Comparative Proteomic Analysis of Walnut (Juglans regia L.) Pellicle Tissues Reveals the Regulation of Nut Quality Attributes

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.

Walnut (Juglans regia L.) Volatile Compounds Indicate Kernel and Oil Oxidation

“…Kernel surface darkness ( Table 1 ) was included in the measured variables not only because it is a quality attribute perceived by consumers, but also its direct relation to the their chemical composition (e.g., phenolics) or moisture content [ 30 ]. Since phenols are mainly found in nut pellicles [ 31 ], their enzymatic or chemical oxidation, proven to be cultivar dependent, can cause browning of the kernels during storage [ 32 ]. All kernels from both cultivars were classified as ‘extra light’ (1 ± 0) for the first 2 weeks of storage.…”

Advances in genomics for diversity studies and trait improvement in temperate fruit and nut crops under changing climatic scenarios

“…A comparative transcriptome analysis among several apple verities exhibited 34 genes regulating the anthocyanin contents which are associated with preferred appearance of apples (El-Sharkawy et al, 2015). Zaini et al (2020) conducted a deep comparative proteomics study in kernel pellicle tissues of two elite walnut cultivars and detected proteins that are concerned with secondary metabolism governing the pigmentation leading to nut qualities. In avocado, an integrated proteomics and metabolomics study indicated the induction of ripening homogeneity through heat treatment that boosts the sugar soluble accumulation, viz., sucrose and galactose and other stress-related enzymes (Gavicho Uarrota et al, 2019).…”

“…A comparative transcriptome analysis among several apple verities exhibited 34 genes regulating the anthocyanin contents which are associated with preferred appearance of apples ( El-Sharkawy et al., 2015 ). Zaini et al. (2020) conducted a deep comparative proteomics study in kernel pellicle tissues of two elite walnut cultivars and detected proteins that are concerned with secondary metabolism governing the pigmentation leading to nut qualities.…”

Postharvest processing of tree nuts: Current status and future prospects—A comprehensive review

“…The peel on the kernel surface, also known as the “seed coat” or “pellicle,” has dark color and usually has high contents of natural antioxidants, such as tannins, phenolics, and flavonoids (Medic et al., 2021; Tsantili et al., 2011; Yan & Zhou, 2021). They protect the kernel from natural oxidations and show good antibacterial activities (Acquaviva et al., 2021; Salcedo et al., 2015; Zaini et al., 2020). However, due to the abundance in antioxidants and fiber, pellicles usually have bitter taste, high chewiness, and low solubility in drinks, which lower the sensory satisfaction and affect the palatability (Li et al., 2020).…”