Study of water–sugar interactions at increasing sugar concentration by NIR spectroscopy

Near infrared spectroscopy has been extensively used to determine the water behaviour at different temperatures and different physical state.The purpose of the present work was to investigate the spectroscopic response in the range 1100–2400 nm of solutions of glucose, fructose, and sucrose at concentrations 5–65%.Data indicate that by increasing sugar concentration the water band becomes more symmetric and there is a shift of the absorption maximum toward longer wavelengths. Spectra were interpreted in terms of “structure-maker” and “structure-breaker” effects of increasing sugar concentration.Sugars at low concentrations behave as structure breaker of the water cluster, while at higher concentrations they act as structure makers.These results could be of some interest when monitoring by NIR processes as freezing, freeze-drying, drying, cryoconcentration, etc. of fruits and vegetables, where the removal or separation of large amounts of water induce the formation of very concentrated sugars solutions.