Tryptophan content was determined in raw, cooked and cooked & chilled loin chops (Fig. 2a) by measuring the natural fluorescence emitted by this amino acid. Tryptophan concentration decreased 50 % on average in pork samples after cooking, and an additional 20 % during the following chilled storage. The loss of tryptophan fluorescence has been attributed to its oxidative degradation and its conversion into free radicals at an early stage and into kynurenine derivatives as final oxidation products (Giessauf et al. 1995). The analysis of tryptophan through the measurement of its fluorescence is fairly specific for meat systems given the differences between this and other aromatic amino acids for their spectral properties (Bell 1981). This phenomenon is has also been reported to occur as a