THE EFFECT OF SUNLIGHT ON CRUDE LIPIDS EXTRACTED FROM FRESH AND FROZEN VEGETABLES^a,b,c,

Abstract

It is known that light causes the development of peroxides in oils ( 4 ) , and in unsaturated fatty acids which are mixed with chlorophyll previous to exposure (3). Autoxidation of certain oils in the presence of chlorophyll has been reported ( 2 , l l ) . Past work at the Geneva Station gave indication that vegetable crude lipids were sensitive to sunlight. Dr. A. C. Wagenknecht of the Geneva Laboratory obtained some evidence of this also, in work with extracts from dehydrated peas. It was shown in these laboratories ( 6 ) that carotene reduces drastically the formation of peroxides by chlorophyll in vegetable oils when exposed to direct sunlight. Because of these facts, a study was undertaken to determine the effect of sunlight on the crude lipids extracted from vegetables. MATERIALS AND METHODSSix vegetables were employed : asparagus, Martha Washington variety ; sweet corn, Golden Cross variety; lima beans, Fordhooks; peas, Thomas Laxton variety; peas, purchased on the market, probably a Telephone type; spinach, Nobel and Heavy Pack varieties ; and snap beans, Tendergreen variety. Blanched and unblanched sampres were held in frozen storage at 0°F. (-173°C.) for varying periods of time. I n addition to these, freshly harvested and unblanched and the corresponding blanched samples of lima beans, peas, and sweet corn, of the same varieties noted before, were frozen overnight. This was followed by immediate lyophilization and extraction t o determine differences which might be found when the lipids from fresh and stored materials were exposed to the action of sunlight.The vegetables were dried by lyophilization and the crude lipids prepared as described in previous publications (5, 7). Twenty-milligram (2 10%) samples were distributed as evenly as possible in white porcelain evaporating dishes, 100 mm. in diameter, from ethyl ether solutions of the crude lipids. The ether was evaporated by swirling. These operations were conducted in the dark or in dim red light. The samples were exposed to bright mid-day sunlight (10,000 foot candles in intensity), as measured by a Weston illumination meter model 603, reading from 0 to 10,000 foot candles, or an instrument calibrated t o be its equivalent, for varying periods of time from 0 to 120 minutes exposure. Cloudless days were selected for this work. Ambient temperatures were taken during most of the exposures. Some samples were exposed under glass to cut out the shorter ultraviolet rays.