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Effect of a Cell-Wall-Degrading Enzyme Complex on Starch Recovery and Steeping Requirements of Sorghum and Maize

¹Professor and Department Head, Departamento de Tecnología de Alimentos, Instituto Tecnológico y de Estudios Superiores de Monterrey, Av. Eugenio Garza Sada 2501 Sur, CP 64849, Monterrey, N.L. México. ²Corresponding author. Phone: (81)83284262. Fax: (81)83284322. E-mail: sserna@itesm.mx. ³Graduate student, Centro de Biotecnología. Instituto Tecnológico y de Estudios Superiores de Monterrey, Av. Eugenio Garza Sada 2501 Sur, CP 64849, Monterrey, N.L. México.

The effect of a commercial cell-wall-degrading enzyme (CWDE) complex on the steeping time and starch yields of white regular sorghum (RSOR) compared with yellow maize (YMZ) was determined. An in vitro wet-milling method standardized to test dosages of 0–120 fungal β-glucanase units (FBG)/100 mL indicated that starch yields were significantly higher for YMZ than RSOR and increased proportionally as enzyme dosage increased. A factorial experiment with a level of confidence of P < 0.05 was performed to study the effect of CWDE addition to coarsely ground grains for 4 hr after 20 or 44 hr of SO₂ steeping of whole grains. At both regular steep times, YMZ yielded significantly higher amounts of starch than RSOR. When steep times were compared, grains soaked for 48 hr produced 1.7% higher starch yields than counterparts treated for 24 hr. CWDE significantly increased starch yields and recoveries. Enzyme-treated grains yielded 2.5% more starch than counterparts steeped regularly. For both grains, the best wet-milling conditions to obtain the highest amount of starch were 48 hr of steeping and CWDE addition. Under these conditions, YMZ and RSOR yielded 66.9 and 66.6% starch, respectively. Starches obtained after the enzyme treatment at both steep times contained higher amounts of residual protein and ash compared with the untreated counterparts. Rapid viscoamylograph properties of YMZ and RSOR starches were not affected by the use of the CWDE nor the steep time. In comparison with RSOR starch, the YMZ starch initiated gelatinization at lower temperature, had less shear thinning and higher viscosity or setback at the end of cooling.