Study Of Processing Technology Of Okra Concentrated Juice And Related Beverage

Okra is a therophyte plant which is valued for its nutrition and high health function.However,okra is hard to store and easy to spoil.Thus,in this study,techniques of okra preservation,concentrated juice production and compound beverage production were investigated.The quality of okra juice during the production process was also evaluated.The conclusions are as follows:(1)The effects of different storage temperature on the quality of fresh okra were investigated.Fresh okras were stored at 4°C,8°C and 25°C respectively.The optimum temperature of okra storage was obtained by evaluating the changes of storage time,sensory quality,nutrition constituents and physiological index.The result showed that the longest preservation time was 24 days at 4°C,followed by 8°C,storage period of 15 days,the shortest period of storage was 10 days at 25°C.Therefore,the optimum storage temperature for okra was 4°C.Under this condition,okra respiration rate could be effectively suppressed and it was optimal for maintaining nutrients,slowing the aging process of okra.The appearing time of black spots on its surface was the longest,and the sensory quality was the best at 4°C,compared to that at 8°C and 25°C.At the end of storage period at 4°C,soluble solids content of okra was 3.57 °Brix,chlorophyll content was 9.05 mg/100 g,protein content was 1.74%,ascorbic acid content was 5.16 mg/100 g,total phenol content was 8.43 mgGAE/g,total flavonoid content was 1.14 mg/g,crude fiber content was 3.23%,caffeine content was 1.60 mg/g.Compared with 8°C and 25°C,okra stored at 4°C showed a slow speed of aging process,and maintained nutrients throughout the period.Thus,the optimum temperature for fresh okra storage was 4°C.(2)The process parameters of okra juice clarification techniques were optimized.The okra juice was firstly pre-clarified using pectinase to remove partial pomace and haze substances.Then the acquired enzymolysis okra juice was further processed by ultrafiltration to acquire the clarified okra juice.The optimal conditions acquired by response surface optimization method to get enzymolysis okra juice were: enzymolysis temperature 41°C,enzymolysis time 65 min,pectase addition 0.21 g/L.Under this condition,the value of transmittance was 41.5%,meaning that the pretreatment of pectinase could effectively remove the foreign substances in okra juice and reduce the loss of ultrafiltration membranes during ultrafiltration,which was helpful to improving the production efficiency and reducing production costs.In the ultrafiltration process,polysulfone amide(PSA)ultrafiltration membranes with pore sizes of 6 kDa,20 kDa,67 kDa and 100 kDa were used to clarify the enzymolysis okra juice respectively,and soluble solids,total sugar,total phenols,flavonoids,polyphenols,caffeine component,clarifying effect and color were compared.Results showed that the sample treated by 67 kDa ultrafiltration membrane exhibited better clarification effect,including preserving the flavor and color,with a relatively small loss of nutrients.(3)The quality changes during the process of concentrated okra juice producted were investigated.The clarified okra juice was concentrated by vacuum concentration technology.The nutrition constituents and the production time of concentrated okra juice at different tempretures(40°C,45°C,50°C,55°C,60°C)were compared,results showed that 45°C was the optimum temperature.The soluble solids,total sugar,total phenol,total flavonoids,caffeine and other major nutrients composition of okra juice was changing during the production process.The above indexes were increased slightly in the pectinase treatment process,soluble solids content was increased by 0.2 °Brix,total sugar content increased by 1.48 mg/mL,total phenol content increased by 3.48 mgGAE/g,total flavonoid content increased by 0.02 mg/g,caffeine content increased by 0.02 mg/g.The loss of nutrients significantly was reduced in ultrafiltration process,and the retention rate was between 65% and 84%,while maintained above 90% in vacuum concentration process.Furthermore,phenolics components of okra juice in the key steps were tested,the results showed that 9 kinds of phenolics components including protocatechuic acid,catechin,chlorogenic acid,caffeic acid,p-hydroxycinnamic,ferulic acid,rutin,hyperin and myricetin hyperoside were observed in enzyme-hydrolyzed okra juice,ultrafiltration juice and concentrated juice.However,there were no p-hydroxycinnamic and ferulic acid detected in the original okra juice.(4)Concentrated orange juice and okra juice were blended,and the optimal formula for the compound beverage was as follows: the ratio of concentrated orange juice to concentrated okra juice was 1:2,the amount of sucrose addition was 7.5%,the amount of stabilizer was 0.15%.The soluble solides content of the acquired beverage reached 10.3 °Brix.The higher Vc from orange juice made up for the lower content of Vc in okra.Furthermore,the acquired beverage was sweet and sour with fresh flavor and natural color.Both orange juice and okra juice tasted distinct,with stable structure and good drinking quality.