| Although the traditional Yuba drying process(hot air drying)is simple to start and low cost,but the quality of the dried Yuba is not good,the palatability is poor and the soaking time before consumption is too long.If you want to improve the quality of Yuba from the drying method,you need to combine the drying treatment methods of mainstream food,use new drying technology while controlling costs as much as possible,so that Yuba appears in the consumer market with a new product and a different taste.In this project,the drying process of Yuba stick was first studied,and the effects of different drying methods on its physicochemical indexes and properties were obtained by comparing and analyzing the quality characteristics and microstructure of Hot air drying(HAD)and Vacuum freeze drying(VFD).The results showed that the ability of freeze-dried Yuba stick to maintain its original color was better than that of traditional Yuba stick,and the five sensory evaluation scores were the highest and uniform.Compared with traditional hot air treatment,vacuum freeze drying has significant advantages in maintaining the quality characteristics of Yuba stick and improving the texture of Yuba stick,which can be used as a new type of Yuba stick processing technology.Secondly,in order to improve the quality of Jiusan freeze-dried Yuba and reduce its processing cost,a double-chamber freeze-drying testing machine was selected in this experiment to explore the effects of pre-freezing temperature,heating plate temperature and vacuum degree on the drying time and sensory quality of Yuba stick,and the process parameters of vacuum freeze-drying of Jiusan Yuba were optimized by the three-way quadratic orthogonal rotation combination design,and the drying time and quality of the dried products before optimization were compared and analyzed.The best process parameters were obtained as follows: pre-freezing temperature-39°C,heating plate temperature 51°C,vacuum degree 28 Pa,drying time 10.57 h,sensory score 8.95 points.The drying time after process optimization was shortened by 11.9% compared with the actual processing without optimization,the sensory score was increased by 32.6%,The results of this test can provide a theoretical reference for VFD processing of Jiusan Yuba stick.Finally,the freeze-dried Yuba stick prepared by the best drying process parameters was selected as the test material,and the quality change law of freeze-dried Yuba stick at storage temperature of 20°C,30°C and 40°C was studied by using the classic constant temperature acceleration test,and the shelf life regression equation was obtained,and the Weibull model was used to analyze the hazard of Yuba stick and predict that the shelf life would be 19 months when the storage temperature was 20°C.12 months shelf life at 30°C;The shelf life at 40°C is 6 months,and finally the Weibull shelf life prediction equation is obtained.According to Arrhenius’ theory,the kinetic equation was established to obtain the reaction rate constant based on the change of physical and chemical indexes,and the shelf life prediction model of lyophilized Yuba stick based on the change of single index was obtained,and the shelf life based on the change of color difference at 20 °C was about 20 months,and the shelf life based on the change of protein content was about 21 months.The prediction method of the sensory endpoint to determine the end point of the quality index of freezedried Yuba stick can obtain the shelf life prediction value similar to the sensory end point,so this paper finally takes the shelf life predicted by the Weibull model as the criterion,and obtains that the shelf life of freeze-dried Yuba stick under room temperature storage conditions is 19 months,which can provide a theoretical basis for the quality monitoring of freeze-dried Yuba stick products in Jiusan. |
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