## 3 Results
### Operating Conditions
#### 3.1.3 Influence of the Packaging and Centrifugation Conditions  
It is known that the oxygen has a role on the oxidation of myoglobin. Thus, it is necessary to determine whether the packaging conditions of the meat, in air or under vacuum, before freezing/thawing, have an influence on the color change of the juice from which it comes. Two rib steak muscles were packed whole under two conditions, one in air (21% of O\({}_{2}\)) and the other in vacuum (0% of O\({}_{2}\)) before being frozen/thawed. The juices obtained were diluted 1/5 in 50 mL of milliQ water, centrifuged, filtered, and then placed at 20 \({}^{\circ}\)C in the climatic chamber. It was found that the meat packaged in air gives more volume of juice (Factor 2) than that packed in vacuum. Figure 3a shows that the normalized values of a* are identical.  
When the juice has been collected after the freeze/thaw step, it may contain residues of connective tissue and adipose tissue. In order not to affect the color change due to the presence of residual, easily oxidizable fats, and so that the juice passes more easily through the filter during the filtration stage, the juice has been centrifuged and therefore clarified. The aim of this experiment was to verify the possible impact of centrifugation on the color change of the meat juice. The juice samples from a vacuum-packed whole rib steak were centrifuged or not centrifuged then filtered (through a 0.22 \(\upmu\)  
Figure 1: Visualization of the color of the same rib steak juice with different volumes (20 mL, 35 mL, and 50 mL) and different dilutions (1/5, 1/10, and 1/15) at t = 0 h and t = 24 h, at 20 \({}^{\circ}\)C. Pure meat juice (undiluted) is also presented for comparison to diluted juices.  
porosity filter) and diluted 1/5 in 50 mL with milliQ water. Monitoring of the color change of duplicate juices was implemented at 4 \({}^{\circ}\)C in the climatic chamber. This temperature of 4 \({}^{\circ}\)C was chosen compared to previous experiments at 20 \({}^{\circ}\)C in order to have a first approximation of the transfer time of a juice at 4 \({}^{\circ}\)C. After normalization, it was found that the curves of the a* values of the centrifuged and non-centrifuged juices are identical (Figure 3b).  
Figure 3: Monitoring of the color change (normalized values of a*) as a function of time for (**a**) a rib steak juice (50 mL of centrifuged juice, filtered and 1/5 diluted) at 20 \({}^{\circ}\)C depending on the type of packaging (air, in black solid line), or under vacuum, in grey dashed line) and (**b**) a rib steak juice (50 mL of filtered juice and diluted 1/5) at 4 \({}^{\circ}\)C with, in grey dashed line, or without, black solid line, the step of centrifugation (centrifuged or not centrifuged).  
Figure 2: Monitoring of the color change (**a*)** as a function of time of (**a**) a rib steak juice (50 mL of centrifuged juice, filtered and 1/5 diluted) at 20 \({}^{\circ}\)C according to the type of water (milliQ water, black solid line, or physiological water, grey dashed line) used to dilute the meat juice as a function of time and (**b**) the same data in normalized values, using Equation (1).