Study On Fermentation And Drying Process Of High-quality Fermented-and-dried Bamboo Shoot

Fermented-and-dried bamboo shoot with unique flavor and high nutritional value is paid much more attention. The traditional fermented-and-dried bamboo shoot is made firstly through several months's natural fermentation, then by air drying or baking. However, the traditional fermented-and-dried bamboo shoot has the disadvantages such as: long production cycle, impure flavor, uneven drying, high water content, prone to browning and mildew, severe fibrosis and poor rehydration character. fermentation by inoculation with lactic acid bacteria can solve the problems of traditional natural fermentation: the long fermentation cycle, impure flavor, tasting fibrosis. Vacuum frozen drying technology can overcome the problems of traditional natural drying: uneven drying, high water content, browning, long rehydration time, and poor rehydration.Therefore, with fresh bamboo as material, we made high quality fermented-and-dried bamboo shoot by fermentation by inoculation with lactic acid bacteria and vacuum frozen drying technology according to dried bamboo shoots standards. The main contents and results are summarized as follows:(1) Lactobacillus plantarum and Lactobacillus brevis were adopted to find the optimum kinds of lactic acid bacteria for fermentation by inoculation with lactic acid bacteria, through single strain, mixed strains and complex strains fermentation experiments, compared with natural fermentation experiment. As seen from the results, fermentation by inoculation with lactic acid bacteria was significantly better than natural fermentation,and the fermentation was the best when the ratio between Lactobacillus plantarum and Lactobacillus brevis for fermenting bamboo shoot slice was 1:1.(2) Single factor and orthogonal experiment were designed to find the parameters of fermentation by inoculation with lactic acid bacteria. The optimal parameters of fermentation condition were as follows: ratio of liquid to solid was 1.6:1, inoculation amount of lactic acid bacteria was 4.0%, fermentation time was 74 hours, fermentation temperature was 32℃. Under this condition, lactic acid content and crude fiber content of fermented bamboo shoot slice were 0.89% and 0.71%, respectively. Both were better than the results of natural fermentation. (3) Compared with three drying methods of fermented bamboo shoot slice,hot-air drying,vacuum drying and vacuum frozen drying, the result indicated that the quality of fermented-and-dried bamboo shoot by vacuum frozen drying was better than by air drying and vacuum drying.(4) The eutectic temperature of fermented bamboo shoot slice measured by the electric resistance was -18℃. The results of single factor test and two factors interaction test showed that, in the treatment of pre-freezing temperature -29℃, pre-freezing time 210 minutes, rehydration of the fermented-and-dried bamboo shoot had an optimum quality.(5) Based on single factor test, adopting quadratic orthogonal regression rotary combination design, the mathematical regression model between rehydration rate (Y) and drying chamber pressure (X1), sublimation temperature on heating plate (X2) and resolution temperature on heating plate (X3) was established. The regression equation was as follows:Y=0.856286-0.010647X₁-0.004786X₂+0.002014X₃-0.011528X₁²-0.006875X₂X₁ -0.009937X₂²-0.006125X₃X₁-0.000875X₃X₂-0.003398X₃².According to the regression model,parameters of drying condition of fermented bamboo shoot slice were optimized. The optimum parameters were drying chamber pressure 20.8Pa, sublimation temperature on heating plate 34.8℃, the resolution temperature on heating plate 62.8℃.(6) The rehydration rate of the fermented-and-dried bamboo shoot was 0.863 min-1 under the parameters of vacuum frozen drying: pre-freezing temperature -29℃, pre-freezing time 210 minutes, drying chamber pressure 21Pa, sublimation temperature on heating plate 35℃and resolution temperature on heating plate 63℃. Meanwhile, we drew the drying curve of fermented bamboo shoot slice according to the drying process parameters.