Manufacturing Technologies And Directional Control Of Fresh Edible Corn Juice

Fresh-edible corn is the corn harvested from the milk stage to the early dough stage.In China,sweet corn and waxy corn are the main type of fresh-edible corn.Considering the high sugar and moisture content,corn is always used for corn juice making.To date,more than 400 fresh-edible cultivars of fresh corn have been developed,and eating quality propertie are varied of the cultivars.However,there are few studies about which cultivar is suiTab.le for juice-making,and how flavor changes during corn juice processing are even less cared.In this study,for corn juice pressing,first the fresh corn kernels were vacuum packaged and frozen storaged,then thawed at low temperature and cold pressed to get the juice,at last sterilized using autoclaving methods.The juice properties from different sweet and waxy corn varieties and maturity were compared,as well as the flavor components during pretreatment and sterilization were determined.Moreover,effects of ultra-high pressure pretreatment and sterilization on the juice quality were evaluated.This paper aimed at the theoretical basis for suiTab.le fresh corn materials and processing methods for pure juice with natral corn flavor.The main results are as follows(I)Seven waxy corn and three sweet corn varieties were collected and their suiTab.ility for juice making was compared.The results showed that the moisture content of sweet corn was higher than that of waxy corn,and the juice yield of sweet corn was 39.51-47.97%,the soluble solid content was 10.77-13.13%,there were significant differences among three sweet corn varieties.The yield of waxy corn was 18.92-33.39%,and the soluble solid content was 4.34-9.83%.The juice yield and soluble solids content of sweet corn were significantly higher than those of waxy corn.According to the difference of 100-grain weight,the three varieties of sweet corn were divided into three maturity stages as I,II and III.It was found that the moisture content and juice yield of stage I were higher than other maturity stages II and III,but the content of soluble solid content was lower.Further determination of free sugar,free amino acid,flavor nucleotides,volatile components and sensory attributes in corn juice.The results showed that the soluble solids content,sucrose content,sweet and delicious amino acids and the percentage of two methyl sulfide and pyrazine compounds of SKT-1506 maturity II were higher than those of the other two varieties.(II)The effects of vacuum packaging on the quality of corn juice after freezing at-20?,freezing at-20?,and vacuum packaging after freezing in liquid nitrogen at-20? and-80?were compared.The results showed that the free sugar content of corn juice treated at-20?after freezing at-20? was 1.18 and 1.26 times higher than that of the other 1.18,and the content of sweet amino acids was 1.22 and 1.37 times of the other two treatments.It is more prominent,and has the lowest content of hexanal that characterizes raw and green flavors,and the highest content of dimethyl sulfide,the characteristic aroma of corn.The effects of thawing on the quality of corn kernel at 4?,25? and 40? were compared,and combined with the results of principal component analysis showed:The content of sweet amino acids glycine and alanine,umami amino acids glutamic acid and asparagine,sucrose,maltose and pyrazine are the highest in corn grains thawed at 4?.The single factor experiment proves that the better pretreatment method of corn juice is:fresh corn kernels are frozen at-20?,frozen at-20?,and thawed at 4?.(?)The effects of different sterilization methods on the quality of sweet corn juice and the changes of volatile and non-volatile components.were compared.It was found that the content of soluble solids in corn juice after heat treatment sterilization increased significantly.The non-volatile components constituents were not changed under different sterilization condition,but their contents were significantly changed.The heat-treated sucrose content,total sugar content,sweet amino acids and The umami taste amino acid was significantly higher than that of raw juice and HPP treatment.The components of dimethyl sulfide and pyrazine appear only in the samples subjected to heat sterilization,but not detected in the samples subjected to cold sterilization.According to the fuzzy comprehensive evaluation method,the sensory order of corn juice in different sterilization groups is as follows:high-pressure heat treatment>normal pressure heat treatment>HPP+high pressure heat treatment>HPP+normal pressure heat treatment>raw juice>HPP.Comprehensive consideration is to choose high-pressure heat treatment as a suiTab.le sterilization method for processing corn juice.