Yusuf B. Byaruhanga

The dominant microbial community associated with fermentation of Obushera (sorghum and millet beverages) determined by culture-dependent and culture-independent methods

Obushera includes four fermented cereal beverages from Uganda namely: Obutoko, Enturire, Ekitiribita and Obuteire, whose microbial diversity has not hitherto been fully investigated. Knowledge of the microbial diversity and dynamics in these products is crucial for understanding their safety and development of appropriate starter cultures for controlled industrial processing. Culture-dependent and culture-independent techniques including denaturating gradient gel electrophoresis (DGGE) and mixed DNA sequencing of polymerase chain reaction (PCR) amplified ribosomal RNA genes were used to study the bacteria and yeast diversity of Obushera. The pH dropped from 6.0-4.6 to 3.5-4.0 within 1-2 days for Obutoko, Enturire and Obuteire whereas that of Ekitiribita decreased to 4.4 after 4 days. Counts of lactic acid bacteria (LAB) increased from 5.0 to 11.0 log cfug(-1) and yeasts increased from 3.4 to 7.1 log cfug(-1) while coliform counts decreased from 2.0 to <1 log cfug(-1) during four days of fermentation. LAB and yeast isolates were identified by rRNA gene sequence analysis. LAB isolates included: Enterococcus spp., Lactobacillus (Lb.) plantarum, Lb. fermentum, Lb. delbrueckii, Lactococcus lactis, Leuconostoc lactis, Streptococcus (S.) infantarius subsp. infantarius, Pediococcus pentosaceus and Weisella (W.) confusa. DGGE indicated predominance of S. gallolyticus, S. infantarius subsp. infantarius, Lb. fermentum, Lb. delbrueckii, W. confusa, Lb. reuteri, Fructobacillus spp., L. lactis and L. lactis. Yeast isolates included Clavispora lusitaniae, Cyberlindnera fabianii, Issatchenkia orientalis and Saccharomyces cerevisiae. DGGE indicated predominance of S. cerevisiae in Obutoko, Enturire and Obuteire and also detected Pichia spp. and I. orientalis in Obutoko. Obushera produced in the laboratory was initially dominated by Enterobacteriaceae and later by Lactococcus spp. Enterobacteriaceae and Bacillus spp. were also detected in Ekitiribita. Development of starters for Obushera may require combinations of LAB and S. cerevisiae for Obutoko, Enturire and Obuteire and LAB for Ekitiribita.

Influence of Cofermentation by Amylolytic Lactobacillus plantarum and Lactococcus lactis Strains on the Fermentation Process and Rheology of Sorghum Porridge

ABSTRACT Amylolytic lactic acid bacteria (ALAB) can potentially replace malt in reducing the viscosity of starchy porridges. However, the drawback of using ALAB is their low and delayed amylolytic activity. This necessitates searching for efficient ALAB and strategies to improve their amylolytic activity. Two ALAB, Lactobacillus plantarum MNC 21 and Lactococcus lactis MNC 24, isolated from Obushera, were used to ferment starches in MRS broth: sorghum, millet, sweet potato, and commercial soluble starch. The amylolytic activity of MNC 21 was comparable to that of the ALAB collection strain Lb. plantarum A6, while that of MNC 24 was extremely low. MNC 21, MNC 24, and their coculture were compared to A6 and sorghum malt for ability to ferment and reduce the viscosity of sorghum porridge (11.6% dry matter). ALAB and the coculture lowered the pH from 6.2 to <4.5 within 12 h, while malt as a carrier of wild starter took about 20 h. Coculturing increased lactic acid yield by 46% and 76.8% compared to the yields of MNC 21 and MNC 24 monocultures, respectively. The coculture accumulated significantly larger (P < 0.05) amounts of maltose and diacetyl than the monocultures. Sorghum malt control and the coculture hydrolyzed more starch in sorghum porridge than the monocultures. The coculture initiated changes in the rheological parameters storage modulus (G′), loss modulus (G″), phase angle (δ), and complex viscosity (η*) earlier than its constituent monocultures. The shear viscosity of sorghum porridge was reduced significantly (P < 0.05) from 1950 cP to 110 cP (malt), 281 cP (coculture), 382 cP (MNC 21), 713 cP (MNC 24), and 722 cP (A6). Coculturing strong ALAB with weak ALAB or non-ALAB can be exploited for preparation of nutrient-dense weaning foods and increasing lactic acid yield from starchy materials.

Production of organic flavor compounds by dominant lactic acid bacteria and yeasts from Obushera, a traditional sorghum malt fermented beverage

Abstract Single and mixed starter cultures of lactic acid bacteria (LAB): Weissella confusa MNC20, Lactobacillus plantarum MNC21, Lactococcus lactis MNC24 and Lactobacillus fermentum MNC34 and yeasts: Issatchenkia orientalis MNC20Y and Saccharomyces cerevisiae MNC21Y were used to produce Obushera, a fermented sorghum beverage. Microbial counts, pH, sugars, organic acids, and volatile compounds in starter culture and spontaneous fermentations were monitored during 48 hrs. Maximum counts of LAB (8.4–9.4 log cfu g−1) and yeasts (7.5 ± 0.1 cfu g−1) starter cultures were attained in 6–48 hrs. Weissella confusa, Lc. lactis, and Lb. fermentum showed possible acid sensitivity while I. orientalis produced surface films. LAB starter cultures and their combinations with S. cerevisiae lowered pH from 5.83 to <4.5 (3.50–4.13) in a shorter time (12 hrs) than spontaneous fermentations (24 hrs). Lactococcus lactis and W. confusa metabolized glucose the fastest (p < .05) during the first 6 hrs. Lactobacillus fermentum, Lb. plantarum, and S. cerevisiae utilized glucose and maltose concurrently. Lactobacillus plantarum and S. cerevisiae additionally utilized fructose. S. cerevisiae metabolized sugars the fastest (p < .05) during the first 12–24 hrs. Lactobacillus plantarum and W. confusa produced the highest (p < .05) amounts of lactate (5.43 g kg−1) and diacetyl (9.5 mg kg−1), respectively. LAB also produced acetate, ethanol, acetaldehyde, acetone, and acetoin. Coculturing LAB with S. cerevisiae reduced (p < .05) lactate and diacetyl yield. Yeasts produced high amounts of acetaldehyde and methyl alcohols. Issatchenkia orientalis produced higher (p < .05) amounts of 2‐methy‐1‐propanol and 3‐methyl‐1‐butanol than S. cerevisiae. Combinations of LAB with S. cerevisiae produced a profile flavor compounds close to that of spontaneously fermented Obushera. These combinations can be adopted for controlled fermentation of Obushera and related fermented cereal products.

Formulation of a drinkable peanut-based therapeutic food for malnourished children using plant sources

High ingredient costs continue to hamper local production of therapeutic foods (TFs). Development of formulations without milk, the most expensive ingredient, is one way of reducing cost. This study formulated a ready-to-drink peanut-based TF that matched the nutrient composition of F100 using plant sources. Three least cost formulations namely, A, B and C were designed using computer formulation software with peanuts, beans, sesame, cowpeas and grain amaranth as ingredients. A 100 g portion of the TF provided 101–111 kcal, 5 g protein and 5.3–6.5 g fat. Consumer acceptability hedonic tests showed that the products were liked (extremely and moderately) by 62–65% of mothers. These results suggest that nutrient dense TFs formulated from only plant sources have the potential to be used in the rehabilitation phase of the management of malnourished children after clinical testing.

Viscoelastic properties of sweet potato complementary porridges as influenced by endogenous amylases

Abstract Sweet potato (Ipomoea batatas L.) roots contain amylolytic enzymes, which hydrolyze starch thus having the potential to affect the viscosity of sweet potato porridges provided the appropriate working conditions for the enzymes are attained. In this study, the effect of sweet potato variety, postharvest handling conditions, freshly harvested and room/ambient stored roots (3 weeks), and slurry solids content on the viscoelastic properties of complementary porridges prepared using amylase enzyme activation technique were investigated. Five temperatures (55°C, 65°C, 70°C, 75°C, and 80°C) were used to activate sweet potato amylases and the optimum temperature was found to be 75°C. Stored sweet potato roots had higher soluble solids (⁰Brix) content in the pastes compared to fresh roots. In all samples, activation of amylases at 75°C caused changes in the viscoelastic parameters: phase angle (tan δ) and complex viscosity (η*). Postharvest handling conditions and slurry solids content significantly affected the viscoelastic properties of the porridges with flours from stored roots yielding viscous (liquid‐like) porridges and fresh roots producing elastic (solid‐like) porridges. Increase in slurry solids content caused reduction in the phase angle values and increase in the viscosity of the sweet potato porridges. The viscosity of the porridges decreased with storage of sweet potato roots. These results provide a possibility for exploiting sweet potato endogenous amylases in the preparation of complementary porridges with both drinkable viscosities and appropriate energy and nutrient densities for children with varying energy needs.

Development of the process for a drinkable plant-based infant food.

Provision of nutritionally adequate foods is crucial for the prevention and management of malnutrition. In order to meet the nutrient requirements of infants and young children using locally available cereals and legumes, foods need to be of low viscosity, of high caloric content and nutrient density and easily digestible. This study developed a processing protocol for three plant food formulations to yield nutrient dense, easily digestible and safe therapeutic foods for malnourished children. Pre-digestion of the milled ingredients at 40°C for 4 hours with grain amaranth that was malted for 48 hours and 1% Bromelain achieved 70-84% starch hydrolysis and 55-61% protein hydrolysis. Sterilization of the therapeutic food in glass jars in an autoclave at 121°C, 15 PSI for 20 minutesgave non- detectable total plate and yeast and mold counts. The final products had viscosities of 2745-2913 Cps. These results show that pre-digestion can improve the nutrition quality of infant foods made from plant sources.

Lipid Lowering Potential of Malakwang ( Hibiscus ) Species Leaf Extract in Hyperlipidaemia-Induced Rats

Malakwang (Hibiscus species) is a common vegetable regularly used in the diet and traditional health care support in Uganda. In this study, the efficacy of malakwang leaf extract as a potential regulator of serum lipids, urea and creatinine was investigated in hyperlipidemic rats. Forty two albino rats were arranged randomly into seven groups of six and fed with diets. Four experimental and three control groups were considered in the design. The rats in the experimental groups were fed on high fat diets containing different amounts of leaf extract from red and white malakwang variants. Control groups were fed on diets devoid of malakwang: a basic standard rat diet; high fat diet; and high fat with atorvastatin. The diets were administered daily and rat weight determined. On the last day, blood was drawn from the rats and the serum analysed for lipids, creatinine and urea using spectrophotometric techniques. Statistical analysis was used to estimate mean differences in weight and concentration of the biochemical parameters between experimental and control groups. Results indicated a decrease in weight gained up to the fourth week in rats fed on the high fat diet with malakwang leaf extract. There was a significant difference in the levels of low density lipoprotein cholesterol (p < 0.05), with lower levels in rats fed on 200 mg/kg red and 400 mg/kg white malakwang leaf extract. No significant change was noted in total cholesterol and triglycerides. Whereas there was a higher level of serum creatinine with the two malakwang variants (p < 0.05), serum urea levels were significantly lower. Leaf extracts of both red and white malakwang (Hibiscus) exhibited capacity to reduce low density lipoprotein cholesterol, maintained serum urea but not creatinine. This may offer prospects for using malakwang in the dietary approaches to address public health concerns linked to high level of cholesterols.

Influence of development, postharvest handling, and storage conditions on the carbohydrate components of sweetpotato (Ipomea batatas Lam.) roots

Abstract Changes in total starch and reducing sugar content in five sweetpotato varieties were investigated weekly during root development and following subjection of the roots to different postharvest handling and storage conditions. Freshly harvested (noncured) roots and cured roots (spread under the sun for 4 days at 29–31°C and 63–65% relative humidity [RH]) were separately stored at ambient conditions (23°C–26°C and 70–80% RH) and in a semiunderground pit (19–21°C and 90–95% RH). Changes in pasting properties of flour from sweetpotato roots during storage were analyzed at 14‐day intervals. Significant varietal differences (p < .05) in total starch, sucrose, glucose, maltose, and fructose concentrations were registered. The total starch and sucrose content of the roots did not change significantly (p < .05) during root development (72.4 and 7.4%, respectively), whereas the average concentrations of glucose, maltose, and fructose decreased markedly (0.46–0.18%, 0.55–0.28%, and 0.43–0.21%), respectively. Storage led to decrease in total starch content (73–47.7%) and increase in sucrose and glucose concentrations (8.1–11.2% and 0.22–1.57%, respectively). Storage also resulted in reduction in sweetpotato flour pasting viscosities. Curing resulted in increased sucrose and glucose concentrations (9.1–11.2% and 0.45–0.85%, respectively) and marked reduction (p < .05) in total starch content (72.9–47.6%). This resulted in low pasting viscosities compared to flour from storage of uncured roots. These findings show that significant changes occur in the carbohydrate components of sweetpotato roots during storage compared to development and present an opportunity for diverse utilization of flours from sweetpotato roots in the food industry.