Submitted to: Bioresource Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/26/2007
Publication Date: 5/8/2008
Citation: Ledbetter, C.A. 2008. Shell Cracking Strength in Almond (Prunus dulcis [Mill.] D.A. Webb.)and its implication in uses as a value-added product. Bioresource Technology. 99(13): 5567-5573.
Interpretive Summary: In the past, abundant agricultural by-products such as almond shells were disposed of with little thought of the potential value-added products that might be available. But diminishing profit margins have forced agricultural producers to examine more carefully the large volume agricultural by-products as revenue sources. We evaluated the shell cracking strength of eight diverse almond varieties, and examined the relationship between shell strength and kernel percentage. In general there was a strong relationship between shell strength and kernel percentage, with stronger shelled almonds being those having a lower kernel percentage (higher shell percentage). But we also found that among these almond varieties, there were cases where the varieties did not differ in kernel percentage, but did differ a great deal in shell strength. This indicated chemical differences in the shell composition, and demonstrated the non-homogeneous nature of almond shell materials. The significance of this work is in demonstrating varietal variability in almond shells. This fact is an important first step in determining which specific variety’s shells are best suited to the many new industrial processes utilizing agricultural by-products.
Technical Abstract: Researchers are currently developing new uses for almond shells, an abundant agricultural by-product. While almond varieties are classified by processing facilities as being either hard or soft shelled, shell morphological characteristics and compositional components contribute to the variability present within each of these broad classes. Eight diverse almond accessions were evaluated in two consecutive harvest seasons for nut and kernel weight, kernel percentage (crackout) and shell cracking strength. Harvest year by almond accession interactions were highly significant (p<0.01) for each of the analyzed variables. Significant (p<0.01) correlations were noted for average nut weight with kernel weight, crackout and shell cracking strength. A significant (p<0.01) negative correlation for shell cracking strength with crackout was noted. In some cases shell cracking strength was independent of the almond accession’s crackout value which suggests that either variety compositional differences or shell morphology affect the shell cracking strength. The varietal characterization of almond shell materials will assist in determining the best value-added uses for this abundant agricultural by-product.