## 3 Results and Discussion
### Temperature-Dependent Variations of Carbonyl Compound Levels in Adult Formulas During Storage  
Four samples were selected in the target stability study using the US-DLLME-GC-MS method. They included two standard adult formulas and two high-protein adult formulas from the same brand, differing only in protein content. Carbonyl compounds were detected in all samples, though quantification was only possible in HP samples at all time periods and in SAF at later stages. Results are summarized in Table 3.  
In HP formulas, MDA levels increased over time under different storage conditions. At 4 \({}^{\circ}\)C, MDA remained relatively stable, detectable only in one HP sample, showing a slight increase at the end of 30 days. In the other HP sample, MDA became quantifiable by day 30. At room temperature, MDA accumulated more, reaching 2.01 ug/mL and 0.37 ug/mL after 30 days. Storage at 60 \({}^{\circ}\)C showed a similar trend, with MDA reaching comparable levels. MGO also showed accumulation over time, becoming detectable in HP samples after 7 days at 4 \({}^{\circ}\)C and increasing to 0.64 ug/mL and 0.98 ug/mL after 30 days. MGO levels rose further at higher temperatures, reaching 1.52-1.98 ug/mL after 30 days at room temperature and 2.54-2.78 ug/mL after 30 days at 60 \({}^{\circ}\)C. FCHO accumulated more gradually at 4 \({}^{\circ}\)C, becoming quantifiable only after 30 days at 0.5 ug/mL in one HP sample, while the other sample showed a higher range (0.94-1.93 ug/mL). FCHO accumulation intensified with higher storage temperatures, reaching up to 2.73 ug/mL at 60 \({}^{\circ}\)C after 30 days. In contrast, ACE and ACRL showed only slight and relatively stable increases across all temperatures. Figure 3: Box-and-whisker plot showing the occurrence of carbonyl compounds in adult formula samples. MDA, malondialdehydedehyde; FCHO, formaldehyde; ACE, acetaldehyde; ACRL, acrolein; MGO, methylglyoxal; DA, diacetyl. In SAF samples, most compounds were undetectable until 7 days at both 4 \({}^{\circ}\)C and room temperature. MDA was below the limit of quantification in one SAF sample throughout the study, and ACRL and DA were undetectable in all SAF samples across temperatures. At 4 \({}^{\circ}\)C, only ACE was quantifiable in one sample after 14 days, rising to 0.37-1.38 \(\upmu\)g/mL after 30 days. MGO was quantifiable in one SAF sample after 21 and 30 days at 0.25 and 0.71 \(\upmu\)g/mL, respectively. In the other SAF sample, MDA, FCHO, and ACE were quantifiable only after 30 days, with concentrations of 0.28, 0.71, and 0.37 \(\upmu\)g/mL, respectively. MDA and FCHO became quantifiable at room temperature in one SAF sample after 14 days, reaching 0.58 and 1.79 \(\upmu\)g/mL by day 30. ACE was quantifiable in both SAF samples after 30 days, with concentrations of 0.57-1.94 \(\upmu\)g/mL, while MGO reached 1.23 \(\upmu\)g/mL in one sample after 21 days. At 60 \({}^{\circ}\)C, MDA became quantifiable after 14 days, reaching 0.32-0.88 \(\upmu\)g/mL after 30 days. FCHO was quantifiable in one sample after 7 days, accumulating from 0.93 to 1.79 \(\upmu\)g/mL by day 30. ACE became quantifiable in both samples after 14 and 21 days, reaching 0.62-2.27 \(\upmu\)g/mL after 30 days, while MGO was only quantifiable in one sample after 14 days, reaching 1.43-1.94 \(\upmu\)g/mL. Although no data is available on the variations in carbonyl content in adult formula during one month of storage, our findings are consistent with those reported by other researchers in infant formula, milk, and dairy products. [PERSON] et al. (2018) noted temperature-related differences in FCHO levels in milk powders, finding that FCHO levels were lower at room temperature than at 60 \({}^{\circ}\)C ([PERSON] et al., 2015) reported a significant increase in MDA content in infant formula stored for two weeks at 55 \({}^{\circ}\)C ([PERSON] et al., 2015). [PERSON] et al.