The Effect Of Bitter Almond Bitterness And Drying Process On The Quality Of Almonds

Bitter apricot kernel is a kind of typical natural plant resource used as medicine and food. Recently, more and more series products of apricot kernel were developed by bitter apricot nuts and obtained love and praise by consumers. The dried apricot kernel is one of them which received high praise of consumers, and the requirements of dried kernels are increasing. Some nutrient of apricot kernels was lost and the coloration compositions was produced during the debittering and drying of them caused the decreaing kernels quality whieh affect the vaule and sales of dried apricot kernels. In this paper, the effects of debittering and drying treatments on the nutrition loss, quality and color of apricot kernels were studied. The drying characteristics of debittered apricot kernels were investigated, and the optimal models providing satisfactory descriptions of drying characteristics of debittered apricot kernels were established. Non-enzymic browning reactions during drying of debittered apricot kernels were investigated by establishing model solutions. The present research was expected to provide theoretical basis and technical reference for design and implement processing technology of bitter apricot kernels and debittered aprictot nuts during debittering and drying, respestively.The main results of this research are as follows:1. Hot water debittering method was chosen in present research. Effects of debittering temperatures (50,60,70 ℃) on the main components (amygdalin, protein, tatal sugar, total phenolics) loss of bitter apricot kernels were investigated. The quality change of bitter apricot kernels before and after debittering were studied in this research. The results of the experiment showed that the effects of debittering temperatures on the loss of nutrition were significant, and the debittering time requrid to complete debitterizing is different due to the difference in debittering temperature. The content of major compotent of bitter apricot kernels lossed significantly during debittering process. The differences of weight, peroxide value, palmitic acid, oleic acid and stearic acid between blanched bitter apricot kernels and bitterness nuts were significant, and the difference of acid value, linoleic acid, elaidic acid and palmitoleic acid between them were not obvious.2. Effect of drying temperature on the drying characteristics of the debittered and skin-removed apricot kernels was investigated, and the mathematical models of debittered apricot kernels during drying were established. The results indicated that the effect of drying temperature on the drying rate was siginificant. The drying rate increased with the inprovement of drying temperature. The Midilli et al. and Approximation of diffusion models were selected to describe the drying characteristics of apricot kernels due to their relatively higher coefficient of determination (R2), and lower chi-square (χ2) and root mean square error (RMSE). The range of effective moisture diffusivity (Deff) of the kernels is 1.39×10-8 to 3.5×10-8 m2/s. The activation energy (Ea) required during whole drying process was 16.5 kJ/mol.3. Changes of major components (crude fat, protein, total sugar, reducing sugar and amino acids) and color of debittered apricot kernels during drying process were researched and the correlation between the major components and color (L*, a*, b*) was analyzed. The results suggested that the contents of crude fat revealed a decline, the content of total sugar increased, the content of protein, reducing sugar and amino acids revealed an initial increase followed by a decrease in debittered apricot kernels during drying process. There was a given relevance between the cysteine, methionine and color of debittered apricot kernels. It can be concluded that the Maillard reaction has significant effect on the changes of color. Overall, the content of principal component in dried debittered apricot kernels and color were relative high and light, respectively, when the drying process continued to 2.5 h, so the drying time of 2.5 h is the best time.4. Effects of the drying temperature (60,80,100,110,120,130,140 ℃) on the major quality of debittered apricot kernels drying products were studied. Experiments showed that effects of drying temperature on the content of main component (crude fat, protein, total sugar, reducing sugar and amino acid) and peroxide value, acid value, color were significant. There was a good correlation between the protein, reducing sugar, aspartic acid, glutamic acid, valine, leucine, isoleucine and histidine, arginine and color of debittered apricot kernels. It can be infered that the drying temperature in the range of 100-110 ℃, the retention rate of nutrient components was higher, and the color of apricot kernels is bitter.5. Non-enzymic browning reactions during drying of debittered apricot kernels were investigated by establishing amino acid and sugar (M1, M2), sugar (M3, M4), amino (M5) model solutions. The results showed that the absorbance at 420 nm,284 nm and color of the model solutions with ammo acid and sugar (M1, M2) presented significantly change during drying process. Among the value of L*, a*, b*, the change of b* value was more obvious than others. It can be deduced from the above analysis that the maillard reaction was the major non-enzymic browning reaction which affect the color of debittered apricot kernels during drying, and the color change in dried products of debittered apricot nuts was mainly reflected in the yellowness of them.