Physicochemical Properties of Black Walnut (Juglans nigra L.) in the Western Mid-hills of Nepal

The black walnut (Juglans nigra L.) is an underutilized fruit in the mid-hills of Nepal. However, the physico-chemical properties of Nepalese black walnut are almost unavailable in the literature. Four walnut growing districts namely Baitadi, Dadeldhura, Jumla and East Rukum selected and the black walnut collected at commercial maturity from the local markets. The physical properties were assessed following the IPGRI descriptors, whilst chemical composition by the proximate method across the location. The energy content estimated from the fat, protein and carbohydrate values obtained from the proximate content. The nut weight, kernel weight, nut length, nut diameter were found significantly affected by site, while the effect was similar for the kernel ratio (19-23%). A strong positive correlation (r2 = 0.58) was found between moisture and nut diameter, between moisture and nut weight (r2 = 0.52) and between nut weight and kernel weight (r2 = 0.64). The moisture content, crude protein and total ash content were unaffected by site, whilst the crude fibre, crude fat and soluble carbohydrate content were differed by location of sample collection. The proximate revealed the very best fat or oil content in Dadeldhura district (53.05%), the highest crude fibre in East Rukum district (7.26%), whilst the carbohydrate was found highest in the Jumla (24.69%). The low carbohydrate content in walnut of Dadeldhura might be a hint for the drought tolerance genotype of black walnut. It’s still early to conclude the location effect on black walnut quality without a detailed analysis of environmental and genotypic studies.