Quality assessment of some Tanzanian traditional brews in relation to associated health risks
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Date
2000
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University of Dar es Salaam
Abstract
The affordability, competitiveness, the large and expanding market share of traditional brews (over 89% of Tanzania's national alcohol consumption - 1989) have prompted us to launch a programme to examine the quality and health status of various brands due to their immense national socio-economic impact. Ethanol, the target of fermentative conversion of sugar, is variable both within and between brands and ranges from ca. 2.4% (v/v) to 8.2% (v/v). Unconverted sugar (nutrient) follows similar (but reverse) trends and the maximum of ca. 12% w/v sugar is found in kangara and uraka. Other quality parameters examined include acidity (and pH), conductivity. Total Dissolved Solids (TDS) and Total Suspended Solids (TSS). The constituents of serious human health concern are examined: methanol, fusel oils, acetaldehyde, ethyl acetate and heavy metals. Acidities of up to ca. 90 mmol/1 are recorded in some brands while uraka records the highest concentration of methanol (10.4 ppm). All the brew samples contain relatively high levels of isoamyl alcohol. Butanol concentrations of between 45.7-73.5 ppm are found in kabungusi and kibuku-Mtwara while uraka records the lowest. An acetaldehyde content of up to 80.2 ppm is recorded in kangara. The highest average conductivity value is recorded in uraka (2.87 mScm-1). This is probably due to physiological electrolytes in the plant sap. High acidity also enhances leaching of metals from metaware container surfaces. The highest TDS value is recorded in kangara followed by that of uraka (40.3 g/dm3). This is correlated to the average sugar contents of the two brands which are also bigger than the rest. TSS data ranges between 0.794 g/dm3 and 30.4 g/dm3 with the highest in kangara due to high unrefined carbohydrate material. Average density data appears to correlate with TDS in brews with substantial suspended solids (kangara: 1.02224 g/cm3 vs. 35.6 g/dm3; kibuku-Mtwara.: 0.9911 g/cm3 vs. 24.0 g/dm3, for density and TDS respectively) and also in those from plant saps (uraka and dengelua) and kabungus: 0.9955 g/cm3 vs. 6.02 g/dm3 for density and TDS respectively). Density varies in the same way with TSS. Safe-shelf life (beyond which quality deterioration is unacceptable) has been seen to diminish with increasing storage temperature. Some selected quality-vs-shelf-life trends are presented and reasons explored. Heavy metals in the brews were determined. The concentration of zinc in two samples of kangara is above WHO standards. One sample of kangara also records high levels of iron exceeding both WHO and Tanzanian standards for drinking water are recorded in all the samples investigated while about 72% of the brew samples contain lead levels above these standards. High levels of copper exceeding the WHO maximum permissible level were found in one sample of kangara. The fruits of Kigelia africana are added to sugar-cane brew (dengelun) to enhance the fermentation process. Alcohol yields increase by about fifty times with the use of commercially pre-used Kigelia fruits over the sterilised counterpart. Chopping the fruit to segments or powdering (surface area differentials) are also shown to have no significant effect on the fermentation process. Repetitive use of fresh Kigelia additive progressively increases fermentation efficiency. The quality parameters have been evaluated: Methanol, acetaldehyde and fusel oils attaining alarming levels of ca. 28, ca. 57, and ca. 237 ppm respectively at 24 hours. The fruit has an internal structure suitable for supporting large bacterial and yeast colonies. Two yeast strains were identified and isolated from the fruit and fermentation efficiency of each strain examined. The effect of temperature and air on the fermentation efficiency of Kigelia fruit was studied. The production of ethanol and fusel oils increases as temperature increases between 8°C and 30°C with the highest concentration of ethanol recorded at 17°C. There is however; an apparent inverse relationship between the change in temperature and the maximum final concentration of ethyl acetate. Excess air on the other hand has the effect of shortening the shelf-life of brews. These parameters were found to affect the production of the components. Leaching of metals from metal ware surfaces into brews is enhanced by increased acidity while increased sugar and alcohol strength generally suppresses this. The levels of tin leached however are small compared to other studies giving evidence of its resistance to corrosion. Suggestions on safeguards on human health including a proposal on electrodepositional techniques to selectively lower the brew content of toxic metals by introducing less objectionable ones is examined.
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Available in print form
Keywords
Brewing, Health risk assessment
Citation
Mbulumi, D. L. (2000) Quality assessment of some Tanzanian traditional brews in relation to associated health risks, Masters dissertation, University of Dar es Salaam. Available at (http://41.86.178.3/internetserver3.1.2/detail.aspx)