Investigation on torsional forces and angles at the nut and pedicel junction (NPJ) revealed varying cashew apple (hypocarp) and nut separation efficiency at different developmental stages in cashew

Abstract

Cashew is a highly valued tree nut crop that is widely grown for nourishment and industrial applications. The study of fruit and nut separation forces is a necessary for efficiently detaching the nuts from the swollen pedicel or hypocarp referred to as cashew apple (pseudo fruit). In this study, the torsional/twisting forces (TF) required for separating the nuts from the cashew apples (CA) were analyzed at the nut pedicel junction (NPJ) in different cultivars at different fruit developmental stages [BBCH (BiologischeBundesanstalt, Bundessortenamt und ChemischeIndustrie) stage code: 711, 713, 715, 717, 719, 811, 813, 815, 817, 819] and days after fall to devise strategies for efficient separation of nuts and CAs. The TF and torsional/twisting angle (TA) were measured using a novel strain gauge-based reaction type torque transducer and a customized fixture. The CA firmness (CAF), and CA cavity depth, length, and width at the NPJ were also measured. Significant variations were observed in the TF and the TA at different fruit developmental stages and days after fall (DAF) in the studied cultivars. The TFs increased from 711 to 813 stages and subsequently declined from 813 to 819 stages and with increasing DAF. Further, the TA increased significantly with the development of fruits from 711 to 819 stages and days after fall. The analysis of the relationship between TF and the physical properties of CA showed that CA firmness and CA cavity depth at the NPJ had significant positive correlations. Further, the analysis of the relationship between the TA and the CA properties showed that CA firmness has significantly negative correlations. The findings of this study are valuable for the development of new cashew cultivars with low TF and TA suitable for mechanical separation and the designing of machinery with versatile end-effectors and twisting mechanisms for efficient separation of nuts from CAs.