A Study on Ingredient and Bacterial Contamination of Bean Curd on the Market

市販豆腐 成分 및 細菌汚染에 관한 硏究

The purpose of this study was to analyze general ingredient of bean cured on the market and to examine its exposure to bacterial contamination. For this study, 17 samples (each 9 samples for general bean curd, soft bean curd, and uncurdled bean curd) were randomly collected from nine areas in Seoul from the beginning of April, 1983 to the beginning of June, 1983. The result of ingredient analysis of moisture, ash, and protein of bean curd was compared with the standard set by the Ministry of Health & Social Affairs. In order to find out exposure of bean curd on the market to bacterial contamination, total biological bacteria and coliform group were examined. Experimental results were shown as follows 1) Results of ingredient analysis of moisture, ash, and protein of general bean curd showed that total samples in both moisture and protein met the standard set by the Ministry of Health & Social Affairs but 44.4% of the samples in ash was below the above standard, indicating average 82.0%, 0.9% and 9.6% in moisture, ash, and protein order. 2) Experimental results of moisture, ash, and protein of soft bean curd demonstrated 90.2%, 0.5% and 4.3% respectively total samples in both moisture and protein satisfied the self-criteria set by the Soft Food Co-operative Association of Seoul City but 11.1% of the samples in ash didn't meet the self-criteria. 3) Total samples of uncurdled bean curd satisfied the self-criteria set by the above association, indicating average 92.0%, 0.4%, and 3.5% in moisture, ash, and protein order. 4) Total biological bacteria and coliform group detected in general bean curd showed that more than 10$^5$/g in total biological bacteria accounted for 88.8% of the samples and that 10$^4$/g or more in coliform group accounted for 77.7% of the samples. The result proves that general bean curd has been exposured to a severe bacterial contamination. 5) Result of total biological bacteria and coliform group detected in such packed bean curd as uncurdled bean curd and soft bean curd showed that 61.6% of the samples exceeded 10$^6$/g in total biological bacteria and 27.7% of the samples exceeded 10$^3$/g in coliform group. 6) According to the change with time and temperatures in total biological bacteria and coliform group of general bean curd, general bean curd began to decay around 72 hours at 4$\circ$C and around 48 hours at 23$\circ$C and around 24 hours at 37$\circ$C and, at that time, total biological bacteria approached 10$^6$/g while coliform group did 10$^6$/g. The result indicates that temperature has a great effect on bacteria counts and decay.