Exploring the use of natural antimicrobial agents and pulsed electric fields to control spoilage bacteria during a beer production process / Exploración del uso de agentes antimicrobianos naturales y de campos eléctricos pulsantes para el control de bacterias contaminantes durante el proceso de elaboración de cerveza

Different natural antimicrobials affected viability of bacterial contaminants isolated at critical steps during a beer production process. In the presence of 1 mg/ml chitosan and 0.3 mg/ml hops, the viability of Escherichia coli in an all malt barley extract wort could be reduced to 0.7 and 0.1% respectively after 2 hour- incubation at 4 °C. The addition of 0.0002 mg/ml nisin, 0.1 mg/ml chitosan or 0.3 mg/ml hops, selectively inhibited growth of Pediococcus sp. in more than 10,000 times with respect to brewing yeast in a mixed culture. In the presence of 0.1mg ml chitosan in beer, no viable cells of the thermoresistant strain Bacillus megaterium were detected. Nisin, chitosan and hops increased microbiological stability during storage of a local commercial beer inoculated with Lactobacillus plantarum or Pediococcus sp. isolated from wort. Pulsed Electric Field (PEF) (8 kV/cm, 3 pulses) application enhanced antibacterial activity of nisin and hops but not that of chitosan. The results herein obtained suggest that the use of these antimicrobial compounds in isolation or in combination with PEF would be effective to control bacterial contamination during beer production and storage.

Diferentes antimicrobianos naturales disminuyeron la viabilidad de bacterias contaminantes aisladas en etapas críticas del proceso de producción de cerveza. En un extracto de malta, el agregado de 1 mg/ml de quitosano y de 0,3 mg ml de lúpulo permitió reducir la viabilidad de Escherichia coli a 0,7 y 0,1%, respectivamente, al cabo de 2 horas de incubación a 4 °C. El agregado de 0,0002 mg/ml de nisina, 0,1 mg/ml de quitosano o de 0,3 mg/ml de lúpulo inhibió selectivamente (10.000 veces más) el crecimiento de Pediococcus sp. respecto de la levadura de cerveza en un cultivo mixto. El agregado de 0,1 mg/ml de quitosano permitió disminuir la viabilidad de una cepa bacteriana termorresistente, Bacillus megaterium, hasta niveles no detectables. Por otra parte, el agregado de nisina, quitosano y lúpulo aumentó la estabilidad microbiológica durante el almacenamiento de cervezas inoculadas con Lactobacillus plantarum y Pediococcus sp. aislados de mosto de cerveza. La aplicación de campos eléctricos pulsantes (CEP) (3 pulsos de 8kV/cm) aumentó el efecto antimicrobiano de la nisina y del lúpulo, pero no el del quitosano. Los resultados obtenidos indicarían que el uso de antimicrobianos naturales en forma individual o en combinación con CEP puede constituir un procedimiento efectivo para el control de la contaminación bacteriana durante el proceso de elaboración y almacenamiento de la cerveza.

Growth of Pediococcus acidilactici on sugar cane blackstrap molasses

Pediococcus acidilactici (IL01) has grown in MRS (Man, Rogosa and Sharpe) broth modified by substitution of glucose by 2.0(per cent) (MRS-2), 3.0(per cent) (MRS-3), 4.0(per cent) (MRS-4) and 5.0 (per cent) (MRS-5) sugar cane blackstrap molasses. The highest acid production was obtained in MRS-5 broth maintained at a constant pH of 5.0. The higest biomass production was obtained when P. acilactici was grown in MRS-5 broth at initial pH6.5, while productivity was higher in MRS-2 broth (28.16per cent). When the MRS-2broth was utilized at initial pH 6.5 for a 20-hour fermentation period, the highest growth rate (dx/dt) was found in a period of 8 to 16 hours (0.290 g cells/L.h), while the specific growth rate (µ) was 0.175 (h-1) for that period, differently from the 0,441 (h-1) obtained for the period comprising the 4th to the 12th hour. The growth in MRS broth was 5.08(per cent) (2.95g/1) higher than in MRS-2 broth (2.80 g/1). The data obtained have shown that P. acidilactici has had a significant growth in molasses as the main carbon source, and that it is possible to substitute MRS glucose by this carbon source with the purpose of obtaining a more economical growth medium for the potential large scale productions.