The action of sunlight on milk

Abstract

SUNLIGHT has a specific and very interesting action on milk. Viale [1925], investigating the Schardinger reaction, observed that milk decolorizes methylene blue even without the addition of aldehyde if exposed to sunlight. Furthermore boiled milk retains this property although the aldehyde hydrogenase is destroyed, enzymic action being thus excluded.Whitehead [1930] also studied this phenomenon and attributed it to an oxido-reduction in which the unsaturated fat acts as oxygen acceptor. This interesting hypothesis was not supported by further investigations. From Whitehead's experiments this explanation appears very probable. In fact, if the fat is removed, the milk no longer decolorizes methylene blue when exposed to sunlight. If a salt of an unsaturated fatty acid (e.g. sodium oleate) is now added, the phenomenon reappears. When the methylene blue is reduced, the milk acquires an unpleasant characteristic fishy odour. In 1928 Frazier also observed this phenomenon and attributed the unpleasant odour and flavour of the milk to the oxidation of the fat.Whitehead attributed the changes undergone by the milk in his experiments to the action of ultraviolet radiations, being led to this suggestion by the fact that it has long been known that ultraviolet radiations catalyse the oxidation of unsaturated fats.

Preparation of waterborne polyurethane with outstanding fluorescence properties and programmable emission intensity

“…The Stokes shift values for FWPU indicate that the less non-radiative process of FWPU is relatively important. 28 The fluorescence decay behaviors of FWPU as determined from time-resolved fluorescence measurements are exhibited in Figs 8 and 9, which illustrate the effects of hard segment content and hydrophilic group content, respectively, on the fluorescence lifetime ( ) of FWPU. A longer lifetime of FWPU is due to the increasing hard segment content and appropriate hydrophilicity.…”