title: Effect of thermostable α-amylase injection on mechanical and physiochemical properties for saccharification of extruded corn starch.
abstract: BACKGROUND
  In industry, a jet cooker is used to gelatinize starch by mixing the starch slurry with steam under pressure at 100-175 °C. A higher degree of starch hydrolysis in an extruder is possible with glucoamylase. Unfortunately, it is difficult to carry out liquefaction and saccharification in parallel, because the temperature of gelatinization will be too high and will inactivate glucoamylase. Since the temperature for liquefaction and saccharification is different, it is hard to change the temperature from high (required for liquefaction) to low (required for saccharification). The industrial gelatinization process is usually carried out with 30-35% (w/w) dry solids starch slurry. Conventional jet cookers cannot be used any more at high substrate concentrations owing to higher viscosity. In this study, therefore, corn starch was extruded at different melt temperatures to overcome these limitations and to produce the highest enzyme-accessible starch extrudates.
  
  
  RESULTS
  Significant effects on physical properties (water solubility index, water absorption index and color) and chemical properties (reducing sugar and % increase in reducing sugar after saccharification) were achieved by addition of thermostable α-amylase at melt temperatures of 115 and 135 °C. However, there was no significant effect on % increase in reducing sugar of extruded corn starch at 95 °C.
  
  
  CONCLUSIONS
  The results show the great potential of extrusion with thermostable α-amylase injection at 115 and 135 °C as an effective pretreatment for breaking down starch granules, because of the significant increase (P < 0.05) in % reducing sugar and enzyme-accessible extrudates for saccharification yield.
authors.affiliation: Department of Food Science and Technology, Kongju National University, Yesan, Choongnam, 340-802, Korea.
authors.forename: Lin
authors.initials: L
authors.lastname: Myat
authors.forename: Gi-Hyung
authors.initials: GH
authors.lastname: Ryu
mesh_terms: D001230:Aspergillus / Q000201:enzymology; D001407:Bacillus / Q000201:enzymology; D050260:Carbohydrate Metabolism; D003116:Color; D005782:Gels; D005087:Glucan 1,4-alpha-Glucosidase / Q000378:metabolism*; D006868:Hydrolysis; D012995:Solubility; D013213:Starch / Q000737:chemistry* / Q000378:metabolism; D013696:Temperature; D014783:Viscosity; D014867:Water; D003313:Zea mays / Q000737:chemistry*; D000516:alpha-Amylases / Q000378:metabolism*
chemical_list: D005782:Gels; D014867:Water; D013213:Starch; D000516:alpha-Amylases; D005087:Glucan 1,4-alpha-Glucosidase
keywords: corn starch; extrusion process; saccharification; thermostable α-amylase