The pH of the samples was measured 48 h after frankfurter manufacturing, using a HI 221 pH meter (Hanna Instruments, Germany). For the pH determination, 20 g of frankfurters were homogenized with 80 ml distilled water. All pH measurements were performed in duplicate.
Instrumental colour measurements were performed 48 h after sausage production using a CR-400 chromameter colorimeter (Konica-Minolta, Osaka, Japan) equipped with an 8 mm port size, D65 illuminant and a 10° standard observer. Before colour measurements, the instrument was calibrated using a white calibration plate provided by the manufacturer. CIE L*, a* and b* values were determined as indicators of lightness, redness and yellowness, respectively. Five sausages from every treatment were randomly selected and cut to various 2–3 cm long pieces. Instrumental colour measurements were taken both on the surface and the cross-section of sausages immediately after the frankfurters were cut. Colour values reported hereinafter represent the mean of ten measurements per treatment.
The 2-thiobarbituric acid (TBA) test, according to Salih, Smith, Price, and Dawson (1987), was used to determine the extent of lipid oxidation in frankfurters stored for 30 days at 4 °C. The results are expressed in ppm of malonaldehyde and represent the average of two measurements for each treatment.