Tribology of Sustainable Protein Concentrates

With increasing concerns about environmental sustainability, there is growing demand to use low carbon-intensive, sustainable, plant proteins, or at least partially replace conventional animal proteins such as whey or egg white proteins with plant proteins. However, one of the key barriers to consumer acceptance of plant protein-based foods is their undesirable mouthfeel, which often include: (a) astringency, hypothesised to result from oral lubrication failure of plant proteins [1] (b) grittiness, associated with protein-protein aggregation [2] causing high boundary friction and limited/ excessive surface adhesion, leading to undesirable mouthcoating during oral processing. Often highly purified plant protein isolates are used in food formulation and their delubrication performance has been relatively well-studied in the literature, where research is now evolved and focusing on understanding their behaviour in real food formulations [3]. However, the area which remains relatively less-explored is the tribological behaviour of plant protein concentrates, which naturally contain remnant polysaccharides and starches, and have not been through extensive fractionation and isolation processes. These inherent polysaccharides depending upon their structure may offer lubrication benefits, by modifying viscosity, while reducing additional costs and energy for protein purification. However, the mechanism by which these crude plant protein concentrate mixtures interact with oral surfaces to form tribological films remains poorly understood to date. Informed by advances in lubrication theory, this PhD project aims to systematically elucidate the mechanisms of boundary friction in plant protein concentrates. The project will investigate how these crude concentrates behave on deformable, model saliva-coated surfaces, focusing on surface roughness and wettability of oral surfaces. We will employ novel experimental and theoretical approaches, including: Dynamic friction measurements using 3D tongue-like deformable, weakly polar surfaces developed in our lab, which replicates the spatial distribution of papillae using 3D printing, soft lithography and model salivary coating [4];high-speed fluorescence imaging of tribological films; Quartz Crystal Microbalance with Dissipation Monitoring (QCM-D) to assess affinity of these concentrates to oral films. Combining experimental data with indentation theory [5], we aim to understand how plant protein concentrates can form stable, lubricating tribofilms capable of supporting load, and to improve lubrication in food, diminishing astringency. There will be opportunities to investigate development of a novel theoretical framework from first principles and/or utilising statistical methods. This work will ultimately provide novel design rules for development of next-generation, cost-effective, sustainable plant protein-based foods. The PhD will offer an opportunity to collaborate with the National Alternative Protein Innovation (NAPIC).

<p>[1] Sarkar A. (<strong>2024</strong>). Oral astringency in plant proteins: An underestimated issue in formulating next-generation plant-based foods. <em>Annual Review of Food Science and Technology</em>. <strong>15 (1), </strong><a href="https://doi.org/10.1146/annurev-food-072023-034510">https://doi.org/10.1146/annurev-food-072023-034510</a></p> <p>[2] Brown F,  Soltanahmadi S, He Q, Pfeifer J, Mackie AR, Sarkar A. (<strong>2025</strong>).Comparing frictional behaviour of plant and dairy proteins: Case study on high protein concentration. <em>Food Research International. </em><strong>209</strong>, Article No.116322 <a href="https://doi.org/10.1016/j.foodres.2025.116322">https://doi.org/10.1016/j.foodres.2025.116322</a></p> <p>[3] Kew B, Guo X, Heath A, Tuohy K, Buckley A, Sarkar A. <strong>(</strong><strong>2026</strong>). Relating tribology to astringency perception in acidic plant protein-fortified fiber-based smoothies. <em>Food Hydrocolloids</em>, <strong>171</strong>, Article No. 111770 <a href="https://doi.org/10.1016/j.foodhyd.2025.111770">https://doi.org/10.1016/j.foodhyd.2025.111770</a></p> <p>[4] Andablo-Reyes E, Bryant M, Neville A, Hyde TP, Sarkar R, Francis M, Sarkar A. (<strong>2020</strong>). 3D biomimetic tongue-emulating surfaces for tribological applications. <em>ACS Applied Materials and Interfaces</em>, <em><strong>12</strong></em>, <em>pp. 49371–49385</em> <a href="https://doi.org/10.1021/acsami.0c12925">https://doi.org/10.1021/acsami.0c12925</a></p> <p>[5] Kew B, Holmes, M, Liamas E, Ettelaie R, Connell S, Dini D, Sarkar A. (<strong>2023</strong>).Transforming sustainable plant proteins into high performance lubricating microgels. <em>Nature Communications</em>, <em><strong>15, </strong></em>Art No. 4743 <a href="https://doi.org/10.1038/s41467-023-40414-7">https://doi.org/10.1038/s41467-023-40414-7</a></p>

<p paraeid="{cc558561-e300-45f5-a898-3bd20c9a5968}{113}" paraid="1539768372"><strong>You must contact the proposed supervisor for this project before you make a formal application. </strong></p> <p paraeid="{cc558561-e300-45f5-a898-3bd20c9a5968}{119}" paraid="1895649428">A formal application for research degree study should then be made online through the <a href="https://www.leeds.ac.uk/research-applying/doc/applying-research-degrees" rel="noreferrer noopener" target="_blank">University's website</a>. You will need to create a login ID with a username and PIN: </p> <ul> <li paraeid="{cc558561-e300-45f5-a898-3bd20c9a5968}{125}" paraid="1717955186">For ‘Application type’ please select ‘Research Degrees – Research Postgraduate’. </li> <li paraeid="{cc558561-e300-45f5-a898-3bd20c9a5968}{131}" paraid="1941411394">The admission year for this project is 2026/27 Academic Year.   </li> <li paraeid="{cc558561-e300-45f5-a898-3bd20c9a5968}{137}" paraid="1823221166">You will need to select your ‘Planned Course of Study’ from a drop-down menu. For this project, scroll down and select ‘PhD Food Science and Nutrition Full-time’.   </li> <li paraeid="{cc558561-e300-45f5-a898-3bd20c9a5968}{143}" paraid="754352421">The project start date for this project is October 2026, please use this as your Proposed Start Date of Research. </li> <li paraeid="{cc558561-e300-45f5-a898-3bd20c9a5968}{149}" paraid="202248598">Please state clearly in the research information section that the research degree you wish to be considered for is ‘Tribology of sustainable plant protein concentrates’ as well as <a href="https://environment.leeds.ac.uk/food-nutrition/staff/7151/professor-anwesha-sarkar">Prof Anwesha Sarkar</a> as your proposed supervisor. </li> </ul> <p paraeid="{cc558561-e300-45f5-a898-3bd20c9a5968}{155}" paraid="812110430">If English is not your first language, you must provide evidence that you meet the University's minimum English language requirements (below). </p> <p paraeid="{cc558561-e300-45f5-a898-3bd20c9a5968}{161}" paraid="1891516213">More information on how to apply is available on our website <a href="https://www.leeds.ac.uk/research-applying/doc/applying-research-degrees" rel="noreferrer noopener" target="_blank">here</a>. You will need to provide copies of the following documents:</p> <ul> <li paraeid="{cc558561-e300-45f5-a898-3bd20c9a5968}{172}" paraid="1858125611">a research proposal for this project</li> <li paraeid="{cc558561-e300-45f5-a898-3bd20c9a5968}{172}" paraid="1858125611">your CV </li> <li paraeid="{cc558561-e300-45f5-a898-3bd20c9a5968}{184}" paraid="1448270499">certificates and transcripts of all academic qualifications </li> <li paraeid="{cc558561-e300-45f5-a898-3bd20c9a5968}{190}" paraid="932080590">English language qualification certificates </li> <li paraeid="{cc558561-e300-45f5-a898-3bd20c9a5968}{196}" paraid="1315959137">visa and immigration documents, if applicable </li> <li paraeid="{cc558561-e300-45f5-a898-3bd20c9a5968}{202}" paraid="226045984">funding information – sources of funding that you are applying for (e.g. government scholarship), or if you are able to pay your own fees and maintenance  </li> </ul> <p><em>As an international research-intensive university, we welcome students from all walks of life and from across the world. We foster an inclusive environment where all can flourish and prosper, and we are proud of our strong commitment to student education. Across all Faculties we are dedicated to diversifying our community and we welcome the unique contributions that individuals can bring, and particularly encourage applications from, but not limited to Black, Asian, people who belong to a minority ethnic community, people who identify as LGBT+ and people with disabilities. Applicants will always be selected based on merit and ability. </em></p>

Applicants to research degree programmes should normally have at least a first class or an upper second class British Bachelors Honours degree (or equivalent) in an appropriate discipline.

For start dates from September 2026, the minimum English language entry requirement for research postgraduate research study in the School of Food Science and Nutrition is an IELTS of 6.0 overall with at least 5.5 in each component (reading, writing, listening and speaking) or equivalent. The test must be dated within two years of the start date of the course in order to be valid.

<p paraeid="{3d04e34c-3522-40f3-8630-c6f14cbc41d0}{143}" paraid="557166827"><strong>This is not a funded project, but you can apply for funding separately. Self-funding students are also welcome to apply. </strong></p> <p paraeid="{3d04e34c-3522-40f3-8630-c6f14cbc41d0}{149}" paraid="1936376053"><strong>Please note that in addition to the <a href="https://www.leeds.ac.uk/research-fees/doc/research-degrees-fees" rel="noreferrer noopener" target="_blank">tuition fee</a> for the programme there will also be a <a href="https://www.leeds.ac.uk/research-fees/doc/postgraduate-research-bench-policy" rel="noreferrer noopener" target="_blank">bench fee</a> of £5,000 per year for this project.   </strong></p> <p paraeid="{3d04e34c-3522-40f3-8630-c6f14cbc41d0}{171}" paraid="1993701339">Funding opportunities for Home students – The <a href="https://phd.leeds.ac.uk/funding/209-leeds-doctoral-scholarships-2026" rel="noreferrer noopener" target="_blank">Leeds Doctoral Scholarship</a> and <a href="https://phd.leeds.ac.uk/funding/234-leeds-opportunity-research-scholarship-2026" rel="noreferrer noopener" target="_blank">Leeds Opportunity Research Scholarship</a> are available to UK applicants.  <a href="https://phd.leeds.ac.uk/funding/60-alumni-bursary" rel="noreferrer noopener" target="_blank">Alumni Bursary</a> is available to graduates of the University of Leeds. </p> <p paraeid="{3d04e34c-3522-40f3-8630-c6f14cbc41d0}{194}" paraid="629442306">Funding opportunities for International students –The <a href="https://phd.leeds.ac.uk/funding/48-china-scholarship-council-university-of-leeds-scholarships-2021" rel="noreferrer noopener" target="_blank">China Scholarship Council - University of Leeds Scholarship</a> is available to nationals of China. <a href="https://phd.leeds.ac.uk/funding/60-alumni-bursary" rel="noreferrer noopener" target="_blank">Alumni Bursary</a> is available to graduates of the University of Leeds. </p>

<p>For further information regarding the project, please contact Professor Anwesha Sarkar by email (<a href="mailto:A.Sarkar@leeds.ac.uk">A.Sarkar@leeds.ac.uk</a>). You must contact Anwesha before making a formal application. </p>