Textural and microstructural changes associated with post-harvest hardening of trifoliate yam ( Dioscorea dumetorum) pax tubers

Abstract

The textural and microstructural changes associated with the post-harvest hardening phenomenon of Dioscorea dumetorum tubers were studied to determine how texture relates to microstructure during the hardening process. A 2×2×4 factorial experiment with sample treatment, storage conditions and storage time as variables was performed. The tubers were harvested, matured and stored under prevailing tropical ambient conditions (28 °C) and cold room conditions (4 °C) for the study. All the samples were evaluated for their hardness (peak force) and adhesiveness (curve areas). Starch microscopy was done on the freshly harvested tubers, hardened tubers and tubers stored under low temperature conditions (4 °C) during the study. TA.XT2 analyses on the textural properties revealed consistent increases in the hardness and adhesiveness levels, measured during the hardening process of the tubers. Hardness levels increased markedly to significant levels ( P<0.05) in the tubers (from 1208.4 g to 7801.6 g). Similarly, adhesiveness levels increased from 12.5462 to 30.2218 g m in the tubers within 72 h after harvest. Starch microscopy revealed variations in the cell microstructure of the hardened and unhardened tubers. Hardening of D. dumetorum was characterized by thickened cell walls and middle lamella in the cells of the tuber. The hardening varied according tuber treatment and temperature of storage. Several treatments and storage methods were tested and those that limited the contact of the tubers with the external environment were found to slow down the hardening process.