**1. Introduction**

Edible oils contain ubiquitous dietary ingredients that may contain high quantities of bioactive compounds, such as sterols, tocopherols, and unsaturated fatty acids [1]. The cold-pressed extracted oils are not subjected to any refining and chemical processes. Also, cold-pressed oil by-products can be used in the food industry as they are not exposed to a solvent such as hexane. The moisture is removed before the processing of cold-pressed oil by-products and the oil is removed during production. The obtained byproducts are rich in proteins and polysaccharides. Today, although cold-press oil byproducts are an important source in terms of nutrition and technology, they have not taken their place in the food industry sufficiently. However, the development of new uses for cold-pressed oil byproducts of the edible oil industry by converting them to value-added products would prevent their disposal as waste and would encourage sustainable and competitive industrial supply [2]. Cold-pressed oil byproducts of seeds, such as flaxseed, chia seed, and rocket seed have an important potential in terms of natural gum. These byproducts have high gum content and can be easily extracted from food.

**Citation:** Hijazi, T.; Karasu, S.; Tekin-Çakmak, Z.H.; Bozkurt, F. Extraction of Natural Gum from Cold-Pressed Chia Seed, Flaxseed, and Rocket Seed Oil By-Product and Application in Low Fat Vegan Mayonnaise. *Foods* **2022**, *11*, 363. https://doi.org/10.3390/ foods11030363

Academic Editors: Marco Poiana, Francesco Caponio and Antonio Piga

Received: 15 December 2021 Accepted: 19 January 2022 Published: 27 January 2022

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**Copyright:** © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

Flaxseed (*Linum usitatissimum* L.) contains rich dietary fiber (~30% by weight), unsaturated fat (~40% by weight), and bioactive protein/peptides (~20% by weight) [3,4]. Cold-pressed flaxseed oil byproducts (FOB) contained 46.37% of carbohydrate, 27.67% of protein, 9.15% of oil, and 2.87% of ash on a wet basis [5]. Flaxseed gum (FG) is a natural polysaccharide and protein blend derived from flaxseed. FG is rich in soluble dietary fiber (3–9 wt% of the flaxseed) and can be used as a thickener, a stabilizer, a gelling agent, and an emulsifier [6–8].

Chia seed (*Salvia hispanica* L.) is rich in carbohydrates (~42%, mainly dietary fiber), proteins (17–24%), oil (25–40%), and omega-3/omega-6 fatty acids (60–80% of total oil) [9]. Chia seed polysaccharide (CSP), also known as chia seed gum (CSG), is a water-soluble anionic heteropolysaccharide isolated from the chia seed coat [10]. Chia seed contains about 5% mucilage, which can also act as soluble fiber [11]. Cold-pressed chia seed oil by-products obtained from the oil industry can be considered as a natural source of oil substitutes due to its high polysaccharide and protein content [12]. Chia seed gum can be used in a variety of industrial applications, including dietary fiber supplements, fat replacer, gelling agents, thickeners, stabilizers, emulsifiers, bulking agents, and film/coating agents [13].

Rocket seed (*Eruca sativa*) contains a variety of health-promoting phytochemical compounds, such as polyphenols, fibers, and glucosinolates. It has been used in the industry for oil production due to its high oil contents (20.0%) and Erucic acid used for the manufacture of a wide range of industrial products, e.g., plasticizers, surfactants, detergents, coatings, and polyesters. [14]. The rocket seed has a significant amount of total carbohydrate (23.1%), crude fibers (20.4%), and protein (31.0%) [15]. Thanks to their carbohydrate and protein content, rocket seeds have reasonable gum content with outstanding functional properties. Rocket seed gum (RSG) has high carbohydrate (80.38%) and low protein (5.81%) contents so the purification method used when obtaining gum could be appropriate. The protein content of gum is a crucial parameter determining its emulsion, foaming, and film-forming capacity. When comparing commercial gums, the protein content of RSG was higher than that of xanthan gum (2.125%), lower than that of guar gum (8.19%), and close to that of locust bean gum (5.2–7.4%) [16].

Mayonnaise is a semi-solid oil in water (O/W) emulsion that mainly consists of vegetable oil (70–80%), egg yolk, vinegar, and salt [17]. Egg yolk has an important place among the components to ensure the stability of mayonnaise and contributes to the overall organoleptic properties of the final product [18]. However, there has been a growing tendency toward substituting eggs with plant-based components, particularly in the creation of mayonnaise analogs, due to health and environmental concerns, recently. Egg yolk is an important ingredient that affects oil droplet distribution and emulsion stability in emulsion products, such as mayonnaise. Therefore, it is very difficult to find an alternative stabilizing agen<sup>t</sup> to egg yolk in vegan mayonnaise production. In recent years, the number of studies on alternatives to egg yolk has been increasing. In this study, low-fat vegan mayonnaise samples were prepared using CSG, FSG, RSG, AG, GG, and XG, and rheological properties were compared.

There are many studies on the rheological properties of different gum solutions. However, the researchers focused more on the steady and dynamic rheological properties of the gums. The number of studies on the thixotropic properties of natural gums is limited. In this sense, there are important gaps in the literature. In this study, natural gums were produced from the cold-pressed chia seed, flaxseed, and rocket seed oil by-products. This study will also demonstrate the thixotropic behavior of a wide range of gums using specific rheological tests such as 3-ITT. Also, gums produced from cold-pressed oil by-products can be used as an alternative emulsifier for oil in water (O/W) emulsions such as mayonnaise and salad dressings to obtain a more stable O/W emulsion having expected quality. In this study, by-product gums were utilized as egg yolk replacers to produce vegan mayonnaise.
