# Comparison of Automated Extraction Techniques for Volatile Analysis of Whole Milk Powder  
[PERSON]  
1 Food Quality and Sensory Science, Teagasc Food Research Centre, Moorepark, P61 C996 Cork, Ireland; [PERSON]L_ADDRESS] (Z.C. ); [EMAIL_ADDRESS] (D.T.M.) 2 Sensory Group, School of Food and Nutritional Sciences, University College Cork, T12 R229 Cork, Ireland; [EMAIL_ADDRESS]  
3 Department of Food Chemistry and Technology, Teagasc Food Research Centre, Moorepark, P61 C996 Cork, Ireland; [EMAIL_ADDRESS]  
4 China-Ireland International Cooperation Centre for Food Material Science and Structure Design, Fujian Agriculture and Forestry University, Fuzhou 350002, China  
5 Food Packaging Group, School of Food and Nutritional Sciences, University College Cork, T12 R229 Cork, Ireland; [EMAIL_ADDRESS]  
5 Correspondence: [EMAIL_ADDRESS]; Tel. : +353-25-42245  
and parameters of the extraction technique [5], it is therefore useful to evaluate a wider range of extraction techniques in order to get the best possible representative volatile profile of a sample. Arguably the most widely used volatile extraction technique to date is solid phase microextraction (SPME), mainly due to its versatility, ease of use (as it is fully automatable), the wide range of coating materials available (single, dual, or multiple phases in different thicknesses), and its general robustness. It can be used as a direct immersion (DI) technique or, most commonly, as a headspace (HS) technique. Headspace solid phase microextraction (HS-SPME) is a static HS technique that has been extensively applied to analyze VOCs in dairy products, with the divinylbenzene/carboxen/polydimethylsiloxane (DVB/CAR/PDMS) fiber finding the greatest use, due to its potential ability to capture a broader range of VOCs owing to the inherent properties of each phase [6; 7; 8]. However, the relatively limited surface capacity of the fiber can result in competition between analytes for adsorption/absorbtion sites and displacement resulting in increased bias for certain VOCs [9]. Thermal desorption (TD) is a well-established dynamic extraction technique, where an inert carrier gas strips the volatiles from a sample where they are subsequently trapped in a sorbent packed tube with absorbent/adsorbent material [10; 11]. The main advantages are the wide range of sorbent phases available and the large capacity of sorbent phase. However, managing moisture can be problematic, and this may be why its use in dairy applications is limited [12; 13]. Tenax (TEN) is typically the most widely used sorbent material in TD because of its affinity for VOCs with a very wide range of boiling points between 60 \({}^{\circ}\)C and 300 \({}^{\circ}\)C [14]. Recently, another passive sorbent extraction technique was developed called HiSorbTM (Markes International Ltd., Llantrisant, UK). It is somewhat similar to stir bar sorptive extraction (SBSE) [15] and can also be performed as a headspace (HS) or as a direct immersion (DI) technique. With HiSorb to date, a single sorbent phase polydimethylsiloxane (PDMS) is coated in a specially designed probe that can be either exposed to a HS above a sample or directly immersed in a liquid sample under controlled conditions. After exposure, the probe is placed in an empty sorbent tube and treated in a similar manner to a TD sorbent tube, where it is desorbed. In terms of sample preparation, \"salting out\" is a useful practice to potentially increase the extraction efficiency of certain volatile analytes. Salt, usually sodium chloride (NaCl), is added to the sample, which reduces the solubility of hydrophobic compounds, resulting in decreased water availability and thus, in theory, making polar and low molecular weight VOCs easier to extract [16]. The polarity of the gas chromatography (GC) column is also an important factor in relation to the separation of individual VOCs. The most common types are polar and non-polar phases, both of which offer better separation and resolution for specific chemical classes [17], with non-polar phases having greater stability.