Effects Of Postharvest Heat Shock Treatment On Callus Formation And Storage Quality Of Sweet Potato

Sweet potato(Ipomone batatas L)is a kind of food and vegetable crop with wide planting area and high yield.The thin skin of sweet potato roots tuber is easy to be damaged and the sweet potato tuber damage will cause root nutrition loss and pathogen invasion.Appropriate callus treatment will help to improve the resistance of sweet potato and prolong the storage period.The existing callus technology has the features of long processing time,complicated process,and limited processing capacity,which cannot meet the requirements of modern warehousing and production.In this study,‘Dayehong’sweet potato tuber was selected as the test material to investigate the most suitable heat shock callus conditions for sweet potato,discussing the effect of the heat shock treatment on sweet potato tuber callus from the aspects of phenylpropane metabolism,active oxygen metabolism,antioxidant capacity and tissue structure observation.In the meanwhile,comparative analysis of the effects of traditional callus treatment and heat shock treatment on storage quality of sweet potato will be explored.The specific research results are stated as follows:1.The optimal heat shock callus conditions for sweet potato are: heat shock treatment at 65℃ for 15 min.The treatment can maintain the good appearance and color of sweet potato,slow down the browning of sweet potato,promote the accumulation of lignin content in sweet potato wounds,and enhance the thickness of the cork layer and the hardness of the callus layer,thereby reducing the weightlessness of the sweet potato and pulling down the exogenous bacterial disease index.In addition,the thermal efficiency of the skin and interior of the sweet potato treated with 65℃ heat shock treatment for 15 min is improved rapidly,achieving the same callus effect with the traditional callus treatment in a short time,with less energy consumption and higher efficiency.2.In order to explore the effect of heat shock treatment on sweet potato tuber callus,sweet potatoes were first treated in different conditions,including heat shock treatment at65℃ for 15 min,traditional callus treatment(35℃ 2 d,CK+)and noncallus treatment(CK-)and then were stored.After 7 days of storage,tested from the aspects of phenylpropane metabolism,active oxygen metabolism,antioxidant capacity and tissue structure observation,it was found that heat shock treatment can make the sweet potato maintain higher respiratory intensity and boost enzyme activity of phenylpropane metabolic pathway increased during sweet potato callus induction,promoting the accumulation of total phenols,flavonoids and lignin during sweet potato callus.HPLC identification showed that the main phenolic compounds in sweet potato callus are neochlorogenic acid,catechin,chlorogenic acid,epicatechin and rutin,of which chlorogenic acid is the monophenol with the highest content.At the same time,heast shock treatment can also significantly promote the rapid accumulation of three reactive oxygen components,which are seen as a signal molecules to activate sweet potato callus defenes reactions and induce the activities increase of active oxygen metabolism scavenging enzyme,improving the antioxidant capacity of the sweet potato during callus.During the callus,the deposition of lignin and softwood resin observation found that the lignin and softwood resin has the fastest deposition rate when sweet potatoes were treated with heat shock at 65℃ for 15 min,and the callus effect was similar to that of traditional callus treatment CK+.3.In order to study the effect of heat shock treatment on the storage quality of sweet potato after callus,the sweet potato ware treated with the traditional callus treatment(35℃2 d,CK+)and 65℃ heat shock for 15 min treatment separately,and then were stored for35 d.Comparative analysis found that 65℃ heat shock for 15 min treatment and CK+ can maintain good appearance and color of sweet potato,reduce browning of sweet potato tissue,inhibit abnormal fluctuation of respiratory intensity during storage,slow down the increase of content of the cell membrane permeability and malondialdehyde(MDA)of sweet potato tissue,and keep the higher hardness,water content,starch,soluble sugar,soluble protein,ascorbic acid content and antioxidant capacity of sweet potato tubers effectively,reducing the weight loss,cold damage and rot loss of sweet potato.In summary,postharvest heat shock treatment can effectively shorten the callus treatment time of sweet potato and promote the rapid formation of sweet potato tuber callus.The callus process is a result of the joint action of various physiological and metabolic pathways including phenylpropane metabolism,active oxygen metabolism,antioxidant activity,respiratory metabolism,etc.The heat shock treatment can effectively improve the storage quality of sweet potato,and achieve the same callus effect with that of the traditional callus treatment in a short time.