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INDUSTRIAL AND ENGINEERING CHEMISTRY
beans. All cooking tests were carried out, however, after the storage period, as originally planned. After &month storage a t -6 O F. a set of each lot was removed for chemical analysis. At the same time a duplicate set was removed for cooking tests. Both peas and snap beans were cooked after storage by a common method in which a relatively large volume of cooking water was used, as would be done in many homes. According to this method, two cupfuls of boiling water were used for each carton of vegetable. The peas were cooked for 9 minutes after immersion in the boiling water; the snap beans were cooked for 10 minutes. Then the samples were frozen and prepared for analysis as before. TASTE AND VITAMIN CONTENT
The tasters for the cooked samples were a group of six disinterested, qualified judges who were uninformed as to the treatments until the tests were concluded. Two of the judges felt that the samples of peas frozen in the insulated boxes were slightly offflavor, but agreed that it would not have been detected if the other lots had not been available for comparison. However, the textures of all the samples were judged to be the same, with the exception of the one frozen in liquid air which was considered a little more tender. This was probably due to the fact that tlie units were cracked and broken by this treatment, and the cooked product as served had the appearance of being broken. Little difference was detected in any of the bean samples. As far as taste tests are concerned, the results from these two vegetables suggest that both starchy and nonstarchy vegetables are little affected by rate of freezing, even when that rate is extremely slow. Data for both peas and snap beans (Tables I1 and 111) show that even with the very slow rate of freezing (resulting when the cartons were put into the freezer inside an insulated box) there were only slight vitamin differences, even after cooking’. These similarities are especially noteworthy in the case of ascorbic acid. Only after cooking in large volumes of water did large losses result, but this happened in all cases, regardless of the freezing rate of the vegetable analyzed. Before this study was completed, it was suspected that ice crystals might cause enough tissue damage, especially in slow-frozen samples, to result in excessive leaching loss of vitamins if the vegetable was cooked in a relatively large volume of water, in comparison with rapid-frozen samples. This has been shown to be contrary to fact. We do not wish to create the impression that we recommend for use the slowest freezing conditions described in this study because, under some conditions, difficulties of a bacteriological nature might be encountered. We used the very slow rate solely for comparative purposes. Also, we do not mean to confuse rate of freezing with over-all time of handling. The work described in this paper deals only with a comparison of the several rates of freezing described. This should not be confused with an overall time of handling with which this paper is not concerned. The photomicrographs (Figures 3 and 4) disclose that in each successive case the more slowly frozen vegetable shows larger ice crystals and apparently greater damage to the tissues; in the corresponding thawed samples these differences disappear, and all samples look alike, regardless of the conditions under which they were originally frozen, This is true for both peas and snap beans. Because of space limitations photomicrographs are presented only for those vegetables frozen a t one intermediate and the two extremes in freezing rates after six-month storags. Those taken immediately after freezing could not be distinguished from the pictures shown here. Pictures of the cross sections of the vegetables from two boxes of commercial frozen peas and snap beans are shown for comparison. 1 The only exception was carotene which showed slight progressive increase. These apparent increases in carotene have been noted in other laboratories (personal communication from Walter L. Nelson).
Vol. 38, No. 3
SUMMARY
Peas and snap beans show few differences in vitamin content or palatability whether frozen very slowly, very rapidly, or a t intermediate rates. Photomicrographs of cross sections show the formation of large veins of ice in the slow-frozen products, but when thawed no injury is evident. Analyses indicated no significant differences in the vitamin contents of the peas or snap beans, frozen a t greatly different speeds, after freezing, after storage, or after cooking. No significant organoleptic differences could be distinguished by a group of experienced judges. ACKNOWLEDGMENT
This report is based on one of a series of studies supported largely by the Consolidated Edison Company of New York, Inc. The studies are being carried out under the direction of the Research Committee on Food Processing and Storage appointed from the staff of Cornell University. The vegetables used in this study were supplied by W. T. Tapley, of the Division of Vegetable Crops of this station. We wish to acknowledge the technical assistance of Michael R. Sfat. LITERATURE CITED
Diehl, H. C., and Berry, J. A., Proc. Am. SOC.Hort. Sci., 30 496500 (1933).
Eickelberg, E. n7.,Cunning Age, 1 9 , 4 9 8 - 9 , 5 1 2 (1938). Fenton, Faith, Cornell Eztenaion Bull. 628 (Dec., 1943). Joslyn, M. A., and Marsh, G. L., Fruit Products J., 12, 203-5, 220 (1933).
MacArthur, Mary, Ibid., 24, 238-40 (1945). Martin, W. M c K . , Canning Trade, 59, No. 29, 7-14 (1937). Moyer, J. C., and Tressler, D. K., IND.ENQ.CHEM.,ANAL.ED., 14, 788-90 (1942).
Pickett, T. A., and Brown, W. L., Fruit Products J . , 12, 134 (1933).
Plagge, H. H., Ice and Refrig., 94, 220-3 (1938). Robinson, W. B., and Stotz, E. H., J. Bid. Chem., 160, 217-25 (1945).
Snell, E. E., and Strong, F. M., IND.ENQ.CHBM.,ANAL.ED.,11, 346-50 (1939).
Woodroof. J. G.. Ga. Agr. - Expt. . Sta., Bull. 168 (1931). (13) Zbid., 201 (1938). (14) Zimmerman, W. I., Tressler, D. K . , and Maynard, L. A, Food Research, 6,57-68 (1941). APPROVED by the Director of the New York State Agricultural Experiment Station for publication as Joulnal Paper No. 644.
Thermodynamic. Properties of _Wethane at Low Temperature-Correc tion An error of statement has been found on page 827 of this article in the September, 1945, issue. This inaccuracy was found as a result of discussion of the results by C. S. Matthews and C. 0. Hurd. The sentence beginning in the tenth line, “Enthalpies of saturated gas . . . , given reference point”, should be replaced by the following sentences: Enthalpies of saturated gas were obtained from the values given by the latter authors by coordinating their value for - 163’ F. n ith the values obtained for the single-phase region and then utilizing their enthalpy differences along the saturation curve. The enthalpies of the saturated liquid were obtained from those of the saturated gas and the enthalpy changes for vaporization given by Keyes, Taylor, and Smith ( 5 ) and also tabulated by Wiebe and Brevoort (11). Some mbdification of the data of Keyes et al. was made near tlie critical state in tlic interest of internal consistenry in the final values. W. H. CORCORAN CALIFORNIA INSTITUTE OF TECHNOLOGY PABADENA, C A L I F .
