Non-destructive Determination of Chemical and Microbial Spoilage Indicators of Beef for Freshness Evaluation Using Front-Face Synchronous Fluorescence Spectroscopy.

We investigated the potential of front-face synchronous fluorescence spectroscopy (Delta lambda = 75 nm) to non-destructively evaluate beef freshness and quality decline during chilled storage. The total volatile basic nitrogen (TVB-N), thiobarbituric acid reactive substances (TBARS) and total viable count (TVC) values were used as standard freshness indicators. The fluorescent substances, including amino acids, collagen and conjugated Schiff bases, were highly correlated with the chemical and microbial deterioration of the beef. Quantitative models for simultaneously predicting the three freshness indicators were built combined with partial least squares (PLS) algorithm and showed good reliability. For TVB-N and TBARS values, R-c(2) and R-p(2) were both above 0.900, and for TVC values R-c(2) and R-p(2) were 0.912 and 0.871, respectively. The qualitative model established by partial least squares discriminant analysis (PLS-DA) algorithm could accurately classify beef samples as fresh, acceptable or spoiled. The accuracy of the calibration and validation sets were 92.54% and 86.96%, respectively.