The term ‘food additives’ represents the substances that are added to food to retain or preserve and/or improve some physical properties, often taste, texture, freshness and appearance, along with its safety. However, it is additionally imperative to evaluate the food additives themselves for their potential harmful effects on human health before they are utilized for their desired applications. Among several substances available, surfactants are considered as the most multifarious agents explored for varied applications, such as detergents, pesticide application, cosmetics and microbial enhanced oil recovery processes, and the food-processing industry ^[1][2][3][1,2,3]. Surfactants are obtained from various sources, e.g., petrochemicals, fatty acids, microbial cells, etc. ^[4][5][4,5]. Some known natural surfactants, such as lecithin from egg yolk and milk proteins, are prominently used in salad dressings and for the enhancement of flavor, appearance, and texture of desserts ^[6][7][6,7]. The growing interest in surfactants and the identification of appropriate molecules with less toxicity and efficient surface characteristics have been of immense interest for both industrial and scientific communities.

Synthetic surfactants are linked with many health-related issues and drawbacks, among which intestinal dysfunction [8] is reported prominently. Surfactants are used in foods in relatively high concentrations, which might lead to severe intestinal permeability, which in turn may elicit various allergic and autoimmune diseases [9]. Surfactants increase intestinal permeability for a limited time in a precise and recurrent way in the presence of antigens and pathogens. It is crucial to note that there are no acceptable daily intake (ADI) guidelines for the use of surfactants in food production [10]. The ADI guidelines specify the highest amount or the limit of a particular chemical which can be consumed regularly over the period of a life span without any health-related issues or apparent side effects. Demands of green ingredients over synthetic additives (“green label”) have led to extensive research in pursuit of new microbial sources for the production of effective surface-active or emulsifying agents ^[11][12][11,12].

BSs are generally low-molecular-weight compounds with the ability to reduce surface tension noticeably, whereas BEs are high-molecular-weight molecules with efficient emulsifying abilities. BSs represent surface-active compounds of microbial origin. BEs are considered as BSs that are used as emulsifiers; therefore, the term BS is much wider and inclusive of BEs. Multifarious BS/BE molecules confer or provide various functional properties to food, such as emulsifying, additive, foam-forming, and wetting agents, in addition to pharmaceutical-related properties (antimicrobial, antiadhesive, antiviral, antibiofilm, etc.) ^[12][13][12,13]. Even though BSs and BEs have an unquestionable potential for replacing synthetic surfactants, with huge importance to food industries. Major blockages include high production cost and apprehension regarding their safety. The present research about BSs/BEs in food production is restricted to laboratory conditions, without detailing any assessment regarding their safety and hazard analysis, which has restricted their acceptance for several food-related applications ^[12][13][14][12,13,14]. It is important to note that committed guidelines for adopting BSs/BEs in food formulations do not exist; however, the recommendations to include them as all-purpose food additives might be accepted, and would grant their primary approval.

2. Biosurfactants as Food Additives

Food additives are compounds or substances that facilitate the enhancement of overall food properties. Since ancient times, some food additives such as salt, sugar, and SO₂, have been utilized to preserve meats, fishes, beverages, etc. Currently, the journey of food additives has made huge advances, from kitchens and small factories to the advanced commercial scale. Food additives have been obtained from various natural sources, or synthesized chemically, and added to food items to achieve some positive technological benefits. Thus, food additives should solely serve the intended desired aims of preserving the nutritional quality of food, and not result in any negative effects. Based upon their functional properties, the World Health Organization (WHO) and the Food and Agriculture Organization (FAO) have broadly categorized additive compounds as (1) flavoring agents, (2) enzyme preparations, and (3) other additives. Microbial surfactants as food additives comprise molecules that may be introduced to food in order to confer emulsifying, foaming, thickening, texture-improving, and/or preserving properties, along with the encapsulation of fat-soluble substances such as vitamins (called “direct food additives”). Attributes such as antiadhesive/antimicrobial or food surface cleaning are termed as “indirect food additives” that are fulfilled through packaging, coating, or transport and storage processes. Microbial BSs pose antiadhesive and antimicrobial activity against several pathogens and have been listed in Table 1. BSs may interact with porins (proteins of cross cellular membranes) and may lead to leakage of the cytoplasmic content of the cell, resulting in cell death [13]. However, prior to the inclusion of BSs/BEs in food processing, they must undergo critical toxicological assessment protocols which test synergistic compatibility with food molecules, dosage limit determinations for daily intake, and potential protective effects of their use. Rhamnolipids (RLs) have been reported to improve various properties, such as dough stability, batter texture, and the volume and shape of bakery products [14]. A patent on ‘RLs in bakery products’ emphasizes the improvement of dough characteristics and the volume of bakery products after mixing with RLs [15]. Basically, L-rhamnose is a methyl pentose natural sugar found in varied microbial RLs [16], which is useful as a food additive. Kiran et al. [17] described the BSs of Nesterenkonia sp. for the enhancement of muffin texture. The Nesterenkonia sp. are obligate aerobes, grouped under the genus Micrococci, which grow optimally between 25 and 37 °C. Phylogenetic and chemotaxonomic analysis of isolates showed Kocuria, Kytococcus Dermacoccus, and Nesterenkonia under the genus Micrococcus [18]. Use of Nesterenkonia provides various additional benefits to the muffins, including a decrease in hardness, chewiness and gumminess compared to control treatments in the presence of 0.75% lipopeptide in the preparation mixture. The roles of microbial BSs/BEs (e.g., surfactin, RLs, lipopeptides, glycolipids, and emulsan) as emulsifiers, bakery additives, flavor enhancers, bread improvers, etc., are outlined in Figure 1 and listed in Table 2. Campos et al. [34] established the varied formulations of mayonnaise with Candida utilis derived BE as a key ingredient to confer stability to the emulsion during storage process. Dough properties and volume were considerably improved with the use of the chemical emulsifier glycerol monostearate at the application of 0.1% BSs. In another example B. subtilis-derived surfactants were reported highlighting their ability to enhance dough structural properties and the textural quality of cookies [37]. Similarly, Mnif et al. [38] reported the enhancement of bread dough quality with a B. subtilis-derived BS at a concentration of 0.075% (w/w) in comparison to soya lecithin. Other additional improvements in the structural properties of bread, such as chewiness, cohesion, and reduction in firmness were also reported. In a bakery-related application, Silva et al. [39] had incorporated a BS into cupcakes as a replacement of 50–100% of the plant fat contents. The replacement of plant fat by a BS resulted in some improvement in the nutritional value of the cupcake, through the reduction of trans-fatty acids (prevalent in plant fat). Microbial BSs have also been explored to improve animal feed by enriching rapeseed meal with GRAS microorganisms. Much longer ago (1951), it was already well known that surfactants encourage the growth of chickens [50]. It was also later suggested that non-ionic surfactants do have an additional impact on animals, in improving their weight, milk production capacity, and feed hydrolysis [51]. Enriching rapeseed meal with BSs produced by GRAS microorganisms successfully hydrolyzes the rapeseed meal and provides several benefits in terms of probiotic concepts. Therefore, BSs can be used as a magnificent substitute to antibiotics, some of which are restricted for use in animal feed [41]. The emulsification activity of BS/BE molecules is decisive for food industries and can be predicted by thorough understanding of their hydrophilic-lipophilic balance (HLB), which designates their usage in the preparations of water-in-oil (W/O) or oil-in water (O/W) emulsions. Based on the HLB scale (0–20), each BS/BE can be categorized, in order to explore them further for suitable applications. HLB values between 3 and 6 are desired for W/O microemulsions, while those between 8 and 18 buoy up O/W microemulsions. For instance, RLs, surfactin, and sophorolipids (SLs), according to their HLB values, favor the improvement of O/W emulsions. Some of the HLB values for representative BSs and Polysorbate 80 (as a reference) are listed in Table 3 [52]. The foremost role of surface-active agents is dropping the interfacial tension that permits the formation of small droplets in an insoluble liquid (oil and water). Surfactants reduce adverse interactions between a water–oil (W/O) interface and permit the dispersion of droplets of one phase into the other. The decrease in the droplet size of an emulsion improves the stability of suspension or liquid solutions [53]. Another potential application of BSs and BEs is their ability to form micro-emulsions, which can be utilized as carriers for fat-soluble vitamins and value-added molecules [54]. Research published by Farheen et al. [55] suggested P. aeruginosa-derived RLs, based in nano-BS preparation and its application in bakery industry facilitating enhanced emulsifying potential, as equated to synthetic surfactants. SLs are recognized for their substantial emulsification potential towards vegetable oil utilized in bakery preparations. Gaur et al. [62] reported the production of SLs by Candida spp. and further explored its applications as an emulsifier for the food industry. BSs exhibited substantial emulsification activity with olive (51%), soybean (39%), almond (50%), and mustard (50%) oils. It is a well-established fact that BSs can act as efficient emulsifying agents for several oils, and thus can probably be used in several food-related applications. Various other “indirect” applications, including biocidal, food preservation, and antibiofilm applications, need more substantiation and standardization protocols, environmental aspect assessments, along with synergy-supporting evidence ^[36][37][36,37]. Overall, applications of BSs/BEs in food, including their antimicrobial activities against pathogens, are certainly promising and are represented in Figure 2.