Reduction of biogenic amines in sufu by ethanol addition during ripening stage

Authors: QIU, SHUANG - China Agricultural University; WANG, YING - China Agricultural University; CHEN, HAO - China Agricultural University; LIU, YAN - China Agricultural University; Yadav, Madhav; YIN, LIJUN - China Agricultural University

Submitted to: Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/11/2017
Publication Date: 1/15/2018
Publication URL: http://handle.nal.usda.gov/10113/5734244
Citation: Qiu, S., Wang, Y., Chen, H., Liu, Y., Yadav, M.P., Yin, L. 2018. Reduction of biogenic amines in sufu by ethanol addition during ripening stage. Food Chemistry. 239:1244-1252.

Interpretive Summary: Sufu, a fermented soybean product, has been prepared from fermented tofu (soybean curd) by aging in salt solution and dressing mixture for improving its quality. It is a low oil and cholesterol-free food of plant origin. Sufu is a popular appetizer and side-dish in China and also in the USA. Several types of Sufu can be distinguished based on its production method, color or flavor. Sufu is consumed in a similar way as cheese and it has a creamy texture and a unique flavor. Making fermented sufu includes four steps: (1) preparing tofu by salt precipitation from boiled soymilk (2) preparing pehtze with a pure fermentation starter culture, (3) salting of pehtze, (4) ripening in dressing mixture. Biogenic amines (BAs) are basic nitrogenous compounds with low molecular weight. They are formed mainly by degradation of amino acids or by transformation of aldehydes and ketones, as a result of microbial action during food storage. The most important BAs in foods are histamine, tyramine, putrescine, cadaverine, tryptamine, beta-phenylethylamine, spermine and spermidine. Although BAs are essential for many functions in humans and animals, consumption of food containing high amounts of these amines may have toxic effects. For example, some BAs may cause hypertensive crises and migraines in humans. An increase in BAs has been widely reported during fermentation in soybean products. We studied 16 commercial Sufu samples and compared the levels of BAs. In order to test our hypothesis that addition of ethanol may reduce levels of BAs, four sufu samples were prepared in the laboratory with or without ethanol. A few previous studies have focused on the reduction of BA levels in food. Methods included irradiation, laboratory sanitized starter culture and inoculation with selected lactic acid bacteria to reduce the level of BAs in food products. With our current studies, we have found that addition of ethanol can reduce the amount of BAs produced during sufu preparation. This new technique may be useful for making sufu as a healthy appetizer and side-dish all over the world. These findings will benefit soybean processors by adding value and creating additional applications of soybean. The addition of ethanol will also benefit manufacturers of sufu, who will be able to produce a healthy product with more flavor and less BAs.

Technical Abstract: The aim of this study was to investigate the contents of biogenic amines (BAs) in different types of sufu samples obtained from different producers, and also the possible effect of addition of ethanol on reducing the levels of BAs during sufu ripening. The levels of BAs in sufu samples were analyzed by HPLC after pre-column derivatization. Salt content, water soluble protein, polypeptide and amino nitrogen were also determined in the sufu prepared in the laboratory (Laboratory made sufu) by soaking in the dressing mixture in the presence of ethanol. The results showed that changing the manufacturing process altered the distribution of BAs of commercial sufu. Putrescine, cadaverine, histamine, and tryptamine were the main and common BAs in red, white and grey types of sufu. The content of putrescine, cadaverine, tryptamine, beta-phenylethylamine and tyramine in the grey sufu of all producer brands were significantly (p < 0.05) higher than those in the white and red sufu. During sufu preparation, the levels of BAs in pehtze increased sharply after pre-fermentation and salting. The addition of ethanol to the dressing mixture had a significant influence on declining the total content of BAs in laboratory-made sufu. Cadaverine, tyramine, histamine and beta-phenylethylamine contents in those sufu samples were significantly decreased. The levels of BAs in all samples soaked in the dressing mixture containing ethanol did not exceed the allowable limit (50.0 mg/kg). Examination of the physicochemical properties of sufu, revealed that the polypeptide and amino nitrogen contents increased very little after the addition of enthanol, indicating a reduction in the degredation of water soluble protein during ripening.