Abstract
Inherent changes in foods during storage are often caused by water sorption or desorption that often results in product matrix instability. Water sorption behavior differs depending on the matrix through which it moves. Often, concurrent phenomenon such as crystallization modifies water’s movement. We describe a novel use of hyperspectral imaging combined with Fourier Transform Near Infrared (FT-NIR) spectroscopy to map where water molecules are in two dimensions while concurrently quantifying the crystallization motif as water sorbs into a carbohydrate matrix over a month’s storage time. This methodology allows us to identify and quantify sucrose crystals formed within a carbohydrate matrix while also mapping water migration through this complex matrix. We compared corn syrup/sucrose blends where sucrose is supersaturated (high sucrose, HS), sucrose is below saturation (low sucrose, LS), sucrose below saturation with embedded sucrose crystals (LSS) and maltotriose is supersaturated within a corn syrup matrix (high maltotriose, LSM). This FT-NIR method was used to characterize water sorption through a carbohydrate matrix over time and measured both the propensity of the systems to form sucrose crystals and the influence sucrose crystals have on water sorption. We observed water diffusion was slower in lower sugar carbohydrate glasses, and the process of sorption was different. Amorphous systems supersaturated in sucrose allow crystallization when sufficient water is sorbed and thus, this concurrent action disrupts normal Fickian diffusion. The water front compresses to a narrow band as it sorbs through the matrix. The presence of embedded crystals in an amorphous matrix slows overall water penetration through the matrix by convoluting the path of moving water molecules. This did not appear to change the rate of diffusion. Experiments with maltotriose at supersaturation concentration showed the crystallization rate was slower than sucrose. Thus, pure maltotriose is not a practical solution as a potential replacement for sucrose to slow sorption in food systems.
Highlights
The process of sorption encompasses both adsorption and absorption
Water sorption rates measure average weight gain over time to accurately describe how much total water is present in a sample with respect to time while stored at selected humidity/temperature conditions [7]. This approach has successfully shown that sorption rates differ between compositions high in sucrose content, where water sorption is influenced by concurrent sucrose crystallization, and compositions too low in sucrose for crystallization to occur [7,8,9,10]
Water sorption proceeded from a high moisture environment (65 % relative humidity) towards a low moisture environment (2 % moisture carbohydrate matrix) in amorphous films regardless of carbohydrate composition
Summary
The process of sorption encompasses both adsorption and absorption. Water sorption in amorphous solids is interesting to the food industry because of its impact on stability and consumer-expected product behavior [1,2,3]. In amorphous solids supersaturated with respective molecules there is a tendency to crystallize; Food Biophysics (2015) 10:207–216 sorbed water allows for sufficient viscosity reduction for this to occur. Another organoleptic change occurs in foods often referred to as ‘bloom’. This approach has successfully shown that sorption rates differ between compositions high in sucrose content, where water sorption is influenced by concurrent sucrose crystallization, and compositions too low in sucrose for crystallization to occur [7,8,9,10] These studies describe model systems as a whole and are unable to predict the impact of water on local carbohydrate hydrogen bonding as water moves through amorphous foods. We report for the first time the methodology and results of a FTNIR hyperspectral imaging study on moisture migration in a variety of glass phase sugar films
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