Not all in the mind – the chemistry of flavour
Transcription
Not all in the mind – the chemistry of flavour
Not all in the mind – the chemistry of flavour John R. Piggott Faculdade de Ciências Farmacêuticas Universidade Estadual Paulista Araraquara Brasil [email protected] What is flavour? • “The sensation arising from the integration or interplay of signals produced as a consequence of sensing smell, taste and irritating stimuli from a food or beverage” • The “psychological interpretation of a physiological response to a physical stimulus” Laing & Jinks, Trends in Food Science & Technol. 7, 387, 1996; Noble, Trends in Food Science & Technol. 7, 439, 1996 1 Flavour is • “Flavour … is an interaction of food and consumer” • Therefore sensory methods must be used to measure flavour (and all other sensory characteristics) • However, physical/chemical methods, if properly validated by sensory tests, are often cheaper and more efficient von Sydow, Food Technol. 25(1), 40, 1971; Piggott, Food Qual. Pref. 6, 217, 1995 The stimulus • Flavour cannot exist without a physical stimulus • Compounds must be released from food to interact with the receptors – Volatile compounds provide smell – Non-volatile compounds provide taste – Spiciness, pungency, etc. 2 Key questions • • • • What is in there? Does it matter? Where did it come from? How can it be changed or controlled? Contents • This is not a complete review – 4,500 items in Web of Science in 5 years • Some topics which I think are interesting • Examples • Cachaça 3 Cachaça, sugar-cane spirit • Brazilian “national drink” • Process overlaps with some definitions of rum • Accepted as being a uniquely Brazilian product • Often drunk as a caipirinha, with sugar, lime, and ice Photo: Christian "VisualBeo" Horvat http://commons.wikimedia.org/wiki/File%3AZutaten_caipirinha.jpg 4 Photo: Christian http://commons.wikimedia.org/wiki/File%3ACocktail_Caipirinha_raw.jpg Process • • • • • Cane harvested Milled to produce juice Clarified Spontaneous or pitched fermentation Distillation – Single distillation in small pot still – Some double distillation – Some column distillation • Maturation in casks (optional) Faria, in Distilled Spirits Production, Technology and Innovation, Bryce et al. (eds), Nottingham Univ Press, 2008, p 327 5 Photo: J.R. Piggott Photo: J.R. Piggott 6 Photo: J.R. Piggott Photo: J.R. Piggott 7 Photo: J.R. Piggott Photo: J.R. Piggott 8 Photo: J.R. Piggott Photo: J.R. Piggott 9 Photo: J.R. Piggott What is in there (and how much)? • Representative extract for analysis – Odour-active volatiles – Taste-active non-volatiles – Avoid changing the compounds present in the food – Sufficient extract to identify compounds at very low levels – Methods select for certain compound classes – Combine techniques for analysis Croissant et al., Annu. Rev. Food Sci. Technol. 2, 395, 2011 10 Common methods • Simultaneous distillation extraction – Cooked foods • Liquid extraction • Direct injection – Distillates • Headspace sampling – Static or dynamic, SPME, full evaporation • In-mouth analysis Analysis • Gas chromatography • Modern analytical instruments can often identify dozens or hundreds of volatile compounds in an extract 11 Common GC detectors • Flame Ionisation Detector (FID) – good for quantitation • Mass spectrometer (MS) – very sensitive • Various specialised detectors e.g. for sulphur or nitrogen – can be very sensitive • Disadvantage: they do not tell you what is important http://www.chromatography-online.org/2/contents.html Dimethyl sulphide (DMS) in cachaça • Off-flavour at > 8 x 10-7 mol L-1 (50 µg L-1) • Threshold (in wine) 10 – 160 µg L-1 • Use of copper in stills has been shown to reduce DMS concentration in distillates • Purge-and-trap concentrator • Quantitation by GC with mass selective detector Cardoso et al., J. Braz. Chem. Soc. 15, 277, 2004; Ledauphin et al., J. Food Comp. Anal. 19, 28, 2006 12 DMS in spirit samples • Averages of non-zero samples (mol L-1) – – – – – – Cachaça 1.6 x 10-5 Grappa 1 x 10-7 Whisky 4 x 10-7 Brandy 1 x 10-7 Tiquira 1 x 10-7 Vodka and Rum: < detection limit Cardoso et al., J. Braz. Chem. Soc. 15, 277, 2004 Does it matter? • The closer the relationship between the instrumental method and the actual perception of the food properties, the more relevant and valid the instrumental method • Sensory impact may be related to rate of release of a volatile, not its concentration Dijksterhuis & Piggott, Trends in Food Science & Technol. 11, 284, 2001; Baek et al., Chemical Senses 24, 155, 1999 13 Resolution and relevance • Table showing methods providing differing temporal resolution and differing relevance and validity Dijksterhuis & Piggott, Trends in Food Science & Technol. 11, 284, 2001 Sensory-instrumental relations • Attempts to model flavour in chemical terms are not always successful • Sensory analysis • Instrumental analysis • Complexity of flavour Chambers & Koppel, Molecules 18, 4887, 2013 14 Finding the important compounds • A few “flavour impact compounds” might represent a flavour • Even in simple cases they are unlikely to convey the complete sensation • Most convincing demonstration of success is a reconstructed flavour which is indistinguishable from the original Grosch, Chemical Senses 26, 533, 2001 How to use a sensory method? • Use a human nose as the detector – GCOlfactometry • Advantages: – Validity and relevance • Disadvantages: – Individual variations – Variable sensitivity – Unreliable computer (the brain) 15 Developments of early GC-O • Dilution methods – CHARM (Combined Hedonic Aroma Response Measurement) – AEDA (Aroma Extract Dilution Analysis) • Intensity methods – OSME (Odour Specific Magnitude Estimation) • Detection frequency Van Ruth, Biomol. Eng. 17, 121, 2001 Cachaça and rum aroma: descriptive sensory analysis • “Spider’s web” plot showing sensory profiles of cachaça and rum De Souza et al., J. Agric. Food Chem. 54, 485, 2006 16 Most potent odorants (CHARM values) • “Spider’s web” plot showing most potent odorants in cachaça and rum • Eugenol particularly strong in cachaça De Souza et al., J. Agric. Food Chem. 54, 485, 2006 Gas Chromatography Recomposition • Extract (SPME) is separated by GC • Sections of the chromatogram are recombined for sensory analysis and comparison with the original Johnson et al., PLOS One. 7, e42693, 2012 17 Changes the questions Not • What is it, and does it matter? But • What is important, and what is it? GC-R instrumentation • Flow diagram showing GC fitted with a switch to pass part of the column effluent to waste, and a cryo trap before the sniff-port Johnson et al., PLOS One. 7, e42693, 2012 18 Application to lavander aroma • Chromatogram showing sensory descriptions applied to various cuts from chromatogram of lavender Johnson et al., PLOS One. 7, e42693, 2012 Flavour release The process of flavor release and perception is controlled • by the properties of the flavor compounds • by the nature of the food matrix • by the physiological conditions of the mouth, nose and throat during consumption Ross, Trends in Food Science & Technol. 20, 63, 2009 19 Individual differences • Biting force • Incisors – 110 – 370 N (n = 18) • Mean force (N) – American males 534, females 378 – Eskimo males 1202, females 890 Chen, Food Hydrocolloids 23, 1, 2009 Saliva flow • • • • • Unstimulated, range 0.04 – 1.83 ml/min Stimulated, range 0.77 – 4.15 ml/min Variation during the day Reduction with age (> 70 years) Variation with health status and drugs Chen, Food Hydrocolloids 23, 1, 2009 20 Effect of the matrix • Reconstitution of Dornfelder red wine • Aroma profiles of – Wine – Recombinates in aqueous ethanol • A: 28 aroma compounds • B: Aroma and 35 LMW taste compounds • C: Aroma and all taste compounds Frank et al., J. Agric. Food Chem. 59, 8866, 2011 Aroma profiles 3 Intensity 2.5 wine C B A 2 1.5 1 0.5 flo w er y m al ty co ok fr ed ui -a ty pp le -li ke cl ov elik e sw ea ty sm ok va y ni lla lik co co e nu t- l ik vi e ne ga rlik bu co e tte ok ed rlik -p e ot at olik e 0 Frank et al., J. Agric. Food Chem. 59, 8866, 2011 21 Where did it come from? • Materials – May be simple – fresh fruit • Process – Main compounds produced in alcoholic fermentation by yeast are well known – There may be many steps in a manufacturing process – They can all add, subtract, or change flavour compounds Post-fermentation processing of Pisco • Analysis of distillate fractions to identify chemical markers for each stage Peña y Lillo et al., J. Food Science 70, S432, 2005 22 Correlations of markers with sensory notes • Table showing correlations between sensory notes and chemical components, characteristic of stage fractions taken from Pisco production process Peña y Lillo et al., J. Food Science 70, S432, 2005 How can it be controlled or changed? • Process development and control – Controlling flavour to prevent or limit deviations – Understand how a food or beverage “works” – Allow unimportant deviations in process or composition – Prevent important deviations 23 Cachaça fermentation (1) • Typically, spontaneous fermentation • Variable flavour • Select yeast producing desirable chemical profile Congener production by two isolated yeast strains and a mutant The strains show different production rates of isoamyl alcohol and isoamyl acetate, and different final concentrations Vicente et al., Int. J. Food Microbiol. 108, 51, 2006 24 Cachaça fermentation (2) • Supplementation of sugar cane juice (SCJ) with medium (MAS) and high (HAS) levels of ammonium sulphate Vidal et al., Food Chemistry 138, 701, 2013 Ester concentrations Results show different concentrations of the esters depending on ammonium sulphate addition EO ethyl octanoate; EH ethyl hexanoate; 3-MBA 3-methylbutyl acetate; EA ethyl acetate Vidal et al., Food Chemistry 138, 701, 2013 25 Cachaça fermentation (3) • Fermentation of cane juice with yeast (S. cerevisiae), and with yeast plus Lactobacillus fermentum (LAB) Duarte et al., J. Food Science 76, C1307, 2011 Major volatiles Yeast Yeast + LAB 400 mg/L 300 200 100 M 3- an ol he ny l et h no l 2P et h yl -1 yl -1 -b ut a -b ut a no l an ol et h M 2- l-1 -p ro p an ol et hy 12M * Significantly different at 0.05 Pr op te ce ta Et hy la * * Ac e ta ld eh yd e 0 Duarte et al., J. Food Science 76, C1307, 2011 26 Minor volatiles • Some minor volatiles also showed differences • Gamma-lactones are formed by LAB, and are thought to be important in malt whisky • Not analysed in this case Wanikawa et al., J. Inst. Brewing 106, 39, 2000 Whisky fermentation • “Precondition” yeast cells with zinc • Affects flavour congeners in the distillates produced from fermented cultures • Distillates had an altered flavour and aroma profile • Production of some higher alcohols increased when yeast cells were preconditioned with zinc De Nicola et al., J. Institute Brewing 115, 265, 2009 27 Aldehydes and esters 800 600 mg/L Control Preconditioned 400 200 ta te ta l Is oam yl -a Fu rf ce Ac e e Et hy l -a ce ta t ld eh yd e ta Ac e ur al 0 De Nicola et al., J. Institute Brewing 115, 265, 2009 Alcohols 600 400 Control Preconditioned mg/L 200 3M et hy l-1 -b ut an ol ut an ol l-1 -b an ol 2M et hy nBu t ro pa no l nP M et h an ol 0 De Nicola et al., J. Institute Brewing 115, 265, 2009 28 Cachaça distillation (1) • Material of the still affects distillate composition • Comparison of still materials Cardoso et al., Quim. Nova 26, 165, 2003 DMS in cane spirit distilled in columns with different packing 700 600 DMS 500 400 300 200 100 0 Copper Stainless Aluminium Ceramic Cardoso et al., Quim. Nova 26, 165, 2003 29 Cachaça distillation (2) • Double distillation: – Increases ethanol content of distillate – Reduces concentrations of congeners • Comparison of single distillation with 3 procedures for double distillation Alcarde et al., Ciência e Tecnologia de Alimentos 31, 355, 2011 Effects of distillation procedure Single Volatile acidity Furfural Aldehydes Esters Methanol Higher alcohols Congeners Double Cognac Whisky Varying concentrations of all analytes according to the distillation process used, with generally lower concentrations from the whisky process Alcarde et al., Ciência e Tecnologia de Alimentos 31, 355, 2011 30 Case study of a distilled spirit • Grain spirits used as material for pure or flavoured vodka in Poland • To identify compounds responsible for offflavours • 39 spirit samples – 13 good, 13 doubtful, 13 poor Plutowska & Wardencki, Flavour & Fragrance J. 24, 177, 2009 Experimental • Assessor training for GC-O with model mixtures of relevant compounds • Sensory profiling • HS-SPME • GC-O-MS – Fingerspan intensity scaling in GC-O Plutowska & Wardencki, Flavour & Fragrance J. 24, 177, 2009 31 Example olfactogram Plutowska & Wardencki, Flavour & Fragrance J. 24, 177, 2009 Sensory profiling confirmed original classification Plutowska & Wardencki, Flavour & Fragrance J. 24, 177, 2009 32 Results • About 40 odours in aroma profiles of spirits • Some odour peaks not observed in chromatograms • Lag between chromatogram and olfactogram • Individual differences between asessors Plutowska & Wardencki, Flavour & Fragrance J. 24, 177, 2009 Dimethyltrisulphide by GC-O and GC-MS • High levels of DMTS with corresponding high GC-O scores in “poor” samples Plutowska & Wardencki, Flavour & Fragrance J. 24, 177, 2009 33 Geosmin by GC-O and GC-MS • High levels of geosmin with corresponding high GC-O scores in “poor” samples Plutowska & Wardencki, Flavour & Fragrance J. 24, 177, 2009 Conclusion • Dimethyltrisulphide (DMTS) and geosmin were the two most useful indicators of poor sensory quality • Determination of these compounds could be used for quality control of distillates in production – DMTS (and DMDS) are associated with high methional levels in grain fermentations – Geosmin probably originates in contaminated water Plutowska & Wardencki, Flavour & Fragrance J. 24, 177, 2009; Prentice et al., J. Amer. Soc. Brewing Chemists 56, 99, 1998 34