Influence of ripeness stage on the rate of pigment degradation in blackberry fruits during frozen storage

Abstract

Background of the study - The high proportion of the blackberry (Rubus subg. Rubus Watson) cultivar Cacanska Bestrna in commercial orchards (about 60%) in the Republic of Serbia is one of the reasons for the standstill in blackberry marketing as the market value of blackberries is often lowered due to the poor stability of their black colour during frozen storage. With this in mind, the aim of this study was to determine the relationship between the rate of pigment degradation and soluble solids content in the blackberry fruit during frozen storage. Materials and methods - Blackberry fruits of three cultivars were collected at different ripeness stages and frozen at -20 degrees C for 7 and 30 days. Pigment degradation was determined by counting fruits showing pigment degradation after two freezing periods. Soluble solids content (SSC) was measured by a digital refractometer, and total anthocyanins content (TAC) was assessed by the pH-differential method. Results and discussion - The highest rate of pigment degradation (PD) during freezing was found in Cacanska Bestrna', as induced by the lowest SSC and TAC. A lower rate of PD was recorded in berries sampled at the over-ripe stage, whereas an increase in the rate of PD and a decrease in SSC and TA contents were determined during frozen storage. Conclusion - To prolong the shelf life of blackberries whilst maintaining the health benefits and stable colour of fruits, freezing is the best method, but the rate of PD, SSC and TAC during freezing varies with cultivar and ripeness stage.