| Raspberry has high nutritional value and health benefits due to its richness in anthocyanin and vitamin C. Dehydrated berry products could effectively extend the storage period, but the active components in dehydrated berry products degrades rapidly due to the influence of light, heat and oxygen during storage. In this paper, spraying and coating technology is proposed. Formation of the coating layer by spraying the protective liquid may reduce the degradation of bioactive substances in berry puree, which improved the quality of dried berries. The microwave foam-mat drying characteristics of pulp and the stability of dry pulp products during storage were analyzed to develop the optimal conditions. The dry goods were obtained for the protective effect of comparative analysis, micro-structural analysis and composition of anthocyanin analysis. As a result, quality evaluation system and hierarchical model of raspberry powder were proposed. In this study, spraying and coating technology was provided for protective processing of dehydrated berry product.Drying characteristics of pulp in condition of microwave foam-mat, and the stability of dry pulp products during storage were analyzed. The microwave intensity, mass ratio of constituents of protective liquid and mass ratio of foamed berry puree and protective liquid were selected as influencing factors, and moisture content, drying temperature and degradation ratio of bioactive substance were selected as objective factors. The results showed no significant effect on the trying characteristics between ratio of constituents of protective liquid and mass ratio of foamed berry puree and protective liquid. The content of anthocyanin and vitamin C leveled off after declining as the content of maltodextrin in protective liquid increased. The content of anthocyanin and vitamin C increased significantly as the mass ratio of foamed berry puree and protective liquid increased.The impact on the degradation ratio of anthocyanin and vitamin C by different factors was studied by using the method of central composite test. The results showed that different factors on the order of degradation ratio of anthocyanin were mass ratio of foamed berry puree and protective liquid, mass ratio of constituents of protective liquid and microwave intensity. The results were the same as the degradation ratio of vitamin C. Mass ratio of foamed berry puree and protective liquid, mass ratio of constituents of protective liquid were important factors in storage stability. The optimal parameters were microwave intensity of 14 W/g, quality of maltodextrin in protective liquid of 7.30 g, quality of soy protein isolate of 3.00 g, quality of foamed berry puree of 40.00 g, and quality of protective liquid of 10.50 g.Comparative experiments, scanning electron microscope test and high performance liquid chromatography were implemented to analyze the protective mechanism of spraying and coating technology on the anthocyanin within dehydration berry puree. The results showed that dense protective layer was formed on the surface of dehydration berry puree to shield the, oxygen and light and weaken degradation of the bioactive substances. The content of cyanidin and pelargonidin was increased(75%) with high levels content in anthocyanin and vitamin C.Combined machine vision technology and near infrared spectroscopy was employed to detect and evaluate the internal and external quality of dehydrated berry powde. The characteristics on color of berry powder were extracted by machine vision technology. Quantitative analysis of the mathematical model of anthocyanin, vitamin C and granularity were established by near infrared spectroscopy with the algorithm of multiple linear regressions. Red value, green value, blue value, hue, saturation, brightness, granularity, the content of anthocyanin, vitamin C were selected to evaluate the berry powder. The weight of each index and the comprehensive score of each sample were calculated by entropy weight coefficient method.Praying and coating technology during microwave foam-mat drying is proposed in this study. Spraying and coating technology may protect the bioactive substances of berry fruit in microwave-assisted foam-mat drying to ensure the nutrition value of dehydrated berry product. Theory and technical basis are provided for the research on agricultural products processing. The comprehensive quality evaluation and classification system are proposed by machine vision technology and near infrared spectroscopy. An efficient, fast, convenient and nondestructive detection and classification method can be satisfied by using this system. Evaluation and grading can be realized. |
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