Analytical determination of antioxidant capacity of hop-derived compounds in beer using specific rapid assays (ORAC, FRAP) and ESR-spectroscopy

Abstract

There is a relationship between antioxidant activity and ageing stability of beer. The high-throughput antioxidant capacity assays ORAC and FRAP, which rely on specific reaction mechanisms, are validated as an addition to the established ESR-ST method with a focus on hop-derived antioxidants. Beers were brewed with systematic variations in hop variety, hop product, and the hopping regime (late hopping) to achieve sample beers varying widely in the concentrations of hop-derived antioxidants (α- and iso-α-acids, phenolic compounds). A significant positive correlation between phenolic compounds and the ORAC- and FRAP-values (p < 0.01) was found. The effect of individual resinous substances and free phenolic acids and flavonoids on the antioxidant capacity of beer (ORAC, FRAP, and ESR-ST) was proven in spiking trials. We found a correlation between the occurrence of the o-di-OH-group and the ORAC- and FRAP-values of phenolic compounds. Phenolic compounds did not react as anti- or prooxidants in the radical generation (ESR-ST). Higher concentrations of unisomerized α-acids significantly reduced ESR-signal intensity but had no significant effect on ORAC- or FRAP-values. Beers brewed with late hop addition, which yielded higher concentrations of unisomerized α-acids and phenolic compounds, had higher ORAC, FRAP-values and a reduced ESR-signal intensity. These three methods rely on different reaction principles, and therefore, different groups of hop-derived compounds act as antioxidants in these assays. A combination of the two high-throughput methods (ORAC, FRAP) and ESR-ST is advantageous for the evaluation of the antioxidant capacity of beers varying in hop-derived compounds.

Natural Occurrence of Nitrite-Related Compounds in Malt and Beer

“…It may point out that their precursors (phenolic compounds) originate from other raw materials (e.g., hop) and/or insufficient conditions for their formation are in malt (such as nitrosoguaiacol formation during the preparation of congress wort; Table 1). 32 Regarding N-products of tyrosine, the important reaction product was 4-cyanophenol (N-05, detected in all beers), followed by N-18 and N-19 (detected in up to 77% of tested beers; see Table 1). Based on the low detection frequency of remaining tyrosine products (N-14, N-20, N-21, N-22) and observation of nitrosated malt by nitrogen dioxide (Figure 1), the standard malting conditions supposedly do not lead to the formation of these structures.…”

Antioxidant Activity of Different Hop (Humulus lupulus L.) Genotypes

“…However, it is important to select the appropriate hop genotype for a specific purpose, as there are statistically significant differences between them in the case of all three AA determination methods (p < 0.05). The relationship between AA and the ageing stability of beer has already been observed [28,29]. To this end, and according to our results showing different AA with different hop genotypes, it is important to know which hop genotype is applied in the brewing process to achieve stability during beer aging with minimal use of food additives.…”

Use of Botanical Ingredients: Nice Opportunities to Avoid Premature Oxidation of NABLABs by Increasing Their ORAC Values Strongly Impacted by Dealcoholization or Pasteurization

“…Increasing antioxidant concentrations can also inhibit the effects of oxygen by scavenging reactive oxygen species or free radicals, chelating transition metal ions (copper and iron), decomposing peroxides, etc. [3,[7][8][9][10][11][12]. A large number of assays have been published in the literature for measuring antioxidant activity, some of them taking into account more specific properties [7,11,13,14].…”

“…Interest was first concentrated on the oxidoreduction reactions (colorimetric or electrochemical methods), which could inform about the reducing power of wort and beer (e.g., 2,6dichlorophenolindophenol in the indicator time test (ITT) [15], iron dipyridyl complex [16], redox potential [17], FRAP (ferric reducing antioxidant parameter) [9], and CUPRAC (cupric reducing antioxidant capacity) [18]) (Figure 1a). Nowadays, it is accepted that reactive oxygen species (ROS) such as hydroxyl radical HO • and superoxide radical O 2…”