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Influence of jam processing upon the contents of phenolics and antioxidant capacity in strawberry (Fragaria ananssa x Duch.)

The aim of this study was to evaluate changes after thermal processing by characterizing three strawberry cultivars through their content of individual anthocyanins, phenolic acids and flavonols, as well as antioxidant capacity and colour parameters, before and after jam production. Jams were prepared under vacuum with addition of sucrose and under atmospheric pressure with addition of sucrose or fructose. Strawberry fruits (Fragaria x ananassa Duch.) of three cultivars (Honeoye, Clery and Asia) were obtained from commercial orchards near Zagreb (Croatia) and hand-harvested at the commercial maturity stage. All phenolic compounds were determined by HPLC-UV/VIS PDA analysis. Antioxidant capacities were measured by four different methods: DPPH, ABTS, FRAP and ORAC. Colour parameters were measured by tristimulus colourimeter (CIELAB system). The major anthocyanin in all investigated samples was pelargonidin-3-glucoside, without considerable differences found among investigated cultivars. Regarding to phenolic acids, in all investigated samples hydroxybenzoic acids were predominant, followed by hydroxycinnamic acids and flavonols. Ellagic acid was found in the highest concentrations, followed by p-hydroxybenzoic acid and p-coumaric acid. When looking concentrations of phenolic acids, remarkably variations among investigated cultivars were found. During processing the most stable were hydroxybenzoic acids where vacuum procedure influenced increase by 1-49 % and atmospheric pressure by 17-41 %. The stability of anthocyanins did not considerably differed by various processing procedure, but in most cases, jams prepared with addition of fructose showed lower stability during processing compared to jams with added sucrose. Furthermore, during processing, determined colour parameters L, a, b and C decreased, while H values increased, with no considerably influence of processing procedure, added sugar or strawberry cultivar. Principal component analysis was found to be of value in visual representation of fruit samples based on processing procedure where fresh strawberries and jams distinguished well on the score plot and loading plot.

Strawberry (Fragariaananassa Duch.); processing; phenolic compounds; antioxidant capacity; colour parameters

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