On the origin of thaw loss: Relationship between freezing rate and protein denaturation.

The role of protein denaturation in formation of thaw loss is currently not well understood. This study investigated denaturation of myofibrillar and sarcoplasmic proteins of pork loins caused by freezing-thawing in relation to freezing rate. Compared to fast freezing, slow freezing caused 28% larger thaw loss, decreased water-holding capacity of myofibrils and increased surface hydrophobicity, indicating more pronounced denaturation of myofibrillar proteins. We here propose a model: In slow freezing protons are concentrated in the unfrozen water resulting in reduced pH in proximity of structural proteins causing protein denaturation. In parallel, large ice crystals are formed outside of muscle fibers resulting in transversal shrinkage. In fast freezing small ice crystals trap protons and cause less severe protein denaturation and reduced thaw loss. Differential scanning calorimetry and tryptophan fluorescence spectra indicated sarcoplasmic protein denaturation in drip due to freezing-thawing. However, sarcoplasmic protein denaturation was independent of freezing rate.