A NEW APPROACH FOR ASSESSING

Transcription

1 5 TH YOUNG SCIENTISTS SYMPOSIUM IN MALTING, BREWING AND DISTILLING APRIL 2016, CHICO, USA A NEW APPROACH FOR ASSESSING THE INTRINSIC ALDEHYDE CONTENT OF BEER Jessika De Clippeleer, Jeroen Baert, Guido Aerts and Luc De Cooman Laboratory of Enzyme, Fermentation and Brewing Technology (EFBT) Dept. of Microbial and Molecular Sytems (M 2 S) KU Leuven, Technology Campus Ghent, Belgium

2 WHY IS BEER FLAVOUR STABILITY SO IMPORTANT FOR THE BREWER? Freshness vs. Brand identity Freshness: The flavour of the fresh beer is determined by the brewer. Brewers prefer customers perceiving the fresh flavour. 2

3 WHY IS BEER FLAVOUR STABILITY SO IMPORTANT FOR THE BREWER? 3

4 WHY IS BEER FLAVOUR STABILITY SO IMPORTANT FOR THE BREWER? Freshness vs. Brand identity Freshness: As the fresh beer flavour deteriorates with time the consumer does not taste the beer as it is intended to be. 4

5 WHY IS BEER FLAVOUR STABILITY SO IMPORTANT FOR THE BREWER? Freshness vs. Brand identity Brand identity: Note that consumer expectations are important! How do consumers recognize the brand? Do consumers perceive the beer how it is intended to be by the brewer? 5

6 WHY IS BEER FLAVOUR STABILITY SO IMPORTANT FOR THE BREWER? Consumer expectations vs. Reduced drinkability 6

7 WHY IS BEER FLAVOUR STABILITY SO IMPORTANT FOR THE BREWER? beer volume (hl) Reduced drinkability 13,000,000 12,000,000 11,000,000 10,000,000 9,000,000 8,000,000 7,000,000 6,000,000 5,000,000 4,000,000 3,000,000 2,000,000 1,000,000 0 > 60% of production domestic consumption of Belgian beer export of Belgian beer Export: increasing competition with local brewers year Belgian Brewers (2013) Time span between beer bottling and actual consumption. Inadequate transport and/or storage conditions. 7

8 WHY IS BEER FLAVOUR STABILITY SO IMPORTANT FOR THE BREWER? Reduced Freshness drinkability Sensory alterations of the fresh lager beer flavour as a function of forced ageing (28 C) according to Zufall et al. (2005) Beer ageing: Disappearance of characteristic desirable flavour compounds Appearance of typical ageing flavours 8

9 WHY IS BEER FLAVOUR STABILITY SO IMPORTANT FOR THE BREWER? Fresh beer flavour Pleasant flavour Flavour consistency Reproducible flavour profile Sufficiently stable during ageing Flavour stability as one of the main quality criteria for beer during storage is still difficult to control Complex composition of the beer matrix Complexity of both the malt and beer production processes A multitude of parameters influence beer flavour stability 9

10 KEY ROLE FOR ALDEHYDES IN BEER FLAVOUR INSTABILITY Aldehyde (Taste/Mouthfeel Intensity) Strecker aldehydes Bitterness Mouthfeel Odour/Aroma OAS 2-Methylpropanal (3.7) Sharp, lingering Astringency Medicinal 3.5 Methional (2.7) Astringency Potato, medicinal 4.3 Phenylacetaldehyde (0.8) Softer, smooth, less bitter Floral 0.7 Linear fatty acid aldehydes trans-2-nonenal (2.9) Astringency Paper, cardboard 4.9 Maillard reaction products Furfural (3.5) Sharp, harsh, lingering Astringency Mix ½ (4.5) Sharp, harsh, lingering Astringency Paper, potato 5.1 Mix 1 (5.7) Sharp, harsh, lingering Astringency 10 Paper, potato, undrinkable Overall ageing scores (OAS): 0 = fresh; 2 = very weakly aged; 4 = weakly aged; 6 = clearly aged; 8 = strongly aged, undrinkable Spiked concentrations: 2-methylpropanal 100 µg/l; methional 15 µg/l; phenylacetaldehyde 25 µg/l; trans-2-nonenal 0. 2 µg/l; furfural 400 µg/l; Mix ½ all together 2x diluted; Mix 1 all together undiluted. De Clippeleer J. et al. (EBC, Glasgow, 2011) 7.1

11 HOW TO REDUCE ALDEHYDES AND IMPROVE BEER FLAVOUR STABILITY? Upstream processes RAW MATERIAL MALT Next to the brewing quality of malt e.g. enzyme content, evenly modified endosperm, sharp and low peak viscosity during gelatinization and a good lautering performance 11

12 HOW TO REDUCE ALDEHYDES AND IMPROVE BEER FLAVOUR STABILITY? Upstream processes RAW MATERIAL MALT it is recommended to evaluate positive and negative enzyme activities in relation to flavour stability as well as the reducing capacity, the heat load and the FAN content as well as the aldehyde profile of the malt 12

13 HOW TO REDUCE ALDEHYDES AND IMPROVE BEER FLAVOUR STABILITY? Upstream processes BREWHOUSE Anti-oxidative brewing conditions: mashing-in at ph 5.2 and 63 C, avoid copper brewhouses, avoid iron ions Brewing process as short as possible: less heat load Minimize oxygen uptake 13

14 HOW TO REDUCE ALDEHYDES AND IMPROVE BEER FLAVOUR STABILITY? BOTTLING CONDITIONS Downstream processes The oxygen level in the bottled beer should be as low as possible: < 50 µg/l! COLD TRANSPORT AND STORAGE: critical but expensive! SO 2 (SULFUR DIOXIDE or METABISULFITE): Bisulfite is excreted by yeast during fermentation and can be added as food additive: > 10 mg/l on the label Bound aldehydes: Bisulfite adducts 14

15 UNRAVELLING THE ROLE OF FREE AND BOUND ALDEHYDES IN BEER FLAVOUR INSTABILITY Bound aldehydes: Bisulfite adducts O HSO 3 - OH R H aldehyde Bound aldehydes: Imines ( Schiffs bases ) Aldehydes can bind to amino acids, peptides and proteins R H SO 3 - -hydroxy sulfonate R 1 O H aldehyde + N H 2 R 2 amino group + H 3 O R 1 H N imine R 2 Baert J. et al. (2015) 15

16 EXPERIMENT: ALDEHYDE BINDING TO AMINO ACIDS phosphate buffer (0.05 M, ph 6.0) nonanal and (E)-2-nonenal (1 µm) individual amino acids (1 mm) Baert J. et al. (2015) 16

17 UNRAVELLING THE ROLE OF FREE AND BOUND ALDEHYDES IN BEER FLAVOUR INSTABILITY Bound aldehydes: aldehyde-cysteine adducts or thiazolidines Sulfhydryl group of cysteine attacks aldehyde, stabilization by cyclization HO O NH 2 S H + R O cysteine aldehyde hemithioacetal HO O Not yet considered in beer flavour instability! NH 2 S R OH HO O H N S R 2-substituted 1,3-thiazolidine- 4-carboxylic acid Baert J. et al. (2015) 17

18 EXPERIMENT: ALDEHYDE BINDING TO CYSTEINE Lower aldehyde levels in fresh beer Far lower aldehyde levels in forced aged beer Cysteine affects beer flavour stability! Baert J. et al. (2015) 18

19 UNRAVELLING THE ROLE OF FREE AND BOUND ALDEHYDES IN BEER FLAVOUR INSTABILITY Origin of the aldehyde-cysteine adducts (thiazolidines)? and/or HO O H N S R Present in the raw materials and ending up in the final beer? Upstream formation during brewing and transfer to final beer? Aldehyde release from this bound state during beer storage AVOID the transfer of ALDEHYDE CYSTEINE ADDUCTS, introduced or formed anywhere in the process, to the final beer to increase the time until unwanted ageing flavours appear from release 19

20 METHODOLOGY: MEASURING FREE AND BOUND ALDEHYDES Pool of bound aldehydes = the intrinsic aldehyde content Measurement after release from bound state as free aldehydes by automated headspace solid-phase microextraction (HS SPME) coupled to gas chromatography mass spectrometry (GC-MS) 20

21 METHODOLOGY: MEASURING FREE AND BOUND ALDEHYDES HIGH concentration + aldehyde GC-MS LOW concentration + aldehyde GC-MS + cysteine or SO 2 Baert J. et al. (2015) 21

22 METHODOLOGY: MEASURING FREE AND BOUND ALDEHYDES How to release aldehydes from thiazolidines? + + cysteine- bound aldehyde competitor cysteine - competitor free aldehyde 4-vinylpyridine (4VP) Baert J. et al. (2015) 22

23 METHODOLOGY: MEASURING FREE AND BOUND ALDEHYDES HIGH concentration + aldehyde + 4VP GC-MS HIGH concentration + aldehyde + 4VP GC-MS + cysteine or SO 2 Baert J. et al. (2015) 23

24 EXPERIMENT: ALDEHYDE RELEASE FROM CYSTEINE AND SO 2 IN MODEL SOLUTION phosphate buffer (0.05 M) nonanal and (E)-2-nonenal (1 µm) cysteine (500 µm) bisulfite (500 µm) 4-vinylpyridine (500 mm) Similarly: 2-methylpropanal 2-methylbutanal 3-methylbutanal phenylacetaldehyde methional Similarly: 2-methylpropanal 2-methylbutanal 3-methylbutanal phenylacetaldehyde methional benzaldehyde furfural (release) Similarly: furfural benzaldehyde Similarly: furfural (binding) Baert J. et al. (2015) 24

25 EXPERIMENT: ALDEHYDE RELEASE IN GREEN MALT VS. FINISHED MALT (PALE LAGER) aldehydes µg/kg DM

26 EXPERIMENT: ALDEHYDE RELEASE FROM CYSTEINE AND SO 2 IN BEER four commercial pale lager beers forced aged at 30 C for 90 days 4-vinylpyridine (500 mm) 4-vinylpyridine (500 mm) differences between aldehydes and among beers concerning release from bound state! Baert J. et al. (2015) 26

27 CONCLUSIONS AND PERSPECTIVES Spiking fresh beer with cysteine strongly reduces the free aldehydes concentrations in forced aged samples: increased flavour stability! 4-Vinylpyridine (4-VP) proved to release aldehydes from both cysteine and bisulfite adducts, making them quantifiable as free aldehydes. A large amount of aldehydes was released from malt and several fresh beers upon 4-VP addition, showing that both raw materials and final beers contain relatively high amounts of bound aldehydes (cysteine and/or bisulfite adducts). However, addition of cysteine is not a solution. To avoid release of aldehydes from cysteine adducts during beer ageing, the pool of bound aldehydes introduced and formed during upstream processes and transferred to the final beer needs to be reduced. 27

28 CONCLUSIONS AND PERSPECTIVES 28

29 THANK YOU FOR YOUR KIND ATTENTION 5 th YSS 2016, Chico, USA 29