Microbiological safety and quality of commercial sufu - a Chinese fermented soybean food

In this study, the microbiological safety and quality of commercial sufu we re investigated. Twenty-three samples of three different types of sufu were obtained, mainly in China and some in The Netherlands. Chemical parameters analysed included moisture, pH, free amino N, NaCl, ethanol, sucrose, gluc ose, and fructose. Concentrations of NaCl, ethanol, glucose and fructose va ried from 6.2%, 0.5%, 0% and 0% to 14.8%, 6.3%, 6.2% and 4.8%, respectively . Microbiological analyses were done for total count of mesophilic aerobic bacteria (TMAB), bacterial endospores, total count of halotolerant bacteria at 10% (THB10) and at 17.5% NaCl (THB17.5), lactic acid bacteria (LAB), fu ngi, Enterobacteriaceae, and the following pathogens: Bacillus cereus, Clos tridium perfringens, Staphylococcus aureus and Listeria monocytogenes. High levels (> 10(5) CFU/g) of TMAB and bacterial endospores were found in most samples, and 85% of TMA-B was identified as Gram-positive. Considerable le vels (10(5) and 10(7) CFU/g) of LAB were detected in two samples of white s ufu, and isolates of LAB were identified as most probably Lb. casei. One-th ird of the samples contained less then 10(3) CFU/g A cereus, but three samp les had over 105 CFU/g indicating potential hazard to consumers. All sample s had less than 10(3) CFU/g C perfringens, except sample R11 (similar to 10 (5) CFU/g). S. aureus could not be detected in any of the samples tested si nce the competitive microflora (usually bacilli) disturbed typical features on the selective medium used; however S. aureus enterotoxin A was detected in some of the white and grey sufu samples. Fungi, Enterobacteriaceae, and L. monocytogenes were not detected in any of the samples. Based on these r esults, a microbiological guideline for safe commercial sufu is proposed. ( C) 2001 Elsevier Science Ltd. All rights reserved.