Abstract
Near infrared (NIR) and nuclear magnetic resonance (NMR) spectroscopy studies were performed to determine the behaviour of water during an osmotic process of apple spheres in concentrated sugar solutions. The osmotic dehydration is a process of water removal from cellular structures through immersion in a hypertonic solution. Relationships between sugars and water were studied using both two-dimensional correlation, calculated on NIR spectra recorded during the process, and NIR–NMR outer product analysis (OPA). We found that there was a shift of 7nm towards higher wavelengths in the maximum absorbance of the first overtone range of the water O–H stretching, due to the increase of hydrogen bonds implicated in the binding of the sugars progressively increasing in concentration during water removal. The absorptions detected by two-dimensional correlation, using processing time as the dynamic variable, belong to the elements which have more OH free as indicated from the outer product analysis, i.e. free water at 1936 nm followed by bonded water at 1393 nm and 1518 nm and sugars at 2131 nm, respectively.
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