Screening of Almond Germplasm for Bioactive-Rich Skin Recovery and Application of Liquid Nitrogen Peeling

Almond skins represent an underexploited by-product of the almond processing chain, despite being a rich source of bioactive compounds with potential applications as a functional food ingredient. However, the Traditional Blanching Peeling (TBP) process, which involves the use of hot water, causes the leaching and degradation of bioactive compounds, reducing the functional value of the recovered skins. In this study, liquid nitrogen peeling (LNP) was investigated as an alternative approach to enhance the recovery of bioactive-rich almond skins. To assess the variability of bioactive compounds in different cultivars, a total of 106 almond genotypes from a germplasm collection were screened for skin yield, total polyphenol content, and antioxidant activity. Principal component analysis (PCA) was applied to select a representative subset of cultivars capturing the variability of the germplasm in terms of bioactive composition and technological traits. The skins obtained using LNP exhibited higher polyphenol content and antioxidant activity compared to those obtained using conventional peeling. Despite variability among samples, in some cultivars such as 'Universo', TPC increased from 570.58 mg GAE/100 g after TBP to 1588.05 mg GAE/100 g after LNP, corresponding to an increase of approximately 178% (p < 0.05). Moreover, in all selected cultivars, kernel color (CIELab*) was not significantly affected by LNP, confirming the preservation of kernel quality. These results highlight the importance of cultivar selection and support LNP as a promising approach for the valorization of almond skins as functional by-products.