Graduate Thesis Or Dissertation
 

Preparation of a potato hydrolysate with Bacillus subtilis α-amylase

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  • Bacillus subtilis α-amylase was used to hydrolyze starch from peeled and whole potatoes (Solanum tuberosum). Effect of gelatinization temperature, pH, enzyme concentration, temperature of hydrolysis and presence of calcium ions were investigated. Optimum conditions for hydrolysis were when α-amylase levels were 0.3 percent of the starch concentration in the presence of 400 ppm calcium at pH 7.0 and 80°C for 2 hr. After centrifugation to remove residual material, the supernatants were adjusted to pH 5.0 to 5.5 with 30 percent sulfuric acid and heated at 100°C for 10 min to inactivate α-amylase. Treatment with four percent activated charcoal decolorized the clear hydrolysate before the product was spray dried. The dried product was a light yellow powder, slightly sweet, relatively bland in taste and readily soluble in water. Dried potato hydrolysate made from peeled potatoes had a dextrose equivalent of 30 and contained 85 percent carbohydrates, 8.4 percent protein and 5.5 percent ash; while the hydrolysate from whole potatoes had a dextrose equivalent of 26 and contained 86 percent carbohydrates, 8.4 percent protein and 6.0 percent ash. The composition of the carbohydrates of the two hydrolysates were similar except the hydrolysate from peeled contained a higher concentration of glucose and lower concentration of saccharides with a degree of polymerization greater than four. At concentrations of greater than 40 percent, the potato hydrolysate made from whole potatoes did not show as high a viscosity as commercial corn syrup solids with a dextrose equivalent of 24; the potato hydrolysate adsorbed twice as much moisture as the commercial corn syrup solids at 75 percent relative humidity at 23°C for 30 days. Substitution of sucrose with whole potato hydrolysate in chocolate milk revealed that substitution of two parts of sucrose by two parts of potato hydrolysate could be used with a slight loss of desirability. Fifty and one hundred percent addition of whole potato hydrolysate to a commercial dehydrated vegetable soup mix showed no decrease in the desirability of the product. This work has shown that a useful potato hydrolysate containing significant amounts of protein can be prepared from either peeled or whole potatoes.
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