Analysis of the influencing mechanism of the freeze–thawing cycles on in vitro chicken meat digestion based on protein structural changes

The effect of freeze-thaw (F-T) cycles on the digestive and protein structural properties of chicken breasts during in vitro digestion was investigated. With F-T cycles increased, the hardiness, chewiness, and shear force of chicken breasts increased, whereas the digestibility decreased, and particle size of digestive samples increased was evidenced by laser particle size analyzer and confocal fluorescence microscopy. The digestibility of the fifth F-T cycle samples in pepsin and pepsin/trypsin decreased by 25.99% and 11.82% compared to fresh samples, respectively. During F-T cycles, the disruption of protein structure was confirmed by the α-Helix decrease, β-sheet increase, the intrinsic tryptophan intensities decrease and a redshift in the maximum value. Therefore, F-T cycles destroyed protein structure and induced the protein aggregation, resulting in chicken that was difficult to digest in the simulated digestion. The phenomenon became more acute as the number of F-T cycles increased.