EVALUACIÓN DE LA ACTIVIDAD AMILOLÍTICA Y PRODUCCIÓN DE ÁCIDO GLUCÓNICO DE Aureobasidium pullulans EN CULTIVOS POR LOTE Y SEMILOTE UTILIZANDO ALMIDÓN EXTRAÍDO DE CEBADA MALTERA DE BAJA CALIDAD

Abstract

Although, there is one market for all malt Barley produced in Mexico, some portion of it is rejected because did not fulfill the grain quality requirements established by for malt production industry. Hence, local farmers stored the grains for several months or barley grain is sold as cattle food. This low quality grain could be useful as a low cost raw material for production of value added products due to its starch content. Aureobasidium pullulans is fungus yeast like that has been recognized as important industrial yeast that produces amylolytic enzymes and gluconic acid. The goal of this study was to evaluate gluconic acid production and amylolytic activities using starch extracted from low quality Barley grain from Hidalgo State, Mexico. In this study, it was established a methodology to extract barley starch, the yield obtained was 31.8% on dry mass basis. This barley starch were used to formulate solid and liquid media culture with different carbon:nitrogen ratio. The strains A. pullulans ATCC15233 and CDBB-L1345 were evaluated. The strain ATCC15233 showed a faster growth in solid media at C:N ratio of eight. The experiments conducted in reactor with 5-liters were focused in gluconic acid production, but maximum acid concentration was 3.5 g/l in media formulated with barley starch and C:N of 500. However, it was noticed the hydrolytic capacity of A. pullulans to barley starch due to the accumulation of reduced sugars as well as residual glucose determined in fermentations. Maximum enzymatic activities determined in batch cultures at reactor level were glucoamylases, 291 U/ml; α-glucosidases, 7.6 U/ml; β-glucosidases, 1.7 y α-amylases, 10.8 U/ml. For semibatch culture the activities were glucoamylases, 260 U/ml; α-glucosidasas, 2.6 U/ml y β-glucosidasas, 0.38 U/ml. Also, it were determined the glucoamylase activities by cell free supernatants on gelatinized and ungelatinized barley starch. These enzymes are important for efficient hydrolysis of starch. These results demonstrate that starch extracted from low quality barley grain could be useful as an economic raw material to produce value added products like amylolytic enzymes that have industrial interest applications.