P-12 - Unraveling the Role of Fructose in 2-acetyl-3,4,5,6-tetrahydropyridine (ATHP) Production During Beer Brewing

2-Acetyl-3,4,5,6-tetrahydropyridine (ATHP) is an important aroma compound in beer, contributing to a popcorn-like grainy odor. However, its excessive presence can be perceived as an off-flavor, which has garnered attention in recent years.

ATHP is detected in a wide range of beer types, including Pilsners. Often in these cases, ATHP is derived from malt and is formed during the brewing process. The precursor is proline, which is present in malt, and it has been reported that ATHP is generated from proline during the brewing process, particularly during wort boiling.

In test-tube experiments simulating the wort boiling process, the conditions under which ATHP is formed from proline were investigated. It was found that boiling an aqueous solution of proline alone did not produce ATHP. It was hypothesized that specific conditions are required for ATHP formation from proline, and an investigation was conducted. The ultimate goal of this research is to control the ATHP content in beer.

A simple screening was conducted to explore another substrate in addition to proline. As a result, it was found that ATHP is formed when proline is heated in an aqueous solution with certain sugars or sugar alcohols. Additionally, it was discovered that small molecular weight substances with hydroxyl groups, such as glycerol and propylene glycol, also produce ATHP. The amount of ATHP produced varied significantly depending on the combination of proline and the other substrate. This suggests that multiple sugars are involved in ATHP formation during the actual wort boiling process, and the contribution may vary depending on the type of sugar.

By boiling a reconstituted sugar-proline solution mimicking wort components, ATHP was produced. In this case, a mixture of fructose, glucose, maltose, and glycerol, which were originally present in wort and considered to produce a significant amount of ATHP in preliminary screening tests, was used. ATHP was produced in this mixture. To identify the major contributing component to ATHP formation, tests were conducted by omitting one component at a time. It was found that omitting fructose drastically reduced the amount of ATHP produced. Next, fructose, glucose, maltose, and glycerol were individually prepared in amounts equivalent to those detected in wort and heated with proline to measure ATHP levels. The results indicated that fructose produced the highest amount of ATHP, suggesting that fructose is the most significant contributor to ATHP formation in wort. Interestingly, the amount of ATHP produced when heating fructose and proline alone was significantly higher than when heating the mixture of fructose, glucose, maltose, glycerol, and proline. This suggests that sugars other than fructose may inhibit ATHP formation.

The trace amounts of fructose present in wort have not been widely discussed due to their low concentration. This report is a rare study suggesting that trace amounts of fructose play an important role in the aroma formation process of beer.