RESUMO
BACKGROUND: Arabinoxylans (AX) are polysaccharides consisting of a backbone of xyloses with arabinose substituents ester-linked to ferulic acid (FA). The arabinose to xylose ratio (A/X) in AX may vary from 0.3 to 1.1. AX form covalent gels by cross-linking of FA but physical interactions between AX chains also contribute to the network formation. The present study aimed to investigate the rheological and microstructural characteristics of gels based on AX enzymatically modified in A/X. RESULTS: Tailored AX presented A/X ranging from 0.68 to 0.51 and formed covalent gels. Dimers of FA content and elasticity (G') increased from 0.31 to 0.39 g kg-1 AX and from 106 to 164 Pa when the A/X in the polysaccharide decreased from 0.68 to 0.51. Atomic force microscopy images of AX gels showed a sponge-like microstructure at A/X = 0.68, whereas, at lower values, gels presented a more compact microstructure. Scanning electron microscopy analysis of AX gels show an arrangement of different morphology, passing from an imperfect honeycomb (A/X = 0.68) to a flake-like microstructure (A/X = 0.51). CONCLUSION: Lower A/X values favor the aggregation of AX chains resulting in an increase in di-FA content, which improves the rheological and microstructural characteristics of the gel formed. © 2017 Society of Chemical Industry.
Assuntos
Arabinose/química , Extratos Vegetais/química , Triticum/química , Xilanos/química , Xilose/química , Biocatálise , Elasticidade , Manipulação de Alimentos , Géis/química , Glicosídeo Hidrolases/química , Lacase , Reologia , ViscosidadeRESUMO
Wheat bran arabinoxylan (WBAX) gels entrapping standard model proteins at different mass ratios were formed. The entrapment of protein affected the gel elasticity and viscosity values, which decreased from 177 to 138 Pa. The presence of protein did not modify the covalent cross-links content of the gel. The distribution of protein through the network was investigated by confocal laser scanning microscopy. In mixed gels, protein aggregates forming clusters were detected at protein/polysaccharide ratios higher than 0.25. These clusters were not homogeneously distributed, suggesting that WBAX and protein are located in two different phases. The apparent diffusion coefficient (Dm) of proteins during release from mixed gels was investigated for mass ratios of 0.06 and 0.12. For insulin, Dm increased significantly from 2.64 × 10-7 to 3.20 × 10-7 cm2/s as the mass ratio augmented from 0.06 to 0.12. No significant difference was found for Dm values of ovalbumin and bovine serum albumin released from the mixed gels. The results indicate that homogeneous protein/WBAX gels can be formed at low mass ratios, allowing the estimation of Dm by using an analytical solution of the second Fick's law.