Aroma Activity Research Articles

Historical Review of Citrus Flavor Research during the Past 100 Years

Citrus juices are a complex mixture of flavor and taste components. Historically, the contributions of taste components such as sugar (sweet) and acid (sour) components were understood before impactful aroma volatiles because they existed at higher concentrations and could be measured with the technologies of the 1920s and 1930s. The advent of gas chromatography in the 1950s allowed citrus researchers to separate and tentatively identify the major citrus volatiles. Additional volatiles were identified when mass spectrometry was coupled to capillary GC. Unfortunately, the major citrus volatiles were not major influences of citrus flavor. The major aroma impact compounds were found at trace concentrations. With the advent of increasingly more sensitive instrumental techniques, juice sample size shrank from 2025 L in the 1920s to 10 mL today and detection limits fell from percent to micrograms per liter. Currently gas chromatography-olfactometry is the technique of choice to identify which volatiles in citrus juices possess aroma activity, determine their relative aroma strength, and characterize their aroma quality but does not indicate how they interact together or with the juice matrix. Flavor equations based primarily on nonvolatiles and other physical measurements have been largely unsuccessful. The most successful flavor prediction equations that employ instrumental concentration values are based on a combination of aroma active volatiles and degrees Brix (sugar) values.

Determination of the role of valencene in orange oil as a direct contributor to aroma quality

Valencene is the major sesquiterpene in orange peel oil and its concentration has been traditionally used to determine the oil's commercial value. Multidimensional GC–O[sol ]GC–MS was employed to determine the contribution of valencene to the aroma quality of a commercial orange oil. Thirty-seven aroma-active components were found in this orange oil. One of these components possessed a citrusy[sol ]woody aroma similar to that of valencene and eluted in the expected time region for valencene on a polar column. The volatiles in the valencene region were isolated by the heartcutting technique, directed to a second GC capillary column (DB-5) and split between a mass spectrometer and an olfactory port. Aroma activity was detected only from a peak identified as dodecanal, and not valencene. The identities of both compounds were confirmed from full scan mass spectra and reconfirmed with standards. Valencene concentrations in the original orange oil and three additional commercial orange oils were determined to be 54–68 µg[sol ]g, using GC–FID with an internal standard. The results indicated that valencene produced no aroma activity at the levels found in orange oil. Its use as a causative indicator of good quality orange oil must be questioned. Valencene may simply be an easy to measure marker for increased fruit maturity, which is known to correlate positively with increased orange flavour quality. This study also demonstrates the need for careful chromatography involving multiple columns whenever assigning aroma activity to a particular compound in GC–O studies. Copyright © 2005 John Wiley & Sons, Ltd.

Identification of aroma active compounds in orange essence oil using gas chromatography–olfactometry and gas chromatography–mass spectrometry

Using GC–MS and GC–flame ionization detection (FID)/olfactometry, 95 volatile components were detected in orange essence oil, of which 55 were aroma active. In terms of FID peak area the most abundant compounds were: limonene, 94.5%; myrcene, 1%; valencene, 0.8%; linalool, 0.7%, and octanal, decanal, and ethyl butyrate, 0.3% each. One hundred percent of the aroma activity was generated by slightly more than 4% of the total volatiles. The most intense aromas were produced by octanal, wine lactone, linalool, decanal, β-ionone, citronellal, and β-sinensal. Potent aroma components reported for the first time in orange essence oil include: E-2-octenal, 1-octen-3-ol, Z-4-decenal, E, E-2,4-nonadienal, guaiacol, γ-octalactone, and m-cresol. Over 20 compounds were identified for the first time in orange essence oil using MS, however, most did not exhibit aroma activity.

GC-olfactometric characterization of aroma volatiles from the thermal degradation of thiamin in model orange juice.

Model orange juice solutions containing 0.024 mM thiamin hydrochloride were stored for up to 8 weeks at 35 degrees C in amber glass containers. Volatiles were evaluated, primarily, using gas chromatography (GC) with olfactometry but also with flame ionization detector, pulsed-flame photometer detector (PFPD) (sulfur specific), and MS detection. Both 2-methyl-3-furanthiol (MFT) and its dimer, bis(2-methyl-3-furyl) disulfide (MFT-MFT) were identified thus confirming that thiamin could serve as the precursor to these potent off-flavors in thermally degraded citrus juices. Thirteen aroma active components were observed. MFT and MFT-MFT were observed after only a few days storage, and produced 33% of the total aroma activity after 7 d storage. Both compounds were observed olfactometrically earlier than they could be detected using PFPD. Other aroma-active compounds included 4,5-dimethylthiazole (skunky, earthy), 3-thiophenethiol (meaty, cooked), 2-methyl-4,5-dihydro-3(2H)-thiophenone (sour-fruity, musty, green), 2-acethylthiophene (burnt), 2-formyl-5-methylthiophene (meaty), and 2-methyl-3-(methyldithio) furan (meaty).

Aroma-active components in fermented bamboo shoots.

Bamboo shoots (Phyllostachys pubescens) were fermented and prepared in a traditional Taiwanese manner. Static and dynamic headspace extractions of volatile compounds were conducted by solid phase microextraction (SPME) and by cryogenic focusing purge and trap, respectively. Volatile analysis was conducted with gas chromatography and mass spectrometry. Gas chromatography-olfactometry (GCO) was conducted utilizing the Osme time-intensity method. Of 70 volatile compounds detected, 29 possessed aroma activity, and the most odor active included p-cresol (barn-like), 2-heptanol (mushroom), acetic acid (vinegar), and 1-octen-3-ol (mushroom). SPME extracted 66 compounds, purge and trap extracted 14 compounds, and 12 compounds were common to both methods. The Osme GCO technique coupled with SPME is an effective tool for the extraction and evaluation of aroma-active headspace volatiles.

Characterization of aroma‐impact compounds in cold‐pressed grapefruit oil using time–intensity GC–olfactometry and GC–MS

AbstractThirty‐eight aroma‐active compounds were detected in commercial cold‐pressed grapefruit oil using a time–intensity GC–olfactometry procedure. Identification of the aroma‐active components was based on the combination of sensory descriptors, linear retention index values from DB‐Wax and DB‐1 columns and GC–MS data. Thirteen flavour components, which had not been previously reported in grapefruit oil, were identified. Compounds with the greatest aroma intensities include: 1,8‐cineole, octanal, dodecanal, trans‐4,5‐epoxy‐(E)‐2‐decenal, β‐sinensal and nootkatone. The aroma activities of sulphur compounds such as 4‐mercapto‐4‐methyl‐2‐pentanol and methional were surprisingly low and neither of the two putative grapefruit aroma impact compounds, 4‐mercapto‐4‐methyl‐2‐pentanone and 1‐p‐menthene‐8‐thiol, was detected. Over 200 volatiles have been reported in grapefruit oil, but only 38 have significant aroma activity and 22 of these can be considered major aroma impact compounds. Copyright © 2001 John Wiley & Sons, Ltd.

Sensory study of the character impact aroma compounds of a coffee beverage

The more potent odorants in a sample of medium-roasted Arabica coffee and in the corresponding brew were quantified. Large amounts ( >75%) of acetaldehyde, 2,3-butanedione, 2,3-pentanedione, vanillin and some furanones were extracted from the coffee brew, whereas the yields of the more unpolar compounds, such as 3-isobutyl-2-methoxypyrazine, (E)-β-damascenone and the unstable 2-furfurylthiol were low (<25%). On the basis of quantitative data an aroma model was prepared for the brew. In triangle tests, models containing the complete set of 24 odorants were compared with a model missing one or more odorants. These experiments indicated that the aroma of the brew was mainly caused by some alkylpyrazines, furanones and phenols, and by 2-furfurylthiol, methional and 3-mercapto-3-methylbutyl formate. The higher impact of both methional and the formate on the aroma of the brew and the lower aroma activity of 4-vinylguaiacol were in contrast to results obtained in a previous study for ground coffee of the same provenance and roast degree.

Physiological Activity of Deep‐Frozen Concentrates of Leuconostoc Strains

Abstract11 strains of Leuconostoc cremoris and 1 strain of Leuconostoc lactis were the subject of investigations. Basing on the evaluation of growth parameters in the different cultivation media and on the diacetyl production ability in milk 2 strains of Leuconostoc cremoris and 1 strain of Leuconostoc lactis were chosen for preparing frozen concentrated biomass. Sterile milk or cream (18% fat) were used as protecting agents. Concentrated biomass was frozen at −70 °C and stored at −30 °C for 3 months. The prepared concentrates contained from 1.6 × 1011 to 2.8 × 1011 colony forming units (CFU)/g. Except for one (strain “S”) the strains retained 100% survival. All the strains showed high growth activity after their recovery in milk (3.3 × 108 ‐ 8.4 × 108 CFU/ml). Both protecting agents applied proved to be equally good for preserving viability of the cells and for their acidifying activity. In spite of the protecting agent a decrease in the aroma activity by 25–50% was observed after one month of the biomass storage. Nevertheless, concentrated frozen multicomponent starters containing Leuconostoc strains retained the ability to produce diacetyl and acetoin on the unchanged level during the three months storage period.