Evaluation of the quality of coffee extracts concentrated by osmotic evaporation

Concentration of commercialized beverages is of the utmost importance for the reduction of transportation, storage, packaging and conservation costs. Osmotic evaporation (OE) is a process widely used in beverage concentration avoiding degradation of color and aromas associated with the use of higher temperatures. In this work, the concentration of aqueous coffee extracts was carried out by OE in a hollow fiber membrane contactor. The coffee samples obtained with this process were analyzed over time in terms of their antioxidant activity (using the DPPH and FRAP methods) and the content of antioxidants compounds (by HPLC). The variation of coffee aroma characteristics and pH throughout the concentration process was also studied. The concentration of total soluble solids of the coffee extracts increased from 30.7 to 123.7 g/L in 4 h of operation, while maintaining both the antioxidant activity and the antioxidant compound concentration per mass of total solids. The pH analyses show that the OE process had no effect on the pH of the coffee solution. The effect of the storage temperature of the concentrated solution on the respective pH was also evaluated; pH decreased from 5.6 to 5.2 and 4.9 when stored at 4 °C and ambient temperature, respectively. Finally, the aroma profile of the initial and concentrated coffee solution was characterized by GC/MS. It was observed that during the OE process the loss of aroma components of the coffee solution was not significant. From the 13 components identified and analyzed, corresponding to 64-69% of the total peak area of the volatile composition, only two showed a significant loss during the concentration process.