Biocompounds recovery from purple corn cob by-product: extraction kinetics, thermal and physicochemical stability of liquid and powdered anthocyanin-rich extract

This study evaluated the thermal degradation kinetics of total monomeric anthocyanins (TMA) from in-natura purple corn cob and the recovery of bioactive compounds from their by-products. The TMA and antioxidant capacity (AC) extraction kinetics were evaluated by conventional (CE) and ultrasound-assisted extraction (UAE, 25°C, 40 kHz, 32 W/L) methods. The stability of liquid and powdered extract by using maltodextrin (M) [M(2 %)] and corn starch (C) [M(1.5 %) + C(0.5 %)], was evaluated. Thermal degradation kinetics (65–90 °C) showed that TMA are relatively stable at high temperatures, with a half-life of 5.3 h at 90 °C and an activation energy of 949.2 J·mol⁻¹. The TMA and AC extraction kinetics from corn cob by-product, described by the Peleg model, showed that the UAE had the highest extraction rate (<k₁) and equilibrium yield (<k₂), reducing CE times by up to 58 % and 67 %, for TMA and AC respectively. Furthermore, the stability of this extract was greater at pH ≤ 3, decreasing at neutral and alkaline pH. On the other hand, the water adsorption isotherms modeled by GAB model showed that the powder [M(1.5 %) + C(0.5 %)] had greater stability (Xm = 5.97 g/100 g d.m.) compared to the powder [M(2 %)] (Xm = 3.71 g/100 g d.m.). Additionally, significant differences were observed between treatments in terms of color density, polymeric color, and % tannin contribution, where the powder [M(1.5 %) + C(0.5 %)] demonstrated greater stability. These results highlight the effectiveness of the UAE method for recovering TMA and AC from purple corn cob by-products and the importance of storage conditions and pH in the stability of anthocyanin-rich extracts and powders with potential applications in food and non-food industries.