Besides texture degradation and aroma loss colour fading and browning of processed fruits, in particular strawberries, displaying comparatively low amounts of non-acylated anthocyanins, still pose a serious problem. Therefore, in the present study the colour of texture-improved canned strawberries was stabilised using commercial concentrates from black carrots and elderberries as natural colourants. CIE L*a*b* values of the fruit surface and of the brine solutions were monitored over a period of 24 weeks under light exposure. Furthermore, the contents of individual anthocyanins were analysed by HPLC-DAD. The colour of the processed control fruits (without added colourant) was unacceptable even at the beginning of the storage. Their anthocyanin contents were reduced by more than 85% at the end of the storage period. In contrast, the colour of canned strawberries containing black carrot and elderberry anthocyanins was significantly improved. Colour difference values ΔE* of black carrot-coloured strawberries were found to be smaller than those of the samples containing elderberry concentrate as a colourant. This could be ascribed to the presence of acylated anthocyanins in the first exhibiting exceptional storage stability, while all non-acylated pigments were degraded. The chill brining process for fruit firming markedly affected pigment stability, which can be attributed to enzymes that are still active at cold storage conditions.
Canned strawberries Black carrot juice concentrate Elderberry juice concentrate Natural food colourants Acylated anthocyanins CIE L*a*b*HPLC-DAD