1. Introduction
Micronutrient malnutrition – also called “hidden hunger” – is a widespread global problem (Welch, 2002). In addition to the direct health effects, the existence of micronutrient malnutrition has profound implications for economic development and productivity, particularly in terms of the potentially huge public health costs and the loss of human capital formation (WHO, 2005). In particular, zinc deficiency is now recognized as one of the most severe problems of human malnutrition world-wide (Gibson, 2006; Prasad, 1985). It is estimated to affect up to one-third of the global human population (Hotz & Brown, 2004) and is particularly frequent in India, Southeast Asia and equatorial Africa. Zinc is an essential component of a large number (>300) of enzymes participating in the synthesis and degradation of carbohydrates, lipids, proteins and nucleic acids as well as in the metabolism of other micronutrients. It also plays a central role in the immune system, affecting a number of aspects of cellular and humoural immunity (FAO/WHO, 2002). The clinical features of severe zinc deficiency in humans are growth retardation, delayed sexual and bone maturation, skin lesions, diarrhoea, alopecia, impaired appetite, increased susceptibility to infections mediated via defects in the immune system, and the appearance of behavioural changes (Hambidge, 1989). The effects of marginal or mild zinc deficiency are less clear. A reduced growth rate and impairment of immune defence are so far the only clearly demonstrated signs of mild zinc deficiency in humans. Other effects, such as impaired taste and wound healing, which have been claimed to result from a low zinc intake, are less consistently observed (Hambidge, 2000). Recently many researchers have focused their attention on carbohydrate to mineral chelates which are demonstrated to be an efficient mineral fortificant for human beings without side effects (Bachran and Beruhard, 1980, Ferrari and Saladini, 2004, Nagy and Burger, 1986 and Wokowiec and Drabent, 1985). During the manufacture of cheese, an enormous amount of whey is produced as a byproduct, which is an excellent source of lactose. Lactose is also a good substrate for microorganisms. Which presents a disposal problem since direct addition of whey to sewage system would raise the biological oxygen demand of the system appreciably. This simple sugar poses a serious potential risk to the environment. Lactose comes under the category of reducing sugars which have a relatively reactive hemi acetal group at C-1, zinc ions may coordinate to the O2 donor atom of carbohydrate. Introduction of an anchoring group into the sugar molecule as primary coordination site may promote the coordination and deprotonation of the alcoholic hydroxylic groups of the carbohydrate moiety (Urbanska & Kozlowski, 1990). Despite the apparent nutrition significance of the lactose–zinc interaction, the nature of zinc binding with caseins has received little study. Therefore, the present study was undertaken with specific objectives attention (i) to preparation of lactose–zinc complex on the basis of maximum zinc binding ability of lactose and to assess microstructure of optimized lactose–zinc complex and (ii) evaluation of the sensory acceptability and physicochemical properties of milk fortified with lactose–zinc complex. In vitro bioavailability of added zinc in milk fortified with lactose–zinc complex was also evaluated.
1. บทนำMicronutrient malnutrition – also called “hidden hunger” – is a widespread global problem (Welch, 2002). In addition to the direct health effects, the existence of micronutrient malnutrition has profound implications for economic development and productivity, particularly in terms of the potentially huge public health costs and the loss of human capital formation (WHO, 2005). In particular, zinc deficiency is now recognized as one of the most severe problems of human malnutrition world-wide (Gibson, 2006; Prasad, 1985). It is estimated to affect up to one-third of the global human population (Hotz & Brown, 2004) and is particularly frequent in India, Southeast Asia and equatorial Africa. Zinc is an essential component of a large number (>300) of enzymes participating in the synthesis and degradation of carbohydrates, lipids, proteins and nucleic acids as well as in the metabolism of other micronutrients. It also plays a central role in the immune system, affecting a number of aspects of cellular and humoural immunity (FAO/WHO, 2002). The clinical features of severe zinc deficiency in humans are growth retardation, delayed sexual and bone maturation, skin lesions, diarrhoea, alopecia, impaired appetite, increased susceptibility to infections mediated via defects in the immune system, and the appearance of behavioural changes (Hambidge, 1989). The effects of marginal or mild zinc deficiency are less clear. A reduced growth rate and impairment of immune defence are so far the only clearly demonstrated signs of mild zinc deficiency in humans. Other effects, such as impaired taste and wound healing, which have been claimed to result from a low zinc intake, are less consistently observed (Hambidge, 2000). Recently many researchers have focused their attention on carbohydrate to mineral chelates which are demonstrated to be an efficient mineral fortificant for human beings without side effects (Bachran and Beruhard, 1980, Ferrari and Saladini, 2004, Nagy and Burger, 1986 and Wokowiec and Drabent, 1985). During the manufacture of cheese, an enormous amount of whey is produced as a byproduct, which is an excellent source of lactose. Lactose is also a good substrate for microorganisms. Which presents a disposal problem since direct addition of whey to sewage system would raise the biological oxygen demand of the system appreciably. This simple sugar poses a serious potential risk to the environment. Lactose comes under the category of reducing sugars which have a relatively reactive hemi acetal group at C-1, zinc ions may coordinate to the O2 donor atom of carbohydrate. Introduction of an anchoring group into the sugar molecule as primary coordination site may promote the coordination and deprotonation of the alcoholic hydroxylic groups of the carbohydrate moiety (Urbanska & Kozlowski, 1990). Despite the apparent nutrition significance of the lactose–zinc interaction, the nature of zinc binding with caseins has received little study. Therefore, the present study was undertaken with specific objectives attention (i) to preparation of lactose–zinc complex on the basis of maximum zinc binding ability of lactose and to assess microstructure of optimized lactose–zinc complex and (ii) evaluation of the sensory acceptability and physicochemical properties of milk fortified with lactose–zinc complex. In vitro bioavailability of added zinc in milk fortified with lactose–zinc complex was also evaluated.
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