The influence of zein microfibre diameter and concentration on the development of mechanical and physico-chemical properties of ɩ-carrageenan

Abstract

This paper explores the effect on mechanical, thermal and physico-chemical properties of ɩ-carrageenan hydrogels when enriched with zein microfibres. The microfibres were generated from varying concentrations (20%W/V, 30%W/V and 40% W/V) of zein using an antisolvent technique. The microfibres were incorporated into ɩ-carrageenan hydrogels at concentrations of 0.2%W/V and 0.5%W/V. Scanning electron microscopy showed that zein concentration correlates with microfibre diameter (ranging from 4.37 ± 0.02 to 11.31 ± 0.1 μm) (p < 0.05). By increasing the zein concentration, the microfibres also become less polar (p < 0.05). Examination by Fourier transform infrared spectroscopy, X-ray diffraction and differential scanning calorimetry indicates that the synthesis of microfibres did not affect protein structure. Zein fibres made from 40%W/V concentration solutions and added to the hydrogel at 0.5%W/V (hereafter Z40%-0.5) exhibited the highest hardness (7.89 g) (p < 0.05). The Z40%-0.5 sample also displayed both the highest storage modulus (G′) value (7550 ± 2.66 Pa) and loss modulus (G″) values (1720 ± 0.47 Pa) (p < 0.05), indicating superior quasi-solid characteristics. Both loss and storage moduli of the samples were frequency-dependent, increasing frequency correlated with higher values for both moduli, signifying weak gel behaviour. The Z40%-0.5 hydrogel (p < 0.05) achieved the highest water holding capacity (WHC) but the highest swelling rate (p < 0.05) was associated with the fibre-free control sample. We demonstrate that incorporating fibres into ɩ-carrageenan hydrogels enhances their mechanical properties, thus addressing a significant commercial application issue.