Study On Color Change And Control Methods During Processing Of Wolfberry Pulp

It is important to study the causes of browning in the pulp and to find a safe processing method to inhibit the color change and maintain the quality of the pulp.In this study,the main browning factors were investigated,the optimum stage of adding additives and the degree of inhibition of browning by each inhibitor were investigated,and the color indexes and various components of different sterilization methods were examined to determine the most suitable sterilization method.The main research contents and results are as follows:1.The effect of temperature on the color and chemical composition of the original Lycium barbarumDifferent temperatures were used to heat the raw wolfberry pulp,and the color,browning degree,total phenol,ascorbic acid,reducing sugar,5-hydroxymethyl furfural,carotenoids,flavonoid content were detected after treatment.The results showed that with the increase of temperature,the browning degree of the raw wolfberry pulp gradually increased,and the total color difference △E all had significant changes,the L value showed an overall decreasing trend,the a value was positive with an overall decreasing trend,the b value was positive with an overall increasing trend,it can be learned that the high temperature will accelerate the browning rate of the samples,making the brightness of the raw wolfberry pulp darker,the red color lighter and the yellow color darker,the main pigment in wolfberry is carotenoid The main pigment in Lycium is carotenoid,and the color of the pulp changed from red to yellow due to the increase of temperature may be due to the degradation of carotenoid caused by high temperature.After heat treatment,the ascorbic acid content was significantly reduced.When the heat treatment temperature was 100 ℃,the loss was more serious,indicating that ascorbic acid is easily degraded during heat treatment,and the higher the temperature,the more the ascorbic acid content decreased.5-HMF content in the raw Lycium barbarum treated at 100 ℃ was significantly higher than that in the samples treated from 60 ℃ to 90 ℃,indicating that the raw Lycium barbarum is more suitable for sterilization under temperature conditions lower than 90 ℃.The browning degree was negatively correlated with carotenoid content,ascorbic acid content,L value,a value,and flavonoid content,and positively correlated with 5-hydroxymethylfurfural,b value,and △E value.5-hydroxymethylfurfural and vitamin C were significantly correlated,so it was inferred that the production of 5-hydroxymethylfurfural might be mainly related to the oxidative decomposition reaction of vitamin C itself.The correlation coefficients of carotenoids and a-and b-values were 0.987 and-0.986,respectively,indicating that the degradation of carotenoids would lead to a decrease in the red color and a deepening of the yellow color of the raw wolfberry pulp.In summary,the color change of raw wolfberry syrup after heat treatment may be mainly due to the oxidative decomposition of ascorbic acid itself and the degradation of carotenoids.2.The influence of each single factor on the color of raw wolfberry pulp during processingSamples were taken at the pulping,enzyme inactivation,filtration and sterilization stages to test the color indexes,and different concentrations and types of antioxidants were added to the raw wolfberry pulp to test the browning degree,color difference and carotenoid content,and to investigate the optimum stage of adding additives and the degree of inhibition of browning by each inhibitor.The results showed that the browning degree of raw wolfberry pulp increased significantly after sterilization,the L value and a value decreased significantly,and the b value showed an increasing trend,indicating that crushing and filtration had less effect on browning degree and color,and the sterilization process had the greatest effect on browning degree,which also led to darkening of brightness,lightening of red color and darkening of yellow color.The carotenoid content changed less after enzyme inactivation and filtration,and the carotenoid content decreased significantly after sterilization,so the selection of adding color protector before sterilization was more appropriate.Compared with the control group without food additives,tocopherol at a concentration of 0.3% had the best protective effect on the brightness of the raw wolfberry pulp,with a retention rate of 4.24% for L value,phytic acid at a concentration of 0.4% had the best protective effect on the red value,with a value retention rate of 16.76% and b value inhibition rate of 11.94%,and ascorbic acid at a concentration of 0.15% had the highest browning inhibition rate on the raw wolfberry pulp Citric acid at 0.6% and sodium D-isoascorbate at 0.2% had the best effect on the carotenoid protection of Lycium barbarum,with retention rates of 26.30% and26.92%,respectively.The antioxidant with the best color protection effect was 0.2%sodium D-isoascorbate.3.Study on the effect of sterilization method on the color and composition of the raw wolfberry syrupThe color change of raw wolfberry syrup after high pressure treatment was small,the brightness and red value decreased slightly,the yellow value increased slightly,the flavonoid content decreased,the browning degree,carotenoids,total phenols and reducing sugar content did not change significantly compared with the control group,the sterilization under 500 MPa pressure for 15 min The lowest centrifugal sedimentation rate was observed after sterilization,indicating that high pressure treatment could improve the pulp stability of raw wolfberry pulp and prevent pulp separation during processing.Microwave sterilization and pasteurization had less effect on the stability and reducing sugar content of the raw wolfberry pulp,and the effect on the polyphenol content was greater than that of the high-pressure treatment.The highest brightness and highest yellow value of raw wolfberry pulp after microwave sterilization indicated that microwave processing had the effect of improving brightness,but it would lead to a decrease in carotenoid content.121℃high temperature sterilization significantly increased centrifugal sedimentation rate,browning degree,flavonoids,reducing sugar content,significantly decreased brightness,red value,carotenoid content,and the lowest yellow value,therefore,the production process is not suitable for ultra-high temperature sterilization processing Raw wolfberry syrup.The sweetness,freshness,bitterness and sourness were the heaviest after microwave sterilization and pasteurization,and the bitterness,sweetness and sourness were the lightest in the control group,and the freshness was the lightest after high temperature sterilization at 121°C,followed by the control group,and the taste of raw wolfberry syrup after high pressure treatment was the closest to the control group,while microwave treatment and pasteurization had a greater effect on the taste.In summary,high-pressure sterilization is most suitable for the sterilization treatment of raw wolfberry syrup,which has less impact on the quality of raw wolfberry syrup.