Freshness and Quality Change in Tofu Measured by Glucose Level

Introduction:  Tofu is a healthy, popular and traditional soy food in Asian diets, since it is rich in protein, calcium, B-vitamins, iron and magnesium. However, it is very sensitive to microbial growth even under refrigeration because of its relatively high moisture content and pH. In quality deterioration of tofu, the level of glucose could be one of the excellent indicators.

Purpose:  The purpose of this study was to evaluate the freshness and quality change of tofu during storage under refrigeration after opening it. The relationship between freshness of tofu and glucose concentration was determined.

Methods:  The degree of freshness was measured by glucose concentration, total bacterial counts, surface pH and sensory evaluation. To estimate glucose concentration in tofu, glucose oxidation assay was carried out. APHA (American Public Health Association) method was used for the examination of total bacterial counts.

Results: After storage of 5 days at 4°C Tofu had a change in decrease of glucose concentration by 20.3%, and its pH and total bacterial counts reached 6.1 and 2.80 log CFU/g, respectively. In the equation of relationship between glucose concentration and microbial growth is  (where y = glucose concentration and x = total bacterial counts). Glucose concentration and microbial growth are in inverse proportion to each other.

Significance:  Based on this study, the freshness of tofu could be evaluated by measuring glucose concentration, establishing a new freshness indicator for tofu.