Characterising the flavonoid profile of various citrus varieties and investigating the effect of processing on the flavonoid content

Hunlun, Cindy (2016-03)

Thesis (PhD)--Stellenbosch University, 2016.

Thesis

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.

AFRIKAANSE OPSOMMING: Fenoliese verbindings wat in sitrus vrugte voorkom is kenmerkend ten op sigte van spesie en varieteit en word beïnvloed deur omgewingsfaktore gedurende die verbouingseisoen asook as gevolg van na-oes hantering. The presiese chemiese samestelling van sitrus wat in Suid-Afrika verbou word is tans onbekend ongeag die feit dat die land ‘n jaarlikse sitrus produksie van 2 miljoen ton gehad het in 2012. Verskeie sitrus varieteite word vir die uitvoermark geproduseer terwyl ander vrygestel word vir die plaaslike vars mark en/of verwerk word as produkte met toegevoegde waarde wat op die plaaslike kleinhandels mark verkoop word. In hierdie studie word sitrus vrugte (satsuma, clementine, navel en valencia) eg aan Suid-Afrika asook produkte soos lemoensapkonsentraat (FCOJ) wat as gevries bemark word en ook sap wat gemaak word van lemoensapkonsentraat (MFC) en ook vars uitgedrukte lemoensap (NFC) geevalueer ten opsigte van chemiese-, fenoliese samestelling en antioksidant aktiwiteit (TAC). Lemoensap monsters van twee verbouingstreke en oor drie seisoene is versamel en ontleed sodat die effek wat varieteit, seisoen en verbouingstreke op die chemise en fenoliese samestelling bepaal kon word. Lemoensap eienskappe is bepaal en sluit in suikergehalte (°Brix), titreerbare suurgehalte (TA), suiker:suur verhouding (°Brix:acid), pH en askorbiensuur (AA). Inwelke die fenoliese samestelling is bepaal deur hoë-druk vloeistof chromatografie met diode-opstelling en deteksie (HPLC-DAD). Die TAC is bepaal deur 2,2’-difeniel-1-picrylhydrazyl (DPPH) radikale blaas toets, Suurstof Radikaal Absorbansie Kapasieit (ORAC) toets en Ferri Vermindering Antioksidant en Askorbiensuur (FRASC) toets. Agt fenoliese verbindings is bepaal en sluit in vier flavanone-C-glikosiede, twee flavonole, ʼn flavone en fenoliese suur. Die fenoliese samestelling van die vier sitrus varieteite het groot variasie getoon tussen verskillende seisoene. Varieteitsverskille was duidelik hoewel daar ook oorvleueling was tussen sommige varieteite van dieselfde streek. Hesperidin en narirutin was die hoof flavanoon-C-glikosiediese verbindings in soet lemoene wat die navel en valencia varieteite insluit. Vicenin-2 en feroeliese suur-O-heksosied was ook teenwoordig in groot hoeveelhede. Wat die FCOJ aanbetref het die resultate van die sapeienskappe getoon dat die monsters vanaf die Wes-Kaap (WC) streek meer volwasse en ryp was vergeleke met die van die Oos-Kaap (EC) streek. Varieteitsverskille was duidelik en was hoofsaaklik die mees bestendige faktor wat aanspreeklik was vir die verskille in die chemise- en fenoliese samestelling. Verskille as gevolg van seisoenale invloed was van mindere belang. Variasie as gevolg van verbouingstreeks verskille was gevind vir die individuele fenoliese verbindings. FCOJ van die EC was gevind om hoër individuele fenole, totale fenoliese vlakke (TP) en TAC te bevat. Dit is bevind dat die FCOJ van die navel varieteit die hoogste TP bevat het en was ook die mees volwasse en/or ryp varieteit ongeag van seisoen of verbouingstreek. Die hoof fenoliese verbindings in die MFC en NFC lemoensappe was hesperidin en narirutin gevolg deur vicenin-2 en feroeliese suur-O-heksosied. Drie ander fenoliese verbindings was bevind om in kleiner hoeveelhede voor te kom. Die resultate het getoon dat NFC sappe hoër individuele fenoliese vlakke en ook hoër TAC gehad het. Verder het die resultate getoon dat die fenoliese samestelling van MFC sappe afhanklik is en beïnvloed word deur die sapformulasie dit wil sê die hoeveelheid lemoensap wat bygevoeg word en nie noodwendig die tipe hitte behandeling (pasteurisasie vs uiterse hoë temperatuur pasteurisasie) wat die sappe aan bloodgestel word nie. Laastens het die resultate van hierdie navorsingstudie die gebrek aan inligting uitgewys wat die stabiliteit van die geïdentifiseerde en bepaalde fenoliese verbindings aanbetref tydens verwerkingsprosesse, opberging en raklewe van lemoensappe.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/98427
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