Efficient freeze-drying of foamed strawberry puree: a study on drying kinetics and physicochemical properties†

The production of high-quality strawberry powder is of significant interest in the food industry. This study examines the impact of shelf temperature (10, 20, and 40 °C) on the foaming properties and freeze-drying behavior of strawberry puree with added egg white (EW), with a particular emphasis on drying kinetics and the physicochemical properties of the dried powder, especially the retention of bioactive compounds. Evaluating various concentrations of EW addition revealed that incorporating 0.75% EW results in an optimal foam with maximum overrun (97.22%). Freeze-drying this optimized foamed strawberry puree significantly reduces the total drying time compared to its non-foamed counterpart, with reductions of 43.90%, 44.55%, and 36.00% at the respective shelf temperatures. The drying kinetics of the strawberry foam is effectively described by the modified Page model. Notably, foam mat dried strawberry powder produced at 40 °C exhibits the lowest moisture content (2.69 ± 0.09%) and water activity (0.189 ± 0.003, aw). The foaming treatment does not significantly impact the retention of total phenolic content, but higher shelf temperatures result in decreased retention. Furthermore, foaming pretreatment does not significantly influence the retention of total anthocyanin content in strawberry powders at 10 and 20 °C, but it enhanced the retention at the highest shelf temperature (40 °C). Our findings suggest that foam mat drying could be a more efficient and cost-effective method for producing high-quality strawberry powder.