NUTRITIONAL VALUE OF WHEAT AND RYE
The kernel of wheat is composed of the outer bran layer, the germ, and the endosperm. It is rich in nutrients, many of which are concentrated in the bran and germ. Of special importance is that it contains the entire B complex, except for vitamin B12. B vitamins function as cofactors in many metabolic reactions involved in the release of energy.
The germ, which includes the scutellum, is especially rich in vitamins B and E, high quality protein, unsaturated fats, minerals, and carbohydrates. The bran consists mostly of the insoluble carbohydrate cellulose, and contains incomplete protein, traces of B vitamins, and minerals - especially iron. The endosperm is the largest part of the grain, and consists mostly of the carbohydrate starch, incomplete protein, and trace amounts of vitamins and minerals.
Because of its high content of vitamin E, wheat germ is promoted as a health food, and has been proposed as a cure for almost every disease.
Recent studies have shown that vitamin E increases the desirable HDL cholesterol in women, though in men only if they initially had low levels. Animal studies have also shown that vitamin E protects against free radicals released by the body when it is exposed to toxic chemicals. Vitamin E is used to treat intermittent claudication, which involves cramps in the calf muscles at night and extreme pain while walking. Vitamin E may be helpful for fibrocystic breast disease .
Stone Grinding of Grain
There are several advantages to stone-ground wheat flour. The endosperm, bran, and germ remain in their natural, original proportions. Because the stones grind slowly, the wheat germ is not exposed to excessive temperatures. Heat causes the fat from the germ portion to oxidize and become rancid and much of the vitamins to be destroyed . Since only a small amount of grain is ground at once, the fat from the germ is well distributed which also minimizes spoilage . Nutritive losses due to oxygen exposure are also limited by the fact that stone-ground flour is usually coarser .
Because grains contain only about 12% water (or about 0.6 water activity), they are not predisposed to spoilage. However, grinding removes the protective layers and endangers the grain's biological stability. Deterioration of sensory and nutritional qualities depends on storage conditions, such as temperature, humidity, oxygen concentration, and light exposure. The lower the water activity, the lower is the loss of vitamins. For example, a vitamin E loss of only about 23% occurred after a 13 months of storage at a 0.6 water activity. In order to reduce oxidation of Essential compounds and the development of rancidity, many authors recommend storing ground flour for no more than two weeks. Antioxidants present naturally in grains (vitamin E and lecithin) help prevent oxidation of the fatty acids and the associated rancidity only for a limited time, and under 'favourable' conditions.
Glutamic acid decarboxylase, the most sensitive enzyme in the grain, is used to indicate the health of the grain. When heated or exposed to increased humidity, even under 'favourable' conditions, it losses activity very quickly in wheat. It was found to be even more sensitive in rye.
The B vitamins are liable to be destroyed by light and air, and it also seems that other substances, still unknown, are quickly destroyed . Other deteriorations include denaturation of lipoproteins, phospholipid hydrolysis, auto-oxidation of unsaturated fatty acids of phospholipids, polymerization within lipoproteins, browning, Maillard reaction of amino groups from phospholipids and aldehyde groups from sugars, and carotene and aroma losses.
Lipids in milled wheat are much more susceptible to enzymatic degradation, because enzymes are incorporated into the flour with fragments of bran and germ and with microorganisms from the surface of the grain. Associated with lipid deterioration are losses of carotenoids and vitamin E .