Lipid in food and effect of lipid in food processing

Lipid in food and effect in food processing Together with proteins, carbohydrates and water, lipids represent a major component of food and important structural and functional constituents of cells in biological systems Lipids are a diverse group of compounds and serve many different functions In foods, lipids contribute to both the flavor and texture of foods and even with better taste when food contain more lipids Definition Lipids represent the major bulk constituents in food and other biological materials Lipids comprise several classes of chemical compounds that have common solubility properties, i.e., soluble in low-polarity organic solvents such as chloroform, diethyl ether and light petroleum, but sparingly soluble in water Lipids are also composed of carbon, hydrogen and oxygen but different to carbohydrate, they not contain multiple hydroxyl groups which cause hydrogen bonding, therefore, they are insoluble in water The term ‘fats’ may be applied to all lipid-soluble extracts from biological materials, or a distinction may be made between oils, which are liquid, and fats which are solid Chemically, fats include many compounds which are fatty acids or esters of fatty acids However, other components are classified as lipids on the basis of their solubility properties, even though they are not esters of fatty acid Lipids can be classified into three groups: simple lipids, compound lipids, and derived lipids Simple lipids are esters of fatty acids which produce two classes of compounds on hydrolysis Compound lipids are esters of fatty acids which produce three or more classes of compounds on hydrolysis Derived lipids cannot be hydrolyzed to fatty acids Classification and characteristic There is only one characteristic that is common to all lipids, and that is their inability to dissolve in water They will, however, dissolve in a variety of organic solvents, such as benzene, acetone, alcohol, carbon tetrachloride, and chloroform This single commonality is generally used to classify something as a lipid Beyond that one charcteristic, lipids display a wide variety of structures and features They can be liquid or solid at room temperature, and they may have other functional groups of various kinds attached Simple lipids The main simple lipids are triglycerides (also known as triacylglycerols), steryl esters, and wax esters Hydrolysis of these lipids yields glycerol and fatty acids, sterols and fatty acids, and fatty alcohols plus fatty acids, respectively The most important of these simple lipids for food scientists are the triglycerides Triglycerides are esters of the trihydric alcohol glycerol with three fatty acids Many of the properties of triglycerides are dependent on the component fatty acids Thus, the melting point of the triglyceride reflects the melting point of the component fatty acids, with three high-meltingpoint fatty acids yielding a high-melting triglyceride Unsaturation in the fatty acids makes the triglyceride susceptible to autoxidation, just as the fatty acid itself would be Reaction of triglycerides Hydrogenation: involves not only the saturation of double bonds but also cis–trans isomerization and migration of some double bonds to neighboring positions in the fatty chains Interesterification: a redistribution of the fatty acid moieties presented in a triglyceride oil over its glycerol moieties Lipolysis: Triglycerides are hydrolyzed, albeit very slowly, by aqueous media, but much more rapidly by basic catalysts and, more importantly, by endogenous lipolytic enzymes Autoxidation: Access of atmospheric oxygen to unsaturated fatty acids or glycerides leads to deterioration through oxidation Saturated and monounsaturated fatty chains oxidize very slowly and not as a rule caused problems Oils such as fish oils are so liable to oxidative degradation that they cannot be used as such in food formulation but must first be hydrogenated Compound lipids: There are many members of this group Probably most important compound lipids for food science are the phospholipids Phospholipids Phospholipids are esters of glycerol, fatty acids, phosphoric acid, and other alcohols The most common phospholipids are phosphatidylcholine, phosphatidylethanolamine, phosphatidylinositol, and phosphatidylserine These phospholipids share the common features of fatty acids esterified to the and positions of the glycerol backbone with the phosphate group esterified to the positions The phosphate group is the negatively-charged polar head, which is hydrophilic whereas the fatty acid chains are the uncharged, nonpolar tails, which are hydrophobic Phospholipids differ from triglycerides in being surface-active and they are used in food products as emulsifiers because they migrate to the interface between oil and water, and reduce the interfacial tension, thereby stabilizing an emulsion Commercial phospholipid preparations are called lecithin Lecithins are mixtures of glycerophospholipids including phosphatidylcholine, phosphatidylethanolamine, phosphatidylinositol, phosphatidylserine, and phosphatidic acid Glycolipids Glycolipids yield fatty acids, glycerol, and carbohydrates on hydrolysis Monogalactosyldiglycerides are glycolipids which are commonly found in plant leaves and algae They contain a high proportion of polyunsaturated fatty acids and appear to play a role in photosynthesis Sulfoquinovosyldiglyceride is one of the most polar plant lipids Cerebrosides and cerebroside sulfates are further examples of glycolipids Sphingolipids Sphingolipids are derivatives of the amino alcohol sphingosine, which is found in animal tissues, or phytosphingosine, which is found in planttissues Lipids derived from other related bases are included in this group Sphingosine is one of more than 60 long-chain amino alcohols found in animals, plants, and microorganisms The bases commonly contain between 12 and 22 carbon atoms in the chain A ceramide, which is an amide formed from a fatty acid and sphingosine, is the characteristic parent structure of all sphingolipids Sphingomyelins are the most abundant sphingolipids in the tissues of higher animals The 1hydroxyl group of ceramide is esterified with phosphoric acid esterified with choline or with ethanolamine Cerebrosides are glycosphingolipids which contain a carbohydrate linked by a glycosidic linkage at the 1-hydroxyl position of the long-chain base Cerebrosides are the major sphingolipids of plants Lipoproteins Lipoproteins may also be classified as compound lipids These are compounds of proteins, fatty acids, and alcohols and may include other classes Lipids and proteins are largely held together by hydrophobic interactions Transport lipoproteins and membrane lipoproteins are important biomolecules in human physiology Derived Lipids This group of lipids includes a range of compounds which vary widely in their structures The main derived lipids include: fatty acids, fat-soluble vitamins and provitamins, alcohols – including sterols – terpenoids and ethers Fatty Acids Although simple and compound lipids are esters of fatty acids, the free fatty acids only occur in relatively small amounts in food and food raw materials A fatty acid is a carboxylic acid with a long aliphatic chain, which is either saturated or unsaturated Most naturally occurring fatty acids have an unbranched chain of an even number of carbon atoms, from to 28 Fatty acids are usually not found in organisms in their standalone form, but instead exist as three main classes of esters: triglycerides, phospholipids, and cholesteryl esters In any of these forms, fatty acids are both important dietary sources of fuel for animals and they are important structural components for cells Essential fatty acids, or EFAs, are fatty acids that humans and other animals must ingest because the body requires them for good health but cannot synthesize them Only two fatty acids are known to be essential for humans: alpha-linolenic acid (an omega-3 fatty acid) and linoleic acid (an omega-6 fatty acid) Some other fatty acids are sometimes classified as "conditionally essential", meaning that they can become essential under some developmental or disease conditions; examples include docosahexaenoic acid (an omega-3 fatty acid) and gamma-linolenic acid (an omega-6 fatty acid) Vitamin A Vitamin A is a C20 primary alcohol occurring either as vitamin A1 or vitamin A2 It is commonly used in the form of acetate or palmitate esters as a food additive Vitamin D The term ‘vitamin D’ refers collectively to a group of compounds derived from sterols, which are effective in preventing the development of rickets in children Ergocalciferol (vitamin D2) and cholecalciferol (vitamin D3) are the most common compounds with vitamin D activity Ergocalciferol is formed by the irradiation of ergosterol with ultraviolet light whereas cholecalciferol is formed in an analogous manner from 7-dehydrocholesterol Vitamin E Eight compounds belonging to the tocopherol and tocotrienol classes have vitamin E activity Vitamin K Compounds exhibiting vitamin K activity possess a 2-methyl-1, 4-naphthoquinone ring with differing chain-length polyprenyl substituents at the position The dietary requirement for vitamin K by the adult human is extremely low, because the vitamin is synthesized in the intestine by intestinal bacteria Carotenoids Carotenoids contribute the yellow, orange, or red colors of many fruits and vegetables, such as carrots, peaches, and tomatoes They are commonly extracted with vegetable oils, including crude palm oil, which is a rich source containing 500 p.p.m Sterols Sterols are termed phytosterols, zoosterols, and mycosterols Cholesterol is the main zoosterol, but sterols in plants commonly occur as mixtures with b-sitosterol, campesterol, and stigmasterol representing three of the major phytosterols Molecules with a sterol-type structure that lack an endocyclic double bond are termed sterols Methyl sterols, also known as triterpenyl alcohol, have an additional methyl group at carbon-4 in the A-ring of the molecule Methyl sterols and dimethylsterols commonly occur with sterols in plant membranes Terpenes Terpenes are oligomers or polymers of isoprene, 2-methyl-1, 3-butadiene Monoterpenoids and sesquiterpenoids contain 10 and 15 carbon atoms respectively, and these components occur in essential oils and are very important flavor compounds Monoterpenoids include acyclic and cyclic hydrocarbons, alcohols, ketones, or lactones such as myrcene, limonene, and menthol Sesquiterpenoids include bicyclic or tricyclic compounds such as zingiberene, which is the main constituent of the oil of ginger, or caryophyllene, which occurs in the oil of cloves Diterpenoids include the bitter principles, which are commonly bitter and have physiological effects Triterpenoids and higher terpenoids have no flavor properties Triterpene alcohols have been found useful in the identification of oils in blends Carotenoids are the major tetraterpenoids, while chicle, which is used in chewing gum, is the main polyterpenoid used in foods Ethers Ether lipids occur in which one of the hydroxyl groups of a diglyceride or phosphatidyl ester is linked to an alkyl group The alkyldiacylglycerols are common constituents of some marine oils while vinyl ethers or plasmalogens are found in blood Source of some lipids Simple lipids In foods, lipids are mainly found in the form of triglycerides which make up to 99% of lipids of plant and animal origin Triglycerides are the major components of edible oils and fats, often representing more than 95% of refined oils The major vegetable oils and fats: castor oil, cocoa butter, coconut oil, corn oil, cottonseed oil, groundnut oil, linseed oil, olive oil, palm and palm kernel oil, rapeseed oil, rice bran oil, safflower oil, sesame oil, soybean oil, sunflower oil, etc Fats of animal origin: butter fat, lard and animal tallows, fish oils Compound lipids Phospholipids are the major components of cell membranes All oils and fats in their crude state probably contain phospholipids as minor components This is commercially available mainly from soybean but also from rape, corn, and sunflower Egg yolk is also a significant source of phospholipids However, the bulk of the phospholipids are removed by degumming during the refining of edible oils Glycolipids are also found in the central nervous systems of some animals Some can be found in the chloroplasts of higher plants and algae, but generally at lower concentrations Sphingolipids are important membrane components in both plant and animal cells They are present in especially large amounts in brain and nerve tissue Derived Lipids Fatty Acids Edible oils usually contain only small amounts of free fatty acids when isolated from the plant, animal, or microbiological source Normal values of free fatty acids are below 5% in most crude edible oils The free fatty acids present are mixtures similar to those present in the triglycerides Most free fatty acids are removed from crude edible oils during refining because of the undesirable effects on flavor, and the reduction of the smoke point caused by free fatty acids A refined oil usually contains less than 0.1% free fatty acids Vitamin Vitamin A occurs in animal and marine products such as butter (1 mg per 100 g) and eggs (3.7 mg per 100 g) Vitamin A can also be formed in vivo from some carotenoids such as b-carotene Vitamin D occurs in fatty fish, dairy products and yolk milk Vegetable oils in general contain more vitamin E than animal fats, and vegetable oils rich in polyunsaturated fatty acids tend to be good sources of vitamin E The main dietary sources of vitamin K are green vegetables, which commonly contain > 100 mg per 100 g Carotenoids Carotenoids contribute the yellow, orange, or red colors of many fruits and vegetables, such as carrots, peaches, and tomatoes They are commonly extracted with vegetable oils, including crude palm oil, which is a rich source containing 500 p.p.m Sterols Sterols occur in the membranes of plants, animals, and microorganisms Algae produce a wide variety of sterols Cheese, egg, organ meat are rich of cholesterol, the main sterolls Emulsification Oil and water produce emulsion by stirring, however, the emulsion starts to break down immediately after stirring is stopped The purpose of emulsification is to stabilize emulsion state by preventing break down which occurs due to creaming aggregation and coalescence To solve these issues, decreasing size of dispersed particles, reducing the density different of dispersion and protecting the surface of oil droplets are effective There are two types of emulsion, O/W emulsion or oil droplets in water, which can be found in ice cream and or milk, and W/O emulsion or water droplets in oil, found in butter and margarine Recently, developments of W/O/W type emulsion or water dispersed within oil droplets of O/W type emulsion and O/W/O type, an opposite type emulsion have been progressing These multiple type emulsions not only make low calorie items such as cream which contain less oil, but also stabilize the emulsion by dissolving the unstable substance present in the deepest region of water droplets Taste can also be enhanced by injecting seasonings and flavors into the water droplets When fats and oils form into crystal, an emulsifier promotes and inhibits the growth which prevents the formation of abnormal crystal This function is utilized for margarine, shortening and chocolate Emulsifiers are molecules that contain both a hydrophilic, water loving, and hydrophobic, water hating, portion Lecithin is an important emulsifier Two of the bonded molecules are fatty acids - these are hydrophobic The third substance attached to glycerol is phosphoric acid that has an amino alcohol attached called choline Lecithin makes a good emulsifier because the hydrophobic end dissolves in oil droplets and the hydrophilic end dissolves in water In emulsions the only place lecithin likes to be is at the edge of oil droplets with its hydrophobic end in the oil and the hydrophilic end in the water Oil droplets in water are protected in the same way by lecithin so the emulsion stays stable for a long time Gelation Gelation is the process of formation of gel from sol, in the so-called “sol–gel” process Sol is a colloidal liquid wherein nanoparticles are dispersed throughout Sols are produced either by growing nanoparticles within the liquid or by dispersing the nanoparticles (which are synthesized by other means) in the liquid Gelation properties are important in determining the quality of various food products In addition to myofibrillar proteins, lipids play an important role in the formation of gel Phospholipids are amphoteric lipids that cannot be removed through rinsing Paradoxically, the addition of phospholipids increases or decreases gel strength The textural characteristics and gel strength were dependent on the phospholipids content, including total lipid levels and the types of fatty acids The gelation properties increased with increasing concentrations of sphingomyelin and phosphatidylserine Furthermore, increased levels of saturated fatty acids (SFAs) and decreased levels of polyunsaturated fatty acids (PUFAs) increased gelation properties Finally, higher hydrophobic interactions and more disulfide bonds were shown to increase gel network structure stability, resulting in improving gel strength Application of some lipids on processing of food Fat and oils Fats and oils are important ingredients in a variety of foods They confer desirable characteristics on several foods, contribute to tenderness to shortened cake, and by aerating batter, fats aid in establishing texture in cakes; they also add flavor to foods and influence the order in which components of flavor are released when foods are eaten, besides having a lubricating effect and producing a sensation of moistness in the mouth They are a medium for transferring heat to foods For consumers, textural attributes of fats that arise from their molecular states are of primary importance Food texture is affected by fats by forming structures of crystalline networks and by disruption of structure by interfering with non-fat networks Fats present polymorphism, an ability to exist in different crystal forms and the three major are α, β, and β' that differ in melting points The melting profile of the fat crystals play key roles in determining properties such as texture, stability, spreadability, and mouthfeel The texture of products such as chocolate, shortenings, and especially butter is determined by the concentration, morphology, and interactions of fat crystals Shortenings are fats that provide specific functional properties (softness, texture, mouthfeel, structural integrity, air incorporation, heat transfer, and shelf life increase) to pies, breads, pasta and others There has been an increase in the percentage of the population that is either overweight or obese over the last years The growing concern with the relationship between health, feeding, and maintenance of healthy weight has boosted the market of foods with reduced energy value Since fat has higher caloric density than that of most nutrients in foods, reducing fat and cholesterol content is currently one of primary trends in food product innovation However, the successful development of these products remains a challenge because fat plays multiple roles in determining their desirable physicochemical and sensory attributes Important attributes such as smooth/creamy/rich texture, milky/creamy appearance, desirable flavor, and satiating effects are influenced by the droplets of fat Therefore, it is important to identify commercially viable strategies that are capable of removal or reducing fat content of food products without altering their sensory and nutritional characteristics There are some products in which fat plays important structural role, such as chocolate, ice cream, and bakery products like biscuits, breads, and cakes Phospholipids The molecular characteristics of the phospholipids dictate the application of lecithin The presence of both hydrophilic and lipophilic groups within a phospholipid molecule makes it surface-active This surface-active property plus the natural nature of lecithin contribute to emulsification, anti-spattering, wetting, anti-staling, dough-conditioning and antioxidant functions in foods Emulsifiers are used in many food products owing to their ability to stabilize oil and water dispersions Another use of lecithin that directly relates to its emulsification property is anti-spattering In margarine, which is a water-in-oil emulsion, spattering happens when water droplets coalesce during heating Lecithin surrounds water particles to slow down this coalescence and thus reduce spattering Lecithin also serves as a wetting agent in powdered or granular products For example, the addition of lecithin helps cocoa powder disperse easily in water Lecithin is also able to form complexes with starch and protein One example is the ability of lyso-lecithin to form a lipid–amylose complex that decreases wheat starch retrogradation Rancidification of fats and oils Rancidification Rancidification is the process of complete or incomplete oxidation or hydrolysis of fats and oils when exposed to air, light, or moisture or by bacterial action, resulting in unpleasant taste and odor Specifically, it is the hydrolysis or autoxidation of fats into short-chain aldehydes and ketones, which are objectionable in taste and odor In the presence of oxygen and/or ultraviolet (UV) radiation, most lipids will break down and degrade, forming several other compounds Oxygen is eight times more soluble in fats than it is in water; it is this exposure that is the main cause of the autoxidation process, increasing the saturation of the oil Hydrolytic rancidity, also called hydrolysis or enzymatic oxidation, occurs in the absence of air, but with moisture present This normally is accomplished through enzymatic peroxidation, where enzymes found naturally in plant oils (i.e., lipoxygenase, cyclooxygenase) and animal fats (i.e., lipase) can catalyze reactions between water and oil Another degradation process is microbial rancidity, in which micro-organisms such as bacteria, molds and yeast use their enzymes to break down chemical structures in the oil, producing unwanted odors and flavors Water needs to be present for microbial growth to occur There are other contributing factors that can significantly speed up the rancidity process, including: temperature, time, light, water, catalyst Appropriate storage Rancidification can be decreased, but not completely eliminated, by storing fats and oils in a place with little or no exposure to oxygen or free radicals, at a low temperature, and away from light Many oils are packed with nitrogen gas to help limit exposure to oxygen Antioxidants are often added to fats and oils to retard the development of rancidity due to oxidation and hydrolysis Antioxidants retard oxidation primarily by either hydrogen donation or electron donation Processors can use natural antioxidants such as carotenes, flavonoids, polyphenols, ascorbic acid and tocopherols, or select from a range of synthetic antioxidants However, these natural antioxidants tend to be shorter-lived, so many bulk producers prefer using synthetic antioxidants when a longer shelf-life is preferred Vitamin E is among the best antioxidants for oil because it is a powerful antioxidant that is soluble in oils and is considered a natural compound  ... plasmalogens are found in blood Source of some lipids Simple lipids In foods, lipids are mainly found in the form of triglycerides which make up to 99% of lipids of plant and animal origin Triglycerides... sphingolipids of plants Lipoproteins Lipoproteins may also be classified as compound lipids These are compounds of proteins, fatty acids, and alcohols and may include other classes Lipids and. .. is one of the most polar plant lipids Cerebrosides and cerebroside sulfates are further examples of glycolipids Sphingolipids Sphingolipids are derivatives of the amino alcohol sphingosine, which