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Agriculture and Food

Foods are complex mixtures of components with diverse thermal, mechanical, rheological and aging properties. Synchrotron techniques allow researchers to correlate the macroscopic properties of a sample with its microstructure, helping companies meet consumer demand for nutritional value, novelty and ease of use, across products ranging from bread to butter.

The food industry benefits from the advantages of synchrotron radiation in different ways. A few of the possibilities of research that the ESRF offers are:

• Visualising the multi-length scale pore structure of samples, for example, freeze-dried vegetables.
• Understanding how the microstructure of food changes due to temperature abuse using high-resolution tomography imaging.
• Detecting trace elements and mapping molecular groups and structures on the nanoscale using infrared spectroscopy.

CASE STUDY

TRACKING IRON IN PROCESSED GRAINS

Company

University of Ljubljana (Slovenia), Chalmers University of Technology (Sweden), University of Nova Gorica (Slovenia), Jozef Stefan Institute (Slovenia), Nutrition Institute (Slovenia).

Challenge

Grains are a main component in the human diet and a major source of essential mineral elements. Unfortunately, many of these elements, such as magnesium, zinc or iron, for example, are tightly bound in the so-called phytate salts and the body does not easily absorb them. There are some ways of making these elements more bioavailable, namely through thermal and mechanical processing, soaking, fermentation, and germination/malting of seeds and grain. These processes enable the release of tightly bound mineral elements, especially those bound in phytate.

Among mineral elements, iron is particularly poorly bioavailable, and this is especially problematic in vegetarian diet. Researchers are now working to determine speciation and bioaccessibility of iron in processed grains in comparison to un-processed grains.  Knowing only the amounts of iron in foods is not enough, researchers need to determine speciation and binding states of iron to understand the bioavailability of iron. Having great concentrations of iron is not effective if all iron is bound too strongly to be absorbed during digestion. Fortification is a costly procedure and not very efficient in the case of iron, as iron is easily reduced and can affect the taste of the produce. Promoting staple food as a good source of bioavailable iron, especially for gluten intolerant individuals (they can consume buckwheat), would be interesting for industry.

Sample

Tartary buckwheat is a gluten-free crop with great potential as a wheat substitute. It has relatively high concentration of iron, which occurs predominantly bound in phytate. The team studied the mineral element concentrations and iron speciation in grains and their processed counterparts, namely groats (hydrothermally processed grains that have the outer grain layers removed) and sprouts (7-day-old seedlings). Grains and groats of two buckwheat species were obtained from Mlin Rangus (Slovenia).

Solution

The ESRF micro-X-ray fluorescence spectroscopy’s beamline ID21 provided the spatial distribution of mineral elements and iron speciation in grains, groats and sprouts It also showed that germination affects the mineral element distribution and speciation of iron. They found that iron bioaccessibility was 4.5-fold greater for grains than groats, suggesting that iron is more bioaccessible in the outer layers of un-processed grains than in the rest of the grain. Bioaccessibility of iron in sprouts was lower than in the grains indicating that germination does not favourably affect the bioaccessibility of iron.

Benefits

This study showed that iron in the outer layers of the grain is most bioaccessible. It would be thus useful to include part of these layers in the flour and in products produced from tartary buckwheat flour to ensure greater iron intake. Iron dense products are highly desired for alleviation of iron deficiency, which occurs particularly in pregnant and breastfeeding women, children and elderly.

buckwheatmariluna.jpg 

Buckwheat. Credits: Mariluna.

 

 

Company
Unilever

Challenge
Freeze-dried vegetables form the basis of many instant foods such as soups and sauces. Unilever wanted to optimise the freeze-drying and rehydration process to produce products with higher quality flavours and textures and with better convenience for the customer. They came to the ESRF to study the effect of different freeze-drying conditions on the microstructure of carrots. Having already carried out extensive characterisation of freeze-dried carrots using techniques that included SEM, MRI, NMR and laboratory source X-ray microtomography (µCT), the aim of the synchrotron experiments was to provide quantitative data through high-resolution 3-D µCT imaging.

Sample
Samples were cylinders cut from the cortical tissue of winter carrots (sample dimensions were typically 10 mm by 6 mm). Pre-treatment to freeze-drying included blanching for one minute in boiling water. Freeze-drying was carried out at various temperatures between -28°C and -150°C.

Solution
High-resolution micro computed tomography was used at beamline ID19 providing non-destructive imaging with sub-micrometre resolution. Synchrotron scans are faster than conventional CT, typically a few minutes compared to hours for conventional CT, which leads to less motion artefacts for evolving samples and the corresponding image quality is much better through its better signal to noise ratio.  Boundaries between regions of different density can be enhanced with phase-contrast imaging. Using 3-D models of the data, segmentation can be used to isolate and reveal regions of similar absorption, i.e. density, which can be used for an accurate estimate of the volume of components.

3-D X-ray tomography imaging of freeze-dried carrot

a) 3-D X-ray tomography imaging of freeze-dried carrot for blanched samples frozen at -28°C and -150°C. b) Representative cross sections of the 3D tomography images. Image credit: G. van Dalen, Unilever.

Benefits
For dehydrated carrot, image analysis of the 3D data sets permitted determination of the size (distribution) of the cell wall thickness and pore diameter. In rehydration experiments, it was possible to visualise rehydration of a sample over a time period of many hours.

The experiments revealed that freeze-drying at lower temperatures produces dehydrated carrots with smaller and more homogenous granular structures, which translates to improved textures in rehydrated material. Furthermore, the blanching pre-treatment produces dehydrated carrot samples with significantly thinner cell walls than non-blanched samples, which helps explain why they rehydrate faster leading to a better texture and appearance for the customer.

 

References

Conference papers:
Multi-length scale structural imaging of freeze-dried carrots and their rehydration behaviour, Gerard van Dalen, Adrian Voda, Arno Duijster, Lucas van Vliet, Frank Vergeldtd, Ruud van der Sman, Henk Van As, John van Duynhoven (2013), InsideFood Symposium, 9-12 April 2013, Leuven, Belgium.

Study of the water vapour sorption of freeze dried carrots using micro-CT, Martin Koster, Gerard van Dalen, InsideFood Symposium, 9-12 April 2013, Leuven, Belgium.

Publications:
Rehydration kinetics of freeze-dried carrots, F.J. Vergeldt, G. van Dalen, A.J. Duijster, A. Voda, S. Khalloufi, L.J. van Vliet, H. Van As, J.P.M. van Duynhoven, R.G.M. van der Sman, Innovative Food Science and Emerging Technologies 24 (2014) 40–47; doi: 10.1016/j.ifset.2013.12.002.

Multiphysics pore-scale model for the rehydration of porous foods, R.G.M. van der Sman, F.J. Vergeldt, H. Van As, G. van Dalen, A. Voda, J.P.M. van Duynhoven, Innovative Food Science & Emerging Technologies 24, 2014, 69-79; doi: 10.1016/j.ifset.2013.11.008.

partners

European Synchrotron Radiation Facility - 71, avenue des Martyrs, CS 40220, 38043 Grenoble Cedex 9, France.