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FEFA and red wine grape colour measurements

P.G. Lye1, M Boerkamp2, R. Bradbury1, D.W. Lamb1

1University of New England, Armidale, Australia,
Hanze University for Professional Education, Groningen, Netherlands


In this contribution the performance of unclad silica and plastic optical fibres and there potential to perform UV-Vis absorption measurements in optically dense solutions, free of or containing suspended solids, is assessed. The basis of such measurements is via the process known as Optical Fibre Evanescent Field Absorbance (FEFA). This phenomenon actually underpins attenuated total reflection (ATR) spectroscopy which, itself is a well-established chemical analysis technique that makes use of evanescent wave interactions at the surface of a crystal waveguide using NIR and/or IR radiation. Changes in parameters such as the angle at which light enters the optical fibre (launch angle), fibre diameter, fibre length and fibre coiling, amongst other things, are discussed in terms of their effect on the sensitivity and signal to noise ratio of the spectral measurements.

The application of FEFA to the measurement of red wine grape colour is also reported. Colour (total anthocyanins) is one of a number of key quality indicators of red wine grapes. The red colour of red wine grapes results from the presence of red coloured pigments called anthocyanins with the colour of the final wine largely determined by their presence. Increasingly, the sale price of red wine grapes is based, in part, on measurements of the colour. While there is an economic incentives for growers to be aware of colour in their fruit there is currently no field-based or handheld device for measuring colour. FEFA spectra from 126 homogenised berry samples, from the New England region, were used to measure the colour of red wine grapes with the measurements compared to the standard spectrophotometric reference method.

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