The phenolic compounds of 25 peach, nectarine, and plum cultivars were studied and quantified by HPLC-DAD-ESIMS. Hydroxycinnamates, procyanidins, flavonols, and anthocyanins were detected and quantified. White and yellow flesh nectarines and peaches, and yellow and red plums, were analyzed at two different maturity stages with consideration of both peel and flesh tissues. HPLC-MS analyses allowed the identification of procyanidin dimers of the B- and A-types, as well as the presence of procyanidin trimers in plums. As a general rule, the peel tissues contained higher amounts of phenolics, and anthocyanins and flavonols were almost exclusively located in this tissue. No clear differences in the phenolic content of nectarines and peaches were detected or between white flesh and yellow flesh cultivars. There was no clear trend in phenolic content with ripening of the different cultivars. Some cultivars, however, had a very high phenolic content. For example, the white flesh nectarine cultivar Brite Pearl (350-460 mg/kg hydroxycinnamates and 430-550 mg/kg procyanidins in flesh) and the yellow flesh cv. Red Jim (180-190 mg/kg hydroxycinnamates and 210-330 mg/kg procyanidins in flesh), contained 10 times more phenolics than cultivars such as Fire Pearl (38-50 mg/kg hydroxycinnamates and 23-30 mg/kg procyanidins in flesh). Among white flesh peaches, cultivars Snow King (300-320 mg/kg hydroxycinnamates and 660-695 mg/kg procyanidins in flesh) and Snow Giant (125-130 mg/kg hydroxycinnamates and 520-540 mg/kg procyanidins in flesh) showed the highest content. The plum cultivars Black Beaut and Angeleno were especially rich in phenolics.

The phenolic antioxidant phytochemicals in wines have been implicated for the lower rates of cardiac disease mortality among people drinking wine regularly in certain European populations. The activities of 20 selected California wines in inhibiting the copper-catalyzed oxidation of human lowdensity lipoproteins (LDL) were determined. This antioxidant activity was related to the major phenolic compounds and not to resveratrol analyzed in wines by HPLC and GC-MS. The relative inhibition of LDL oxidation varied from 46 to 100% with the red wines and from 3 to 6% with the white wines. When compared at the same total phenol concentration, the inhibition of LDL oxidation varied from 37 to 65% with the red wines and from 27 to 46% with the white wines. The relative antioxidant activity correlated with total phenol contents of wines (r = 0.94) and with the concentrations of gallic acid (r = 0.92), catechin (r = 0.76), myricetin (r = 0.70), quercetin (r = 0.68), caffeic acid (r = 0.63), rutin (r = 0.50), epicatechin (r = 0.45), cyanidin (r = 0.43), and malvidin 3-glucoside (r = 0.38). Therefore, the activity of wines to protect LDL from oxidation appeared to be distributed widely among the principal phenolic compounds.

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