5 Salts of milk 5.1 Introduction The salts of milk are mainly the phosphates, citrates, chlorides, sulphates, carbonates and bicarbonates of sodium, potassium, calcium and mag- nesium. Approximately 20 other elements are found in milk in trace amounts, including copper, iron, silicon, zinc and iodine. Strictly speaking, the proteins of milk should be included as part of the salt system since they carry positively and negatively charged groups and can form salts with counter-ions; however, they are not normally treated as such. There is no lactate in freshly drawn milk but it may be present in stored milk and in milk products. The major elements are of importance in nutrition, in the reparation, processing and storage of milk products due to their marked influence on the conformation and stability of milk proteins, especially caseins, and to a lesser extent the stability of lipids and the activity of some indigenous enzymes 5.2 Method of analysis he mineral content of foods is usually determined from the ash prepared by heating a sample at 500-600 C in a muffle furnace for about 4 h to oxidize organic matter. The ash does not represent the salts as present in he food because 1. the ash is a mixture, not of the original salts, but of the carbonates and oxides of the elements present in the food; 2. phosphorus and sulphur from proteins and lipids are t in the ash while organic ions, such as citrate, are lost during incineration; and 3. the temperature usually employed in ashing may vaporize certain volatile elements, e.g. sodium and potassium Therefore, it is difficult or impossible to relate the ash obtained from a food with its salts system, and low values are obtained for certain mineral elements by analysis of the ash compared to direct analysis of the intact food. Titrimetric, colorimetric, polarographic, flame photometric and atomic absorption spectrophotometric techniques are frequently used to analyse for the various mineral constituents; however, the quantitative estimation of5 Salts of milk 5.1 Introduction The salts of milk are mainly the phosphates, citrates, chlorides, sulphates, carbonates and bicarbonates of sodium, potassium, calcium and mag￾nesium. Approximately 20 other elements are found in milk in trace amounts, including copper, iron, silicon, zinc and iodine. Strictly speaking, the proteins of milk should be included as part of the salt system since they carry positively and negatively charged groups and can form salts with counter-ions; however, they are not normally treated as such. There is no lactate in freshly drawn milk but it may be present in stored milk and in milk products. The major elements are of importance in nutrition, in the preparation, processing and storage of milk products due to their marked influence on the conformation and stability of milk proteins, especially caseins, and to a lesser extent the stability of lipids and the activity of some indigenous enzymes. 5.2 Method of analysis The mineral content of foods is usually determined from the ash prepared by heating a sample at 500-600°C in a muffle furnace for about 4h to oxidize organic matter. The ash does not represent the salts as present in the food because: 1. the ash is a mixture, not of the original salts, but of the carbonates and 2. phosphorus and sulphur from proteins and lipids are present in the ash, 3. the temperature usually employed in ashing may vaporize certain volatile oxides of the elements present in the food; while organic ions, such as citrate, are lost during incineration; and elements, e.g. sodium and potassium. Therefore, it is difficult or impossible to relate the ash obtained from a food with its salts system, and low values are obtained for certain mineral elements by analysis of the ash compared to direct analysis of the intact food. Titrimetric, colorimetric, polarographic, flame photometric and atomic absorption spectrophotometric techniques are frequently used to analyse for the various mineral constituents; however, the quantitative estimation of