RESUMO

Lactic acid bacteria and more particularly lactobacilli and Leuconostoc, are widely found in a wide variety of traditional fermented foods of tropical countries, made with cereals, tubers, meat or fish. These products represent a source of bacterial diversity that cannot be accurately analysed using classical phenotypic and biochemical tests. In the present work, the identification and the molecular diversity of lactic acid bacteria isolated from cassava sour starch fermentation were assessed by using a combination of complementary molecular methods: Randomly Amplified Polymorphic DNA fingerprinting (RAPD), plasmid profiling, hybridization using rRNA phylogenetic probes and partial 16S rDNA sequencing. The results revealed a large diversity of bacterial species (Lb. manihotivorans, Lb. plantarum, Lb. casei, Lb. hilgardii, Lb. buchneri, Lb. fermentum, Ln. mesenteroides and Pediococcus sp.). However, the most frequently isolated species were Lb. plantarum and Lb. manihotivorans. The RAPD analysis revealed a large molecular diversity between Lb. manihotivorans or Lb. plantarum strains. These results, observed on a rather limited number of samples, reveal that significant bacterial diversity is generated in traditional cassava sour starch fermentations. We propose that the presence of the amylolytic Lb. manihotivorans strains could have a role in sour starch processing.

Assuntos

Microbiologia de Alimentos , Ácido Láctico , Lactobacillus/genética , Manihot/microbiologia , Pediococcus/genética , DNA Ribossômico , Fermentação , Variação Genética , Lactobacillus/classificação , Dados de Sequência Molecular , Pediococcus/classificação , Filogenia , Plasmídeos/genética , RNA Ribossômico 16S , Técnica de Amplificação ao Acaso de DNA Polimórfico , Amido

RESUMO

The microheterogeneous native amylolytic complex secreted by the isolate A6 of Lactobacillus plantarum revealed a selective enzyme specificity loss when submitted to a limited proteolysis under a suboptimum pH condition. A clear electrophoretic profile change toward just one shorter, more acidic, and equally active polypeptide fragment resulted from the pronase E pretreatment. Although the whole enzyme activity remained apparently unaffected for soluble starch, the native parallel activity on intact and non-gelatinized starch granules either from cereals or tubers was dramatically reduced. This phenomenon was more clearly documented by scanning electron microscopy using the easiest accessible native substrate: wheat starch granules. The anion-exchange-purified native enzymes from L. plantarum displayed a different optimum pH curve when compared with the thermotolerant alpha-amylase from Bacillus licheniformis. The alpha-amylases from the lactic-acid-producing A6 isolate presented an electrophoretic profile easily distinguishable from those from B. liqueniformis and B. subtilis species.

Assuntos

Amilases/metabolismo , Lactobacillus/enzimologia , Amido/metabolismo , Amilases/química , Biomassa , Metabolismo dos Carboidratos , Fermentação , Concentração de Íons de Hidrogênio , Isoenzimas/química , Isoenzimas/metabolismo , Cinética , Ácido Láctico/metabolismo , Lactobacillus/crescimento & desenvolvimento , Fragmentos de Peptídeos/metabolismo , Pronase , Amido/ultraestrutura , Triticum

RESUMO

A mathematical model was developed and tested to simulate the generation and transfer of heat in solid substrate fermentation (SSF). The experimental studies were realized in a 1-L static bioreactor packed with cassava wet meal and inoculated with Aspergillus niger. A simplified pseudohomogeneous monodimensional dynamic model was used for the energy balance. Kinetic equations taking into account biomass formation (logistic), sugar consumption (with maintenance), and carbon dioxide formation were used. Model verification was achieved by comparison of calculated and experimental temperatures. Heat transfer was evaluated by the estimation of Biot and Peclet heat dimensionless numbers 5-10 and 2550-2750, respectively. It was shown that conduction through the fermentation fixed bed was the main heat transfer resistance. This model intends to reach a better understanding of transport phenomena in SSF, a fact which could be used to evaluate various alternatives for temperature control of SSF, i.e., changing air flow rates and increasing water content. Dimensionless numbers could be used as scale-up criteria of large fermentors, since in those ratios are described the operating conditions, geometry, and size of the bioreactor. It could lead to improved solid reactor systems. The model can be used as a basis for automatic control of SSF for the production of valuable metabolites in static fermentors.