The use of the impedance measurements to distinguish between fresh and frozen-thawed chicken breast muscle.

An impedance system was built to differentiate fresh chicken breasts from those that had been frozen and thawed. Inserting needle electrode pairs of the detecting probe aligned with the longitudinal direction of muscle myofibers (PL) gave more satisfactory results. Learning vector quantization neural network (LVQNN) and partial least square-discriminant analysis (PLS-DA) were employed to acquire the prediction accuracy. The results demonstrated that the model using LVQNN achieved a satisfactory prediction accuracy, with a discrimination accuracy for fresh breasts of 100%. Additionally, the recognition results for a single frozen-thawed cycle were greater than 90%, and for two cycles were greater than 88%. The values obtained from PLS-DA were somewhat lower than for LVQNN, being 100% for fresh samples, in excess of 90% for single frozen-thawed cycle and more than 84% for those that had been multiple frozen-thawed. In conclusion, these results showed that the impedance system is a simple and effective application for the discrimination of fresh chicken breasts from frozen-thawed ones.

Raman spectroscopic study of heat-induced gelation of pork myofibrillar proteins and its relationship with textural characteristic.

Structural changes, textural properties and their relationships in pork myofibrillar proteins (PMP) were studied by Raman spectroscopy, texture profile analysis (TPA) and principal component analysis (PCA). Raman spectroscopy analysis revealed the occurrence of secondary structural changes in myofibrillar proteins. Modifications in the amide I (1600-1700 cm(-1)) and amide III (1200-1300 cm(-1)) regions indicated a significant (p<0.05) decrease in α-helix content, accompanied by a significant (p<0.05) increase in ß-sheets, ß-turns and random coil content. Texture property changes were also determined by TPA. All these features contributed to the formation of strong, irreversible heat-induced gels. The application of a dimensionality reducing technique such as PCA proved to be useful to determine the most influential properties of heat-induced gel. Significant (p<0.05) correlations were found between these structural changes and the textural characteristic (hardness) in the pork myofibrillar proteins system by PCA.