Date of Award

Spring 5-8-2020

Level of Access Assigned by Author

Open-Access Thesis

Degree Name

Doctor of Philosophy (PhD)

Department

Chemistry

Advisor

Barbara J. W. Cole

Second Committee Member

Raymond C. Fort, Jr.

Third Committee Member

Angela D. Myracle

Additional Committee Members

Matthew Brichacek

Renae E. Moran

Abstract

Plum fruits of 16 plum cultivars derived from three species, Asian, American-hybrid, and European plums, and one cultivar of an interspecific hybrid between Asian plum and apricot were investigated to identify and quantify two major groups of phenolic phytochemicals, anthocyanins and hydroxycinnamic acids (HCAs) by HPLC–DAD/MS. The plums were harvested from 2014 to 2017. Some cultivars were analyzed through consecutive years to determine year-to-year differences and to evaluate the maturity impacts on the concentration of anthocyanins and HCAs from the partial-ripe stage and tree-ripe stage. Anthocyanins were present in red−purple colored plums, but their profiles varied among cultivars and species. The two major anthocyanins, cyanidin 3−O−glucoside and cyanidin 3−O−rutinoside were detected in most cultivars, but their concentrations varied depending on the levels of their accumulation in the peel and flesh of the fruits. The total anthocyanin concentration was significantly higher in the tree-ripe stage of plums than in the partial-ripe stage of plums but year-to-year difference in harvest date was not significant. In addition, anthocyanin accumulation in each cultivar was affected by the year-to-year differences in weather condition and crop load, but their specific profiles and the proportion of individual anthocyanins was maintained. Overall, cultivar and maturity differences were dominant in anthocyanin accumulation.

Hydroxycinnamic acids (HCAs) also varied among cultivars, but they showed distinguishable concentration differences between species, having significantly higher concentrations in European cultivars than Asian and American cultivars. All cultivars had neochlorogenic acid as a major HCA except the two American-hybrids, ‘Alderman’ and ‘Toka’, in which chlorogenic acid was the major HCA. Unlike anthocyanins, total HCA concentration was not dependent on the year of harvest or maturity at harvest.

Total phenolic concentrations (TPC) by the Folin−Ciocalteu method and antioxidant activity (AOA) by the DPPH assay were also measured for three years, from 2015 to 2017. The American-hybrid cultivars displayed greater TPCs than Asian and European cultivars despite having lower concentrations of anthocyanins and moderate concentrations of HCAs. On the contrary, the European cultivars had lower TPCs even though they had higher HCA concentrations than other species. Thus, there was no significant relationship between concentrations of anthocyanins or HCAs and TPCs; however, a curvilinear relationship between TPC and AOA was observed with high coefficients R2=0.89, 0.75, and 0.84 in 2015, 2016, and 2017, respectively. Unlike the linear relationship between TPC and AOA observed in most other studies, the curvilinear relationship found in this study likely results because plums with higher TPC have higher AOA, and AOA was affected more by changes at lower values than at higher TPC values. This suggests that the concentration level of TPC may play a role on AOA in plum extracts.

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