Study On Cooling And Frozen Technology Of Cooked Spring Rolls

Spring rolls, one of the traditional Chinese foods, are loved by many consumers. Most of the frozen spring roll products sold in the market are raw products or half-products. People must cook by themselves after purchase the products. With the continuous improvement of living standards, people’s demands for quick life are increasingly high. Therefore, the development of a safe, convenient and delicious cooked spring rolls product will become a trend. The cooked spring rolls after frozen we studied in this topic don’t need to be fried before be eaten. Just put them into a microwave machine to reheat them if you want some. The production process and storage are the key to the quality of frozen food. This paper studied the quality of cooked spring rolls, including four parts: cooling method, storage conditions, production process improvement, and shelf-life prediction.1. The samples were cooled by four different treatments: slow-air cooling, air-blast cooling, vacuum cooling and hybrid cooling. The center temperature of the samples was cooled from 80℃ to 20℃. Then they were stored at 4℃ for 18 days. After samples being cooled, the weight loss, color, texture, odor, sensory evaluation were determined, and the pH, total number of colonies were determined 6 days a time. The results showed that, vacuum cooling method had the fastest efficiency, but the highest weight loss. Samples under vacuum cooling had higher hardness and brittleness, but the sensory evaluations on their color, shape and smell were lower. Hybrid cooling improved the shortcomings of vacuum cooling. With the extension of storage time, the pH of the samples under vacuum cooling or hybrid cooling had small change. And these two methods could significantly reduced microbial contaminations, so as to extend the shelf-life of the products.2. After cooked, cooled, and quick-froze, the spring rolls were stored at-3 ℃and-18℃. Our work aimed to explore the quality changes of the samples during their storage at two different temperatures. Indicators of measurement included water activity, texture, color, degree of fat oxidation, total number of colonies and odors. The results showed that: with the extension of storage time, water activity of spring rolls filler stored at-3 ℃declined, and water activity of their corresponding spring rolls outer rose. Water activity of spring rolls filler stored at-18 ℃changed little, and water activity of their corresponding spring rolls outer has not increased significantly. Hardness of spring rolls stored at-18 is ℃significantly higher than those stored at-3℃. The spring rolls lost crispness as soon as they stored at-3℃, but those stored at-18 ℃still showed 1686.08 after 28 days storage. The elasticity of both samples had different levels of increase. The lightness of spring rolls stored at-18 was higher than those stored at ℃-3℃, and the yellowness was more stable. The difference of absorbance between two samples is significant. Both of fat oxidation showed an increasing trend. Both of the total number of colonies showed an increasing trend but became significantly different in the latter part of the storage. The LDA analysis could distinguish samples under different temperatures well.3. We studied using zein film to increase the crispness of cooked spring rolls by microwave reheating. By studying the forming conditions and mechanism of zein film, we took the single factor experiment and orthogonal experiment, and concluded the optimal formula: glycerin 25%(glycerin/protein), TG enzyme 2%(TG enzyme/protein), beeswax 3%(beeswax/protein), at this point, the overall performance of film showed the best. Applied this film on the spring rolls’ outer, and made end product, then stored at frozen environment. 30 days later, put them to microwave reheated, then determined the crispness and made sensory evaluation immediately. The result showed that, after using zein film, the crispness of the samples increased significantly( p<0.05). In addition, the overall acceptability of sensory evaluation also got higher.4. The spring rolls with zein film were cooked and then cooled. After sealed packaging, they were stored at three different temperatures(4℃, 15℃, 25℃) for 10 days. The samples were measured every day. Determination of indicators included water activity, color, texture, the total number of colonies and sensory evaluation. The results showed that, with the extension of storage time, the water activity of spring rolls filler decreased, the water activity of spring rolls outer increased; the brightness increased and yellowness increased first then decreased; the hardness decreased, crispness lost, elasticity increased; the total number of colonies increased; and the sensory scores decreased. Made pearson correlation analysis between these indicators and sensory scores and ultimately determined the total number of colonies as the indicator index. Established quality change dynamics model, obtained the prediction model: k=8.80×109exp(-58450/RT). Took-18℃, 10℃ and 20℃ as the verification temperatures. The results showed that the error was small, so the model could well predict the shelf-life of the product.