32 MASS. EXPERIMENT STATION BULLETIN 354 



DISCUSSION OF RESULTS 



The chemical determination of ascorbic acid in tomato juice by the 2, 6-di- 

 chlorophenolindophenol method was found to check closely the bioassay method 

 of Sherman, La Mer, and Campbell (1922). This is in agreement with the results 

 of Manning (1936) on tomatoes and with King's (1936) conclusion from a review 

 of the literature. The modified iodine method of Lorenz, Reynolds, and Stevens 

 (1934) gave consistently higher results (factor 0.7) than the guinea pig assay for 

 ascorbic acid. 



No reversibly oxidized (dehydro) ascorbic acid was found in tomato juice when 

 reduced by hydrogen sulfide. Hauck (1938) found a small amount present in 

 tomato juice but the quantity indicated is of doubtful significance. McHenry 

 and Graham (1935) reported 0.15 mg. ascorbic acid per gram of tomato tissue 

 both before and after reduction. 



The enzymic oxidase for ascorbic acid suggested by Tauber and Kleiner (1935) 

 for the measurement of interfering substances in the titration was not found to 

 be quantitatively specific. These results are in agreement with those of Stotz, 

 Harrier, and King (1937). 



The oxidation of ascorbic acid may be catalyzed by copper (Barron, De Meio, 

 and Klemperer, 1936 and Kellie and Zilva, 1935) and by other metals (Mawson, 

 1935); but iron and tin salts did not interfere with the titration procedure used 

 in these studies. Consequently, ascorbic acid is determined as specifically in 

 tinned tomato juice as in fresh samples by this chemical method. 



The probable error in determining the end point of the chemical titration for 

 ascorbic acid was found to be ±2 percent. The difficulty in obtaining uniform 

 samples even from the same batch is well represented in Table 2 where there is a 

 variation of approximately +10 percent in titrated values. Because of this 

 variation in supposedly identical samples, it is inadvisable to draw definite con- 

 clusions from results within a 10 percent range. 



Two extractions for ascorbic acid in plant tissue have been shown to be nec- 

 essary in approximating the true antiscorbutic activity. In routine examinations, 

 however, one extraction is sufficient and the second extraction can be compen- 

 sated for by the addition of 10 percent of the value for tomato flesh or 16 percent 

 for tomato juice. 



Ninety-eight distinct varieties or strains of tomatoes were grown under con- 

 stant field conditions in 1936 and compared as to ascorbic acid content. The 

 tomato showed considerable variation, with values ranging from a maximum 

 of 249 international units per ounce to a minimum of 74 units. Krauss, Wash- 

 burn, and Hoffman (1937, 1938), Hoffman^, and Tripp, Satterfield, and Holmes 

 (1937) reported a considerable variation in tomato strains and varieties. Tripp 

 and his associates in 1936 found the Pritchard variety of tomato grown in Tennes- 

 see to have the highest ascorbic acid content of all the varieties tested. In the 

 same year and on similar soil types, but grown in Massachusetts, this variety 

 was shown to be the least potent source of ascorbic acid. This variation seems to 

 be due to many influencing factors but can be attributed to no definite one of the 

 conditions so far studied. A continued study of varieties and strains in 1937 

 and 1938 showed some correlation between varieties and ascorbic acid content. 

 By selection, it may be possible to increase considerably the ascorbic acid content 

 of the tomato crop. The ascorbic acid content in the tomatoes grown in 1937 

 was found to be lower than in the tomatoes produced in 1936. The 1938 crop 

 was comparable to 1936. Cultural practices were identical in all three years so 

 the variation is presumably the result of the many influencing factors of the 



sHoffman, I. C, 1937. Personal communication. 



