Antioxidant properties of industrial heat-treated milk

Abstract

Milk is a source of antioxidant compounds in a delicate balance between anti- and pro-oxidative processes. This research aims at evaluating the antioxidant properties of industrial heat treated milk (UHT, Microfiltered and High Quality Pasteurized) with particular attention towards the characterization of unsaponifiable fraction, rich in antioxidant compounds, and its contribution to radical scavenging activity. Total polyphenol content, FRAP, DPPH and colour, often related to antioxidant properties, were performed on milk. Moreover, the unsaponifiable fraction of milk samples was studied for: (a) α-tocopherol, β-carotene, retinol isomers, cholesterol and two previously developed indices Degree of Retinol Isomerization (DRI) and Degree of Antioxidant Protection (DAP); (b) DPPH assay; (c) a qualitative analysis of its major functional groups by Fourier Transformed infrared spectroscopy (FTIR) on Attenuated Total Reflectance (ATR). UHT milk showed the highest values in all assays, probably due to the development of antioxidant compounds, that occur during this severe heat-treatment and confirmed by a moderate correlation (r = 0.6791) between DPPH and b*(yellowness). On unsaponifiable fraction, differences were detected on 13-cis retinol and confirmed by DRI index and specific vibrations of functional groups of antioxidants were identified in FTIR-ATR spectra.