Combined Addition of Citric Acid and Ascorbic Acid Significantly Inhibits Browning in Chinese Yam (Dioscorea polystachya Turczaninow) Processing

Chinese yam (Dioscorea polystachya Turczaninow) is widely cultivated in East Asia, whose edible stem is a common vegetable and herb in traditional Chinese medicine. In fruit and vegetable processing, browning is estimated to be a major reason of waste. Browning lowers the nutrition value and brings undesired characteristics in food processing. To develop a secure and low-cost browning inhibiting protocol in yam processing, different thermal treatment conditions and color protectants were tested for their color-protecting ability. Color difference ΔE was calculated to evaluate the browning with a colorimeter. To ensure that the color-protecting treatment does not influence the quality of yam, texture properties and nutrition compositions were quantified. The optimal treatment is as follows: deactivate yam in water bath of 60°C for 10 min and then incubate in 2 g/L citric acid and 1 g/L ascorbic acid for 1 hour. The treatment led to significant decrease of the color difference, with no obvious changes in the texture properties and nutrition value. To summarize, this research provides an ideal color-protecting solution in yam processing.