Bioconversion of Industrial Food Waste and Agricultural Waste into Bio-Based Products


Student thesis: Doctoral Thesis

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Award date12 Aug 2019


Biorefineries are one of the best alternatives for replacing petroleum refineries. The need for substitution of fossil fuels is based on the various problems arise from them. Biomass is the best candidate as a feedstock because it is a low-cost and widely available renewable resource. Food and agricultural waste are globally produced in enormous quantities, therefore, they serve as a strong resource for bio-based product production. Consequently, conversion of industrial food and beverage (F&B) waste into fructose and hydroxymethylfurfural, co-fermentation of glucose and xylose from sugarcane bagasse into succinic acid (SA) by Yarrowia lipolytica and enhancing of SA productivity in the yeast, Y. lipolytica, with improved glycerol uptake rates are presented in this thesis.

Firstly, the study of bioconversion of industrial food and beverage waste into fructose using commercial enzyme is discussed. A solid-to-liquid ratio of 70% was applied to hydrolyse F&B waste by glucoamylase and sucrase to yield a hydrolysate consisting of glucose and fructose. After impurity removal using chromatography columns, the purified hydrolysate was processed by glucose isomerase to yield a syrup with a fructose-to-glucose ratio of 1:1. After removal of the residual impurities with ion exchange columns, a simulated moving-bed system was applied to separate sugars in fructose-glucose syrup. The resultant high-concentration fructose syrup contained 89.0 g/L fructose, which was demonstrated as an ideal feedstock for the synthesis of HMF. By employing a commercial solid acid catalyst (Amberlyst 36), 71 mol% HMF with a high selectivity of 77 mol% was generated from this high-fructose syrup under mild microwave heating at 140 oC within 40 min. The increase in catalyst loading accelerated both HMF formation and HMF-consuming side reactions, underscoring the trade-off between the conversion rate and product selectivity. An overall conversion yield of 30 g HMF/kg F&B waste was achieved. This work emphasises a novel integration of chemical and biological technologies for selective production of HMF from mixed F&B waste.

Secondly, investigations of co-fermentation of glucose and xylose from sugarcane bagasse into succinic acid by Yarrowia lipolytica is presented. A feasibility study using a 2.5-L bioreactor demonstrated that mixed glucose and xylose could be utilised for SA production, with the resultant SA titre, yield and productivity of 28.2±0.6 g/L, 0.55±0.01 g/g and 0.36±0.01 g/L/h, respectively. Specifically, SA production employing sugarcane bagasse hydrolysate was conducted, in which SA titre, yield and productivity were 33.2±0.3 g/L, 0.58±0.01 g/g and 0.33±0.01 g/L/h, respectively. The experimental results reported in this study show that glucose and xylose in sugarcane bagasse hydrolysate were successfully co-utilised by Y. lipolytica PSA02004 during SA production. This implies a sugarcane waste biorefinery that could lead to generic feedstock for the efficient production of SA.

Finally, the study of enhancing of SA productivity in the yeast, Yarrowia lipolytica, with improved glycerol uptake rates is featured. Development of cost-effective and highly efficient processes for bio-based SA production is a main concern for industry. The metabolically engineered Y. lipolytica strain, PGC01003, was successfully applied to SA production with high titre. However, this strain possesses as a main drawback a low growth rate when glycerol is used as a feedstock. Herein, the gene, GUT1, encoding glycerol kinase, was overexpressed in strain PGC01003 with the aim of improving glycerol uptake capacity. In the resulting strain, RIY420, glycerol uptake was 13.5% higher than for the parental strain. GUT1 gene overexpression also positively influences SA production. In a batch bioreactor, SA titre, yield and productivity were 32%, 39% and 143% higher, respectively, than for the parental strain, PGC01003. Utilising a glycerol feeding strategy, SA titre, yield and productivity were further enhanced by 11%, 5% and 10%, respectively. Moreover, the process duration to yield the highest concentration of SA in the culture supernatant was reduced by 9%. This demonstrated the contribution of a metabolically engineered strain, RIY420, to lower SA process costs and increase the efficiency of bio-based SA production.

In conclusion, fructose and hydroxymethyl furfural were successfully produced from industrial food waste through enzyme hydrolysis, purification, isomerisation, separation using simulated moving bed and catalysis reaction, respectively in the study. On the other hand, glucose and xylose in sugarcane bagasse were successfully transformed into SA by Y. lipolytica in the study. SA productivity for fermentation of an engineered strain of Y. lipolytica also has been enhanced through metabolic engineering. These studies successfully apply biorefinery methods to upcycle industrial F&B waste and agricultural waste into bio-based products, which facilitates resource management within the circular bio-economy. These studies also provide evidence for new approaches to transforming the current waste management system.