Analysis of caseins in cheese using ion-exchange chromatography

Peer Reviewe

Método eletroforético rápido para detecção da adulteração do leite caprino com leite bovino Fast electrophoretic detection method of adulteration of caprine milk by bovine milk

Avaliaram-se os métodos de eletroforese em gel de poliacrilamida (PAGE) em presença de uréia (uréia-PAGE) e dodecil sulfato de sódio (SDS-PAGE) para identificar a adulteração do leite de cabra pela adição do leite de vaca. Um método foi otimizado para preparação do caseinato de sódio em poucos minutos para análise eletroforética. Uréia-PAGE foi o método mais apropriado para identificação desse tipo de fraude, em decorrência da presença da caseína alfas1 com migração mais rápida no leite bovino. A presença da alfas1-caseína bovina foi detectada a partir da adição de 2,5% de leite de vaca utilizando uréia-PAGE. O limite de detecção, a repetibilidade, o tempo para execução indicaram que esse método pode ser aplicado como rotina no controle de qualidade do leite de cabra recebido pelas indústrias de processamento.<br>Polyacrylamide gel electrophoresis (PAGE) in presence of urea (urea-PAGE) or sodium dodecyl sulfate (SDS-PAGE) was evaluated to detect the presence of cow milk added to goat milk. A method was optimized to prepare sodium caseinate from milk in few minutes. After that, the sodium caseinate was analyzed by PAGE. The urea-PAGE was the most appropriated method to identify adulteration as caprine and bovine alphas1-caseins displayed different migration rates. When cow milk was added to goat milk at different proportions, the presence of bovine alphas1-casein was detected in the mixture by urea-PAGE for a minimal proportion of 2.5% of cow milk added to goat milk. The good sensitivity, the repeatability and the short time for execution indicate that the described method will be able to be routinely applied for the quality control of goat milk in dairy industry

Lipolytic enzymes and hydrolytic rancidity

Lipolysis, the enzymic hydrolysis of milk lipids to free fatty acids and partial glycerides, is a constant concern to the dairy industry because of the detrimental effcts it can have on the flvor and other properties of milk and milk products. However, free fatty acids also contribute to the desirable flavor of milk and milk products when present at low concentrations and, in some cheeses, when present at high concentrations. The enzymes responsible for the detrimental effects of lipolysis are of two main types: those indigenous to milk, and those of microbial origin. The major indigenous milk enzyme is lipoprotein lipase. It is active on the fat in natural milk fat globules only after their disruption by physical treatments or if certain blood serum lipoproteins are present. The major microbial lipases are produced by psychrotrophic bacteria. Many of these enzymes are heat stable and are particularly significant in stored products. Human milk differs from cows' milk in that it contains two lipases, a lipoprotein lipase and a bile salt-stimulated lipase. The ability of the latter to cause considerable hydrolysis of ingested milk lipids has important nutritional implications