Sweet potato processing color protection process
Sweet potato, also known as yam or Chinese yam, is a widely cultivated root vegetable that has gained increasing popularity due to its rich nutritional profile and numerous health benefits. As food technology continues to advance, a variety of sweet potato-based products have emerged in the market. However, during processing, one major challenge remains: the browning of sweet potato, which not only affects the visual appeal but also lowers the overall quality of the final product. This browning is primarily caused by the enzyme polyphenol oxidase, which reacts with oxygen and phenolic compounds in the sweet potato, leading to discoloration.
To address this issue, researchers have focused on inhibiting the activity of polyphenol oxidase. In this study, common color-protecting agents such as citric acid, ascorbic acid, and sodium bisulfite were tested. Different concentrations—0.1%, 0.2%, 0.4%, 0.6%, 0.75%, and 1.0%—were used, and the slices were soaked for one hour. The results showed that citric acid at around 0.75% and ascorbic acid below 0.6% provided effective protection, while sodium bisulfite worked best at approximately 0.4%.
Further experiments explored the effect of soaking time on browning. At a concentration of 0.5%, the optimal soaking time was found to be one hour, as it significantly reduced the relative activity of polyphenol oxidase. Too short or too long a time resulted in either poor color retention or an undesirable impact on flavor and sulfur residue.
In addition, the influence of temperature on polyphenol oxidase activity was investigated. It was observed that the enzyme's activity increased with rising temperature, peaking at 35°C, and then decreased at higher temperatures. Therefore, maintaining a processing temperature below 25°C is recommended to minimize browning.
To further optimize the process, a four-factor, three-level orthogonal experiment was conducted. The results indicated that the most effective combination was 0.8% citric acid, 0.6% sodium bisulfite, 0.4% ascorbic acid, and a soaking time of one hour. This combination not only effectively controlled browning but also maintained the sensory quality of the sweet potato products. By carefully adjusting these factors, manufacturers can enhance both the appearance and the overall value of sweet potato-based foods.
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