Impact of food processing on protein digestibility, amino acid metabolism and the gut brain axis

Summary

Consumer demand for plant-based proteins has risen steadily over the past decade (Cardello et al., 2022), largely driven by consumer adoption of a more environmentally friendly and sustainable diet as recommended by EAT-LANCET Commission (Willet et al., 2019).

A shift toward more plant-based protein sources to feed the human population is not without its challenges, in some cases as a result of the lower variety of essential amino acids compared to animal-based sources (Gorissen et al. 2018).

Especially leucine, lysine and methionine which are found to be less abundant in plant-based proteins (Gorissen et al. 2018). The utilisation of dietary protein in the human body is therefore highly dependent on the digestibility and absorption of AA and peptides within the gastrointestinal tract (Santos-Sánchez et al., 2024).

The higher percentage of β-sheet structures in plant proteins can hinder access of gastrointestinal digestive enzymes decreasing digestion of the protein.

Moreover, this can be affected by food processing (Ferrara et al., 2025) as too the levels of free amino acids such a glutamate in processed foods (Hermanussen et al 2012).

A relatively large portion of the plant-based proteins may reach the large intestine to be metabolised by the gut microbiota and impact health status (Canfora et al. 2019).

Recent studies highlight the important role of gut microbiota amino acid metabolism in regulating the gut:brain axis through neurotransmitter production, interactions with the neuroendocrine system and systemic immune function (Rinott et al. 2022, Belelli et al. 2025, Tanaka et al. 2025).

As part collaborative PhD project with the National Alternative Protein Centre (NAPIC.ac.uk) we will explore the impact of food processing on a range of protein rich foods (animal, plant, fungal) using in vitro (Brodkorb et al., 2019) and in vivo digestion models coupled to in vitro colonic fermentation (Diotallevi et al 2021) specifically focusing on amino acid metabolism and chronic disease risk.

Important Information: Applications for more than one PhD studentship are welcome, however if you apply for more than one PhD project within Biomedical Sciences, your first application on the system will be deemed your first-choice preference and further applications will be ordered based on the sequential time of submission.

If you are successfully shortlisted, you will be interviewed only on your first-choice application and ranked accordingly. Those ranked highest will be offered a PhD studentship.

In the situation where you are ranked highly and your first-choice project is already allocated to someone who was ranked higher than you, you may be offered your 2nd or 3rd choice project depending on the availability of this project.

Essential criteria

Applicants should hold, or expect to obtain, a First or Upper Second Class Honours Degree in a subject relevant to the proposed area of study.

We may also consider applications from those who hold equivalent qualifications, for example, a Lower Second Class Honours Degree plus a Master’s Degree with Distinction.

In exceptional circumstances, the University may consider a portfolio of evidence from applicants who have appropriate professional experience which is equivalent to the learning outcomes of an Honours degree in lieu of academic qualifications.

• Sound understanding of subject area as evidenced by a comprehensive research proposal
• A comprehensive and articulate personal statement

Desirable Criteria

If the University receives a large number of applicants for the project, the following desirable criteria may be applied to shortlist applicants for interview.

• First Class Honours (1st) Degree
• Completion of Masters at a level equivalent to commendation or distinction at Ulster
• Practice-based research experience and/or dissemination
• Experience using research methods or other approaches relevant to the subject domain
• Work experience relevant to the proposed project
• Publications record appropriate to career stage
• Experience of presentation of research findings

Equal Opportunities

The University is an equal opportunities employer and welcomes applicants from all sections of the community, particularly from those with disabilities.

Appointment will be made on merit.

Funding and eligibility

This project is funded by:

• Department for the Economy (DfE)

This scholarship will cover tuition fees and provide a maintenance allowance of £21,000* (tbc) per annum for three years (subject to satisfactory academic performance).  A Research Training Support Grant (RTSG) of approximately £900 per annum is also available.

To be eligible for these scholarships, applicants must meet the following criteria:

• Be a UK National, or

• Have settled status, or

• Have pre-settled status, or

• Have indefinite leave to remain or enter, or

• be an Irish National

Applicants should also meet the residency criteria which requires that they have lived in the EEA, Switzerland, the UK or Gibraltar for at least the three years preceding the start date of the research degree programme.

Applicants who already hold a doctoral degree or who have been registered on a programme of research leading to the award of a doctoral degree on a full-time basis for more than one year (or part-time equivalent) are NOT eligible to apply for an award.

Due consideration should be given to financing your studies.

*Part time PhD scholarships may be available, based on 0.5 of the full time rate, and will require a six year registration period