Regulation Of Temperature And Humidity On The Formation Of Oil Quality And Volatile Compounds Of Torreya Grandis ‘Merrilli' Seeds During The Post-Harvest Ripening Stage

Torreya grandis‘Merrilli'?T.grandis‘Merrilli'?,a kind of coniferous evergreen plant belongs to the genus Torreya family Taxaceae,which is an unique species in China.The nuts have high nutritional value with crisp texture and rich aroma after toasting.The nuts need to undergo a highly coordinated and complex ripening process after harvest to finish fully maturation,including nutrient conversion and the volatile compounds formation,which become the key step to the formation of quality in the post-harvest ripening stage.The quality of T.grandis‘Merrilli'nuts is affected and regulated by many environment factors,among which temperature and humidity are the important factors during this process.In our study,different temperature(T₂₀:20±2?,T₃₀:30±2?)and humidity?LH:70±5%,HH:90±5%?were set as ripening environmental conditions to study the changes in appearance quality,nutrient content,fatty acid and the volatile compounds of T.grandis‘Merrilli'during the post-harvest ripening stage.We have clarified the suitable temperature and humidity parameters,discussed the mechanism of temperature and humidity regulation of the lipid oxidation,revealed the changes of the volatile compounds,and analyzed the related genes of main metabolic pathway of volatile compounds in T.grandis‘Merrilli'nuts,which provide a theoretical and technical guidance to improve the quality of T.grandis‘Merrilli'during the post-harvest ripening stage.The results showed as follows:?1?Temperature and humidity have a significant effect on conversion of nutrients of T.grandis‘Merrilli'nuts during the post-harvest ripening stage.Compared with LH?completed on day 12?,seed coat darken preceded about 4 day under HH?completed on day 8?regardless of whether T₂₀ or T₃₀.In addition,the distance between the kernel and the seed coat was significantly larger under HH than LH both for T₂₀ and T₃₀.The starch content decreased while the soluble sugar,oil and protein content increased during the post-harvest ripening stage.Compared with 0d,the starch content under T₂₀-LH,T₂₀-HH,T₃₀-LH and T₃₀-HH respectively decreased by 29.4%,33.6%,25.4%,and 32.6%on 16d,while the soluble sugar content respectively increased by 17.7%,33.8%,26.1%and 33.6%in the same condition.And on the 16d of post-harvest ripening stage,the oil content under T₂₀-HH was higher than the other three treatments.Meanwhile,the synthesis of soluble protein was significantly promoted under HH compared with LH at T₃₀ on 4-16d.Therefore,humidity has a significant influence on the conversion of nutrients of T.grandis‘Merrilli'nuts during post-harvest ripening stage,which could not only shorten the ripening time of T.grandis‘Merrilli',but also promotes the conversion of nutrients.?2?Temperature and humidity treated have significant effect on rancidity of fatty of T.grandis‘Merrilli'nuts during the post-harvest ripening stage.The acid value and peroxide value continuously increased during this process.Compared with T₂₀,the acid value and peroxide value under T₃₀ was respectively increased by 58.1%and 22.7%on 16d.Unsaturated fatty acid/saturated fatty acid?UFA/SFA?and the double bond index?DBI index?were significantly lower under T₃₀ than T₂₀.In addition,both lipase and lipoxygenase?LOX?activities significantly increased at T₃₀ compared with T₂₀under HH on the 8d of ripening time.Malondialdehyde?MDA?increased with superoxide anion?O₂.^-?and hydrogen peroxid?H₂O₂?during the post-harvest ripening stage.The significantly higher superoxide dismutase?SOD?activity,Catalase?CAT?activity,MDA and O₂.^-content was found in T₃₀compared to T₂₀ under HH on the 8-12d of ripening stage.Thus,compared with T₂₀,T₃₀0 was more likely to promote the degradation of unsaturated fatty acids,causing lipid peroxidation and leading to an increase in the activity of related antioxidant enzymes.Principal component analysis?PCA?indicated that T₂₀ under HH possessed a better performance to maintain nut quality based on the reduced activities of lipase and LOX and enhanced activities of Peroxidase?POD?and 1,1-diphenyl-2-picrylhydrazy?DPPH?free radical scavenging than T₃₀ under HH.Thus,we finally adopt the treatment of T₂₀-HH as the optimal condition for the ripening of T.grandis‘Merrilli'nuts,which could not only ensure the complete conversion of the nutrient conversion,but also make the oxidation of the lipid at a low level.?3?Gas Chromatography-Mass Spectrometer?GC-MS?was used to analyze the volatile compounds of T.grandis‘Merrilli'kernel.19 kinds of terpenoids,19 kinds of alcohols,8 kinds of aldehydes,5 kinds of esters and 5 kinds of alkanes were detected.The terpenoid content was found to be the major volatile compounds,of which D-limonene content accounts for more than 80%of terpenoids of T.grandis‘Merrilli'nuts.Terpenoids showed a significant increasing trend from 4 to 12day of ripening time.Irrespective of retting temperature,the terpenoid content was signficantly higher under HH than that under LH from 8 to 12 day of ripening time(except form at T₂₀ on 8 day of ripening time).Moreover,the terpenoid content was significantly higher at T₃₀ than that at T₂₀ under HH from 4to 8 day of ripening stage.Compared with 0d,the D-limonene content under T₂₀-LH,T₂₀-HH,T₃₀-LH and T₃₀-HH respectively increased by 31.8?g·g^-1,31.5?g·g^-1,17.2?g·g^-1 and 32.7?g·g^-1.Meanwhile,the synthesis of D-limonene was significantly promoted under HH compared with LH.Then,we analysed the significant correlation between the expression of the related genes and formation of volatile compounds by transcriptome analysis,and 7 key genes were identified to be related to the synthesis of terpenes which are TgHMGS₁136698,TgHMGR₆6471,TgDXS₁32342,TgDXR₁133829,TgHDS₁134183,TgHDR₁133129 and TgTPS₈6232.