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Effect of Steaming Method and Time on the Physical and Chemical Properties of Flour from Yam Tubers
Abstract
Raw and pre-gelatinized flour samples were produced from four yam species, which were D. dumetorum, D. alata, D. rotundata and D. cayenensis. Pre-gelatinization was done by steaming diced yam cubes in autoclave (68,950 Nm-2) for 5 min and in Barlet steamer (100±5oC)
for 10, 20 and 30 min. Raw and pre-gelatinized flour samples were analyzed for colour, bulk density, starch, sugar and oxalate contents. Results showed that the properties of the flours were affected by both species and steaming time. Increase in steaming time in Barlet steamer
increased the intensity of dark colouration in pregelatinized samples. Pre-gelatinized flour samples from all the species had significantly (p<0.05) higher values for bulk density than their corresponding raw flour samples. Values also increased with increase in steaming time in
Barlet steamed samples, but values from autoclaved samples were higher than those that were steamed for 30 min. While there was a significant (p<0.05) decrease in the starch content of flour samples with increase in steaming time, sugar content of the flour samples followed the opposite trend. Oxalate content was highest in raw
flour samples but with least value of 5.14 mg/100 g in D. dumetorum. Values obtained in autoclaved samples were closer to those obtained in samples that were steamed in Barlet steamer for 20 min than others for most parameters that were measured. Steaming for 10 min in Barlet
steamer could be appropriate since increase in steaming time produced darker products with reduced starch content.
for 10, 20 and 30 min. Raw and pre-gelatinized flour samples were analyzed for colour, bulk density, starch, sugar and oxalate contents. Results showed that the properties of the flours were affected by both species and steaming time. Increase in steaming time in Barlet steamer
increased the intensity of dark colouration in pregelatinized samples. Pre-gelatinized flour samples from all the species had significantly (p<0.05) higher values for bulk density than their corresponding raw flour samples. Values also increased with increase in steaming time in
Barlet steamed samples, but values from autoclaved samples were higher than those that were steamed for 30 min. While there was a significant (p<0.05) decrease in the starch content of flour samples with increase in steaming time, sugar content of the flour samples followed the opposite trend. Oxalate content was highest in raw
flour samples but with least value of 5.14 mg/100 g in D. dumetorum. Values obtained in autoclaved samples were closer to those obtained in samples that were steamed in Barlet steamer for 20 min than others for most parameters that were measured. Steaming for 10 min in Barlet
steamer could be appropriate since increase in steaming time produced darker products with reduced starch content.
