Anthony N. Mutukumira

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 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

Partial purification and characterisation of a xylanase enzyme produced by a micro-organism isolated from selected indigenous fruits of Zimbabwe

Abstract Aerobic bacteria and fungi isolated from Ziziphus mauritiana, Scierocarya birrea fruits and a cattle compost were screened for production of endo-xylanase enzyme. Xylanolytic activity was found in 10 of the 88 isolates obtained. Two best endo-xylanase enzyme producers (SB-9a and TC-17d) were selected for further investigations. The two isolates were classified as belonging to the genus Bacillus. The endo-xylanase enzymes from both isolates were optimally active at pH 8 and stable over a pH range of 6.0–9.0. The optimum temperature for xylanase activity, assayed at pH 8 was 60°C. The endo-xylanase from isolate SB-9a was stable at 50°C, maintaining over 50% of its activity for 1 h at pH 8. The endo-xylanase from isolate TC-17d was less stable, maintaining about 20% of its activity for 20 mm at 50°C and pH 8. Endo-xylanase activity for isolate SB-9a was inhibited by Hg 2+ , Ag + and Mn 2+ ions while Fe 3+ , K+, Nat, Ca 2+ , and Cu 2+ ions stimulated xylanase activity. The endo-xylanase enzyme from isolate SB-9a was partially purified by ammonium sulphate precipitation, and gel filtration chromatography. It had a specific activity of 308 nkat/mg protein. This enzyme could have potential uses in biotechnological applications such as in pulp, paper and food manufacture due to its high specific activity and alkaline pH optima.

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.

Arabinogalactan proteins contribute to the immunostimulatory properties of New Zealand honeys.

Context: Factors in honey that improve wound healing are poorly understood, but are thought to include lipopolysaccharide (LPS), apalbumin-1 and -2, and a 5.8 kDa component that stimulate cytokine release from macrophages. Objective: To characterize the ability of New Zealand honeys to elicit the release of tumor necrosis factor-α (TNF-α) from monocytic cell lines as a model for early events within a wound site. Materials and methods: The ability of kanuka (Kunzea ericoides), manuka (Leptospermum scoparium), and clover (Trifolium spp.) honeys to stimulate the release of TNF-α from monocytic cell lines THP-1 and U937 was assayed by ELISA. Results: All three honeys stimulated TNF-α release from THP-1 cells, with kanuka honey being the most active. The activity of kanuka honey was associated with a high molecular weight (>30 kDa) component that was partially heat labile and inhibitable with polymyxin B. LPS concentrations in the honeys were too low to adequately explain the level of immunostimulation. The contribution of type II arabinogalactan proteins (AGPs) we recently identified in kanuka honey was tested, as AGPs are known immunostimulators. AGPs purified from kanuka honey stimulated the release of TNF-α from THP-1 and U937 cells. Discussion: Here we demonstrated that AGPs we recently identified in kanuka honey have immunostimulatory activity. We propose that the immunostimulatory properties of individual honeys relate to their particular content of LPS, apalbumins, the 5.8 kDa component and AGPs. Conclusion: The immunostimulatory activity of kanuka honey may be particularly dependent on AGPs derived from the nectar of kanuka flowers.

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.

Chemical and Microbiological Quality of Raw Milk Produced by Smallholder Farmers in Zimbabwe

Chemical and microbiological analyses were carried out on 10 samples of raw milk collected over 6 months from the Nharira/Lancashire Milk Collection Center. The milk center is run by smallholder farmers. The purpose of the study was to evaluate the quality of the raw milk delivered to the milk collection center. The average chemical characteristics of the milk were (%): titratable acidity expressed as lactic acid, 0.21; total protein, 3.19; fat, 3.52; total solids, 11.76; and solids not fat, 8.25; the pH varied from 6.15 to 6.65. There were large variations in the microbiological composition of the raw milk with total aerobic counts ranging from 6.2 × 103 to 7.8 × 107 CFU/ml, coli forms from 3.2 × 102 to 2.3 × 105, and lactic acid bacteria from less than 1 × 103 to 2.9 × 106 CFU/ml. Yeasts and molds were less than 100 CFU/ml in 7 of the 10 samples analyzed.

A household-level sweet potato-based infant food to complement vitamin A supplementation initiatives

Vitamin A deficiency (VAD) prevalence in Sub-Saharan Africa is high in spite of vitamin A supplementation programmes among children in most countries. Plant-based complementary foods remain the key source of nutrients in addition to breast milk for infants in lower income countries. Cereal-legume blends are superior in protein and energy densities compared with maize, millet or sorghum-only porridge. However, unfortified cereal-legume and cereal-only porridges are low in vitamin A. A household-level sweet potato-based infant food, rich in vitamin A, has been developed to complement vitamin A supplementation initiatives in Sub-Saharan Africa. A composite flour containing sweet potato, soybean, soybean oil and fishmeal was processed as complementary food by oven toasting (denoted oven-toasted ComFa). The oven-toasted ComFa and enriched Weanimix (processed from dehulled maize, dehulled soybean, groundnut and fishmeal) were assessed for suitability as complementary food based on the nutrient composition using specifications in the Codex Standard (CS) as a reference. The sweet potato-based formulation and enriched Weanimix met the energy, protein, fructose and fat specifications but barely met the amino acid score as indicated in the CS. However, only the oven-toasted ComFa met the calcium and almost half the vitamin A levels as specified in the CS. Oven-toasted ComFa was slightly lower in energy, protein and fat by a difference not greater than 4.0% but was higher by more than 100% in fructose and vitamin A levels. Therefore, the sweet potato-based complementary food is likely to support vitamin A supplementation initiatives in low-income countries better than the cereal-based formulation.

Carbohydrate composition, viscosity, solubility, and sensory acceptance of sweetpotato- and maize-based complementary foods

Background Cereal-based complementary foods from non-malted ingredients form a relatively high viscous porridge. Therefore, excessive dilution, usually with water, is required to reduce the viscosity to be appropriate for infant feeding. The dilution invariably leads to energy and nutrient thinning, that is, the reduction of energy and nutrient densities. Carbohydrate is the major constituent of food that significantly influences viscosity when heated in water. Objectives To compare the sweetpotato-based complementary foods (extrusion-cooked ComFa, roller-dried ComFa, and oven-toasted ComFa) and enriched Weanimix (maize-based formulation) regarding their 1) carbohydrate composition, 2) viscosity and water solubility index (WSI), and 3) sensory acceptance evaluated by sub-Sahara African women as model caregivers. Methods The level of simple sugars/carbohydrates was analysed by spectrophotometry, total dietary fibre by enzymatic-gravimetric method, and total carbohydrate and starch levels estimated by calculation. A Rapid Visco™ Analyser was used to measure viscosity. WSI was determined gravimetrically. A consumer sensory evaluation was used to evaluate the product acceptance of the roller-dried ComFa, oven-toasted ComFa, and enriched Weanimix. Results The sweetpotato-based complementary foods were, on average, significantly higher in maltose, sucrose, free glucose and fructose, and total dietary fibre, but they were markedly lower in starch content compared with the levels in the enriched Weanimix. Consequently, the sweetpotato-based complementary foods had relatively low apparent viscosity, and high WSI, than that of enriched Weanimix. The scores of sensory liking given by the caregivers were highest for the roller-dried ComFa, followed by the oven-toasted ComFa, and, finally, the enriched Weanimix. Conclusion The sweetpotato-based formulations have significant advantages as complementary food due to the high level of endogenous sugars and low starch content that reduce the viscosity, increase the solubility, impart desirable sensory characteristics, and potentially avoid excessive energy and nutrient thinning.

SWEET POTATO-BASED COMPLEMENTARY FOOD FOR INFANTS IN LOW-INCOME COUNTRIES

Background In low-income countries, most infants are given cereal-based complementary foods prepared at the household level. Such foods are high in phytate, which limits the bioavailability of nutrients, including iron, calcium, zinc, and in some cases proteins, which are crucial to the development of infants. Objective To compare the levels of macronutrients (protein, fat, and carbohydrate), gross energy, and fructose in sweet potato-based (denoted ComFa) formulations and enriched Weanimix (dehulled maize–dehulled soybean–groundnut blend with fish powder and sugar incorporated). The phytate level was also compared. Methods A composite flour of sweet potato and soybeans containing fish powder was processed by oven toasting as a home-based complementary food. Another blend containing skim milk powder was processed by extrusion cooking or roller drying as industrial-based prototypes. The macronutrient composition and the levels of fructose and phytate were determined in the ComFa formulations and enriched Weanimix. Results The ComFa formulations and the enriched Weanimix met the stipulated values in the Codex Alimentarius Commission standard for energy (400 kcal/100 g), protein (15 g/100 g), and fat (10 to 25 g/100 g) for complementary food, with the exception of the industrial-based ComFa formulations, which satisfied 83% of the protein requirement (15 g/100 g). The ComFa formulations had a quarter of the phytate level of enriched Weanimix. The fructose level in the sweet potato-based complementary foods was more than five times that in enriched Weanimix. Conclusions The sweet potato-based formulations were superior to enriched Weanimix as complementary foods for infants in low-income countries, based on the fructose (which makes the porridge naturally sweet) and phytate levels.