Valorizing sunflower processing byproducts for a sustainable bioeconomy: Fungal fermentation and characterization of hulls and screens

Background

Sunflower hulls (SFH) and screens (SFS) are byproducts of sunflower seed processing with limited alternative applications. This study investigates the submerged fermentation of SFH and SFS by Aureobasidium pullulans-(Ap), Trichoderma reesei-(Tr), Aspergillus oryzae-(Ao), Neurospora crassa-(Nc), and Aspergillus niger-(An) to alter their chemical composition and enhance nutritional value for their value-added applications such as functional feed ingredients and sources of bioactive phenolics.

Results

Chemical characterization revealed high crude fiber (CF) (>34%) and low crude protein (CP) (<11%) in both the SFH and SFS. During fermentation, pH profiles varied significantly, with An demonstrating substantial acidification. Protein distribution in pellet and supernatant fractions was influenced by substrate composition and fungal strains. After 5 days, Nc and An significantly increased CP in SFH pellets (p < 0.05), while Ao, Tr, Nc, and An increased CP in SFS pellets (p < 0.05). The CF content of SFH reduced significantly post-fermentation, with Ao showing the highest reduction (p < 0.05), whereas SFS remained unchanged. Except for Nc, all fungal strains significantly increased total phenolic content (TPC) in both SFH and SFS after 5 days of fermentation (p < 0.05), correlating with enhanced antioxidant activity. Additionally, Ao, Tr, and An significantly reduced phytic acid in SFS (p < 0.05). Overall, An exhibited the best performance, enhancing CP, TPC, and antioxidant activity while reducing antinutrients like CF and phytic acid levels.

Conclusion

The findings suggest that fungal fermentation effectively modulates the applicability of SFH and SFS as functional feed ingredients and/or sources of bioactive phenolics, thereby providing a sustainable approach to valorize these agricultural byproducts.