# Optimization of HS-SPME-GC-MS for the Determination of Volatile Flavor Compounds in Ningxiang Park
## 1 Introduction  
Volatile flavor compounds (VFCs) of meat are produced during the cooking process by a series of chemical reactions of meat flavor precursor substances [1]. Meat flavor is a broad sense of food stimulation produced by the human senses of smell and taste and the trigeminal nerve [2]. Meat flavor precursors serve as the foundation for flavor formation. Water-soluble flavor precursors primarily produce VFCs via the Maillard reaction and thermal degradation of thiamine, both of which significantly contribute to meat aroma [3; 4; 5]. Lipids primarily generate VFCs through lipid oxidative degradation reactions, which are the key substances in the formation of meat aroma [6; 7; 8], the majority of which are carbonyl compounds and ester compounds produced by thermally induced lipid acyl chain oxidation reactions [9; 10]. These substances are concentrated in the sensory aspect as aroma [11; 12; 13].  
The VFCs produced by the Maillard and Streck reactions of pork have a greater contribution to the sensory evaluation of meat quality, particularly the aldehydes produced by lipids, ketones, esters, furans, and other volatile compound reactions [14; 15; 16]. As a typical indigenous Chinese breed of pig, the Ningxiang pig is one of China's four famous pigs [17]. Its meat is tender and fresh, with a moderate intramuscular fat content and an excellent flavor. Intramuscular fat can significantly contribute to the flavor of meat. Pork flavor detection methods generally include sensory inspection, electronic nose, and GC-MS [18; 19; 20]. Human factors greatly influence sensory testing, and electronic nosescan only detect a broad range of volatile compounds but cannot perform qualitative or quantitative analysis.  
Headspace solid-phase microextraction and gas chromatography-mass spectrometry (HS-SPME-GC-MS) extracts target analytes using a polymer coating or adsorbent coated on quartz glass fiber as an adsorption medium. The extraction effect was primarily influenced by the coating composition, thickness, length of the fiber tip, and distribution of VFCs in the headspace volume, based on the balance of VFCs in the headspace, the extraction phase, and the sample. Previous research has shown that HS-SPME-GC-MS has the characteristics of objective, accurate, and rapid qualitative and quantitative determination of volatile substances, as well as good repeatability [21]. HS-SPME-GC-MS has been widely utilized in recent years to detect VFCs in meat [19; 22; 23; 24], wine [25; 26; 27], tea [28], potato [29], cheese [30], and fruit [31; 32]. There are still significant discrepancies in the quantity of chemicals detected in the VFCs of water-bath, heat-treated pork by different researchers, although numerous pretreatment protocols for the detection of pig VFCs by HS-SPME-GC-MS have been described [23; 33; 34; 35]. The detection criteria for VFCs of pork heat-treated in a water bath have not been standardized. To compare VFCs among meats, the development of a reliable and repeatable detection method is essential.  
In this study, the effects of heat treatment time, equilibrium time and temperature, and extraction time and temperature on the detection of VFCs in Ningxiang pork were given based on the HS-SPME-GC-MS method. This task was accomplished by combining a single factor and orthogonal test. Additionally, the optimal pretreatment conditions for detecting pig VFCs can be determined. The VFCs of Ningxiang, Duroc, and DLY (Landrace (Yorkshire \(\times\) Duroc), Ternary hybrid) pigs were detected to confirm the viability and representativeness of the experimental detection conditions. This work is important for creating a reliable and dependable VFCs detection method for pigs.