Indoxylsulfate in milk

Abstract        

Indoxylsulfate in 27 individual milk samples ranged from 25.4 to 111 µg/l (average 52.3 µg/l); pooled milk samples from 12 farms contained 81.1 µg/l (46.4 – 146 µg/l); the variation in indoxylsulfate concentration of dried skimmed milk over a period of one year amounted to 23%. This variability is likely attributable to regional and seasonal, and hence to feeding effects. The indoxylsulfate content of milk seems also to be dependente upon the degree of fermentation during processing of milk; yogurt contained very low amounts of this component (6.4 µg/kg). On the other hand, heat treatment of the milk (HTST, UHT, sterilization) apparently does not affect its indoxylsulfate contente. Indoxylsulfate concentrations in milk correlated positively with blood-serum indoxylsulfate content (r = 0.752, n = 20) and with the urea content of milk (r = 0.61, n = 12 pooled milks). Further research is suggested on the use of indoxylsulfate determinations as an aid to determine sweet whey added to dried skimmed milk, also as an analytical tool to differentiate bovine and sheep milk.

Introduction 

Indoxylsulfate (1-H-Indol-3yl-sulfate) is one of the final products of tryptophan catabolism and is excreted by mammals as a detoxication product of the índole produced by the bacterial flora of the gut [1, 2]. Its normal occurence in urine and blood has been establisched [3. 4] and its presence in milk was also reported [5], and very recently confirmed by means of reversed-phase high-performance liquid chromatography with fluorescence detection [6].

Our previous work on the indoxylsulfate content of cows milk has been continued. To provide more information, more milk sampless and other dairy products, as well as blood sera, have been collected and analyzed for indoxylsulfate. Analysis on milk other than bovine milk have also been carried out. Furthermore, since the possibility could exist of exploring indoxylsulfate as a marker for dairy products, the influence of technological treatments (e. g. heating, fermentation) on it has also been studied, and laboratory mistures of skimmed milk powder and rennet whey powder were also analyzed for indoxylsulfate.

This report outlines the results obtained.

References 

1. DALGLIESH, E. C. Adv Prot Chem, v. 10, p. 31-150, 1955.

2. MAYER, P. J.; BEEKEN, W. L. Am J Dig Dis, v. 20, p. 1003-1010, 1975.

3. BARNET, A. L.; VEENING, H. Clin Chem., v. 31, p. 127-130, 1985.

4. BÖHM, F. Biochem Z, v. 290, p. 137-171, 1937.

5. SPINELLI, F. Boll Soc It Biol Sperimental, v. 22, p. 211-212, 1946.

6. WOLFSCHOON-POMBO, A. F.; WEISS, G.; MILLER, M.; KLOSTERMEYER, H. Milchwissenschaft (in press).

[90] WOLFSCHOO-POMBO, A. F.; KLOSTERMEYER, H. Indoxylsulfate in milk. Z Lebensm Unters Forsch, v. 182, p. 103-106, 1986.