## 3 Results and Discussion
### Effects of Different Types on Amino Acid Derivatives in Beers (GABA and GSH)  
GABA performs a variety of physiological functions and is known to have anti-hypertensive and anti-stress effects on human health [7; 34; 35]. Barley, as one of the raw materials used in beer, is rich in GABA, and yeast exhibits glutamic acid decarboxylase activity, which can aid in the catalysis of glutamic acid decarboxylation to produce GABA. It can be used as an antidepressant, diuretic, and antioxidant. Our results showed that the concentrations of GABA in the different types of beers ranged from 60 to 110 mg/L, and there was no significant difference in GABA content between the draft and ripe beer (Figure 1A), indicating that the process of pasteurization does not lead to a loss of GABA content in beer. Although it has been reported that GABA undergoes the Maillard reaction when it reacts with sugar, resulting in a 10% loss in GABA content at high temperatures [36], pasteurization at a temperature of 60 \({}^{\circ}\)C does not affect the stability of GABA. The content of GABA in pure draft beer (PDB) is lower than that in classic ripe beer (CDB), with there being no significant difference among the lager mature beers. The content of GABA in the ale draft beer (ADB) (105.79 mg/L) was found to be 26.40% higher than the value in classic ripe beer (CDB) (77.90 mg/L). Rice adjunct in lager beers is high in starch and low in protein and is added as an additional carbon source during saccharification, but this addition also reduces the proportion of soluble nitrogen and amino acids in the word. In addition, as the brewing yeast generates GABA throughout the process of beer fermentation [37], the different synthetic capacities of amino acids from various types of yeast can activate and/or inhibit the formation of GABA in wine [38], which may be caused by the higher GABA synthetic capacity of top-fermenting yeast used in ale than the capacity of bottom-fermenting yeast used in lager. This difference has also been noted in previous studies.  
Regarding GSH, glutathione (GSH) is widely used in functional foods and has been found to delay aging, enhance immunity, and prevent tumors [8; 39]. GSH in beer not only plays an antioxidant role but also maintains the flavor stability of beer. It can be seen from Figure 1B that the GSH content in the beers studied was incredibly low, and its content in beer was between 1 and 2 mg/L (Figure 1B). No significant difference in the GSH content was found between the two types of lager (classic beer and draft beer); however, the content of GSH in ale draft beer (ADB) (1.82 mg/L) was 43.96% higher than the content in classic draft beer (CDB) (1.02 mg/L). This difference is mainly determined by the metabolism in yeast under varied raw material conditions and manufacturing techniques. Similar to the synthetic capacity of GABA, the GSH synthetic ability of top-fermenting beer yeast is stronger than that of lower beer yeast. Our results are consistent with those of previous studies in that the abilities of GSH synthesis significantly differ among the different industrial strains for beer production [40]. Despite the fact that GSH is readily oxidized to oxiglutathione (GSSG) [41], no significant difference in GSH content was found before and after pasteurization, indicating that the GSH content in beer is not affected by pasteurization.