Optimization of electronic nose drift correction applied to tomato volatile profiling

E-noses can be routinely used to evaluate the volatile profile of tomato samples once the sensor drift and standardization issues are adequately solved. Short-term drift can be corrected using a strategy based on a multiplicative drift correction procedure coupled with a PLS adaptation of the component correction. It must be performed specifically for each sequence, using all sequence signals data. With this procedure, a drastic reduction of sensor signal %RSD can be obtained, ranging between 91.5 and 99.7% for long sequences and between 75.7 and 98.8% for short sequences. On the other hand, long-term drift can be fixed up using a synthetic reference standard mix (with a representation of main aroma volatiles of the species) to be included in each sequence that would enable sequence standardization. With this integral strategy, a high number of samples can be analyzed in different sequences, with a 94.4% success in the aggrupation of the same materials in PLS-DA two-dimensional graphical representations. Using this graphical interface, e-noses can be used to developed expandable maps of volatile profile similitudes, which will be useful to select the materials that most resemble breeding objectives or to analyze which preharvest and postharvest procedures have a lower impact on the volatile profile, avoiding the costs and sample limitations of gas chromatography.

FT-MIR determination of taste-related compounds in tomato: a high throughput phenotyping analysis for selection programs

BACKGROUND

Tomato taste is defined by the accumulation of sugars and organic acids. Individual analyses of these compounds using high-performance liquid chromatography (HPLC) or capillary zone electrophoresis (CZE) are expensive, time-consuming and are not feasible for large number of samples, justifying the interest of spectroscopic methods such as Fourier-transform mid-infrared (FT-MIR). This work analyzed the performance of FT-MIR models to determine the accumulation of sugars and acids, considering the efficiency of models obtained with different ranges of variation.

RESULTS

FT-MIR spectra (five-bounce attenuated total reflectance, ATR) were used to obtain partial least squares (PLS) models to predict sugar and acid contents in specific sample sets representing different varietal types. A general model was also developed, obtaining R² values for prediction higher than 0.84 for main components (soluble solids content, fructose, glucose, and citric acid). Root mean squared error of prediction (RMSEP) for these components were lower than 15% of the mean contents and lower than 6% of the highest contents. Even more, the model sensitivity and specificity for those variables with a 10% selection pressure was 100%. That means that all samples with the 10% highest content were correctly identified. The model was applied to an external assay and it exhibited, for main components, high sensitivities (> 70%) and specificities (> 96%). RMSEP values for main compounds were lower than 21% and 13% of the mean and maximum content respectively.

CONCLUSION

The models obtained confirm the effectiveness of FT-MIR models to select samples with high contents of taste-related compounds, even when the calibration has not been performed within the same assay. © 2019 Society of Chemical Industry.

1-Methyltryptophan Modifies Apoplast Content in Tomato Plants Improving Resistance Against Pseudomonas syringae

Plants can produce numerous natural products, many of which have been shown to confer protection against microbial attack. In this way, we identified 1-methyltryptophan (1-MT), a natural compound produced by tomato plants in response to Pseudomonas syringae attack, whose application by soil drench provided protection against this pathogen. In the present work, we have studied the mechanisms underlying this protection. The results demonstrated that 1-MT can be considered a new activator of plant defense responses that acts by inhibiting the stomatal opening produced by coronatine (COR) and could thereby, prevent bacteria entering the mesophyll. Besides, 1-MT acts by blocking the jasmonic acid (JA) pathway that, could avoid manipulation of the salicylic acid (SA) pathway by the bacterium, and thus hinder its growth. Although the concentration of 1-MT reached in the plant did not show antimicrobial effects, we cannot rule out a role for 1-MT acting alone because it affects the expression of the fliC gene that is involved in synthesis of the flagellum. These changes would result in reduced bacterium motility and, therefore, infective capacity. The results highlight the effect of a tryptophan derivative on induced resistance in plants.

Influence of controlled deficit irrigation on tomato functional value

The effect of controlled deficit irrigation (CDI) on the accumulation of carotenoids, polyphenols and l-ascorbic acid was studied in conventional and high lycopene tomato cultivars. Plants were initially irrigated to cover 100%ET_c and after the fruit set phase, the dose was reduced to 75% or 50% of ET_c. CDI had no significant effect on the accumulation of carotenoids, while it increased the levels of the hydroxycinnamic acids chlorogenic and ferulic acids, the flavonoid rutin and l-ascorbic acid. Nevertheless, there were important interactions and this effect was highly dependent on the year and site of cultivation. Certain growing areas would be more favorable to supply high quality markets, and, fortunately, CDI would maximize polyphenol (100-75%ET_c) and l-ascorbic acid (100-50%ET_c) in these areas. A combination of the best genotype and growing area with CDI would offer high quality products, preserving a scarce resource: water.

Different natures of surface electronic transitions of carbon nanoparticles

Pictorial representation of the fluorescence mechanisms proposed for carbon nanodots. Blue: tunable visible emission from surface-delocalized electronic states. Violet: UV emission from localized, quasi-molecular chromophores.

Semiconductor and carbon-based fluorescent nanodots: the need for consistency

The need for establishing the bases and definitions of photoluminescent nanodots is discussed and their state-of-the-art in analytical and biomedical research fields is highlighted.

Development of a biosensing system for tacrine based on nitrogen-doped graphene quantum dots and acetylcholinesterase

The graphene quantum dot-based sensor is sensitive to reaction products resulting from acetylcholinesterase activity and it allows for the determination of tacrine acting as an enzyme inhibitor.

Fast simultaneous determination of prominent polyphenols in vegetables and fruits by reversed phase liquid chromatography using a fused-core column

A reversed-phase high-performance liquid chromatography method with photodiode array detection has been developed enabling the joint determination of 17 prominent flavonoids and phenolic acids in vegetables and fruits. A multi-segmented gradient program using a fused-core column for the separation of several phenolic classes (phenolic acids and flavonoids) has been optimised. The influence of extraction conditions (sample freeze-drying, ultrasound extraction, solvent composition and extraction time) has been also optimised using response surface methodology with tomato samples as a model. Complete recoveries (76-108%) were obtained for the phenolic compounds present in tomato. The developed method provided satisfactory repeatability in terms of peak area (RSD<2.9%) and retention time (RSD<0.2%) both for standards and real samples. Detection limits ranged between 3 and 44μgkg(-1) for the detected polyphenols. This method is recommended for routine analysis of large number of samples typical of production quality systems or plant breeding programs.

Effects of the interaction of single-walled carbon nanotubes with 4-nonylphenol on their in vitro toxicity

The aim of this study was to assess the toxicological risks arising from the coexistence of polyethylene glycol coated single-walled carbon nanotubes (SWCNTs-PEG) and a known environmental contaminant: 4-nonylphenol (NP). To this end, in vitro toxicity assays involving the exposure of 3T3-L1 cells (mouse embryonic fibroblasts) to SWCNTs-PEG alone or in combination with NP for 24 or 48 h were performed. Experimental treatments were conducted in both presence (10%) and absence of serum in order to evaluate its influence on the toxicity of SWCNTs-PEG. Although the results provided no unambiguous evidences of synergistic toxicity between SWCNTs-PEG and NP, some specific treatments with mixtures (SWCNTs-PEG+NP) resulted in an unexpected combined toxicity in relation to the individual treatments. Only in those cases the interaction between SWCNTs-PEG and NP could have a synergistic effect on the resulting toxicity. The addition of 10% serum increased the stability of SWCNTs-PEG in the culture medium-possibly by steric repulsions-and reduced the toxicity of nanoparticles as a result. Overall, the serum had a "protective effect" on cells against all treatments: SWCNTs-PEG, NP or their mixtures (SWCNTs-PEG+NP). Raman spectroscopy allowed the intracellular distribution of SWCNTs-PEG to be elucidated.

A quantitative model to assess Social Responsibility in Environmental Science and Technology

The awareness of the impact of human activities in society and environment is known as "Social Responsibility" (SR). It has been a topic of growing interest in many enterprises since the fifties of the past Century, and its implementation/assessment is nowadays supported by international standards. There is a tendency to amplify its scope of application to other areas of the human activities, such as Research, Development and Innovation (R + D + I). In this paper, a model of quantitative assessment of Social Responsibility in Environmental Science and Technology (SR EST) is described in detail. This model is based on well established written standards as the EFQM Excellence model and the ISO 26000:2010 Guidance on SR. The definition of five hierarchies of indicators, the transformation of qualitative information into quantitative data and the dual procedure of self-evaluation and external evaluation are the milestones of the proposed model, which can be applied to Environmental Research Centres and institutions. In addition, a simplified model that facilitates its implementation is presented in the article.

Evaluation of hippuric acid content in goat milk as a marker of feeding regimen

Organic producers, traders, and consumers must address 2 issues related to milk: authentication of the production system and nutritional differentiation. The presence of hippuric acid (HA) in goat milk samples has been proposed as a possible marker to differentiate the feeding regimen of goats. The objective of this work is to check the hypothesis that HA could be a marker for the type of feeding regimen of goats by studying the influence of production system (conventional or organic) and feeding regimen (with or without grazing fodder). With this purpose, commercial cow and goat milk samples (n=27) and raw goat milk samples (n=185; collected from different breeds, localizations, and dates) were analyzed. Samples were grouped according to breed, feeding regimen, production system, and origin to compare HA content by ANOVA and honestly significant difference Tukey test at a confidence level of ≥95%. Hippuric acid content was obtained by analyzing milk samples with capillary electrophoresis. This method was validated by analyzing part of the samples with HPLC as a reference technique. Sixty-nine raw goat milk samples (of the total 158 samples analyzed in this work) were quantified by capillary electrophoresis. In these samples, the lowest average content for HA was 7±3 mg/L. This value corresponds to a group of conventional raw milk samples from goats fed with compound feed. The highest value of this group was 28±10 mg/L, corresponding to goats fed compound feed plus grass. Conversely, for organic raw goat milk samples, the highest concentration was 67±14 mg/L, which corresponds to goats fed grass. By contrast, the lowest value of this organic group was 26±10 mg/L, which belongs to goats fed organic compounds. Notice that the highest HA average content was found in samples from grazing animals corresponding to the organic group. This result suggests that HA is a good marker to determine the type of goats feeding regimen; a high content of HA represents a diet based mainly or exclusively on eating green grass (grazing), independently of the production system. Hence, this marker would not be useful for the actual organic policies to distinguish organic milk under the current regulations, because organic dairy ruminants can be fed organic compound feed and conserved fodder without grazing at all.

High efficiency joint CZE determination of sugars and acids in vegetables and fruits

In this work, an improved CE method for the medium-throughput determination of main organic acids (oxalate, malate, citrate), the amino acid glutamate and the sugars fructose, glucose and sucrose in several food matrices is described. These compounds have been identified as key components in the taste intensity of fruit and vegetable crops. Using a running buffer with 20 mM 2,6-pyridine dicarboxylic acid pH 12.1 and 0.1% hexadimethrine bromide, replacing it every 5 h to avoid pH decrease, and optimizing capillary conditioning between runs with 58 mM SDS during 2 min at 20 psi, it is possible to effectively quantify these compounds while increasing medium throughput repeatability. This procedure resolves problems such as increases in migration time and reduction of resolution between problematic peaks (malate/citrate and fructose/glucose) detected in a previous method. The new procedure even considerably reduced time analysis down to 12 min. Under optimal conditions, a large number of injections (200) could be administered without any disturbances in the same capillary. The reliability of the proposed method was further investigated with several food matrix samples, including tomato, pepper, muskmelon, winter squash, and orange. This method is recommended for routine analysis of large number of samples typical of production quality systems or plant breeding programs.

Selective extraction of astaxanthin from crustaceans by use of supercritical carbon dioxide

An on-line supercritical fluid extraction (SFE) system coupled to a continuous flow manifold including a UV detector was used as a screening system to extract astaxanthin from crayfish, which was found to be the major carotenoid present in the samples. This compound constitutes the principal additive used to dye salmon flesh. The flow manifold was used to confirm the presence of astaxanthin in the crustacean samples. Also, an HPLC/UV-vis method was used to ascertain that this compound was the major carotenoid extracted under the optimum SFE conditions employed. The influence of SFE operating variables such as pressure, temperature, equilibration time, extraction time, trap temperature, and volume of CO(2) modifier was examined in order to maximize the efficiency of analyte extraction. The use of supercritical CO(2) enables the expeditious, selective, quantitative extraction of astaxanthin from crustaceans.

Evaluation of genotype and environment effects on taste and aroma flavor components of Spanish fresh tomato varieties

Taste and aroma related compounds have been analyzed in a collection of four traditional varieties and two tomato hybrids, representing a wide variability in fruit shape and color, grown in different environments: screenhouse and open field. Protected cultivation tended to show lower sugar concentration (fructose and glucose) but similar acid contents (citric, malic, and glutamic acids). The decreased levels of sucrose equivalents and the similar ratios of sucrose equivalents to citric or glutamic acid contents indicated that protected cultivation, despite being useful to reduce the incidence of pests and viral diseases, reduces the organoleptic quality. Additionally, it doubles the interaccession variability and increased the level of intra-accession variability. In the case of aroma, the genotypic effect was considerably higher than the environmental component on the 12 main volatiles analyzed. Only hexanal and methyl salicylate were significantly affected by environment, while 10 out of 12 volatiles were affected by the genotype. Biplot analysis showed that, even in considerably different environments, it is possible to identify genotype-dependent main aroma profiles. In the case of 13 background volatiles, the environment showed no significant effects and the genotypic effect was lower, though it is possible to identify genotypic trends in background notes.

Modulation of organic acids and sugar content in tomato fruits by an abscisic acid-regulated transcription factor

Growing evidence suggests that the phytohormone abscisic acid (ABA) plays a role in fruit development. ABA signaling components of developmental programs and responses to stress conditions include the group of basic leucine zipper transcriptional activators known as ABA-response element binding factors (AREBs/ABFs). AREB transcription factors mediate ABA-regulated gene expression involved in desiccation tolerance and are expressed mainly in seeds and in vegetative tissues under stress; however, they are also expressed in some fruits such as tomato. In order to get an insight into the role of ABA signaling in fruit development, the expression of two AREB-like factors were investigated during different developmental stages. In addition, tomato transgenic lines that overexpress and downregulate one AREB-like transcription factor, SlAREB1, were used to determine its effect on the levels of some metabolites determining fruit quality. Higher levels of citric acid, malic acid, glutamic acid, glucose and fructose were observed in SlAREB1-overexpressing lines compared with those in antisense suppression lines in red mature fruit pericarp. The higher hexose concentration correlated with increased expression of genes encoding a vacuolar invertase (EC 3.2.1.26) and a sucrose synthase (EC 2.4.1.13). No significant changes were found in ethylene content which agrees with the normal ripening phenotype observed in transgenic fruits. These results suggest that an AREB-mediated ABA signal affects the metabolism of these compounds during the fruit developmental program.