Variety and Processing Effects on the Structure–Function Properties of Upcycled Durian Seed Flours

Durian (Durio zibethinus Murray) seeds, an underutilized by-product of durian processing, were upcycled into functional flours to elucidate how varietal origin and processing govern structure–function relationships. Durian seed flours from local Bang Nara (L) and Monthong (M) varieties were prepared using three methods: native durian seed flour (NDSF; control), boiled durian seed flour (BDSF), and hydrated durian seed flour (HDSF), and benchmarked against commercial mung bean flour (MBF) and almond flour (ALF). Proximate composition, total phenolic content (TPC) and DPPH•- scavenging activity, structural characteristics (Fourier transform infrared, FTIR; X-ray diffraction, XRD), thermal behavior, and microstructure were assessed alongside functional properties including water/oil absorption, emulsion performance, and gelation. M flours contained higher protein (8.46–10.73%), dietary fiber (6.26–9.37%), ash (3.59–4.38%), TPC (53.17–87.40 mg gallic acid equivalent/g), and DPPH•- scavenging activity (92.39–94.54%) than L flours, whereas L flours had higher carbohydrate content (78.87–82.54%) than M flours (68.32–72.21%). Crude fat remained below 1% across all samples. FTIR and XRD profiles were comparable to MBF, confirming starch-based similarities, but distinct differences in color, bulk density, crystallinity, gelatinization behavior, and granule morphology reflected processing-driven structural modification. Functionally, NDSF exhibited the highest water absorption capacity (4.28 g/g); all durian seed flours showed low oil absorption (0.58–0.88 g/g) and gelation at 10–12%. Most samples demonstrated good emulsion activity and stability, except HDSF. Overall, NDSF and BDSF provided the best balance of yield, hydration capacity, and structural stability, demonstrating that both variety and processing determine the performance of upcycled durian seed flours. These findings support the valorization of durian seeds as sustainable, value-added functional ingredients aligned with circular economy and zero-waste food processing.