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100% 50% 0% starch-iodine index core stain

flesh stain

FIGURE F4.2. Generic starch-iodine chart (Source: Modified from Blanpied and Silsby, 1992.)

color, seed color, loss of bitter flavor, appearance of watercore, and separation force.

Pears

The pressure test (firmness) has proven to be the most reliable and seasonally consistent method for determining harvest maturity of all pear cultivars (Hansen and Mellenthin, 1979). Each cultivar has a specific firmness range for optimal harvest. Other indices include ground color, development of a smooth, waxy skin (especially for 'D'Anjou'), a moist rather than dry cut surface on cross-sectioned fruit, days from full bloom and temperature records, heat accumulation, the starch index, size, and optical density of fruit. SSC is unreliable as a maturity index, but a minimum concentration of 10 percent is required for best quality and prevention of freezing during storage (Hansen and Mellenthin, 1979). Fruit are usually harvested pre-climacteric, and, therefore, ethylene production is not a useful maturity index for pears.

Peaches, Nectarines, and Plums

Maturity indices include fruit size and shape, ethylene production, respiration rate, firmness (cheek and blossom end), SSC, TA, SSC/TA ratio, and background color (on cheeks and blossom end). Other investigated indices include near-infrared light, magnetic resonance, light transmittance, delayed light emission, and microwave permittivity. A study of several maturity indices in plums demonstrates that none are reliable and applicable to all cultivars (Abdi et al., 1997).

Cherries

Fruit color is the most commonly used indicator of ripeness, that of black sweet cherries progressing from straw color to very light red, followed by red, which darkens to mahogany (Looney, Webster, and Kupferman, 1996). Yellow sweet cherries develop yellow flesh and skins as one of the first signs of maturity, and some cultivars are harvested when a red blush develops on the cheek. Color of black cherries is judged commercially using color comparators or cards and must be shiny, not dull, in appearance. Other indices include size, firmness, and flavor (SSC and acidity). Fruit retention strength is used as the main maturity guide for cherries that are harvested mechanically.

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