Effect of time and temperature on vitamin C stability in horticultural extracts. UHPLC-PDA vs iodometric titration as analytical methods

Several fruits and vegetables from Madeira Island (Portugal) were evaluated by two analytical methods for their total vitamin C content (l-ascorbic acid, l-AA and dehydroascorbic acid, DHAA). DHAA was determined indirectly with DL-1,4-dithiotreitol (DTT) applied as a pre-column reductant. Ultra high performance liquid chromatography coupled to photodiode array (UHPLC-PDA) determinations were compared with l-AA content obtained by a classic iodometric titration method. The stability of vitamin C in horticultural extracts stored at different temperatures was also investigated. Red peppers represented the better source of vitamin C followed by green peppers and papayas. Passion fruits and cherimoyas were the analyzed foodstuffs with lowest vitamin C content. Both analytical methods were suitable for l-AA analysis in various food commodities, the UHPLC-PDA technique being preferred due to its advantages of selectivity, speed and accuracy. The degradation study showed that horticultural extracts were stable at least 24 h at 4 °C and during 4 weeks when stored at −80 °C.

► Total vitamin C (l-AA plus DHAA) can be determined by UHPLC-PDA. ► Iodometric titration only evaluates l-AA. ► Time between picking and consuming is crucial for vitamin C degradation. ► l-AA loss depends directly on pulp pH at to pH 5. ► Vitamin C is stable for long time periods on horticultural extracts stored at −80 °C.