Variability of almond shell mechanical strength
Shell hardness is usually grouped in classes, from very hard to paper-shell, depending on the shelling proportion. In addition, some cultivars present a very low cracking efficiency - below 30% - due to the so-called double shell characteristic. This consists on the easy breakage of the outer shell without breaking the inner shell. The genetic variability of shell mechanical strength was tested in the progeny of 'R1000' × 'Desmayo Largueta' from CEBAS-CSIC in Murcia (Spain). Physical traits studied were: kernel %, outer shell strength, flexibility and required energy to breakage (compression test using an INSTRON texture analyzer), total shell thickness, inner shell and outer shell thickness, number of inner vascular bundles and their diameter, shell section surface and perimeter and shell mineral content. Results show that outer shell strength is a continuous variable presenting significant differences between almond cultivars. Total strength ranges from 62-942 N and it is correlated with kernel percentage (r=-0.78), outer shell thickness (r=0.62) and mineral content (r=-0.56). Shell flexibility is correlated to the vascular bundles structure as it is the bundle diameter (r=0.49) and the empty cavity (r=0.35). Significant differences in the shell structure were pointed out among almond cultivars.
Romero, A., Dicenta, F., Miarnau, X., Batlle, I. and Chamakh, M. (2018). Variability of almond shell mechanical strength. Acta Hortic. 1219, 45-50
double shell, texture analysis, shell structure