Behavior And Mechanism Research On Vacuum-microwave Drying Of Ginger Based On Carbonic Maceration Pretreatment

Ginger is the rhizome of zingiberaceae,which is an important edible and medicinal material in China.Gingerol,as a characteristic spicy ingredient,is an important functional component of ginger.It also has outstanding antioxidant properties.The storage process has a great influence on gingerol.The water content of ginger is over 90%,and the ginger is easy to spoil under normal temperature.Therefore,the development of new ginger drying technology and processing technology has important practical significance.In this study,the drying characteristics and nutritional quality of ginger were studied by using carbonic maceration pretreatment and vacuum-microwave drying technology.And the mechanism of carbonic maceration on ginger was also studied.Therefore,an important recommendation for the further development and industrialization of ginger products was offered.1.Orthogonal test method was used to optimize the vacuum-microwave drying parameters of ginger.At first,effects of the first-stage pulse ratio（PR1）,transition point moisture content,second-stage pulse ratio（PR2）and drying temperature on ginger drying time,energy consumption,color and total phenol content were investigated by single factor test.And the four-factor and three-level orthogonal experiment was used to optimize the vacuum-microwave drying process parameters.The results showed that the optimal drying conditions of vacuum-microwave drying were as follows: PR1=1.7,transition point moisture content of 30%,PR2=3.0,drying temperature of 50℃.Under this condition,the drying time of ginger was 31.5 min,the energy consumption was 9.57 k W·h/kg H₂ O,the total phenol content was 19.32mg/g d.w.,and the total color difference Δ E was 13.16.2.Study on the drying characteristics and microstructures of ginger after carbonic maceration.The drying rates and the effective diffusion coefficient increased significantly after carbonic maceration pretreatment.The drying time of carbonic maceration treated sample was up to 47% shorter than that of directly dried sample.By nonlinear fitting with five thin-layer drying models,the results showed that the vacuum-microwave drying process of ginger after carbonic maceration can be described by the Modified Page model.In addition,the internal pores of the ginger were opened,the area of cell was increased,and the skeleton structure was more clear and more complete after carbonic maceration.3.Study on the quality of dried ginger after carbonic maceration.The results showed that carbonic maceration pretreatment had good protection on the color of dried ginger,and the content of phenolic substances in ginger after carbonic maceration increased significantly.After carbonic maceration pretreatment,the total phenolic content of dried ginger was increased by 15.71-44.07% compared with the directly dried sample,the free phenol was increased by 135.96-256.65%,the combined phenol was increased by 9.54-38.42%,the contents of 6,8,10-gingerol and 6-shogaol were increased by 9.96-20.79%,6.45-37.27%,12.90-36.80% and 25.87-68.53%,respectively.Meanwhile,the antioxidant capacity of dried ginger was also significantly improved.4.Study on mechanism of carbonic maceration on enhancing active components of ginger.By measuring the enzyme activity and conformation of polyphenol oxidase and peroxidase before and after carbonic maceration,the results showed that the polyphenol oxidase and peroxidase were inactivated after carbonic maceration pretreatments.The secondary structure of polyphenol oxidase and peroxidase was changed.The relative content of α-helix decreased,and that of β-fold increased.And the tertiary structure of enzyme was also changed after carbonic maceration,which was mainly manifested by the decrease of fluorescence intensity and the red shift of the maximum emission peak.In addition,the intracellular p H of ginger after carbonic maceration was significantly reduced,the cell permeability was significantly increased,and the internal bound water of ginger was transformed into free water,which were beneficial to the retention of nutrients and the diffusion of water in ginger.