Study On Technology And Quality Of Blackcurrant (Ribes Nigrum L.) Snack Subjected To Microwave Vacuum Puffing Method

As a kind of berry fruit with rich nutritionous ingredient and special flavor, blackcurrant berry has the great potential market for its products. The blackcurrant snack puffed subjected to microwave vacuum method is a new type of berry's product. There is high retention rate of nutrition, and the flavor of blackcurrant.In this research, according to the single factor experiment, the influences of the different factors on the characteristics of blackcurrant subjected to microwave vacuum puffing were analysed. And the mathematic models of the temperature, moisture content and shape were developed in the puffing process using computer simulation method. The conclusions were obtained as follows:1. The puffing time of blackcurrant snack decreased with the increase of microwave intensity and microwave power. As the vacuum pressure increasing, puffing time first increased, and then decreased. And the puffing time increased with initial moisture content increasing.2. The moisture content of the blackcurrant snacks were in the period of accelerating dehydration during the first 10 s of puffing process. Thereafter, the dehydration rates were different for the different initial conditions. When the initial moisture content was 25% or vacuum pressure was 15 kPa, the dehydration rate is constant. Under the 35% initial moisture content, or 30 kPa vacuum pressure, or 0.93 kW microwave power, or all levels of microwave intensity, the snacks firstly remained constant dehydration and afterwards were in the decelerating dehydration. When the microwave power of 1.57 kW or 2.48 kW, the dehydration rate was increasing firstly, and then decreasing. Under 45% initial moisture content, the snacks were in the period of decelerating dehydration, and then converted into the constant dehydration. While the dehydration rate was firstly increasing, and then remained the contant up to the decrease at last period under 45 kPa vacuum pressure.3. As the increase of puffing time, the temperature of blackcurrant snack was gradually arising at a slow trend.4. Subjected to the microwave power was 2.48 kW, the puffing process of blackcurrant snack was divided into two periods, the period of volume puffing rapidly and the period of constant volume. For the other factors and levels, the puffing process can be divided into three periods based on the shape change of snack. In the first period, there were no changed in the volume of snack, but the shape was changed, where the diameter was increase and the thickness was decrease. Under 45 kPa vacuum pressure, in this period the thickness and diameter of snack were decreasing, and the volume shrank. In the second period, the volume of blackcurrant snack rapidly puffed, the thickness increased and diameter decreased. In the third period, no significant change of diameter, thickness and volume of blackcurrant snack were found. When the vacuum pressure was in 15 kPa or 45 kPa, the volume shrank.5. During computer simulation, the temperature change of blackcurrant snack can be simulated according to Fourier's equations of heat conduction. The conclusions were that the temperature increased gradually with the increase of puffing time, and the rising rate was faster in the early stage and then was slower in the late stage, accompied with the temperature increasing from inner to outer. The moisture change of snack can be simulated using moisture diffusion equation. The result was that the moisture content of snack was decreasing with time increase. At any time, the moisture diffusion rate is the same in any point of snack, and there was no significant difference. The shape change of snack can be simulated according to stress-strain the deformation equation. It was found that the thickness shrank in the first 10 s before its increasing.A contrasting experiment on the qualities of snack between microwave puffing and microwave vacuum puffing blackcurrant chip was conducted. The results suggested that the the snack producted by microwave vacuum method was superior to that by the microwave method in the quality attributes in terms of volume, expansion ratio, the micro-structure of small molecules, loose and mult-layer structure, the cavity in the inner of chip. The hardness of snack was decreased and its crispness was increased, and the color was lighter, the loss of anthocyanin was decreased subjected to the microwave vacuum puffing.In this research, the optimization prescription, with the addition content of 10% soft sugar and 1% saleratus at weight ratio, respectively, to the blackcurrant fresh slice was obtained. On the basis of the optimization prescription, the regression models between the different factors and puffing qualities were obtained by responding surface methodology, and the optimization process parameters were developed.1. The interaction influence of every factor on quality of chip: The sequence of the effect of single factor on expansion ratio was that initial moisture content >microwave power >vacuum pressure >puffing time. In the regression model, the influences of the monimial and quadratic term of initial moisture content, and the interaction between initial moisture content and the other factors were significant, while the effect of the other terms was not significant on the expansion ratio. For the color, the relation of the single factors showed that the puffing time is the most important factor, followed by microwave power and initial moisture content, and the vacuum pressure is the least important. The results of regression analysis found the significant effects of monimial term of puffing time, the interaction of microwave power and initial moisture content, between vacuum pressure and initial moisture content, as well as between microwave power and puffing time, and the quadratic terms of vacuum pressure, initial moisture content and puffing time. For the anthocyanin content, the initial moisture content is the most important factor, followed by microwave power and puffing time, and the vacuum pressure is the least important. In the regression model, the interaction of vacuum pressure and initial moisture content, between vacuum pressure and puffing time, as well as the quadratic term of initial moisture content had significant influence on anthocyanin content. For finial moisture content and sensory score, the monimial and quadratic term of microwave power, initial moisture content and puffing time had significant effect. Accordint to the relation between single factors and finial moisture content, the initial moisture content is the most important factor, followed by microwave power and puffing time, and the vacuum pressure is the least important. While the sequence on the sensory score showed that microwave power >puffing time >initial moisture content >vacuum pressure. For the texture characteristics index, the sequence of the single factors was that puffing time >initial moisture content >microwave power >vacuum pressure. In the regression model, the effect of the monimial term of microwave power, the monimial and quadratic term of initial moisture content and puffing time, and the interaction between microwave power and puffing time, as well as between initial moisture content and puffing time was significant.2. The optimization process parameters of blackcurrant chip by microwave vacuum puffing were as follow: the microwave power of 3.35 kW, the vacuum pressure of 23 kPa, the initial moisture content of 35.59% and puffing time was 100 s. On the basis of optimization process parameters, the quality results of snack puffed from a verified experiment were that expansion ratio was 200%, the color value was 31.44, the anthocyanin content was 47.73, the finial moisture content was 10.62%, the sensory score was 9.08, and the texture characteristics index was 2.51. Comparing with the predicted values, the maximum relative error was less than 10%. It suggested that the optimization parameters were acceptable.In this research, the mechanism and the optimization process parameters of blackcurrant puffing by microwave vacuum method can be used to guide the practical production. The puffing crips can enrich the kind of berry's futher processing.