Role of Pellicle Integrity on Walnut (Juglans regia L.) Kernel Quality

FIELDS R.; ORTIZ C.M.; CRISOSTO, C. H.; LABAVITCH J.M.; LAMPINEN B.; VICENTE A.R.

Santiago de Chile

Congreso; IX Congreso Iberoamericano de Tecnología Postcosecha y Agroexportaciones; 2017

Facultad de Ciencias Agronómicas Universidad de Chile

European walnuts (Juglans regia L.) are increasing in global availability and as a result postharvest kernel color and flavor are becoming economically important. In fruits, the function of the seed coat is to prevent seed-embryo deterioration; however, their role in walnut cultivars has not been established. In this study, we evaluated the influence of pellicle integrity on kernel quality during postharvest life of ?Chandler? and ?Howard? walnut cultivars. Commercial mature harvested walnuts were randomly divided into two groups: The first group was shelled gently and slowly to prevent visual physical damage (low damage), and the second group was subjected to a shelling process that visually compromises the kernel pellicle integrity (high damage). Then, walnuts packed in net perforated bags were stored at 35°C (forced storage test) for 0, 3 and 6 weeks for further postharvest quality evaluations. During this warm storage period, we evaluated kernels for visual and colorimeter (L*, Hue) color, ethanol soluble phenolics, oil free fatty acids, and peroxide values. The kernel color changed from ?light? to ?amber? color during storage, as demonstrated by the increase in DFA scores and by the reduction in lightness (L*) and Hue values. Kernel browning incidence was higher on high damage shelled kernels than on low damage shelled kernels and was always higher in ?Howard? than in ?Chandler?. The kernels with visually intact pellicles (low damage) had lower losses of phenolic antioxidants throughout the storage period, suggesting that the pellicle plays a beneficial role in preventing kernel darkening. The pellicle damage also affected walnut oil stability by accelerating triglycerides hydrolysis and lipid peroxidation, increasing oil free acidity. Our results indicate that reducing walnut pellicle damage during shelling delays postharvest kernel browning, improves walnut oil stability, and prevents antioxidant turnover in shelled walnuts. Therefore, pellicle damage should be minimized during shelling and kernels should be immediately protected from oxidation to avoid color darkening and rancidity development during postharvest life.