Browsing by Author "Hunlun, Cindy"

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    Characterising the flavonoid profile of various citrus varieties and investigating the effect of processing on the flavonoid content
    (Stellenbosch : Stellenbosch University, 2016-03) Hunlun, Cindy; Sigge, G. O.; De Beer, D.; Van Wyk, J.; Stellenbosch University. Faculty of Agrisciences. Dept. of Food Science.
    ENGLISH ABSTRACT: Phenolic compounds in citrus fruit are specific for each species and variety and may be influenced by environmental conditions during the growing season and post-harvest practices. The exact chemical composition of citrus produced in South Africa is currently not known even though 2 million tonnes were produced in 2012. Various citrus varieties are produced for export, local fresh markets as well as processed into value-added products sold on the local market. In the current study South African citrus fruit (satsuma, clementine, navel and valencia) as well as products such as frozen concentrated orange juice (FCOJ), made-from-concentrate and not-from-concentrate orange juices produced from these varieties were characterised in terms of chemical and phenolic composition as well as total antioxidant capacity (TAC). Samples from two regions and three seasons were evaluated to determine the effect of variety as well as seasonal and regional differences. Citrus juice characteristics evaluated, included: °Brix, titratable acidity (TA), °Brix:acid ratio, pH as well as ascorbic acid (AA). Furthermore, the phenolic composition of the citrus fruit was quantified using high-performance liquid chromatography coupled with diode-array detection (HPLC-DAD). The TAC was determined using 2,2’-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging assay, Oxygen Radical Absorbance Capacity (ORAC) assay and Ferric Reducing Antioxidant and Ascorbic Acid (FRASC) assay. Eight phenolic compounds were quantified and included four flavanone-O-glycosides, two flavonols, a flavone and phenolic acid. The phenolic composition of different citrus varieties showed great variation between different seasons. Varietal difference was evident although there was some overlap between citrus varieties within the same season. Hesperidin and narirutin were the predominant flavanone-O-glycosides in sweet oranges, which included navel and valencia varieties, with vicenin-2 and ferulic acid-O-hexoside also present in high quantities. Regarding the FCOJ samples the results of the juice characteristics indicated that those from the WC sampling site were more mature compared to those of EC. Varietal differences were evident and variety proved to be the most significant factor that accounted for the variances in juice characteristics and phenolic composition. Seasonal differences were less evident. Variation that could be ascribed to regional differences was found for the individual phenolic composition. FCOJ from EC were characterised as having higher levels of the individual phenolics, total phenolic composition (TP) and TACDPPH and TACORAC. Of all the FCOJ varieties, navel was found to be the most mature, irrespective of season and region and was the variety with the highest TP. The predominant flavanone found in the MFC and NFC orange juices were hesperidin (HD) and narirutin (NART) followed by the flavone-C-glucoside vicenin-2 (VIC2) and a hydroxycinnamic acid namely ferulic acid-O-hexoside. Three other minor phenolic compounds where also quantified. The results indicated that NFC juices had higher levels of the individual phenolics as well as higher TACORAC. The results further showed that the phenolic composition of the MFC juices where dependent on the juice formulation, i.e. the quantity of orange juice added and not the treatment type (pasteurisation versus ultra-high temperature pasteurisation). Lastly, the results highlighted the lack of information pertaining to the processing, storage and shelf-life stability of the identified and evaluated phenolic compounds.