The solubility of phosphatidylcholine in ethanol, for example, decreases as the length of the acyl-chains increases. Whilst phospholipids usually do not dissolve in acetone see Section 1. Nevertheless, complete separation of individual phospholipids on the basis of their different solubility in certain solvents is not possible, as each effects the solubility of the other.
In certain organic solvents the solutions formed are not molecular dispersions but molecular aggregates are formed. By analogy to its thermal behaviour, this phenomenon is known as lyotropic polymorphism. The formation and structure of these phases are linked to concentration and temperature and are also induced by pH shifts. Structures such as inverse micelles globular and tubular , single and multilamellar systems, single- and multilayer liposomes as well as the typical micelles are known.
Typically, the melting behaviour is superseded by chemical degradation processes. In general, the melting behaviour of phospholipids can be better determined by the structure of the polar headgroups than by the length and saturation level of the acyl chains.
Average melting points for selected phospholipids can be seen from Table 1. This is typical e. Another aspect of surface activity that plays a crucial role in the formation of emulsions are kinetic effects. Again the difference between regular and hydrolysed phospholipids becomes obvious, not only with regard to the equilibrium surface tension being reached, but also with regard to the time to reach a certain reduction.
The basic HLB equation is valid for non-ionic molecules. However, this methodology fails when trying to apply it to lecithins. They are rarely rated higher than an HLB value of 9 this would be for hydrolysed acetylated lecithins. This would imply that lecithins are actually not capable of forming oil-in-water emulsions. Chocolates are very complicated rheological products due to their disperse systems consisting of sugar, cocoa particles, milk ingredients and cocoa butter. The rheology plays a key role not only under processing conditions e.
During the complex manufacturing process of chocolates one major effect is the grinding of the sugars. At a certain point the chocolate mass, even above the melting point of the fat phase, would become solid. Fortunately, with cocoa butter being the most expensive material, there is a much more elegant and cheaper way to solve the problem.
Adding only very little quantities of lecithin, the viscous behaviour can easily be adjusted. These kinds of molecular layers act as lubricant and thereby reduce internal friction and thus viscosity. When adding too much lecithin more than typically 0. How can this be explained? Here the phase behaviour of phospholipids and their tendency of forming lamellar structures are the explanations. However, now with the fatty acid chains aligning to each other and thereby making the outside of the entire structure more hydrophilic, The result is an increase in viscosity.
This in turn makes it easier to standardise production conditions. By choosing a fractionated lecithin with an increased level of phosphatidylcholine, particularly the yield value can be affected in a controlled way. But the combination with lecithin is necessary to achieve low viscosity.
The point at which the lecithin is added during the production process is very important. Also, if allowed to take effect for too long, some of the lecithin may penetrate into the cocoa particles and be lost as functional ingredient acting on the surface of the particles. It is typically recommended that the lecithin be added towards the end of the conching process with the remaining conching time being at least 60 minutes.
These coating compounds may be prepared from cocoa butter or cocoa butter substitutes. Generally, such compounds have one thing in common which is a much lower dry-matter content than real chocolate, thereby having lower viscosity effects and therefore they usually do not require lecithin at all. In the particular case of ice cream coatings, however, we may be confronted with a different problem, i. Coating materials are usually poured over conveyor belts with the ice cream products transported underneath, or the products are dipped into a bath of coating material.
The excess coating mass is typically re-circulated during the process. Coming into contact with moisture from the ice cream, the coating mass, over time, takes up reasonable quantities of water. Figures 1. In this particular application again PC-enriched lecithins give superior results than normal lecithins. The process slowly takes place during shelf life. It could be shown that a de-oiled lecithin can deliver this functionality.
In fact, it will even worsen the problem as it brings additional soybean oil into the formulation. In this case hydrolysed lecithins show their optimal properties. Sugars, for example, start to re-crystallise. If crystal growth exceeds a certain size, the texture of the product becomes brittle. Hydrolysed lecithins are known to control such re-crystallisation processes, keeping crystal growth limited. For the same reason, very often glucose or dextrose syrups are used instead of crystalline sugar.
Again, due to their emulsifying properties, lecithins deliver this functionality. Traditionally, lecithin is used as a dispersing aid in the manufacture of gum base. The technological effect of lecithin differs according to the kind of product. In yeast-leavened wheat doughs, lecithin improves the extensibility of the gluten. This leads to better dough processing, an improved fermentation stability, and ensures a higher volume and a more uniform texture.
In cake, pastry and biscuits lecithin brings about an improved distribution of the basic substances. This essentially yields a homogeneous fat distribution, better paste processing properties and uniform browning. Using lecithin in wafer masses results in a homogeneous distribution of the ingredients, in a good release effect of the wafers from the irons, in an improved texture of the wafer sheets, and in a more even browning.
Looking at the different categories and related functionalities, it becomes clear why the baking industry uses the widest range of lecithin products. Hess and Mahl have proposed that protein is bound to starch granules via a phospholipid layer. Grosskreuz postulated that phospholipids form bi-molecular layers in gluten, with the protein chains bound to the lecithin through salt-type linkages between acidic groups of phospholipids and basic groups of proteins.
Hosney proposed a gliadin—phospholipid—glutenin complex as expressed in [6,7]. Another particular effect of hydrolysed lecithins in shelf life improvement is the anti-staling effects. In the original helix, water is complexed. During the retrogradation process, the helix transforms into another conformation Fig. This results in a loss of moisture and therefore freshness. By avoiding the helical change this effect can be suppressed.
Thus, the retrogradation is hindered, water complexation is maintained, and thereby freshness extended. Bread, rolls and buns lose their freshness very rapidly. The consumer prefers baked goods fresh from the oven, but with conventional methods this cannot always be fully achieved. In practice, this means that yeast doughs are frozen after shaping. The freezing process, however, bears one risk: through the ice crystal formation the sensitive gluten network of the dough, as well as the cell membranes of the yeast cells, may be physically damaged by the sharp crystal structure.
It is evident that the extent of damage depends on the size of the ice crystals. In other words, the smaller the ice crystals, the less the damage. Two main aspects affect crystal size: freezing velocity and storage conditions. The higher the freezing velocity, the smaller the crystals. Using hydrolysed lecithins solves these problems and minimises the associated risks. The reduced surface tension also results in small crystals and limits re-crystallisation effects. Therefore, the gluten network and the yeast cells are optimally protected. There is, however, one additional aspect here that should be mentioned, which to a certain extent can be extended to other applications as well.
Theoretically, if the dosage of a lecithin is based on a comparative AI Acetone Insoluble, Active Ingredients , the effects would be expected to be the same. Some interesting effects can be observed from the manufacture of wafers. While comparing these two methods, we in fact see the same functionality when adding the same lecithins 29 Fig. Another possible way of adding de-oiled lecithin to the formula is to prepare a pre-dispersion of some of the water in the recipie with the de-oiled product and then incorporate it into the mixture. When following this approach the dosage of AI can be reduced by approx.
This implies that phospholipids generate a higher functionality when in an aqueous environment. We will come back to these effects when discussing emulsion systems in Section 1. For the food industry this effect is important from the cost point of view. Thus, the additional advantages of de-oiled lecithins such as easier handling, neutral taste and less colour impact, do pay off.
Typical instant products include: whole milk powder, skim milk powder, infant formulations, coffee whitener, protein drinks, cocoa and chocolate drinks, soups, sauces etc. When adding these products to a liquid water, milk the expectation of consumers is an immediate reconstitution and the formation of a homogeneous, non-sedimenting drink. As a result of the formation of hydrates, a gel-like layer is built on the surface and this prevents water from penetrating fast enough into the particle structure.
The second problem occurs when the surface of the powder is rich in hydrophobic components. This can happen in products with a large amount of free surface fat e. By optimising the instantising process, the instant characteristics can significantly be improved. Processes for obtaining this effect can be divided into two basic groups: Agglomeration.
Creation of a coarse particle structure with porous properties, The porous structure supports the penetration of liquids by capillary forces. Coating the product surface with a surface-active substance. Both these processes encourage instant performance and are typically combined. A typical in-line process is the production of whole milk powder. By applying lecithin to the powders, an agglomeration and the lecithination takes place.
Thus, individual singular powder particles are coated with lecithin and at the same time start to agglomerate due to adhesive forces generated by the phospholipids, and in certain cases, the carrying liquid. However, it can also be any kind of oil or fat such as butter fat in which a de-oiled lecithin has been dissolved. It can also be water with de-oiled lecithin dispersed in it, in some cases together with agglomeration aids, e.
Spray drying technology is applied to a wide variety of other liquid starting materials. Even de-oiled lecithins may be used within the blend, in this case however, a high shear mixing with choppers is necessary, as the phospholipids have to be applied to the primary particle surface by pure mechanical energy. Another example of lecithination by pure mechanical energy is the production of defatted cocoa powder as a basis for instant cocoa drinks.
In Fig. The two de-oiled varieties were dissolved in butter fat in order to make them sprayable. Concentrations refer to the addition of the lecithin: based on AI these are 0. The result of the lecithination, expressed as wetting time being measured by a standardised method is initially the same. This behaviour can be explained by migration and re-organisation effects.
So the local phospholipid concentration on the surface declines. In the case of butter fat such effects are limited as butter fat at ambient temperatures is basically solid and migration processes are at least reduced. In this case diffusion and re-orientation processes can also take place. It becomes obvious that phosphatidylcholine maintains its orientation at the surface lecithins 33 to a larger extent than other phospholipids.
Thus, PC-enriched lecithins maintain their instant effects over a longer time. Both emulsion types are possible! In this context, the versatility of lecithin again becomes evident. The fractionation of lecithins, in particular, leads to products that predominantly form either the one or the other type of emulsion. This implies that different phospholipids do have different emulsifying properties and that the phospholipid pattern of a lecithin determines the emulsion type that is formed.
This shape might not exclusively be generated by the molecular structure itself, but also by interactive forces between molecules. Several possible geometries are shown together with a correlation to different types of phospho- lipids Fig. How this might look like is shown in Fig. Even products like sausages and, in particular, liver pates can be considered as oil-in-water emulsions. Considering what has been mentioned earlier we would expect that hydrolysed lecithins as well as PC-enriched lecithins should deliver superior o-w emulsion capacity than standard lecithins.
In order to exclude concentration effects a high concentration was chosen i. The most interesting results, however, were found when dispersing the lecithins in the water phase rather than dissolving them in the oil phase. It is important to note that this is not related to the lecithin concentration when calculated on the emulsion basis 0. This, however, is different when talking about long-term emulsion stability. Another important aspect that needs to be mentioned when using lecithins is their comparison against mono-di-glycerides, which are traditionally more commonly used.
At ambient temperature they are in a crystalline stage. As plant lecithins are mainly unsaturated see Section 1. Even though such processes very often involve a heat treatment e. PC-depleted lecithins have the functionality to stabilise these water-in-oil emulsions because of their predominant content in phosphatidylethanolamine and phosphatidic acid see Figs 1. In order to understand the complex interactions, it is required to have a closer look at the processes that take place in the manufacture and also use of margarines and spreads.
But still new water droplets are formed due to the mechanical energy input in the combinators scraped surface coolers. The stability of the emulsion is later challenged again, when exposed to elevated temperatures. Again, the lecithins take the primary role of stabilising the emulsion. If the individual water droplets are not kept separated but start to form bigger clusters and recombine, they may explosively evaporate resulting in a severe spattering of the fat phase. Here lecithins play their key role in yellow fat applications.
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Together with whey proteins the phospholipids stabilise the individual water droplets under these extreme conditions and thus help to avoid spattering effects. But it is the predominant capability of phosphatidylcholine and lyso-phospholipids to form protein-phospholipid complexes as interfacial membranes. With higher water contents reduced fat spreads, low fat spreads a lecithin has to be chosen that supports the formation of the right type of emulsion, process functionality being the same as for margarines and high fat spreads.
With higher water content however, the risk of a phase inversion increases especially during the cooling stage. The lecithins that are now taking over the emulsifying function must not be biased towards Fig. It is in these reduced and low fat spreads that PC-depleted lecithins are successfully used. Further examples of the use of lecithins and additional functionality in yellow fat products are as follow: Cream margarines are whipped products, for example, for the preparation of sponge mixtures and butter creams. In this case, lecithin helps to stabilise the light, spongy texture.
Release agents are preparations that prevent bakery products and confectionery from sticking to the tins and moulds during production. It is evident that these effects can be transferred to other products as well.
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Lecithins can play their role in the whole range of food products where any kind of surface-active subtance is required. This chapter has tried to make it clear that it is crucial to select the right lecithin quality in order to have maximum success. The complexity of the composition of lecithins necessitates the consideration of interactions with other components of a food formulation.
Very often functionalities in particular products cannot be generalized to the food category, but depend on a number of further contributing factors in the individual formulation. This is one reason why leading lecithin manufacturers offer application support to the food industry and assist them in their product development work. Despite 75 years of experience, new questions are still arising, which are to awaiting answers. Christie ed , The Oily Press, Dundee, The major breakthrough, however, was the application of mono- and diglycerides in the s in the margarine industry on a large scale .
In , the use of mono- and diglycerides was patented for ice cream applications. The major applications are bread, sponge cakes, cakes, margarines, ice cream, chewing gum and chews. Bakery overall is by far the biggest application. Monoglycerides are applied in food technology for several functions see Table 2. These functions are discussed in more detail in Sections 2.
Mono- and diglycerides are manufactured by the batch process or by the continuous process. In the batch process the reaction time varies form 1 to 4 hours and in the continuous process the time may be less than 12 hour [4, 5]. The reaction is carried out at a very high temperature e.
The concentration by molecular or short-path distillation takes place under high vacuum condition i. Monoglycerides produced in this way contain an equilibrium of 1-monoglycerides and 2-monoglycerides. The ratio between the two isomers is dependent on temperature. The rate constant of the equilibrium is low at room temperature and depends on fatty acid composition, crystal form and traces of basic catalyst present. Monoglycerides are insoluble in water, but can form stable hydrated dispersions. Distilled monoglycerides have a better dispersibility in water than mono- and diglycerides, because the former form liquid crystalline mesomorphic phases, whereas mono- and diglycerides, in most cases, form emulsions due to a relatively high content of triglycerides.
Distilled monoglycerides form ordered bilayers of the fatty acid chains, separated by water layers associated with the polar groups . They crystallise from melt in the metastable alpha form and transform via beta prime form to the most stable beta crystal form.
For some applications the alpha form has some most advantageous effects: such as easier dispersibility, improved aerating properties and increased emulsifying activity. Therefore, it is highly desirable to retard the conversion of the alpha to the beta form. Monoglycerides possess a lipophilic character and are therefore assigned with a low HLB number 3—6. This is an autocatalytic free-radical chain reaction and takes place in three stages via initiation, propagation and termination Scheme 2.
During the initiation reaction, unstable fatty acid radicals are formed by initiators, such as light, heat or heavy metals Cu, Fe. The fatty acid radicals react with atmospheric oxygen to form peroxide radicals, which in turn react again with the fatty acid substrate to produce new radicals and hydroperoxides propagation. The radical chain reactions can be terminated by antioxidants, which retard the oxidation of fatty acid derivatives.
Antioxidants usually have a phenolic structure and are good free-radical acceptors, which inhibit or interfere with the free-radical mechanism of auto-oxidation. The formed antioxidant free radical is highly stable due to its resonance and will not propagate further oxidation of the oil or fat. All vegetable oils and fats contain natural antioxidants i. Synthetic antioxidants related to tocopherol have been developed , such as alkyl gallate, butylated hydroxyanisole BHA or butylated hydroxy toluene BHT. Mono- and diglycerides have no limitation on the acceptable daily intact ADI value; they can be added to foods quantum satis .
Table 2. The structure of a gel is similar to the lamellar phase, with water layers alternating with lipid bilayers Fig. The exact temperature of gel formation depends on the chain length of the fatty acid and on the purity of the monoglyceride. The main applications of mono- and diglycerides in food are typically in fat-based products, such as margarine, spreads and bakery fats shortenings and cake mixes. In dairy emulsions, mono- and diglycerides are used in ice cream and recombined milk, in combination with hydrocolloids.
All products containing nutrients must be labeled appropriately. Mono- and diglycerides are registered under fat, because of their similarity with triglyceride esters. Distilled monoglycerides are also used in fat-free foodstuffs or products with very low fat content . Fermentation stability of bread doughs.
The hardness of the monoglyceride is mainly determined by the hardness of the edible fat from which the monoglyceride has been produced. Monoglycerides are added to bread doughs for the following reasons: primarily, it is known that monoglycerides increase the fermentation stability of doughs. In the laboratory this can be demonstrated by putting fully fermented doughs on a laboratory shaker and vibrating them vigorously for 1 minute. Alternatively, mono- and diglycerides 47 Fig. The doughs on the left-hand side contain 0. Figure 2. Shelf life in this context mean crumb softness.
Freshness of baked goods and the postulated mechanism behind it has been extensively discussed in Zobel and Kulp , see Fig. In a nutshell, during baking, starch granules will swell and absorb water resulting in the amylose to transfer from an amorphous state into a soluble state and the amylopectin from a crystalline state into a gelatinised state.
During cooling of the freshly baked bread, amylose will retrograde immediately by complex formation with another amylose molecule, or form a complex with a polar lipid thus producing a softer crumb. During storage gelatinised amylopectin will recrystallise again, leading to a harder crumb.
The interaction of monoglycerides with amylose has been extensively studied, see  for review. The studies of Lagendijk and Pennings  and of Carlson et al. Lagendijk and Pennings proved that complex formation between amylose and monoglycerides is preferred over complex formation between amylopectin and monoglycerides. They also studied the effect of different fatty acid chain lengths on complex formations and found C16 most active, followed by C Carlson et al. Clearly, ingredients that have to be functional during bread baking have to disperse in an active form during dough mixing.
In bread baking industry this is still done mainly by the addition of hydrates. Upon cooling, the fatty acid chains will be structured again mono- and diglycerides 49 Resistance g Blank 0. This opaque white paste called coagel is known as hydrate in bakery literature. In this physical state monoglycerides are very effective regarding complexation with amylose, but it involves a rather complicated way of adding the monoglyceride paste to the dough. In general, the monoglyceride has to be scooped manually from the packaging.
The effect of the addition of appropriate monoglycerides on crumb softness can be studied by measuring crumb hardness by a texture analyser during the storage of bread.
As shown in Fig. Interaction of monoglycerides with starch, and in particular amylose, is also important in the production of dry pasta. Bread at top: reference with no monoglycerides added. Bread at bottom: addition of 0. Another interesting application of monoglycerides is the decrease in blisters in bread prepared with retarded doughs. This process has gained increased popularity with artisan bakers because it reduces working at night.
According to the French patent 92 , the addition of monoglycerides to retarded dough decreases the occurrence of blisters dramatically. This is shown in Fig. The effect of the addition of powdered monoglycerides is evident, as without monoglycerides there is an unacceptable formation of blisters in baked products and with monoglycerides a smooth surface with less blisters is obtained. A typical composition of gels is shown in Table 2.
The humectant part can have varying compositions depending on required functionality, cost in use and local legislation. The gels are added approximately 2—2. For the artisan bakers or in household sponge cake mixes, the application of gels is too cumbersome. The shortenings are mainly applied in industrial cake baking. The level of monoglyceride used in low fat spreads is equal to table spreads; i.
There is one major difference in this application because unsaturated monoglycerides are used. The reasons for this might be twofold, although different views do exist about the importance of unsaturated monoglycerides in this application. After preparation of the gels, they are transformed into coagels, in which monoglycerides crystallise in a plate-like structure entrapping large quantities of water.
Saturated monoglycerides 0. Ice cream interfaces are schematically shown in Fig. Monoglycerides are mainly responsible for the partial destabilisation of the fat emulsion. Proteins are the prime emulsifying agents in most dairy products and also ice cream. Only by applying milk proteins we can obtain very good and stable emulsions.
Proteins are surface active and partially cover the fat globules and air bubbles. The usual monoglyceride dosage in ice cream is 0. The second and most important role of the monoglycerides is to promote the desorption of milk protein from the interface. Partial replacement of milk proteins by whey protein is a common practice in the ice cream industry to achieve cost optimisation. The reason for this is that whey protein has stronger emulsifying properties than milk protein, and consequently whey protein desorption from the interface by monoglycerides is less effective as compared to milk protein.
Acknowledgements The authors would like to thank many Kerry Bio-Science colleagues for their inputs and suggestions. References  Hasenhuettl, R. Chemists Soc. Cosmetic Chemicals, , 1, Sherwin, E. Brokaw, G. Chemist Soc. Krog, N. Lipids, , 2, — Zobel, H. Cereal Sci. Lagendijk, J. Today, , 15, , , Carlson, T. Boyle, E. Kielmeyer, F. Schuster ed. Dairy J. The possible variations of the above are shown in Table 3. So a mixture of esters formed by the reaction of acetic acid and fatty acids derived from of edible food fats with glycerol will result.
So they show chemical reactions of rearrangement, intra- and intermolecular migration of acylic groups and certain sensitivity towards hydrolysis. The amount of this migration depends on the time and intensity of the thermal stress and also on the degree of acetylation of monoglyceride with acetic acid. The more hydrolysed species present in the system, the higher its acid value will be. Another method to prove this behaviour will be the measurement of the content of 1-monoglyceride.
Its concentration will decrease with increasing hydrolysis via migration of acylic groups. Hydrolysis of ACETEM with alkaline solutions will result in the alkaline salts of the released fatty acids, acetic acid and glycerol; and hydrolysis with acids will result in free fatty acids, acetic acid and glycerol. All these reactions of hydrolysis are rapid and run completely when the concentration of the substances with hydrolytic activity is high enough . Due to the low sensitivity towards hydrolysis at low and moderate temperatures, ACETEM can be used in aqueous systems, even if they are stored for a certain period.
Any surplus triacetin must be removed by distillation. After the reaction of mono- and diglyceride and monoglyceride with acetic acid anhydride, the result will be a mixture of different species with more or less free hydroxylic groups. These are obtained either via non-processed reactants or via intramolecular migration of acylic groups from acetylated molecules.
So isomers of mono-acetylated monoglycerides, di-acetylated monoglycerides, acetylated diglycerides, besides various amounts of mono- and diglycerides and small amounts of free glycerol, triacetin, acetic acid and fatty acids, will be present. The other method, via acetylation of mono- and diglycerides of fatty acids is shown in Fig. Almost all ACETEM vary from colourless to ivory coloured and from oily to wax-like, with a consistency determined by the fatty acids and the proportion of acetic acid included in the molecules.
This range may vary from liquid to solid and wax-like consistency. The taste will be oily, lard-like or often neutral. Free acetic acid will always indicate some hydrolysis. In general, ACETEM have a softer consistency and a lower melting point compared to the mono- and diglycerides they are derived from. On the other hand, they are dispersible to soluble in all kinds of edible oils and fats and some alcohols, such as ethanol, or iso-propanol.
The stability of liquid ACETEM towards oxidation can also be explained by the stability of the totally saturated fatty acids within these molecules. Consequently, ACETEM are often used as synergistic components in the recipes of whipped toppings and shortenings [3, 4]. They are also used as lubricants and release agents.
Applications include topping powders, whipped topping concentrates, chewing gum base, coatings cakes. So a mixture of esters formed by lactic acid and fatty acids of edible food fats with glycerol will result. The distribution of the principal components depends on the proportion of lactic acid, fatty acids, glycerol and the current conditions of reaction. The amount of this migration depends on the time and intensity of the thermal stress. This is due to the reduced number of free hydroxyl groups resulting from the higher degree of lactylation.
Another method to prove this is the measurement of the content of 1-monoglyceride. Its concentration will decrease with increasing hydrolysis, via migration of acylic groups. Figure 3.
Apart from the changes in the chemical parameters, a deterioration of the sensory properties will always occur. LACTEM are hydrolysed similar to triglycerides, using acids, alkaline solutions and lipolytic enzymes. Hydrolysis of LACTEM with acids will result in free fatty acids, lactic acid and glycerol; and hydrolysis with alkaline solutions will result in the alkaline salts of the fatty acids and the lactic acid, as well as glycerol.
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The enzymatic hydrolysis will results in free fatty acids, lactic acid and glycerol. All these hydrolytic reactions are rapid and complete when the concentration of enzymes, acids and alkaline solutions is high. The non-catalysed acid esters of mono- and diglycerides 71 hydrolysis of LACTEM essentially depends on temperature and time, and is rather slow.
The food technologist may pay some attention to this fact during their use in aqueous systems or during a rather long storage time by preventing them from higher temperatures . The resulting number of different positional isomers will be high. Their distribution in LACTEM depends on the molar ratios of the processed raw materials and also on the temperature and time of reaction. The largest number of positional isomers are of mono- and dilactoyl-monoglycerides and also mono- and diglycerides. The by-products will be glycerol, free lactic acid, polymerised lactic acid, esters and free fatty acids.
The product will be slightly yellow to amber-coloured, and oily to wax-like in consistency. The taste and odour may vary from neutral to bitter. They are soluble in some hot alcohols ethanol, iso-propanol or xylol and fats, such as soybean oil or lard. These groups are responsible for their hydrophilic character. Therefore, its HLB value will be lower compared to the mono- and diglycerides. Table 3. Lactic acid esters of mono- and diglycerides are used to improve aeration and foam stability as well as texture and volume. The distribution of the principal components is dependant on the proportion of citric acid, fatty acids, glycerol and the reaction conditions being used.
The product can be partially or wholly neutralised resulting in the corresponding sodium or potassium salts. One represents a fatty acid moiety, and the remainder may represent citric acid, fatty acid or hydrogen. Additionally, free carboxylic groups derived from the citric acid moiety will always present in these molecules showing all the corresponding reactive possibilities.
Besides the decrease of the acid value, a drastic coloration caused by the decomposition of citric acid and the formation of polymeric substances will result . They may be cleaved using acids, alkaline solutions acid esters of mono- and diglycerides 77 and lipolytic enzymes, in the same way as triglycerides. Hydrolysis with acids will result in free fatty acids, citric acid and glycerol; and hydrolysis with alkaline solutions will release their alkaline salts with fatty acids or citric acid, and free glycerol. All the above-mentioned reactions of hydrolysis will be faster and complete.
The non-catalysed hydrolysis depends on temperature and time, and runs remarkably slower. The number of the possible individual species will therefore be rather high due to numerous possible positional isomers. Besides these species, monoglycerides, glycerol and free citric acid will also be present.
Mono- and diglycerides are rather lipophilic substances and citric acid is a very hydrophilic component. This depends on the fatty acid moiety of the used mono- and diglycerides, irrespective of whether they are saturated or unsaturated. The colours range from white- to ivory-coloured. The odour is neutral to slightly fatty and their taste will also be fatty to slightly sour, for the neutralised types, and fully sour for all the others.
They form stable emulsions above their melting points. They show a tendency towards thermotrophic mesomorphism, which is caused by a strong molecular interaction between the participating polar groups . The hydrophilic part of the whole molecule is therefore formed by hydroxylic groups, deriving from the mono- and diglyceride part, the hydroxylic group of the citric acid and their carboxylic group.
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