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

Abstract

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.

Physical, Chemical, Microbiological and Sensory Characteristics of a Probiotic Beverage Produced from Different Mixtures of Cow's Milk and Soy Beverage by Lactobacillus acidophilus La5 and Yoghurt Culture

“…However, Cruz et al (30) found 128 mg of lactic acid per 100 mL on the first day, which increased to 306 mg per 100 mL during 28 days. Dominant acid in soy beverage sample in the present work was acetic acid, which is consistent with the research of other authors (29,31). High concentrations of acetic acid in yoghurts are generally connected with fermentation of lactose to lactic acid, and this is called the heterofermentative pathway of lactose produced by strains of bifidobacteria.…”

Determination of trace chelating carboxylic acids in rice by green extraction combined with liquid chromatography–mass spectrometry analysis and its application in the evaluation of old and new rice

“…27 The content of several organic acids, which was determined by liquid chromatography-mass spectrometry (LC/MS) analysis, was reported to predict the freshness of tofu. 28 In our previous work, the concentration of several CCAs was found to increase by several times in tea drinks during their spoilage period, in which that of succinic acid had increased by 75 times. 26 The increase in CCA content is likely to be related to the boom in the TCA cycle of microorganisms in the process of deterioration of tea beverages.…”

“…The concentrations of CCAs and their variations are regarded as important indicators for the ripeness, decay and fermentation of foods 27 . The content of several organic acids, which was determined by liquid chromatography–mass spectrometry (LC/MS) analysis, was reported to predict the freshness of tofu 28 . In our previous work, the concentration of several CCAs was found to increase by several times in tea drinks during their spoilage period, in which that of succinic acid had increased by 75 times 26 .…”