Effect Of UV-B/C Or Oxalic Acid Treatment On Improving Quality In Bamboo Shoots(P.Prominens Or B.oldhami) Without Sheaths And Its Involved Mechanism During Cold Storage

Bamboo shoots,the tender culms sprouting from the nodes of bamboo rhizome underground,are considered as traditional and ideal vegetables to benefit to human health.However,the edible quality of bamboo shoots is deteriorated rapidly by tissue lignification along with flesh browning during postharvest.Recently,many works have revealed that postharvest UV-B and UV-C irradiation or oxalic acid treatment is beneficial to delaying ripening,controlling rot development,alleviating chilling injury,and inhibiting browning in some selected fruits and vegetables,and in turn enhancing their commercial and nutritional value,as well as retaining the quality during postharvest.However,to our best knowledge,no imformation is available on the use of UV-B/C irradiation or oxalic acid for maintaining quality and extending shelf life of bamboo shoots without sheaths during storage.In this paper,for better clarifying the mechanism of UV-B/C irradiation or oxalic acid to improve the edible quality of postharvest bamboo shoots,the effects of UV-B/C irradiation or oxalic acid on the quality,antioxidant capacity,lignin metabolism and their involved gene expression in bamboo shoots of.Prominens or B.oldhami without sheaths were investigated during storage at 6±1 0C,after the bamboo shoots of.prominens were treated with UV-B at dose of 8.0 kJ m-2,or the bamboo shoots of B.oldhami treated with UV-C at dose of 3.0 kJ m-2,or the two varieties of bamboo shoots without sheaths were soaked in 5 mM oxalic acid solution for 10 min.The main results were as following:1.UV-B and UV-C irradiation significantly reduced the respiration and ethylene production rate,delayed the increase in firmness and accumulation of reducing sugar,lignin and cellulose,reduced losses of total sugar content,free amino acid content,soluble protein content,ascorbic acid content and weight,increased the contents of flavonoid and total phenolic,decreased disease incidence,which were collectively contributed to maintaining the edible quality of bamboo shoots of.prominens and B.oldhami,respectively.Furthermore,UV-B and UV-C irradiation significantly enhanced the activities of superoxide disumutase(SOD),catalase(CAT)and ascorbate peroxidase(APX)and the expression of their encoding genes,slowed down the increase in the production rate of superoxide anion(O2-)and the content of hydrogen peroxide(H2O2),and significantly decreased the activities of polyphenol oxidase(PPO)and its gene expression,which were of benefit to controlling MDA content and relative leakage rate associated with the maintenance of membrane integrity and inhibition to enzymatic browning in bamboo shoots of P.prominens and B.oldhami,respectively.UV-B and UV-C irradiation treatment significantly decreased the activities of phenylalanine ammonia lyase(PAL),cinnamyl alcohol dehydrogenase(CAD),peroxidase(POD)and 4-coumarate CoA ligase(4CL)and the expressionof their encoding genes in bamboo shoots during cold storage,which contributed to retarding lignification process.These effects were collectively contributed to maintenance of the edible quality of bamboo shoots of P.prominens and B.oldhami respectively.2 Oxalic acid treatment significantly reduced the respiration and ethylene production rate,significantly reduced the losses of total sugar content,free amino acid content,soluble protein content,ascorbic acid content and weight,significantly increased the content of flavonoid,which were contributed to improving the edible quality of bamboo shoots of.prominens and B.oldhami,respectively.Oxalic acid treatment also enhanced the activities of SOD,CAT and APX and up-regulated their gene expression,reduced the H2O2 content and the production rate of O2-,decreased the PPO activity and down-regulated its gene expression,which were contributed to inhibiting enzymatic browning of bamboo shoots of.prominens and B.oldhami by enhancing membrane integrity and delaying the increase of MDA content and relative leakage rate.In addition,oxalic acid treatment retarded lignification process by decreasing the activities of PAL,CAD,4CL and POD and down-regulated the gene expression of 4CL,CAD and POD,which resulted in lower firmness and slower accumulation of lignin and cellulose in flesh of bamboo shoots of P.prominens and B.oldhami during cold storage.These effects showed oxalic acid treatment as a promising postharvest technique to maintain the quality and inhibit the lignification and browning of bamboo shoots.In conclusion,the results indicated that proper dosage of UV-B/C radiation or suitable concentration of oxalic acid might be a promising method of maintaining quality of bamboo shoots without sheaths by regulating antioxidant system and lignin metabolism during cold storage.This paper provides the reference for developing new preservation methods for quality control of bamboo shoots postharvest.