Physicochemical and bioactive properties of edible films developed from repeatedly autoclaved–cooled purple yam (Dioscorea alata L.) starch

This study aimed to analyze the effect of purple yam (Dioscorea alata L.) starch modification through repeated autoclaving–cooling cycles and different starch concentrations on the characteristics of edible films, as well as to determine the best treatment combination. A factorial Completely Randomized Design (CRD) was applied with two factors, namely starch modification (native, one cycle, and two cycles) and starch concentration (5%, 6%, and 7%), with three replications, resulting in 27 experimental units. The native purple yam starch extraction yield was 48.98%, while the percentage of starch mass retained after modification was 90.13% after one autoclaving–cooling cycle and 98.16% after two cycles. Starch pH increased from 5.80 to 6.81–6.89, while water content varied from 8.72 ± 0.87% in native starch to 7.51 ± 0.16% after one cycle and 8.75 ± 0.30% after two cycles. Crude fiber content increased from 5.22 ± 0.01% to 6.56 ± 0.01%. SEM analysis revealed progressive granule disruption, producing edible films with denser, more homogeneous, and crack-free structures. Starch color parameters indicated decreased lightness (L*) from 67.49 to 65.59, increased a* from 5.95 to 6.39, and increased b* from 13.20 to 14.35. In contrast, edible film color varied with L* values of 71.96–77.47, a* values of 3.56–5.17, and b* values of 14.78–18.91, influenced by the interaction between starch concentration and modification cycles. Anthocyanin content increased from 3.17 to 5.82–5.86 mg C3G/g dry starch in starch and from 8.07 to 11.10–11.12 mg C3G/g dry film in edible films. The functional properties of the edible films showed stable thickness (0.20–0.24 mm), variable transparency and solubility, reduced water vapor transmission rate (WVTR) to 3.69 g/m²/h, and increased compression force. In addition, crude fiber content in edible films increased up to 4.70%, with relatively stable pH values ranging from 5.72 to 6.17. Overall, repeated autoclaving–cooling modification of purple yam starch improved several physicochemical, barrier, mechanical, and anthocyanin-related properties of the edible films. The increased anthocyanin content indicates the potential of the films for bioactive and intelligent packaging applications; however, antioxidant activity, pH-response behavior, food freshness monitoring, migration, and storage stability were not experimentally evaluated in the present study. Overall, repeated autoclaving–cooling modification of purple yam starch improved several physicochemical, barrier, mechanical, and anthocyanin-related properties of the edible films. The increased anthocyanin content indicates the potential of the films for bioactive and intelligent packaging applications; however, antioxidant activity, pH-response behavior, food freshness monitoring, migration, and storage stability were not experimentally evaluated in the present study.