RESUMEN
Glucose isomerase (GI) is used in vitro to convert d-glucose to d-fructose, which is capable of commercial producing high fructose corn syrup (HFCS). To manufacture HFCS at elevated temperature and reduce the cost of enriching syrups, novel refractory GIs from Thermoanaerobacterium xylanolyticum (TxGI), Thermus oshimai (ToGI), Geobacillus thermocatenulatus (GtGI) and Thermoanaerobacter siderophilus (TsGI) were screened via genome mining approach. The enzymatic characteristics research showed that ToGI had higher catalytic efficiency and superior thermostability toward d-glucose among the screened GIs. Its optimum temperature reached 95°C and could retain more than 80% of initial activity in the presence of 20mM Mn2+ at 85°C for 48h. The Km and kcat/Km values for ToGI were 81.46mM and 21.77min-1mM-1, respectively. Furthermore, the maximum conversion yield of 400g/L d-glucose to d-fructose at 85°C was 52.16%. Considering its excellent high thermostability and ameliorable application performance, ToGI might be promising for realization of future industrial production of HFCS at elevated temperature.
Asunto(s)
Isomerasas Aldosa-Cetosa/metabolismo , Proteínas Bacterianas/metabolismo , Jarabe de Maíz Alto en Fructosa/aislamiento & purificación , Thermus/enzimología , Isomerasas Aldosa-Cetosa/genética , Secuencia de Aminoácidos , Proteínas Bacterianas/genética , Biotecnología , Estabilidad de Enzimas , Tecnología de Alimentos , Fructosa/biosíntesis , Geobacillus/enzimología , Geobacillus/genética , Glucosa/metabolismo , Calor , Concentración de Iones de Hidrógeno , Microbiología Industrial , Cinética , Proteínas Recombinantes/genética , Proteínas Recombinantes/metabolismo , Homología de Secuencia de Aminoácido , Thermoanaerobacter/enzimología , Thermoanaerobacter/genética , Thermoanaerobacterium/enzimología , Thermoanaerobacterium/genética , Thermus/genéticaRESUMEN
The effects of AFEX™ pretreatment, feedstock moisture content (5,10, and 15 % wb), particle size (screen sizes of 2, 4, and 8 mm), and extrusion temperature (75, 100, and 125 °C) on pellet bulk density, pellet hardness, and sugar recovery from corn stover, prairie cord grass, and switchgrass were investigated. Pellets were produced from untreated and AFEX™ pretreated feedstocks using a laboratory-scale extruder. AFEX™ pretreatment increased subsequent pellet bulk density from 453.0 to 650.6 kg m(-3) for corn stover from 463.2 to 680.1 kg m(-3) for prairie cord grass, and from 433.9 to 627.7 kg m(-3) for switchgrass. Maximum pellet hardness of 2342.8, 2424.3, and 1298.6 N was recorded for AFEX™ pretreated corn stover, prairie cord grass, and switchgrass, respectively. Glucose yields of AFEX™ corn stover pellets, prairie cord grass, and switchgrass pellets varied from 88.9 to 94.9 %, 90.1 to 94.9 %, and 87.0 to 92.9 %, respectively. Glucose and xylose yields of AFEX™ pellets were not affected by the extruder barrel temperature and the hammer mill screen size. The results obtained showed that low temperature and large particle size during the extrusion pelleting process can be employed for AFEX™-treated biomass without compromising sugar yields.