Dairy Chemistry And Biochemistry

280 DAIRY CHEMISTRY AND BIOCHEMISTRY

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The classical niacin deficiency disease is pellagra, which is characterized
by symptoms including diarrhoea, dermatitis, dementia and eventually
death. High-protein diets are rarely deficient in niacin since, in addition to
the preformed vitamin, such diets supply sufficient tryptophan to meet
dietary requirements. Large doses of niacin can cause the dilation of
capillaries, resulting in a painful tingling sensation.
The RDA for niacin is expressed in terms of energy intake; 6.6 mg niacin
equivalent (NE, 1 mg niacin or 60 mg tryptophan) per 1000 kcal (4186 kJ)
per day is recommended (13 NE day-’ minimum). This is approximately
equivalent to 19 and 15 mg NE day- for men and women, respectively. The
UK RNI value for niacin is 6.6 mg NE per 1000 kcal (4186 kJ) per day for
adults. The richest dietary sources of niacin are meat, poultry, fish and
whole-grain cereals.
Milk contains about 0.1 mg niacin per lOOg and thus is not a rich source
of the preformed vitamin. Tryptophan contributes roughly 0.7 mg NE per
100 g milk. In milk, niacin exists primarily as nicotinamide and its concen-
tration does not appear to be affected greatly by breed of cow, feed, season
or stage of lactation. Pasteurized goats’ (0.3 mg niacin and 0.7 mg NE from
tryptophan per 100 g) and raw sheep’s (0.4 mg niacin and 1.3 mg NE from
tryptophan per lOOg) milk are somewhat richer than cows’ milk. Niacin
levels in human milk are 0.2 mg niacin and 0.5 mg NE from tryptophan per
100 g. The concentration of niacin in most dairy products is low (Appendix
6A) but is compensated somewhat by tryptophan released on hydrolysis of
the proteins.
Niacin is relatively stable to most food-processing operations. It is stable
to exposure to air and resistant to autoclaving (and is therefore stable to
pasteurization and UHT treatments). The amide linkage of nicotinamide
can be hydrolysed to the free carboxylic acid (nicotinic acid) by treament
with acid but the vitamin activity is unaffected. Like other water-soluble
vitamins, niacin can be lost by leaching.