Generally, as grapefruit mature through the season the limonin content decreases. Tatum et al. (35) used a TLC method to analyze samples at about weekly intervals from two Florida plants from late November 1971, when the limonin level was 10 /¿g/mL, through May 1972, when the level had decreased to 2 /¿g/mL. The decline in limonin was gradual over the study period. Dougherty et al. (36), working with Marsh grapefruit from Florida packinghouse eliminations (fruit that was not suitable for marketing fresh, primarily because of skin blemishes, but was of processing quality), reported limonin contents by HPLC of juice from five separate batches of fruit harvested between September 12 and December 17, 1974, at irregular intervals. Using the mean limonin levels for the juice obtained with soft and hard extractor settings (to produce soft and hard squeezes) for each batch of fruit, the limonin content was found to decline gradually from 7.5 /¿g/mL in the first juice extracted to 2.5 /¿g/mL in the last. A gradual decrease in limonin content was again noted over the time period.

Until late 1989 it was generally believed that decreasing limonin as fruit matured was the result of transport of limonin from the fruit to developing seeds. Grapefruit seeds contain very high concentrations of limonin (37). However, Hasagawa et al. (38) discovered an enzyme that bound the limonin as a nonbitter glucoside as the fruit matured. Early season grapefruit contain few limonoid glu-cosides while mature grapefruit contain approximately 240 /ug/g limonoid glucosides on average.

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