Dr. Fernanda Peyronel, Senior Technical Associate – University of Guelph

Dr. Fernanda Peyronel is a world expert in the technique of Ultra Small Angle X-Ray Scattering (USAXS), based at the University of Guelph in the Food Science Department. She uses the USAXS technique to study food structures at the nano- and micro- level. Her latest research focuses on chocolate structures, with a special emphasis on chocolate aromas. Her short course, offered at the University of Guelph, covers all the steps require to process the cacao bean into a chocolate bar. She is further concerned with the waste product from chocolate making, and is looking for application of the cacao bean shells in her research. Dr. Peyronel has guided Food Science graduate students through their research, by helping them carry out projects as well as teaching them how to use different techniques within the Department of Food Science her advanced knowledge of USAXS.

PRESENTATION:

Using X-rays to reveal nano- to micro-structure of under- and well-tempered dark chocolate

Fernanda Peyronel^a, David Pink^b,a

^a University of Guelph, Guelph

^b St. Francis Xavier University, Antigonish

X-rays interact with matter in such a way that the internal structure of materials can be studied when appropriate mathematical and computational models are used. A typical X-ray experiment requires the bombardment of X-rays onto a sample and the subsequent detection of those “scattered” X-rays after interactions with the sample has taken place. Data is labelled by a scattering vector q in “reciprocal space”, and not in the real or direct space, as is done in microscopy. Depending on the set up, the X-rays can probe different regions of the reciprocal space and consequently it contains structural information at different length scales. Typical X-ray techniques used nowadays are X-ray diffraction or Wide Angle X-ray Scattering (WAXS), Small Angle X-ray Scattering (SAXS) and Ultra Small Angle X-ray Scattering (USAXS). Atomistic distances (Å) are covered by WAXS, molecular distances (nanometers) are covered by SAXS and USAXS can revealed information regarding the aggregation of not only molecules into nanocrystals but also clusters of nanocrystals.

This work used the three above-mentioned techniques to study the internal structure of 70% dark chocolates made under two different processing conditions, while keeping the ingredients the same. One set of chocolates was made following the protocol leading to a well-tempered sample, while the other set was manufactured in a way to result in under-tempered sample. Results from the WAXS and SAXS techniques were used to confirm that in fact the protocols used in the manufacture of chocolate gave well- and under-tempered chocolates. The USAXS results showed similarities among the two chocolates for the larger q-values but differences for the smallest q-values. Since the USAXS data was interpreted using the Porod and the Guinier theory within the context of the Unified Fit model, this allowed us to make conclusions and to propose a model regarding the aggregates in the length scale between 6 to 20 µm.

The model suggests that the under-tempered chocolate aggregates will persist after the bulk chocolate is melted, which could be perceived as grittiness in the mouth. However, the model proposes that the aggregates for well-tempered chocolate melt at the same or lower temperatures than the bulk chocolate melting temperature; hence no grittiness is perceived. This model fits well with reports that the mouth can perceive grittiness when particles are as small as 15 µm. Work is underway to do sensory evaluation to stablish whether humans can detect grittiness when the chocolate is under-tempered. This work will open the doors to chocolate manufacturing companies that would like to give consumers different textural experiences.

Louis A. Colaruotolo, Ph.D. Candidate – University of Guelph

Louis started his educational journey in culinary trade school, and driven by a mixture of curiosity, luck, and stubbornness, he is currently pursuing a Ph.D. in food science. His research focuses on observing how good food goes bad at macroscopic, microscopic, and molecular levels to better understand food deterioration to make longer lasting foods in the future. Louis’ work in extending the shelf life of foods contributes to the overall goal of making a more equitable and sustainable food system for the future. In addition to his research, Louis is an active science communicator, hosting a radio show “We Know Some Stuff” that aims to make science a conversation rather than a lesson or lecture.

PRESENTATION:

Non-invasive optical techniques

Non-invasive optical techniques are exceptional tools to identify the deteriorative mechanisms in novel food-grade materials, such as protein-lipid nanowovens. Luminescence and vibrational spectroscopy can be used to scout undisturbed food matrices and characterize physical and chemical changes that occur through a material’s shelflife. Moreover, sample preparation requirements for spectroscopic techniques are low and often non-destructive, providing a more realistic assessment of the material (i.e., unaltered) and facilitating rapid and frequent testing during storage. When coupled with mechanical and chemical testing, optical tools can provide additional insights into the drivers of change in a material’s bulk properties during storage. In this study, luminescence and vibrational spectroscopy and microsspectroscopy techniques were applied to elucidate the mechanisms of physical and chemical deterioration in electrospun zein nanowovens with encapsulated corn oil. A zein solution (20% w/w), prepared in 7:3 propanol:water, was dopped with corn oil (3:10 oil:protein ratio). The solution was electrospun through a needle spinneret (0.7 mm diameter orifice) at 150 mm s-1 carriage speed for 10 min. Nanowoven samples were stored under controlled conditions (dark, 23°C & 33% RH) for 28 days and tested at selected intervals. Thread morphology and nonwoven mechanical properties were assessed by scanning electron microscopy (SEM) and tensile tests, respectively. The overall lipid oxidation was assessed using a TBARS assay. The protein secondary structure was probed using Fourier Transform Infrared Spectroscopy (FTIRS) and the lipid distribution was assessed by microspectroscopic techniques (Raman and luminescence). The photophysical properties of intrinsic (Tyr) and extrinsic (BODIPY C11) lumiphores were also monitored during storage to assess changes in local molecular rigidity, and oxidation. SEM revealed ribbon-like fibers whose diameter significantly decreased during storage (701±23 nm vs. 620±44 nm). Breakage of the fibers correlated with increased brittleness of the material, as reported from bulk measurements, e.g., reduction in extensibility by 26%. FTIRS reported a shift from unordered secondary structures (25% vs. 0%) to ordered structures (β[1]sheets) (2% vs. 19%) during storage. Tyr emission intensity increased 40% indicating a decrease in molecular mobility of the protein matrix. Increased brittleness could be correlated to the rearrangement of the protein secondary structure as identified from FTIRS measurements. The predominance of highly ordered protein structures limited protein mobility and increased propensity to breakage. BODIPY C11 emission allowed gaining insights into lipid oxidation kinetics during storage. The results correlated well with bulk oxidation, as reported by the TBARS assay. BODIPY C11 luminescence and Raman micrographs revealed oil migration towards the surface of the ribbons and selective oxidation of the migrated oil. The correlation between local rigidity and lipid distribution/oxidation suggests protein structure reorganization not only increases material brittleness and propensity to physical breakage, but also displaces encapsulated oils enhancing deterioration. Spectroscopic techniques unveiled the mechanisms that drove changes in physical and chemical properties at the bulk level, identifying factors that limit the shelf life of this material. This study demonstrated the potential applications of non-invasive methods to better understand the mechanisms of deterioration in novel food-based materials and other systems.

Azin Sadat, Ph.D. Candidate – University of Guelph

Azin Sadat started her Ph.D. research in the Department of Food Science in 2018. Her research focuses on the structure and interactions of cereal proteins in complex food matrices. In this context, she is exploring the potential of non[1]invasive, but underutilized techniques such as fluorescence and vibrational spectroscopy to study the (sub/supra-)molecular properties of cereal proteins in a complex matrix. Her project is important to the cereal industry as it will not only lead to the development of innovative tools to study complex systems, but will also shed light on the protein structures that are crucial to cereal product quality. Her project is fully funded by the prestigious Ontario Trillium Scholarship.

PRESENTATION:

Application of Non-invasive (micro) Spectroscopy Techniques to Study Complex Zein-Gluten Dough Systems

Background The volume-spanning network formed by gluten during breadmaking is crucial in the production of high-quality bread products. Zein proteins are also capable of forming a protein network under specific conditions. Vibrational (Fourier transform infrared spectroscopy (FTIR) and Raman scattering) and fluorescence spectroscopy are powerful, non-invasive techniques capable of assessing protein structures and interactions. Objectives The main objective of this project was to explore the suitability of these techniques to study zein and gluten structures and interactions in complex dough systems. In addition, extensional and rheological measurements on zein-gluten dough systems were used to further support the structure and interaction hypotheses. Material and methods Gluten and zein dough samples were prepared by mixing 20 w/w% of protein (different zein-gluten proportions) and 80 w/w% of corn starch. FTIR and FT-Raman spectra of dough samples were collected immediately after dough preparation. To identify the different protein secondary structures, the amide I band (1600-1700 cm-1) in both FTIR and FT-Raman was subjected to curve fitting based on second derivative hidden peak analysis. In addition, the disulfide bridge region (490-550 cm-1) and aromatic amino acids regions (Tyr doublet band [I850/I830]) were analyzed in FT-Raman spectra to detect the percentage distribution of the SS bond conformations and to monitor the microenvironment around Tyr residues, respectively. Fluorescence emission spectra of the intrinsic luminescent aromatic amino acids, Tyr and Trp, and extrinsic Thioflavin T (ThT) were analyzed to assess the protein structure and extent of the β-sheet structure formation, respectively. Scanning electron microscopy (SEM) and confocal Raman microscopy (CRM) were used to visualize the dough structure (SEM and CRM) and obtain a chemical map of the component distribution (CRM). Dough viscoelasticity was assessed using creep- 3 of 3 recovery and small amplitude oscillatory shear tests. The extensibility of dough samples was examined by texture analysis with a Kieffer extensibility rig. Results Detailed analysis of IR and Raman spectra showed the dominant presence of intermolecular β-sheets in gluten-rich dough samples, which decreased steadily upon addition of zein. It can be assumed that the lower water-binding capacity of zein compared with gluten resulted in more available water in the dough samples. This would have promoted the formation of more water-protein hydrogen bonds and decreased the intermolecular β-sheet content. The higher water availability in the zein-rich dough samples resulted in a red-shifted Trp emission in the fluorescence spectra of dough samples, likely indicating the exposure of Trp residues to a more hydrophilic environment. The fluorescence spectra of zein-containing dough samples consistently included a Tyr peak. However, in the only-gluten samples, very efficient Tyr fluorescence quenching occurs. This suggests that the tyrosine (Tyr) moieties (stemming from zein) are not in close proximity to tryptophan (Trp) of gluten. Based on Raman scattering results it is clear that the ratio of fully solvent-exposed and buried Tyr residues, and conformations of disulfide bridges largely differ in between in zein and gluten samples. Based on the results from spectroscopic measurements and scanning electron microscopy (SEM), it was hypothesized that gluten and zein form two distinct network structures in the mixed dough systems. ThT fluorescence intensity increased with increasing zein concentration and pointed to the presence of a higher structured fibrillar network with zein addition to the dough samples, providing more binding sites for ThT. In addition, increasing the proportion of zein in dough increased the dough extensibility and resistance to extension, which can also be attributed to the formation of highly structured β-sheet rich fibrils. On the other hand, gluten-rich doughs, conversely, had a higher elasticity as shown by high values of creep recoverable strain, higher storage moduli, and lower loss tangent values. Strong correlations were found between the molecular information obtained via spectroscopic methods and the physical properties of the samples. Conclusions The present study provides complementary submolecular, molecular, supramolecular, and microstructural information on dough structures made with zein and gluten proteins. Zein, with its lower water-binding capacity, may increase the available water content in the dough samples, creating a more hydrophilic environment for the gluten proteins, leading to a weakening of the intermolecular β-sheet structure, increased exposure of cystine, Trp, and Tyr residues to water, and more pronounced syneresis of the zein-containing dough samples. Furthermore, zein and gluten do not seem to interact tightly with each other. The formation of two ‘separate’ protein network structures is likely and supported by Tyr quenching experiments and SEM analysis. Zein is known to form more fibrillar structures, while gluten upon hydration and shear forms film-like structures. The nature of the formed gluten-zein protein network and hypothesized protein incompatibility upon dough formation were also supported by the rheology and extensibility experiments. The obtained information in this study demonstrated the suitability and complementarity of spectroscopy techniques to study complex cereal systems in a non-invasive way.