## 3 Results
### Free Amino Acids  
Not only do free amino acids contribute to taste, but they are also the precursors of volatile compounds formed via hydrolysis and the chemical transformation of Strecker degradation [13]. While some free amino acids directly improve taste, there are other amino acids that contribute to key aromatic compounds as precursors in beef steak. For example, glutamic acid and aspartic acid produce the umami taste, while leucine, phenylalanine, isoleucine, valine, methionine, and arginine form bitter flavors, and sour flavors are related to aspartic acid and histidine [14; 15].  
In this study, 19 free amino acids were identified, and their contents are shown in Table 2. Caronsine was the most abundant free amino acid, followed by taurine, anserine, alanine, and glutamic acid. Caronsine is a dipeptide of \(\beta\)-alanine and L-histidine and exhibits antioxidant, antiaging, and hypoglycemic effects; it is known to improve exercise performance and relieve muscle fatigue by neutralizing lactic acid produced during anaerobic glycolysis [16]. Taurine is a critical free amino acid that supports infant development and prevents medical conditions such as cardiovascular disease, hypertension, and diabetes [17]. Additionally, increased glutamic acid content contributes to the \"umami\" flavor of the meat. In addition, it increases the neuron fibers, detoxifies copper, enhances leukocyte activity, enhances immunity, and promotes insulin secretion [18]. The concentration of sulfur-containing amino acids, such as methionine, which are crucial for producing \"meaty\" odors after the Maillard reaction, only accounted for 3.3 mg and 3.57 mg of the total amino acid content in SSs and RSSs, respectively.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Free Amino Acids** & **Seared Steak** & **Reverse-Seared Steak** & **t** \\ \hline Taurine & 90.4 \(\pm\) 45.66 & 111.67 \(\pm\) 13.05 & \(-\)0.78 \\ Aspartic acid & 0.13 \(\pm\) 0.23 & 0.53 \(\pm\) 0.11 & \(-\)2.50 \\ Threonine & 4.67 \(\pm\) 0.67 & 5.97 \(\pm\) 0.45 & \(-\)2.76 \\ Serine & 5.90 \(\pm\) 1.30 & 7.07 \(\pm\) 0.55 & \(-\)1.42 \\ Glutamic acid & 13.70 \(\pm\) 0.98  & \(-\)3.73  \\ Glycine & 8.00 \(\pm\) 1.14  & 10.47 \(\pm\) 0.35  & \(-\)3.59  \\ Alanine & 28.53 \(\pm\) 3.64 & 34.70 \(\pm\) 2.16 & \(-\)2.50 \\ Valine & 5.37 \(\pm\) 1.46 & 6.87 \(\pm\) 0.50 & \(-\)1.69 \\ Methionine & 3.37 \(\pm\) 1.93 & 3.57 \(\pm\) 0.05 & \(-\)0.18 \\ Isoleucine & 3.73 \(\pm\) 1.62 & 4.43 \(\pm\) 0.15 & \(-\)0.75 \\ Leucine & 7.33 \(\pm\) 3.27 & 8.50 \(\pm\) 0.35 & \(-\)0.62 \\ Tyrosine & 4.03 \(\pm\) 1.70 & 4.77 \(\pm\) 0.25 & \(-\)0.74 \\ Phenylalanine & 4.77 \(\pm\) 2.02 & 5.87 \(\pm\) 0.10 & \(-\)0.94 \\ Ornithine & 1.7 \(\pm\) 0.52 & 1.43 \(\pm\) 0.05 & 0.88 \\ Lysine & 4.93 \(\pm\) 0.76 & 6.30 \(\pm\) 0.45 & \(-\)2.67 \\ Histidine & 3.27 \(\pm\) 0.06  & 3.93 \(\pm\) 0.20  & \(-\)5.35  \\ Anserine & 77.63 \(\pm\) 15.70  & 105.80 \(\pm\) 5.95  & \(-\)2.81  \\ Caronsine & 265.97 \(\pm\) 49.00 & 277.53 \(\pm\) 13.83 & \(-\)0.37 \\ Arginine & 5.27 \(\pm\) 0.47 & 6.03 \(\pm\) 0.55 & \(-\)1.80 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Free amino acids (mg/100 g) in seared and reverse-seared steaks.