pH, Acidity, and Vitamin C Content of Fresh and Canned Homegrown Washington Tomatoes

Abstract

The safety of home canned tomato products in the Pacific Northwest has been questioned because of publicity surrounding low-acid tomato varieties recommended for gardens. One hundred fifty-two samples of home grown tomatoes collected from 19 counties in Washington were subjectively ranked into maturity categories by appearance. They were found to decrease in acidity and increase in pH with maturity, while the vitamin C content increased to a maximum in slightly overripe tomatoes. Ripe tomatoes grown in eastern Washington under low relative humidity and high temperatures may have greater pH values than tomatoes grown under high relative humidity and lower temperatures in western Washington. Ninety-one of the fresh tomato samples were canned with salt in a boiling water bath and stored 4 months at 4 C. The pH of the canned tomatoes decreased by 0.10 unit from the fresh values, while acidity did not change; vitamin C decreased by 30%. Overripe tomatoes had the lowest acidity and greatest pH. Thirty-one jars of tomatoes canned by home canners were collected and analyzed. The pH was sufficient in all samples to inhibit growth of Clostridium botulinum; however, two jars canned with no acidulant added had a pH> 4.6. Vacuum in jars ranged from 10.6 to 22.9 inches of mercury. All jars submitted were adequate for the home preservation of tomatoes.