Determining properties of almond kernel under various moisture content levels

Abstract

Almond fruit are subjected to various mechanical stresses in production from harvest through to processing, storage and packaging. Hulling and shelling operations of almonds consist of continuous compression and shear to break the hull and shell layers and release the kernel. Properties of the kernel play an important role in reducing mechanical damage such as scratches and penetration of shell pieces on the final kernel product. Knowledge of kernel mechanical properties under various fruit conditions can assist to optimise post-harvest and processing lines to minimise kernel damage and maximise final kernel quality. Kernel moisture content is one of the main attributes that affects the kernel response to the mechanical operation. Maintaining the kernel moisture content to optimum level through wetting fruit prior to processing can lead to increase in percentage of undamaged kernel recovery by increasing kernel pliability to mechanical damage. Water added to the structure of kernel acts as plasticiser and helps the kernel absorbing the mechanical loading instead of breaking to pieces. In this study Nano-indentation tests were conducted on almond kernel in different moisture content level. Kernels from 'Nonpareil' cultivar were tested in dry and wetted conditions. Test results showed that kernels with higher moisture content are able to resist larger deformation at a given force value in comparison with dry kernels. Effects of pellicle (kernel skin) on mechanical properties of kernel was studied. The tests showed a peak force value in samples tested with pellicle in comparison with the kernels tested without pellicle.