A B S T R A C TConcentrations of the major jlavonoids and phenolic acids in the peel und cortex of fiuit of eight commercial apple cultivars were determined by H P L C . The multivariate statistical technique of correspondence analysis was applied to the polyphenol profiles to describe distinctive groups of cultivars and of polyphenois, and their joint correspondences.Cultural and growing conditions had u limited eflect on the polyphenol profiles of the cortex and peel. Chlorogenic acid was the principal polyphenol in the cortex with the lowest levels being in Red Delicious and the highest in Jerseymac, which were compensated by changes in phlorizin. Cortland had low levels of' chlorogenic acid and Gravenstein had high levels, but these were oflset by the levels of catechins.The quercetin, rhamnoside, was the principal phenolic compound for the peel data with low levels in Red Delicious, Cortland, Spartan and Jerseymac and high levels in Golden Delicious, Gravenstein and Northern Spy. Levels of chlorogenic acid, offset by levels of phlorizin and catechins, distinguished between Red Delicious and Cortland. Rutin was important in distinguishing between Jerseymac and Spartan.

The flavonoid glycosides of Spartan apples were isolated by column chromatography on polyamide and Sephadex resins and by RP-HPLC. They were characterized by and 13C NMR as phlorizin and the following glycosides of quercetin: -L-arabinofuranoside, d-D-galactopyranoside, /3-D-glucopyranoside, -L-rhamnopyranoside, /3-D-xylopyranoside. The coupling constants in the XH NMR spectra were used to establish anomeric configurations of all glycosides.

Extraction of Spartan apple (Malus domestica) fruit acetone powder and fractionation of the extract on DEAE‐agarose allowed detection and quantification of 10 glycosidases active toward 4‐methylumbelliferyl glycosides. Hydrolysis was measured fluorimetrically. The predominant activity, a β‐d‐galactosidase (EC 3.2.1.23), labile upon purification, was stabilized by soluble PVP. Molecular weights, measured by gel permeation HPLC, pH optima and Km values were obtained for most glycosidase activities. Multiple forms of several activities were found. The major α‐d‐ and β‐d‐galactosidases were resolved on phosphocellulose. The β‐d‐galactosidase so obtained had associated α‐l‐arabinopyranosidase and β‐d‐fucosidase activities which were retained upon GP‐HPLC. Mixed substrate kinetic analysis and inhibition analysis of this fraction indicated that the enzyme has 3 catalytic sites, 1 for each substrate, whose substrates mutually influence each other's activity positively.

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The inhibition of a purified β‐galactosidase from “Spartan” apples by flavonoids and related compounds has been studied with a fluorimetric assay using the substrate 4‐methylumbelliferyl β‐D‐galactoside. Certain flavonoids, flavonoid glycosides, phenolic acids, and polyphenols (quercetin, fustin, rutin, p‐coumaric acid, and catechol) gave classical noncompetitive inhibition at moderate substrate concentrations. Others (kaempferol, chlorogenic acid) gave nonlinear Dixon plots. The best inhibitors were flavones. In general, the degree of inhibition increased with the degree of hydroxylation and glycosylation of the phenol. Correlation of the structure of these substances with the observed inhibition suggests that the trans‐3‐(4‐hydroxyphenyl)‐propenoyl group, common to 4′‐hydroxyflavones and p‐hydroxyphenolic acids, is important for effective inhibition.