Development of novel methods for tannin quantification in grapes and wine

Terblanche, Elsa (2017-03)

Thesis (MScAgric)--Stellenbosch University, 2017.

Thesis

ENGLISH ABSTRACT: Phenolic compounds, and condensed tannins in particular, are of utmost importance in red grapes and wine due to their contribution to the sensory properties and potential health benefits. However, the detailed analysis of these compounds is hampered by their complexity and the lack of reliable quantitative analytical methods. In this study, the analysis of wine tannins using different chromatographic methods was evaluated in order to develop an improved methodology for their accurate characterisation and quantification. Standard compounds for use in calibration were isolated from cocoa using semi-preparative high performance liquid chromatography or purchased commercially. Calibration curves were constructed and relative response factors based on degree of polymerisation (DP), class of compound and mobile phase composition were determined. Response factors were found to vary as a function of DP and class, indicating the errors associated with quantification as (epi)-catechin equivalents as is often done due to the lack of standards. Both hydrophilic interaction chromatography (HILIC) and reversed-phase liquid chromatography (RP-LC) methods for tannin analysis were developed. For HILIC, an amide column was used, which provided separation according to DP as well as a separation of isomers within specific elution windows. In RP-LC compounds were separated based on hydrophobicity, resulting in separation of isomers, with compounds of various DPs overlapping. In both separation modes, three detectors were connected in series: a photodiode array ultraviolet (UV) detector, a fluorescence detector (FLD) and a quadrupole-time-of-flight mass spectrometer (Q-TOF-MS). FLD was found to be the most sensitive for procyanidins (PCs), while UV demonstrated the best sensitivity toward gallated PCs. Negative electrospray ionisation (ESI)-Q-TOF-MS proved essential in identifying 161 tannin species based on accurate mass data, and was the most selective of the detectors when using extracted ion chromatograms. Quantification of tannins in 9 red wine samples and a grape seed extracts indicated that each of the detectors was useful for particular compounds. Co-elution caused overestimation of some compounds by UV and occasionally by FLD as well. Nevertheless, there was good agreement between the HILIC and RPLC methods, as well as between the various detectors in each mode. Quantitative data for the red wine and seed samples were in agreement with those obtained in previous studies. The total number of compounds identified (161) and quantified (74 and 41 in HILIC and RP-LC, respectively), was greater than could previously be obtained. Both methods were shown to be viable options for the analysis of condensed tannins in grape and wine samples. HILIC was found to be more sensitive, and therefore HILIC-UV-FLD-Q-TOF-MS is recommended as the method of choice for detailed quantitative condensed tannin analysis.

AFRIKAANSE OPSOMMING: Fenoliese verbindings, en veral tanniene, is van kardinale belang in rooi druiwe en wyn as gevolg van hul bydrae tot die sensoriese eienskappe en potensiële gesondheidsvoordele. Die gedetailleerde analise van hierdie verbindings word egter belemmer deur hulle kompleksiteit en die gebrek aan betroubare kwantitatiewe analitiese metodes. In hierdie studie is verskillende chromatografiese metodes geëvalueer om ´n gevorderde metode daar te stel vir meer akkurate karakterisering en kwantifisering van tanniene in wyn. Standaard verbindings vir die gebruik in kalibrasie is kommersieel verkry of geïsoleer van kakao met die behulp van semi-preparatiewe hoëdruk-vloeistof-chromatografie. Kalibrasie kurwes is ontwikkel en relatiewe respons-faktore, gebaseer op graad van polimerisasie (DP), klas van tannien en mobiele fase samestelling, is vasgestel. Daar is gevind dat respons-faktore wissel met die DP, sowel as klas van tannien teenwoordig, wat dui op foute wat dikwels gemaak word met kwantifisering in (epi)-katesjien ekwivalente as gevolg van´n tekort aan kommersieel beskikbare standaarde. Beide hidrofiliese interaksie chromatografie (HILIC) en omgekeerde-fase vloeistofchromatografie (RP-LC) metodes vir analise van tanniene is ontwikkel. Vir HILIC is ´n amied kolom gebruik, wat skeiding verskaf volgens DP sowel as isomeriese komposisie binne spesifieke eluerings-gebiede. In RP-LC is verbindings geskei gebaseer op hidrofobisiteit, wat lei tot skeiding van isomere, met verbindings van verskillende DP´s wat soms oorvleuel. In beide skeidings vorms is drie detektors in´n reeks gekoppel: "fotodiode reeks ultraviolet" (UV) detektor, ´n fluoressensie detektor (FLD) en ´n kwadrupool-tyd-van-vlug massaspektrometer (Q-TOF-MS). Daar is gevind dat die FLD die mees sensitief vir prosianidiene (PC´s) is, terwyl UV die beste sensitiwiteit teenoor gallaat PC´s toon. Negatiewe elektrosproei ionisasie (ESI)-Q-TOF-MS was noodsaaklik vir die identifisering van 161 tannien spesies gebaseer op akkurate massa data. Dit was die mees selektiewe van die detektors (wanneer geëkstraheerde ioon chromatogramme gebruik word). Kwantifisering van tanniene in 9 rooiwyn monsters en 'n druiwesaad ekstrak, het aangedui dat elkeen van die detektors nuttig was vir spesifieke verbindings. As gevolg van onvolledige skeiding, is sommige verbindings se vlakke oorskat deur UV en soms ook FLD deteksie. Nietemin was daar goeie ooreenstemming tussen die HILIC en RP-LC metodes sowel as tussen die detektor gebruik in kombinasie met elke metode. Kwantitatiewe data vir die rooiwyn en saad monsters was in ooreenstemming met dié wat in vorige studies verkry is. Die totale aantal verbindings wat geïdentifiseer is (161) en gekwantifiseer is (74 en 41 in HILIC en RP-LC onderskeidelik) was groter as voorheen verkry. Daar is gevind dat beide metodes aanvaarbare opsies is vir die ontleding van gekondenseerde tanniene in druiwe- en wynmonsters. HILIC het beter sensitiwiteit getoon en daarom word HILIC-UV-FLD-Q-TOF-MS aanbeveel.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/101290
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