The visual appearance of fruit and vegetable is the most important quality factor, which decides its price in the market. The consumer (wholesaler or retailer) observes the quality of fresh fruits and vegetables with their visual or external appearance. The produce should attain proper shape and size. Medium size produce is always preferred by the consumers, because they tend to view large fruits as more mature. The appearance of the product is the most critical factor in the initial purchase, while subsequent purchase may be more related to texture and flavour.
Therefore, subjective evaluation of size and shape of the produce should be conducted to meet the desired quality characteristics.
b) Colour: The loss of green colour of many fruits is a valuable guide to maturity as shown in Plate 1. There is initially a gradual loss in intensity of colour from deep green to lighter green and with many commodities, a complete loss of green colour with the development of yellow, red or purple pigments. Ground colour as measured by colour charts, is useful index of maturity for apple, pear and stone fruits, but is not entirely reliable as it is influenced by factors other than maturity. For some fruits, as they mature on the tree, development of blush colour, that is additional colour superimposed on the ground colour, can be a good indicator of maturity. Examples are red or red-streaked apple cultivars and red blush on some cultivars of peach.
Objective measurement of colour is possible using a variety of reflectance or light transmitance spectrophotometer. Colour perception depends on the type and intensity of light, chemical and physical characteristics of the commodity, and person’s ability to characterize colour. Although human eye is used to evaluate colour but results can vary considerably due to human differences in colour perception. Therefore, an instrument (objective method) is used to provide a specific colour value based on the amount of light reflected off the commodity surface or light transmitted through the commodity. This instrument can measure small differences in colour accurately and can be automated in the packing line. This instrument is popularly known as Colour Difference Meter. This instrument use colorimetric method for colour measurement.