# Untargeted Profiling and Differentiation of Volatiles in Varieties of Meat Using GC Orbitrap MS
## 3 Results and Discussions
### Optimization of Extraction  
SPME is one of the most widely used extraction methods for volatile compound analysis. Among the influencing parameters, the fiber type could be the most crucial one, which could significantly affect the profiling pattern [24]. The extracted compound types and their signal intensity would vary a lot according to the different fiber types. Totals of 85 \(\upmu\)m Polyacrylate (PA), 50 \(\upmu\)m/30 \(\upmu\)m DVB/CAR/PDMS, 95 \(\upmu\)m Carbon WR, and 30 \(\upmu\)m PDMS were selected as the representative fibers for evaluating the extraction efficiency. Figure 1 shows the tendency of volatile compounds' intensities with four kinds of fibers. Obviously, DVB/CAR/PDMS and Carbon WR showed better performance with higher signal intensities for most of the compounds. However, Carbon WR showed poor performance for sulfur-containing compounds. Considering that sulfur-containing compounds play pivotal roles in the meat flavor [25], DVB/CAR/PDMS would be selected for the further analysis.  
Figure 1: Intensities of typical volatiles detected using different SPME fibers. The shadow in means the emphasis on the sulphur-containing compounds.  
The equilibriums of volatile compounds among the fibers, the sample matrices, and the gas phase would determine the actions of volatile compounds in the extraction [13]. As for the extraction efficiency, the extraction temperature and the extraction time contributed a lot with a specified fiber [26]. Those two parameters were optimized comprehensively in this research. Figure 2 shows the influences of the extraction temperature and the extraction time on the intensities of the main volatile compounds in meat, including hydrocarbons, aldehydes, ketones, esters, furans, sulfur-containing compounds, and other heterolytic compounds. Basically, with the extraction time prolonged, the intensities of the typical volatile compounds were increased, especially for the aldehydes, furans, and sulfur-containing compounds. However, different situations would happen to some other compounds, such as ketones, alcohols, and hydrocarbons. Extraction for 60 min would give rise to the enhanced desorbing of those compounds. Taken together, 50 min would be chosen as the optimum extraction time in the profiling of volatile compounds. As for the extraction temperature, the intensities of the typical volatile compounds would reach the highest at 55 \({}^{\circ}\)C when the extraction lasted for 50 min, possibly because the desorbing would be the dominant action with the temperature continually increased. The duration of desorbing in the injector would be also highly associated with the sensitivity and the reproducibility. Here, the desorbing time ranging from 1 min to 7 min was investigated.  
Figure 2: The influences of the extraction temperature and the extraction time on the intensities of some typical volatiles.  
As shown in Figure 3, with the increase in the desorbing time, the signal intensities for most of the compounds were steadily increased at the beginning. However, the intensities for some of the compounds were decreased when the desorbing was further proceeding. Therefore, the SPME conditions of incubation at 55 \({}^{\circ}\)C for 10 min, extraction at 55 \({}^{\circ}\)C for 50 min, desorbing at 270 \({}^{\circ}\)C for 3 min would be considered as the optimum.