EFFECT OF PROCESSING CONDITIONS ON THE FORMATION OF BIOGENIC AMINES AND ETHYL CARBAMATE IN SOYBEAN TEMPE

Abstract

ABSTRACT Tempe is a fermented soybean product originating from Indonesia. The effects of manufacturing conditions, i.e., soaking, boiling, fermentation and home cooking by stewing or frying, and the effect of pure cultures of microorganisms commonly occurring in tempe towards their production of toxicants like biogenic amines and ethyl carbamate were investigated. The level of biogenic amines in soaked soybeans was rather low (total < 280 ppm), and not significantly affected by boiling, but considerably increased by fermentation. The functional fungus Rhizopus oligosporus mainly produced tyramine and some putrescine (total biogenic amines approximately 1800 ppm). With added inoculation of Klebsiella pneumoniae and Trichosporon beigelii, the total amount of biogenic amines increased slightly (2000, resp. 2100 ppm) with a shift towards cadaverine. With added Lactobacillus plantarum, a reduction of tyramine levels resulted in a considerably lower total level of biogenic amines (approx. 1000 ppm). Storage at 5C did not affect the level of biogenic amines, whereas at 25C, increased levels of putrescine were observed. Home cooking by stewing had little effect, but frying in oil resulted in significant decreases of both putrescine and tyramine. Preventive measures to keep biogenic amines at low levels in tempe are recommended. They include inoculation with selected lactic acid bacteria which cannot produce but can degrade biogenic amines, and frying instead of stewing of tempe. Ethyl carbamate levels were negligible (<11 ppb) in all treatments; this was attributed to the absence of significant concentrations of ethanol in the product.