Interaction and fragility study in salmon gelatin-oligosaccharide composite films at low moisture conditions

Abstract

Non mammalian gelatin under low moisture conditions could potentially be used in encapsulation technologies in food and pharmaceutical applications. This work explored the interactions between salmon gelatin (SG) and different molecular weight oligosaccharides (at 0.2, 0.4, 0.6 wt fraction) with ∼5% moisture content. SG and glucose, sucrose and maltodextrin were combined to produce visually transparent composites films. Fourier-transformed infrared spectroscopy showed that changes in secondary structure towards a less ordered configuration occurred upon increasing oligosaccharides weight fraction. This interaction was identified as physical in nature and possibly sustained by hydrogen bonding between components. The oligosaccharides also reduced water sorption as indicated by Guggenheim, Anderson and de Boer monolayer parameters derived from dynamic vapour sorption data. This reduction was higher for glucose, possibly due to reduction in free volume in the composite films in the glassy state. Powder X-ray diffraction showed only diffraction peaks associated to the triple helices of the gelatin, which were reduced significantly upon adding glucose and sucrose. Differential scanning calorimetry data showed reductions in Tg and Tm but higher ΔCp values upon increasing oligosaccharides weight fraction, indicating changes in molecular dynamics. Fragility values indicated strong materials; more likely following an Arrhenius-like dependency between the structure relaxation time and temperature. This work provides valuable information about the nature of the interaction between a non-mammalian gelatin and oligosaccharides with different molecular weight. Our findings could be applied for a number of technological applications including encapsulation.