Study On Combined Superheated Steam And Cold-air Drying Technology And Product Characteristics Of Abalone

Superheated steam drying technology is a new food processing technology which developed in recent years. It has many advantages such as fast drying rate, short drying time, saving energy and pro-environment. However, high temperature and imperfect equipment have extensively restricted applications in drying field. In order to reduce drying time of cold-air drying and improved superheated steam dehydrated products qualities, studied the effects of combined drying of superheated steam and cold-air drying on the qualities of dehydrated abalone.In order to research the effect of steam temperature, steam pressure, steam flow rate on the quality of abalone in drying process, the test considered the effect of three factors on the sensory evaluation of abalone by single factor experiments. Determined steam temperatures are 115℃,120℃,125℃, steam pressures are 121.33kPa, 131.33kPa,141.33kPa, steam flow rates are 1.2m/s,1.4m/s,1.6m/s in the superheated steam drying optimize experiment of abalone.In order to get the best drying technology of drying process, the expriment studied the effect of factors of superheated steam drying on the quality of abalone. A three-factor, three-level orthogonal optimization experiment design based on the single factor test, was chosen to evaluate steam temperature, steam pressure, steam flow rate effecting on sensory evaluation of abalone. The results showed that:the effect order of factors on the sensory evaluation of dried abalone in the experimental range:steam temperature>steam flow rate>steam pressure, as well as the optimum superheated steam drying conditions:steams temperature:120℃, steam pressure: 121.33kpa, steam flow rate:1.4m/s.In order to solve the quality problem of the product caused by high temperature for long time during superheated steam drying, the combined technique of superheated steam drying and cold-air drying was studied in this experiment, by which the drying method and conversion time were determined. By respectively studying the characteristics of superheated steam drying and cold-air drying and according to the features of the abalone, we determined the combined drying method. That is using superheated steam drying in earlier stage and using cold-air drying in later stage.In order to get the optimal condition of combined drying process, orthogonal experiment was carried out by selecting the steam temperature, conversion time and cold-air temperature as the factors while using the sensory evaluation value, rehydration, shrinkage and protein content of abalone as the indexes. The results showed that:the effect order of three factors on comprehensive score of abalone: conversion time>steam temperature>cold-air temperature; and the optimal condition of combined drying process of abalone is that:steam temperature 115℃, conversion time 2h, cold-air drying temperature.To illustrate the superiority of the combined drying method, so the test compared with hot-air drying, superheated steam drying, cold-air drying and analyzed all indicators. a.By the comparison of drying time, showed that under the premise of ensure the quality of products, combined drying can greatly reduce the drying time and improve the efficiency of drying. b.By the analysis of protein, showed the protein content of abalone by combined drying reach 56.9% and it is higher than hot-air drying and superheated steam drying, slightly lower than cold-air drying. c.By the rehydration analysis, found that the rehydration of combined drying was lower than superheated steam and hot-air drying, but it was higher than cold-air drying. d.By the comparison of shrinkage, showed the shrinkage of combined drying was 72.1% and lower than other three drying methods. e.By the comparison of sensory score, showed product by combined drying has highest score 88.5; it like ellipsoid and individual was even, the edge of abalone has no gaps and cracks and the column is full of meat. It has rich aromas, soft and delicious taste, and no peculiar smell. f.By the comparison of color, showed that abalone which is fully rosy by combined drying largely better than hot-air drying and superheated steam drying, but is slightly weaker than cold-air drying. g.By the analysis of texture, showed that the hardness, elasticity, viscosity and chewiness are suitable, so its taste is the best. The abalone can conform to most people’s taste which is soft and delicious, as well as full-flavoured. h.By different magnification microstructure, observed that abalones which have the larger gap of muscle fibers and myofibril by combined drying, hot-air drying and superheated steam drying are good to improve the speed of moisture movement and rehydration. By the above analysis, showed that abalone was the best by combined drying.