Red wine is rich in phenolic compounds, which chiefly determine its characteristic taste. One of its major phenolic acid constituents for which an astringency, yet no clear contribution to bitter taste has been reported, is gallic acid (GA). In previous studies, we have demonstrated bitter-tasting constituents to regulate cellular proton secretion (PS) as a key mechanism of gastric acid secretion via activation of bitter taste sensing receptors (TAS2Rs). Here, we hypothesized a contributing role of GA to the red wine-stimulated effect on PS in human gastric tumor cells (HGT-1 cells). Sensory analyses revealed that 10 μM GA as the lowest concentration tested more bitter than tap water, with increasing bitter ratings up to 1000 μM. In HGT-1 cells, the concentration of 10 μM GA evoked the most pronounced effect on PS secretion, either when added to cells as in-water solution or when spiked to a red wine matrix. GA-spiking of Zweigelt and Blaufrankisch red wine samples up to a concentration of 10 μM resulted in an equally stimulated PS, whereas the non-GA-spiked wine samples demonstrated contrary effects on PS, indicating a functional role of GA on PS. Involvement of TAS2R4 in the GA-induced PS was verified by means of an HGT-1 homozygote CRISPR-Cas9 TAS2R4 knockout approach. Moreover, gene expression analyses revealed GA to increase TAS2R4. These results demonstrate a functional role of TAS2R4 in GA-evoked PS as a key mechanism of gastric acid secretion aiding digestion. Moreover, our data provide mechanistic insights, which will help to produce stomach-friendly red wines.
Brewing using enzyme rich ‘green’ (germinated, but not kilned) malt has the potential to unlock considerable energy savings in the malting and brewing chain. This paper examines the major quality issues associated with green malt, by monitoring lipoxygenase (LOX) activity and S‐methyl methionine (SMM) levels through a micromalting cycle both with and without rootlets after 48 h of germination. The data suggest that rootlets are a major concern when brewing with green malt and that their influence on wort and beer quality needs to be further investigated. Lipoxygenase activity and nonenal potential were measured following treatment under varying conditions of pH, temperature and pre‐treatment. Results indicated that lipoxygenase activity can be controlled to a substantial degree by manipulating these limiting factors, while preserving diastatic enzyme activity. Green malt worts were then prepared from (i) whole green malt immediately post‐germination; (ii) heat treated green malt (65°C x 1 h); (iii) re‐steeped green malt and (iv) endosperm‐rich extracts of green malt after the husk and rootlets had been removed; using laboratory mashing with a ‘LOX‐hostile’ mash schedule. Data were compared with mashing of kilned pale malt made from the same green malt, as a reference point. Based on the present data, re‐steeping of green malt in combination with a LOX hostile mashing environment (63°C, pH 5.2) could help to control LOX activity and the trans‐2‐nonenal potential of green malt. The resultant brewing process would need to be optimised to deal with the elevated SMM levels in green malt worts. © 2020 The Authors. Journal of the Institute of Brewing published by John Wiley & Sons Ltd on behalf of The Institute of Brewing & Distilling
In malting, the kilning step is by far the dominant user of energy and has thus become the main target in reducing the carbon footprint of malting operations. Brewing beer using 'green' (germinated, but not dried) malt, thus saving the substantial energy input associated with kilning and conserving the water contained in the green malt, could improve the energy and water efficiency of malting operations.Furthermore, the high enzyme complement in green malt could enable more efficient brewing using unmalted cereals (e.g. raw barley) to create highly attenuated beers, without the use of exogenous enzymes. The objective of this review is to unravel the major advantages, but also quality and technical challenges, which could serve as a base for future studies on successfully brewing with green malt.Furthermore, the aim is to evaluate the impacts of such a process on beer flavour and flavour (in)stability. This is important to establish because one can make arguments that such a process will either improve flavour stability (reduced heat load should reduce the pool of staling aldehydes) or worsen it (since lipoxygenase activity and dimethyl sulphide potential can be regulated by heat treatment during kilning).
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