Study On Technology And Quality Of Blackcurrant Berry Under Osmotic Dehydration And Microwave Vacuum Method

Blackcurrant berry has rich nutrition constituent and special flavor with medical value and health functions. The fresh blackcurrant berry is not suitable for directly eating due to high acidity but its product has favorable flavor. The sour taste of product has been improved and shows high additional value, which has broad market prospects. A combination of osmotic dehydration followed by microwave vacuum puffing has been demonstrated to improve drying rate, short drying time and provide high quality dried product with low energy consumption. It has been considered to be a potential technology. The objective of this research was to determine the optimal technological parameters for the process of blackcurrant berry on the basis of the dehydration and puffing characteristics of dried blackcurrant during osmotic pretreatment followed by microwave vacuum process, and to analyze the effect of process parameters on the quality of final dried blackcurrant. The study contents and conclusions are as follows:1) A single-factor experimental design was used to study the effect of osmotic concentration, temperature, time and sucrose-fruit ratio on the dehydration characteristics during osmotic dehydration of blackcurrant. The results show that the increase of osmotic solution concentration resulted in an increase in water loss and solid gain, and a decrease in moisture content. As the increase of osmotic temperature, water loss and solid gain gradually increase, but the outer peel of blackcurrant was damaged when the temperature exceeded60℃. The longer the immersion time, the more the water loss, while solid gain increased at the first period and then slightly reduced at the later stage. The sucrose-fruit ratio had no significant effect on the water loss and solid gain.2) Response surface methodology (RSM) was used to investigate the effect of various process parameters on water loss, solid gain, anthocyanin content and vitamin C content. The regression models between independent variables and values of responses were obtained and the optimum conditions for osmotic dehydration process of blackcurrant were70%solution concentration,50℃solution temperature and19h process duration.3) The influences of microwave power, vacuum degree, initial moisture content, and mass on the final moisture content, expansion ratio were studied by a single-factor experiment in the process of microwave vacuum puffing. The results indicated that the puffing time had significantly negative correlation. The final moisture content of dried blackcurrant dropped rapidly with the decreasing initial moisture content and mass. The expansion ratio was affected by puffing time, microwave power, vacuum degree, initial moisture content and mass.4) The experiment was carried out by using the design of the quadratic regression orthogonal rotary to analyze the effect of microwave intensity, initial moisture content, vacuum degree and puffing time on the expansion ratio, final moisture content, anthocyanin content, vitamin C content and sensory score. The corresponding regression model was established and the sequence of the contribution of process variables on responses was obtained by analysis of variance (ANOVA). In order to obtain high quality of production, the optimum processing parameters and verification test were conducted. The optimum operating conditions for blackcurrant subjected to microwave vacuum puffing by numerical optimization method was obtained as follows:the microwave intensity of30W/g, the initial moisture content of60%, vacuum degree of70kPa and puffing time of6min.In this research, in the condition of the optimization process parameters of blackcurrant by osmotic dehydration and microwave vacuum puffing method, the dried blackcurrant product had a high quality and favorable taste. It may provide the important theoretical basis for subsequent practical production of blackcurrant.