34 MASS. EXPERIMENT STATION BULLETIN 354 



SUMMARY 



L A four-year investigation was conducted on methods for the determination 

 of ascorbic acid in tomatoes and tomato products. Sampling methods, reagents 

 and technic were studied in adapting the chemical methods to the problem of 

 evaluating the tomato as an antiscorbutic. Effect of season, variety, maturity, 

 storage, and other factors influencing the ascorbic acid content of canned and 

 fresh tomato products were studied. 



2. The 2, 6-dichlorophenolindophenol titration for ascorbic acid was found 

 to check more closely with the guinea pig bioassay results than did the modified 

 iodine method. Adaptation of the dye technic to tomato studies included a second 

 extraction for ascorbic acid using a mixture of 2 percent metaphosphoric and 

 3 percent trichloroacetic acid. 



3. No oxidized (dehydro) ascorbic acid was found in raw or cooked tomatoes 

 and tomato products. 



4. An oxidase enzyme method for differentiating ascorbic acid from other 

 reducing substances did not yield satisfactory results in this tomato study. 



5. The chemical titration for ascorbic acid is as specific on canned tomato 

 juice as on fresh samples. 



6. The chemical determination of ascorbic acid in tomatoes or tomato products 

 is subject to an error of approximately ±2 percent. Unavoidable variations in 

 sampling increase this to a probable error of at least ± 10 percent. 



7. Tomato varieties and strains showed considerable range in ascorbic acid 

 content (74 to 249 international units per ounce). The possibility that ascorbic 

 acid content may be an inherited characteristic is indicated by three seasons' 

 study of several strains of many varieties of tomatoes. Tomatoes should exceed 

 150 international units per ounce to be classed as higher than average in ascorbic 

 acid content. 



8. Outside flesh and skin were found to contribute the most ascorbic acid 

 to the whole tomato, but if was in the seeds and gelatinous material of the locule 

 section that this acid was most concentrated. Neither fruit size nor degree of 

 ripeness influenced the ascorbic acid content. * 



9. The use of parchment wrappers was not detrimental to the ascorbic acid 

 content of tomatoes when they were held for 10 days in cold storage or at room 

 temperature. 



10. Concentration of tomato juice to prevent separation of suspended solids 

 destroyed 25 percent of the ascorbic acid originally present. Storage of tomato 

 juice under either dark or light conditions for 400 days caused not more than a 

 25 percent loss of ascorbic acid. The carotene content of canned or bottled tomato 

 juice was not seriously affected by ordinary storage of a few months. 



11. Commercial brands of tomato juice contained 40 to 100 international 

 units of ascorbic acid per ounce, and the variation within one brand was found 

 to be from 28 to 85 units per ounce. 



