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Don’t forget your broccoli this Christmas

As we all sit down to a slap-up Christmas meal in a few days’ time, chances are that along with all the turkey, stuffing and sausages wrapped in bacon on our plates there will also be some broccoli. As usual, green vegetables such as broccoli will probably be one of the healthiest foodstuffs we eat at Christmas, and this is mainly due to the fact that green vegetables contain sulphur-containing secondary metabolites known as glucosinolates.

In 2012, a team of food scientists from Ireland and Spain, led by Gerard Downey at the Teagasc Food Research Centre Ashtown in Dublin, showed that NIR spectroscopy can determine the concentration of glucosinolates in freeze-dried broccoli powders. Ideally, though, they really wanted to determine the concentration of glucosinolates in whole broccoli stalks, in fact to identify which bits of the stalk contain the highest concentrations, and so they turned to NIR hyperspectral imaging.

This is a fairly new technique that involves combining NIR spectroscopy with a charged coupled device and data processing software to produce a two-dimensional image of a sample, in which each pixel contains spectral data. Relate this spectral data to some property of interest and you have an image showing how that property varies over the whole sample. Hyperspectral imaging has already been used to map the chemical composition of foods such as strawberries, apples, prawns and pork chops (see Nothing like a good pork chop).

First off, though, Downey and his team used hyperspectral imaging to analyse freeze-dried broccoli powders, which obviously have no structure. They did this to construct a calibration model relating the hyperspectral NIR signal to glucosinolate concentrations, as determined by micellar electrokinetic capillary chromatography. Then they analysed whole freeze-dried broccoli with hyperspectral imaging, using their calibration model to determine the glucosinolate concentrations in different parts.

As they report in the Journal of Food Engineering, this process could produce accurate predictions of glucosinolate concentrations in different parts of whole broccoli, with the outer sections of the florets proving to possess the highest concentrations. So make sure not to leave those bits when you have your Christmas meal.

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