| Fresh in-husk walnut(Juglans regia L.)fruit has higher consumer demand and greater commercial prospect due to its abundant nutrition and unique flavor.But these benefits are offset by its short market supplements,because green husk of fresh in-husk walnut fruit undergoes enzymatic browning easily resulting in short storage longevity.Cultivar is a crucial factor to influence storage longevity,while few studies comparing storage life among different fresh in-husk walnut cultivars has been carried out,which leading to storage adaption among different fresh walnut cultivars is not clear to date.In this study,eight local representative walnut cultivars in Shaanxi province including ‘Xifu2’,‘Shaanhe’,‘Weina’,‘Xiangling’,‘Xiluo3’,‘Xifu1’,‘Liaoning4’ and ‘Qingxiang’ were involved.Fresh walnut fruits were stored at 0±0.5℃,70%-80% relative humidity.We compared the difference of fruit storability among eight fresh in-husk walnut cultivars,and analyzed relationship of fruit storability with morphology characteristics,postharvest physio-biochemistry characteristics and quality characteristics.The results will be helpful to screen storage tolerant cultivar and establish storability evaluation system of fresh in-husk walnut fruits.And these results will provide some theoretical basis and technical support for extending market supplements of fresh in-husk walnut fruits.The main results were as follows.(1)During storage,all cultivars were terminated storage with a standard of total browning index over 30%.‘Xifu2’,‘Shaanhe’ and ‘Weina’,which developed browning quickly than other cultivars,were terminated storage at 60 d.‘Xiangling’ with moderately browning rate,and ‘Xiluo3’,‘Xifu1’,‘Liaoning4’ and ‘Qingxiang’ with slowly browning rate,were all terminated storage at 72 d.(2)Fresh in-husk walnut fruits of eight cultivars all presented an obvious peak of ethylene production rate at 12-36 d and an end dramatic increase of respiration rate,and all cultivars except for ‘Shaanhe’ and ‘Xiangling’ had the first weak peak of respiration rate.The results of correlation analysis of physiological indicators with browning index showed that terminal browning index of each cultivar positively correlated with PPO activity at 18-30 d,LOX activity at 18 d,MDA content at 18 d and respiration rate at 42 d,but negatively correlated with total phenolic at 18 d and PAL activity at 12 d respectively.(3)The comparison experiments showed that fruit macro morphological characteristics and economic traits(fruit size,green husk thickness,endocarp thickness,green husk rate,kernel rate)had no significant correlation with weight loss rate and browning index.And the results of scanning electron microscopy showed that cuticles on the epidermal cells of ‘Xifu2’,‘Shaanhe’ and ‘Weina’ were dissolved and thiner.Amorphous cuticular waxes with few falttened plates were observed on epidermal cells of ‘Xiluo3’,‘Xifu1’ and ‘Qingxiang’.Differently,for ‘Xiangling’ and ‘Liaoning4’,cuticles were uneven and had some microcracks.Stomatal density,trichome length and trichome density in epidermal cells positively correlated with fruit weight loss rate,but no significantly correlated with browning index.(4)After storage,quality characteristics of fresh in-husk walnut fruit changed as: water content and soluble sugar content in kernel increased significantly,and crude fat content in kernel and sensory quality of kernel decreased significantly among eight cultivars,but crude protein content in kernel changed depending upon cultivars.Besides,acid value of walnut oil increased significantly,while peroxide value and carbonyl value of walnut oil changed depending upon cultivars.The nutrient content,sensory quality and oil stability of ‘Qingxiang’and ‘Xifu1’ were better than other cultivars.(5)Comprehensive evaluation and cluster analysis were employed to order the storability of fresh in-husk walnut fruits among eight cultivars based on terminal browning index,acid value and sensory quality value.The cold storage adaptions of 8 walnut cultivars were ordered as: ‘Qingxiang’ and ‘Xifu1’ > ‘Liaoning4’ and ‘Xiluo3’ > ‘Xifu2’ and‘Xiangling’ > ‘Shaanhe’ and ‘Weina’.These results revealed that fresh in-husk walnut fruit could be classified as climacteric fruit of late-peak type in general but with a new feature that former weak climacteric or non-climacteric mixed.Browning index of different fresh in-husk walnut cultivars had close relationship with enzymatic browning potential at former storage time.During storage,cultivars,with low activities of phenolics oxidation and membrane lipid degradation around12-18 d,had slowly increase rate of browning index.Besides,cultivar with thicker and flat cuticular wax in husk epidermal cells would be more resistant to loss water and storage.The storage resistance of fresh in-husk walnut fruit depended on the browning process,sensory quality and acid value.Among these eight cultivars,‘Qingxiang’ and ‘Xifu1’ had better storage adaption,on the contrary,‘Shaanhe’ and ‘Weina’ were not suitable to cold storage. |
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