Soy milk is an excellent substitute for cow’s milk and is far more digestible and compatible with human nutritional requirements than is cow’s milk. The amount of fat in soy milk is less than that of cow’s milk, but the oil in soy beans consists mainly of mono- and polyunsaturated fats and is cholesterol free, in contrast with the fat in cow’s milk which consists of saturated fats and is not cholesterol free. The oil in the soya bean and soya bean milk also contains a considerable quantity of essential fatty acids, particularly α-linolenic acid, and thus provides a convenient source, together with whole grains, for meeting the body’s requirements for these essential fatty acids. In addition, soya beans are also rich in vitamin E, thus preventing harmful oxidation of these polyunsaturated fatty acids.
In contrast to cow’s milk, the proteins in soy milk are readily digestible and do not produce the adverse side-effects associated with casein, the principle protein of cow’s milk. Casein is known to elicit a hypercholesterolaemic effect when fed to a variety of animals, and will even result in the animals developing arteriosclerosis.67 These effects were diminished in rabbits if casein was replaced with soy protein.67 With the exception of vitamin B-12, soy milk also contains substantially higher concentrations of the B-group vitamins than does cow’s milk. Vitamin B-12 can, however, be added to home-made soy milk, as is currently being done in the case of commercial soy milks and infant formulas. Contrary to popular belief, fermented soy products also do not contain vitamin B-12, except if it was added or is present as a contaminant. The vitamin B-12 that is presumed to be present in these foods is in the form of analogues, and not as cobalamine, which is the active vitamin.68
In the past, soy milks were rather unpalatable as a result of a strong beany flavour, however, this drawback has to a large extent been eliminated and sales of soy milk have rocketed in countries where the new generation of milks is readily available. The beany flavour of soy milk is caused by the action of enzymes such as lipoxygenase during the preparation process.
Modern processing thus inactivates lipoxygenase through heat treatment whilst at the same time ensuring that the solubility of the other soya proteins is not too greatly affected, as this would reduce the amount of soluble protein that can be extracted from the milk. Heating soaked, dehulled beans to 80-85°C for not more than 2 minutes will inactivate the lipoxygenase whilst still allowing 80% of the protein to be extracted from the beans.69 It was also found that soaking dehulled beans at 70°C for 5 minutes prior to liquidizing and extracting of the milk would reduce the n-hexanal content of the soy milk and improve the flavour.70
Commercial soy milk and soy products are a great time saver, but for the industrious or for those living in areas where these products are not available or too expensive, soy milks can be prepared at home, which will rival any of the modern commercial products. Moreover, the concentrated soy bean extract can be used to make a variety of sauces and soy cheeses such as tofu, which is obtained by precipitating the protein from the milk. These products can be incorporated into many dishes to improve their nutritional value, texture and taste. Try some of the recipes given in the last chapter.