Effects of blanching pre-treatment and sugar composition of the osmotic solution on physico-chemical, morphological and antioxidant characteristics of osmodehydrated blueberries (Vaccinium corymbosum L.)

The effect of a steam blanching preconditioning step was investigated on the chemical, nutraceutical and morphological characteristics of osmo-dehydrated blueberries (Vaccinium corymbosum L.) in sucrose or glucose/fructose osmotic solutions. Mass transfer phenomena (solid gain, water loss and sugar gain) were monitored into the samples at intervals over a 24-h period of osmodehydration. The antioxidant capacity of untreated and osmo-dehydrated fruits was evaluated by total phenolics, total and individual anthocyanins and antioxidant activity (amperometric method), while colorimetric (luminance) and morphological (area, shape factor, fractal dimension) characteristics of the berries were determined by image-analysis technique. Results showed that the blanching step increased mass transfer phenomena in the course of the osmodehydration treatments (approx + 55% solid gain and + 33% water loss) and reduced the loss of phenolic compounds, improving the retention of antioxidant capacity in the final product (from approx 66.9-56.9% in not blanched berries to 88.6-95.7% in blanched ones). Blanched berries had also deeper colour and smoother surface. Slight differences in mass balances and in the final composition of berries could be ascribed to the kind of osmotic solution used.

► Influence of steam-blanching pretreatment on the quality of osmodehydrated blueberries ► Mass transfer phenomena are enhanced by a steam blanching pretreatment ► Higher sugar gain is obtained in glucose/fructose and higher water loss in sucrose ► The loss of phenolic antioxidants is partially prevented by berry blanching ► Blanched osmo-dehydrated berries have deeper colour, higher turgidity and smoother surface