Dr Terri Grassby
I am a lecturer in food science in the department of Nutritional Sciences. My research interests are based on plant polysaccharides and their direct and indirect nutritional effects. I originally studied chemistry, but have gradually moved towards food science and nutrition, via plant biology.
Areas of specialism
University roles and responsibilities
- Module Organiser, BMS2053 Food Analysis and Quality Control (2016 onwards)
- Module Organiser, BMS3059 Food Chemistry (2016 onwards)
Affiliations and memberships
My research interests are based on plant polysaccharides and their direct and indirect nutritional effects. I am applying this knowledge to a wide range of projects involving industrial and academic partners.
I have taught food science to undergraduate students for the last 5 years, first at King's College London and now at the University of Surrey. I supervise undergraduate and postgraduate projects related to food science, often involving new product development. I am an Associate Fellow of the Higher Education Academy. My office hours are 10-6 Mon-Fri, please email me for an appointment.
Courses I teach on
Postgraduate research supervision
Design of functional oligosaccharides as sucrose replacers
Postgraduate research supervision
Understanding consumer perceptions of processed foods - to support informed healthful choices
PJ Butterworth, FJ Warren, T Grassby, H Patel, PR Ellis
Carbohydrate Polymers (2012) 87(3), 2189-2197
Intact plant cell walls and NSP affect the rate and extent of nutrient digestion, with important implications for health and disease. Certain types of fibre reduce the rate of starch digestion, which in turn can significantly attenuate the postprandial rise in blood glucose and insulin concentrations. This is potentially beneficial in the prevention and treatment of diseases, including diabetes mellitus and cardiovascular disease. However, the mechanisms of action of NSP in relation to the digestive process are still not well understood. They are thought to include formation of viscous solutions, encapsulation of nutrients and inhibition of digestive enzymes.
These mechanisms are illustrated using specific examples. Oat ²-glucan is used to show the effects of various processing techniques on ²-glucan molecular weight, and hence viscosity, on risk factors for diabetes and cardiovascular disease. Evidence for guar galactomannan acting as an inhibitor of ±-amylase, in addition to forming viscous solutions, is presented. Finally, the effect of intact plant cell walls on the bioaccessibility of nutrients is discussed.
almond muffins: The importance of the cell-wall barrier mechanism, Journal of Functional Foods 37 pp. 263-271 Elsevier
within this matrix. Muffins containing small (AF) or large (AP) particles of almond were digested
in triplicate using an in vitro dynamic gastric model (DGM, 1 h) followed by a static duodenal digestion
(8 h). AF muffins had 97.1 ± 1.7% of their lipid digested, whereas AP muffins had 57.6 ± 1.1% digested. In
vivo digestion of these muffins by an ileostomy volunteer (0?10 h) gave similar results with 96.5% and
56.5% lipid digested, respectively. The AF muffins produced a higher postprandial triacylglycerol iAUC
response (by 61%) than the AP muffins. Microstructural analysis showed that some lipid remained encapsulated
within the plant tissue throughout digestion. The cell-wall barrier mechanism is the main factor
in regulating lipid bioaccessibility from almond particles.
The proportion of lipid released during mastication of nuts is strongly influenced by particle size, due to natural encapsulation of the lipid by the walls of intact cells. The cell walls may act as barriers to digestion and may partially explain why nuts have reduced metabolizable energy versus the energy content predicted by Atwater factors. The lipid released from masticated nuts can be calculated using a mathematical model which has the cell diameter and the particle size distribution (PSD) of the bolus as variables. This study measured the cell size and PSD of four tree nuts (raw cashews, raw walnuts, roasted pistachios and raw Brazil nuts) to predict the lipid released due to their mastication.
To predict the proportion of lipid released from masticated tree nuts, using measurements of cell size and PSD of masticated tree nuts (including cashews, walnuts, pistachios and Brazil nuts). To compare the results for these nuts to those already published for almonds.
Transverse and longitudinal sections were cut from each nut (including almonds) and micrographs processed using image analysis software to calculate the average cell diameter. Two randomized, un-blinded, cross-over trials were conducted. In each trial, 10 healthy volunteers attended two sessions, at which they chewed eight samples of a randomly allocated nut. For determination of PSDs, the expectorated boluses were sieved (2 boluses) or analyzed by laser diffraction (2 boluses). Initial lipid release was then predicted using the mathematical model.
The cashew cells (34.3 ¼m) were smaller than the almond (45.1 ¼m), walnut (49.4 ¼m), pistachio (53.1 ¼m), and Brazil nut cells (60.8 ¼m). Laser diffraction showed that masticated nut boluses had median particle sizes (± SEM) which were smaller (cashews, 178 ± 12 ¼m; walnuts, 179 ± 8 ¼m; pistachios, 123 ± 10 ¼m; Brazil nuts, 145 ± 8 ¼m) than that for almonds measured previously (550 ± 18 ¼m). This results in higher predicted lipid release, calculated from the mathematical model, (mean, range) for cashews (12.3%, 8.7?16.3%), walnuts (14.5%, 12.0?18.0%), pistachios (11.0%, 8.7?13.0%) and Brazil nuts (14.4%, 11.9?17.3%) than for almonds (9.5%, 7.4?11.1%).
All of the five nuts had predicted lipid releases of less than 18%, which would be expected to attenuate postprandial lipemia and total nutrient availability relative to that expected due to their total lipid content. Due to their higher lipid content and predicted lipid release, walnuts and Brazil nuts (after mastication) are likely to release more fat on mastication than the other nuts tested.
and Processing on Almond Lipid Bioaccessibility
through Microstructural Analysis: From Mastication
to Faecal Collection, Nutrients 10 (2) 213 MDPI
digestion in the upper gastrointestinal tract (GIT). In the present study, we quantified the lipid released
during artificial mastication from four almond meals: natural raw almonds (NA), roasted almonds
(RA), roasted diced almonds (DA) and almond butter from roasted almonds (AB). Lipid release after
mastication (8.9% from NA, 11.8% from RA, 12.4% from DA and 6.2% from AB) was used to validate
our theoretical mathematical model of lipid bioaccessibility. The total lipid potentially available
for digestion in AB was 94.0%, which included the freely available lipid resulting from the initial
sample processing and the further small amount of lipid released from the intact almond particles
during mastication. Particle size distributions measured after mastication in NA, RA and DA showed
most of the particles had a size of 1000 µm and above, whereas AB bolus mainly contained small
particles ( DA and AB confirmed that some lipid in NA, RA and DA remained encapsulated within the plant
tissue throughout digestion, whereas almost complete digestion was observed in the AB sample.
We conclude that the structure and particle size of the almond meals are the main factors in regulating
lipid bioaccessibility in the gut.
- Mandalari, G., Parker, M.L., Grundy, M.M.L., Grassby, T., Smeriglio, A., et. al. (2018) Understanding the Effect of Particle Size and Processing on Almond Lipid Bioaccessibility through Microstructural Analysis: From Mastication to Faecal Collection. Nutrients 10(2): 213
- Grassby, T., Giuseppina, M., Grundy, M.M.L, Edwards, C.H., Bisignano, C., Trombetta, D., et al. (2017) In vitro and in vivo modeling of nutrient bioaccessibility and digestion from almond muffins: The importance of the cell-wall barrier mechanism. J. Funct. Foods 37:263-271. DOI: 10.1016/j.jff.2017.07.046
- Edwards, C.H., Grundy, M.M.L, Grassby, T., Vasilopoulou, D., Frost, G.S., Butterworth, P.J., et. al. (2015) Manipulation of starch bioaccessibility in wheat endosperm to regulate starch digestion, postprandial glycemia, insulinemia and gut hormone responses: A randomized controlled trial in healthy ileostomy participants. Am. J. Clin. Nutr. 102(4):791-800. DOI: 10.3945/ajcn.114.106203
- Grundy, M.M.L., Grassby, T., Mandalari, G., Waldron, K.W., Butterworth, P.J., Berry, S.E. et. al. (2015) Effect of mastication on lipid bioaccessibility of almonds in a randomized human study and its implications for digestion kinetics, metabolizable energy, and postprandial lipemia. Am. J. Clin. Nutr. 101(1):25-33. DOI: 10.3945/ajcn.114.088328
- Grassby, T., Picout, D.R., Mandalari, G., Faulks, R.M., Kendall, C.W.C., Rich, G.T., et. al. (2014) Modelling of nutrient bioaccessibility in almond seeds based on the fracture properties of their cell walls. Food Funct. 5(12):3096-3106. DOI: 10.1039/C4FO00659C
- Mandalari, G., Grundy, M.M.L., Grassby, T., Parker, M.L., Cross, K.L., Chessa, S., et. al. (2014) The effects of processing and mastication on almond lipid bioaccessibility using novel methods of in vitro digestion modelling and micro-structural analysis. Brit. J. Nutr. 112(9):1521-1529. DOI: 10.1017/S0007114514002414
- Grassby, T., Jay, A.J., Merali, Z., Parker, M.L., Parr, A.J., Faulds, C.B., Waldron, K.W. (2013) Compositional analysis of Chinese water chestnut (Eleocharis dulcis) cell-wall material from parenchyma, epidermis and sub-epidermal tissues. J. Agr. Food Chem. 61(40):9680-9688. DOI: 10.1021/jf401863n
- Butterworth, P.J., Warren, F.J., Grassby, T., Patel, H., Ellis, P.R. (2012) Analysis of starch amylolysis using plots for first-order kinetics. Carbohydr. Polym. 87(3):2189-2197. DOI: 10.1016/j.carbpol.2011.10.048
- Knudsen, G.M., Nielsen, M.-B., Grassby, T., Danino-Appleton, V., Thomsen, L.E., Colquhoun, I.J., et. al. (2012) A third mode of surface-associated growth: immobilization of Salmonella enterica serovar Typhimurium modulates the RpoS-directed transcriptional programme. Environ. Microbiol. 14(8): 1855-1875. DOI: 10.1111/j.1462-2920.2012.02703.x
Reviews and book chapters:
- Lovegrove, A., Edwards, C., De Noni, I., Patel, H., El, S.N., Grassby, T., et. al. (2017) Role of polysaccharides in food, digestion and health. Crit. Rev. Food Sci. 57(2): 237-253. DOI: 10.1080/10408398.2014.939263
- Grassby, T., Edwards, C.H., Grundy, M., Ellis, P.R. (2012) Chapter 4: Functional components and mechanisms of action of ‘dietary fibre’ in the upper gastrointestinal tract: implications for health. In: Harding, S. E. (ed) Stability of complex carbohydrate structures: biofuels, foods, vaccines and shipwrecks. Royal Society of Chemistry, Cambridge. DOI:10.1039/9781849735643-00036.