Acta Microbiologica Bulgarica

133-140

Authors: Accossato, S., Granata, M., Faè, M., Cella, R., Tosi, S., Picco, A. M.

Rice straw is a cheap and widely available agro-waste biomass that can be used to generate renewable biofuel. However, due to its composition, it is particularly recalcitrant to enzymatic degradation. Here, prior to enzymatic hydrolysis, biological pre-treatment of rice straw for saccharification by solid-state fermentation (SSF) was performed using a new isolate of Trichoderma asperellum called UNIPV1. More specifically, the study aimed to investigate the effect of adding the fungus to rice straw on the temporal activity of secreted enzymes, and reducing sugar formation. As excepted, under long-term solid-state fermentation (SSF), depolymerizing enzymes such as xylanases and exo/endo-cellulases were secreted by Trichoderma asperellum UNIPV1 during its growth. T. asperellum was an excellent producer of cellulolytic enzymes; a significant peak in reducing sugars occurred between 10-20 days. Trichoderma initially showed a high preference for the secretion of xylanases to degrade the linear polysaccharide beta-1,4-xylan into xylose. Afterwards, endoglucanase and exoglucanase enzymes were secreted to complete the hydrolytic activity on the substrate. This result is consistent with the trend of total protein accumulated in the secretome and the fungal metabolic activity measured by CO2 production. Overall, our findings suggest that a short fungal pre-treatment of rice straw might be useful to begin the degradation of cell-wall polymers, and can therefore effectively improve saccharification. That said, further work is required to improve the fungal pre-treatment, since alone does not entirely complete the degradation of lignocellulosic insoluble material.

147-154

Authors: Satchanska, G., Tsenova, M., Sasheva, A.

In this study we describe the assessment of the microbiological quality of 12 commercial pasteurized apple and orange juices. Orange juice is the most widely consumed fruit juice in the world and together with apple juice are an essential part of human diet. Although pasteurization is the preferable method for bacterial elimination, some heat-resistant microorganisms and their spores could survive the heat treatment and cause spoilage hence triggering serious outbreaks. Our study revealed that the microbiological quality of all 12 investigated pasteurized juices (6 apple juices and 6 orange juices) meet the national, European and international standards. The results obtained indicated that the juices were free of aerobic mesophilic bacteria and facultative anaerobes, yeasts, molds or of diarrheagenic E. coli and coliform bacteria described in the standards. No heat-resistant spore-forming bacteria had grown during the enrichment experiment. Based on our results, we can conclude that all tested juices are safe for consumption.