The understanding of complex food structures is essential in providing new insights into diet-related diseases and the development of novel foods. Our work focuses on proteins and carbohydrates looking not only at the structural components but also at the dynamics using neutron and X-ray scattering [1].
Demonstrating the capabilities of these techniques, we have recently established a food consortium collaborating with other research institutes and major food companies to investigate a range of food proteins.
Governments around the world are concerned about the spiralling cost of healthcare. In the US, life expectancy is anticipated to decline for the first time, partly due to diet-related diseases such as type-II diabetes.
Consumers, too, arebecoming increasingly aware of the importance of what they eat and are demanding new products with enhanced nutritional or diseasepreventing components.
However, changing the composition of the product inevitably leads to a change in the physicochemical properties, which can significantly alter its processing properties, as well as texture and flavour. To develop new food formulations therefore requires a better understanding of how structure at the mesoand nano-scale affects these characteristics.
In addition, techniques that cover a broad range of timescales are also necessary to describe foodstructure from milliseconds to hours (processing) and minutes to months (product stability).
Until relatively recently, structure in foods was considered too complex to be studied with X-ray and neutron scattering techniques. However, with the availability of more intense sources, and advanced instrumentation and computer methods, food-based problems can now be properly addressed.
In addition, for neutron scattering, when combined with socalled contrast-variation methods that rely on the sensitivity to the isotopic composition of the material under study, different structural components may be readily distinguished.
Neutrons are also capable of penetrating complex sample environments - which opens up the opportunity to study industrially relevant processes in real time. Recently, we have used neutron and X-ray scattering to study structures and dynamics in two important food groups - proteins and carbohydrates [2-4].
Proteins as dried ingredients
Proteins are often incorporated in foods in a dried form. However when re-hydrated, they do not have the same properties as the hydrated protein in its native folded state.
The absorption of water may be a relatively slow process due to the formation of a metastable glassy state, during which conformational changes happen only very slowly. Such characteristic structures govern the material properties of the protein and impact on their potential to be processed, in an extruder for example.
Through understanding how water impacts on the material properties, the food industry will be able to predict the behaviour of the protein, thus improving the quality of the product and shelf life leading to reduced waste.
To probe these changes, we studied the proteinwater interaction in dried glycinin - a protein extracted from soybean and used as a gelling, emulsifying and foaming agent [3-4] (Figure 1). At low levels of hydration, small angle X-ray scattered identified the presence of Bragg peaks associated with the presence of some degree of long-range order in the protein.
With increasing moisture content, the intensity and resolution of the scattering peaks decreases significantly. Using neutrons, and deuterated water to improve the scattering contrast, it was possible to demonstrate that hydration causes the peaks to shift to a lower angle, indicating that expanded (Figure 2).
More recently, we employed quasi-elastic neutron scattering methods to follow the moisture-dependent dynamics of the structure and related this behaviour to the macroscopic glass transition behaviour. Using pure proteins as model systems provides the basis for the study of protein mixtures and the influence of additives.
Since proteins as ingredients are subject to storage under varying humidity and environmental conditions, the results from these studies will assist food manufacturers in developing new formulations with predictable behaviour. Indeed, this work, in collaboration with CSIRO Food and Nutritional Sciences and The University of Queensland,has resulted in sufficient interest from several major food companies that are providing funding to investigate a range of other food proteins.
Combating Disease
Resistant Starch (RS) is a fraction of starch that is not digested in the small intestine of healthy individuals and arrives to the colon where it is fermented into short-chain fatty acids.
The latter molecules are beneficial for the correct functioning of the bowel and implicated in disease prevention including colorectal cancer. Furthermore, because its breakdown into glucose is slow, RS has a role to play in combating obesity and type II diabetes.
RS in processed food is believed to be formed by one of the constituents of starch, amylose, which forms digestion-resistant crystallites on cooling. We have investigated the structure of starch as a function of amylose content, processing conditions and in-vitro digestion time, with the aim of understanding how RS levels can be enhanced in processed food.
Combined X-ray and neutron scattering revealed regions of crystalline material in an amorphous matrix, and allowed us to determine the physical density of the RS fraction (see Figure 2). This provides a unique insight into this extremely important food ingredient.
Authors
Elliot Gilbert1, Catherine Kealley2, Amparo Lopez-Rubio3, Anna Sokolova1, Jaroslav Blazek1 and Jitendra Mata1
1ANSTO, 2University of Technology, Sydney, Australia and 3Novel Materials and Nanotechnology Laboratory, Valencia, Spain
References
- Lopez-Rubio A and Gilbert E. P, Trends in Food Science and Technology, 20 (2009) 576.
- Htoon A, Shrestha A. K, Flanagan B. M, Lopez-Rubio A, Uthayakumaran S, Chanvrier H, Bird A.R, Gilbert E.P and Gidley M. J, “Effects of processing high amylose maize starches under controlled conditions on structural organization and amylase digestibility.”, Carbohydrate Polymers, 75 (2009) 236–245.
- Kealley C. S, Rout M. K, Dezfouli M. R, Strounina E, Whittaker A. K, Appelqvist I.A.M, Lillford P. J, Gilbert E. P and Gidley M. J, “Solid- State Structure and Molecular Mobility of Native 11S Soy Glycinin as a Function of Moisture Content”, Biomacromolecules, 9 (2008) 2937- 2946.
- Kealley C.S, Kearley G.J, Kemner E, Russina M, Faraone A, Hamilton W.A, Gilbert E.P, “Novel Relaxation in Hydrated Solid-State