Abstract
Walnuts (Juglans regia L.) are a valuable dietary source of polyphenols and lipids, with increasing worldwide consumption. California is a major producer, with ’Chandler’ and ’Tulare’ among the cultivars more widely grown. ’Chandler’ produces kernels with extra light color at a higher frequency than other cultivars, gaining preference by growers and consumers. Here we performed a deep comparative proteome analysis of kernel pellicle tissue from these two valued genotypes at three harvest maturities, detecting a total of 4937 J. regia proteins. Late and early maturity stages were compared for each cultivar, revealing many developmental responses common or specific for each cultivar. Top protein biomarkers for each developmental stage were also selected based on larger fold-change differences and lower variance among replicates, including proteins for biosynthesis of lipids and phenols, defense-related proteins and desiccation stress-related proteins. Comparison between the genotypes also revealed the common and specific protein repertoires, totaling 321 pellicle proteins with differential abundance at harvest stage. The proteomics data provides clues on antioxidant, secondary, and hormonal metabolism that could be involved in the loss of quality in the pellicles during processing for commercialization.
Highlights
Walnuts, the seed of trees from the genus Juglans, are prized among the edible nuts for their unique quality attributes, visual appearance, taste, texture, and nutritional components
When the inner side of the hull reached 100% packing tissue brown” (PTB), walnuts were at maturity 1 (M1); maturity 2 was at the onset of hull split (M2), and at full hull dehiscence, walnuts were at maturity 3 (M3) (Figure 1A)
We studied the maturity stages M1, M2, and M3
Summary
The seed of trees from the genus Juglans, are prized among the edible nuts for their unique quality attributes, visual appearance, taste, texture, and nutritional components. Walnuts have grown in popularity around the globe due in large part to their perceived health benefits [1,2,3,4]. Current research indicates that some of these bioactive compounds present in walnuts could provide cardiovascular and cognitive health-protective benefits [3,4,8,9,10,11]. Demand for walnuts is highest in China, comprising nearly half of all global walnut consumption, followed by Iran, the United States, and Turkey [12]. China is the global leader followed by the United States with the California walnut industry accounting for most domestic production, generating an annual revenue of $1.28 billion and producing 653,000 tons as of 2019 [13,14,15].
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