Syneresis in Gels of Highly Ferulated Arabinoxylans: Characterization of Covalent Cross-Linking, Rheology, and Microstructure

Abstract

Arabinoxylans (AXs) with high ferulic acid (FA) content (7.18 µg/mg AXs) were cross-linked using laccase. Storage (G') modulus of AX solutions at 1% (AX-1) and 2% (AX-2) (w/v) registered maximum values of 409 Pa and 889 Pa at 180 min and 83 min, respectively. Atomic force microscopy revealed the grained and irregular surface of the AX-1 gel and the smoother surface without significant depressions of the AX-2 gel. Cured AX gels exhibited a liquid phase surrounding the samples indicating syneresis. The syneresis ratio percentage (% R s ) of the gels was registered over time reaching stabilization at 20 h. The % R s was not significantly different between AX-1 (60.0%) and AX-2 (62.8%) gels. After 20 h of syneresis development, the dimers of the FA in the AX-1 and AX-2 gels significantly increased by 9% and 78%, respectively; moreover, the trimers of the FA in the AX-1 and AX-2 gels, by 94% and 300%, respectively. Scanning electron microscopy showed that, after syneresis stabilization, AX gels presented a more compact microstructure. Syneresis development in the gels of highly ferulated AXs could be related to the polymer network contraction due to the additional formation of dimers and trimers of the FA (cross-linking structures), which may act like a "zipping" process, increasing the polymer chains connectivity.

Partial removal of protein associated with arabinoxylans: Impact on the viscoelasticity, crosslinking content, and microstructure of the gels formed

“…The protein content in AX was 8.2%, which is similar to the values previously obtained for another maize AX . AX has a high FA content (7.53 μg/mg AX), which is similar to the recent value reported by Morales‐Burgos et al . for maize bran AX (7.18 μg/mg AX).…”

“…A residual amount of glucose in AX was also quantified, which was similar to the previous reports for maize bran AX . It has been reported that maize bran AX presents a complex structure and may contain small amounts of galactose, mannose, glucuronic acid, and other hydroxycinnamic acids such as coumaric acid . The protein content in AX was 8.2%, which is similar to the values previously obtained for another maize AX .…”

“…AX content was estimated from the sum of xylose + arabinose and found to be 64% on dry basis of the total recovered carbohydrate (69%). A residual amount of glucose in AX was also quantified, which was similar to the previous reports for maize bran AX . It has been reported that maize bran AX presents a complex structure and may contain small amounts of galactose, mannose, glucuronic acid, and other hydroxycinnamic acids such as coumaric acid .…”

“…The microstructure of the freeze‐dried gels was analyzed by SEM using a microscope JEOL 5410LV (JEOL, Peabody, Massachusetts) at 20 kV accelerating voltage according to Morales‐Burgos et al …”

Tailoring reversible insulin aggregates loaded in electrosprayed arabinoxylan microspheres intended for colon‐targeted delivery

“…Previous reports for AX microspheres presented a q of 18 g H 2 O/g AX with equilibrium being reached ~8–12 min . This difference in swelling ratios could be explained from the higher amount of FA covalent crosslinks and the more compact structure presented in highly ferulated AX gels that restricts the swelling . The data acquired from the swelling experiments allow calculating the structural parameters of the gels using the Flory and Rehner model modified by Peppas and Merrill .…”