Challenges and approaches for production of a healthy and functional mayonnaise sauce

Abstract Mayonnaise is a semisolid oil‐in‐water (O/W) emulsion which is made through the careful blending of oil, vinegar, egg yolk, and spices (especially mustard). In addition, mayonnaise traditionally contains 70%–80% oil, and egg yolk is a key ingredient contributing to its stability. Despite concerns about high cholesterol level in egg yolk, it is yet the most widely utilized emulsifying agent owing to its high emulsifying capacity. Today, the public knowledge about diet and health has been incremented, compelling the people to consume foodstuffs containing functional features. Thus, consumers, aware of the considerable influence of the diet on their health, demand nutritious and healthier food. Mayonnaise is usually cited by health‐related issues due to its high cholesterol and fat content. Many researchers have tried to replace fat, as well as egg yolk completely or partially; however, low‐fat mayonnaises require extra ingredients to keep the stability. In other words, each ingredient plays a specific role in textural and oxidative stability, and using alternative emulsifiers and fat replacers may affect the sensorial, textural, and antioxidant features of mayonnaise. Furthermore, mayonnaise, like other high‐fat foodstuffs, is vulnerable to auto‐oxidation. In addition to using fat replacers, mayonnaise is accompanied with bioactive ingredients to produce a healthy system. Therefore in this review, we gathered a quick summary of the ideas, including lowering the cholesterol and fat and using natural antioxidants, prebiotics, and probiotics in order to produce a healthy and functional mayonnaise sauce.


| INTRODUC TI ON
The development of new food products seems to be increasingly challenging, because it has to comply with the consumers' satisfaction, especially for relish health foodstuffs. In this concern, functional foods that have health benefits in addition to nutritional contents and particularly foods with reduced fat are of great importance (Bigdelian & Razavi, 2014;Miele, Di Monaco, Cavella, & Masi, 2010). From the marketing point of view, it is vital to know about the importance of the health claim of functional foods.
Food fulfills three principal functions: the first one is nutrition, followed by reducing lifestyle-related illnesses. These two functions were primarily described in 1984 in the deployment and systematic analysis of functional food research project funded by the Ministry of Education, Culture, Sports, Science, and Technology, Japan. The third function, defined in terms of foodstuffs with health claims (FHCs), was first labeled in Japan, which established regulations for expanding FHCs. Nowadays, the consumption of functional foods has spread throughout the world and been encouraged by the increasing dietary interest of consumers. Consumers demand to purchase functional foods, in which they recognize the health-promoting features, not found in conventional foods.
Over the past decades, the number of studies, pertaining the low-fat edible products, has increased with considerable regard to diseases such as obesity, cardiovascular diseases, and cancer (Chang et al., 2017). Fat, as a substantial constituent of foods, has long been noted as the main source of energy and the satiety. Gradually, other benefits of edible products as fat-soluble vitamin carriers and major sources of essential fatty acids were likewise recognized (Emadzadeh & Ghorani, 2015). However, on account of lifestyle changes and the lack of any balance between the intake and expenditure of energy, obesity has incremented globally (Aganovic, Bindrich, & Heinz, 2018). Considering the over-consumption of fat as a deciding factor in obesity, the production of low-fat foodstuffs has stimulated many research interests (Ma & Boye, 2013). In this regard, no-fat and lowfat sausages, cream, yoghurt, and mayonnaise have been developed (Sun et al., 2018). Regarding this, mayonnaise manufacturers now tend to produce low-fat mayonnaise, because oil is commonly the most expensive ingredient of mayonnaise (Depree & Savage, 2001).
Although replacing the fat is the crucial part of producing healthy mayonnaise, in these days, consumers demand not only a healthy food, but also a functional product, a product that can respond to medical needs of people beyond their nutritional requirements. To this end, several beneficial ingredients, such as probiotics, prebiotics, antioxidants, and phytosterols, have been added to mayonnaise. Thus, this paper mainly aimed to describe the properties of functional mayonnaise, as well as explaining the role of its different ingredients.

| MAYONNAIS E ING REDIENTS AND FE ATU R E S
Mayonnaise is an oil-in-water (O/W) emulsion and is widely consumed as a traditional seasoning due to its creamy mouthfeel and special flavor. The conventional mayonnaise contains 65%-80% fat, which contributes to its texture, appearance, flavor, and shelf life (Sun et al., 2018;Worrasinchai, Suphantharika, Pinjai, & Jamnong, 2006). Mayonnaise is presumed to have originated from Port Mahon, France, in 1756. It was produced for celebrating the conquering the Port Mahon by forces under the command of Louis Francois Armand de Vignerot du Plessis, duc de Richelieu (1696-1788), a marshal of France, and it was called Maho´nnaise. The word was later changed to mayonnaise, probably because of the old French words for egg yolk and to stir, moyen and manier (Morley, 2016).
Mayonnaise was produced commercially in the early 1900s for the first time and then became popular in America from 1917 to 1927 (Harrison & Cunningham, 1985). Later in Japan, the mayonnaise price was incremented by 21% from 1987 to 1990 (Le, 1992).
This emulsion includes an aqueous solution as a constant phase and oil as a dispersed phase (Aganovic et al., 2018). It is produced using vegetable oil, emulsifier (egg lecithin), acidic components (acetic acid, citric acid, and maleic acid), flavoring agents (sweetener, salt, mustard, or garlic), texture enhancers, stabilizers, and an inhibitor for unwanted crystals (Yildirim, Sumnu, & Sahin, 2016). Some features of mayonnaise ingredients are illustrated in Figure 1.

| The role of oil fraction
The mayonnaise emulsion is formed by leisurely blending of the oil with a premix, including vinegar, mustard, and egg yolk, because blending the aqueous phase and oil at once would result in the creation of a water-in-oil emulsion (Liu, Xu, & Guo, 2007). Traditional production of the emulsion often includes batch mixers, meaning that the oil is gradually added to an aqueous phase under extreme mixing, though production by the use of a high speed mixer and the batch process is fairly inefficient (Depree & Savage, 2001). Continuous procedures are available for making mayonnaise as well. In these methods, there are pumps, which blend three phases of egg, oil, and water in a mixer, following continuous homogenization. Furthermore, a batch-continuous method exists, which is a mixture of both procedures, where coarse-form emulsion is made batch-wise, following continuous steps to decrease the fat droplets (Aganovic et al., 2018).
Mayonnaise is a microbe-stable foodstuff due to its high fat content and acidic conditions and may be kept at room temperature; nevertheless, the loss of quality always exists owing to the auto-oxidation of unsaturated fatty acids (Aganovic et al., 2018).
Fat, as one of the major ingredients, positively affects the rheological attributes and sensory characteristics of the final produced mayonnaise. It also contributes to the flavor, texture, creaminess, palatability, appearance, and shelf life of mayonnaise (Mun et al., 2009). Moreover, one of the most important features of mayonnaise, basically induced by fat, is the mouthfeel property.
Generally, the mouthfeel for fat in a lipid-based product is a rheological phenomenon. The sensation of fattiness is a complex phenomenon, involving flowability and viscosity properties of a food product. Ma et al. studied the functionality of fat replacers in foods and discovered that particles smaller than 3 µm in diameter could not be distinguished by the human tongue (Ma, Cai, Wang, & Sun, 2006).

| The role of salt and vinegar
The most important role of vinegar is pH adjustment. The mayonnaise pH has a profound impact on the emulsion structure. The stability and viscoelasticity of mayonnaise would be at its highest point when the pH value reaches the isoelectric point of egg yolk proteins, to such a degree that the proteins' surface charge is lessened.
The flocculation of proteins would never happen if the proteins are highly charged (Depree & Savage, 2001).
Mayonnaise oil droplets are positively charged owing to the composition of proteins in the interface, as well as the medium pH (<4.2 for mayonnaise). It has been proved that droplets containing negative charge tend to adsorb metal ions with positive charge, which can favor the development of lipid oxidation (Aleman et al., 2015). In addition, a low pH value (pH = 4) breaks the ion bridges present between phosvitin and iron. Moreover, ferric ions are insoluble and soluble in neutral and low pH values, respectively. Therefore, decreasing the pH value may also render the incremented solubilization of iron ions in the mayonnaise (Jacobsen, Timm, & Meyer, 2001), which is important from the oxidation point of view.
From the microbiological viewpoint, Xiong, Xie, and Edmondson (2000) suggested that at least 60 ml vinegar per fresh whole egg, 40 ml per fresh egg white, or 20 ml per fresh egg yolk (6% w/v acetic acid) is required to produce Salmonella-free mayonnaise in the kitchen.
Concerning the salt, its addition can enhance the mayonnaise characteristics for three main reasons. First, salt aids in dispersing the egg yolk granules and increasing the availability of more surfaceactive materials. Second, salt neutralizes protein charges, so the proteins can easily be adsorbed to the surface of the oil droplets.
Third, it provides the proximity of oil droplets to each other, thereby interacting more strongly. However, excessive salt may trigger the aggregation of egg yolk proteins in the aqueous phase owing to the salting-out effect (Depree & Savage, 2001).
F I G U R E 1 Main constituents of mayonnaise and their roles

| The role of egg and its substitution challenges
Egg is well-known for its gelling, whipping, and emulsification features. It plays a significant role in the preparation of foods.
The three most known usages for eggs are as follows: liquid egg, which solidify or coagulate when heated (in order to solidify and produce cakes and so on); aeration or whipping which generates lighter and airier products (e.g., merengue); and the emulsifying phospholipids existed in egg yolk and lipoproteins, which would make sauces and salad dressings (Abu-Salem & Abou-Arab, 2008).
Although egg possesses brilliant emulsifying property, the constraints are the possibility of contamination with Salmonella sp., and price, as well as high cholesterol content of egg yolk (Smittle, 2000).
For these concerns, scientists have researched into the role of animal proteins to replace the egg yolk. Therefore, emulsification properties of animal proteins such as casein, whey protein, and meat protein have been widely investigated by a number of researchers (Nikzade et al., 2012). In addition to animal protein, plant ones have also been considered. The utilization of plant proteins is needed to support the production of protein-rich foods which can find itself properly in the human diet. Hence, the use of plant proteins (e.g., lupin protein, soybean protein, and pea protein) instead of egg yolk to stabilize the oil-in-water emulsion is the most popular method for preparing mayonnaise-like emulsions (Diftis, Biliaderis, & Kiosseoglou, 2005). For example, starch paste has been used to replace egg yolk (Dolz, Hernández, & Delegido, 2006;Mancini, Montanari, Peressini, & Fantozzi, 2002). However, the usage of starch paste extends the duration and price of processing along with an unfavorable possible effect on the texture and flavor of mayonnaise. The other approach is the use of egg yolk containing low cholesterol as the emulsifying agent in mayonnaise (Laca et al., 2010). Oxalate calcium crystals were present in the Opuntia robusta, and mucilage with druses morphology was not observed due to the product acidic pH; so it is suitable to develop a functional low-fat mayonnaise.

F I G U R E 2 Functional ingredients added to mayonnaise and their importance
Bernardino-Nicanor et al.

50%
No rheological and sensorial differences between treated and control mayonnaises Su, Lien, Lee, and Ho (2010)

| COND ITI ON S US ED TO PRODUCE HE ALTHY AND FUN C TIONAL MAYONNAIS E
The investigation of researchers demonstrates that two main approaches are considered in producing a healthy and functional mayonnaise: using fat replacers, or/and adding some functional ingredients to mayonnaise, which usually are composed of prebiotic, antioxidant, or phytosterol ( Figure 2). The application of these ingredients in mayonnaise is discussed in the following parts.

| Replacement for fat/oil
The American Heart Association has suggested limiting the fat usage to lower than 30% of the whole consumed calories (Amin, Elbeltagy, Mustafa, & Khalil, 2014). In addition, the substitution of a part of fat without decreasing the taste is a key factor in producing low-fat foodstuffs (Santipanichwong & Suphantharika, 2007). Moreover, the sensory and physiochemical properties of mayonnaise are significantly affected by the elimination of fat; hence, the attention to fat replacers is increasing (Chung, Degner, & McClements, 2014).
From a physical point of view, decreasing the dispersed phase and increasing the water content are necessary to create a low-fat emulsion (Izidoro, Scheer, Sierakowski, & Haminiuk, 2015).
Unfortunately, decreasing the oil proportion in mayonnaise decreases the oil droplets density, thereby weakening the stability and interactions between droplets and emulsion. In addition, stability of low-fat emulsions can get better through decreasing the droplet size, which also provides a "creamier" appearance (Depree & Savage, 2001). In another word, reducing the fat level would result in the increment of the water content and aqueous phase, as well as inducing the decrease in the firmness and viscosity of emulsion. Furthermore, fat substitutes are used to produce mayonnaise with a texture near to those of traditional ones (Chang et al., 2017).
Viscosity, in a low-fat mayonnaise, is incremented by additives, especially hydrocolloids, which would result in the increase of density and stability of the emulsion by reducing the coalescence (Karas, Skvarča, & Žlender, 2002). To replace fats, substances mostly should hold the following attributes: empty of osmotic and diarrhea effects, toxicologically safe, functionality analogues to fat, mouthfeel-like fat, and a similar price to fat (Cheung, Gomes, Ramsden, & Roberts, 2002). Different roles of fat replacers in mayonnaise are summarized in Table 1. 4aGTase-modified rice starch (Mun et al., 2009), oat dextrin (Shen, Luo, & Dong, 2011), modified starch (Ali, Waqar, Ali, Mehboob, & Hasnain, 2015), inulin (Alimi, Mizani, Naderi, & Shokoohi, 2013), pectin (Chang et al., 2017), and some thickeners have been investigated to replace fat in mayonnaise. In the meantime, there is an interesting point about pectin, because it has the potential to inhibit the digestion of lipid along with increasing the stability and reducing the creaming of oil droplets (Sun et al., 2018).

| Fat mimetic
Moreover, whey protein is commonly utilized in the production of fat mimetics because of its ability in the coagulation of a gel under distinct temperature and pH circumstances. Microparticulated whey protein (MWP) covers taste buds analogues to lipids. This coating manner helps flavors to gradually reach the receptors and helps to mask some astringent and bitter flavors in low-fat products (Chung et al., 2014).

| Antioxidants
Oxidation reactions are considered as interfacial phenomena, which are influenced by a number of different parameters such as physicochemical properties of water and oil phases, chemical composition, the kind of surfactants, and the oil phase surface area (Kishk & Elsheshetawy, 2013). In addition, interfacial oxidation is a critical issue about emulsified foods such as mayonnaise, because it affects the shelf life of the food (Calligaris, Manzocco, & Nicoli, 2007).
Moreover, mayonnaise is at risk of lipid oxidation when kept at 4°C (Raikos, Neacsu, Morrice, & Duthie, 2015). Mayonnaise oxidative stability is largely affected by its ingredients and especially the kind of oil. For example, the production of mayonnaise with n-3 polyunsaturated fatty acids (PUFAs) increases the possibility of oxidation.
Although PUFAs have nutritional and health benefits, their oxidation leads to the development of reactive aldehydes, free radicals, off-flavor, and the decrease in the shelf life of mayonnaise (Aleman et al., 2015).
Normally, synthetic antioxidants of TBHQ, BHA, and BHT are utilized to suppress the rancidity of fats. Although the antioxidant strength of these synthetic antioxidants is more than that of natural antioxidants in many cases, the toxicity of these antioxidants and consumer demands for natural products have turned the attention toward the use of natural antioxidants (Kishk & Elsheshetawy, 2013). Natural antioxidants originate from several marine algae and plants, many of which display a high potential to enhance the stability of foodstuffs against oxidation. Moreover, these antioxidant substances have a wide spectrum of health-promoting advantages .
In a study, Jacobsen, Hartvigsen, et al. (2001) investigated the antioxidant impacts of EDTA gallic acid, and extra Panodan DATEM TR as emulsifiers in mayonnaise incorporated with 16% fish oil.
EDTA decreased the production of lipid hydroperoxides, free radicals, and rancid and fishy off-flavors. These results were attributed to the chelation of iron and free metal ions by EDTA from egg yolk.
Gallic acid decreased concentrations of lipid hydroperoxides and free radicals, but increased slightly the oxidative off-flavor. Finally, the addition of extra emulsifier decreased only the level of lipid hydroperoxide, but did not affect the concentration of free radicals or the off-flavor in mayonnaise. Honold, Jacobsen, Jónsdóttir, Kristinsson, and Hermund (2008) considered the potential of seaweed-based food antioxidants to delay the oxidation of lipid in the mayonnaise enriched with fish oil.
In this study, acetone, ethanol, and water were used to extract the phenolic contents of F. vesiculosus. Ethanol and acetone successfully extracted high concentrations of carotenoids and phenolic compounds. In addition, water was found to not only extract some phenolic substances, but also to extract higher concentrations of chlorophyll derivates and metals. Results showed that ethanol and acetone extracts had the highest antioxidant capacities.
The potential to chelate trace metals is also an important parameter of antioxidant activities, specifically in the mayonnaise (Honold et al., 2008). The trace metals like copper and iron may interact with unsaturated fats to produce radicals (alkyl radicals) or cause peroxides degradation to alkoxyl radicals. A large value of iron in mayonnaise is originated from the egg yolk. In egg yolks, the chief proportion of iron has been bonded to the phosvitin. However, by the incorporation of egg yolk to mayonnaise, the low pH (pH = 4) breaks the ion bridges between phosvitin and iron, thereby enabling the participation of iron in lipid oxidation .
The synthetic chelating agents like EDTA have been observed to be the highest effective inhibitors against metal-catalyzed oxidation in mayonnaise (Jacobsen, Hartvigsen, et al., 2001).
In addition, Sørensen, Nielsen, Hyldig, and Jacobsen (2010)  One of the most widely used approaches to deal with mayonnaise oxidation is adding vegetables, containing high antioxidant capacity. For example, Raikos et al. (2015) supplemented mayonnaise with some vegetables (5% w/w) and investigated the impact of storing time at 4°C on the stability of dispersed phase against oxidation. Results inferred from both TBARS and Rancimat indicated that the vegetable type utilized for the reformulation of mayonnaise is substantial in the inhibition of oxidation, and followed the order beetroot > carrot ≈ onion regarding the antioxidant capacity. Fucus vesiculosus , lipophilized caffeine (Aleman et al., 2015), ginger powder (Kishk & Elsheshetawy, 2013), eugenol-lean clove extract (Chatterjee & Bhattacharjee, 2015), and microwavingprocessed beetroot (Raikos, McDonagh, Ranawana, & Duthie, 2016) are other examples.
Prebiotics also play an imperative role in modulating the expression of genes and have a high impact on human metabolism to control diabetes mellitus type two.
According to Global Market Insights, INC, the global market of prebiotics is expected to surpass 8.5 billion US dollars by 2024 (Fonteles & Rodrigues, 2018). Statistics show that more than five hundred new products enriched with prebiotics have been offered to the market during the past few years (Silveira et al., 2015).
Inulin is one of the most recently used prebiotics in the mayonnaise formulation. Along with the prebiotic property, inulin forms insoluble crystals in food systems when contacting with water, causing a unique gel structure and making a spreadable texture (Franck, 2002). In addition, inulin particles function in the same way to oil droplets in O/W emulsions and can be used as the fat replacer

| Probiotics and the effects of encapsulation by prebiotics
Food and Agricultural Organization of the World Health Organization has defined probiotics as "live microorganisms which when administered in adequate amounts confer a health benefit on the host" (Hill et al., 2014). Like prebiotics, probiotics can amend the arrangement of the gut microflora and affect both intestinal and body functions (Roberfroid, 2010). The consumption of probiotics affects various aspects of immune system such as increasing mucin production, inhibiting pathogens colonization, decreasing gut permeability, and activating macrophages and natural killer cells. Concerning the adaptive immune system, the observed effects include the increase in the antibodies (IgA, IgM, and IgG) production, and an arrangement in the branches of the immune system through the production of cytokines (Anadón, martinez-larrañaga, ArÉS, & MartÍNez, 2016).
Probiotic bacteria such as lactobacillus and bifidobacteria have therapeutic performances by lowering cholesterol, preventing cancer, alleviating constipation, and reducing lactose intolerance (Guerin, Vuillemard, & Subirade, 2003). Yet, to make these functions, probiotics should be stable while passing the gastrointestinal tract, along with colonizing in the intestine (Brinques & Ayub, 2011). For applying these advantages, probiotics should be added at the concentration of 10 6 CFU/g to the products (Chan & Zhang, 2002). Mayonnaise sauce can be a suitable carrier for probiotics owing to its high water activity .
Foods containing high buffering capacity increment the pH of the gastric tract and result in improving the stability of probiotics, thereby making mayonnaise a good matrix for probiotics (Shen et al., 2011).
Furthermore, probiotics are not usually used in direct form in foodstuffs due to the sensorial and stability issues (de Vos, Faas, Spasojevic, & Sikkema, 2010); therefore, many researchers are trying to find a way to increase the survival of probiotic cells. To protect probiotics against adverse environmental, processing, and intestinal conditions, these cells have to be protected with a physical barrier (Kailasapathy, 2009;Schell & Beermann, 2014). Microencapsulation is considered a useful method to protect probiotics (Burgain, Gaiani, Linder, & Scher, 2011).

added Bifidobacterium bifidum and
Bifidobacterium infantis to mayonnaise as free and alginate encapsulated cells. The viability of free cells was totally destroyed after 2 weeks; nevertheless, encapsulated B. bifidum survived up to 12 weeks and B. infantis for 8 weeks (Khalil & Mansour, 1998). Bigdelian and Razavi (2014)

| Natural preservatives used in mayonnaise
Mayonnaise sauce is a relatively microbial safe product owing to its high fat content and presence of acidic ingredients which reduce the pH of product to a lower value of 4.8 (Depree & Savage, 2001;Karas et al., 2002). Most pathogenic bacteria such as Escherichia coli, L. monocytogenes, Salmonella, Yersinia enterocolitica, and Staphylococcus aureus are destroyed when inoculating into mayonnaise. However, spoilage microorganisms such as lactobacilli might grow in mayonnaise and affect its shelf life and safety (Fialová, Chumchalová, Miková, & Hrůšová, 2008). In addition, certain organisms such as E. coli can be broken out by mayonnaise. Furthermore, the colonization of microbes in mayonnaise differs based on the type of acid used, temperature, pH, and storage time (Yolmeh, Habibi Najafi, Farhoosh, & Salehi, 2014).
In these days, the usage of natural preservatives instead of synthetic ones is promising, because synthetic preservatives are suspended to be nonsafe and possibly harmful. To control the growth of microorganisms, organic acids such as sorbic acid and benzoic acid and/or a mixture of them have usually been advised as the most applicable preservatives in mayonnaise. The maximum allowed concentrations of sorbic acid and benzoic acid, in this regard, are 1 g/kg and 2 g/kg of mayonnaise, respectively. However, these preservatives are not capable of controlling the growth of lactobacilli (Yolmeh et al., 2014). Along with organic acids, some naturally occurring preservatives such as bacteriocins and H 2 O 2 can be used in mayonnaise (Fialová et al., 2008).
The following examples clarify the application of some natural preservatives in mayonnaise: Adeli Milani, Mizani, Ghavami, and Eshratabadi (2014) (2006) functional mayonnaise sauce were discussed here. Every ingredient has a specific role, and the increase or decrease of any particle will affect the texture, stability, and sensory attributes, as well as antioxidant stability of the product. Taking this fact into account, many researchers successfully reduced oil content even up to 60% by replacement of oil for various stabilizers and this reduction of oil content of the product could decrease oxidation indirectly. This review had a quick look to the attempts made during two recent decades about reducing fat, using probiotics, prebiotics, and natural preservatives; decreasing cholesterol content; and adding nutritious supplements like phytosterol to prevent cholesterol adsorption. Overall, it could be noted that it is possible to design a nutritious and healthy mayonnaise with lower fat and cholesterol.

ACK N OWLED G M ENTS
We thank Mr. Rahmanopour for his attempts in providing some materials.

CO N FLI C T O F I NTE R E S T S
The authors declare that they have no conflict of interest.

E TH I C A L S TATEM ENT
The authors state that human and vertebrate animal testing was unnecessary in this study.