The effect of light on the vitamin C of milk

Abstract

IN estimating vitamin C chemically in milk by the method of Birch et al. [1933], Kon [1933] observed very marked fluctuations in the concentration of that vitamin from day to day.The possible causes of this phenomenon were investigated by Mattick & Kon [1933], who ultimately found that milk which originally gave a positive vitamin C titration failed to reduce the indophenol reagent after a short exposure to light in glass bottles. Some time later Booth & Kon [1934] showed that 90 % of the original power of reducing the reagent could be restored after short exposures to light by treating the milk with hydrogen sulphide. Longer exposure entailed greater irreversible losses.An example of the effect of light will be found in Table I.Table I. Vitamin C estimations carried out on milk from a pint bottle before and after half-an-hour's exposure to sunlight.

A STUDY OF CERTAIN REDUCING SUBSTANCES IN CITRUS FRUITS 1

“…Solutions of pure crystalline ascorbic acid showed similar behavior on irradiation followed by reduction with H,S. The work of Kon and Watson (1936), which appeared during this investigation, confirms the statement as to the oxidative nature of the destruction of ascorbic acid by ultra-violet irradiation. An increase in the acidity of the juice failed to produce any change in the reducing properties.…”

The effect of oxygen content on flavour and chemical changes during aseptic storage of whole milk after ultra-high-temperature processing

“…Hand, Guthrie & Sharp (1938) demonstrated that removal of O 2 from pasteurized milk by controlled vacuum treatment, and its subsequent exclusion, prevented flavour defects due to oxidation and preserved the reduced ascorbic acid naturally present or added to milk. Kon & Watson (1936) had previously demonstrated the latter effect. Ford et al (1969) have shown that in ultra-high-temperature (UHT) treated milk processed by direct heating and containing less than 0-1 ppm of O 2 both ascorbic acid and folic acid were retained during storage.…”

The photochemical decomposition of l-ascorbic acid

“…It may be observed in this connexion that the slightly increased decomposition of ascorbic acid recorded by Kon & Watson [1936] when milk was exposed in quartz rather than in glass vessels, was presumably due to the direct action of ultraviolet light. The greater part of the decomposition of the acid in the quartz vessel was, however, brought about probably in the same way as in the glass vessel, namely, as suggested by Hopkins [1938], by the action of visible light sensitized by the lactoflavin of the milk.…”

“…Martini & Bonsignore [1934] found that i-ascorbic acid reduced methylene blue to its leuco base when exposed to the light of an ordinary electric lamp. Kon & Watson [1936] observed that on exposure to visible light of short wave length (blue and violet) I-ascorbic acid in milk was oxidized to dehydroascorbic acid. A probable explanation for this phenomenon is found in the observation made by Hopkins [1937; 1938] that lactoflavin and to a lesser extent lumichrome could act as sensitizers in the oxidation of i-ascorbic acid when exposed to solar radiation.…”