Tomatoes are borderline in pH between acid and low acid foods, so the USDA preparation directions for these products call for acidification to allow a less severe heat treatment than would be required without it. To ensure safe acidity in whole, crushed, or juiced tomatoes, add two tablespoons of bottled lemon juice or ½ teaspoon of citric acid per quart of tomatoes. For pints, use one tablespoon bottled lemon juice or ¼ teaspoon citric acid. Add acid directly to jars before filling. Sugar may be added to offset an acid taste, if desired, but the acid cannot be decreased to taste.
No matter how you choose to can your tomatoes, all steps in preparing and cooking the foods still need to be followed for the process time(s) printed with them. The process times are very different for tomatoes packed in water compared to tomato juice or without added liquid. For many of these tomato products, there are canning options for both boiling water and pressure canning available in our directions.
Source: https://nchfp.uga.edu/tips/summer/canned_tomato_types.html
See KSRE Preserving Tomatoes for more information
