Comparison of the energy values of different dairy products obtained by various methods

The objectives of this study were to evaluate and compare different methods of determination and/or prediction of the energy value of milk and milk products. The influence, if any, of season and locality on the energy value of whole milk and 2% fat milk were also investigated. Milk (whole and 2% fat) was collected in five specified regions in South Africa during winter and summer. Milk powder was collected in different regions only in one season. The samples were drawn from large supermarkets in each city in the packaging normally presented to the public. A total of 200 samples for milk (whole and 2% fat) and 100 samples of milk powder were collected. Sixty cheddar, 60 gouda and 30 cottage cheeses were sampled at the factories in the different regions due to the fact that the manufacturing of these products is localized. Accredited methods were used to determine the energy, protein, fat, ash, carbohydrate and water content of the samples. In cheddar, gouda and cottage cheese the carbohydrates were calculated by difference. It was clear that gross energy values of milk and milk products could be calculated from heat of combustion when the protein, fat and carbohydrate contents are known. These values were in good agreement with those obtained by bomb calorimetry. There was a significant difference (P < 0.001) in the energy content of cheddar and gouda cheese produced by different factories. One region differed significantly (P < 0.001) in energy content of whole milk from the other four regions. Variations in the energy content of cheddar and gouda cheese can generally be related to the manufacturing process, feed composition and feeding management of the animals. Significant differences in energy content between the regions for 2% fat milk and milk powder were found. Standardized whole milk was analysed and it was assumed that there are only small differences in the concentration of the macronutrients. It was found in practise that the differences were not that narrow as for instance the fat content varied between 3.12% and 3.94%, therefore reflecting a difference in the energy content.