Quality of Dioscorea persimilis Tubers Harvested at different Stages

  Objective   Tuber quality of Dioscorea persimilis at different times of harvesting were compared.

  Method  Tubers from a local Ninghua variety of D. persimilis were collected in 9 batches from October 20 to May 5 in the following year. Quality indicators including drying rate, protein, starch, amino acid, soluble sugar, sucrose, crude polysaccharide, allantoin, and total phenol of the tubers were determined. Multiple comparison and correlation analysis were performed on the data for analysis.

  Result  On October 20 when biomass accumulation in tubers is normally near completion in a year, the contents of soluble sugar, sucrose, and crude polysaccharide reached their high levels, that were up to 5.69%, 5.29%, and 2.73%, respectively. The harvested tubers at the time generally taste better, but the total phenol content tends to be high, which make them more suitable for fresh consumption. Whereas, the tubers harvested around December 5 as the stems and leaves largely withered and those picked from March 15, at which time the tuber dormancy had terminated, till April 10, when germination already began, had a drying rate of 33.84%-35.50% along with the contents of starch, protein, allantoin, total amino acids, essential amino acids, and flavor amino acids up to 73.14%-78.12%, 6.33%-6.51%, 3.95-4.29 mg·g⁻¹, 48.5-50.8 mg·g⁻¹, 15.0-15.5 mg·g⁻¹, and 18.9-20.2 mg·g⁻¹, respectively. The polysaccharides in the tubers harvested between March 15 and April 10 were more than 2.92%. The compositional change led to a more desirable eating quality of the tubers harvested during those two periods. In addition, the change also reduced the rate of tuber breakage at and after harvest. In contrast, tube harvesting on around November 10 and from the end of December to the following March would result in an increase on the drying rate to above 36% making the tubers break more easily after picking that rendered them fit only for further processing. In between April 10 and May 5, when new shoots started to appear, nutritional quality and appearance became less desirable, and the total phenol content rose to a high level on the tubers, the planting of following crop was disrupted and tuber-harvesting was deemed improper.

  Conclusion   Depending upon market demand for fresh consumption or need for further processing, D. persimilis tubers could be harvested from the time the biomass accumulation was completed till the beginning of new shoot germination. However, when tuber yield, breakage, post-harvest browning, appearance, nutritional quality, and new crop planting of D. persimilis are taken into consideration, the optimum harvest time would fall in the periods between when the stems and leaves wither on the plants and as the tuber dormancy ends before new shoots start to emerge in the following year.