Yoghurt Production by Lactobacillus Fermentation of Soybean Milk

SOYBEANS rich in protein have been an important food item in Asia for centuries. In the 20th century. eYen in Europe and the United States. soybeens have become increasingly· pop. ular as a protein source to reolace. meet and dairy produets. HOWeYM. the use of soybeans as food is still limited. partly because of their obiectionable flavour and also because they contribute flatulence. Numerous methods. therefore. have ~ deYeloped eithM to remove or to reduce these undesirable factora. A large variety of compounds that m3Y contribute to the flavour of soybeen products have been isolated. but specific compounds responsible for the flavour have not been identified. One of the theories is that some undll1lirable flavours are not originally present in the beens. but when the beens are cracked or damaged in the presence of moisture and air. rancid and off-flavours develop. Wilkens at al' observed that soybean milk prepared from fuil-fat soybeans was described as beany. rancid. and off.. flavoured. whereas soybean milk from defatted beens had a comparatively bland cereal-type odour. They postulated that off-flavours are due to the oxidation of polyunsaturated fats by Iipoxygenase. Mustaltas at ai' also concluded that inactivation of lipoxygenase is an important step in the preparation of bland-flavoured full-fat soybean flour. Several methods have since been proposed to inactivate the enzyme. Wilkens at ai' suggested a high-temperature. rapidhydration grinding process for m!lking a nearly bland soybean milk. Mustaltas at af proposed a dry-heat preconditioning step to inactivate lipoxygenase and other enzymes. Nelson et sf' recommended blanching in boiling weter before grinding. Because Iipoxygenase is inactive at low