Cross-Linking of Fibrex Gel by Fungal Laccase: Gel Rheological and Structural Characteristics

Sanaz Khalighi,Ralf G Berger,Franziska Ersoy

doi:10.3390/pr8010016

Abstract

Sugar beet fibre (fibrex) is an abundant side-stream from the sugar refining industry. A self-produced laccase from Funalia trogii (LccFtr) (0.05 U/µg FA) successfully cross-linked fibrex to an edible gel. Dynamic oscillation measurements of the 10% fibrex gels showed a storage modulus of 5.52 kPa and loss factors ≤ 0.36 in the range from 20 to 80 Hz. Comparing storage stability of sweetened 10% fibrex gels with sweetened commercial 6% gelatin gels (10% and 30% d-sucrose) indicated a constant storage modulus and loss factors ≤ 0.7 during four weeks of storage in fibrex gels. Loss factors of sweetened gelatin gels were ≤0.2, and their storage modulus decreased from 9 to 7 kPa after adding d-sucrose and remained steady for four weeks of storage. Fibrex gel characteristics, including high water holding capacity, swelling ratio in saliva, and heat resistance are attributed to a covalently cross-linked network. Vanillin, as a mediator, and citrus pectin did not enhance covalent cross-links and elastic properties of the fibrex gels. Thus, laccase as an oxidative agent provided gels with a solid and stable texture. Fibrex gels may find uses in pharmaceutical and other industrial applications, which require a heat-resistant gel that forms easily at room temperature. They also represent an ethical alternative for manufacturing vegan, halal, and kosher food.

Highlights

Fibrex is a dietary fibre, which represents an abundant side-stream from the sugar refining industry [1,2]
Most of the ferulic acid ester linked to arabinan and/or galactan can be recovered as ferulate ester of their oligosaccharides under hydrothermal conditions [2]
The higher storage modulus of cross-linked arabinoxylan gel than fibrex gel can be attributed to the lower ferulic acid content of the extracted fibrex [13]

Summary

Introduction

Fibrex is a dietary fibre, which represents an abundant side-stream from the sugar refining industry (approximately 200 kg of beet pulp per ton of sugar beet root) [1,2]. The main fibre types in fibrex are soluble pectin and insoluble hemi cellulose, and small amounts of cellulose and lignin [3]. Sugar beet pectin contains arabinan (α-(1, 5)-linked l-arabinofuranosyl residues), and/or galactan (β-(1, 4)-linked d-galactose residues) as side chains of the rhamnogalacturonan main chain [4]. These side chains can be feruloyl substituted either on O-2 in the main backbone of rhamnogalacturonan-(1, 5)-linked arabinan, on O-5 in the terminal arabinose, or on O-6 in the main backbone of galactan [5]. Most of the ferulic acid ester linked to arabinan and/or galactan can be recovered as ferulate ester of their oligosaccharides under hydrothermal conditions [2].

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Discussion

Conclusion