Effects of industrial heat treatments on the kinetics of inactivation of antimicrobial bovine milk xanthine oxidase

Gulustan Ozturk,Juliana M L N De Moura Bell,J Bruce German

doi:10.1038/s41538-019-0046-8

Gulustan Ozturk, Juliana M L N De Moura Bell + Show 1 more

Open Access

https://doi.org/10.1038/s41538-019-0046-8

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Abstract

Milk is a source of antimicrobial systems such as xanthine oxidoreductase, which has been proposed to modulate the oral and gut microbiota of infants. Heat treatments are applied to milk to ensure its microbial safety, however, the effects of heat on this antimicrobial enzyme are not known. The effects of batch pasteurization (BP), high-temperature short time (HTST), and ultra high temperature (UHT) on kinetics of inactivation of xanthine oxidase and its antimicrobial properties were determined. Xanthine oxidase activity was preserved by HTST (100%). Partial (8%) and nearly complete (95%) enzyme inactivation were observed for BP and UHT milks, respectively. Km values of 100 μM and Vmax values of 6.85, 5.12, 6.31, and 0.40 μmol/min/mg were determined for xanthine oxidase in raw, BP, HTST, and UHT milks, respectively. These results demonstrate that xanthine oxidase maintains apparent affinity and activity for its substrate when milk is treated by BP and HTST and yet the enzyme is inactivated with UHT. To investigate heat treatment-induced alterations in the biological activity of xanthine oxidase, heat treated milks were compared to raw milk for their ability to inhibit the growth of S. aureus. Raw, BP, and HTST milk xanthine oxidase efficiently inhibited S. aureus growth. However, these antibacterial properties were lost when milk was subjected to UHT. These results demonstrate that HTST and BP preserves bovine milk xanthine oxidase activity compared with UHT and that, the judicious selection of thermal treatments could be exploited to preserve the antimicrobial properties of bovine milk.

Highlights

Milk is a complex fluid that evolved to provide complete postnatal nutrition for mammalian infants.[1]
Raw milk was used as a control for all experiments and exhibited an average activity of 200.0 ± 12.3, 62.6 ± 8.5, and 263.2 ± 8.2 U/L for xanthine oxidase, xanthine dehydrogenase, and xanthine oxidoreductase, respectively
Despite differences in the methods used in both studies, similar values of xanthine oxidase activity were observed in both studies (208 vs. 200 U/L)

Summary

Introduction

Milk is a complex fluid that evolved to provide complete postnatal nutrition for mammalian infants.[1] Research is revealing that milk acts to provide a selective microenvironment for the development of the oral and gut microbiota in the neonate.[2,3,4,5] Milk both feeds and prevents microbial growth. Milk is a source of enzyme, such as xanthine oxidoreductase, that recent research has shown to produce anti-microbial metabolites, notably H2O2 These metabolites have been interpreted to modulate both the oral and gut microbiota.[5] Xanthine oxidoreductase is widely distributed in mammalian tissues and is a major constituent of the milk fat globule membrane, that surrounds fat globules in milk.[6,7]

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