Studies on Akamu, a Traditional Fermented Maize Food Estudios En Akamu, Una Comida Tradicional De Maiz Fermentado

Rev Chil Nutr Vol. 39, Nº4, Diciembre 2012 Studies on Akamu, a traditional fermented maize food Estudios en Akamu, una comida tradicional de maiz fermentado ABSTRACT 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 of a 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 after 24 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 Nwokoro, Ogbonnaya (1) after 72 h. Enterobacteriaceae count decreased from 6.3 x103 cfu/g Chukwu, Bernice Chidinma (2) after 24 h to 2.5x102 cfu/g after 72 h, although this level remained (1) Industrial Microbiology and Biotechnology Laboratory, significantly high for a finished food product. Yeasts increased Department of Microbiology, University of Nigeria, Nsukka, Nigeria. steadily and reached 6.8 x105 cfu/g after 72 h. Mould counts de- (2) Department of Biochemistry, creased from 6.3 x103 cfu/g after 24 h to 1.3 x102 cfu/g after 72 University of Nigeria, Nsukka, Nigeria. h. Moulds were largely responsible for amylolytic activity in pure culture. Fermentation caused a general decrease in pH from 6.6 Corresponding author: to 3.9 after 72 h and titratable acidity increased from 0.48 to 0.79 Nwokoro Ogbonnaya Industrial Microbiology and Biotechnology Laboratory after 72 h. Starch concentration decreased from 68 g/100 g to 37.4 Department of Microbiology g/100g. Protein and reducing sugar concentrations increased from University of Nigeria, 12.8 g/100 g to 18.5 g/100 g and from 5.3 g/100 g to 17.6 g/100 Nsukka, Nigeria Tel: +2348034402414 g, respectively. The types and numbers of microorganisms isolated E-mail: [email protected] from akamu could pose a health risk to consumers especially where this food product is used as a weaning product for infants. Key words: Akamu, microbial population levels, protein, reducing Este trabajo fue recibido el 24 de Mayo de 2012 sugar, starch. y aceptado para ser publicado el 28 de Octubre de 2012. INTRODUCTION is sieved to smooth slurry which is allowed to settle and the Fermentation process serves as a mean of providing a supernatant decanted. The slurry is mixed with hot water with source of nourishment for large rural populations Fermentation stirring until it forms a get which serves as food. enhances the nutrient content of foods through the synthesis Fermented foods have become a major source of dia- of proteins, vitamin, and essential amino acids (1). rrhoeal diseases (5, 6). Moterjemi et al., (7) reported that Akamu is a porridge prepared from fermented maize. It maize porridge samples prepared for infants in Ghana were is a popular breakfast cereal and infant weaning food among contaminated with pathogenic bacteria including Aeromonas, the Igbo – speaking people of Nigeria. Akamu is similar to Bacillus cereus, Salmonella, Staphylococcus aureus and Vibrio ogi, a lactic acid fermented food made from maize, sorghum cholerae. This present investigation was aimed at assessing or millet which may the fortified with legumes (2-4). Akamu the microbiological and some physicochemical properties of is prepared by soaking clean maize grains in water for 2-3 akamu and the association of some pathogenic microorganisms days. The grains are washed and ground to a paste. The paste with the food. 180 Studies on Akamu, a traditional fermented maize food MATERIALS AND METHODS bottle. An aliquot (4 mL) of this reagent was added to tubes Traditional preparation of Akamu: Five kilograms of maize containing 1mL of glucose solution and to distilled water (Zea mays) was cleaned and steeped in 6 L of tap water in a blanks. The tubes were placed in boiling water for 10 minutes plastic container for three days. The water was decanted and and cooled to room temperature. The solutions were read the grains were wet – milled before sieving with muslin cloth. in a Spectrum Lab 23A spectrophotometer at 540 nm. The The pomace was discarded and the starch suspension was readings were used to draw a standard curve for micrograms allowed to sediment during which fermentation occurred by glucose equivalents per mL against absorbance. Titratable the natural flora of the grains. acidity was determined using the standard method described by Amoa – Awua et al; (12). A 10 g sample was blended with Isolation of microorganisms 100 mL of distilled water and filtered through two successive At 0 h and then at 24 h intervals, 1 g sample was asep- Whatman No 1 filter papers. Then 25 mL of the filtrate was tically withdrawn and used for microbiological analysis. The titrated with 0.25M NaOH and 1% phenolphthalein as an sample was homogenized in 10 mL of sterile distilled water indicator. The titratable acidity was calculated as percent lactic using a sterile mortar and pestle. Then 1mL of the pulp was acid in the sample using the relationship given by Kimaryo et added into a test tube containing 9 mL 0.1% sterile peptone al., (13). Starch content was determined by anthrone method water diluents and mixed. Then 0.1mL was aseptically with- of Clegg (14). drawn with a sterile pipette and inoculated onto MRS agar (Oxoid Ltd., UK) for the isolation of lactic acid bacteria, Plate RESULTS AND DISCUSSION Count Agar (Difco) plates for total aerobic mesophilic bac- The microbial composition of akamu sample is shown in teria, Mac Conkey agar (Oxoid ) for Enterobacteriaceae and table 1. Within the first 48 h of fermentation, the organisms Sabouraud Dextrose agar containing 0.1% chloramphenicol isolated included Lactobacillus delbrueckii, Lactobacillus plan- for yeasts and mould counts. The plates were incubated at tarum, Lactobacillus fermentum, Lactobacillus amylovorus, 30 oC for 24-72 h and the number of colony forming units Pseudomonas aeruginosa, Pseudomonas alkaligenes, Bacillus per gram (CFU/g) was determined. The morphological, cereus, Bacillus licheniformis, Bacillus subtilis, Candida utilis, physiological and biochemical characterization of bacterial Candida tropicalis, Saccharomyces cerevisiae, Aspergillus isolates were carried out as described by Holt et al., (8). Car- oryzae, Aspergillus niger, Penicillium citrinum, Rhizopus mi- bohydrate fermentation patterns of the lactic acid bacterial crosporus and Rhizopus oligosporus. The presence of these (LAB) isolates were determined by using API 50 CHL test kit. organisms in significant numbers at this time indicated that On-line software of Bio Merieux (www.apiweb.biomerieux. they constituted part of the maize microflora. Mucor circi- com) was used to identify the isolates. Yeasts and fungi were nelloides and Rhodotorula glutinis were the only organisms identified based on the taxonomic schemes described by Pitt isolated beyond 48 h. and Hocking (9). Qualitative test for starch hydrolysis by the Bacillus subtilis, Bacillus cereus and Bacillus licheniformis isolates was done by surface – plating starch (Merck) agar showed saccharolytic activities and these organisms persisted plates with the isolates. The plates were flooded with 5 mL towards the end of the fermentation indicating that they iodine solution and visualized for zones of clearing around continued the saacharification of maize starch to release su- the colonies after 2 d incubation. gars. The majority of lactic acid bacteria isolated from akamu belonged to the genera Lactobacillus. These organisms arose Chemical analyses early in the fermentation, increasing rapidly from1.6 x107 Sample (100 g) was treated with 5% NaOH, 8% urea and cfu/g to 7.1 x 108 cfu/g after 72 h. The decrease in sugar 0.05 % sodium dodecyl sulphate and incubated at 32oC for 16 concentrations could be attributed largely to the activities h. After incubation, the sample was centrifuged at 2515xg and of these organisms which metabolized and converted sugars the supernatant was used for protein assay. Protein content into organic acids during maize fermentation (15). Giraud was determined by the method of Lowry et al., (10) using et al., (16) demonstrated amylase ability of Lactobacillus bovine serum albumin (Sigma-Aldrich) as a standard. The pH plantarum but all the lactic acid bacteria isolated from akamu was determined using a glass electrode pH meter (PYE Unicam, were unable to hydrolyze starch in pure culture. Lactobacilli England). Reducing sugar was assayed by a modification of the are the most important organisms that produced acidity in dinitrosalicylic acid (DNS) method of Miller (11): DNS (10 g) maize fermentation (17).These organisms have also been was dissolved in 200 mL of 0.2 M NaOH. Potassium sodium implicated as partly responsible for initiating acidification tartrate (300 g) was dissolved in 800 mL of distilled water. in fermenting maize dough (18). This work confirms this The two solutions were mixed and stored in an air tight dark suggestion because lactobacilli had the highest population TABLE 1 Microbial population levels (cfu/g) during the fermentation of Akamu Fermentation Lactic Total aerobic Enterobacteriaceae Yeasts Moulds Time (h) acid bacteria mesophilic bacteria 0 1.6x 107 2.5 x 109 6.3 x 103 2.0 x 104 6.3 x 103 24 3.2 x 107 4.0 x 109 1.6 x 103 8.0 x 104 7.9 x 102 48 4.0 x 107 7.9 x 108 3.8 x 102 1.6 x 105 2.5 x 102 72 7.1 x 108 4.2 x 108 2.5 x 102 6.8 x 105 1.3 x 102 181 Ogbonnaya N.

Load more