Hydrolysis of raw tuber starches by amylase of Aspergillus niger AM07 isolated from the soil

Eight Aspergillus niger strains which produced strong starch degrading amylase were isolated from the soil using a medium containing Remazol Brilliant Blue (RBB) starch as substrate. Amylase production was detected by the disappearance of the blue colour around the colony. Among the isolates, A. niger AM07 produced the largest clear zone (7.0mm) on Remazol Brilliant Blue (RBB) agar plate and also gave the highest amylase yield (806 U/ml) in solid-state fermentation process, hence it was selected for further studies. The crude amylase preparation of A. niger AM07 had temperature and pH optima activities at 60oC and 4.0 respectively. The optimum substrate concentration was 3 %. The action of the crude amylase of A. niger on raw tuber starches of yam, cassava, sweet potato and cocoyam were studied in comparison with the well known maize starch which is a cereal starch. The crude amylase was able to hydrolyze all the raw starches tested. Hydrolysis was significantly (

A survey of the microflora of Hibiscus sabdariffa (Roselle) and the resulting “Zobo” juice

The dried calyx of Hibiscus sabdariffa (Roselle) is locally processed into a non alcoholic drink known as ‘Zobo’ in Nigeria. This popular drink is quite cheap compared to other bottled soft drinks but its acceptability is still limited because of its very short shelf life (24 h at room temperature). The composition and numbers of the microflora of the dried calyx of the Roselle plant and its resulting juice (Zobo) were examined using standard microbiological methods. The dried calyx obtained from a retail market was processed into juice that was compared with commercially sold (retail) juice. The microorganisms isolated from the dried calyx and the juices included the fungi, Aspergillus niger, Aspergillus flavus, Rhizopus oligosporus, Penicillium citrinum, Mucor spp., Saccharomyces cerevisiae, and Candida krusei, while Bacillus subtilis, Pseudomonas spp., Staphylococcus aureus, Streptococcus faecalis, Escherichia coli, Proteus mirabilis, Serratia spp., Lactobacillus brevis and Lactobacillus fermentum represented the bacterial isolates. Viable counts ranged from 0.4 x 104 to 3.2 x 104 cfu/ml. Aerobic and anaerobic bacterial counts were higher in the retail juice (1.1 to 2.2 x104 cfu/ml) than in the laboratory-prepared juice (0.8 to 1.4 x104 cfu/ml) while the dried calyx had the highest fungal counts of 3.2 x 104 cfu/ml. pH of the juices ranged between 2.67 and 2.77 while total titratable acidity values were between 0.02 and 0.08.Keywords: Dried calyx, microflora, viable counts, Zobo juic

Amylase Recovery From Mouldy Bran Of Aspergillus niger AM07

A simple and efficient laboratory procedure for the recovery of amylase from the moist mouldy bran obtained during a solid-state fermentation (SSF) process is described. Aspergillus niger AM07 was used in the production of amylase and recovery of the amylase from mouldy bran was effected under agitated (150 rpm) and static conditions using water and citrate phosphate buffer (pH 4.5) as solvent. Recovery was significantly (p=0.05) dependent on the solvent, mechanical agitation and contact time. The highest recovery (628 U/ml) obtained with citrate phosphate buffer (pH 4.5) as solvent was significantly higher than 588 U/ml obtained with tap water. Maximum recovery under mechanical agitation and static condition were 628 U/ml and 570 U/ml respectively. The overall maximum recovery (628 U/ml) was obtained with citrate phosphate buffer (pH 4.5) and agitation for 1 h. Key words: Amylase, mouldy bran, agitation, static, buffer and tap water. Nigerian Food Journal Vol.22 2004: 60-6

Effect of Honey as Partial Sugar Substitute on Pasting Properties, Consumer Preference and Shelf Stability of Cassava-Wheat Composite Bread

The effect of partial substitution of sugar with liquid honey on the pasting properties of cooked dough made from cassava-wheat composite (10:90) flour as well as the sensory preference and shelf stability of its bread wasinvestigated. Sucrose (S) in the bread recipe formulation was substituted with honey (H) at levels 0, 10, 20, 30, 40 and 50%, respectively to give 6 treatments, namely 0H:100S, 10H:90S, 20H:80S, 30H:70S, 40H:60S and 50H:50S. Amylograph pasting properties of the dried crumbs were determined using standard analytical procedures. Fresh bread samples were subjected to sensory evaluation and fungal count during storage (6 days). Peak, final and setback viscosities of bread crumb decreased (32.29 to 25.33, 58.54 to 43.00 and 30.96 to 23.66 RVU), respectively as the level of honey inclusion increased. Honey substitution levels used did not significantly (p > 0.05) affect aroma and texture of the bread samples but composite bread with 20% level of honey substitution was most preferred in terms of colour while composite bread with 30% level of honey substitution was most acceptable in terms of taste and overall acceptability. Fungal count in stored honey-cassava-wheat bread varied significantly (p < 0.05) from 0.6 to 4.0 × 102, 1.0 to 6.9 × 102, 2.2 to 57.0×102, 32.0 to 135.7×102, 34.0 to 140.0×102 and 42.0 to 159.3 ×102) cfu/ml from day 1 to day 6, respectively. From the study, it was concluded that substitution of sugar with honey in dough formulations significantly (p < 0.05) affects dough pasting properties, improves acceptability of the composite bread and reduces staling rate.Keywords: Honey, sucrose sugar, cassava-wheat bread, dough, pasting properties

Safety Assessment of Donkwa – An Indigenous Maize-Peanut Street- Vended Snack

Donkwa is a maize-peanut based street-vended snack commonly consumed in Nigeria and other West African countries. Donkwa is produced from the mixture of roasted-ground peanut and maize with or without addition of pepper, which is then moulded into small shapes. The safety of the street-vended donkwa, which was randomly procured from eight vendors in Southwest, Nigeria was assessed through physical, chemical and microbiological hazard analysis. Hazard analysis was also used to assess the safety of samples obtained along the different processing stages of donkwa obtained from four main processors. The results showed that the street-vended samples were contaminated with sand while the fungi, Staphylococcus spp and Bacillus spp counts ranged from 0.13 to 0.80, 0.50 to 2.50 and 0.25 to 4.75 x 104Cfu/g, respectively. Lead, arsenic and cadbium were respectively present in 7.14, 42.86 and 96.42% of the samples obtained from the processors while the cadbium levels among the positive samples ranged from 0.12 – 10.77 mg/kg which was higher than the permissible level of 0.1mg/kg stipulated by CODEX. The presence of hazards in the samples constitutes a food safety issue and control measures should be enacted to include educating processors and vendors on good hygienic and manufacturing practices in order to reduce or eliminate these hazards.Keywords: Safety, street foods, hazards, donkwa