Spray-Drying of Milk-Blackberry Pulp Mixture: Effect of Carrier Agent on the Physical Properties of Powder, Water Sorption, and Glass Transition Temperature.

Spray dryer was used to produce particles from a milk-blackberry pulp mixture (25%:75% (w/w)). Maltodextrin 10DE and 20DE and gum Arabic were used as adjuvants in order to improve powder quality. The particles were analyzed with emphasis on physical and physicochemical characteristics: moisture content, bulk density, particle size, morphology, water activity, anthocyanins retention, anthocyanins content, hygroscopicity, solubility, water sorption, and glass transition temperature. The best results were obtained for the paste composition of 25% concentrated milk-70% blackberry pulp-5% gum Arabic, yielding high anthocyanins retention (>87.5%), low powder moisture content of 0.0265 g H2 O/g dry matter and a higher powder solubility (>71.8%) when compared with other formulations. The increase of water content led to a decrease of powder's glass transition temperature. Powder stability was evaluated and the critical values of relative humidity and moisture content were estimated based on state diagrams of glass transition combined with sorption isotherm data.

PRACTICAL APPLICATION: The growing interest in blackberries is due to the presence of anthocyanins which have shown possible application as a natural dye for food and pharmaceutical products. Drying a mixture of blackberry pulp and milk may produce particles with a broad range of intrinsic nutrients. Milk components could act as a wall material and emulsifying agent, protecting the flavonoids from blackberry. Therefore, a milk-blackberry powder becomes an alternative, which may reduce postharvesting waste and increase the shelf life of the product without significantly altering its nutritional characteristics.