Chemical Analysis of Value Added Dairy Products and Their Quality ...

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Chemical Analysis of Value Added Dairy Products and Their Quality AssuranceIntroduction:Methods of Cholesterol Removal to DevelopLow – Cholesterol Dairy ProductsDarshan Lal and Vivek SharmaDairy Chemistry Division, NDRI, KarnalThe importance of milk and milk products, in India, has been recognized since Vedic times.Milk is considered to be a complete food as it contains almost all essential nutrients required forhuman health and growth. Lipids, the most important constituent of milk, play significant role in thenutrition, flavour and physico-chemical properties of milk and milk products. They are also rich sourceof fat-soluble vitamins (A, D, E & K) and essential fatty acids, apart from having pleasant sensoryattributes. Milk fat is easily digestible than other oils and fats. It contains number of componentswhich show anticarcinogenic activity, e.g. sphingomyeline, conjugated linoleic acid, β-carotene etc.So one (especially vegetarians) cannot avoid it in one’s diet. But recent trend, in the society, is againstfat-rich dairy products due to the presence of saturated fat & cholesterol as these are known to increasethe incidence of coronary heart disease (CHD).CHD is one of the common causes of heart attack. Through a period of time, many researchers haveshown that dietary cholesterol, serum cholesterol and occurrence of coronary heart disease (CHD)have positive correlation. Milk fat contains about 0.25 to 0.40% cholesterol. Consumption of gheeand other fat-rich dairy products makes appreciable contribution to cholesterol intake. Furthermore,some cholesterol oxidation products (COPs) have been reported to be more harmful than cholesterolitself as they are cytotoxic, atherogenic, mutagenic and carcinogenic. Recent wave against cholesterolcontainingfoods has damaged the image and market growth of fat-rich dairy products. The educatedand urban society, in particular, is more conscious about the presence of cholesterol in their diet.This segment of the society is the major consumer of dairy and other food items manufactured by theorganized sector. In recent years, demand of cholesterol-free foods has increased tremendously. Thishas led to increase in market of margarine, vegetable fat filled dairy products, milk fat replaced dairyproducts, etc.Owing to the adverse affects of cholesterol on human health, various physical, chemical andbiological methods have been developed for reducing cholesterol in foods. These include blending ofmilk fat with vegetable oils, extraction with organic solvent, adsorption with activated charcoal andsaponin, vacuum distillation, molecular distillation, degradation of cholesterol by enzyme (cholesteroloxidase) and removal of cholesterol by supercritical carbon dioxide. Recently, β- cyclodextrin (a starchhydrolysed product) has been effectively used for cholesterol removal from milk, cream, cheese, lardand egg-yolk. Beta cyclodextrin is reported to be non-toxic, non-hygroscopic, chemically stable andedible.Cholesterol:Cholesterol is a waxy material found in all cells of the bodyand is a necessary part of cell membranes, some hormonesand other body components. In particular, it participates inthe formation of myelin sheaths in the brain and peripheralnerves, and modulates the absorption of dietary fats in theintestine. It also acts as a precursor in the biosynthesis ofbile acids, steroid hormones and vitamin D. The body makesall the cholesterol it needs; it is not necessary to get anycholesterol from the diet. A high level of cholesterol in theblood is a major risk factor for CHD and heart attack.22
Methods of Cholesterol Removal to Develop Low – Cholesterol Dairy ProductsStructure and properties of cholesterol:The term cholesterol was derived from the Greek words chole and stear, which mean “bile”and “hard fat,” respectively. The origin of the term is a reflection of the fact that the substance wasfirst identified as a hard & white solid in gallstones. Though discovered by Poulletier de la Salle in1769, cholesterol was not named until 1818, when Michel Chevreul rediscovered it and dubbed it ascholesterine, believing that the material was like a fat (Sabine, 1977). Cholesterol is a hydrophobic sterolconsisting of a four-ring structure (Figure A) with molecular weight 386.66 and molecular formula:C 27H 46O.Cholesterol is insoluble in water, sparingly soluble in cold alcohol or petroleum ether, and solublein hot alcohol and most other organic solvents. Cholesterol melts at 148.5ºC. It can be sublimed anddistilled under high vacuum. The polar hydroxyl group, which gives cholesterol a slightly hydrophilicnature, can be esterified to a fatty acid, producing cholesterol ester. Both cholesterol and cholesterolester are important structural components of cell membranes. Cholesterol is also a major determinantof membrane fluidity due to its hydrophobic and hydrophilic regions (Webb et al, 1987).Sources of cholesterol in body:In the body, cholesterol appears through endogenous synthesis and from the diet. Cholesterolsynthesis in the body is most active in the liver and intestine and averages 11 mg per kg body weightper day. This equals 770 mg for a 70 kg man on a low (less than 300 mg per day) cholesterol diet(McNamara, 1987). Normally, liver makes 80% of the total blood cholesterol and only 20% comes fromthe diet (Renner and Gurr, 1991; Allred, 1993). Cholesterol is not considered as an essential dietarynutrient because of its endogenous synthesis. On the other hand, Thomas and Holub (1994) reportedthat if less dietary cholesterol is consumed, the body compensates by making more cholesterol.Digestion, absorption and transportation of cholesterol in the blood:Digestion and absorption of cholesterol occurs in the small intestine (Grundy, 1983). Cholesterolester is broken down by a pancreatic cholesterol esterase into free cholesterol, which, absorbed into thecells lining of the intestine. The absorption of endogenous cholesterol (as bile acids) is more efficientthan dietary cholesterol absorption.Fat, including cholesterol, absorbed from the diet, is insoluble in the aqueous medium of theblood. To enable transport through blood system, the various fat components are incorporated intoparticles called lipoproteins (Grundy, 1983; Mahley and Innerarity, 1983). Lipoproteins consist of alipid core of triglyceride and cholesterol ester with a surface of mainly phospholipids, protein andsome free cholesterol. The four major lipoprotein fractions found in the blood are chylomicrons, verylowdensity lipoprotein (VLDL), low-density lipoprotein (LDL) and high-density lipoprotein (HDL).Chylomicrons are very rich in triglycerides (about 85%) but also contain absorbed cholesterol inthe free or esterified form. VLDL is also rich in triglyceride (about 50%) and contains a substantialportion of cholesterol mainly as cholesterol ester. VLDL transport about 15% of the total cholesterolfound in the blood.LDL is enriched in cholesterol and accounts for about 60% of the total blood cholesterol level. It isdeposited in artery walls, increasing the buildup of plaque and hence also known as bad cholesterol.HDL carries as much as 20% of the total blood cholesterol level. HDL is thought to be antiatherogenicsince it picks up cholesterol from peripheral tissues for delivery to the liver and excretion. Consequently,HDL is called good cholesterol. A better indicator of risk for CHD is the LDL/HDL cholesterol ratio(Thomas and Holub, 1994; Gurr, 1995).Synergistic effect of cholesterol with saturated fatty acids on plasma cholesterol level:Some saturated fatty acids are reported to affect total plasma cholesterol concentration. While,stearic acid has little effect on plasma cholesterol concentration, myristic and palmitic acids havebeen reported to have the greatest cholesterol raising potential (Hegsted et al., 1965). Some evidencesuggests that the effect of myristic and palmitic acids depends on the concomitant intake of dietary23
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