Nanostructures based on pullulan and pumpkin green leaf proteins as carriers for vitamin B12

Abstract

Leaves available as by-products from some crops could be used as a major protein source for food applications. Here, pumpkin leaves from field crop side streams were used for the preparation of a protein-rich extract. Namely, pumpkin leaves were mechanically processed with additional steps of acidic treatment and lyophilization to produce the extract. The extract (1 mass%) was mixed with a spinnable biopolymer-pullulan (5 mass%) with the addition of vitamin B12 (vitB12) as a model vitamin. This homogeneous mixture was electrospuned through a stainless-steel needle (18G) at a steady flow rate of 25.2 mL/h using a syringe pump and an electric field (17 kV) between the positively charged needle and grounded metallic collector plate. The starting solutions (plain pullulan-PUL, pullulan with extract-PUL+E, and pullulan with extract and vitB12-PUL+E+B12) as well as the resulting structures were analyzed regarding physicochemical and morphological properties. The addition of the extract increases the surface tension of the PUL solution, but vitB12 decreases it. On the other hand, the viscosity measurements showed an increase in the value with the addition of extract and vitB12. PUL solution had a conductivity of 0.163 mS/cm, and the value increased upon adding the extract and vitB12 (1.420 mS/cm and 0.978 mS/cm, respectively). According to SEM images, electrospinning resulted in the formation of beaded fibers. The lower the viscosity of the solution, the greater the proportion of particles observed, which is in accordance with literature data. The mean value of the particle size decreases from 388.89 nm (PUL) to 176.68 nm (PUL+E). However, the addition of vitB12 leads to an increase in the mean particle size to 255.94 nm. The addition of extract didn't have a strong effect on average fiber diameter, while a slight increase was observed in PUL+E+B12. FTIR analysis suggests intermolecular interactions between the constituents of the pullulan-extract-vitamin B12 fibers. As a conclusion, the combination of pullulan and protein-rich extract has the properties of a stable carrier for the encapsulation of vitamin B12.