Studies on Akamu, a traditional fermented maize food / Estudios en Akamu, una comida tradicional de maiz fermentado

Microbiological and some physicochemical properties of akamu, a fermented maize food were studied. Microbial population, pH, titratable acidity, protein, sugar and starch were measured during the fermentation. The initial microflora consisted ofa heterogenous mixture of microorganisms namely Lactobacillus delbrueckii, Lactobacillus plantarum, Lactobacillus fermentum, Lactobacillus amylovorus, Pseudomonas aeruginosa, Pseudomonas alkaligenes, Bacillus cereus, Bacillus licheniformis, Bacillus subtilis, Candida utilis, Candida tropicalis, Saccharomyces cerevisiae, Aspergillus oryzae, Aspergillus niger, Penicillium citrinum, Rhizopus micros-porus and Rhizopus oligosporus. Within 24 h, lactobacilli and aerobic mesophilic bacteria accounted for a major portion of the total microflora. The lactobacilli numbers increased from 1.6 x107 cfu/g after24 h to 7.1 x108 cfu/g after 72 h. Total aerobic mesophilic bacteria increased from 2.5 x109 cfu/g after 24 h to 4.2 x108 cfu/g after 72 h. Enterobacteriaceae count decreased from 6.3 x 103 cfu/g after 24 h to 2.5x102 cfu/g after 72 h, although this level remained significantly high for a finished food product. Yeasts increased steadily and reached 6.8 x105 cfu/g after 72 h. Mould counts decreased from 6.3 x103 cfu/g after 24 h to 1.3 x102 cfu/g after 72 h. Moulds were largely responsible for amylolytic activity in pure culture. Fermentation caused a general decrease in pH from 6.6 to 3.9 after 72 h and titratable acidity increased from 0.48 to 0.79 after 72 h. Starch concentration decreased from 68 g/100 g to 37.4 g/100g. Protein and reducing sugar concentrations increased from 12.8 g/100 g to 18.5 g/100 g and from 5.3 g/100 g to 17.6 g/100 g, respectively. The types and numbers of microorganisms isolated from akamu could pose a health risk to consumers especially where this food product is used as a weaning product for infants.

Se estudiaron las propiedades microbiológicas y fisicoquímicas del akamu, un alimento fermentado a base de maíz. Se midió la población microbiológica, el pH, la acidez por titulación, azúcar y almidón durante la fermentación. La microflora inicial consistía en una mezcla heterógenea de microrganismos denominados Lactobacillus delbruecki, Lactobacillus plantarum, Lactobacillus fermentum, Lactoba-cillus amylovorus, Pseudonomas aeruginosa, Pseudomonas alkaligenes, Bacillus cereus, Bacillus licheniformis, Bacillus subtilis, Candida utilis, Candida tropicvallis, Saccharomyces cerevisiae,Aspergillus oryzae, Aspergillus niger, Penicillium citrinum, Rhizopus microsporus y Rhizopus oligosporus. Al cabo de 24 horas, las bacterias lactobacillus y mesofílicas aeróbicas formaron una parte importante de la microflora total. Las bacterias lactobacilli aumentaron a 1.6 x107 cfu/g a las 24 horas y al cabo de 72 horas a 7.1 x 10 8 cfu/g. El total de bacterias mesofílicas aeróbicas aumentaron desde 2.5 x 109 en 24 horas y a 4.2 x 10 8 a las 72 horas. El recuento de enterobacterias disminuyó de 6.3 x 103 en 24 horas a 2.5x 102 cfu/g a las 72 horas, aunque este nivel permaneció significativamente alto para un producto alimentario final. Las levaduras aumentaron en forma significativa y alcanzaron un rango de 6.8 x 105 a las 72 horas. Los recuentos de hongos disminuyeron desde 6.3 x 103 cfu/g a las 24 horas a un rango de 1.3 x 102 cfu/g a las 72 horas. Los hongos fueron responsables de la actividad amilolitica en el cultivo puro. La fermentación provocó una disminución general en el pH desde 6.6 a 3.9 a las 72 horas y la acidez por titulación aumentó a 0.48 a 0.79 a las 72 horas. La concentración de almidón disminuyó desde 68 g/100 g a 37.4 g/100 g. Las concentraciones de proteínas y azúcar reducida aumentaron desde 12.8 g/100 g a 18.5 g/100 g y desde 5.3 g/100 g a 17.6 g/100 g respectivamente. Los tipos y cantidades de microrganismos aislados del akamu suponen un riesgo sanitario para los consumidores especialmente dado que este producto es utilizado como una formula láctea para lactantes.

Influence of media composition on the production of alkaline α-amylase from Bacillus subtilis CB-18.

BACKGROUND: Starch, a homopolysaccharide is an important and an abundant food reserve and energy source. Starches are processed to yield different products which find many industrial applications. Alpha-amylases hydrolyze starch by cleaving α-1,4-glucosidic bonds and have been used in food, textile and pharmaceutical industries [Sun et al. 2010]. Enzymatic conversion of starch with amylase presents an economically superior alternative to the conventional method of starch gelatinization. Alkaline α-amylase has an important position in the global enzyme market as a constituent of detergent. In this paper, we screened soil bacteria and an isolate, alkalophilic Bacillus subtilis CB-18 was found to produce an alkaline α-amylase in different media. MATERIAL AND METHODS. Screening of the isolates for amylolytic activity was carried out by growing bacteria isolated from the soil in starch agar plates and subsequently staining the plates with iodine solution to reveal zones of hydrolysis of starch. The selected isolate, Bacillus subtlis CB-18 was grown in different media at alkaline pH to evaluate the influence of media composition on alkaline α-amylase production. Enzyme assay was carried out by growing the culture in a broth medium and obtaining cell - free culture supernatant after centrifugation at 2515 × g for 15 minutes Amylase activity was determined by incubating 0.5 ml of crude enzyme solution in 0.1M Tris/HCl buffer (pH 8.5) with 0.5 ml of 1% soluble starch solution. The reaction was terminated by the addition of DNS reagent and reducing sugar produced from the amylolytic reaction was determined. RESULTS: Bacillus subtilis CB-18 used for this work was selected because it produced 7 mm zone diameter on starch agar plate. This organism was cultured in different alkaline broth media containing 2% soluble starch as inducer carbohydrate for α-amylase production. Among the carbon sources used for enzyme production, sorbitol was the best to stimulate enzyme production with α-amylase activity of 758 U/mL after 48 h. Peptone was the best nitrogen source for enzyme production with α-amylase activity of 680 U/mL after 48 h. Metal ions including Ca (2+), Mn(2+) and Mg(2+) stimulated enzyme production while Hg(2+) and Ag(+) repressed enzyme production. The best enzyme yields were observed in basal media containing agro-based substrates. CONCLUSION: This work reports the production of alkaline α-amylase by Bacillus subtlis CB-18 in different media. Enzyme production was highest when agro-based media were used to formulate the media.