Quality assessment of olive oils based on temperature-ramped HS-GC-IMS and sensory evaluation: Comparison of different processing approaches by LDA, kNN, and SVM.

For the first time, this study describes a HS-GC-IMS strategy for analyzing non-targeted volatile organic compounds (VOCs) profiles to distinguish between virgin olive oils of different classification. Correlations among measured flavor characteristics and sensory attributes evaluated by a test panel were determined by applying unsupervised (PCA, HCA) and supervised (LDA, kNN and SVM) chemometric techniques. PCA and HCA were applied for natural clustering of the samples and LDA, kNN, and SVM methods were used to create predictive models for olive oil classification. Identification of 26 target compounds revealed which compounds are responsible for discrimination, and how their distribution correlates with the sensory evaluation. In the investigated samples, LDA, kNN, and SVM models correctly classified 83.3%, 73.8%, and 88.1% of the samples, respectively. This suggests that mathematical correlations of HS-GC-IMS 3D fingerprints with the sensory analysis may be appropriate for calculating a good predictive value to classify virgin olive oils.

Processing and storage effects on orange juice aroma: a review.

Freshly squeezed orange juice aroma is due to a complex mixture of volatile compounds as it lacks a specific character impact compound. Fresh hand-extracted juice is unstable, and thermal processing is required to reduce enzyme and microbial activity. Heating protocols range from the lightly heated not from concentrate, NFC, to the twice heated, reconstituted from concentrate, RFC, juices. Thermal processing profoundly effects aroma composition. Aroma volatiles are further altered by subsequent time-temperature storage conditions. Heating reduces levels of reactive aroma impact compounds such as neral and geranial, and creates off-flavors or their precursors from Maillard, Strecker, and acid catalyzed hydration reactions. Off-flavors such as 4-vinylguaiacol, p-cymene, and carvone are the products of chemical reactions. Other off-flavors such as butane-2,3-dione, guaiacol, and 2,6-dichlorophenol are indicators of microbial contaminations. Since most orange juice consumed worldwide is processed, the goal of this review is to summarize the widely scattered reports on orange juice aroma differences in the three major juice products and subsequent aroma changes due to packaging, storage, and microbial contamination with special emphasis on results from GC-O studies.

Fresh squeezed orange juice odor: a review.

Fresh orange juice is a highly desirable but unstable product. This review examines analytical findings, odor activity, and variations due to cultivar, sampling methods, manner of juicing, plus possible enzymatic and microbial artifacts. Initial attempts to characterize orange juice odor were based on volatile quantitation and overemphasized the importance of high concentration volatiles. Although over 300 volatiles have been reported from GC-MS analytical studies, this review presents 36 consensus aroma active components from GC-olfactometry studies consisting of 14 aldehydes, 7 esters, 5 terpenes, 6 alcohols, and 4 ketones. Most are trace (microg/L) components. (+)-Limonene is an essential component in orange juice odor although its exact function is still uncertain. Total amounts of volatiles in mechanically squeezed juices are three to 10 times greater than hand-squeezed juices because of elevated peel oil levels. Elevated peel oil changes the relative proportion of several key odorants. Odor active components from solvent extraction studies differ from those collected using headspace techniques as they include volatiles with low vapor pressure such as vanillin. Some reported odorants such as 2,3-butanedione are microbial contamination artifacts. Orange juice odor models confirm that fresh orange aroma is complex as the most successful models contain 23 odorants.

Identification of sulfur volatiles in canned orange juices lacking orange flavor.

The purpose of this study was to understand why some canned orange juices are not perceived as orange juice. Sensory flavor profile data indicated that the primary odor (orthonasal) attributes were tropical fruit/grapefruit, cooked/caramel, musty, and medicine. By comparison fresh-squeezed juice lacked these odor attributes. GC-O analysis found 43 odor-active components in canned juices. Eight of these aroma volatiles were sulfur based. Four of the 12 most intense aroma peaks were sulfur compounds that included methanethiol, 1-p-menth-1-ene-8-thiol, 2-methyl-3-furanthiol, and dimethyl trisulfide. The other most intense odorants included 7-methyl-3-methylene-1,6-octadiene (myrcene), octanal, 2-methoxyphenol (guaiacol), 2-ethyl-4-hydroxy-5-methyl-3(2H)-furanone (homofuraneol), (E)-non-2-enal, (E,E)-deca-2,4-dienal, 4-hydroxy-3-methoxybenzaldehyde (vanillin), and alpha-sinensal. Odorants probably responsible for the undesirable sensory attributes included grapefruit (1-p-menth-1-ene-8-thiol), cooked [2-ethyl-4-hydroxy-5-methyl-3(2H)-furanone, 4-hydroxy-2,5-dimethyl-3(2H)-furanone (Furaneol), and 3-(methylthio)propanal (methional)], musty [7-methyl-3-methylene-1,6-octadiene and (E)-non-2-enal], and medicine (2-methoxyphenol). The canned juices also lacked several aldehydes and esters normally found in fresh orange juice.

Comparison of three lychee cultivar odor profiles using gas chromatography-olfactometry and gas chromatography-sulfur detection.

Odor volatiles in three major lychee cultivars (Mauritius, Brewster, and Hak Ip) were examined using gas chromatography-olfactometry, gas chromatography-mass spectrometry, and gas chromatography-pulsed flame photometric detection. Fifty-nine odor-active compounds were observed including 11 peaks, which were associated with sulfur detector responses. Eight sulfur volatiles were identified as follows: hydrogen sulfide, dimethyl sulfide, diethyl disulfide, 2-acetyl-2-thiazoline, 2-methyl thiazole, 2,4-dithiopentane, dimethyl trisulfide, and methional. Mauritius contained 25% and Brewster contained 81% as much total sulfur volatiles as Hak Ip. Cultivars were evaluated using eight odor attributes: floral, honey, green/woody, tropical fruit, peach/apricot, citrus, cabbage, and garlic. Major odor differences in cabbage and garlic attributes correlated with cultivar sulfur volatile composition. The 24 odor volatiles common to all three cultivars were acetaldehyde, ethanol, ethyl-3-methylbutanoate, diethyl disulfide, 2-methyl thiazole, 1-octen-3-one, cis-rose oxide, hexanol, dimethyl trisulfide, alpha-thujone, methional, 2-ethyl hexanol, citronellal, (E)-2-nonenal, linalool, octanol, (E,Z)-2,6-nonadienal, menthol, 2-acetyl-2-thiazoline, (E,E)-2,4-nonadienal, beta-damascenone, 2-phenylethanol, beta-ionone, and 4-vinyl-guaiacol.