Flavor is generally related to the relative concentrations of sugars and acids in the fruit, mainly fructose and citric acid. The best, most flavorsome combination is a high sugar and high acid content. A normal pH range in tomatoes is 4.0- 4.5 and the lower the pH, the more tart or sour the fruit.
Fresh market tomato
Flavor, color, shape and texture are all important characteristics of fresh tomatoes. Fruit also needs to be clean and clear of blemishes such as decay or disease. They should be of uniform shape, symmetry and size. Tomatoes need to be bright and uniform in color, without green shoulders or immature green spots or blotches.
Depending upon the relative levels of carotenoid pigments in the fruit, color can range from yellow to orange, pink, red or even white. The specific carotenoid, lycopene provides the fruit with its red color. Higher levels of beta-carotene provide an orange color.
The texture depends upon how tough the skin is, the firmness of the flesh, and the proportion of the locular (gel-like structures) and pericarp tissues. Firmer tomatoes are less prone to damage and have a longer shelf life. Higher levels of calcium in the cell wall will improve fruit firmness and as a result, transportation and storage characteristics. Fresh tomatoes are graded according to their quality characteristics, as table below shows:
Timing of harvest depends upon end market requirements and local practices. Picking can start at the mature-green stage, but practices that harvest before this can result in fruit, once ripened, that has poor color and flavor. Thus, the ‘breaker’ or ‘turning’ stage of fruit development – when color is turning from green to tannish-yellow - is when most fresh fruit is picked, particularly if it is to be shipped considerable distances, e.g. glasshouse production in countries such as the USA, Turkey and Morocco.
Cluster tomatoes are picked when the least mature fruit on the truss begins to show red color. This helps ensure uniformity when the crop reaches the consumer.
Increasing storage temperature and using ethylene can bring ripening forward.
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.
In general, smaller, cherry tomatoes have a higher brix ratio and are sweeter than larger round or common tomatoes.
There are a wide range of processed tomato products on the market, from canned tomatoes, juice, soup, sauce, paste, ketchup, pulp to puree.
Color is particularly important for processed tomatoes and fruit need to be of a uniform, strong red, and free of defects such as cracks and bruises. This is measured using a range of methods including spectrophotometry and colorimetry. Processors lay down a strict range of values. Processed crops must ripen evenly and at least 75% of the fruit has to be mature at harvest.
Various countries have different acceptable size ranges for different processed products. In Spain, for example, fruits used for juice usually weigh between 60–100g. For canning as whole tomatoes, fruits are within the 30–60g weight range. When used for canning, fruit must have a thick, firm wall so that they retain their shape when cooked. The peduncle must also be easy to remove from the fruit.
Firmness decreases during fruit maturation. The use of calcium will help minimize breakdown of pectins by holding the pectic matrix together, maintaining the cell wall strength. Firmness is assessed by pressure load or shear press tests. Tomatoes with a Durofel rating of >75 are described as firm, 60-70 are soft, and <60 limp.
Peelability is important for whole or diced processing tomatoes.
Fruit crops with a high TSS content reduce the need for, and costs of, removal of water and disposal of wastewater during processing.
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 and should follow the ranges on the table next.
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.
Viscosity – which is important in paste products - is related to the level of insoluble solids. It is normally measured using a viscometer or consistometer – with results expressed as Bostwick unit (cm) or centipoises. Acceptable ranges depend on methods and products. In Spain, processors desire a Bostwick reading of 4 - 8 in tomatoes with 12°Brix. Acids – mainly citric and malic acid, determine the flavor of the processed product.
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.
Acids – mainly citric and malic acid, determine the flavor of the processed product. 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.