Organic acids as a freshness indicator for tofu (soybean curd).

The aim of this study was to evaluate organic acids as potential indicators of tofu freshness. To achieve this, relationships between organic acids concentrations and the growth of microorganisms in fresh tofu were investigated. The levels of microorganisms (total bacterial count) and organic acids (phytic acid, oxalic acid, citric acid, lactic acid, formic acid and acetic acid) were analyzed in tofu (packed and unpacked) every 3 days during 15 days of storage at different temperatures (4, 10, and 25 °C). Organic acids were analyzed by high performance liquid chromatography and microbial analysis was conducted by plate counting method. The levels of oxalic acid, citric acid and formic acid decreased significantly during the storage period, while the levels of lactic acid and acetic acid increased significantly when stored at 10 °C. The acetic, lactic and formic acids showed significant correlation to the levels of microorganisms in packed tofu, suggesting the use of these organic acids as potential freshness quality indicators of tofu. Current study demonstrated the effective way of predicting freshness of tofu by utilizing organic acid analysis, as opposed to traditional method relying on microbial count.