Current legislation in Spain indicates that table olives must be free of off-odors and off-flavors and without symptoms of ongoing alteration or abnormal fermentations. In this regard, the International Olive Council (IOC) has developed a protocol for the sensory classification of table olives according to the intensity of the predominantly perceived defect (PPD). An electronic nose (e-nose) was used to assess the abnormal fermentation defects of Spanish-style table olives that were previously classified by a tasting panel according to the IOC protocol, namely zapateria, butyric, putrid, and musty or humidity. When olives with different defects were mixed, the putrid defect had the greatest sensory impact on the others, while the butyric defect had the least sensory dominance. A total of 49 volatile compounds were identified by gas chromatography, and each defect was characterized by a specific profile. The e-nose data were analyzed using principal component analysis (PCA) and partial least square discriminant analysis (PLS-DA). The different defects were clearly separated from each other and from the control treatment, independently of PPD intensity. Moreover, the e-nose differentiated control olives from table olives with combined sensory defects despite the dilution effect resulting from the combination. These results demonstrate that e-nose can be used as an olfactory sensor for the organoleptic classification of table olives and can successfully support the tasting panel.
BACKGROUND: Olive oil continues to be the main destination for olives. The production of table olives is increasing. 'Californian-style' processes are among the most frequently employed to produce oxidized olives. Sensory evaluation requires the development of an instrumental detection method that can be used as an adjunct to traditional tasting panels.RESULTS: An electronic nose (E-nose) was used to classify two varieties of olives following exposure to different sterilization. Principal component analysis (PCA) revealed that both varieties had different volatile profiles. Sensory panel evaluations were similar for both. Partial least squares-discriminant analysis (PLS-DA) obtained from the E-nose was able to separate the two varieties and explained 82% of total variance. Moreover, volatile profiles correctly classified olives according to sterilization times recorded up to 121 °C . The only exception was at F 0 ≥ 22 min, at which a plot of PCA outcomes failed to differentiate scores. E-nose data showed similar results to those produced from the volatile analysis when grouping samples were sterilized to F 0 ≥ 18 min, at the same time distinguishing these samples from those subjected to less intense thermal treatments. A partial least squares (PLS) chemometric approach was evaluated for quantifying important olive quality parameters. With regards to validation parameters, R 2 P pertaining to perceived defect was 0.88, whilst R 2 P pertaining to overall assessment was 0.78. CONCLUSIONS: E-nose offers a fast, inexpensive and non-destructive method for discriminating between varieties and thermal treatments up to a point at which cooking defects are highly similar (from F 0 = 18 onwards).
Acrylamide, a compound identified as a probable carcinogen, is generated during the sterilization phase employed during the processing of Californian-style green ripe olives. It is possible to reduce the content of this toxic compound by applying different strategies during the processing of green ripe olives. The influence of different processing conditions on acrylamide content was studied in three olives varieties (“Manzanilla de Sevilla”, “Hojiblanca”, and “Manzanilla Cacereña”). Olives harvested during the yellow–green stage presented higher acrylamide concentrations than green olives. A significant reduction in acrylamide content was observed when olives were washed with water at 25 °C for 45 min (25% reduction) and for 2 h (45% reduction) prior to lye treatment. Stone olives had 21–26% higher acrylamide levels than pitted olives and 42–50% higher levels than sliced olives in the three studied varieties. When calcium chloride (CaCl2) was added to the brine and brine sodium chloride (NaCl) increased from 2% to 4%, olives presented higher concentrations of this contaminant. The addition of additives did not affect acrylamide levels when olives were canned without brine. Results from this study are very useful for the table olive industry to identify critical points in the production of Californian-style green ripe olives, thus, helping to control acrylamide formation in this foodstuff.
open Scientific RepoRtS | (2020) 10:6246 | https://doi.org/10.1038/s41598-020-63407-8 www.nature.com/scientificreports www.nature.com/scientificreports/ by using portable NIR instruments. Determination coefficients around 0.90 between NIR spectra and pressure chamber measurements were obtained 7,8 . Recently, a NIR spectrophotometer mounted on a vehicle and operating without plant contact was used with the same purpose and a correlation coefficient (R 2 ) of 0.88 was obtained for the estimation of the estomatal conductance 9 . Leaf relative water content has also been addressed with R 2 between 0.66 and 0.81 10 . Infrared spectroscopy techniques have also been applied in grapevine leaves for classification purposes. Grapevine varietal and clone identification were successfully tested using the hyperspectral image of a leaf measured in reflectance mode and proper classifications around 95% were obtained in both cases 11,12 . In the same context, Gutierrez et al. (2015) used a portable NIR instrument for in-field grapevine varieties discrimination using the leaves spectra 13 . A total of 20 different grapevine varieties were included in this study and around 85% of correct predictions were obtained. In another work, the accuracy of Vis-NIR spectroscopy to discriminate between vineyard soils using leaves spectra was demonstrated. A comparison with the existing soil map proved that the NIR spectroscopy based estimation was very similar 14 . Moreover, the results obtained in this work confirmed that the same variety planted in different soils will grow differently, or in other words, the grapevine leaves reflect the soil where the vines are located. However, as far as we know, there are no studies regarding the discrimination of leaves of the same grapevine variety collected at different vineyards located in two geographical regions using infrared spectroscopy.The analysis of grapevine leaves should also take into account the vegetative cycle of the plant. The vegetative cycle is a process that takes place in the vineyard each year and comprises all the morphological and biological changes. These changes are called phenological stages and their occurrence and duration is influenced by climatic factors 15 . It is known that leaf metabolites composition vary significantly over the vegetative cycle, especially during the ripening period due to environmental factors or the plant development 16 . These parameters are genetically determined, however their expression throughout the grape ripening process change with agricultural and environmental factors 17 .In this sense, this work intends to investigate the suitability of two infrared techniques, near and mid infrared spectroscopy, for the discrimination of grapevine leaves of the same variety growing in two different geographical locations (different leaves vegetative cycles were also considered by collecting samples over different months during the ripening process), for the discrimination leaves' vegetative cycle and also for the determination of total chlorophylls and ...
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