Dehydrated vegetables as a new type of food more and more people's attention. In the same country, the United States, Hong Kong and other countries and regions, dehydrated vegetables has become a popular lifestyle fast-paced modern food. In our country, it is not only used extensively in the field of instant food, but also an effective method to solve the trouble of eating vegetables in the departments of tourism, army and geology. Dehydrated vegetables with raw materials to maintain the color, smell, taste and nutritional content, food is not perishable, rehydration, light weight, can be stored at room temperature and so on. In this experiment, the mushrooms were stored and kept fresh first, then the dehydrated mushrooms were produced by the vacuum freeze-drying technology, the optimal experimental conditions were optimized and compared with the traditional hot-air drying method. The results showed that the freeze- , The retention of aroma components and rehydration, etc. than the hot air drying has obvious advantages.
1.Mushroom preservation technology and the characteristics of aroma in the preservation of the law of change.
(1) The selection of browning inhibitors, the sensory score and the characteristic aroma of mushroom as indicators of browning inhibitors, the results showed that adding browning inhibitors cysteine 1.0g / L, ascorbic acid 0.8g / L, citric acid 20g / L, soaking time 20min, get the sensory score and the characteristic aroma component 1-octen-3-ol content of high storage mushrooms, mushrooms obtained at this time the degree of browning is small, high sensory score The preparation for the drying of the subsequent mushrooms, the purpose of its preservation is to ensure the quality of raw materials before processing, to prevent browning, decay and the measures taken.
(2) By analyzing the main characteristic aroma of mushroom during storage, the results showed that with the extension of storage time, the content of 1-octen-3-ol gradually decreased, the relative content of the total volatile aroma components More than 80%, other ingredients such as benzaldehyde, 3-octanol, 3-octanone content did not change much during storage, the choice of good quality raw materials for the dehydration of mushrooms.
2. Mushroom vacuum freeze-drying process. The quadratic universal rotary combination design was used to establish the regression equation of pre-thawing rate and sublimation temperature, and to analyze the temperature on the recovery ratio of mushrooms after drying. The results showed that at the pre-freezing rate of 2.5 ℃ / min, ℃ for 5h and maintained at 13 ℃ for 6h, the rehydration ratio obtained was 5.62. The rehydration ratio after drying was 5.49 and the relative error was 2.37%, which provided some theoretical data for the future production of fruits and vegetables by freeze-drying. 3. Drying methods on the quality of mushrooms.
(1) The effects of hot air drying and freeze drying on the quality of dried mushrooms were compared. The nutrients such as ash, polysaccharides, proteins and amino acids were compared. The results showed that the content of ash and crude fiber had little difference, while the content of polysaccharides, protein, free amino acids and water-soluble vitamins of mushroom after freeze-drying was higher than that of hot-air drying. As the freeze-dried slices of mushroom slices covered with uniform size, a large number of micropores, showing sponge-like porous structure, and hot air dried mushroom slices after a large number of micropores, the number of small and uneven, the appearance of shrinkage, the formation of dense The hard shell, resulting in freeze-dried mushrooms than the hot air drying has good rehydration performance. The characteristic aroma components after lyophilization are the same as those of fresh mushrooms and contain benzaldehyde, 1-octen-3-ol, 3-octanol and 3-octanone, while the dried mushrooms have only benzaldehyde , So hot-air dried mushrooms do not have the smell of fresh mushrooms.
(2) A high performance capillary electrophoresis method was established for the determination of water-soluble vitamins in mushrooms. The pressure was injected for 5sec, the column temperature was 25 ℃, the separation voltage was 20KV, vitamin V, B1, V, B6, , B2> and Vc detection wavelength 190nm. , The electrophoresis buffer is 20mM borax ~ boric acid buffer pH8.72, running time 10min, you can achieve a good separation of vitamins in mushrooms, and compared by freeze drying and hot air drying two kinds of mushrooms dried, the results show that freezing Drying of mushrooms on vitamin retention was significantly higher than the hot air drying method.
(3) The common fruits and vegetables were dried by microwave vacuum drying and freeze-drying respectively. Onion, apple slices, banana slices, garlic slices, mushrooms and onions were dried by microwave vacuum. Slices of carrots, ginger, chives and red peppers are also dried. It has been found that lyophilized fruits and vegetables have the advantages of less deformation and less degree of browning than microwave vacuum drying.