Sweet potato processing color protection process
Sweet potato, also known as yam or Chinese yam, is a vital root vegetable that has gained increasing popularity due to its rich nutritional profile and numerous health benefits. As food science and technology continue to advance, various sweet potato-based products have been developed to meet consumer demands. However, during the processing of these products, a common issue arises: browning. This discoloration not only affects the appearance but also lowers the overall quality and market value of the final product. Controlling this browning process is therefore a critical challenge in sweet potato food production.
Research has shown that the primary cause of browning in sweet potatoes is the enzyme polyphenol oxidase (PPO), which catalyzes the oxidation of phenolic compounds, leading to darkening. To address this issue, it's essential to inhibit PPO activity. In this study, the author explored the effectiveness of three common color-protecting agents—citric acid, ascorbic acid, and sodium bisulfite—by testing different concentrations and soaking times to determine the most effective method for preventing browning.
The first set of experiments involved testing six concentration levels of each agent: 0.1%, 0.2%, 0.4%, 0.6%, 0.75%, and 1.0%. Sweet potato slices were soaked in these solutions for one hour, and the relative PPO activity was measured using spectrophotometry. The results indicated that citric acid at around 0.75% and ascorbic acid below 0.6% provided the best color protection. Sodium bisulfite showed optimal results at approximately 0.4%.
Next, the effect of soaking time on PPO activity was evaluated. At a fixed concentration of 0.5% for all three agents, the slices were soaked for 0.5, 1, and 1.5 hours. After two hours, PPO activity was measured again. The results revealed that a soaking time of 1 hour yielded the lowest PPO activity, indicating the most effective color preservation.
In addition, the impact of processing temperature on PPO activity was studied. The findings showed that PPO activity increased with rising temperature, peaking at 35°C, and then declined at higher temperatures. Therefore, maintaining a processing temperature below 25°C is recommended to minimize browning.
To further refine the color protection process, a four-factor, three-level orthogonal experiment was conducted based on the single-factor results. The range analysis identified the optimal conditions: a combination of 0.8% citric acid, 0.6% sodium bisulfite, 0.4% ascorbic acid, and a soaking time of 1 hour. Too short a time failed to provide adequate protection, while too long a time negatively affected the product’s flavor and increased sulfur residue.
By optimizing these parameters, it is possible to significantly reduce browning and improve the quality of sweet potato-based foods, making them more appealing and commercially viable.
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