食品在加工、贮藏过程中，经常会发生褐、红、蓝、绿、黄等各种变色现象，本质上都是酶促或非酶 促化学反应的结果。其中最普遍、最重要的是褐变。在面包、糕点、咖啡等食品的焙烤过程中，褐变产生 诱人的焦黄色和特征香气；而在水果、蔬菜加工、贮藏过程中，褐变则影响外观、降低营养价值和风味等

4.7.I Occurrence and microheterogeneity B-Lactoglobulin is a major protein in bovine milk, representing about 50% of total whey protein and 12% of the total protein of milk. It was among the first proteins to be crystallized, and since crystallizability was long considered to be a good criterion of homogeneity, B-Ig, which is a typical

Lactose is the principal carbohydrate in the milks of all mammals; non mammalian sources are very rare. Milk contains only trace amounts of other sugars, including glucose(50 mg\), fructose, glucosamine, galac- tosamine, neuraminic acid and neutral and acidic oligosaccharides The concentration of lactose in milk varies widely between species(Table 2.1). The lactose content of cows'milk varies with the breed of cow

The milks of all mammals contain lipids but the concentration varies widely between species from c. 2% to greater than 50%(Table 3. 1). The principal function of dietary lipids is to serve as a source of energy for the neonate and the fat content in milk largely reflects the energy requirements of the species, e.g. land animals indigenous to cold environments and marine

The water content of dairy products ranges from around 2.5 to 94%(w/w) (Table 7.1) and is the principal component by weight in most dairy products, including milk, cream, ice-cream, yogurt and most cheeses. The moisture content of foods (or more correctly their water activity, section 7.3), together with temperature and pH, are of great importance to food technology. As described in section 7.8 water plays an extremely important

Milk is a dilute emulsion consisting of an oil/fat dispersed phase and an aqueous colloidal continuous phase. The physical properties of milk are similar to those of water but are modified by the presence of various solutes (proteins, lactose and salts) in the continuous phase and by the degree of dispersion of the emulsified and colloidal components

Cheese is a very varied group of dairy products, produced mainly in Europe, North and South America, Australia and New Zealand and to a lesser extent in North Africa and the Middle East, where it originated during the Agricultural Revolution, 6000-8000 years ago. Cheese production and con- 10A and 10B), is increasing in traditional

Like all other foods of plant or animal origin, milk contains several indigenous enzymes which are constituents of the milk as secreted. The principal constituents of milk (lactose, lipids and proteins) can be modified by exogenous enzymes, added to induce specific changes. Exogenous en- zymes may also be used to analyse for certain constituents in milk. In addition, milk and most dairy products

Vitamins are organic chemicals required by the body in trace amounts but which cannot be synthesized by the body. The vitamins required for growth and maintenance of health differ between species; compounds regarded as vitamins for one species may be synthesized at adequate rates by other species. For example, only primates and the guinea-pig require ascorbic acid (vitamin C; section 6.4) from their diet; other species possess the enzyme gluconolactone oxidase which is necessary for the synthesis of vitamin C from D-glucose or D-galactose

Milk is a fluid secreted by the female of all mamalian species, of which there are more than 4000, for the primary function of meeting the complete nutritional requirements of the neonate of the species. In addition, milk serves several physiological functions for the neonate. Most of the non- nutritional functions of milk are served by proteins and peptides which