ASCORBIC ACID IN TOMATOES 11 



rhages in joints, ribs, muscles, and intestines. One, two, or three plus signs are 

 recorded for each of the eight parts examined, according to the degree of abnor- 

 mality found, thus making possible a maximum scurvyscore of 24. Isham(1932) 

 noted in examining guinea pigs, that hemorrhages of the bladder were often found 

 in cases of scurvy, but absent in all other instances. This characteristic lesion 

 should be taken into account in scoring the hemorrhages of the intestine. Isham 

 (1932) also noted that much less variation in results occurred when the full 90-day 

 feeding period was used. 



Negative controls, which received the basal ration only, died from scurvy 

 in from 23 to 36 days. Positive controls were also used for comparison, the 

 animals receiving two grams of grapefruit juice daily. These positive control 

 guinea pigs usually doubled their weight and showed no evidence of scurvy 

 lesions. 



Chemical 



Of the many procedures mentioned in the literature for chemical estimation 

 of ascorbic acid, only two are used in this study of the tomato and tomato products. 

 Data on the modified iodine titration technic of Lorenz, Reynolds, and Stevens 

 (1934) and Stevens (1938) have not been reported to any extent. Consequently, 

 it was thought best to study this method to prove definitely its value. The 2, 

 6-dichlorophenolindophenol dye suggested by Tillmans, Hirsch, and Hirsch 

 (1932) is accepted to date as the most accurate quantitative method for deter- 

 mining ascorbic acid. Therefore, this dye was used in this study. 



Modified Iodine Titration for Ascorbic Acid 



Extracted serum from the material to be tested for ascorbic acid was acidified 

 with 12N sulfuric acid. Standardized O.OIN iodine solution containing 25 grams 

 of potassium iodide per liter was added until an excess was indicated by a brown 

 color. Standardized O.OIN sodium thiosulfate solution was added in slight 

 excess, followed by a small quantity of 0.5 percent starch solution. Finally, more 

 of the O.OIN iodine solution was added slowly until the well-known starch-iodine 

 end point was reached. Calculation for ascorbic acid content of the sample 

 was as follows: 



Total I J volume less lo equivalent of Na2S2 03 volume = 



volume I 2 for the o.xidation of ascorbic acid. 

 This procedure differs from the ordinary iodine technic in two essential respects. 

 The modified iodine method has a higher acidity and there is a double back titra- 

 tion. If sufficient sulfuric acid is not added, the titration will be sluggish, es- 

 pecially near its completion. When sufficient acid is present, the end point 

 persists for a longer period of time. Furthermore, at the lower pH, the iodine 

 oxidizes less of the reducing substances, other than ascorbic acid, which may 

 be present. 



Dye Titration for Ascorbic Acid 



Extracted serum from the sample was adjusted approximately to neutrality 

 according to the method of Tillmans, Hirsch, and Hirsch (1932), by the addition 

 of sodium acetate. Standardized 0.05 percent 2, 6-dichlorophenolindophenol 

 was added until oxidation of the ascorbic acid was complete. This was indicated 

 by the excess of dye which was blue in neutral solutions. The total volume of 

 dye utilized is a measure of a part of the reducing capacity of the tested material. 

 This portion of the reducing capacity of plant substances is closely correlated 

 with the ascorbic acid content. 



