Study On Softening Technology Of Jujube Peel And Water Dynamic Characteristics During Blackening Process

Blackened jujube is the product of jujube after solid fermentation and maturation under the condition of high temperature and high humidity,its taste and nutritional value have changed significantly.The content of polysaccharides,polyphenols and ursolic acid in blackened jujube increased obviously,and compared to jujube,blackened jujube have shown superiority in some functional effects.Therefore,blackened jujube has broad prospects for development.However,there are currently quality problems associated with blackened jujube products such as poor taste.In this project,blackened jujube was used as raw material,and on the basis of single-factor experiment,combined with the results of orthogonal design experiment,taking the hardness of blackened jujube peel as the index,to optimize the enzymatic hydrolysis process,and the optimal enzymatic hydrolysis conditions were obtained.As well as the influence of enzymatic hydrolysis on the hardness of blackened jujube peel was tracked and analyzed,and the changes of hardness,elasticity,adhesion,cohesiveness,chewability and other indexes of blackened jujube before and after enzymatic hydrolysis were measured by texture analyzer.At the same time,low field nuclear magnetic resonance（LF-NMR）was used to analyze the transverse relaxation time（T₂）and nuclear magnetic resonance imaging（MRI）during the blackening of jujube,and understand the water content,water status and water migration dynamic process of blackened jujube during the blackening of jujube,so as to improve the quality of blackened jujube and provide a theoretical basis for the blackened jujube products and its in-depth development,and have great practical significance for promoting the deep-processing and industrial development of blackened jujube.The main results are as follows:（1）Determination of the composition of blackened jujube peelThe composition of blackened jujube peel was detected and analyzed by carbazole colorimetry,3,5-dinitrosalicylic acid colorimetric and anthrone-sulfuric acid colorimetric.The results showed that the main components of blackened jujube peel were cellulose（13.59%）,hemicellulose（3.24%）and pectin（2.98%）,and the tenderness of jujube peel was related to cellulose,hemicellulose and pectin content.The degradation of the constituent substances of blackened jujube peel will lead to its structural destruction,thereby reducing the strength and toughness of jujube peel.（2）Study on enzymatic hydrolysis process conditions of blackened jujubeUsing enzymatic hydrolysis process,optimization by single-factor test and orthogonal test,the process of softening blackened jujube peel in four ways:single pectinase,single cellulase,single hemicellulase and complex enzyme was discussed.The results showed that the optimal process of pectinase enzymatic hydrolysis of blackened jujube was as follows:the amount of pectinase added was 0.3%,the enzymatic hydrolysis time of pectinase was 80 min,and the enzymatic hydrolysis temperature of pectinase was 45℃.The hardness of blackened jujube peel obtained after enzymatic hydrolysis was 0.353 N.The optimal process of hemicellulase enzymatic hydrolysis of blackened jujube was as follows:the amount of hemicellulase added was 0.4%,the enzymatic hydrolysis time of hemicellulase was 110 min,and the enzymatic hydrolysis temperature of hemicellulase was 45℃.The hardness of blackened jujube peel obtained after enzymatic hydrolysis was 0.395 N.The optimal process of cellulase enzymatic hydrolysis of blackened jujube was as follows:the amount of cellulase added was 0.6%,the enzymatic hydrolysis time of cellulase was 100 min,and the enzymatic hydrolysis temperature of cellulase was 55℃.The hardness of blackened jujube peel obtained after enzymatic hydrolysis was 0.343 N.The optimal process of complex enzyme（cellulase and pectinase）enzymatic hydrolysis of blackened jujube was as follows:the ratio of complex enzyme was 6:4（cellulase:pectinase）,the amount of complex enzyme added was 0.5%,the enzymatic hydrolysis time of complex enzyme was 90 min,and the enzymatic hydrolysis temperature of complex enzyme was 55℃.The hardness of blackened jujube peel obtained after enzymatic hydrolysis was 0.324 N.Comparative analysis,the enzymatic hydrolysis of complex enzyme had the best effect.（3）Determination of various indexes of blackened jujube after enzymatic hydrolysisTexture profile analysis of blackened jujube after enzymatic hydrolysis was carried out by texture analyzer.The results showed that the hardness of blackened jujube was 3.49±0.50N,elasticity was 3.17±0.19 mm,cohesiveness was 3.86±0.17,chewability was 10.42±1.02and adhesion was-0.12±0.04 after enzymatic hydrolysis,and compared with before enzymatic hydrolysis,the hardness,elasticity,cohesion and chewability of blackened jujube decreased by 13.40%,13.86%,11.06%and 13.09%respectively.（4）Study on the regularity of water migration during the blackening process of jujubeLF-NMR was used to collect signals during the blackening process of jujube.The results showed that there were three states of water in the jujube during the blackening process,namely bound water(T₂₁),immobilized water(T₂₂)and mobile water(T₂₃).Among them,the content of immobilized water is the highest,the content of bound water is the second,and the content of mobile water is the least.During different periods of blackening,the peak area and transverse relaxation time（T₂）of the three states of water changed.With the progress of the blackening,the T₂₂peak changed the most,the curve shifted to the left as a whole,and the peak area decreased significantly,all these phenomena indicated that the moisture content and moisture fluidity of immobilized water decreased with the increase of blackening time.During the blackening process of jujube,the moisture change of the bound water showed a similar trend,with the passage of time,the curve showed a trend of continuous shift to the left and the peak area continued to decrease,indicating that the fluidity and content of the bound water decreased continuously during the blackening period.After 60 h of blackening of jujube,the moisture change curve of mobile water showed a trend of constantly moving to the left and increasing peak area,indicating that during the blackening period,the fluidity of mobile water decreased and the content of mobile water increased with the increase of blackening time.（5）Study on MRI during the blackening process of jujubeMRI was used to detect the moisture status of jujube samples during the blackening process.The results showed that in the early stage of blackening,the image was relatively bright,indicating that the moisture content in the sample was sufficient and uniformly distributed.With the extension of blackening time,the MRI of blackened jujube became more and more dim.At the same time,the edges of the blackened jujube are brighter,which is mainly due to the gradual water migration of the jujube and the reduced uniformity of water distribution,the water content of the fruit edge is higher,and the closer the fruit core is,the less water content is.