Hexyl Acetate Research Articles

EDIBLE COATINGS COMPOSED OF METHYLCELLULOSE, STEARIC ACID, AND ADDITIVES TO PRESERVE QUALITY OF PEAR WEDGES

The ability of methylcellulose and methylcellulose-stearic acid coatings to preserve the quality of Anjou pear wedges stored at 4C and 78% relative himidity over a period of 12 days was assessed. The effect of some additives (ascorbic acid, calcium chloride, and sorbic acid) alone or in combination with the edible coatings was also evaluated. The use of edible coatings and additives prolonged the shelf life of treated samples by retarding browning and enhancing texture when compared to control samples. Methylcellulose-stearic acid coatings played an important role in avoiding weight loss, while methylcellulose-only coatings showed poor water vapor barrier properties. Pear wedges coated with the methylcellulose-stearic acid formulation contained higher amounts of hexyl acetate throughout the storage period, probably due to synthesis by wounded tissue from the stearic acid contained in the coating. No effect from the applied treatments on the titratable acidity, soluble solids content, and microbial load of treated pear wedges was found.

Expression levels of the yeast alcohol acetyltransferase genes ATF1, Lg-ATF1, and ATF2 control the formation of a broad range of volatile esters.

Volatile aroma-active esters are responsible for the fruity character of fermented alcoholic beverages such as beer and wine. Esters are produced by fermenting yeast cells in an enzyme-catalyzed intracellular reaction. In order to investigate and compare the roles of the known Saccharomyces cerevisiae alcohol acetyltransferases, Atf1p, Atf2p and Lg-Atf1p, in volatile ester production, the respective genes were either deleted or overexpressed in a laboratory strain and a commercial brewing strain. Subsequently, the ester formation of the transformants was monitored by headspace gas chromatography and gas chromatography combined with mass spectroscopy (GC-MS). Analysis of the fermentation products confirmed that the expression levels of ATF1 and ATF2 greatly affect the production of ethyl acetate and isoamyl acetate. GC-MS analysis revealed that Atf1p and Atf2p are also responsible for the formation of a broad range of less volatile esters, such as propyl acetate, isobutyl acetate, pentyl acetate, hexyl acetate, heptyl acetate, octyl acetate, and phenyl ethyl acetate. With respect to the esters analyzed in this study, Atf2p seemed to play only a minor role compared to Atf1p. The atf1Delta atf2Delta double deletion strain did not form any isoamyl acetate, showing that together, Atf1p and Atf2p are responsible for the total cellular isoamyl alcohol acetyltransferase activity. However, the double deletion strain still produced considerable amounts of certain other esters, such as ethyl acetate (50% of the wild-type strain), propyl acetate (50%), and isobutyl acetate (40%), which provides evidence for the existence of additional, as-yet-unknown ester synthases in the yeast proteome. Interestingly, overexpression of different alleles of ATF1 and ATF2 led to different ester production rates, indicating that differences in the aroma profiles of yeast strains may be partially due to mutations in their ATF genes.

Characterization of Cider Brandy on the Basis of Aging Time

ABSTRACT: To characterize cider brandies on the basis of age, chemometric techniques (principal component analysis, linear discriminant analysis, and Bayesean analysis) together with contents of volatile, furanic, and phenolic compounds were used. Significant principal components computed by a double cross‐validation procedure allowed us to visualize the structure of the database as a function of the aging time to which the cider brandies had been subjected. Feasible and robust discriminant rules were computed and validated by a cross‐validation procedure that allowed suitable classification of fresh and aged brandies, obtaining classification hits >; 90%. The most discriminant variables for characterizing cider brandies according to their aging level were as follows: ethyl caprylate > ethyl isovalerate > 1‐propanol > hexyl acetate.

Influence of Operating Conditions and Column Configuration on the Performance of Reactive Distillation Columns with Liquid—Liquid Separators

AbstractThe synthesis of two different esters, ethyl acetate and hexyl acetate, by heterogeneously catalysed reactive distillation has been studied. The investigated column set‐ups were equipped with liquid—liquid separators for the distillate to separate water from the organic components. Experimental and theoretical investigations of operating conditions and different catalytic column internals, as well as different scales were performed. For the modelling and simulation of the reactive distillation columns, the rate‐based approach was applied. The simulation results are in satisfactory agreement with the experimental data. Performed simulation studies demonstrate the influence of both operating conditions and catalytic internals on the overall process performance.

Biosynthesis of volatile aroma compounds in pear fruit stored under long-term controlled-atmosphere conditions

The production of butyl and hexyl acetates and the contents of ethanol and acetaldehyde in relation to the activity of some related enzymes (lipoxygenase, pyruvate decarboxylase, alcohol dehydrogenase and alcohol o -acyltransferase) was studied in ‘Doyenne du Comice’ pears during ripening at 20 8C, following long-term cold storage under different conditions: air, or CA in 2 kPa O2 with various CO2 partial pressures (0.7, 2 or 5 kPa). A decrease in volatile production was found for fruit stored under low O2 upon return to ambient conditions. Results suggest that inhibition of volatile biosynthesis by CA storage is caused mainly by limited precursor/substrate supply to the related enzymes rather than by enzyme degradation or inactivation. Ethanol production by the fruit did not correlate well with ADH activity. The possibilities of a feedback inhibition of enzyme activity by excess product and of oxidation into acetaldehyde upon return to air are discussed. Hypoxic conditions caused a decrease in LOX activity after 5 months storage, possibly leading to shortage of lipid precursors for ester biosynthesis. # 2002 Elsevier Science B.V. All rights reserved.

Application of hexanal, E-2-hexenal, and hexyl acetate to improve the safety of fresh-sliced apples.

The aims of this work were to evaluate the effects of different concentrations of hexanal, (E)-2-hexenal, hexyl acetate, and their mixtures on the fate of pathogenic species such as Escherichia coli, Salmonella enteritidis, and Listeria monocytogenes inoculated in model systems as well as the antimicrobial activity against the target species of the chosen molecules when added to the packaging atmosphere of inoculated fresh-sliced apples. The result obtained in this work pointed out the potential use of compounds such as hexanal, (E)-2-hexenal, and hexyl acetate for both the extension of shelf life and an improvement of hygienic safety of "minimally processed foods". In fact, hexanal, (E)-2-hexenal, and hexyl acetate had a significant inhibitory effect against pathogen microorganisms frequently isolated from raw materials (E. coli, S. enteritidis, and L. monocytogenes) when inoculated in both model and real systems. In this last condition, these compounds, at the levels used (150, 150, and 20 ppm for hexanal, hexyl acetate, and (E)-2-hexenal, respectively), displayed a bactericide effect on L. monocytogenes and they exhibited significant extensions of lag phase of E. coli and S. enteritidis inoculated at levels of 10(4)-10(5) CFU/g.

Emission patterns of wound volatile compounds following injury of ripe strawberry fruit

AbstractVolatile compounds emitted from plants following wounding influence the growth of fungal pathogens, including Botrytis cinerea (grey mould), which causes serious economic loss of strawberry fruit. In the present study the patterns of volatile compound emission from ripe strawberry fruit, comprising store‐purchased fruit and two known cultivars, were determined following injury, using solid phase microextraction analysis to sample a stream of air continuously flowing over the fruit. The principal compounds produced from all fruits comprised C6 aldehydes, alcohols and acetate and butyrate esters derived from the lipoxygenase–hydroperoxide lyase pathway. There was an initial burst of production of aldehydes, including t‐2‐hexenal, following wounding and then a gradual decline, which in one cultivar continued for 3 h. t‐2‐Hexenal is of special interest, since it has been shown to inhibit or promote Botrytis growth in vitro depending on concentration. The acetate esters t‐2‐hexenyl acetate, c‐3‐hexenyl acetate and hexyl acetate were major wound compounds released by the fruit and were produced for 3 h after wounding. The production of relatively large quantities of wound‐derived esters is markedly different from the patterns observed for most vegetative tissue. Knowledge of the wound compounds produced by strawberry fruit and their profiles of emission after injury provides a basis for studies of the potential roles of these compounds in pathogen development on fruit.© 2003 Society of Chemical Industry

Germination and adhesion of fungal conidia on polycarbonate membranes and on apple fruit exposed to mycoactive acetate esters.

The adhesion and germination of conidia of nine fungal species were assessed on polycarbonate membranes or on the skin of apple fruit in sealed glass bottles injected or not injected with acetate esters. Adhesion was determined after dislodging conidia from surfaces using a sonication probe. Adhesion and germination of conidia of Aspergillus flavus, Aspergillus fumigatus, Aspergillus niger, Penicillium citrinum, Penicillium claviforme, or Trichoderma sp. on membranes after 48 h were not increased in a 1.84 microg mL(-1) headspace of butyl acetate (BA), ethyl acetate, hexyl acetate, 2-methylbutyl acetate, pentyl acetate, or propyl acetate. Adhesion and germination of Botrytis cinerea, Penicillium expansum, and Penicillium roquefortii conidia were stimulated by all esters. Only conidia of B. cinerea and P. expansum exhibited increased adhesion and germination on the skin of apple fruit in bottles exposed to 0.92 microg mL(-1) of BA. Only conidia of B. cinerea and P. expansum produced decay in inoculated puncture wounds on fruit. Freshly made puncture wounds or 24-h-old puncture wounds in fruit were more adhesive than the unpunctured skin of fruit to conidia of B. cinerea or P. expansum. Fresh wounds were more adhesive to both fungi than 24-h-old puncture wounds. The skin and wounds of fruit were as adhesive to B. cinerea conidia as they were to P. expansum conidia. A 4-h exposure to 1.43 microg mL(-1) of BA increased adhesion of B. cinerea and P. expansum conidia in 24-h-old wounds. Results suggest that acetate-ester stimulation most likely is not a rare phenomenon in the fungi. For nutrient-dependent decay pathogens of apple fruit, acetate esters may be an alternative chemical cue used to maintain adhesion of conidia to wound surfaces.

Study on synthesis parameters of lipase‐catalyzed hexyl acetate in supercritical CO2 by response surface methodology

AbstractHexyl acetate, a short‐chain ester with fruity odor, is a significant green note flavor compound that is widely used in the food industry. The ability of immobilized lipase from Rhizomucor miehei (Lipozyme IM‐77) to catalyze the transesterification of hexanol with triacetin in supercritical carbon dioxide was investigated in this study. Response surface methodology and a 3‐level‐3‐factor fractional factorial design were adopted to evaluate the effects of synthesis variables, such as reaction time (30 to 90 min), temperature (35 to 55°C), and pressure (1500 to 3500 psi), on percent molar conversion of hexyl acetate. The results showed that reaction time and pressure were the most important parameters and temperature had less effect on percent molar conversion. Based on canonical analysis, optimal synthesis conditions were as follows: reaction time 69.0 min, synthesis temperature 46.7°C, pressure 2640 psi. The predicted value was 75.6% and the actual value was 77.3% molar conversion.

Pheromones of milkweed bugs (Heteroptera: Lygaeidae) attract wayward plant bugs: Phytocoris mirid sex pheromone.

The synthetic aggregation pheromone of the large milkweed bug, Oncopeltus fasciatus (Dallas) (Lygaeinae), also attracted males of the plant bug, Phytocoris difficilis Knight (Miridae). Field testing partial blends against the six-component blend comprising the Oncopeltus pheromone showed that cross-attraction of P. difficilis males was due to synergism between (E)-2-octenyl acetate and (E,E)-2,4-hexadienyl acetate. Hexyl acetate was abundant in the metathoracic scent gland (MSG) secretion of P. difficilis males, but because female P. difficilis could not initially be found in the field, further combinatorial tests were guided by prior research on the pheromones of two Phytocoris species in the western United States. The combination of hexyl, (E)-2-hexenyl, and (E)-2-octenyl acetates was as attractive to P. difficilis males as the milkweed bug pheromone, yet no milkweed bugs were drawn to this blend. Gas chromatographic (GC)-electroantennographic detection (EAD) and GC-mass spectrometric (MS) analyses of female P. difficilis MSGs determined that their secretion contained predominantly hexyl, (E)-2-hexenyl, and (E)-2-octenyl acetates (all strongly EAD-active)-the latter two compounds found only in trace amounts from males-plus five minor female-specific compounds, three of which were EAD-active. (E,E)-2,4-Hexadienyl acetate was not detected from P. difficilis females or males. The blend of the three major components, hexyl, (E)-2-hexenyl, and (E)-2-octenyl acetates (2:1.5:1 by volume), was as attractive as the blend of all six EAD-active compounds identified from females, indicating that this ternary blend constitutes the sex pheromone of P. difficilis. Hexyl acetate with (E)-2-octenyl acetate also attracted males of another species, P. breviusculus Reuter, but addition of (E)-2-hexenyl acetate and/or (E,E)-2,4-hexadienyl acetate inhibited attraction of P. breviusculus males. Attraction of P. difficilis males occurred mainly during the first half of scotophase. The possible neurophysiological basis for this asymmetrical cross-attraction is discussed.

Influence of flavour absorption by food-packaging materials (low-density polyethylene, polycarbonate and polyethylene terephthalate) on taste perception of a model solution and orange juice

The influence of flavour absorption by low-density polyethylene (LDPE), polycarbonate (PC) and polyethylene terephthalate (PET) on taste perception of a model solution containing seven flavour compounds and orange juice in glass bottles was studied with and without pieces of the respective plastic films after dark storage at 20°C. Owing to absorption, the amount of flavour compounds in the model solution exposed to LDPE decreased substantially. From the model flavour solution valencene was almost completely absorbed by LDPE, followed to a lesser extent by decanal, hexyl acetate, octanal and nonanone. Less flavour compounds were absorbed from the model solution by PC and PET. In contrast to LDPE, valencene was absorbed in the lowest amounts and decanal in the highest. Limonene was readily absorbed from orange juice by LDPE, while myrcene, valencene, pinene and decanal were absorbed in smaller quantities. Only three flavour compounds were absorbed from orange juice by PC and PET in very small amounts: limonene, myrcene and decanal. Although the flavour content between controls and polymer-treated samples differed substantially, the loss of flavour compounds due to absorption by LDPE, PC and PET did not influence taste perception of a model solution and orange juice significantly up to 29 days of dark storage at 20°C as determined by triangular taste panel tests.

Volatile Compounds by SPME-GC as Age Markers of Sparkling Wines

Cava acquires its characteristic aroma during aging. Twenty-eight volatile compounds of 221 sparkling wines made from different base wine were quantified by headspace solid-phase microextraction coupled to gas chromatography-mass spectrometry and discriminant analysis was applied. Isoamyl and hexyl acetates, ethyl decanoate, 2-phenylethyl acetate, and vitispiranes were found to be markers of young sparkling wines (<9 months). Vitispiranes and 1,2-dihydro-1,1,6-trimethylnaphthalene (TDN) were also able to discriminate aged cava (>20 months), while diethyl succinate could be an age marker throughout the aging period.

Multivariate analysis of maturity stages, including quality and aroma, in ‘Royal Glory’ peaches and ‘Big Top’ nectarines

AbstractEthylene production, quality attributes and aroma compounds were analysed to determine the maturity evolution of ‘Big Top’ nectarines and ‘Royal Glory’ peaches at harvest dates ranging from 89 to 116 days after full bloom (DAFB) for nectarines and from 85 to 112 DAFB for peaches. These cultivars are highly coloured even in the early stages of maturity. However, the two cultivars had different patterns of ethylene production, this being slower in nectarines than in peaches. Principal component analysis (PCA) was used to provide partial visualisation of the complete data set in a reduced dimension plot. Separation of the two cultivars can be shown by means of a two‐dimensional plot of the samples. Although only some aroma compounds are slightly correlated with quality parameters, when aroma volatiles were included in the PCA, the aroma compound set allowed both cultivars to be classified into three stages of maturity: immature, intermediate and fully mature. Compounds such as propanol, hexyl acetate, 2‐methylpropyl acetate, limonene, butanol, (Z)‐3‐hexenyl acetate, buthyl acetate, linalool, ethanol, propyl acetate and ethyl acetate are the most important volatiles for ‘Big Top’ nectarines. It is suggested that the presence of these compounds can be used to indicate when the fruit should be harvested. The presence of γ‐decalactone, δ‐octalactone, γ‐octalactone, ethyl butyrate, hexanal and (E)‐2‐hexenol can be used to indicate the harvesting maturity stage for ‘Royal Glory’ peaches. The optimum maturity date for harvest would be 105–107 DAFB for ‘Big Top’ nectarines and 93–95 DAFB for ‘Royal Glory’ peaches.© 2002 Society of Chemical Industry

Partial molar volumes of organic compounds in C8 solvents at 298.15 K

Limiting partial molar volumes of n-hexane, cyclohexane, ethyl ether, tetrahydrofuran, pentan-3-one and cyclopentanone in di- n-butyl ether, hexyl acetate and octan-2-ol were determined at 298.15 K from density measurements of dilute solutions carried out with a vibrating-tube densimeter. The solute–solvent interactions and the effects of the local organisation of the solvent around the solute molecules were discussed using the molar, void, and cavity volumes as different estimates of the intrinsic volume of the molecules. The analysis was then extended to the volumetric behaviour of the same solutes in octan-1-ol. The solvents examined interact with the solutes in different ways. The isomeric octanols show the most significant effects, possibly due to their H-bond donor nature. The solute–solvent interactions seem to prevail over the packaging effects in determining the volumetric behaviour of the solutes.

Influence of a new crushing technique on the composition of the volatile compounds and related sensory quality of virgin olive oil

The influence of a new crusher i.e. blade crusher on the quality of virgin olive oil from two different italian cultivars (Coratina and Oliarola) was determined. In addition the quality of this oil was compared with that of olive oil extracted with the traditional hammer crusher. Tests were performed in an industrial oil mill using the two different crushing instruments. Results obtained showed that quality parameters i.e. free fatty acids, peroxide value, UV absorption and total phenols content as well as the phenolic composition of oils were not significantly affected by the two different crushers used. On the contrary, the use of the blade crusher influenced the composition of the volatile compounds. In particular, the oils obtained using the blade crusher showed significant increases of some aldehydes such as 1-hexanal and trans-2-hexenal, esters such as hexyl acetate and 3hexenyl acetate and a reduction of alcohols such as 1-hexanol. Moreover, the identified pigments of the oils produced using the blade crusher were found at concentrations slightly lower than those in oils obtained after using the hammer crusher. Finally, results of the sensory analysis showed an improved organoleptic quality for the oils obtained using the blade crusher due to an increase of the cut-grass and floral sensory notes.

Sensory evaluation of character impact components in an apple model mixture.

Food aromas generally are complex mixtures of volatiles. In the present study, we investigated the joint effects of hexyl acetate, trans-2-hexenal and 1-hexanol on the multi-attribute perception of an apple aroma. The first two substances were identified earlier as positive contributors to the apple aroma (high character impact), whereas the third component was identified as an irrelevant or negative contributor (low character impact). Aroma quality was quantified using a set of eight graphic rating scales. All three components had significant effects on the aroma profiles. These effects consist mainly of an effect of each component on the attribute that described its individual character and an effect of all three components on ratings on the main character attribute 'apple'. As expected, the high impact components increased 'apple' ratings, whereas the low character impact component decreased 'apple' ratings. Furthermore, intensity ratings on the attribute that corresponded with the odour of the low impact component were suppressed by the presence of high impact components. These results indicate that the contributions of odorants to the mixture's aroma are not linear combinations of separate odour intensities, because sensory interactions were observed. In addition, humans detect components in complex mixtures more accurately than studies on identification performance have suggested. We conclude that for an adequate assessment of the effects of multiple mixture components on changes in aroma perception, it is sufficient to employ multiple response scales measuring intensities of attributes that are distinctive with respect to the expected qualitative changes. Results of this approach should be subjected to multivariate methods of statistical analysis.

Character impact odorants of the apple cultivars Elstar and Cox Orange.

Extracts obtained from Elstar and Cox-Orange apples (Malus var. domestica Borkh.) were screened for potent odorants by aroma extract dilution analysis (AEDA). (E)-beta-Damascenone (I), (E)-beta-damascone (II), hexanal (III), (Z)-3-hexenal (IV), (Z)-2-nonenal (V), linalool (VI), butyl acetate (VII), 2-methylbutyl acetate (VIII) and hexyl acetate (IX) were identified in Elstar and I, III-V, ethyl butanoate (X), ethyl 2-methylbutanoate (XI), 1-octen-3-one (XII), (E)-2-octenal (XIII), methional (XIV), (E)-2-nonenal (XV), eugenol (XVI) and wine lactone (XVII) in Cox Orange. The release of odorants by the cultivars was analysed by gas chromatography-olfactometry of headspace samples. Esters X and XI showed the highest odour activities in the air above Elstar apples and ester X, acetaldehyde (XVIII), 2-methylbutanol (XIX) and ethyl methylpropanoate (XX) in that of Cox Orange. Preparation of a homogenate changed the headspace composition of potent odorants. Hexyl acetate (IX) became the key odorant of Elstar and aldehydes III and IV those of Cox Orange. Quantification and calculation of odour activity values indicated I, IV, V, VII, VIII and IX as the character impact odorants of the fruit flesh of the two cultivars. Elstar contained more I, V, VII and IX and Cox Orange more IV than the other cultivar. The concentrations of VIII were similar.

The occurrence of malolactic fermentation in brandy base wine and its influence on brandy quality.

In this study we determined the extent to which lactic acid bacteria (LAB) occurred in brandy base wines, their ability to catalyse the malolactic fermentation (MLF) and the effect of MLF on the quality of the base wine and the brandy distillate. Lactic acid bacteria were isolated and enumerated from grape juice, experimental and commercially produced brandy base wines. Spontaneous MLF occurred in approximately 50% of the commercial base wines. The occurrence of MLF had an influence on the quality of the base wines and the resulting distillates. In samples where MLF occurred there was a loss of fruitiness and in the intensity of aroma. Volatile compounds like iso-amyl acetate, ethyl acetate, ethyl caproate, 2-phenethyl acetate and hexyl acetate decreased in samples having undergone MLF, while ethyl lactate, acetic acid and diethyl succinate increased in the same samples. Spontaneous malolactic fermentation does occur in commercial brandy base wines and it has an influence on base wine and brandy quality. This study showed that MLF influences the quality of the base wine and the resulting distillate and with this in mind commercial base wine producers should be able to produce brandy of higher quality.

Mycoactive acetate esters from apple fruit stimulate adhesion and germination of conidia of the gray mold fungus.

Ethyl acetate, 2-methylbutyl acetate, butyl acetate (BA), and hexyl acetate were detected by solid-phase microextraction and gas-liquid chromatography inside slices of Golden Delicious apple and in water droplets on the skin of slices incubated in sealed glass jars. Conidial adhesion and germination of the gray mold fungus, Botrytis cinerea, was assessed on apple slices after exposure or no exposure to the esters in the headspaces of glass jars. Attached conidia were dislodged by sonication and remaining conidia on apple slices were counted by microscopy. Adhesion generally increased as BA increased to 7.2 microg mL(-1), but declined with greater concentrations. BA at 0-3.6 microg mL(-1) for 24 h stimulated adhesion 2-fold greater compared to that at 4 h. Adhesion stimulated by BA increased as a function of time (0-24 h), showing linear trends (r (2) = 0.99; p = 0.01) during 0-12 h. The four esters were similar in their ability to stimulate adhesion. Germination of conidia exposed to BA increased linearly (r (2) = 0.95-0.98; p = 0.01) during 4-12 h. Conidial adhesion stimulated by BA preceded conidial germination by 2 h. The four esters stimulated conidial germination to similar levels. Results indicated that acetate esters formed in apple fruit are mycoactive, influencing life-cycle events of B. cinerea important to its survival on the fruit. The similar responses of three B. cinerea isolates to four acetate esters suggests a common stimulation mechanism may operate in B. cinerea.

Influence of flavour absorption on oxygen permeation through LDPE, PP, PC and PET plastics food packaging

The effect of flavour absorption on the oxygen permeability of low-density polyethylene (LDPE), polypropylene (PP), polycarbonate (PC) and polyethylene terephthalate (PET) was studied using an isostatic continuous flow system. Polymer samples were exposed to a model solution containing limonene, hexyl acetate, nonanone and decanal at 40°C. After exposure, one part of each sample was analysed for absorbed flavour compounds using a Large Volume Injection GC Ultrasonic ‘in vial’ extraction method, and from the other part, oxygen permeability was measured in a permeation cell at 25°C. After 8h of exposure, LDPE and PP samples showed a significant linear (R2 = 0.82 and 0.99) increase in oxygen permeability of 21 and 130%, respectively. Owing to swelling of the polymer samples resulting from flavour absorption, the structure of the polymeric network changed (i.e. opened) and consequently increased oxygen permeability. The oxygen permeability of exposed PC showed a significant linear (R2 = 0.78) decrease of 11% after 21 days. PC obviously did not swell like LDPE or PP. Therefore, it was suggested that absorbed flavour compounds occupied or blocked ‘microcavities’ through which normally oxygen is transported. Absorption of flavour compounds by PET did not affect the oxygen permeability of PET significantly.