Rapeseed Meal Pretreatment for Improved Biopolymer Production

Abstract

There are strong incentives for a transition of the current fossil fuel-based economy towards a bio-based one, stemming from the unsustainable nature of fossil fuels, climate change and difficult disposal of non-biodegradable products. As a result, there is increasing interest in waste valorisation, especially of agricultural waste, as this could provide a low-cost feedstock with potential for upgrading to valuable products, and/or contains high-value naturally occurring bioactive compounds. Waste valorisation could also address the problems of purposefully grown biomass feedstocks and the associated negative socio-economic impacts, such as high food prices and deforestation. Additionally, integration of multiple product valorisation processes via a biorefining scheme could lead to more viable economics from product diversification, and may also provide additional economic and environmental benefits via process integration and waste reduction. Rapeseed meal (RSM) is a potential candidate for valorisation due to its high content of potentially valuable phenolics, proteins and polysaccharides. This thesis details the progress made towards RSM valorisation within an integrated biorefinery context, with particular focus on the more sustainable aspects of the scheme, specifically green solvent extraction of RSM phenolics, and the production of biodegradable polymers from RSM polysaccharides. This thesis is presented in a journal format. The experimental phase of the PhD is roughly separated into four stages as follows: Stage I: preliminary work; Stage II: assessment of phenolic extraction and viability of integrated processing; Stage III: optimisation of protein extraction and acid hydrolysis, and in depth investigation into the use of RSM-derived acid hydrolysate for PHA synthesis; Stage IV: Optimisation of enzymatic hydrolysis of untreated and pre-treated RSM for use in PHA synthesis. The work conducted in Stages II, III and IV have been peer-reviewed and published in the Journal of Cleaner production (Wongsirichot et al., 2019), Waste Management (Wongsirichot et al., 2020b) and ACS Sustainable Chemistry and Engineering (Wongsirichot et al., 2020a), respectively. RSM phenolics are of interest due to their antioxidant activities, which could lead to high-value applications such as health supplements in the food industry, or as preservative in the chemical industry. Additionally, the antimicrobial activity of RSM phenolics means that their removal could lead to improved fermentation of other residual fractions. This PhD investigated the extraction of RSM phenolics using novel green deep eutectic solvents (DES). Thermodynamic simulations using the Conductor like Screening Model for Real Solvents (COSMO-RS) shown that DES extractions had greater hydrogen-bonding interaction between the sinapic acid and the DES compared to methanol which has been traditionally used in RSM phenolic extraction. This results in greater yields with DES compared to the methanol. Although this was subjected to the influence of mass transfer, leading to lower yields in the highly viscous glucose-based DES. The highest sinapic acid yield at 91.5 % was achieved using aqueous choline chloride: glycerol (1:1), which outperformed aqueous methanol (68 % yield) at the same conditions. RSM proteins are of interest to the food industry, due to their abundance, and the fact that RSM amino acids are complementary to the amino acid profiles recommended for human consumption. Beyond this, the results found in this thesis demonstrate that the extraction of RSM proteins was crucial for expanding the use of the residual RSM polysaccharides as a fermentation feedstock; as high residual proteins in the polysaccharide fraction hinder its use in nitrogen-limited applications, particularly the synthesis of polyhydroxyalkanoates (PHA) biopolymers. During the PhD, optimisation studies of protein extraction, acid hydrolysis and enzymatic hydrolysis were conducted to determine the m

Date of Award	1 Aug 2023
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Colin Webb (Supervisor), James Winterburn (Supervisor) & Maria Gonzalez Miquel (Supervisor)