Effects of different preservative treatments on the chemical changes of pounded white yam (Dioscorea rotundata) in storage at 28±2°C

The effects of different preservative treatments on the chemical changes of pounded white yam (Dioscorea rotundata) upon storage were investigated. Preservative treatments adopted include steaming at 100°C for 30 min, addition of 0.1% sodium benzoate, treating with 0.1% sodium benzoate plus heating at 85°C for 30 min and finally the samples at room temperature (28±2°C). Changes occurred in the chemical composition of stored untreated pounded yam samples with the product becoming staled. The pH value (6.00), total solids content (30.88%) and crude protein content (5.56%) of fresh untreated samples initially increased before decreasing to 4.80, 25.60% and 5.50%, respectively, after storage for 8 days. Titratable acidity, moisture content and reducing sugars content of fresh samples initially decreased but subsequently increased. Extractable fat, crude fibre and ash contents continually increased from 1.25, 1.20 and 1.90% to 4.10, 2.90 and 8.60% respectively. The rate of change in chemical properties/composition of treated pounded yam samples was affected by the preservation method adopted and time of storage. Samples treated with 0.1% sodium benzoate plus heating at 85°C for 30 min had stable chemical compositions over 8-day periods of storage and possibly longer.