultures in cheese was reviewed by Bintsis and Papademas (2024) (Contribution 5). The review provides an overview of the application of commercial and autochthonous adjunct cultures on the bio-protective potential of cheese. Since LAB have been found to possess antibacterial and antifungal activities, both public health and spoilage aspects are considered. Protective cultures composed of specific strains of LAB species such as Lactococcus lactis, L. plantarum, Lacticaseibacillus paracasei, Lacticaseibacillus rhamnosus, Levilactobacillus brevis, Lactobacillus sakei, Enterococcus faecium and Carnobacterium spp., Bifidobacterium spp. and Propionibacterium spp. were applied to control the growth of pathogenic and spoilage bacteria in different cheeses.

According to Genet et al. (2023), alternative fermented dairy products such as yogurt and particularly ripened hard and semi-soft cheese products are not yet satisfactory (Contribution 6). Since the cheese category has such a broad range of flavors and applications, it has proven complicated to find plant-based sources able to mimic such products in terms of texture, meltability, ripening and flavor. The authors discuss the challenges of both animal- and plant-based cheese products and “hybrid cheeses”, that is, products incorporating plant-based components into the milk matrix and creating a hybrid product.

Future research work on the characterization of the autochthonous LAB microbiota of traditional fermented dairy products will provide insights into the special benefits of such products. In addition, the application of selected cultures from the characterized microbiota as adjunct, probiotic and/or protective cultures looks to be a promising process for the manufacture of a variety of novel dairy, non-dairy and “hybrid” products. However, the evaluation of the effects of these cultures on the overall microbial ecology of each type of fermented product as well as on the physico-chemical, organoleptic, nutritional and functional properties is critical.