DEMAND EQUATIONS FOR SELECTED SOUTH AFRICAN AGRICULTURAL COMMODITIES
ABSTRACT A set of demand equations for 18 South African agricultural products, representing three demand systems (red meats, fruits and vegetables), were estimated from monthly data for the period December 1982 to February 1988. Data were deflated with a commodity price index and natural logarithmic partial adjustment equations were estimated with two-stage least squares to determine demand parameters for each product. Theoretically expected results were obtained and, owing to variability in seasonal data, results were generally highly significant. Beef is confirmed as the dominant commodity in the red meat market, having cross-price flexibilities with mutton and pork of 0,30 and 0,20, respectively. All goods other than pumpkins are shown to be normal and fruits and vegetables (having many substitutes) are shown to be demand elastic. All products are normal goods, with the exception of pumpkins (income flexibility of −0,74), which are inferior. Apples and pineapples were found to be the dominant fruits an...
ECONOMETRIC ESTIMATION OF THE DEMAND FOR MEAT IN SOUTH AFRICA
In this study the demand relations for meat in South Africa are estimated and interpreted. Two demand model specifications, namely the Rotterdam and Linearized Almost Ideal Demand System (LA/AIDS), were estimated and tested in order to determine which model provide the best fit for South African meat data. Tests for separability included an F and Likelihood ratio version. Both tests rejected the null hypothesis of weak separability between meat, eggs and milk as protein sources, indicating that the demand model for meat products should be estimated separately from eggs and milk. Consequently, separability tests between the four meat products fail to reject the null hypothesis, confirming that the four meat products should be modelled together. According to the Hausman exogeneity test, the expenditure term is exogenous. As a result, a Restricted Seemingly Unrelated Regression (RSUR) was used to estimate both models. Annual time series data from 1970 to 2000 were used. Both models were estimated in first differenced format, whereafter the estimated parameters were used to calculate compensated, uncompensated and expenditure elasticities. In a non-nested test, the Saragan's and Vuong's likelihood criterion, selected the LA/AIDS model. In terms of expected sign and statistical significance of the elasticities, the LA/AIDS also proved to be more suitable for South African meat data. Although the magnitudes of most own price and cross-price elasticities were significantly lower than previous estimates of demand relations for meat in South Africa, several reasons, including estimation techniques and time gaps, were offered as explanations for these differences. The uncompensated own price elasticity for beef (-0.7504) is the largest in absolute terms, followed by mutton (-0.4678), pork (-0.36972) and chicken (-0.3502). In terms of the compensated own price elasticities, which contain only the pure price effect, pork (-0.30592) was the most elastic, followed by mutton (-0.27713), chicken (-0.1939) and beef (-0.16111). The expenditure elasticities of beef (1.243) and mutton (1.181) are greater than one, indicating that beef and mutton are luxury goods in South Africa. The expenditure elasticity for beef is the most elastic; indicating that South African consumers as a whole, will increase their beef consumption as the total expenditure on meat products increase.
Development of new analytical methods for the determination of caffeine content in aqueous solution of green coffee beans
BackgroundThis study was conducted to develop fast and cost effective methods for the determination of caffeine in green coffee beans. In the present work direct determination of caffeine in aqueous solution of green coffee bean was performed using FT-IR-ATR and fluorescence spectrophotometry. Caffeine was also directly determined in dimethylformamide solution using NIR spectroscopy with univariate calibration technique.ResultsThe percentage of caffeine for the same sample of green coffee beans was determined using the three newly developed methods. The caffeine content of the green coffee beans was found to be 1.52 ± 0.09 (% w/w) using FT-IR-ATR, 1.50 ± 0.14 (% w/w) using NIR and 1.50 ± 0.05 (% w/w) using fluorescence spectroscopy. The means of the three methods were compared by applying one way analysis of variance and at p = 0.05 significance level the means were not significantly different. The percentage of caffeine in the same sample of green coffee bean was also determined by using the literature reported UV/Vis spectrophotometric method for comparison and found to be 1.40 ± 0.02 (% w/w).ConclusionNew simple, rapid and inexpensive methods were developed for direct determination of caffeine content in aqueous solution of green coffee beans using FT-IR-ATR and fluorescence spectrophotometries. NIR spectrophotometry can also be used as alternative choice of caffeine determination using reduced amount of organic solvent (dimethylformamide) and univariate calibration technique. These analytical methods may therefore, be recommended for the rapid, simple, safe and cost effective determination of caffeine in green coffee beans.