Anthocyanin composition of cauliflower (Brassica oleracea L. var. botrytis) and cabbage (B. oleracea L. var. capitata) and its stability in relation to thermal treatments

Violet cauliflower and red cabbage were analysed for their anthocyanin profiles before and after thermal treatments. Anthocyanins are well-noted as healthy compounds due to their antioxidant properties. Samples were analysed for total anthocyanin content by using a spectrophotometric differential pH method. An MS-based method, combining high-performance liquid chromatography (HPLC) with quadrupole tandem mass spectrometry (HPLC–MS/MS) was developed, aimed to separate, identify and quantify the main anthocyanin forms. The procedure involves a rapid and efficient pre-treatment of the samples by solid-phase extraction, followed by selective determination of all compounds in a single run analysis using HPLC–MS/MS. Structural information for the identification of compounds was obtained from their fragmentation patterns (MS/MS spectra). The compounds were separated by HPLC and detected in the multiple reaction monitoring mode (MRM), which provides a high level of selectivity for targeting the analytes in vegetables. Cauliflower and red cabbage showed differences in their anthocyanin profiles: cyanidin-3,5-diglucoside was absent in cauliflower, while it was well represented in red cabbage, together with the characteristic anthocyanin of Brassica genus, cyanidin-3- sophoroside-5-glucoside. The p-coumaryl and feruloyl esterified forms of cyanidin-3-sophoroside-5-glucoside were predominant in cauliflower, while the sinapyl one was mostly present in red cabbage. Besides, the stability of cauliflower’s anthocyanin profile was evaluated in relation to thermal pre-treatments. All thermal treatments, except microwave heating, drastically reduced total cauliflower anthocyanin content. The amount of individual anthocyanins was expressed as the percentage with respect to total anthocyanin amount, spectrophotometrically measured. Significant individual changes were observed after different thermal treatment with an isomer formation.

Il cavolfiore violetto ed il cavolo cappuccio rosso sono stati analizzati per il profilo delle antocianine prima e dopo essere sottoposti a trattamenti termici. Le antocianine sono note quali composti salutistici grazie alle loro proprietà antiossidanti. Campioni del prodotto delle due colture sono stati analizzati per il loro contenuto in antocianine totali utilizzando metodiche spettrofotometriche differenziate per pH. I risultati sono stati comparati con metodiche basate su MS, combinando analisi HPLC–MS/MS allo scopo di separate, identificare e quantificare le principali antocianine. Il cavolfiore violetto ed il cavolo cappuccio rosso hanno mostrato differenze del profilo delle antocianine: cyanidin-3,5-diglucoside è assente nel cavolfiore mentre è ben rappresentata nel cavolo cappuccio con la caratteristica antocianina evidenziata in diverse specie del genere Brassica cyanidin-3-sophoroside-5-glucoside. Le forme esterificate p-coumaryl e feruloyl esterified della cyanidin-3-sophoroside-5-glucoside sono apparse predominanti nel cavolfiore, mentre la sinapyl è stata evidenziata nel cavolo cappuccio. Inoltre, la stabilità del profilo antocianico del cavolfiore è stato valutato in rapporto a pretrattamenti termici. Tutti i trattamenti termici, tranne la scottatura con microonde, hanno ridotto drasticamente il contenuto di antocianine del cavolfiore.