Because of the increasing popularity of unfiltered ale, new methods for its preservation are needed. 2.2. Effect of High-Pressure Control within the Foam Stability of Unfiltered Ale Beer foam stability (FS) is an important quality parameter due to its direct link to the customers impression of beverage quality, which is being created actually before the start of drinking. Our results showed the FS of unfiltered ale improved with HPP and higher processing pressure was associated with the highest FS immediately after treatment and after two months of storage (Number 1). These results are in accordance with Prez-Lamela et al. . Open in a separate window Number 1 Effect of high-pressure treatment at 250 MPa for 5 purchase Omniscan min or 550 MPa for 5 min within the foam stability (FS, in columns) and the activity of proteinase A (pro-A, inline contacts) compared with the untreated sample during 8 weeks of storage at (A) purchase Omniscan 8 C or (B) 22 C. We evaluated the effect of temp on changes in FS during storage. On the two-month monitoring period, FS declined significantly in all samples including the control samples and final FS values of the sample sets stored at room temperature were comparable to those purchase Omniscan that were kept refrigerated at 8 C. However, the decrease in FS was more rapid during the first three weeks of storage in beers kept at room temperature, while in the refrigerated samples, the decline was linear over the whole storage period. The decline of FS could be related to the release of fatty acids from the yeast cells as a result of autolysis . Fatty acids gather on the liquidCgas interphase, where they interfere with foam-stabilizing proteins and cause coalescence of air bubbles, leading to foam destruction . Higher storage temperature accelerates yeast autolysis, which clarifies the faster decrease of FS in examples kept at space temperature . The best pro-A activity was within the control test at the start of storage space. purchase Omniscan In the 550 MPa-processed ale, enzyme activity continued to be the lowest for the whole storage period, whereas in the 250 MPa-treated and in the control samples, pro-A activity further declined during storage (Figure 1). These findings indicate that pro-A is inactivated by a pressure of 550 MPa. In samples stored at 22 C, the decrease of pro-A activity in control beer could be associated with the release of yeast inhibitors, such as IA3, which binds to the enzyme and causes a formation of an inactive complex IA3, pro-A . 2.3. Changes in Concentrations of Carbonyl Compounds after Processing and during Storage Flavor instability is related to changes in concentrations of many different compounds, however, carbonyl compounds have been identified as markers of beer staleness . We analyzed the aldehyde content of beer after pascalization to examine the effect of different pressures (250 MPa and 550 MPa). In addition, pascalized beers were stored at different temperatures to assess the impact of higher temperatures on reactions connected to beer aging. Obtained data were processed by the ShapiroCWilk test which has shown data were normally distributed (data not shown). Table 2 shows that concentrations TSPAN9 of compounds from a group of Strecker aldehydes (SA, 2-methylpropanal, 2-methylbutanal, 3-methylbutanal and benzaldehyde) increased proportionally with the applied pressure. The increase in SA in pressurized beers was even higher in samples stored at 22 C and the highest concentration of SA was found in the sample treated with 550 MPa at the end of the 2-month storage period at 22 C. SA are degradation products of amino acids, or they can result from oxidative degradation of.