Valorization Of Almond Hull: Enhancing Functional Properties And Bioavailability As A Value-Added Food Ingredient

Abstract

The almond hull, a principal byproduct from almond trees, rich in dietary fibers and bioactive compounds, holds significant importance in global nut tree production. This dissertation research addresses the urgent need for innovative strategies to enhance the value of almond hull remnants, aiming for improved economic returns and environmental sustainability. The primary objective is to convert almond hulls into ingredients for food and nutraceutical products using non-thermal technology.High-Pressure Homogenization (HPH) was used as a non-thermal method to enhance physiochemical and functional properties of almond hull and orange pulp/peel fiber powders. It was found that the HPH treatment reduced the mean particle size and created a porous structure of the almond hull powders after lyophilization (freeze drying); hence, a significant increase (p < 0.05) in water holding capacity and oil holding capacity after processing, resulted in a much-improved emulsifying capability. Similar improvements are observed in orange-pulp and peel dispersions, indicating enhanced stability with extended storage time, all samples showed significant decreases in particle size and increases in ζ-potential (P < 0.05), and could maintain higher stability with extended storage time. Furthermore, Confocal Laser Scanning Microscopy (CLSM) also revealed that emulsion destabilization occurred with increased storage time due to oil-droplet aggregation and coalescence. Additionally, based on their physical properties, the chosen variety (Carmel/Monterey) of almond hull extracts produced using the HPH process, showed the highest (1,1-diphenyl-2-picrylhydrazyl [DPPH]) radical-scavenging capacity (119.11 ± 5.27 mg TE/g dw) and ferric reducing power (167.52 ± 10.55 mg TE/g dw, under 22,000 psi = 152 MPa), along with the highest total flavonoid content (as 107.36 ± 3.76 mg QE/g dw). Application of HPH during extraction enhances functionality, bioavailability, and antioxidant activities of almond hull extracts, suggesting waste reduction and increased value in agricultural byproducts. Almond hulls, abundant in flavonoids and phenolic acids, demonstrate potent antioxidant activity. Extracts by mixture of ethanol and water from almond hull powders shows higher levels of free phenolic content and total flavonoids, along with superior ABTS radical scavenging ability and ferric reducing antioxidant power, show potential absorption in the small intestine. UPLC-MS analysis identifies 11 phenolic compounds, showcasing significant antioxidant activity. Phenolic-rich almond hulls mitigate oxidative stress in Caco-2 cells, restoring redox balance and potentially enhancing health benefits. The study combining both in vitro and in vivo methods confirms the bioaccessibility and bioavailability of almond hull polyphenols in humans, positioning them as natural antioxidants. Moreover, an acute oral toxicity study on rodents affirms the non-toxic nature of almond hull powders, supporting their safe consumption as edible food ingredients. In conclusion, this research illuminates the potential of almond hulls as a valuable resource, providing a comprehensive exploration of their physicochemical properties, bioavailability, and safety aspects. The findings encourage further research into incorporating almond hulls into various food matrices, promoting their role in sustainable and functional food development.