148 CEREAL CHEMISTRY Effect of a Cell-Wall-Degrading Enzyme Complex on Starch Recovery and Steeping Requirements of Sorghum and Maize Sergio O. Serna-Saldívar 1,2 and Martha Mezo-Villanueva 3 ABSTRACT Cereal Chem. 80(2):148–153 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 - glucanase units (FBG)/100 mL indicated that starch yields were signi- ficantly higher for YMZ than RSOR and increased proportionally as enzyme dosage increased. A factorial experiment with a level of con- fidence 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 SO 2 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 counter- parts 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 pro- tein and ash compared with the untreated counterparts. Rapid visco- amylograph 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. One of the main industrial uses of maize is for starch pro- duction. The wet-milling industry has grown because starch is bio- enzymatically converted into high-fructose corn syrups (HFCS) and others used in soft drinks. Since the 40s, sorghum has been seen as a possible alternative to maize for starch (Watson et al 1951, 1955; Watson and Hirata 1955). Sorghum presents several dis- advantages for wet milling such as the presence of peripheral endosperm which acts as a barrier against the penetration of the steep solution, a harder protein matrix and cross-linking which engulfs starch granules, thus lowering yields and starch quality. The leaching of phenolic pigments present in the pericarp, testa, and aleurone tissues produce off-colored starch (Rooney and Serna Saldivar 2000). Several researchers have found that sorghum generally yields  10% less prime starch than maize (Watson et al 1951, 1955; Norris and Rooney 1970; Watson 1984; Caransa and Bakker 1987). Once separated, sorghum starch can be used inter- changeably with maize starch because both starches have almost identical viscoamylograph characteristics (Watson 1984; Moheno- Perez et al 1999). In Mexico, sorghum is second to maize in terms of area planted and production, with an estimated production in 2001 of 5.5 million MT (FAO http//apps.fao.org/). Currently, the relative international cost of sorghum is  90% the price of maize. However, in Mexico, the differential has been higher because sorghum is used as animal feed, whereas maize is channeled directly for human foods. In 2001, the domestic cost of maize was  20% higher than sorghum (Secre- taría de Agricultura, Ganadería, Desarrollo Rural, Pesca y Alimen- tación Centro de Estadística Agropecuaria. www.sagar.gob.mx). To fulfill demands for maize, during 2001 Mexico imported 5.54 million MT, mainly from the United States, with an estimated value of 0.5 billion dollars. Therefore, the utilization of sorghum starch and syrup production can lower maize importation and production costs. Pioneer research performed by Watson and Hirata (1955) and Watson et al (1955), in which sorghum was wet-milled in a manner similar to that of maize, the authors stated that the major difference is the difficulty of separating sorghum starch and gluten. In addition, sorghum pericarp is more fragile than the maize pericarp, thus small pericarp particles impede the clear separation of the starch and protein and give the starch an off-color. Norris and Rooney (1970) studied the wet-milling properties of sorghum and found that the genotype influenced starch recoveries and quality. Peripheral endosperm content was significantly positively correlated with protein content of the starch and negatively related to starch yield and recovery. Steinke and Johnson (1991), Steinke et al (1991), and Johnston and Singh (2001) demonstrated that the use of proteolytic and cell-wall-degrading enzymes (CWDE) during wet-milling of maize significantly lowered SO 2 steeping require- ments while maintaining similar starch yields. Recently, Johnston and Singh (2001) effectively used proteases to reduce steep time and SO 2 requirements in a two-stage wet-milling process. Wang et al (2000) tested a multiple enzyme cocktail with pectolytic, cellu- lolytic, hemicellulolytic, and proteolytic activities for wet-milling of sorghum and found that the enzymes slightly increased starch yield and produced a more refined starch when compared with grains steeped with SO 2 . However, the best wet-milling conditions were achieved with the use of SO 2 and lactic acid. In a previous experiment, Moheno-Perez et al (1999) found that maize yielded amounts of starch similar to that of waxy sorghum, and both grains produced higher amounts of starch than regular or heterowaxy sorghums. The addition of a fiber-degrading-enzyme complex to whole grains did not improve the wet-milling process, with the exception of regular sorghum, where the CWDE reduced steep time while producing the same starch recovery. The objectives of this experiment were to compare yields, com- position, and viscoamylograph properties of starches extracted from regular sorghum (RSOR) with regular yellow maize (YMZ) and to determine whether the addition of commercial CWDE to coarsely ground grains increased starch yields or decreased steep time. MATERIALS AND METHODS Grain Utilized A commercial YMZ with a relatively soft endosperm was used as the control treatment. The experimental white RSOR (ATX 631*TX436), classed as Type 1, had an intermediate endosperm texture and regular endosperm. Grains were tested for test weight, 1,000 kernel weight (TKW) and density. Test weight (kg/hL) was measured with a Winchester bushel meter (Seedburo Equipment, 1 Professor 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. 2 Corresponding author. Phone: (81)83284262. Fax: (81)83284322. E-mail: sserna@itesm.mx. 3 Graduate student, Centro de Biotecnología. Instituto Tecnológico y de Estudios Superiores de Monterrey, Av. Eugenio Garza Sada 2501 Sur, CP 64849, Mon- terrey, N.L. México. Publication no. C-2003-0211-02R. © 2003 American Association of Cereal Chemists, Inc.