Abstract
A solid phase enzyme immunoassay (EIA) for the quantitative determination of the phytonutrient component, limonin glucoside, in citrus juice was developed. Limonin glucoside and limonin were in aqueous and methylene chloride fractions respectively when juice was partitioned with methylene chloride. The assay was carried out by indirect competitive immunoassay (ICEIA) with a biotin-avidin system (BAS) using anti-limonin antiserum (Yamamoto and Matsumoto, 1999) and limonin glucoside-ovalbumin conjugate as the solid phase. The assay showed a high sensitivity within a range extending from 10 pg to 100 ng of limonin glucoside. Limonin glucoside and limonin concentration in the juice of 128 cultivars of citrus were determined by ICEIA-BAS. Limonin glucoside constituted over 90% of the total limonin in juice from almost all cultivars except for pummelos. The limonin glucoside concentration in juice was high in all navel oranges and a few mandarins at more than 100 ppm. Juice from pummelos, yuzu and its relatives, lemon and kumquat contained low concentrations of limonin glucoside. Limonin, the bitter component, was high in juice from pummelos, navel oranges and others. However, there did not seem to be a problem of bitterness in the many remaining cultivars because the limonin concentration in their juice was low.
