Study On The Effect Of Processing Technologies On The Quality Of Concentrated Grape Juice

Taking Cabernet Sauvignon grape as test materials, vitamin c, flavonoids, phenols, anthocyanin, color, and volatile components, total number of colonies, number of fungi, PPO,POD,SOD activity as main test targets, this project researched the influences of key processes such as "mincrowave and pectinase"pigment solution, microwave sterilization, freeze concentration, membrane filtration on the quality of grape juice. Results are as follows:(1) Optimazed the "mincrowave and pectinase"grape pigment solution technology using Box-behnken method. Established quadratic regression equation, and analysis of variance showed that the two models are greatly significant (P<0.0001), lack of fit are not sifnificant (P>0.1). Optimum conditions were that 1.1‰pectinase, treated at 40℃for 3.15h; on the basis of pectinase treatment, optimum conditions of microwave treatment was129.5g samples treated 3 times with 900W microwave for 19s.(2) 250mL grape juice, concentration of which was 20°Brix, sterilized by microwave and thermal, Achieve similar sterilization effect, microwave sterilization need 80s, yet 60℃thermal sterilization need 2h. Microwave 80s, activity of PPO,POD,SOD were higher than that of 60℃thermal sterilization, the retention rate of vitamin c, flavonoids, phenols, and anthocyanin were higher too. AE of microwave sterilization was 0.50 (little differences),ΔE of thermal sterilization was 2.53(there are differences), and it revealed that the color of thermal sterilized grape juice changed more. The optimum condition was 250mL grape juice 900W microwave treat 80s. Different microwave frequency showed significant differences on the total number of colonies (P<0.05), and increasing microwave frequency coutribute to sterilization effect.Comparison of different sterilization methods:membrane filtration+microwave 80s> microwave 80s> membrane filtration> CK. Membrane filtration+microwave 80s made PPO,POD,SOD inactivited 90.57%, 69.33% and 85.40%; the retention rate of flavonoids, polyphenols, anthocyanin were 54.88%,68.76% and 42.31%. Membrane filtration+microwave can achieve desired sterilization and inactivation effect.(3) During freeze concentration and vacuum thermal concentration, surface tention of the grape juice increased, relative conductivity declined. Content of total sugar and total acid all increased, and so did tartaric acid, however the content of tartaric acid of freeze concentrated grape juice was lower than that of vacuum thermal concentrated grape juice. During freeze concentration and vacuum thermal concentration, content of phenols increased from 9.4mg/mL to 44.4mg/mL,26.5mg/mL separately, flavonoids content increased from 3.12mg/mL to 25.79mg/mL separately,14.60mg/mL separately, anthocyanin content increased from 2.45mg/mL to 10.15mg/mL,6.35mg/mL separately, DPPH·clearance increased from 55.98% to 91.00%,67.00% separately, OH-clearance increased from 26.89% to 96.30%,69.20% separately, VC content increased from 1.63mg/mL to 3.33mg/mL,2.86mg/mL separately.ΔE of freeze concentration was 2.33(feel different),ΔE of thermal concentration was 6.40(significant differences), all these revealed that freeze concentrated grape juice changed less.(4) Qualitive analyzed the volatile compounds using SPME-GC-MS, determined 27 main volatile components from the natural grape juice, including 8 esters,2 alcohols,5 phenols,3 ketones,1 Aldehydes, 1 organic acid,7 aromatic series compounds, and 1 alkane,88.04% of the total relative content. Compared with natural grape juice,2 components of microwave sterilized grape juice increased, which were 0.54% of the total relative content,10 components disappeared, which were 1.39% of the total relative content; 2 components of freeze concentrated grape juice increased, which were 0.17% of the total relative content,10 components disappeared, which were 3.16% of the total relative content; however,21 components of thermal concentrated grape juice increased, which were 15.33% of the total relative content,10 components disappeared, which were 1.21% of the total relative content. All these revealed that microwave sterilization and freeze concentration can maintain the fragrancy of grape fruits.(5) Stored for 120 days at 4℃,20℃and 40℃, number of microorganisms in grape juice increased, vitamin c, content of flavonoids, phenols and anthocyanin all declined at different degree. AE4℃=1.74,ΔE20℃= 2.10,ΔE40℃=2.61. These indexes of grape juice stored at 4℃changed least, and the quality is the most stable.