350 zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA the National Institutes of Health. LITERATURE CITED Association of Official Analytical Chemists, “Official Methods of Analysis”, 12th ed, Washington, D.C., 1975, sections Folch, J., Lees, M., Stanley, G. H. S., zyxwvut HGFEDC J. zyxwvuts A Biol. Chem. zyxwvu KJIHG 226, 497 (1957). Sheppard, A. J., Hubbard, W. D., Prosser, A. R., Interim Methodology Instructions No. 2, for Implementing Require- ments of Section 1.18 of Title 21, Chapter 1, Subchapter A, zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCB J. zyxwvutsrq BA Agric. Food Chem., zyxwvutsrq Vol. 26, No. zyxwvutsr 2, 1978 28.057-28.060. Riemer, Karel Part I (“Labeling of Foods in Relation to Fat, Fatty Acid and Cholesterol Content”) issued June 11, 1974, Division of Nu- trition, Bureau of Foods, Food and Drug Administration, Washington, D.C. Sheppard, A. J., Newkirk, D. R., Hubbard, W. D., Osgood, T., JI Assoc. Off. Anal. Chem. 60, 1302 (1977). J., J. Am. Oil Chem. SOC. 51, 424 (1974). Solomon, H. L., Hubbard, W. D., Prosser, A. R., Sheppard, A. Received for review June 15,1977. Accepted November 8,1977 On the Anaerobic Degradation of Ascorbic Acid in Dehydrated Tomato Juice Joseph Riemer and Marcus Karel* During a study aimed at developing methods for computer-aided simulation of ascorbic acid loss in dehydrated tomato juice, we investigated the influence of environmental variables. Previous studies on dehydrated products showed an aerobic reaction in some cases, but no oxygen effect in others. T establish definitively the existence of anaerobic reaction in our system, reaction rates in a catalytica deoxygenated system were compared with rates in the presence of oxygen; and an oxygen mass bala experiment was conducted in a system containing a known and limited amount of oxygen. The resu definitively establish that ascorbic acid degradation in dehydrated tomato juice is largely anaerobic During storage of dehydrated foods inpermeable packages, many changes occur that lead to quality dete- rioration. An important index in deterioration of dehy- drated juices is the loss of vitamin C. Environmental factors and package properties affect the rate of loss of this vitamin, and environmental conditions may change during storage. Moisture is transferred into the package, resulting in the increase of moisture content and equilibrium relative humidity; oxygen is transferred into the package where it may accumulate in the headspace or react with the food. We have recently conducted a study directed at developing methods for computer-aided simulation of ascorbic acid degradation during storage. Dehydrated tomato juice powder was the food chosen for the study, and oxygen pressure was one of the storage variables to be studied. In the course of the study it became apparent that the effect of this variable was negligible. The present paper reports the results of experiments undertaken to establish whether degradation of the vitamin was truly anaerobic in this system. Vitamin C losses in several dehydrated foods had been reported to be the result of aerobic reaction and, in other foods, an anaerobic degradation reaction. Heberlein and Clifcorn (1944) found that an inert atmosphere favored the retention of ascorbic acid in dehydrated fruits and veg- etables at room temperature. Miers et al. (1958) monitored ascorbic acid retention of spray-dried tomatoes during storage and found that high moisture levels, presence of oxygen, and storage temperature above 90 O F were factors detrimental to the storage stability. On the other hand, the retention of ascorbic acid in storage of tomato flakes was found to be independent of the package atmosphere (Continental Can Co., 1944,1945), and Karel and Nickerson (1964) found that in stored dehydrated orange juice ascorbic acid degradation occurred Department of Nutrition and Food Science, Massa- chusetts Institute of Technology, Cambridge, Massa- chusetts 02139. at the same rate in air and in vacuum. Lempka and Prominski (1967) and Lempka et al. (1969,1970) studied the changes in the ascorbic acid content of dehydrated fruits and vegetables and have shown that storage o freeze-dried products in air had little effect on ascorbic acid. In a study of various tomato products during stora Hummel et al. (1950) found that the amount of oxygen present in the headspace (not considering potential oc cluded air) could not account for the resulting ascorbic a degradation and that the reduction of dissolved air b increasing processing time did not improve ascorbic aci retention. In our studies the effects of various oxygen levels (21, 7.2,3.5, and 0.2%) on the rate of ascorbic acid degradat in dehydrated tomato juice were found to be insignifican These observations necessitated further investigation of the following hypotheses: (a) degradation of ascorbic acid in this system is an anaerobic reaction or oxygen is available in the product in quantities sufficient for aerob degradation; (b) reaction is aerobic, i.e., oxygen is availa in the system in quantities sufficient for aerobic degra- dation; (c) degradation occurs both aerobically and anaerobically. These alternatives are schematically il- lustrated in Figure l. In this study we describe the approaches used in determining which of the alternative is the correct one. EXPERIMENTAL SECTION The Food System. Commercially available frozen tomato concentrate (Vitality Brand, Lykes Pasco Co., Da City, Fla.) was used for preparing a stock of freeze-drie tomato juice powder. The concentrate was diluted 3:l w distilled water, a point at which it had a 6.7’ Brix and a pH value of 4.1. It was frozen (slow freezing, -25 O F ) and freeze-dried (Vacudyne freeze-drier) for 72 h. The de- hydrated tomato juice was kept in desiccators unde vacuum at -25 O F in the dark. Ascorbic Acid Assay. L- Ascorbic acid was determined by a 2,6-dichlorophenolindophenol titration, an AOAC (1975) official method. Since the investigated samples w 0021-8561/78/1426-0350$01.00/0 0 1978 American Chemical Society