Study On The Dehydration Technology By Vacuum Low-Temperature Drying Of Garlic Slice

Garlic has abundant nutrients such as protein, sugar, germanium and selenium. Allicin, as the unique ingredient, is a kind of food with medicinal value. Fresh garlic gets rotted easily, so it’s necessary to extend the shelf life of garlic by dehydrating. So far, the usual method is high-temperature-dehydrating. Although it is time-saving and cost-saving, the dried product has bad quality and nutrients lose a lot during the process. So it will be of great importance to study the technology of dehydrated garlic slice by low-temperature and vacuum.My project focused on three different ways to dehydrate:microwave vacuum drying, vacuum microwave freeze drying and vacuum fried technology. The details are as follows:1. I optimized the common microwave vacuum drying method. According to the segmented drying principle, I used600W-700W microwave to dry garlic, when the water concentration decreased below15%, power changed to175W till the end. After this optimization, garlic slice was better in color, shrinkage rate, and rehydration rate. Shrinkage rate was reduced by22%, and the allicin content increased by26%.2. I dried garlic by vacuum microwave freeze drying. Microwave power, the amount of auxiliary material and pretreatment had impressive impact on drying. Based on shrinkage rate, rehydration rate and allicin content, the best technological parameters are:2.86KW microwave,1Kg/plate auxiliary material, direct freezing.3. After comparison of different drying ways, the vacuum freeze drying method got best-quality product, but it took the longest time. Microwave vacuum drying took the shortest time, but it got worse quality product, although it got most allicin. Vacuum microwave freeze drying got good product and cost less time. It’s a promising technology and has great market prospect.4. The edible coating technology was used to reduce the oil content, and the results showed that the effects of different coating agents were quite different. Due to the viscosity of sodium alginate, it had better isolation properties. Product had low oil content. Meanwhile, different concentration of the same balm produced different results. I got the lowest oil content when concentration of sodium alginate was0.75%.5. The optimal vacuum frying process parameters were determined by pre-drying time, frying temperature, frying time, oil concentration, and sensory scores.2mm thickness of slice was immersed in vinegar solution with salt, after deodorizing for10min at90℃, it was then placed in15%maltodextrin solution at room temperature for30min. And then it was transferred to0.75%sodium alginate solution for30min without shaking, after pre-drying by hot air at60°C for2hours, low-temperature vacuum frying was started. Degree of vacuum was controlled at0.08～0.09MPa, frying temperature at90to100℃, fried time at10to15min. After vacuum centrifugal de-oiling for4min with speed of350r/min, the final oil concentration was10.27%.