Arabinoxylans as co-products of biorefineries and novel bread ingredients

  • Konstantina Solomou

Student thesis: Doctoral Thesis

Abstract

Arabinoxylans (AXs) are long chain polymers of xylose units with arabinose branches that represent a significant hemicellulose fibre component in cereal bran and other grass species. In recent years, AXs have gained prominence as promising by-products of biorefineries with potential use in both food and non-food applications, especially as ingredients in bakery products. The emergence of biorefineries in recent decades has created a conducive environment for the commercial production of a diverse range of AX products. Consequently, there is a growing need to ascertain the functionality of AX products and their suitability for targeted purposes, facilitating the establishment of AX portfolios and markets. In the preliminary work of this thesis, AXs were extracted from wheat bran and sugarcane bagasse via the alkaline oxidative extraction method and were precipitated in different concentrations of ethanol (60%, 70% and 80%) to create three AX fractions: >30 kDa, 10-30 kDa and 5-10 kDa respectively. The effects of AX, their feedstock and molecular weight in bread dough formulations were investigated using an empirical dough rheometer, the Chopin Mixolab 2. AX from sugarcane bagasse increased the water absorption of the dough by more than double their own weight for fractions with molecular weight of 10-30 kDa and >30 kDa and increased dough development time in a Chopin Mixolab, while the highest molecular weight fraction had a significant effect on the stability time. Wheat bran AX increased water absorption by 3%, but did not have any effect on development and stability times.Breadmaking trials were conducted using commercial AX samples from wheat (WhAX) and maize (MzAX) added into the bread dough formulations at levels of 0%, 0.5%, 1%, 1.5% and 2% flour substitution, and their effects on bread loaf volume, height and texture and the average pore area of the bread slices were analysed. WhAX decreased bread specific volume and slice height at 0.5%-1.5%, but showed an increase when added at 2%. Both AXs appeared to decrease crumb springiness 24 hours after baking, but increase springiness 48 hours after baking, suggesting an evolving pattern of interaction between AX and the starch matrix over time that may be relevant to delaying staling. MzAX on its own had a detrimental effect on the volume of the bread loaves and destructive effects on the quality of the bread, although later work (see below) suggests MzAX in combination with other AXs could allow formulations with targeted functionalities to be designed.A novel approach was developed to quantify the effects of arabinoxylans on the required water absorption of a dough formulation and on other parts of the Mixolab torque profile relevant to bread quality. An experimental design and model were formulated to allow the effects of flour removal, AX substitution and water adjustment to be distinguished and quantified accurately. The model was applied to three commercial AX samples, Maize AX (MzAX), Wheat AX (WhAX) and Maize AX with low molecular weight (MzLMWAX), added to Mixolab dough formulations at concentrations of 1%, 2% and 5% and water absorptions of 63%, 63.5%, 64%, 64.5% and 65%. The effect of the three AXs was initially modelled for the water absorption (WA), allowing the water adjustment for constant initial peak torque (C1) to be determined, and an Arabinoxylan Multiplication Factor (AXMF) to be defined that quantified the effect of the AX on WA relative to the effect of flour. The model was then extended to predict the combined effects of AX addition and water adjustment on other Mixolab parameters.The addition of MzAX increased C1 and WA, with nearly double the effect of adding flour to the dough (AXMF = 1.986). By contrast, WhAX had a slightly negative AXMF of –0.1681, indicating that most of effect on C1 was due to the removal of flour, with the WhAX then contributing a small additional negative effect. Addition of MzLMWAX gave a larger negative effect on C1 (AXMF = –0.7390), again indicating that removal of flour decreased C1 and WA, and that addition of MzLMWAX decreased these parameters even further, showing that the AX had the opposite effect to that of flour. MzAX had even larger AXMF values for C3 and C4, but negative values for C2 (indicating softening of the dough during initial heating) and C5 (indicating softening of the dough during cooling, relative to the effect of flour). MzAX decreased Development Time and increased Stability Time significantly. WhAX and MzLMWAX generally had smaller effects, and showed some contrasting effects on the magnitude and direction of the Mixolab parameters. WhAX had similar effects as the addition of flour on most of the Mixolab parameters, while MzLMWAX increased C2 by a factor of 2 and decreased C2-C5 and DT by 2-3 times the effect of flour, and had nearly no effect on stability time. The demonstration of the model allowed the accurate distinction of effects of removed flour, added AX and adjusted water across the whole Mixolab profile, followed by the formulation of mixtures that target specific elements of the profile related to specific elements of bread quality. The potential scope of the model extends beyond these specific AXs to other AX products and to other fibre ingredients in breadmaking, which could be valuable for formulating combinations that harness the benefits of fibre, while mitigating its detrimental effects in bread. By employing this approach, AX products and formulations with specific functionalities in breadmaking can be pinpointed, paving the way for the development of commercial sources and markets for these novel ingredients, contributing to the economic and commercial viability of the emerging biorefining sector while delivering a new class of healthy and functional ingredients to the food industry.
Date of Award12 Apr 2024
Original languageEnglish
SupervisorGrant Campbell (Main Supervisor) & Athanasios Angelis-Dimakis (Co-Supervisor)

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