Postharvest performance of peach in cold storage is influenced by preharvest rain-shelter cultivation

Abstract: 【Objective】Rain shelters have been proven to significantly increase both yield and profits inthe main production area of southeast China,where too much rainfall has long been a problem for main-taining high yield and good quality. Postharvest biology and technology of peach fruit mainly focus on tech-niques that could alleviate chilling induced disorders and regulation mechanisms,however,the effects ofpreharvest cultivation,such as rain shelters,on changes in fruit quality-related attributes during posthar-vest storage are not well understood. So the effects of rain shelters on postharvest performance of peachfruit were investigated in the present study.【Methods】Melting peach [Prunus persica(L.) Batsch‘Hujing-milu'] were grown under rain shelter and in open field for treatment and control,respectively. For therain-shelter cultivation,colorless polyethylene(PE) film(0.5 mm thickness) was applied at beginning ofthe rainy Meiyu season in late June 3 weeks before harvest. Fruits were harvested on the same day,andscreened for uniform size and without visible defects of decay. For postharvest low temperature storage,fruit were stored at 0 ℃ with a relative humidity of 90% for 21 and 28 d followed by transfer to 20 ℃ for 3d. Fruit skin color,firmness and internal browning(IB) were measured at each sampling stage. The contents of soluble sugars and organic acids were determined by high performance liquid chromatography(HPLC). For determination of soluble sugars,an Intersil amino column(4.6 mm×250 mm) with a columntemperature of 25 ℃ was used;the mobile phase was acetonitrile and distilled water(v∶v =8∶2);the flowrate was 1.0 m L·min-1;and the detector was an RI-1530 differential detector(Jasco,Japan). For deter-mining of organic acids,a Beckman ODS C18 column(4.6 mm×250 mm) with a column temperature of25 ℃ was used;the mobile phase was(NH4)2HPO4buffer;and the flow rate was 0.5 m L·min-1. An elec-tronic nose(FOX 4000) with 18 metal sensors(Alpha MOS) was used to analyze the sensory quality ofpeach fruit. The analyses included three biological replicates and two technique repeats. Headspace solidphase micro extraction(HS-SPME) combined with gas chromatography mass spectrometry(GC-MS) wasused to detect changes in peach fruit volatile compounds. The volatile compounds were separated on aDB-WAX column(0.25 mm,30 m,0.25 μm,J&W Scientific) in splitless mode. Temperature programwas as follows: initial oven temperature started at 40 ℃,increased by 3 ℃ to 100 ℃,and then rose to245 ℃. Helium was used as carrier gas at a flow rate of 1.0 m L·min-1.【Results】After 21 d of cold stor-age,peach fruit from rain-shelter system developed chilling injury during shelf-life ripening,accompa-nying flesh browning and texture hardening,while fruit from open field could soften normally,with noflesh browning. These disorders were delayed and observable after 28 d in fruit from open field with 27%IB,significantly lower than 43% IB in rain-sheltered fruit at the same stages. With the extension of lowtemperature storage,the content of sucrose showed significant decrease. The contents of glucose and fruc-tose,products of sucrose hydrolysis,gradually increased,and therefore the content of total soluble sug-ars maintained stable. Significant difference in soluble sugars such as sucrose,glucose and fructose,andin organic acids such as malic acid and citric acid were observed in peach fruit transferred to 20 ℃ for 3 dafter 21 d of cold storage. The content of sucrose in rain-sheltered fruit was lower than the control duringcold storage and shelf-life stages,while the contents of glucose and fructose were higher than the con-trol,indicating that the fruit with different chilling injury degree were different in composition of solublesugars. The ratio of sugars to acids did not show significant difference between the two cultivation modesduring low temperature storage. Statistical quality control(SQC) analysis of electronic nose data showedthat peach fruit from rain-shelter system had significant different sensory quality. SPME coupled withGC-MS analysis demonstrated a high degree of difference in volatile compositions related to cultivationmethods. Compared to peach fruit from the open field,rain-sheltered fruit produced lower levels of lac-tones,esters,furans and norisoprenoids during postharvest cold storage and shelf-life. The contents offruity note volatiles were significantly lower in peach fruit from rain-shelter cultivation after 21 d of coldstorage,including hexyl acetate,(Z)-3-hexenyl acetate,(E)-2-hexenyl acetate and γ-decalactone.δ-decalactone and γ-decalactone were the characteristic aromas of peach fruit. The content of γ-decalac-tone in rain-sheltered fruit transferred to shelf 3 d after 21 d storage was 51% of the control fruit at thesame stage,and δ-decalactone was about 48% of the control. For the fruit 3 d after transferred from 28 dof storage,the contents of γ-decalactone and δ-decalactone were 62% and 43%,respectively. The great-er loss of aromas in rain-sheltered fruit indicated more severe chilling injury symptoms. The total amountof volatile compounds in fruit with severe chilling injury symptoms was less than the control fruit,follow-ing a decrease along with the aggravated chilling injury. Rain shelter treatment significantly reduced lighttransmission and soil water content,which might have delayed fruit maturation and thus resulted in differ-ences in volatiles and chilling injury development during postharvest cold storage and the subsequentshelf-life.【Conclusion】Compared to peach fruit from the open field,rain-sheltered samples tended todevelop chilling injury during postharvest cold storage. The main symptoms included flesh browning,lossof softening,decrease in sucrose content,and significant reduction of fruity lactones and esters.