Objective measurement of colour (CIE L*, a* and b*) was performed at the surface of meat samples using a reflectance spectrophotometer, 30 min after package opening.
Metmyoglobin percentage was estimated spectrophotometrically by measuring the reflectance at 525 and 572 nm
Twenty-five grams of the meat mixture were taken from the patties, and diluted in 225 ml 0.1% peptone water.
Each sample was homogenised in a Stomacher Lab Blender for 1 min.
Serial 10-fold dilutions were prepared by diluting 1 ml in 9 ml of 0.1% peptone water.
Two plates were prepared from each dilution by pouring 1 ml in fluid agar.
Counts of aerobic psychrotrophic flora were determined from plates bearing 20–200 colonies in plate count agar incubated at 7°C for 10 days.