Food Emulsifier

The global food emulsifier market is a rapidly growing segment within the food ingredients market due to the growing trend toward reducing fat content in food products.

From: Glycerol, 2017

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Food Additives: Liquid Chromatography☆

A. Kumar, L.R. Gowda, in Reference Module in Chemistry, Molecular Sciences and Chemical Engineering, 2014

Emulsifiers and Wetting Agents

Food emulsifiers assist the stabilization and formation of emulsions by reducing surface tension at the oil–water interface. Common food emulsifiers used are:

lecithin and lecithin derivatives

glycerol fatty acid esters

hydroxycarboxylic acid and fatty acid esters

lactylate fatty acid esters

polyglycerol fatty acid esters

ethylene or propylene glycol fatty acid esters

ethoxylated derivatives of monoglycerides.

Quantitative analysis of emulsifiers is difficult as most of them are similar in structure, their commercial sources are quite heterogeneous and their extraction from starchy foods is very difficult. A key problem is the quantitative extraction of emulsifiers and the exclusion of interfering substances. This problem is further complicated by the presence of food ingredients such as proteins, and the innate heterogenicity of most of the emulsifiers as well as the wide variation in their composition. The schemes of analysis for lecithin, monoglycerides, TEMS, acetylated monoglycerides, partial polyglycerol esters, propylene glycol esters, polysorbates, lactic acid esters, ethoxylated monoglycerides and sugar esters have been discussed. Baur has recommended solvents for extraction of emulsifiers.

A method for the separation of monoglyceride (E 471), sodium stearoyllactylate (E 481), calcium stearoyllactilate (E 482), diacetyltartaric acid esters of mono- and diglycerides (E 472e) and mixed acetic- and tartaric acid esters of mono- and diglycerides (E 472f) on a semi-preparative column has been described. Various emulsifiers were identified by off-line high resolution mass spectrometer. Analysis of sodium or calcium stearoyllactrylate showed that the major components were 2-stearoyl and 2-palmitoyl lactic acid and their salts.

Sodium dioctylsulfosuccinate, a wetting agent, has been permitted in a variety of food products including dry beverage bases. A post-column ion-pair extraction method was employed using methylene blue as counterion. Then the compound was extracted into chloroform from the aqueous phase. For analysis, a CN column was used with acetone − 0.01 M KH2PO4 (1:5, v/v) as a mobile phase.

Simultaneous determination of preservatives, antioxidants, sweeteners, food dyes in foods

In many processed foods more than one additive is added to the food product. Many foods contain preservatives, antioxidants and sweeteners and very often color also. Therefore analytical methods that simultaneously determine a number of additives are advantageous. Accordingly several methods have been described in literature, which offer the simultaneous detection of a number of food additives. Demiralay et al.3 simultaneously separated a mixture of aspartame, saccharin, acesulfame-K, vannilin, sorbic acid and benzoic in a single run using a C18 column and an ammonium acetate buffer (0.005 M, pH 4.0) containing 15% acetonitrile. The separation required 30 min and was used to determine aspartame, acesulfame-K and benzoic acid in cola and instant powder drinks.

Sweeteners, the Paraben series and BHA were separated and determined taking the advantage of a C18 monolithic column coupled to flow injection analysis.20 The resolution factor for the separation of each of these additives was 1.1 and can be achieved in 400 s using photodiode array spectrometer. The method is very promising and has been validated.

LC with electrospray ionization tandem mass spectrometry (ESI-MS-MS) can not only be used in the identification of a number of known additives but also unknown compounds used in the foods. This is possible by multiple reaction monitoring. Several isomers and breakdown products are detected.21

Flow injection on-line dialysis developed for sample pretreatment prior to the simultaneous determination of a number of additives by HPLC has the advantage of high degrees of automation. On line sample preparation, dilution injection and HPLC analysis reckons low consumption of chemicals and materials.4

Twenty synthetic food additives, which include three sweeteners, nine synthetic preservatives, seven food colorants and caffeine in a single run using the photodiode array detector permits the detection of these in various food stuffs.22

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Oxidation in multiphase systems

Edwin N. Frankel, in Lipid Oxidation (Second Edition), 2012

2 Protein emulsifiers

Proteins are one of the most important natural food emulsifiers because they are surface-active and are effective in preventing coalescence of oil-in-water emulsions. Protein-stabilized oil-in-water emulsions are complicated because protein molecules have various conformations at the oil–water interface. Whey proteins such as β-lactoglobulin adsorb at the oil–water interface without changing their native conformation, whereas milk plasma proteins such as β-casein become unfolded and provide further stabilization by the presence of negative charges (Figure 10.6). These types of adsorption can either be reversible to different extents or be irreversible. The unfolding of certain proteins and exposing their peptide chain at the oil–water interface would be expected to greatly influence lipid oxidation in food emulsions (Chapter 11). Thermal denaturation causes the unfolding of proteins and exposing nonpolar amino acids and cysteine side groups forming disulfide bonds and changing the polarity of the interface.

Figure 10.6. Schematic representation of adsorption of globular proteins such as β-globulin (left) and β-casein (right) at the interface of oil-in-water emulsions.

Adapted from Larsson (1994).

Proteins can be displaced in food emulsions by other surface-active molecules or can exchange with other proteins. Homogenization of milk is an important process to control lipid oxidation by changing the interfacial composition of the fat globules. In the native state in raw milk, a complex mixture of lipoproteins, phospholipids, diacylglycerols, sterols and enzymes surrounds the fat globules. By homogenization, the milk fat membrane becomes resurfaced by adsorption of casein from the aqueous phase to form a protective layer that reduces oxidation. Lipid oxidation in emulsions can thus be inhibited to different degrees, according to the partitioning of proteins between the emulsion interface and the aqueous phase, the composition of the interfacial membrane and the conformation of the protein molecules at the surface (Figures 10.5 and 10.6). As discussed later (Section C. vi), when proteins are used as food emulsifiers, they have complex interfacial effects by either retarding or promoting lipid oxidation in oil-in-water emulsions.

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Biobased Surfactants: Overview and Industrial State of the Art

Douglas G. Hayes, George A. Smith, in Biobased Surfactants (Second Edition), 2019

1.5.3 Amphoteric Surfactants

Amphoterics possess both positive and negative charged groups in the same molecule. Phospholipids are abundant biosurfactants derived from degumming of seed oils and from soap stock during the processing of seed oils (van Nieuwenhuyzen, 2014), many of which are amphoteric (e.g., phosphatidylcholine and phosphatidylethanolamine and their derivatives). Preparation and purification methods, properties, and applications of phospholipids are reviewed in Chapter 7. Alternatively, an ester bond of phospholipids can be hydrolyzed chemically or enzymatically to produce lysophospholipids, which are also common food emulsifiers (that are more polar than phospholipids) and important agents in the treatment of arteriosclerosis (cf. lsyo-phosphatidylcholine, Fig. 1.1) (DArrigo and Servi, 2010). Betaines (Fig. 1.1) are amphoterics that possess both quaternary ammonium and carboxylate groups. Betaines form zwitterions at neutral and alkaline pH and are cationic at low pH due to the protonation of the carboxylate group. Alkylamidopropyl betaines (e.g., cocamidopropyl betaine, Fig. 1.1) are commonly used. Betaines possess many of the same properties discussed below for Nα-acylated amines (Overkempe et al., 2003): good detergency, foaming properties, hard water compatibility, mildness to skin and hair, ability to reduce irritation of anionic systems, viscosity building, pH stability, and excellent biodegradability. Betaines are employed in several personal care products (shampoos, liquid soaps, and hand dishwashing liquids), fabric softeners, and other applications (Herrwerth et al., 2008; Gruning et al., 1997). Betaines are reviewed in Chapter 14. Hydroxysultaines are amphoteric surfactants possessing a quaternary amine and sulfate groups that possess similar properties as betaines (cf. Fig. 1.1; also discussed in Chapter 14). Related to amphoterics are catanionics. Catanionic surfactants are anionic and cationic surfactant mixtures that undergo ion pairing. Catianionics serve as mimics of phospholipids and have been used in self-assembly systems such as vesicles and nanodiscs (Fameau and Zemb, 2014; Zheng et al., 2018). Fatty acid carboxylates are commonly employed as the anionic surfactant component of catanionic mixtures (Fameau and Zemb, 2014; Zheng et al., 2018).

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Production and Applications of Sophorolipids☆

Sophie Roelants, ... Wim Soetaert, in Biobased Surfactants (Second Edition), 2019

3.5.3.2 SLs as Food Emollients and Sensory-Taste Modifiers

The suitability of SL for use as an emulsifying agent in food products was demonstrated by Xue et al. (2013) in the formulation and characterization of O/W emulsions containing the oxidatively stable structured lipid. The structured lipids were first synthesized using lipase as an interesterification enzyme catalyst to react rice bran oil and olive oil. Various O/W emulsions were then prepared from the structured lipids using SL (at 0.1 wt%) as the emulsifying agent in comparison with polysorbate 20 (i.e., a commonly used food emulsifier). The emulsions also contained an antioxidant additive such as propyl gallate, ascorbic acid 6-palmitate, or quercetin hydrate to inhibit peroxide formation. The stability of the emulsions was then determined for up to 20 days at room temperature. The results showed that SL was equally effective as polysorbate 20 in stabilizing the oxidatively stable O/W emulsions containing structured lipids. In another study, Koh and Gross (2016) determined the interfacial surface tensions of a series of alkyl esters of SL added to a mixture of lemon oil and water to form O/W emulsions. Their results showed that SL-ethyl ester at 0.1 wt% was optimal to stabilize the emulsion composed of 20 wt% of aq. lemon oil mixture for up to 1 week. With the application of SLs as excellent emulsifiers in food products verified in the above and other research, it is imperative that the taste sensory property of SL is studied. The binding of taste receptors that resulted in the subsequent activation of the taste-sensing cascade reactions in an in vitro assay system was demonstrated for SLs (Solaiman et al., 2016b). The in vitro assay method was based on human taste papillae (HBO) cells maintained in culture. The study showed that SLs interact with the sweet- and the umami-taste responsive heterodimeric receptor complexes via the T1R3 subunit. Furthermore, it was also demonstrated that SLs were able to inhibit the responses of HBO cells to a mixture of known bitter substances. This discovery is sure to stimulate further research interests to systematically characterize the sensory properties of SLs in order to expand the applications of SLs in the food arena.

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Proteins in food industry

Mahmoud Nasrollahzadeh, ... Nasrin Shafiei, in Biopolymer-Based Metal Nanoparticle Chemistry for Sustainable Applications, 2021

3.3.2 Emulsifying and foaming

Emulsifying and foaming properties are two significant protein functionalities in food products, such as beverages, ice cream, dressings, mousses, whipped toppings, and margarine [7, 24, 31]. Owing to their amphiphilic nature (presence of polar and nonpolar amino acid residues), proteins act as emulsifiers by adsorbing at the interface, coating oil or air droplets, increasing stable films, and stabilizing dispersions. Emulsions (oil-water interface) or foams (air-water interface) are prepared by dispersing oil droplets in an aqueous medium or a film or skin surroundings air cells, respectively. In both examples, the value of the film depends on prevention of coalescence, flocculation, and sedimentation in emulsions and the downfall of air bubbles in the foam. Protein properties such as the hydrophobicity-hydrophilicity ratio and the simplicity of protein folding-unfolding have a substantial effect on their emulsifying behavior [14]. The future of a protein to be applied as a food emulsifier is related to its amino acid sequence, structure, and properties at colloidal interfaces. Animal-based proteins, particularly those derived from eggs and milk, are usually applied to stabilize emulsions and foams [72]. The interfacial structures and properties of plant-based proteins have not been considered in details. However, plant proteins commonly form a moderately thicker interfacial layer at oil-water interfaces due to their low molecular size and structural limitation by disulfide cross links [73]. This compound, which is the result of weak protein interactions in which absorption occurs at the interfaces, contributes to the superior stability of emulsions stabilized by various plant-based proteins compared with, for example, dairy proteins. For example, soy proteins have been studied more than other plant-based proteins for their emulsification properties [74]. Some plant-based proteins, including those derived from peanut, rice, lentil, potato, and pea, have been evaluated for emulsifying properties [75–79]. In the case of foam properties, the capability of a protein to form stable foams is significant for the production of a large number of food products. However, proteins derived from egg white, soy, and milk together with gluten and collagen are the most commonly applied for forming foams in the food industry. Various plant-based proteins have been displayed to own good foaming properties and contribute to the uniform distribution of good air cells in foods [80]. Proteins perform as foam forming and stabilizing agents in different foodstuffs such as baked products, sweets, desserts, and beer. In summary, the perfect foam forming and stabilizing proteins are known by a low molecular weight, high surface hydrophobicity, excellent solubility, a small net charge at the pH of the food, and easy denaturability [32].

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Fatty Acid, Methyl Ester, and Vegetable Oil Ethoxylates

George A. Smith, in Biobased Surfactants (Second Edition), 2019

8.5 Vegetable Oil Ethoxylates

The use of vegetable oil as a raw material for the production of surfactants has been practiced for many years. Partially hydrolyzed triglycerides are widely used as emulsifiers in foods and cosmetics. The products made by interesterification of fats or oils with glycerin are a complex mixture of mono-, di-, and triesters and have limited water solubility. Cosurfactants are usually added to help disperse these materials where they function by adsorbing at the oil-water interface to help stabilize the emulsion.

The water solubility of partially hydrolyzed esters can be improved using polymerized glycerin. Polyglycerol esters (PGEs) are widely used as food emulsifiers (Lauridsen, 1976). The products are made up of glycerin oligomers esterified with fatty acid or interesterified with triglycerides (Benson, 1967). Polymerized glycerin is made by heating glycerin to over 230°C using a base catalyst. Water of reaction is removed to form glycerin oligomers with three or more repeating units (McIntyre, 1979). PGE form hexagonal liquid crystals and α crystalline gels in water that help to stabilize emulsions in food applications (Hemker, 1981).

Purified diglycerol esters have been prepared and the surfactant properties determined (Kumar et al., 1989). Monoesters show better surface tension reduction, emulsification, and foaming properties than diesters. Short-chain esters show better properties than long-chain esters. Unsaturation in the acyl group reduced emulsion stability. A hydroxyl group on the acyl chain increased surface tension and reduced foaming.

The water solubility and surfactant properties of triglycerides can be improved by adding ethylene oxide. Vegetable oil ethoxylates (VOEs) can be made in several different ways. At high temperature and alkaline conditions, triglycerides will hydrolyze to fatty acids and partially hydrolyzed glycerides. Ethylene oxide reacts with the fatty acids and hydroxyl groups of the glyceride in a random fashion. The reaction product is a complex mixture of ethoxylated esters, glycerides, and PEG. This approach is used to make castor oil ethoxylates that are used as emulsifiers in cosmetics, textile processing, and crop protection (Porter, 1994).

A second approach is to use ester insertion catalysts originally developed to ethoxylate methyl esters (Weerasooriya, 1999). The reaction shown in Eq. (8.6) requires high temperature (160–180°C) and exhibits an induction period. The reaction products are dark colored, hard waxy solids at room temperature. Soybean oil with 45 mol of EO (SOE-45) is completely water-soluble (Smith and Sneed, 2006). The CMC of these products is very low with surface tensions in the high 30 mN/m. Dynamic surface tension is high with relatively poor wetting kinetics. Interfacial tension against mineral oil is relatively low and decreases with increasing degree of ethoxylation. The foam height is about half that of AE and increases with increasing degree of ethoxylation. When tested in laundry, SOE-45 shows almost parity performance to mid-cut AE with 9 mol of EO:

(8.6)

The water solubility of VOE can be improved by partially saponifying the ester with sodium hydroxide to obtain a roughly equal mixture of mono-, di-, and triglyceride ethoxylates; fatty acid soap; and glycerol ethoxylate (Cox and Weerasooriya, 2000). The reaction mixture shows good surface tension reduction with a low CMC. Microtox tests and human patch tests show the partially saponified VOEs to be exceptionally mild and nontoxic.

Yet another approach is to react ethylene oxide with glycerin followed by esterification with fatty acid or methyl ester to produce polyoxyethylene glycerin esters. In the case of fatty acids, the reaction is run using a strong acid catalyst, and water of reaction is removed to drive the reaction to completion. This type of surfactant is widely used in cosmetic products as a foam boosters, emulsifier, and emollient to help reduce transdermal water loss. PEG-7 glyceryl cocoate is a well-known example of this type of surfactant. The wetting properties of polyoxyethylene glycerin esters have been determined by cotton disk wetting (Jurado et al., 2012). The wetting properties improve with decreasing moles of EO and show synergy with short-chain AE.

A similar product is obtained by transesterifying triglycerides with ethoxylated glycerin using a conventional base catalyst. The reaction shown in Eq. (8.7) occurs at low temperature (100°C) and produces a light colored liquid product after bleaching. VOE prepared by this reaction are extremely water-soluble and exhibit almost no gel-phase in water.

(8.7)

The reaction product is a complex mixture of mono-, di-, and triacyl ethoxylated glycerides; glycerin ethoxylate; and soap (Smith, 2013). The species distribution can be controlled by changing the ratio of triglyceride to ethoxylated glycerin used in the reaction. The main species formed is the monoacyl ethoxylated glyceride shown in Fig. 8.4. The reaction can be run with any purified triglyceride. The surface properties of coconut, olive, avocado, and soybean oil ethoxylates show low CMC values around 10 ppm and surface tension near 30 mN/m. CMC, surface tension, and foam increase with increasing degree of ethoxylation. Interfacial tension of soybean oil ethoxylates against mineral oil undergoes a minimum around 10 mol of EO. Detergency measurements under standard US wash conditions show optimum cleaning is inversely related to the interfacial tension.

Fig. 8.4. Structure of monoacyl ethoxylated glyceride.

VOE are extremely simple to make and consume 100% of the starting vegetable oil. The resulting product has very low levels of residual EO and 1,4-dioxane that are typically removed during the drying step. The US Environmental Protection Agency (EPA) classifies dioxane as a probable human carcinogen. Dioxane is irritating to the eyes and respiratory tract, and exposure may cause damage to the central nervous system, liver, and kidneys. Under California Proposition 65, dioxane is classified in the state of California to cause cancer.

The properties of the product depend on the alkyl chain distribution and the degree of ethoxylation. Work was done to prepare a series of VOE surfactants using algal oil from microalgae (Smith, 2015). The algal oil was obtained from Solazyme (South San Francisco, CA, United States), which has developed a strain of microalgae that converts plant sugars into triglycerides in high yield. The carbon chain distribution of the oil can be controlled by genetically modifying the microalgae that are grown in large industrial fermenters. The alkyl chain distribution of high lauric and high oleic algal oil is shown in Table 8.2.

Table 8.2. Alkyl Chain Distribution of Algal Oil

Fatty Acid High Lauric Oil (wt%) High Oleic Oil (wt%)
C10 15 0
C12 45 0
C14 14 0
C16 7 4
C18 1 5
C18–1 14 89
C18–2 4 2
C18–3 1 0
Total 100 100

Both strains of algal oil were converted into surfactants by reacting with ethoxylated glycerin with different degrees of ethoxylation using potassium hydroxide as a catalyst. Ethoxylated glycerin and catalyst were heated to 100°C and sparged with nitrogen to remove water from the catalyst. The algal oil was then slowly added over an hour and allowed to digest for 15 min. The reaction product was then cooled below 60°C and bleached with hydrogen peroxide to obtain light straw-colored, low-viscosity liquid products.

The surface properties of algal oil ethoxylates (AOEs) were determined by measuring the surface tension as a function of surfactant concentration. The CMC was determined from the inflection in the surface tension isotherms. AOE prepared using high oleic algal oil shows normal behavior. CMC increases as the mole of EO in the molecule increases. AOE prepared using high lauric algal oil shows surprising behavior. The CMC decreases slightly as the moles of EO increase indicating that ethylene oxide is somehow acting as a hydrophobic material.

The interfacial tension of AOE was determined using a drop volume tensiometer. The IFT shows a minimum around 10–15 mol of EO for both oils. At the minimum, the AOE made from high oleic oil is slightly lower than AOE made from high lauric oil. The IFT of AOE made from algal oil is comparable with that of AE.

The cleaning performance of AOE was determined by measuring soil removal from standard soil swatches under standard US wash conditions. Dirty motor oil, dust sebum, olive oil, and clay on cotton and polyester cotton swatches were washed at 30°C in 150 ppm hard water in a six-pot terg-o-tometer at 200 ppm surfactant concentration in the wash water. The optical reflectance before and after washing was measured with a Hunter Lab spectrophotometer. All soils were run in triplicate and the results averaged. The results indicate that the AOE made using high oleic oil show slightly better detergency. For both algal oils, the detergency increased with increasing moles of EO up to about 15 EO, and further ethoxylation did not affect detergency. Compared with standard AE, AOE exhibits similar parity performance as AE.

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Special Issue in Honor of Dr. K. L. Mittal

Martin E. Leser, ... Heribert J. Watzke, in Advances in Colloid and Interface Science, 2006

1 Introduction

Analyzing the information gathered in Food Science and Engineering so far, we realize that most of our understanding is on the chemistry and functionality of individual food molecules, such as flavor chemistry, oxidation phenomenon, nutritional functionality, etc. on the one hand, and on the bulk behavior of food materials, such as rheological or textural properties, on the other hand. Investigation of structure formation in food materials has been ignored for a long time, since food engineers knew little about the underlying science linking food structure to product properties [1]. However, it becomes more and more evident that the essential properties of food critically depend on phenomena or processes taking place at different length and timescales. Understanding, for instance, self-assembly structure formation will help bridge the gap which exists between Food Chemistry, describing the molecular properties of food molecules, and Food Physics, describing the macroscopic properties of food products [2]. The detailed information available on the main food components must be supplemented with more information on the interaction between the different components and structural entities. The characteristic properties of food systems are more dictated by the interactions between its components than by the properties of the individual components themselves [3].

One important class of components in food is the lipids. Different classes of lipids exist, namely polar lipids (e.g. phospholipids, glycolipids) and nonpolar lipids (e.g. triglycerides, waxes) [4]. Polar lipids usually are referred to as surface active lipids, amphiphiles or low molecular weight emulsifiers (or surfactants) due to the fact that they consist of both a lipophilic and a hydrophilic part [4]. Polar lipids are also abundant in nature, e.g., in living organisms. One class of polar food lipids obtained directly from nature without chemical conversion is the phospholipids. Table 1 summarizes the most commonly used polar lipids in food and their typical applications [5]. Nowadays, the total world production of polar lipids is estimated to be in the order of 300,000 metric tons [5]. This includes approximately 20 different types of emulsifiers. But, monoglycerides and mono-diglycerides, which are glycerol fatty acid esters, and their derivatives account for about 70% of the world production of food polar lipids. They are considered as the most important group of amphiphiles in food [5]. The use of mono-diglycerides dates back to the 1930s when they were first used in margarine production [6]. Their major applications today are in bread, cakes, margarine, ice cream, or chewing gum. Bakery is by far the biggest application; approximately 60% of all monoglycerides are used in this industry [5]. Most of the polar lipids used in food industry are non-ionic or anionic. The phospholipids are the only zwitterionic surfactants. Due to their toxicity, cationic surfactants are not used.

Table 1. Polar food lipids (emulsifiers) and some specific characteristics; adapted from [5,9]

Abbreviation EEC number HLBa Typical applications
Phospholipids PL E322 6–9 Margarine, chocolate, baked goods, sauces, instant drinks, pasta, fats
Mono-diglycerides MG E471 3–6 Margarine, whipped toppings, ice cream, baked goods, pasta
Acetic acid ester of mono-diglycerides ACETEM E472a Fruits, nuts, pizza
Lactic acid ester of mono-diglycerides LACTEM E472b Baked products, whipped toppings
Citric acid ester of mono-diglycerides CITREM E472c Baked goods, spreads, sauces, meat products
Diacetyl tartaric acid ester of MGs DATEM E472e Baked goods, dairy product analogues
Salts of fatty acids (Na, K) E470
Polyglycerol ester of fatty acids PGE E475 Icings, fillings, confectionery, emulsions, cereals
Propylene glycol ester of fatty acids PGMS E477 Cake mixes, whipped toppings
Sodium stearoyl lactylate SSL E481 40 Bread, coffee whiteners, fat emulsions, starch-based products, cereals
Calcium stearoyl lactylate CSL E482 Bread, fat emulsions, cereals
Sucrose ester of fatty acids E473 6–15 Sauces, canned liquid coffee, sausages, surface treatment fresh fruits
Sorbitan monostearate SMS E491 4.7 Yeast for baking, confectionery, fats
Polysorbate 60 PS 60 E435 14.9 Modification of fat crystallization, sauces
Polysorbate 65 PS 65 E436 10.5 Modification of fat crystallization, sauces
Polysorbate 80 PS 80 E433 15 Modification of fat crystallization, sauces
a
Hydrophilic lipophilic balance.

Food emulsifiers are typically used as processing aids for the production and stabilization of emulsions and foams. They can have numerous functional roles in a large variety of products (see Table 1). For instance, phospholipids are used to realize more than 30 different functional roles (Table 2) [7]. Examining these roles in more details, one realizes that most of the functionalities are based on five main physicochemical processes:

Table 2. Functionalities of phospholipids, adapted from [7]

Adhesion aid Emulsifier, surfactant Plasticizer
Antibleed agent Encapsulating agent Release agent (antisticking)
Anticorrosive Flocculant Spreading agent
Antidusting agent Grinding aid Stabilizer
Antioxidant Lubricant Strengthening agent
Antispatter agent Machining aid Suspending agent
Biodegradable additive Mixing and softening agent Synergist
Catalyst Modifier Viscosity modifier
Colour intensifier Moisturizer Water repellent
Conditioning agent Nutritional supplement Wetting agent
Dispersing agent Penetrating agent
(a)

adsorption at interfaces or on solids (such as in emulsions or foams),

(b)

promotion of wetting phenomena,

(c)

co-crystallization,

(d)

complex formation (with proteins or starch components)

(e)

self-association (or self-assembly structure formation).

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Improving method, properties and application of polysaccharide as emulsifier

Qilin Tang, Gangliang Huang, in Food Chemistry, 2022

2.2.4 Interaction between polysaccharides and proteins

Proteins and polysaccharides can be used as food emulsifiers in food, but the results are not ideal. When polysaccharides and protein copolymers are used in stabilizing emulsion, the stabilization effect is determined by polysaccharide/protein properties and their interaction properties (Meng, Liu, Xia, & Hu, 2021; Swa, Jy, & Gs, 2020; Hao, Peng, & Tang, 2020; Yang et al., 2020). Proteins are amphiphilic and can exist at the emulsion interface, while the hydrophilic group of polysaccharides can extend to the aqueous phase, and droplet aggregation is hindered by increased spatial repulsion (Zhang et al., 2021; Zhao et al., 2020; Li & Karboune, 2021; Zhang et al., 2021; Vélez-Erazo, Bosqui, Rabelo, Kurozawa, & Hubinger, 2020). Li (Li, 2018) dissolved chitosan and bovine serum albumin respectively and stirred at room temperature for 2 h, then compared the emulsifying properties of polysaccharide - protein complex under different conditions. It was found that the particle size of emulsion decreased with the increase of protein content. The best emulsion stability was obtained when the volume ratio of protein to polysaccharide was 8:1 ∼ 1:1 and pH was 3.0 or 4.0.

Conjugates of polysaccharides and proteins play an important role in stabilizing water-in-oil emulsions. Polysaccharides give colloidal stability through thickening and gel behavior of water phase, and proteins can adsorb at oil–water interface and form a viscoelastic layer (Abitbol et al., 2021). Studies have shown that the emulsification of polysaccharide - protein conjugate is better than their mixture (Hu et al., 2020; Ding, Chen, & Shi, 2020). The conjugate has higher surface activity and can saturate the interface layer at a lower concentration. Moreover, under unfavorable conditions (high temperature, low pH value), the spatial repulsive force generated by the polysaccharide on the surface of the emulsion droplet can prevent the instability of the protein (Ye et al., 2020). Zhong et al. (2019) prepared the complex of oat protein isolate and streptozoatum β -glucan with the mass ratio of 1:2 at 60 ℃ and 75.0% relative humidity. β -glucan could form spatial repulsion on the surface of the emulsion, promote the formation of stable film around the droplets, and improve the emulsification activity of the complex. Sun et al. (2019) dissolved oat β-glucan in distilled water, added glutamine, dipeptide and glutathione respectively, and obtained the conjugate after reflux reaction at 80 ℃ for 40 h. The emulsification of oat β -glucan was improved due to the introduction of hydrophobic groups, but the emulsification of the three was different, in the order of β-glucan - dipeptide conjugate > β-glucan - glutamine conjugate > β-glucan - glutathione conjugate. Chen et al. (2019) prepared whey protein isolate - gum Arabic complex by dry heat method, and its emulsification was better than that of protein and mixture.

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Gelation behavior of egg yolk under physical and chemical induction: A review

Yan Zhao, ... Yonggang Tu, in Food Chemistry, 2021

3.4 Gelation behavior of egg yolk induced by freezing

Egg yolk in further processed egg products is a high-quality food emulsifier that is widely used in the preparation of mayonnaise, salad dressing and baked goods (Kiosseoglou, 2003). To prolong the shelf life of the egg yolk solution, the solution is always frozen for storage and transportation. When the temperature is less than −6 °C, the freeze-thawed egg yolk forms the gel (Immerseel, Nys, & Bain, 2011), thus, the function and dispersion of the egg yolk reduce. The most common explanation for freeze gelation of egg yolk is attributed to the formation of large ice crystals during the freezing process; thus, the egg yolk components are concentrated, resulting in the accumulation of LDL in plasma. The mechanism of LDL aggregation has been extensively studied. Telis et al. (Telis, & Kieckbusch 1997) proposed that after LDL micelles rupture, protein dehydration on the surface of LDL micelles leads to LDL aggregation. Kurisaki et al. (Kurisaki, Kaminogawa, & Yamauchi, 1980) proposed that the surface components of LDL are released during the process of freezing and thawing, resulting in the accumulation of newly exposed sites. But Wakamatu et al. (Wakamatu, Sato, & Saito, 1982) believed that aggregation of LDL results from the conformational changes rather than the release of LDL components. Another explanation for this kind of egg yolk gel formation is protein aggregation. Specifically, the interaction between ice crystals and proteins and the decrease of the steric hindrance of protein–protein interactions facilitate protein aggregation (Wang, Nema, & Teagarden, 2010). LDL micelles and lipoproteins structure are destroyed by crystallization, and protein molecules are exposed and subsequently interact or combine with each other. The interaction of nonpolar proteins enhances in the plasma, while the yolk granules produce large-grain lipids during the freezing process and enhance the gelation of the egg yolk (Immerseel, et al., 2011). Primacella et al. (Primacella, Fei, Acevedo, & Wang, 2018) suggested that the components in plasma and granules, such as LDL, HDL, and α-livetins, contribute to the formation of the gel. The aggregation of protein was reflected through a large increase in the granules fraction and the appearance of a floating LDL layer upon fractionation of gelation yolk systems (Primacella, et al., 2018). Besides, they presented a schematic diagram of the formation mechanism of egg yolk gel under freezing conditions (Fig. 4). The results of the above studies indicated that the components in the plasma and the granules of the egg yolk contribute to the gelation of the frozen egg yolk. Au et al. (2015) studied the egg yolk gel process during the frozen storage period and proposed a two-stage gelation mechanism. In the first stage, during 28 days of storage of yolk at −20 °C, lipoproteins particles aggregated due to hydrophobic interactions to form a gel network structure. In the second stage, at some point between 28 and 84 days, the protein was released and then the surface area subsequently increased. Thus, more binding sites were exposed, and proteins were further associated with the previously formed network, thus enhancing the protein network structure (Au, Acevedo, Horner, & Wang, 2015).

Fig. 4. Proposed schematic diagram for gelation behavior of egg yolk under freeze treatment.

Research results (Au, et al., 2015; Primacella, et al., 2018) showed that LDL aggregation is a major cause of egg yolk frozen gelation, which causes the leakage of phospholipids. Leaked phospholipids not only form a head-to-head layer structure of phospholipid molecules, but also promote interactions between aggregates. In addition, the structure of granules allows its lipoproteins to be highly resistant to freeze–thaw denaturation (Dou, et al., 2017; Wakamatsu, Handa, & Chiba, 2018).

Irreversible egg yolk gelation will occur when fresh egg yolk is directly preserved under freezing conditions without any other treatments (Wang, Ma, Ma, Du, & Chi, 2020). It is undeniable that during storage or processing, egg yolk gelation has a certain negative impact on egg yolk function. To clarify the mechanism of freezing-induced gelation may help prevent unnecessary gelation of egg yolk. Moran (Moran, & T., 1925) found that rapid freezing to change the size of ice crystals can slow down the gelation of egg yolks. Later, some scholars (Dadashi, Kiani, Rahimi, & Mousavi, 2017; Daizo, et al., 2009; Primacella, et al., 2018) used proteolytic enzymes to prevent the formation of ice crystals or used chemical treatments to change the physicochemical conditions that are conducive to egg yolk protein aggregation, thereby inhibiting the formation the gel (Su, Chen, Li, Chang, Gu, & Yang, 2021). Therefore, it is very important to reveal the mechanism of egg yolk gelation induced by freezing as soon as possible.

To sum up, ice crystal formation removes water molecules from proteins and changes the intramolecular as well as intermolecular interactions. Thus, it might be the main factor involved in protein aggregation as well as proteins and lipids aggregation. Besides, livetins, HDL and LDL are involved in the freezing gelation of egg yolk. Therefore, great efforts must be made to explore the formation mechanism of egg yolk frozen gel.

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URL: https://www.sciencedirect.com/science/article/pii/S0308814621005756

In Honor of Professor Nissim Garti's 60th Birthday

Demet Guzey, D. Julian McClements, in Advances in Colloid and Interface Science, 2006

1.2 Limitations of current emulsifiers

There are limitations to the functional properties that can be achieved using existing food emulsifiers and the conventional method of creating emulsions, for example, limited stability to pH, salt, heating, dehydration, freezing and chilling. These limitations have led to research being carried out to find alternative methods of improving emulsion stability by developing novel emulsifier-based strategies. One strategy has been to create covalent protein–polysaccharide complexes that have good surface activity and provide improved protection against environmental stresses [6,7]. The amphiphilic protein fragment anchors the complexes to the interface, while the hydrophilic polysaccharide fragment protrudes into the aqueous phase and provides stability against droplet aggregation by generating a long-range steric repulsion.

An alternative strategy is to create an interfacial layer around oil droplets that consists of multiple layers of emulsifiers and/or polyelectrolytes using a layer-by-layer (LBL) electrostatic deposition technique [8–16].

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URL: https://www.sciencedirect.com/science/article/pii/S0001868606002004