Original research articles

Evaluation of the colour stability of enocyanines

Abstract

Probably the oldest naturaI food colorant was « enocyanin ». It is produced from grape skins as a byproduct of the wine industry in a number of countries, particularly Italy. The recovery of pigments from grape by-products has received considerable attention. Since wine grape skins are waste disposaI problem, obviously the source material is available at very low cost. The pigments in the Vitis vinifera group are 3-monoglucosides of cyanidin, peonidin, mal vidin, petunidin, plus the same compounds acylated with acetic, coumaric or caffeic acid. The hybrids may aIso contain the 3-5-diglucosides of the same aglycones and acylated compounds. Colorants from grapes may be expected to contain a number of other tlavonoids, tannin, organic acids, etc. The anthocyanins show greatest stability under acidic conditions, but are generally unstable and degrade easily according to various reaction mechanisms. The degradation is intluenced by oxygen, ascorbic acid, light, pH and temperature. Processing conditions used for the extraction and purification of pigments from wine grape skins can intluence color stability. The present work was undertaken to study how pH (pH 2, 3,4,5), time (15 days, 30 days, 60 days, 90 days) and temperature (4 oC, 24 oC, 36°C) intluence the color stability of enocyanins concentrated by ultrafiltration, inverse osmosis and under vacuum. The color of the different samples has been measured both by spectrophotometry and by Hunter L *, a*, b* values. The spectrophotometric (A420 ; A520 ; T ; 1 ) and colorimetrie (L *, a*, b*) data resulted correlated significantly. Therefore colorimetrie parameters which can be obtained by using a simple, rapid and easy method were used in order to study the color changes of the different enocyanins in the storage conditions. The obtained results have shown that the concentration techniques by ultrafiltration and inverse osmosis produced enocyanins characterized by a distinct red color, which was intense, but unstable in relation to pH variation. On the contrary, the enocyanins concentrated under vacuum resulted characterized by a poor red color, which was stable in relation to pH changes. In our experimental conditions, the results obtained showed that the degradation of the red col or, in relation to time and temperature, proved to be independent of the concentration technique used. A ready visuaIization of the chromatic evolution of the different enocyanins, with reference to the stability parameters studied, was obtained using the color diagrams.

Authors


Carla Da Porto

Affiliation : Département des Sciences des Aliments, Université de Udine, via Marangoni 97, 33100 Udine (Italie)

foodsci@dsa.uniud.it

Roberto Zironi

Affiliation : Département des Sciences des Aliments, Université de Udine, via Marangoni 97, 33100 Udine (Italie)


Emilio Celotti

Affiliation : Département des Sciences des Aliments, Université de Udine, via Marangoni 97, 33100 Udine (Italie)


Agnese Bertolo

Affiliation : Département des Sciences des Aliments, Université de Udine, via Marangoni 97, 33100 Udine (Italie)

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