Abstract
In the presented investigation, the chemical composition of malt during roasting is estimated using diffuse reflectance mid-infrared fourier transform (DRIFT-MIR) spectroscopy and multiple linear regressions. Accordingly, the corresponding test setup is presented and evaluated. A total number of sixty-five stop roasting, having temperature range from 140 to 220oC, and one unroasted sample of 1500 g Avalon malt are performed in an eddy current roaster. Roasted and unroasted malt samples are milled and then analysed. Additionally, analytical standard reference methods are performed for colour, spectral tristimulus L*a*b* - values, colour difference (DE), iron-content, quantitative radical generation and the formation of specific intermediates, such as 5-(hydroxymethyl) furfural (HMF) as well as 3?deoxy?hexosulose (3-DH) and end products of Maillard reaction on all sixty-six samples. Multiple linear regression models were used to predict analysed references based on mid-infrared data, modified with spectral pre-processing for better prediction performance. The obtained results indicate that DRIFT-MIR spectrometry, combined with pre-processing and selection of evaluated wave number areas, is a useful analytical tool for the measurement of quality attributes of malt and therefore, shows potential for application in quality and process control. Key words: Malt roasting, mid-infrared, optical spectroscopy, process control, EBC, L*a*b*, DE, quality control.
Highlights
Roasting of malt or barley is a crucial step of roast, caramel- and malt production which defines physical, structural and chemical properties (Yahya et al, 2014)
Near infrared (NIR) spectroscopy has been used in many studies before to monitor the quality of protein content in barley and malt (Fox et al, 2002; Ratcliffe and Panozzo, 1999; Sá and Palmer, 2006; Schmidt et al, 2009) as well as physicochemical changes (Contreras-Jiménez et al, 2019)
The malt samples could have been influenced by the environment after milling and even during diffuse reflection infrared Fourier transform (DRIFT) measurement and the range, where OH- absorption was visible, was not taken into account
Summary
Roasting of malt or barley is a crucial step of roast-, caramel- and malt production which defines physical, structural and chemical properties (Yahya et al, 2014). Chemical composition of ingredients as well as the physical properties of malt e.g. colour or flavour are altered through roasting processes (Coghe et al, 2006; Martins et al, 2000; Mohsin et al, 2018). Near infrared (NIR) spectroscopy has been used in many studies before to monitor the quality of protein content in barley and malt (Fox et al, 2002; Ratcliffe and Panozzo, 1999; Sá and Palmer, 2006; Schmidt et al, 2009) as well as physicochemical changes (Contreras-Jiménez et al, 2019)
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