Revalorisation potential of agricultural waste materials into a sustainable source of health-promoting dietary fibre
Project Lead
Challenges
Agricultural and food production side stream materials represent an under-utilised resource that has great revalorisation potential - the process by which surplus food is transformed into a value-add product. Plant-based materials are rich in non-digestible carbohydrates and therefore a potential novel source of dietary fibre, an essential component of a healthy diet.
Dietary fibre is well-recognised for its health benefits despite intakes in the UK being below current recommendations. Key to these health benefits are the microbes in the intestine that play a crucial role in converting fibre to beneficial compounds. Dietary fibre is not digested in the upper intestine and constitutes the main nutrient source for the resident microbes in the large intestine, the gut microbiota. An appropriate supply of fibre is important for health maintenance, as its microbial fermentation leads to the production of metabolites that play an important role in maintaining gut and systemic health. Thus, short-chain fatty acids produced by the gut microbiota have been implicated in the prevention of several diseases, including colorectal cancer, inflammatory diseases, metabolic syndrome, and type 2 diabetes.
Soluble fibre is largely removed during food production processes, such as during the manufacture of juices. The human microbiota has limited capacity to efficiently break down the residual complex insoluble material in its native state. However, the way the material is processed is highly likely to have a major impact on its fermentability by the gut microbiota. The surface structure of the fibre particle dictates how easily the microbes can attach and gain access to the different fibre components to initiate their deconstruction. More work is needed to obtain proof-of-concept results that can inform the development of agricultural side-stream materials into novel sustainable fibre ingredients, which can be used by the food industry for the reformulation of diets to enhance their health-promoting properties.
Questions
- How can we develop our understanding of the physiological effects of interventions on dietary health?
Solutions
We investigate whether food production side-stream materials can be developed into a novel source of fibre, thus improving the sustainability of agricultural practice. This project also identifies opportunities for innovation in the Scottish food and drink sector and expands on effective pathways to increase fibre in the Scottish diet. Side-stream materials from different crops will be ground into flours with different surface structures and incubated with defined microbial consortia to compare their fermentability and metabolite formation. The results are guiding the selection of the best-performing materials to be subjected to fermentation with human faecal microbiota to assess fermentability and metabolite production by the complete microbial community.
This project is:
- Identifying side-stream materials for fermentation analysis with gut microbes.
- Gathering evidence of the effect of particle surface structure of agricultural waste materials on fermentability, microbiota composition and metabolite formation by the gut microbiota
This project was completed on 31st March 2024. The end of project report can be found here.
Project Partners
Progress
The objective of this project was to assess the gut microbial fermentability of agricultural side-stream materials that have been processed to optimise their surface structure for microbial degradation, using a model system of laboratory simulated upper gut digestion, followed by lower gut microbial fermentation with a model community of twelve gut bacteria. Five plant materials (brewery spent grain, oat husks, blackcurrant skins, broccoli and cauliflower) were prepared as flours in two forms differing in their surface characteristics. The materials were subjected to simulated upper gut digestion by exposing them to the conditions and enzymes present in the mouth, stomach and small intestine. After freeze-drying, the fermentability of the digested materials was assessed with the model gut microbial community. Only minor differences in microbial fermentability, microbiota composition and metabolite production between the two flour types were observed for all of the assessed plant materials. This may have been due to the upper gut digestion procedure not being suitable for the assessment of lower gut microbial fermentation. We therefore tested different approaches to avoid drying of upper gut-digested plant material ahead of microbial fermentation, as this would not happen during the passage of food through the intestinal tract in the human body and as the drying process may affect fibre structure. An improved protocol was established and different flour-types of two different plant materials (brewery spent grain and blackcurrant skins) were subjected to the new protocol, followed by microbial fermentation by the model gut microbial community. Similar to the first experiment, only relatively minor differences in overall fermentability, microbial community and metabolite changes were observed, however, microbial community compositional differences between the two flour types were more pronounced. For example, we observed the trend that the cellulose-degrading bacterium Bacteroides cellulosilyticus had higher relative abundance on traditionally ball-milled flours, whereas the pectin degrader Lachnospira eligens had a trend towards higher relative abundance on micronised flours with a larger surface area.
While we did show only a relatively minor effect of fibre structure on gut microbial fermentability here, it would be worth investigating this area further, by exploring other micronisation techniques and flour particle sizes. This project also provided valuable technical insights on the appropriate setup of laboratory-based model systems for whole intestinal digestion and fermentation of food stuffs in the human body, which will inform other projects that utilise such models.
The objective of this project was to assess the gut microbial fermentability of agricultural side stream materials that have been processed to optimise their surface structure for microbial degradation, using a model system of laboratory simulated upper gut digestion followed by microbial fermentation with a model community of twelve gut bacteria. Work in year 1 had revealed no major impact of fibre structure on microbial fermentation, which may have been due to the upper gut digestion procedure not being suitable for the assessment of lower gut microbial fermentation. In year 2, we therefore tested different approaches to avoid drying of digested plant material ahead of microbial fermentation, as this would not happen during the passage of food through the intestinal tract in the human body and as the drying process may affect fibre structure. We assessed the suitability of ethanol precipitation and dialysis to remove digestion products that would be absorbed in the small intestine. Ethanol precipitation proved unsuccessful, as it was impossible to completely remove the ethanol by evaporation. A dialysis protocol was established and different flour-types of two different plant materials (brewery spent grain and blackcurrant skins) were subjected to the new upper gut digestion protocol, followed by microbial fermentation by the model gut microbial community. Similar to the first experiment, only relatively minor differences in overall fermentability, microbial community and metabolite changes were observed, however, microbial community compositional differences between the two flour types were more pronounced. For example, we observed the trend that the cellulose-degrading bacterium Bacteroides cellulosilyticus had higher relative abundance on traditionally ball-milled flours, whereas the pectin degrader Lachnospira eligens had a trend towards higher relative abundance on micronised flours with a larger surface area.
With regard to the technical approach utilised here, we identified potential technical limitations of the upper gut digestion procedures for the production of materials for simulation of lower gut microbial fermentation. Dialysis of the digested materials to remove digestion products that would be absorbed in the small intestine appears to be a suitable method to avoid drying of the digested materials. However, the upper gut digestion components, especially the pancreatin that supplies small intestinal digestive enzymes, constitute a very large proportion of the insoluble material at the end of the digestion procedure, which may influence microbial access to the material. While control experiments showed no inhibitory effect of the upper gut digestion ingredients on our model microbiota, scanning electron microscopy of digested plant fibres revealed that the fibres had a tendency to clump together and string-like material was coating the fibre particles that was not seen before digestion. This may hamper access of gut microbes and thus reduce fermentability. Further protocol improvements are being explored as part of a current studentship.
Podcasts
Inside Matters Podcast with Dr. James McIlroy on Diets, fibre, supplements and the microbiome.
Publications
Dietary fibre optimisation in support of global health. Review article published in Microbial Biotechnology by Ramsteijn and Louis
Why does increased microbial fermentation in the human colon shift toward butyrate? Review article published in AIMS Microbiol by Flint et al.
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