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UBC Theses and Dissertations

Chemical constituents comprising the antioxidant activity of fresh and dehydrated Saskatoon berries (Amelanchier alnifolia Nutt. cv. Smoky and Thiessen) Kwok, Bonnie


In recent years, numerous studies have shown that the polyphenols present in fruit and vegetable products exhibit a wide range of protective effects against a variety of disease states, including lower incidences and mortality rates of cancer, reduction in blood pressure, stimulation of the immune system, detoxification of contaminants and pollutants; and reduction in inflammation. This protective effect has been thought to be associated with the antioxidant properties of these polyphenolics present in the fruits and vegetables. This thesis research specifically dealt with characterizing the antioxidant capacity of a Canadian prairie small fruit, the Saskatoon berry (Amelanchier alnifolia Nutt.). Two specific Saskatoon berry varieties (Thiessen and Smoky) were investigated. In addition, differences among four different dehydration techniques (freeze-drying, vacuummicrowave drying, air drying, and combination drying of air and vacuum-microwave drying) were examined. Moreover, a partitioning study was performed to explore the berry constituents responsible for the proposed antioxidant activity. Investigation of the antioxidant capacities of this particular fruit and the characterization of the berry components contributing to the purported antioxidant activity was made. It was found that the Saskatoon berry fruit contained a high capacity for antioxidant activity that was associated with the total anthocyanin and phenolic composition of these berries. The reported antioxidant activity for the berry fruit may be attributed to the reducing property of the polyphenolics; in particular the anthocyanins and phenols which were suggested to act as donors of electrons or hydrogen and thereby terminating free radical chain reactions. Results showed that a varietal difference existed between the Thiessen and the Smoky Saskatoon berry cultivars examined in this study. Thiessen berries were found to contain higher amounts of total anthocyanin and phenolic constituents and also associated with higher antioxidant capacities when compared to the Smoky variety. No statistically significant differences in total anthocyanin and phenolic content, and antioxidant activities were found for the three different harvest years (2000, 1999, 1998). As a result, the three harvest years were pooled for each variety. The dehydration processing study performed with the Saskatoon berries showed that a lower retention of antioxidant activity was associated with the loss of anthocyanin pigments and phenolic contents. Greater losses of these compounds were found after those dehydration processes that used longer times and higher heating temperatures. Extracts from freeze-dried Saskatoon berries were found to retain the highest amounts of measured antioxidant activity and measured fruit parameters (anthocyanins, and total phenolics). Extracts from vacuum-microwave dried berries retained the second highest amounts of the measured parameters. The lowest retention of the anthocyanin pigments and phenolic contents, and associated antioxidant capacities, were found in extracts from air-dried berries. The combination method of air drying and vacuum microwave drying was found to provide results in between that of the individual vacuum-microwave dried and air-dried processes themselves. The solvent fractionation study proved that the polar constituents (e.g. anthocyanins and phenolics) from the Saskatoon berry crude extract demonstrated higher antioxidant activities compared to less polar constituents. Possible synergistic effects of the different components in each of the fractions were also observed.

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