Upcycling Jackfruit Seeds as a Sustainable Malt Substitute for Beer Fermentation: Impacts on Physicochemical Quality and Volatile Profile

Jackfruit seeds (JFSs) are an underutilized agro-industrial by-product with considerable nutritional and functional potential for sustainable food fermentation. This study evaluated the feasibility of using jackfruit seed flour as a partial malt substitute in beer brewing at replacement levels of 0%, 25%, 50%, and 75% (w/w). Fresh jackfruit seeds were processed into flour, gelatinized, and mashed with pale ale malt in the presence of α-amylase before fermentation with Saccharomyces cerevisiae, Lutra kveik ale yeast. The physicochemical properties of the raw materials, starch hydrolysis during mashing, beer quality attributes, and volatile aroma compounds were investigated. Compared with pale ale malt, JFS contained higher crude protein (13.22%), total phenolic content (476.66 mg GAE/100 g), and antioxidant activity. HPLC-IR analysis demonstrated the formation of fermentable sugars during mashing, although starch conversion from JFS remained incomplete at higher substitution levels. Increasing JFS substitution significantly enhanced beer foamability (up to 142.22%) and foam stability (112.84 s), which was attributed to the higher protein content of the seeds. However, beers containing higher proportions of JFS exhibited darker color and increased turbidity, reaching 680 NTU at 75% substitution. HS-SPME-GC-MS analysis revealed changes in alcohols, esters, and ketones with increasing JFS substitution. These findings demonstrate that jackfruit seed flour can serve as a sustainable malt adjunct for beer production, improving selected quality attributes while valorizing agricultural by-products. The study highlights the potential of jackfruit seeds as a functional brewing ingredient that supports the development of sustainable and next-generation fermented beverages.