Valorisation of spent coffee grounds as a versatile feedstock for biopolymer production

Lead Research Organisation: University of Manchester
Department Name: Chem Eng and Analytical Science

Abstract

The aim of this project is to develop a novel route for the valorisation of spent coffee grounds (SCG), through the production of polyhydroxyalkanoate (PHA) biopolymers by fermentation of extracted coffee oil recovered from the waste material. The main objectives are; To establish efficient methods for the extraction of coffee oil from spent coffee grounds, based on Soxhlet solvent extraction using a range of green solvents, benchmarked against the recovery achieved with hexane. The extracted coffee oil will be analysed to determine free fatty acid content and to determine the range of fatty acids present. To demonstrate the feasibility of producing PHA biopolymers from the extracted coffee oil in fermentations using Cupriavidus necator, both in shake flask and bioreactor experiments. Investigate a range of methods to improve availability of the carbon substrate (coffee oil), during the fermentation, including saponification and emulsification. The use of saponification as a method to convert the acylglycerides present within SCG oil to potassium salts of fatty acids and glycerol, for the purpose of generating substrates that readily dissolve in water will be investigated; thereby increasing substrate bioavailability to C. necator. The ability of a range of emulsifiers to create coffee oil in water emulsions will also be explored and the influence of the emulsifiers on the fermentation and microorganism quantified.

Publications

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Studentship Projects

Project Reference Relationship Related To Start End Student Name
EP/N509565/1 01/10/2016 30/09/2021
2162737 Studentship EP/N509565/1 14/09/2017 31/03/2021 Haydn Ingram
 
Description Recently, there has been a lot of effort to find suitable materials to replace conventional plastics in a wide variety of applications. Among which, biodegradable and bio-based polymers called polyhydroxyalkanoates (PHA) have high potential due to their similar physical characteristics to some conventional plastics, such as polypropylene. However, PHAs are currently produced by bacteria using relatively expensive carbon feedstocks which results in production costs that are too high to compete with conventional plastics. The use of cheap and readily available carbon feedstocks, such as food wastes, plant oils, and organic industrial wastewater, could help to drastically reduce the overall production cost of PHAs. Plant oils have been demonstrated to be a highly suitable substrate, but their failure to dissolve in aqueous fermentation media limits substrate availability and product recovery.

The bacterium Cupriavidus necator is widely renowned for its ability to produce high levels of PHAs from a wide variety of carbon substrates, including plant oils. Oil extracted from spent coffee grounds (SCG) has been previously demonstrated to be a highly suitable substrate for the production of PHAs by C. necator. Thus, one of the main aims of the project has been to evaluate methods of increasing the bioavailability of the SCG oil to C. necator for the purpose of improving PHA productivity. In this scope, some of the work carried out in this project include:

• A shake flask-based screening study of various surfactants that evaluated their toxicity and use potential carbon or nitrogen substrates to C. necator, as well as their capability to form stable emulsions between SCG oil and the aqueous fermentation media.
• An evaluation of the effects of the selected surfactants on the growth of C. necator its production of PHAs in a 2.2 L bioreactor operated in batch mode.
• A study to find the optimal conditions to convert SCG oil to soap via alkaline hydrolysis (i.e. saponification) for the purpose of creating a substrate that readily dissolves in water.
• An evaluation of using the created SCG oil soap as a potential carbon source for the production of PHAs by C. necator, in comparison to just using crude SCG oil.
Exploitation Route The ultimate goal of this project is to help reduce the cost of PHA production that such PHAs become cheap enough to compete economically with conventional plastics. By improving the bioprocessability of coffee oil in aqueous fermentation systems, we aim to quicken the process and reduce downstream processing costs. In achieving this aim, this project could help PHAs to become industrially viable, as well as serve as a model for lipid-based substrates under consideration in other research projects.
Sectors Agriculture, Food and Drink,Chemicals,Environment,Manufacturing, including Industrial Biotechology