Antioxidant potential of caramel derived from optimized sugar syrup of pineapple plant stem

This study investigates the development and characterisation of antioxidant-rich caramels produced from two distinct sugar syrup streams derived from pineapple (Ananas comosus) plant stem: (i) starch hydrolysate and (ii) whole-stem lignocellulosic hydrolysate. As a significant agricultural by-product, the pineapple stem represents an abundant and underutilized biomass resource. Enzymatic saccharification of both fractions was optimized via Response Surface Methodology (RSM) to maximize reducing sugar yield without requiring pretreatment. The highest sugar yield (135.87 ± 0.57 g/L) was obtained under optimized conditions: 8.52% (w/v) substrate concentration, 1.28% (v/v) enzyme concentration (1:1 ratio of Dextrozyme to Celluclast 1.5 L), 59.05 h incubation, and 59.2 °C. Thermal processing of the resulting hydrolysates yielded caramels with significantly disparate physicochemical and functional profiles. Starch-based caramel exhibited higher total soluble solids (up to 71 °Brix), smoother texture, and lighter colour, whereas whole-stem caramel showed increased viscosity and darker colour intensity. Colorimetric analysis tracked a significant browning progression, with lightness L* values decreasing significantly to ~ 24 in both substrates, while whole-stem samples displayed a more complex chromatic profile a* and b* indices) attributed to their richer composition. Antioxidant activity increased with heating duration, with whole-stem caramel achieving a maximum FRAP value of 158 µmol TE/g and DPPH radical scavenging activity of 35%. GC–MS profiling identified a variety of aroma active and bioactive compounds including furans, phenolics, and fatty acid esters, with whole-stem caramel possessing a richer and more complex volatile profile than starch-based caramel. These results demonstrate the potential of pineapple stem waste as a sustainable feedstock for the production of antioxidant-enriched caramel. The integration of enzymatic hydrolysis and thermal processing offers a promising strategy for developing value-added, functional ingredients aligned with circular bioeconomy principles.

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