# Comparison of Automated Extraction Techniques for Volatile Analysis of Whole Milk Powder
## 3 Results and Discussion
### The Percentage of Each Chemical Class Extracted from Whole Milk Powder by Each Technique

Table 4: Numbers, abundance, and reproducibility of volatile organic compounds in whole milk powder samples extracted by each technique with and without salting out and for polar and non-polar GC columns. \begin{table}
\begin{tabular}{c c c} \hline
**No of VOCs Extracted** & **Non-Polar GC Column** & **Polar GC Column** \\ \hline With salting out & 75 & 48 \\ Without salting out & 72 & 45 \\ Total & 80 & 54 \\ \hline Overall Total & 85 \\ \hline \end{tabular}  
* No. of VOCs (number of volatile organic compounds). Abundance %, (the greatest abundance achieved by a single extraction technique equated to 100% and the remaining extraction techniques were expressed as a percentage thereof). Average RSD % (the average percentage relative standard deviation of all VOCs for extraction technique).  
\end{table} 
Table 3: The numbers of volatile organic compounds extracted in whole milk powder samples. 9-17% recovered on the polar GC column. The percentage recovery of esters by HS-HiSorb S and HS-HiSorb NS were relatively high in comparison to the other extraction methods at \(\sim\)3-5% for the non-polar GC column and \(\sim\)2-4% for the polar GC column. HS-HiSorb NS did not recover any terpen, sulphur compounds, acids, or benzene/phenol compounds using the polar GC column, nor sulphur compounds or acids using the non-polar GC column. TD S and TD NS were characterized as having a high percentage recovery of aldehydes (\(\sim\)30-45%), ketones (\(\sim\)21-48%), and alcohols (\(\sim\)10-22%) that varied with both GC column polarity and salting out. TD, independent of salting out, recovered the highest percentage of benzene/phenol compounds using the non-polar GC column in comparison to all the other extraction techniques. TD S or TD NS did not extract any lactones, acids, or furans independent of salting out or GC column polarity. The impact of salting out was minimal in relation to TD, however the percentage of alcohols decreased with salting out using the polar GC column, but increased using the non-polar GC column. Overall, the combination of TEN/CAR should enable a wide range of VOCs to be recovered, as TEN is particularly suited to the extraction of non-polar and slightly polar VOCs, apart from very low molecular weight (<C6) VOCs, which CAR can extract [24]. The percentage recovery of many chemical classes differed most in relation to both GC column polarity and salting out for HS-SPME than any of the other extraction techniques. Overall, HS-SPME recovered all chemical classes except for acids, independent of salting out and GC column polarity, or furans and lactones by HS-SPME NS using the polar GC column, or furans by HS-SPME S using the non-polar GC column. Overall HS-SPME was characterized by a high percentage recovery of aldehydes (\(\sim\)31-62%), which was reduced with the inclusion of salting out independent of both GC column polarities. For HS-SPME S, the percentage recovery of ketones (25-46%) was much higher using the polar GC column. HS-SPME NS also recovered many more terpenes independent of GC column polarity. Previous studies noted that the DVB/CAR/PDMS multiphase SPME fibers tend to extract the most volatile low boiling point VOCs more effectively [25], which corresponds with the results of this study. No acids were recovered by any technique using the polar GC-column, however it worth pointing out that only one acid (acetic acid) was identified in these WMP samples. The Relationship between the Individual Volatile Compound Chemical Classes Extracted by Each Technique in the Whole Milk Powder  
Figure 2a,b are principal component analysis (PCA) plots, highlighting the associations of the different extraction techniques with each chemical class. The chemical class data used to generate the PCA was based on the percentage of each chemical class, rather than individual VOCs determined for each technique (with and without salting out for each GC column polarity), to visualize the associations between chemical class and individual extraction techniques, rather than individual VOC.