FRUIT CHARACTERISTICS
“The ideal tomato, from the consumer’s viewpoint, is one that is full size, vine ripened, unblemished, and characteristically at the red-ripe stage or anything near that stage.”
Days to Maturity
The approximate time from pollination to market maturity under warm growing conditions for most tomato varieties (cultivars) varies from 35 to 60 days, with the days to maturity depending on the stage of maturity when harvested: Mature green 35 to 45 days, Red ripe 45 to 60 days.
Beginning from seedling stage to mature fruit, varieties can be placed into three time-period classes: early season, 52 to 70 days; mid season, 70 to 80 days; and late season, 80 to 90 days. The actual number of days to mature fruit within each class will also depend on the growing conditions.
Types
The tomato fruit is classified botanically as a berry, the size varying from small cherry types with only two divisions of the ovary (locules) to large multilocular beefsteak types. The number of locules defines the fruit type as follows:
| Number of Locules |
Fruit Type |
| Two |
Cherry and plum or pear types (processing tomatoes) |
| Four to six |
Commercial cultivars for fresh market |
| More than six |
Large beefsteak type for garden or greenhouse production (do not ship well, subject to cracking and irregularly shaped fruit)
|
Basic Types and Size
There are three basic sizes of fruit determined essentially by weight: beefsteak, cherry, and grape (cherry and grape are frequently considered one size type and the intermediate between beefsteak and cherry is called “cocktail”), and two shapes, oxheart and plum (Roma). Some of the processing varieties produce fruit that has a long-shaped (pepper-like shape). The size of a tomato fruit is determined by either its diameter or weight. The weight classes are: 2 to 5 oz, 6 to 10 oz, and greater than 10 oz. Some tomato varieties can produce fruits greater than 16 oz. Beefsteak varieties produce fruit 10 oz or greater in weight. The diameter (millimeters, mm) fruit classifications are: extra small, 48-54 mm; small, 54-58, medium; 58-64, large, 64-73; extra large, 73-88; maximum large, >88 mm.
The Calyx
The calyx is the green stem attached to the fruit that is normally removed if the fruit is not packaged to keep from damaging other fruit, or the calyx is kept on the fruit to make the fruit look as if it has just been taken from the plant.
Color Development
Normally one associates red as the normal tomato fruit color, although fruit at maturity can be either bi-color (mix of red and yellow), pink, various shades of yellow, orange, green, or even black. However, red is still the major fruit color for most of the commonly grown varieties.
Fruit Ripening
Fruit ripening is a complex biochemical process in which the chlorophyll and starch content of the fruit decreases and the softening enzyme polygalacturonase and lycopene increases. With the beginning of the ripening process, respiration [synthesis and release of carbon dioxide (CO2) and generation of ethylene (C4H4) increases, peaking after about 10 days and then declining.
The stages of tomato ripening and color development are used to identify tomato fruit, stages, and their corresponding fruit characteristics.
The ‘breaker’ stage of fruit development is the most commonly chosen stage for picking fresh market fruit that is to be shipped some distance; while locally marketed fruit may stay on the vine until the light red to red stage is reached.
Ripening of mature green and breaker stage fruit can be hastened by treatment with ethylene (C4H4) at 100-150 mg/L (ppm) in the storage atmosphere, mature green developing a red color 5 to 7 days at 65-68°F (18.3-20°C), which can be either increased or decreased by higher or lower temperatures, respectively.
If green fruit is refrigerated at 42°F (5.5°C) (typical refrigerator temperature), the ripening enzymes in the fruit are inactivated, and it will never ripen.
The changes that occur in the tomato fruit with ripening are:
• Degradation of starch and production of glucose and fructose
• Loss of chlorophyll
• Synthesis of pigments such as B-carotene and lycopene
• Increase in soluble pectins resulting from wall softening and degradation
• Production of flavor and aromatic compounds
• Increase in ratio of citric acid and malic acid
• Increase in glutatilic acid
• Breakdown of the toxic alkaloid a-tomatine
Quality Factors
Consumers measure the quality of tomato fruit primarily by three factors: physical appearance (color, size, shape, defects, and decay), firmness, and flavor. Fruit quality is significantly affected by stage of ripeness when removed from the plant, number of times handled, and storage temperature and time. The longer the fruit remains on the plant, the more flavorful the fruit is. Less handling reduces the incidence of bruising, and some have suggested that flavor is reduced with increased handling. It is frequently observed that tomato fruit not ripened on the plant does not have the same flavor and aroma as fruit that has developed its red color (or final fruit color) on the plant.
Flavor
The tomato fruit is mostly water with about 5-7% of the fruit being solids, with most fruit solids content being closer to 5% than to 7%. Of the solids content, about half is composed of sugars and one-eighth, acids. Fruit flavor is a major consumer demand and one that attracts much attention based on acidity (low pH) and sugar content of the fruit as follows:
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| Acidity |
Sugar Content |
Flavor |
________________________________________
| High |
High |
Good |
| High |
Low |
Tart |
| Low |
High |
Bland |
| Low |
Low |
Tasteless |
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In general, the longer the fruit remains on the plant, the better the flavor as sensed by the consumer, although this is not entirely true. Fruit that is harvested at the breaker stage and then properly handled can be flavorful. The term “vine ripe” may be put on the fruit package to attract consumer attention because this term, in the minds of many consumers, is considered to be related to high flavor.
Another aspect of fruit flavor is fruit size. In general, the smaller fruit are more flavorful as compared to larger. Cherry tomatoes are most consistently more flavorful than the other fruits sizes.
Classification of Defects
Defect factors are classified as to level of damage, serious damage, or very serious damage; and the factors include cuts and broken skins, puffiness, catfacing, scars, growth cracks, hail injury, and insect injury.
Various definitions are given that define the factors used to classify fresh tomato fruit, a brief description of each of these follows:
Similar variety characteristics—Tomatoes are alike as to firmness of flesh and shade of color. For example, soft-fleshed, early maturing varieties are not mixed with varieties, midseason or late varieties, or bright red varieties mixed with varieties having a purplish tinge.
Mature—Tomato has reached the stage of development that will ensure a proper completion of the ripening process, and that the contents of two or more seed cavities have developed a jelly-like consistency and the seeds are well developed.
Soft—Tomato yields readily to slight pressure.
Clean—Tomato is practically free from dirt or other foreign material.
Well developed—Tomato shows normal growth. Tomatoes that are ridged and peaked at the stem end, contain dry tissue, and usually contain open spaces below the level of the stem scar are not considered well developed.
Fairly well formed—Tomato is not more than moderately kidney shaped. lopsided, elongated. angular. or otherwise moderately deformed.
Fairly smooth—Tomato is not conspicuously ridged or rough.
Damage—Damage means any specific defect (cuts and broken skins, puffiness, catfacing, scars, growth cracks, hail and insect injury) or any one of these defects, any other defect, or any combination of defects, which materially detracts from the appearance, or the edible or marketing quality of the tomato.
Reasonably well formed—Tomato is not decidedly kidney shaped, lopsided, elongated, angular, or otherwise decidedly deformed.
Slightly rough—Tomato is not decidedly ridged or grooved.
Serious damage—This means specific defects (cuts and broken skins, puffiness, catfacing, scars, growth cracks, hail and insect injury) or an equally objectionable variation of any one of these defects, any other defect, or any combination of defects, which seriously detracts from the appearance, or the edible or marketing quality of the tomato.
Misshapen—Tomato is decidedly kidney shaped, lopsided, elongated, angular, or otherwise deformed, provided that the shape is not affected to an extent that the appearance or the edible quality of the tomato is very seriously affected.
Very serious damage—This means any specific defect (cuts and broken skins, puffiness, catfacing, scars, growth cracks, hail and insect injury) or an equally objectionable variation of any one of these defects, any other defect, or any combination of defects, which seriously detracts from the appearance, or the edible or marketing quality of the tomato.
Fruit Disorders
There are ten commonly occurring fruit disorders that either are genetic in origin or have their origin in production or handling procedures.
Cracking
As the fruit begins to ripen, the skin may crack, particularly during warm wet periods if there has been a preceding dry spell. Fruit cracking occurs when there is a rapid net influx of water and solutes into the fruit at the same time that ripening or other factors reduce the strength and elasticity of the tomato skin. Cracking can be minimized by selecting a variety that has resistance to cracking as well as maintaining a consistent soil moisture to avoid periods of plant moisture stress. Cracking may be concentric encircling the stem end of the fruit or radial starting at the stem end and extending sometimes to the blossom end.
Catfacing
A catfaced fruit is misshapen due to abnormal development that begins at the time of flowering, believed to be due, in part, to cool temperatures [less than 55°F (12.8°C)] and cloudy weather at the time of flowering and fruit set. Although catfacing is usually a specific disorder in terms of fruit appearance any misshapen fruit due to it, complete pollination may be also identified as catfacing.
Misshapen Fruit
Common abnormalities are pointed fruits with an elongated blossom end, puffy fruit in which air spaces have developed, or lack of round smoothness that may be similar to catfacing. The cause is usually due to low air temperature [less than 55°F (12.7°C)] and cloudy weather that interferes with the growth of the pollen tubes and normal fertilization of the ovary.
Puffiness
Puffiness most frequently occurs in early-harvested fruit caused by a variety conditions. such as high [>90°F (32.2°C)] and low [<58°F (14.4°C)] air temperatures, low light, excessive nitrogen (N) fertilization, or heavy rainfall, in which one or more seed cavities are empty.
Blossom-end-rot (BER)
The blossom end of the fruit first turns light brown and then black as the cells at the blossom-end decay. This disorder, frequently referred to by its acronym BER, has several causes, the most common being calcium (Ca) deficiency coupled with moisture stress, which is probably the triggering mechanism. However, a number of other stresses when combined with other types of physiological stress will result in BER-affected fruit.
Sunscald (Solar injury)
Sunscald occurs on green (most sensitive) and ripening (less sensitive) fruit from exposure to direct sunlight for long periods of time. On solar-injured or sunburned (solar yellowing) fruit. Affected areas on the fruit become whitish, translucent, and thin walled; and a netted appearance may develop. Mild solar injury might not be noticeable at harvest, but becomes more apparent after harvest as uneven ripening. Direct sun exposure will result in a significant increase in fruit temperature that affects its development and quality. Foliage cover is the most effective way to reduce sunscalding of fruit.
Green Shoulders
From exposure to direct sunlight, the shoulder of the fruit will remain green. Foliage cover, which is frequently a genetic factor, is one means of reducing the occurrence of this problem.
Russeting
Russeting is characterized by a brownish scarring of the fruit surface, giving it a rough, clouded looking appearance. This is believed to be due to very humid conditions.
Anther Scarring
Anther scarring is the presence of a long scar along the blossom end of the fruit that is probably due to some early injury to the flower, although the exact cause is not known.
Blotchy Ripening
Uneven ripening of the fruit with various areas of green to yellowish green on the fruit is called blotchy ripening. The cause is not exactly known but is frequently associated with low potassium (K) and high nitrogen (N) nutrition of the plant.
Nutritional Characteristics
The tomato fruit has attracted considerable attention since the red pigment in the tomato fruit, lycopene, is an antioxidant; and the fruit also contains substantial quantities of vitamin A [red fruit containing on the average 1000 International Units (IU) per 100 g and ascorbic acid (vitamin C ranging in content from 20-25 mg/100 g), and potassium (K) (200-210 mg/l00 g). Most tomato varieties vary in soluble solids from 4.5-7.0%, with much of the soluble solids being fructose or glucose. Citric acid is the predominate acid in tomato juice and the pH of fruit is normally at or below 4.5.
Based on average fruit composition, the daily consumption of a medium-sized tomato weighing 8 oz would supply the following percentage of the recommended daily adult requirement (RDAR) as set by the Food and Drug Administration (FDA) in the Nutrition Labeling and Education Act (NLEA) of 1990:
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_________________________________
| Vitamin C |
47 |
| Vitamin A |
22 |
| Thiamin |
10 |
| Riboflavin |
6 |
| Niacin |
5 |
| Fiber |
10 |
| Protein |
4 |
| Sodium (Na) |
100 |
| Potassium (K) |
17 |
| Iron (Fe) |
6 |
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Lycopene
Lycopene is being called the “world's most powerful antioxidant,” which can help to prevent the development of many forms of cancer, the effect varying with sex and type of cancer. The best known source of lycopene is in cooked tomatoes or tomato products since lycopene is released from the tomato on cooking. Raw tomatoes have about one-fifth the lycopene “available” content as that found in cooked tomato products. However, tomato, whether raw or cooked, is still the best source for this antioxidant.
Salicylates
Another constituent found in the tomato fruit is salicylate, an aspirin-like substance that has been found to reduce the risk of heart disease.
pH
The range of pH for the tomato fruit is between 4.0 and 4.5; the lower the pH, the greater is the so-called ‘tartness’, a factor by which some consumers judge the quality of the tomato fruit. The average pH range for most fruit lies between 4.3 and 4.4.
The relationship between the pH and solids content (mainly sugars) of the tomato fruit is also a significant factor in its perceived flavor. The degree of ripeness is also a factor that affects the pH of the fruit, The role that factors other than genetics have on fruit flavor external to the plant, such as climate, soil, and cultural practices, may be equally significant, factors that are just beginning to be more carefully investigated.
When canning, the pH of the canned product will determine the safety of the final product. To ensure adequate acidity, 1/4 teaspoon of citric acid or l tablespoon of lemon juice should be added per pint of tomato product prior to canning.
Storage
The relative perishability and potential storage life of fresh tomato fruit in air at near optimum storage temperature and relative humidity is about 2 weeks for ripe fruit and 2 to 4 weeks for partially ripe fruit.
The optimum storage temperature for ripe fruit is between 45 and 50°F (7.2 and 10°C) and the relative humidity is from 85-96%. Mature green fruit can be stored at 55-60°F (12.7-15.5˚C) for several days without significant quality losses. To maintain the quality of red fruit, low temperature exposure must be avoided. The use of controlled atmosphere for tomato fruit storage is not generally practiced, although it would be of considerable benefit for the long-term storage of fruit. The lowest safe temperature by fruit type, temperature, and appearance when stored is 32°F (0°C).
Fresh cooked, or canned and opened tomato fruit can be stored in the refrigerator at 45°F (7.2°C) for 4 to 5 days: cooked tomato dishes, in the refrigerator freezer compartment for 2 to 3 months; and cooked dishes, in a freezer at 32°F (0°C) for l year. Unopened canned tomato can be stored on the kitchen shelf for l year.
Harvested fruit that is bruised at picking and transport will release ethylene (C2H4) that will hasten the ripening process.
