Ultrasound assisted extraction of red cabbage and encapsulation by freeze–drying: moisture sorption isotherms and thermodynamic characteristics of encapsulate

In the present study encapsulation of ultrasound assisted red cabbage extract was carried out using four different carrier agents such as maltodextrin, gum arbic, xanthan gum, and gellan gum. Among the four hydrocolloids investigated, maltodextrin was found to have the least destructive effect on anthocyanin content (14.87 mg C3G/g dw), TPC (54.51 ± 0.09 mg GAE/g dw), TFC (19.82 Mg RE/g dw) and antioxidant activity (74.15%) upon freeze–drying. Subsequently a storage study was conducted using maltodextrin as carrier agent at 25–50 °C. The Clausius–Clapeyron equation was used to evaluate the net isosteric heat (q st ) of water adsorption. The differential entropy (ΔS) and q st decreased from 82.298 to 38.628 J/mol, and 27.518 kJ/mol to 12.505 kJ/mol, respectively as the moisture content increased from 2 to 14%. The value of isokinetic energy and Gibb’s free energy were found to be 364.88 and − 1.596 kJ/mol for freeze dried red cabbage. Graphical abstract