Studies On Browning Mechanism And Key Preservation Technologies Of Fresh-cut Ginger

Fresh-cut fruits and vegetables have exhibited a promising prospect in recent years dueto their potential advantages such as fresh, easy-to-serve and nutritional. Ginger possessessome health-promoting properties, and is widely used as one of traditional spices in China.Fresh-cut technology has the advantages of simple processing and low cost compared withother methods. In order to elucidate the browning mechanism of fresh-cut ginger and improvetheir sensory quality, it is essential to investigate the browning properties and control methodsof fresh-cut ginger. It is of great theoretical and realistic significance for industrialdevelopment of fresh-cut ginger. In the present study, browning degree （BD）, totalphenols（TP）, polyphenoloxidase（PPO）, peroxidase（POD） and Phenylalanine ammonialyase（PAL） activity and their correlation were investigated during the storage of fresh-cutginger using high HPLC-ESI-TOF-MS and transmission electron microscope （TEM）.Browning substrates of fresh-cut ginger were isolated and identified with the purpose ofunderstanding the browning mechanism of fresh-cut ginger. The preservation technology offresh-cut ginger was investigated as well. The results were as follows:（1） PPO, POD and PAL activities were rapidly elevated after cutting of fresh-cut ginger.The increasing PAL activity promoted the production of total phenols in fresh-cut ginger,which provided enough substrates for PPO and POD. The browning of fresh-cut ginger wasattributed to the oxidation of total phenols catalyzed by PPO and POD.（2） Eight compounds were identified from ginger extracts isolated by TLC. They were4-shogaol,1-dehydro-8-gingerdione,6-gingerol,8-shogaol,6-shogaol,8-gingerdione,1-dehydro-6-gingerdione and10-shogaol, which possess the functional group of3-methoxy-4-hydroxyphenyl.（3） The optimum temperature and pH of PPO was30℃and6.8, respectively. PPO wascompletely inactivated at100℃for2min. Vc, NaHSO3,L-Cys and citric acid couldsuppress the PPO activity, and the inhibitory potency was in the order of L-Cys> NaHSO3,Vc> citric acid. Ca²⁺and Cu²⁺could activate PPO activity while Al³⁺and Mg²⁺could inhibit the enzyme.（4） The optimum temperature and pH of POD was45℃and6.0, respectively. It couldbe inactivated at90℃for60s or at100℃for40s. Vc, EDTA-2Na, NaHSO3、citric acid,L-Cys could suppress the POD activity, and the inhibitory potency was in the order of Vc,NaHSO3,L-Cys> EDTA-2Na, citric acid. Ca²⁺, Mg²⁺, Fe³⁺and Zn²⁺could activate PODactivity at5mmol/L while Na+and Mn²⁺could inhibit the enzyme.（5） The optimum temperature and pH value of PAL was60℃and8.2, respectively. Itcould be inactivated at90℃for15min or at100℃for10min, suggesting its high heatresistance. PAL could be activated by Mn²⁺, Zn²⁺, Cu²⁺and Al³⁺, and suppressed by Ni²⁺.（6） Chitosan coating significantly suppressed browning and mass loss of fresh-cut ginger.Meanwhile, the decrease of total soluble sugar and vitamin C, and the increase of crude fiberwere inhibited. The optimal preservation quality of fresh-cut ginger was observed whenchitosan concentration was1.5%, which could delay the occurrence of the plasmolysis, inhibitthe degradation of cell wall as well as the disintegration of nucleus, plastid and mitochondria,maintain the integrity of cell structure, and consequently effectively prolong the shelf-life offresh-cut ginger.（7） The optimum conditions for color protection of fresh-cut ginger were Vc （0.3%）,citric acid （0.5%） and L-Cys （0.4%）, and the optimal coating preservation of fresh-cut gingerwas1.5%chitosan. Moreover, coating preservation exhibited a better preservation quality offresh-cut ginger.