Study On Processing Technology Of Ready-to-eat Freeze Dried Lotus Seeds

Lotus(Semen Nelumbinis),also known as lotus meat,lotus rice,Humu,Shuizhidan,belongs to Nymphaea genus.Lotus is rich in nutrients,except its edible value,which also has extremely high medicinal value,and it has been a medicine and food homogenous food since ancient times.However,for a long time,the lotus seeds are processed in a single form,and the lotus seeds are mostly sold as dry products,and the processing technology is still in the primary stage.Generally,sun drying or drying from heat methods are used for processing.There are only a few ready-to-eat convenience foods made from lotus seeds,which could not meet the needs of consumers.It is better to further improve the processing technology of lotus seeds,and accelerate new product development,which is an urgent problem for the food processing industry.In this paper,vacuum freeze-drying technology was applied to the deep processing of lotus seeds to develop a ready-to-eat lotus seed product.The main research content is as follows:1.Fresh lotus seeds were used as raw materials to study the pretreatment process before lyophilization.The effects of phytic acid,citric acid,calcium chloride,and EDTA-2Na on the color of lotus seeds were studied by single factor and orthogonal experiments.The color difference was used as an indicator to determine the optimum ratio of the color protection process:phytic acid was 0.125%,the lemon acid was 0.2%,the calcium chloride was 0.5%,and the color difference was 1.96.Through the investigation of cooking pretreatment,by which the lotus starch gelatinized to was achieved different degrees using different cooking time the texture,iodine blue value and digestibility of lotus seeds with different degrees of gelatinization were compared.Results found that the best cooking time was 30 min,the gelatinization degree was about 79.74%.Then the corresponding physical and chemical indexes were:hardness 5500.4 g,brittleness 5132.82 g,chewing 91.46 g,iodine blue 0.068,rapidly digestible starch 54.8%,slowly digestible starch 29.34%and resistant starch 15.86%.2.Through the study of the effects of different loadings on the drying rate,the amount of a freeze-drying tray was determined to be 500 g.The rehydration of ready-to-eat freeze-dried lotus seeds,and the effect of different brewing time on the rehydration ratio was investigated.Also,the effect of thawing time on the rehydration of instant lotus seed was studied.Then combined with sensory evaluation,the optimum time for brewing was found to be 15 min,and the effect of refreezing and refreezing was the best.By the quadrature orthogonal rotation combination design test scheme,the dynamic mathematical model between the preheating temperature X1,the sublimation drying temperature X2,the analytical drying temperature X3,and the comprehensive evaluation value Y of the drying rate,moisture content,and rehydration ratio was established:Y=73.72+1.57X1+4.65X2+2.06X3+1.22X1X2-4.13X12-1.92X22-0.65 X32The response surface method was used to optimize the freeze-drying process.The optimal parameters were as follows:preheating temperature 92.73℃,sublimation drying temperature 84.72℃,analytical drying temperature 60.00℃.3.Research on the packaging and storage of ready-to-eat freeze-dried lotus seeds,using different packaging materials(glass bottles,plastic bottles,cooking bags,kraft paper bags)and packaging methods(conventional packaging,vacuum packaging,nitrogen-filled packaging)for packaging processing,the indicators,such as crystallization,moisture content,har-dness,and color,were used to analyze the changes during storage.The results showed that with the prolongation of storage time,the water content and hardness of freeze-dried lotus seeds showed a significant upward trend(p<0.01).The iodine blue value showed a significant decrease trend(p<0.01).The difference in color L*value was in the range of 9.05 to 16.34,and the difference in b*was in the range of 4.3 to 8.42.The crystallinity properties suggested that crystal structure increased,which indicated aging off freeze-dried lotus seeds,but overall,aging was not obvious.There are certain differences between different packaging materials and different packaging methods.Considering comprehensively,kraft paper bags used for vacuum packaging was regarded to have better storage effect.Also,the changing law of aging,moisture content,hardness and color of freeze-dried lotus seeds during shelf life was studied.The results showed that the overall trend was increasing,but the degree of change was not significant,and there was no significant difference compared with lotus seeds during conventional storage.The taste of lotus seeds was kept well and there was no obvious retrogradation flavor,consistent with the fact of the longer shelf life of the freeze-dried product.