Graduate Thesis Or Dissertation
 

Phenolic composition of red raspberry juice : influences of cultivar, processing and environmental factors

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  • Flavonols and ellagic acid compounds were characterized and measured in 55 experimental and commercial red raspberry juices by high performance liquid chromatography (HPLC) and diode array spectral techniques. Samples were prepared using Polyamide-6; a fraction eluted with methanol contained <_ 8 quercetin-glycosides, quercetin and kaempferol. Another fraction, eluted subsequently with 0.5% ammonia in methanol, contained 3 flavonol-glucuronides, 2 flavonol-forms, ellagic acid and <_ 16 ellagic acid derivatives. In addition, 36 flavonol-forms were measured in trace amounts. Experimental (n=45) and commercial (n=7) juices contained mean concentrations of 10 and 30 ppm ellagic acid and _< 3 and 6.7 ppm individual derivatives, respectively. Quercetin-3-glucuronide was the major flavonol in all juices (mean: 51-54 ppm) and a flavonol presumed to be quercetin-3-sophoroside the second major flavonol (29-33 ppm). Mean total concentrations in experimental and commercial juices were, respectively: ellagic acid forms, 28 and 52 ppm; quercetin-forms, 118 and 121 ppm; kaempferol-forms, 3.6 and 3.4 ppm; flavonols, 122 and 125 ppm. Qualitatively, the chromatographic profiles of juices were similar but quantitatively, there were great differences due to cultivar (n=10) and processing method. The cultivars Willamette and Meeker contained the most ellagic acid forms; Heritage, Willamette and Norna the most total quercetin-forms and Heritage and Norna the most total kaempferolforms. Juices made by diffusion extraction or a standard process had the highest concentrations of ellagic acid forms, while juice produced by high-speed centrifugation contained the most total quercetin-forms. Centrifugation reduced total ellagic acid by half compared to diffusion extraction; depectinization and concentration (by vacuum or direct osmosis) decreased total ellagic acid and quercetin-forms further. Mold reduced quercetinglycosides and glucuronides considerably, while it appeared not to effect ellagic acid. Two commercial juice concentrates were found to be adulterated based on their anthocyanin, flavonol and ellagic acid compositions. Flavonol and ellagic acid HPLC profiles have great potential as an auxiliary technique for detecting adulteration. Hydrolysis simplified the chromatographic profile of red raspberry juice phenolics dramatically. In acid-hydrolyzed juices, ellagic acid, 2 ellagic acid compounds, 3 hydroxybenzoic acids, 3 hydroxycinnamic acids, 2 flavan-3-ols, quercetin and kaempferol were identified. In base-hydrolyzed samples one ellagic acid compound was absent and the other was present in smaller quantity. Hydrolysis could become a very useful tool for rapidly screening juices for adulteration and measuring total quantities of phenolic aglycons. Ellagic acid and quercetin (in. glycosylated form) were present in the juices in concentrations which have been shown to have anticarcinogenic effects. Medical evaluations of the positive effects of red raspberry juice on human health could be based on our initial phenolic compositional data.
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