Judith Narvhus

Isolation, characterisation and identification of lactic acid bacteria from bushera: a Ugandan traditional fermented beverage

One hundred and thirteen strains of lactic acid bacteria (LAB) were selected from 351 isolates from 15 samples of traditionally fermented household bushera from Uganda and also from laboratory-prepared bushera. Isolates were phenotypically characterised by their ability to ferment 49 carbohydrates using API 50 CHL kits and additional biochemical tests. Coliforms, yeasts and LAB were enumerated in bushera. The pH, volatile organic compounds and organic acids were also determined. The LAB counts in household bushera varied between 7.1 and 9.4 log cfu ml(-1). The coliform counts varied between < 1 and 5.2 log cfu ml(-1). The pH of bushera ranged from 3.7 to 4.5. Ethanol (max, 0.27%) was the major volatile organic compound while lactic acid (max, 0.52%) was identified as the dominant organic acid in household bushera. The initial numbers of LAB and coliforms in laboratory-fermented bushera were similar; however, the LAB numbers increased faster during the first 24 h. LAB counts increased from 5.5 to 9.0 log cfu ml(-1) during the laboratory fermentation. Coliform counts increased from 5.9 to 7.8 log cfu ml(-1) at 24 h, but after 48 h, counts were less 4 log cfu ml(-1). Yeasts increased from 4.3 to 7.7 log cfu ml(-1) at 48 h, but thereafter decreased slightly. The pH declined from 7.0 to around 4.0. Lactic acid and ethanol increased from zero to 0.75% and 0.20%, respectively. Lactic acid bacteria isolated from household bushera belonged to Lactobacillus, Streptococcus and Enterococcus genera. Tentatively, Lactobacillus isolates were identified as Lactobacillus plantarum, L. paracasei subsp. paracasei, L. fermentum, L. brevis and L. delbrueckii subsp. delbrueckii. Streptococcus thermophilus strains were also identified in household bushera. LAB isolated from bushera produced in the laboratory belonged to five genera (Lactococcus, Leuconostoc, Lactobacillus, Weissella and Enterococcus. Eight isolates were able to produce acid from starch and were identified as Lactococcus lactis subsp. lactis (four strains), Leuconostoc mesenteroides subsp. mesenteroides (one strain), Leuconostoc mesenteroides subsp. dextranicum (one strain), Weissella confusa (one strain) and L. plantarum (one strain).

GROWTH AND METABOLISM OF SELECTED STRAINS OF PROBIOTIC BACTERIA IN MILK

Abstract Growth and metabolism of five probiotic strains with well-documented health effects were studied in ultra-high temperature (UHT) treated milk, supplemented with 0.5% (w/v) tryptone or 0.75% (w/v) fructose. The probiotic strains were Lactobacillus acidophilus La5, Lb. acidophilus 1748, Lactobacillus rhamnosus GG, Lactobacillus reuteri SD 2112 and Bifidobacterium animalis BB12. Fermentation was followed for 72 h at 37 °C and the samples were analysed for pH, log cfu ml−1, volatile compounds, organic acids and carbon dioxide. The strains reduced pH from 6.7 to between 3.9 and 4.4 after 24 h of incubation. All strains attained viable cell counts above 8.7–9.18 log cfu ml−1 after 6–16 h of incubation. The two Lb. acidophilus strains showed a stable level of viable cells during 12–72 h of incubation but the three other strains showed a reduction of 0.4–1.1 log cfu ml−1 from 24 to 72 h of incubation. However, all strains showed cell levels between 7.8 and 8.7 log cfu ml−1 after 72 h of incubation. After 48 h of incubation, the amount of lactic acid produced varied according to strain from 6949 to 14,000 mg kg−1 and acetic acid produced varied from 0 to 6901 mg kg−1. Three of the strains metabolised citrate but only low amounts of diacetyl and acetoin were detected within strains, 0.2–0.8 and 6.5–10 mg kg−1, respectively. Carbon dioxide produced varied from 221 to 3942 mg kg−1 and was connected to the citrate-fermenting ability of the strain used and their carbohydrate fermentation pathway. Three of the strains produced detectable levels of acetaldehyde and the concentration varied from 9.4 to 12.6 mg kg−1 after 24 h of incubation. All five probiotic strains showed very different profiles of metabolites during fermentation; however, the two Lb. acidophilus strains were the most alike. Our findings show the importance of controlling the fermentation time since the probiotic strains produced different amounts of metabolic products according to fermentation time.

A review of traditional fermented foods and beverages of Zimbabwe

Several traditional fermented foods and beverages are produced at household level in Zimbabwe. These include fermented maize porridges (mutwiwa and ilambazi lokubilisa) fermented milk products (mukaka wakakoralamasi and hodzeko) non-alcoholic cereal-based beverages (mahewu, tobwa and mangisi) alcoholic beverages from sorghum or millet malt (doroluthwala and chikokivana) distilled spirits (kachasu) and fermented fruit mashes (makumbi). There are many regional variations to the preparation of each fermented product. Research into the processing technologies of these foods is still in its infancy. It is, therefore, important that the microbiology and biochemistry of these products, as well as their technologies be studied and documented in order to preserve them for future generations. This article reviews the available information regarding traditional fermented foods in Zimbabwe and makes recommendations for potential research areas.

The role of interaction between yeasts and lactic acid bacteria in African fermented milks: a review.

Yeasts are present in indigenous African fermented milks in numbers up to log 8 cfu g(-1), together with a varied lactic acid bacteria (LAB) flora, and therefore potentially contribute to product characteristics. However, interaction between yeasts and LAB in these products has received little notice. In studies of indigenous fermented milk in Zimbabwe and Uganda, many samples contained more than one species of yeast, but Saccharomyces cerevisiae was most commonly isolated. Other frequent isolates were other species of Saccharomyces and several species of Candida. Most yeast isolates were lactose-negative but usually galactose-positive. Some strains assimilated lactate and citrate. The growth in milk of strains of yeasts and LAB, isolated from naturally soured milk in Zimbabwe, and their interaction when selected pairs of strains were grown together has been studied. Interactions were shown by the significantly different amounts of certain metabolites produced, such as acetaldehyde and malty aldehydes, when co-cultures were compared to pure cultures. Preliminary sensory acceptance tests did not show, however, that milks made from a co-culture with Candida kefyr and LAB were preferable to the pure LAB culture. Further work is still needed to elucidate the reactions that may be taking place in fermented milk between varying LAB and yeast populations. The potential for use as starter cultures depends on various aspects, including the final product being prepared. The role of other microorganisms in naturally fermented milk also needs to be studied.

The growth and interaction of yeasts and lactic acid bacteria isolated from Zimbabwean naturally fermented milk in UHT milk.

Nine yeast and four lactic acid bacterial strains, previously isolated from Zimbabwean traditionally fermented milk, were inoculated into ultra-high temperature treated (UHT) milk in both single and yeast-lactic acid bacteria co-culture. The lactic acid bacteria (LAB) strains consisted of Lactococcus lactis subsp. lactis biovar. diacetylactis C1, L. lactis subsp. lactis Lc39, L. lactis subsp. lactis Lc261 and Lactobacillus paracasei subsp. paracasei Lb11. The yeast strains used were Candida kefyr 23, C. lipolytica 57, C. lusitaniae 63, C. lusitaniae 68, C. tropicalis 78, Saccharomyces cerevisiae 71, S. dairenensis 32, C. colliculosa 41 and Dekkera bruxellensis 43. After 48-h fermentation at 25 degrees C, the samples were analysed for pH, viable yeast and bacterial counts, organic acids, volatile organic compounds (VOC) and carbon dioxide. The Lactococcus strains reduced the pH from about 6.6 to between 4.0 and 4.2, while Lb. paracasei subsp. paracasei Lb11 reduced the pH to about 5.4. Most of the yeasts, however, did not affect the final pH of the milk except for C. kefyr 23, which reduced the pH from 6.6 to 5.8. All the Lactococcus strains grew two log cycles during the 48-h fermentation period, while Lb. paracasei subsp. paracasei Lb11 grew about one log cycle. S. cerevisiae 71, C. colliculosa 41 and D. bruxellensis 43 showed poor growth in the milk in both single and co-culture. The other species of yeast grew about two log cycles. Candida colliculosa 41, S. dairenensis 32 and D. bruxellensis 43 showed reduced viability when in co-culture with Lb. paracasei subsp. paracasei Lb11. The samples in which C. kefyr 23 was used were distinct and characterised by large amounts of acetaldehyde, carbon dioxide and ethanol. However, in the samples where S. dairenensis, C. colliculosa, D. bruxellensis, C. lusitaniae, C. tropicalis, C. lipolytica and S. cerevisiae were used in co-culture, the final pH and metabolite content were mainly determined by the correspondin

A review paper: current knowledge of ghee and related products

Ghee is produced mainly by indigenous methods in Asia, the Middle-East and Africa and the methods of manufacture and characteristics vary. Some ambiguity in the definition of ghee occurs mainly due to regional differences and preferences for the product, commonly used for culinary purposes but also for particular social functions and therapeutic purposes. The characteristic flavour of ghee is its major criterion for acceptance. Flavour is greatly influenced by the fermentation of the cream or butter and the heating processes. Carbonyls, lactones and free fatty acids are reported to be the key ghee flavouring compounds. Ghee is fairly shelf-stable largely because of its low moisture content and possible antioxidative properties. Ghee may contain high amounts of conjugated linoleic acid, a newly reported anticarcinogen. However, it is also reported that, under certain circumstances, it may contain certain amounts of cholesterol oxidation compounds (COPS) which may cause adverse health effects.

Improved Bioavailability of Dietary Phenolic Acids in Whole Grain Barley and Oat Groat following Fermentation with Probiotic Lactobacillus acidophilus, Lactobacillus johnsonii, and Lactobacillus reuteri

The aim of this study was to improve the bioavailability of the dietary phenolic acids in flours from whole grain barley and oat groat following fermentation with lactic acid bacteria (LAB) exhibiting high feruloyl esterase activity (FAE). The highest increase of free phenolic acids was observed after fermentation with three probiotic strains, Lactobacillus johnsonii LA1, Lactobacillus reuteri SD2112, and Lactobacillus acidophilus LA-5, with maximum increases from 2.55 to 69.91 μg g(-1) DM and from 4.13 to 109.42 μg g(-1) DM in whole grain barley and oat groat, respectively. Interestingly, higher amounts of bound phenolic acids were detected after both water treatment and LAB fermentation in whole grain barley, indicating higher bioaccessibility, whereas some decrease was detected in oat groat. To conclude, cereal fermentation with specific probiotic strains can lead to significant increase of free phenolic acids, thereby improving their bioavailability.

Utilization of various starter cultures in the production of Amasi, a Zimbabwean naturally fermented raw milk product.

Fermented milk was prepared from unpasteurised milk using natural fermentation (R), back-slopping (B) and by addition of two different starter cultures (C1 and DL). The numbers of Escherichia coli, coliforms, lactic acid bacteria (LAB) and the changes in pH, carbohydrates, organic acids and volatile compounds were recorded during 48-h fermentation. After 48-h fermentation, the highest numbers of E. coli were found in R and B fermentations and the lowest in the DL fermentation. The DL culture reduced the pH faster than the other starter cultures. The DL and C1 had higher levels of LAB in the beginning of the fermentation than the other two. Galactose and lactic acid increased fastest in the DL and C1 fermentation, and R was slowest. The highest levels of succinate, ethanol and malty compounds were found in the R and B fermentations. Lower levels of LAB in the first part of the fermentations, but higher number of E. coli could explain the increased levels of succinate, ethanol and malty compounds.

Smallholder dairy processing in Zimbabwe: hygienic practices during milking and the microbiological quality of the milk at the farm and on delivery

Abstract The hygiene practices during milking and the microbiological quality of milk at the farm and on delivery at three smallholder dairies in Zimbabwe were studied. Petrifilm™ was used for the determination of Escherichia coli, coliforms and aerobic mesophilic counts (AMC). Using AMC Petrifilms™ as contact plates, 83% (n=66) of the utensils used for milking had >300 cfu per 20 cm2. Of milk samples at the farm, 95% (n=24) had E. coli counts 1 cfu ml −1 , and all had AMC 5 cfu ml −1 . On delivery at the dairy, the proportion of milk samples with AMC >10 5 cfu ml −1 was 28%. The increase in number of microorganisms in the milk was correlated with factors which would increase delivery time.

Smallholder dairy processing in Zimbabwe: the production of fermented milk products with particular emphasis on sanitation and microbiological quality

Abstract Microbiological quality and hygienic practice during the production of naturally sour milk (NSM), made of unpasteurised milk, and cultured milk (CM), made of pasteurised milk, were studied at three smallholder dairies in Zimbabwe. Petrifilm™ was used for the determination of Escherichia coli, coliforms and aerobic mesophilic count (AMC). AMC Petrifilms used as contact plates showed that 52% of utensils at the dairies (N=80) were not acceptably clean (>100 CFU per 20 cm 2 ). E. coli was found in 81% of the samples of NSM (N=31) and in all samples of CM (N=70). Approx. 39% of NSM samples and 47% of the CM samples contained more than 1000 CFU E. coli ml−1. The high numbers of E. coli found in pasteurised milk emphasise the need for improved hygiene practice at the dairies. Since NSM is not pasteurised, the hygiene at the farm is additionally important for production of NSM. The hygiene and handling at the farm should therefore be especially emphasised at the dairies where NSM is commonly produced.