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Investigating food structure and interactions of food components using hyperspectral Raman imaging and optical tweezers


   School of Natural Sciences

  Prof Mark Waterland  Applications accepted all year round  Funded PhD Project (Students Worldwide)

About the Project

PhD scholarship award

The 3 year PhD scholarship award consists of:

·      stipend                       $30,000 per year

·      student fees                $8,500 per year

·      project consumables    $10,000 per year

·      publication costs          $4,500

Location

School of Natural Sciences and the Riddet Institute, Massey University, Palmerston North, Manawatu, New Zealand

Application process

Applicants must apply and be accepted for entry to the Massey University PhD programme:

https://www.massey.ac.nz/study/all-qualifications-and-degrees/doctor-of-philosophy-PLPHD/

Applications are accepted at any time during the year. Funding is available immediately.

Advice on the PhD application process and requirements will be provided on request.

Supervisory Team

Chief Supervisor: Mark Waterland

Organisation: Massey University

Other supervisors: Simon Loveday (AgResearch), Bill Williams (Massey University), Geoff Jameson (Massey University), Alejandra Acevedo-Fani (Riddet Institute), Keith Gordon (University of Otago).

Background

Hyperspectral imaging can provide spatial and spectroscopic characterisation of food systems and food components. Raman imaging combines the advantages of stain-free sample preparation with the acquisition of vibrational spectra that can identify chemical species and follow chemical reactions in complex samples. However, most Raman images are obtained on solid, or fixed, samples, making Raman imaging impractical for imaging colloids in liquid phases, or for studying dynamic processes in emulsion systems.

We recently obtained detailed Raman images of oil-in-water emulsions by optically trapping oil-in-water droplets in microfluidic channels (and Raman spectra of optically trapped liposomes). Comparison to reference Raman spectra of the pure components allowed spatial distribution of the components to be determined and provided evidence for the location of model bio-active components at the surface of the emulsion droplets.

Overall goal (including contribution to CoRE research programme)

We will develop new methods for investigating food systems by combining optical trapping methods with Raman imaging (“Raman tweezers’), by employing microfluidic methods with Raman imaging and by developing fast hyperspectral imaging methods (‘wide-field’ Raman). This will allow us to extend the simple studies describe above to investigate dynamic processes involving food systems such as studies of the chemical process of digestion at the emulsion interface, partitioning across interfaces and stability and reactions of bio-active compounds in simulated gastric fluids.

We will also investigate recently developed spectroscopic methods (sum-frequency-generation vibrational spectroscopy) that are specific for molecules at interfaces . SFG-VS can provide information about orientation and organisation of molecules at emulsion interfaces.

These objectives contribute directly to Project 1.2 by providing new spectroscopic methods to investigate interactions of food components using in vitro models of digestion and to Project 1.1 by developing tools that will allow Raman hyperspectral data to be correlated with structural dynamics that control food structure formation 

Specific Objectives

1.   Develop Raman Tweezer methodology for studies at the ‘single emulsion droplet’ level.

2.   Develop wide-field Raman imaging methods, for fast Raman imaging of chemical processes in emulsion systems

3.   Explain the effect of modifications in the structure of food emulsions during digestion on the bioaccessibility of hydrophobic bioactive compounds.

4.   Monitor real-time bioaccessibility of hydrophobic bioactive compounds during in vitro digestion of oil-in-water food emulsions, using Raman spectroscopy. and mass spectrometry (for characterisation of digestion products).

5.  Investigate the application of sum-frequency-generation vibrational spectroscopy to characterization of emulsion interfaces. We will characterize the orientation and structure of bio-actives at emulsion interfaces using SFG-VS in collaboration with Prof Tahei Tahara at RIKEN in Japan

Research Methodology

1). Raman Tweezers. Raman Tweezers brings together chemical characterisation via Raman spectroscopy (Waterland group) with control of position and dynamics of emulsion droplets in the form of Optical Tweezers (Williams group). Preliminary investigations suggest adding the Raman spectroscopy capability to the existing Optical Trapping apparatus is the most feasible approach. Our aim with this approach is to collect either Raman spectra or images on trapped emulsion droplets for digestion studies or for investigating interactions and partitioning between droplet pairs with well-defined geometries.

2). Wide-field (fast) Raman imaging. The bottleneck in current Raman imaging is the point-by-point acquisition of an image by a focussed beam raster-scanned across the sample area. We will avoid the raster-scanned bottleneck by using wide-field illumination (i.e. by not focussing the beam) and employing an aberration-corrected array detector to capture images in a single exposure. We sacrifice multiwavelength collection with this configuration and so implement wavelength selection using narrow bandwidth tunable Bragg filters.

3). Imaging modifications in the structure of food emulsions during digestion. We will investigate the relationship between food composition, mixed micelle structure, and the bioaccessibility of different bioactive compounds. Microfluidic channels allow precise control of flow of simulated gastric fluids past trapped emulsion droplets. Optical trapping allows digestion studies of emulsion droplets. Optical images can be acquired simultaneously. We can follow changes in the Raman spectra of the emulsion model and the digestion products will be characterised by mass spectroscopy to provide a deeper understanding of the chemical reactions occurring during the digestion process.

4). Monitoring real-time bioaccessibility of hydrophobic bioactive compounds during in vitro digestion. We will determine the molecular state of bioactive compounds during digestion and its impact on bioaccessibility in model food systems. With fast imaging methods we can determine the spatiotemporal kinetics of solubilisation and precipitation of lipophilic bioactive compounds during digestion. Similarly, low-frequency Raman imaging can be used to report on phase changes of solid bioactives during solubilisation and digestion.

5). Spectroscopy of molecules (SFG-VS) at emulsion interfaces. SFG-VS exploits the nonlinear optical response of molecules to selectively obtain vibrational spectra of molecules at interfaces. We will use SFG-VS to determine the conformations of lipids and bio-active molecules at food emulsion interfaces and how their conformations differ from their bulk solvated structures. 

Suggested Milestones and Timelines (assuming start date of Jan 2023):

1). Literature review, Raman and optical tweezers training

Jan 2023 - March 2023

2). Completed development of Raman Tweezers methodology

Jan 2023 -Dec 2023

3). Completed development of wide-field Raman methodology

Jan 2023 – Jun 2024

4). Digestion imaging studies completed

Jun 2023 – Jun 2024

5). SFG-VS of food emulsions completed

Jun 2023 – Jun 2024

6). Bioaccessibility studies completed

Jan 2024 – Jun 2025

7). Contingency / thesis writing and submission

Jul 2025 – Dec 2025

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