Cross-Linking of Wheat Bran Arabinoxylan by Fungal Laccases Yields Firm Gels

Sanaz Khalighi,Ralf G Berger,Franziska Ersoy

doi:10.3390/pr8010036

Abstract

The native extractable arabinoxylans (AX) from wheat bran were cross-linked by the commercial laccase C (LccC) and self-produced laccases from Funalia trogii (LccFtr) and Pleurotus pulmonarius (LccPpu) (0.04 U/µg FA, each). Dynamic oscillation measurements of the 6% AX gels demonstrated a storage modulus of 9.4 kPa for LccC, 9.8 kPa for LccFtr, and 10.0 kPa for LccPpu. A loss factor ≤ 0.6 was recorded in the range from 20 to 80 Hz for all three laccases, and remained constant for four weeks of storage, when LccFtr and LccPpu were used. Arabinoxylan gel characteristics, including high water holding capacity, swelling ratio in saliva, and heat resistance indicated a covalently cross-linked network. Neither the mediator compounds caffeic acid and 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid (ABTS), nor citrus pectin, enhanced the elastic properties of the gels. Using laccases as an oxidant provided gels with a solid and stable texture, comparable in firmness to traditional gelatin gels. Thus, AX gels can be presented in the vegan, halal, and kosher food markets. They may also find use in pharmaceutical and other industrial applications.

Highlights

Among commercial hydrocolloids used in the food industry, gelatin is regarded as special and unique, serving multiple functions with a wide range of applications in various industries [1]
To obtain laccase Ftr from Funalia trogii, the fungus was cultivated in SNL medium [21]
Intact ferulic acid in the extracted arabinoxylan was cross-linked with laccase Ftr and Pleurotus pulmonarius (Ppu) to form a hard gel

Summary

Introduction

Among commercial hydrocolloids used in the food industry, gelatin is regarded as special and unique, serving multiple functions with a wide range of applications in various industries [1]. Most of the common hydrocolloids lack the chemical functionalities for creating additional network nodes, which are required for forming solid gels. Wheat bran contains approximately 13 mg/g ferulic acids and up to 50%. Non-digestible fibre, mostly AX [4]. These hemicelluloses consist of β-1,4-d-xylopyranose decorated with α-1,2- and/or α-1,3-l-arabinofuranosyl units. Some of the arabinose residues are ester linked on (O)–5 to FA resulting in ferulated AXs [5,6]. Diferulic (di-FA) and triferulic acids (tri-FA) were identified as covalently cross-linked structures in gelled AX [7,8].

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