Characterization of Microcapsule Containing Walnut (Juglans regia L.) Green Husk Extract as Preventive Antioxidant and Antimicrobial Agent

Abstract

Background: Walnut green husk (WGH) extract has been known as potential preventive and therapeutic antioxidants and antimicrobials due to its high polyphenol content. In this study, preparation of spray dried WGH extract‑loaded microcapsules by maltodextrin and its blending with two other natural biodegradable polymers, pectin, or alginate were investigated.

Methods: In this study, encapsulation effciency (EE), total phenol content (Folin–Ciocalteu reagent method), antioxidant (DPPH scavenging assay) and antimicrobial activities (agar well diffusion method) structural (SEM and FTIR studies), and release properties of WGH extract‑loaded microcapsules
were investigated.

Results: High retention of phenolic content in microcapsules indicated the
successful encapsulation of WGH extract. Addition of biopolymers to maltodextrin matrix has a positive effect on EE and other properties of microcapsules. The microcapsules prepared with mixture of maltodextrin and pectin had higher EE (79.35 ± 0.87%) and total phenolic (TP) content (56.83 ± 1.04 mg gallic acid equivalents [GAE]/100 g) in comparison to maltodextrin and alginate mixture (EE: 75.21 ± 0.24%, TP content: 54.33 ± 1.53 mg GAE/100 g) and maltodextrin only matrix (EE: 72.50 ± 1.00%, TP content: 50.67 ± 1.35 mg GAE/100 g). Extract‑loaded microcapsules also showed nearly spherical structure, good antioxidant (with the percentage DPPH inhibition ranged from 75.17 ± 1.42% to 80.87 ± 2.29%), and antimicrobial properties (with mean inhibition diameter zone ranged from 7.76 ± 0.86 mm to 11.53 ± 0.45 mm). Fourier transform
infrared analyses suggested the presence of extract on microcapsules. The in vitro extract release from microcapsules followed an anomalous non‑Fickian diffusion mechanism with almost complete
release.

Conclusions: WGH extract microcapsules can be used as novel and economic bioactive phytochemical and therapeutic agents to prevent oxidation and microbial activity.

Keywords: Antioxidants, Juglans, microencapsulation, polyphenols