Olfaction (Smell) 22/09/2015. Importance of flavor. Physiology and biochemistry of aroma and off odors in fresh cut produce. Role of aroma volatiles

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1 /9/5 Importance of flavor Physiology and biochemistry of aroma and off odors in fresh cut produce Charles F. Forney Agriculture and Agri Food Canada, Kentville, Nova Scotia, Canada Flavor is a human perception Good flavor is needed to achieve consumer satisfaction Acceptable flavor is often lost prior to decline in visual appearance Maintaining flavor in fresh cut produce can be challenging Role of aroma volatiles Provide unique flavor characteristics 7 8% of flavor attributed to volatiles Most dynamic component Can change dramatically during storage and marketing Product maturity /ripening Altered by storage environment Indicator of quality Sign of spoilage Olfaction (Smell) Interaction of volatile compounds with olfactory receptors in the nasal cavity Orthonasal odor/aroma Retronasal flavor Over 8, volatile compounds in food Fewer than, contribute to odor ppb to ppt or less Chemistry Biochemistry Aroma of fresh cut produce Mechanisms controlling aroma Factors affecting aroma Initial Quality Cutting Packaging Diverse Morphology Physiology Chemistry Fresh fruits and vegetables

2 /9/5 Analyzed using gas chromatography (GC) Mass spectroscopy Olfactory detection Volatile chemistry Volatile profiles Hundreds of compounds Wide range of concentrations Abundance GC volatile profiles Strawberry Raspberry Blueberry Compound Ethanol Ethyl acetate Methyl butanoate Linalool Ethyl hexanoate Ethyl butanoate a Devos et al. (99) b Larson and Pool (99) Olfactory thresholds Olfactory Threshold (ppb), -, a -, b. - b. -. b. -. b. -. b Aroma impact compounds Compound Structure Crop Aroma* Terpenoids α Terpineol α Ionone Geosmin Esters Lime Raspberry Red beet Pine, terpene, lilac, citrus Sweet, woody, floral, violet, tropical fruity Freshly plowed soil, earthy Ethyl methylbutyrate Apple Fruity, estry Allyl caproate * Pineapple Sweet, fruity, pineapple Aroma impact compounds Compound Structure Crop Aroma* Aldehydes Benzaldehyde Cherry Almond, fruity Aroma impact compounds Compound Structure Crop Aroma* Lactones γ Undecalactone Peach Creamy, fruity, coconut, peach (E) Nonenal Cucumber Fatty, green, cucumber 3 Butylphthalide Celery Herbal, celery (Z) 3 Hexenal Tomato Green, fatty, grassy Ketones Octen 3 one Mushroom Herbal, mushroom, earthy Alcohols (Z,Z) 3,6 Nonadienol * Watermelon Fatty, soapy, cucumber, watermelon rind Furans Furaneol Pyrazines Isobutyl 3 methoxypyrazine * Strawberry Green bell pepper Peas Sweet, cotton candy, caramel, strawberry Green pea, green bell pepper

3 /9/5 Aroma impact compounds Compound Structure Crop Aroma* Sulfur compounds Dimethyl sulfide Isobutyl thiazole Asparagus, cabbage, corn Tomato Sulfury, onion, sweet corn, cabbage Green, wasabi, privet, tomato leaf Primary pathways/precursors Terpenoids pathway Isoprene (C 5 ) Fatty acids β oxidation Lipoxygenase (LOX) pathway methythiobutyl isothiocyanate Broccoli Cabbage, radish Amino acids Propyl propanethiosulfonate Onion Roasted alliaceous Carotenoids norisoprenoids * C 5 Terpenoid synthesis Mevalonic Acid Pathway (MVA) Cytosol Isopentanyl diphospate (IPP) C 5 Sesquiterpenes C 3 Triterpenes Norisoprenoids Methylerythritol Pathway (MEP) Plastid Isopentanyl diphospate (IPP) C Monoterpenes C Diterpenes C Tetraterpenes Carotenoids Straight chain alcohols Aldehydes Straight chain esters Acids Ketones Lactones β Oxidation Fatty acids Lipoxygenase (LOX) pathway Amino acids C 8 PUFAs LOX HPL C 6 Aldehydes ADH C 6 Alcohols AAT C 6 Esters C 9 Aldehydes C 9 Alcohols Provide an array of backbones for volatile synthesis Aliphatic Branched Aromatic Source of N and S Precursors Alcohols Acids Esters Glucosinolates/isothiocyanates Sulphoxides 3

4 /9/5 Other Volatiles Fermentation CHO Glycolysis Stress X Acetaldehyde ADH AAT Acetate esters Ethanol Krebs Cycle AAT + Ethyl esters Oxidative Phosphorylation Mitochondia PDC Induction of fermentation Ripening Senescence Stress Low O / high CO Heat Chilling Freezing Water stress Ozone Mechanisms of aroma change Initial Quality Metabolism Synthesis Catabolism Diffusion Gain Loss Taints Package/environment Synthesis Adsorption Aroma Compounds Diffusion Barrier Permeation Catabolism Treatments Atmosphere Cultivar selection Production practices Fertilization Spacing Pruning Environmental stress Water Temperature Postharvest treatments Treatments prior to processing affect aroma Manipulation of ripening Temperature management Postharvest treatments Controlled atmosphere (CA) storage Postharvest ripening Kensington Pride mango Fruit ripened at C to.5 kg cm firmness Total volatiles highest in mature green fruit Monoterpenes Ripe fruit had more esters Percent Percent µg kg -, Titratable acidity Total sugars Volatiles Hard green Total volatiles Monoterpenes Sesquiterpenes Esters Mature Half Ripe green ripe Harvest Maturity Lalel et al., 3

5 /9/5 Heat treatments Broccoli Hot water dips extends shelf life Delays yellowing Reduces decay Off odour produced by 5 C or 3 min treatment Heat treatments Broccoli Heat stress induced volatiles Ethanol cis 3 Hexenol Dimethyltrisulfide (DMTS) GC Olfactory analysis Identified cis 3 hexanol floral, green, hay like DMTS floral, sulfury, green µmol m Ethanol cis-3-hexenol DMTS Control 5 C - min 5 C - min 5 C - 3 min Hours After Treatment CA Storage Package atmospheres Prolonged storage in CA may reduce fruit aroma Low O concentrations can aroma loss May partially recover aroma by holding in air Ambrosia Slices packaged in PE zip-loc bags OTR 35 ml m - d - O decreased to:. kpa Atmosphere (kpa) 8 O 6 CO Days at 5 C Ethanol, Terpenes Score (6%) Ambrosia apple slice volatiles After 6 months CA AP AP AP AP A7P AP A7P A7P Score (3%) Esters AP SCE BCE Acetate Hexanoate Alcohols Ethanol Terpenes Estragole Others,, - weeks aerated (A),7, - days packaged (P) Alters physiology Respiration Volatile synthesis Induces production of secondary volatiles Removes diffusional barriers Increases aroma loss Cutting 5

6 /9/5 Product respiration Product respiration Gala apples Shredding cabbage Increased respiration 5 fold After 9 days remained 3.5 fold greater Doubles CO production Sustained over 8 hours Respiration rate (mgco kg - h - ) Whole Early Whole Mid Whole Late Cut Early Cut Mid Cut Late x Mean Hours Ester release from cut apples Headspace ester s with maturity Cutting stimulates ester production/release Greatest in early harvest fruit Lower MW esters Total Esters (root area counts) Whole, Early Whole, Mid Whole, Late Cut, Early Cut, Mid Cut, Late x Mean Hours Induced fermentation Both ethanol and ethyl acetate d in response to cutting Rise in ethanol transient Fermentation alters ester composition Ethanol (root area counts) Ethyl Acetate (root area counts) x x Whole, Early Whole, Mid Whole, Late Cut, Early Cut, Mid Cut, Late 36 8 Mean Hours Secondary volatile formation Cut onion Volatile sulfur compounds are formed after cutting Reaction of alliinase and cysteine sulfoxides Products are unstable and continue to react Integral part of the fresh cut product Physical protection Packaging Atmosphere modification (MAP) Impact aroma 6

7 /9/5 O Modified Atmosphere Packaging (MAP) O O Volatiles Volatiles Volatiles Package CO CO CO H O H O H O Package atmosphere effects Gala apples slices/apple Sealed in polymer bags Solid film (S) multi layered polyolefin OTR 66 ml m d CO TR 33 ml m d Micro perforated film (P) µm holes/package OTR 37 ml m d CO TR 33 ml m d Stored at 5 C for d Package atmosphere composition Equilibrium package atmospheres Solid film 3 kpao 6 kpa CO Micro-perforated film 6 kpa O 6 kpa CO CO (kpa) O (kpa) solid film micro-perforated film 7 X Data Sensory analysis Fruitiness-by-Mouth 6 Fruity Aroma 5 Sweetness 3 Preference Sourness Visual Hardness solid film micro-perforated 7 Days at 5 C PCA of volatile composition Raspberry volatiles Total variation, 58% Monoterpenes Sesquiterpenes Alkenes Alcohols, BCE Score (7%) 3 S - P S Ctl S PP Score (%) Estragole, Total Ctl Control, Day P Perforated, Day P Perforated, Day P Perforated, Day S Solid, Day S Solid, Day S Solid, Day Straight Chain Esters Branched Chain Esters Terpenes Alcohols Estragole Others Total Terpenes Score, 3% Total volatiles Esters C3 norisoprenoids Alcohol Ketones Aldehydes O 7 O Init Air O CO CO Octavia Moutere Nova Lauren Score, 35% C3 norisoprenoids 7

8 /9/5 Terpenes Score, 3% Volatiles Total variation, 58% Monoterpenes Sesquiterpenes Alkenes Total volatiles Esters C3 norisoprenoids Alcohol Ketones - Aldehydes O 7 O - Init Air O CO CO Octavia Moutere -6 Nova Lauren Score, 35% C3 norisoprenoids Induced by anaerobic conditions/stress Ethanol Air stored doubled % O /.5% CO 5 fold.5% CO fold % O cultivar dependent Acetaldehyde % O /.5% CO 3 fold.5% CO.5 fold % O similar to airstore Anaerobic volatiles Ethanol (µg g - FW) Acetaldehyde (µg g - FW) Initial Octavia Moutere Nova Lauren Col vs Col 8 Air kpa O kpa O.5kPa CO 7.5kPa O.5kPa CO Atmosphere Induced by anaerobic conditions/stress Ethanol Air stored doubled % O /.5% CO 5 fold.5% CO fold % O cultivar dependent Acetaldehyde % O /.5% CO 3 fold.5% CO.5 fold % O similar to airstore Anaerobic volatiles Ethanol (µg g - FW) Acetaldehyde (µg g - FW) Initial Octavia Moutere Nova Lauren Col vs Col 8 Air kpa O kpa O.5kPa CO 7.5kPa O.5kPa CO Atmosphere Induced by anaerobic conditions/stress Ethanol Air stored doubled % O /.5% CO 5 fold.5% CO fold % O cultivar dependent Acetaldehyde % O /.5% CO 3 fold.5% CO.5 fold % O similar to airstore Anaerobic volatiles Ethanol (µg g - FW) Acetaldehyde (µg g - FW) Initial Octavia Moutere Nova Lauren Col vs Col 8 Air kpa O kpa O.5kPa CO 7.5kPa O.5kPa CO Atmosphere Avoid injurious atmospheres in MAP Low O and/or high CO atmospheres may induce off odors Ethanol and acetaldehyde universally produced under stress Not directly responsible for off odor Off odor development variable among commodities Broccoli anaerobic off odor Strong off odour induced by low O Rotten cabbage Identified methanethiol as primary mal odorant Hydrogen sulfide Methanethiol 3 Dimethyl sulfide Dimethyl disulfide Forney et al., 99 8

9 /9/5 Variable response of fresh cut Brassicas to low O Concentration in Head Space mmol m -3 Ethanol 3 5 Methanethiol 5 5 Broccoli florets Pak-choi blades* Savoy cabbage Broccoflower Green cabbage Red cabbage Broccoli stems Kale* Brussels sprouts Pak-choi petioles* Rutabaga Cauliflower Chinese cabbage* Kohlrabi* Interaction of packaging materials Permeation of aroma compounds Adsorption (scalping) of volatiles Determines diffusional loss Dependent on polymer chemistry Polyolefins high affinity for volatiles Polyethylene, polypropylene Polyesters weak affinity for volatiles Polylactic acid (PLA) Packaging effects on aroma retention Onions Diced yellow onions Loss of volatiles Sealed PLA maintained headspace volatiles 9/ S-volatiles significantly greater in sealed PLA Fresh onion aroma maintained for days in sealed PLA Total volatiles (root area counts) PLA - sealed PLA - vented PE bag - sealed x Sealed PLA maintained headspace volatiles 8 S-volatiles significantly greater in Sealed PLAstored onions Dipropyl disulfide (area counts) e+6 8e+5 6e+5 e+5 e+5 Vented PET Clamshell Vented PET Clamshell in CA Sealed PLA Container Sealed PLA Container + pinhole 6 8 Days stored Days at.5 C Diced yellow onions Sensory quality All sensory attributes in PET-air stored onions were poorer than other packages treatments after 8 days Sensory quality of onions from sealed PLA not signifcantly different from those stored in PLA-vent or PET CA Yellow onion sensory quality evaluated by 9 trained panelists after 8 days Attribute PLA PLA-vent PET CA PET air Appearance z.35 Fresh Onion Odor Off-Onion Odor Fresh Onion Flavor Off-Onion Flavor zrating scale excellent, 5 poor, P <. Conclusions Fresh cut produce aroma is complex and dynamic Chemistry, biochemistry and human perception Cutting induces metabolic changes that affect aroma volatiles and enhances diffusional losses Stress can induce fermentation and production of off odors Packaging can alter aroma by atmosphere modification or affecting diffusional loss 9

10 /9/5 Conclusions To optimize the aroma of fresh cut produce: Start with high quality product Minimize stress during processing and marketing Maintain an environment conducive to aroma maintenance