A normal pH range in tomatoes is 4.0- 4.5 and the lower the pH, the more tart or sour the fruit. Flavor is normally measured by taste panels who rate the tomato for a range of characteristics including smell, aroma, firmness, juice, mealiness, skin texture, acids and sugars.
Volatile compounds also contribute to flavor, and more than 130 of these compounds have been identified. There is a direct relationship between the color and flavor because some volatile compounds are derived from oxidation of carotenoids.
Sugar levels in tomato
°Brix is a measure of the Total Soluble Solid (TSS) content in the tomato or tomato product. The TSS in tomatoes is mainly sugars (fructose). A tomato juice, which is assessed as having 20 ° Brix, has 200g/litre of soluble sugars.
Tomatoes for processing require a minimum °Brix of 4.5. This compares with an acceptable range of 3.5 - 5.5 in fresh tomatoes. The TSS of processed products is measured by refractometry.
The °Brix content of the finished tomato product is largely controlled by the processor and manufacturing process. However, some processors do pay a higher price for higher dry matter tomatoes. In general, smaller, cherry tomatoes have a higher brix ratio and are sweeter than larger round or common tomatoes.
High rates of nitrate applied as calcium nitrate increase levels of total soluble solids as measured by °Brix.
Phosphorus ensures a significant increase in TSS, improving tomato processing quality.
Potassium also increases TSS within the tomato. As well as improving processed tomato product quality, this has benefits in terms of improved taste and storage of fresh tomatoes.
Sulfur increases fruit TSS.
Measurement of acidity is by simple pH assessment with a range of pH 4-5 being typical for tomato. Total acidity, can be measured by chromatography or enzymatic reaction – where 0.35 – 0.40g/100cc juice is required. Alternatively, processors measure total titratable acidity or volatile acidity after distillation.
Within the EU, tomato juice and concentrates require titratable acidity of <10% citric acid; juice and soup need a pH of 4.5 - 4.6 for proper sterilization. Often, though, some form of citric acid or lemon juice is added prior to canning.
Higher levels of potassium in the plant, increases the acidity of the fruit and the resultant tomato juice.