Spray-Freeze-Drying approach for soluble coffee processing and its effect on quality characteristics

• Spray-freeze-drying (SFD) technique was used for soluble coffee preparation.
• Product quality was compared against spray-dried and freeze-dried coffee.
• SFD coffee showed highest retention of volatiles, i.e. 93% of that present in feed.
• SFD coffee exhibited instant solubility owing to its porous structure.
• SFD resulted in free-flowing product as indicated by Hausner ratio and Carr index.

The suitability of Spray-Freeze-Drying (SFD) technique for soluble coffee processing was evaluated. The resultant product characteristics were compared against its spray-dried (SD) and freeze-dried (FD) counterparts. SFD and FD coffee powders exhibited a comparable aroma profile as indicated by the electronic nose analysis. SFD resulted in higher volatile retention (93%) than FD (77%) and SD (57%), as inferred from GC–MS analysis. SFD coffee showed instantaneous solubility due to its highly porous nature as observed in morphology studies. SFD coffee depicted monomodal particle size distribution with mean diameter (91.1 μm) ranging between SD (50.41 μm) and FD (636.8 μm) particles. SFD resulted in higher free (ρB, 0.612 g/mL) and tapped (ρT, 0.679 g/mL) bulk densities of the product against SD (ρB: 0.328 g/mL; ρT: 0.388 g/mL) and FD (ρB: 0.345 g/mL; ρT: 0.361 g/mL). SFD coffee exhibited free flowing characteristics as indicated by its Hausner ratio (1.11) and Carr index (10%).