Deep eutectic solvent as an alternative, green medium for enhancing the stability of blackberry (Rubus spp) pigments

Blackberry fruit (Rubus spp.) is a delicious fruit that is rich in pigments such as anthocyanins. Deep eutectic solvents (DES) stand as green efficient solvents for the recovery of pigments from various matrices in the food, cosmetic and pharmaceutical industries. DES showed high efficiency for the recovery of anthocyanins from blackberry fruit. However, scientific data on the protective role and stability of pigments in DES is lacking. In the present study, we investigated the stabilization of anthocyanins from blackberry fruit extracted with choline chloride and glycerol-based DES (CHGLY). Stability tests including storage in darkness, light stability and thermal stability were designed. After storage in the dark, the pigments remained 25.55 ± 0.89–68.62 ± 1.25 % in the DES while they decreased to 0.07 ± 0.00–5.82 ± 0.48 % in the water. The evaluation of the degradation kinetics of anthocyanins revealed that they are more strongly protected and stable in CHGLY than in water. The t_1/2 obtained with the storage in the dark was 91.90 ± 0.07–1238.27 ± 60.03 h for CHGLY and 64.58 ± 0.02–163.79 ± 4.77 h for water. For the light stability test, the t_1/2 value was 283.59 ± 19.58h-589.49 ± 4.97 h for CHGLY and 65.79 ± 0.02h-170.42 ± 5.07 h for water. The thermodynamic properties such as first-order reaction constant k, activation energy (Ea), Gibbs value (∆G ̊), enthalpy (∆H ̊) and entropy (∆S ̊) demonstrated that natural pigments from blackberry fruit are thermally more stable in CHGLY than in a water solution. This work thereby generated important outcomes regarding the ability of DES to stabilize pigments such as anthocyanins.