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Top1. Introduction
The preliminary judgment of fruit quality relies on its general appearance including color, surface structure and shape. Color, in particular, is an important sensory attribute, and this is the main reason why instrumental methods for color measurement are indicated for use under standardized conditions. In cases where color is an important quality indicator, a color evaluation can provide a commercial criterion for certain climacteric vegetables. The tomato fits well into this application, the color giving an indication of both the original fruit quality as well as the efficiency of the maturation process. The tomato is a climacteric and perishable fruit, which requires adequate storage conditions in order to delay the ripening process, minimizing losses and increase the shelf life (Brackmann et al., 2007). Only fruits meeting expected qualities by the consumers will be considered for commercialization. Color is an important quality attribute closely associated with maturity, and together with shape, size, firmness, bruising and defects, affects the choice of the consumer.
Tomato is considered as a horticultural crop with major worldwide commercial interest. As reported by FAO (2014), the world consumption of fresh tomato fruits guarantees it second place in importance. The tomato is cultivated in different zones of Brazil in all seasons and under a variety of crop handling systems. These details promote high production, placing the country amongst the greatest tomato producers in the world, together with China, USA, Italy, Turkey, Spain, Egypt and Mexico (Cardoso et al., 2010). The total cultivated area occupied by the tomato crop in Brazil covers 66,418 hectares, producing 4,146,466 metric tons a year, yielding 62.616 kg/ha (IBGE, 2011).
Pangborn (1967) stated that ‘In foods, colors are identified with previously experienced quality and serve as instant indicators of good or bad, according to the product and its intended use.’ Consumers associate an acceptable color with acceptable flavor, safety, nutrition and satisfaction level (Christensen,1983).
The perception of fruit color is associated with some characteristics such as the combination of certain pigments. Small changes in fruit color are connected with certain factors, such as maturity, exposure to radiant energy, size, burning, tanning, etc. (Little, 1973). Color is a rather subjective fruit quality and therefore it is not easy to quantify. Indeed, in the past the color of a particular fruit was scored based on comparison with a color chart. In 1976, the last version of the Munsell book of color was published, this being the result of many improvements as from its first creation in 1915. The book of color allowed one to assign a number to 1500 color standards (Munsell Color, McBeth Division of the Collmorgen Corporation, Baltimore, Maryland, U.S.A). In the Munsell book, color was classified based on its Hue (Munsell Hue), lightness (Munsell Value) and Saturation (Munsell Chroma). However, due to the particular change in color for each fruit, there was a special chart for each fruit. These charts were so useful that even today many of them are still in use.
When the color of solid opaque foods, such as whole fruits or thick slices of red meat, is measured, the specimen field should be flat and uniform. If a natural flat surface is not available, then it is sometimes acceptable to obtain such a surface by cutting or even rotating the food sample in front of the instrument viewing port (Francis, 1952). Solid foods often show directionality. When the directionality is obvious, the specimen should be measured with the same orientation for each test. When the directionality is haphazard or undefined, one useful technique is to turn the sample through 90º between the two readings, and average the results.
As reported by Nickerson and Lozano (1978), color can be determined by way of an appropriate system based on tonality, luminosity and the chromaticity of our sensations. Instead of describing them, MUNSELL developed a system which established the three-color dimensions, and measuring each one by referring to an appropriate scale.