A qualitative method for the detection of rennet whey in milk

An adaptation and modification of the resorcinol method for rennet whey estimation in milkpowders was made in order to simplify it and make it suitable for a rapid detection of rennet whey added to pasteurized milk. Milks containing added rennet whey show a purple color after reaction with p-dimethylamino-benzaldehyde whereas genuine milks render a pale yellow to slight pink color. Advantages and shortcommings of the method are presented and fully discussed.   

1. Introduction

Studies on the presence of rennet whey in skim milk powder have been carried out recently in France (LOKO8; HAYET 2), the Netherlands (OLIEMAN; VAN DEN BEDEM10), in the Federal Republico of Germany (LECHNER, KLOSTERMEYER7; LECHNER6), and Australia (LORENZ et al.9). Rennet whey is a by product of cheese making and due to ist lower price could be financially attractive to the fluid milk industry as a mean of increasing milk volume sold to the consumers and therefore of increasing industry earnings. According to article 543 of the Brazilian Milk Ordinance the pasteurised milk shall not contain any extraneous added substances (e. g water, preservatives); althought not mentioned, addition of cheese whey to milk consitutes also a fraud.

This paper describes an adaptation and simplification of the current spectrophotometric method for rennet whey detection and quantification in milk powders by means of resorcinol reagente (LOKO8; HAYET2) which could enable laboratory technicians of the Milk Federal Inspection Service to control easily the presence of added whey in pasteurised milk.

4. Resumo

Um método quelitativo para detectar soro de queijo em leite pasteurizado. Foi feita uma simplificação do método de resorcinol para determinar soro de queijo em leite em pó, visando sua adaptação para uma rápida detecção de soro de queijo adicionado ao leite pasteurizado. Após isolamento do ácido siálico solúvel presente no leite adicionado de soro, o mesmo é identificado pela cor púrpura que se desenvolve ao reagir com p-dimetil amino benzaldeído em solução ácida. Leite genuíno apresenta coloração amarelada (palha) ou ligeiramente rósea. Vantagens e restrições do método qualitativo proposto são apresentadas e discutidas.

5. References

2. HAYET, J. L. Recherches sur l’origine de la présence de Lactosérum dans les poudres de lait. Technicien du Lait, n. 20, p. 30-33, 1984. 

6. LECHNER, E. Erfahrungen aus der Untersuchung von Milchtrochenprodukten. Molk. Welt der Milch, v. 35, n. 42, p. 1325-1332, 1981.

7. LECHNER, E.; KLOSTERMEYER, H. Nachweis einer Verälschung von Magermilchpulver mit Molkenpulver (polarographische Methode). Milchwiss., v. 36, n. 5, p. 267-270, 1981.

8. LOKO, R. A propos de la recherche de lactosérum dans les poudres de lait. Technique Laitière, n. 964, p. 23-27, 1982.

9. LORENZ, W.; SCHUBERT, P.; HOFFER, H. Nachweis von Molkenpulver in milchpulver mittels GMP-methode. Milchwirt. Ber., v. 72, p. 196-196, 1982.

10. OLIEMAN, C.; VAN DEN BEDEM, J. W. A sensitive HPCL method of detecting and estimating rennet whey total solids in skim milk powder. Neth. Milk Dairy J., v. 37, n. 1, p. 27-37, 1983.

 [81] WOLFSCHOON-POMBO, A. F.; PINTO, A. P. E. de F. A qualitative method for the detection of remot whey in milk. Ciênc. Tecnol. Aliment., v. 5, n. 2, p. 111-115, 1985.