Color changes of blackberry as affected by freezing rate

Fast frozen blackberry partially change its surface colour from characteristic black to copper-redish colour. This change decreases the market value, especially when the product is intended for export. For these reasons classic tunnels for slow freezing are being more widely used nowadays. In order to clarify mentioned phenomena, a detailed monitoring of preparation process and freezing, as well as changes of frozen blackberry fruits in industrial conditions was carried out. Along with sensory evaluation of surface colour changes, chemical analysis of reference parameters of fresh and frozen fruits were performed. The results of sensory evaluation confirmed evident colour change of fruits frozen by slow (and fast) treatment; the chemical analysis confirmed unchanged total solids and anthocyanin content, as well as changes in pH value and vitamin C, in comparison to fresh blackberry fruits.