Investigation of Structural and Morphological Alterations and Antinutrient Reduction in Bitter Yam (Dioscorea bulbifera) Induced by Different Processing Techniques

Abstract

Antinutrients in plant foods must be removed or reduced during processing before they can be consumed safely. The study evaluated the effectiveness of various processing methods in reducing antinutrient levels in yam flour. The treatments included soaking for varying durations (4, 8, and 12 h), boiling for different time intervals (5, 15, and 25 min), and autoclaving at 100°C for corresponding durations (5, 15, and 25 min). Post-treatment, the yam slices were dehydrated in a hot air oven at 50°C for 10 h and then milled into flour. The study quantitatively assessed the reduction in phytate, oxalate, tannin, saponin, trypsin, and α-amylase inhibitors. The findings demonstrated reduction ranges of 15%–35%, 20%–45%, 50%–82%, 16%–43%, 11%–78%, and 16%–51% across the different pretreatment methods. Additionally, the study investigated the effects of these pretreatments on antioxidant activity, structural modifications (via XRD and FTIR analyses), morphological changes, and thermal properties. A statistically significant impact (p ≤ 0.05) was observed on total phenolics, flavonoids, and antioxidant levels. The crystallinity index and granule particle size varied between 9.82% and 9.61% and 10–140 μm, respectively. Notably, boiling for 25 min emerged as the most efficacious pretreatment for antinutrient reduction, though it also induced considerable alterations in granule size and morphology, as evidenced by SEM micrographs. However, it may be proposed that a combination of boiling followed by soaking could be explored for potentially improved results and warrant further investigation.