CAROTENE DEGRADATION IN DEHYDRATED CARROTS. II. STABILITY OF CAROTENE IN CARROT TISSUE KEPT IN MOIST AIR AT 60°C.

DEHYDRATED VEGETABLES, the importance of which has now greatly increased, are often regarded as relatively imperishable. This view has proved, however, to be far from correct. To determine why these products are perishable is therefore necessary. Theproblem is, moreover, of theoretical interest; such studies may furnish information on the pigments, oil, and protein complexes of the vegetable cell. In carrots, Weier (1942) and Reeve (1943) have shown that the carotene, associated in living cells with starch, or present in crystal-like bodies, goes into solution in oil droplets when the cells are killed. In dried carrots probably 90 per cent of the carotene is thus dissolved in oil. Dried carrots, whether blanched or not, develop off-odors and lose carotene upon prolonged storage, the process of deterioration being much more rapid in the unblanched material. By placing carrots in a moist atmosphere at 600C. this change may be brought about in twenty-one hours2 (Weier, 1944). When the carotene has disappeared from the oil droplets, either upon prolonged storage or upon heating at 600C. for twentyone hours, the oil droplets rapidly regenerate Schiff's reagent. This fact suggests the development of aldehydes and the rancidification of the oil in the droplets, together with the breakdown of carotene. It should be emnphasized that carotene is definitely known to break down when carrots are stored for a long time or subjected to 60?C. The rancidification of the oil and the subsequent formation of aldehydes are only inferred from the regeneration of Schiff's reagent in the droplets of oil when sections are placed in the reagent (Weier, 1944). The hypothesis of the oxidation of the oil in the droplets within the carrot cells, with an associated breakdown of the carotene, is attractive and has many precedents. In some instances an enzyme, lipoxidase, is responsible for the oxidation of the fat (Strain, 1941; Reiser and Fraps, 1943; Sumner and Somers, 1943) which precedes the breakdown of the carotene. In other cases autoxidation of the fat occurs (Gortner, 1938, p. 781-786). Newton (1932) reported -that carotene or some associated substance protected fats against autoxidation. Olcovich andMattill (1930) had previously shown that pure carotene is 1 Received for publication June 13, 1944. 2 Twenty-one hours was selected for these experiments merely as a matter of convenience, both for amount of carotene breakdown and for preparation of the experiment. Carrot cylinders were prepared during the morning and allowed to stand over night in the oven. At 60?C. carotene breakdown is rapid and little protection is afforded the pigment. a proxidant. Olcott (1934) confirmed this, and Olcott and Mattill (1936a) stated that the associated substance in the carotene solutions used by Newton was responsible for protecting the fat against oxidation. According to Olcott and Mattill (1 936b), vegetable oils contain inhibitols, which protect animal fats, but not the vegetable fats in which they are found, against rancidification. Organic acids, however, as well as H2SO4, HPO3, and substances with two free carboxyl groups, under practically anhydrous conditions, prolonged the induction periods of crude esters of vegetable oils. El-Rafey, Richardson, and Henderson (1944), in studies on butteroil, found that heating released phospholipids, which considerably improved the keeping qualities of the butteroil. The phospholipids could be removed by washing the butteroil. Blanching is known to improve the keeping qualities of dehydrated vegetables, although it does not prevent deterioration. According to Cruess and Mackinney (1943, p. 38), one major object of blanching is the destruction of enzymes that may cause undesirable changes in the flavor, texture, and color of the dehydrated product. It seems also possible that in carrots heating may release an inhibitor of some sort, which prolongs the induction period of the oil in which the carotene is dissolved. This paper reports the evidence that carrot cells contain a substance which protects carotene from destruction; this substance is rendered more effective by heating and may be leached from the tissue. The study also includes the influence of blanching, variety, sulphite, leaching, and pH on the stability of the carotene and suggests some ways in which the results may be of practical importance. I am indebted to W. V. Cruess, Gordon Mackinney, L. K. Mann, and W. W. Robbins for their interest and help with the work and to Margaret Ensign and Edith Colville for much technical assistance. MATERIALS AND METHODS.-Two varieties of carrots, Red Core Chantenay and Imperator, were used. They were grown at Davis, California; were planted in April, 1943, and harvested, when mature, during the winter and spring of 1943-44. The results reported apply only to this culture of carrots; they may not necessarily be repeated on cultures of different ages grown at Davis or on cultures grown in other environments or on other varieties. This statement may seem unnecessarily cautious; but we have found considerable variation for instancein the gelatinization temperature of the starch in carrots of different ages (Mann and Weier, 1944). The carotene content is known to vary in carrots of dif-