Dairy products compound concentration

Lactic acid-producing bacteria associated with fermented dairy products have been found to produce antibiotic-like compounds caUed bacteriocins. Concentrations of these natural antibiotics can be added to refrigerated foods in the form of an extract of the fermentation process to help prevent microbial spoilage. Other natural antibiotics are produced by Penicillium wqueforti the mold associated with Roquefort and blue cheese, and by Propionibacterium sp., which produce propionic acid and are associated with Swiss-type cheeses (3). 

The consumption of dairy products plays a significant role in providing high-quality protein, vitamins, minerals, and other bioactive compounds to the American diet. Dairy products are consumed fresh in the United States in the form of fluid milk, cheese, yogurt, butter, and ice cream. Dried and condensed products such as nonfat dried milk, whey, whey protein concentrates, and isolates are also produced which are used as ingredients to boost the nutritional and functional properties of a host of other food... 

Hydroxy-2-butanone (acetoin) is a characteristic constituent of butter flavour used for flavouring margarine and can be obtained as a by-product of molasses-based and lactic acid fermentations [49, 71]. The closely related 2,3-butanedione (diacetyl) has a much lower organoleptic threshold than acetoin and is an important strongly butter-like flavour compound in butter and other dairy products [72] in buttermilk, for instance, the diacetyl concentration is only about 2-4 mg [73]. a-Acetolactate (a-AL) is an intermediate of lactic acid bacteria mainly produced from pyruvate by a-acetolactate synthase. In most lactic acid bacteria, a-AL is decarboxylated to the metabolic end product acetoin by a-AL decarboxylase (ALDB) [71] (Scheme 23.5). 

The major form of vitamin D in both cows and human milk is 25(OH)D3. This compound is reported to be responsible for most of the vitamin D in the blood serum of exclusively breast-fed infants. Whole cows milk contains only about 0.03 pg vitamin D per 100 g and 1 litre of milk per day will supply only 10-20% of the RDA. Therefore, milk is often fortified (at the level of c. 1-10 fig 1 ) with vitamin D. Fortified milk, dairy products or margarine are important dietary sources of vitamin D. The concentration of vitamin D in unfortified dairy products is usually quite low. Vitamin D levels in milk vary with exposure to sunlight. 

Apart from public health impacts, residual antimicrobials in animal products can bring about technoeconomic losses in the food processing industry. It has long been known that the presence of some antimicrobial compounds in milk can dramatically affect the production of fermented dairy products such as yogurt, cheese, buttermilk and sour cream (72, 73). As shown in Table 10.2, even minute concentrations of antibiotics in milk can cause inhibition of the growth of commonly used dairy starter cultures (74). 

The solubility of NHDC in hot water, alcohol, aqueous alkali, acetonitrile, dimethyl sulfoxide, and alcohol/water mixture facilitates its selective extraction from food samples (20,91,94). It is extracted from jams, fruit juices, and dairy products with methanol (66,93) or acetone (95) and filtered or centrifuged. Chewing gum samples are dissolved in chloroform and extracted with water. The extract is centrifuged, and the clear supernatant is injected into the HPLC (95). If necessary, sample cleanup and concentration may be achieved by selective adsorption or desorption (20) on Sep-Pak Cl8 (96). Tomas-Barberan et al. (93) used Amberlite XAD-2 resin for purification of jam extract. Sugars, pectin, and other polar compounds were eluted with water, and NHDC was eluted with methanol. After concentration, the extract was further purified on a Sephadex LH-20 column prior to HPLC analysis. 

In dairy products the lipid component is an important contributor of dairy flavor. Compounds such as mono- and di-carbonyls and volatile fatty acids impart flavor to milk though present only in low concentrations. Saturated and unsaturated aldehydes and various ketones affect flavor though present in concentrations of ppm or ppb (15). 

Another area of food research is the study of flavor perception. This involves attempts to detect VOCs emitting from foods on-line, with the flavor characteristics perceived by human beings, and to quantify the concentrations of flavor compounds with PTR-MS. To date, only a few specific groups have been studied mainly including foodstuffs, vegetables, and dairy products. 

The foods that are rich in selenium are mainly marine fish, crustaceans and molluscs (such as oysters and prawns), freshwater fish and offal (mainly kidneys). Eggs also have relatively high levels most selenium is contained in the yolk. The content of selenium in mflk, dairy products and meat is lower and is highly dependent on the animal nutrition. Concentrations of selenium in fruits and vegetables, except garhc, are very low (<0.02 mg/kg). Mushrooms contain selenium at the level of 0.03-1.4 mg/kg. The selenium content in foods of plant origin is fundamentally influenced by the selenium content in the soil or fertiliser used and its availability to the plant The concentration of selenium in foods of animal origin is determined by the selenium content in the animal feed. Some pet foods are dehberately fortified with selenium compounds. 

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