Gema Flores

Impact of postharvest methyl jasmonate treatment on the volatile composition and flavonol content of strawberries

BACKGROUND Although strawberry aroma is very complex, certain compounds have been described as main contributors, i.e. furanones, aldehydes, alcohols, sulfur compounds and particularly methyl and ethyl esters. In addition, strawberries possess potent antioxidant activity because of their high content of phenolic compounds. Among them, flavonols are highlighted as important antioxidant compounds in strawberry. The objective of this study was to assess the effect of methyl jasmonate (MJ) on the composition of the major contributors to aroma and on the content of certain flavonols in strawberry fruits. RESULTS The levels of all studied volatile compounds were significantly affected by MJ treatment, though the individual effect differed according to the specific compound considered. Most of them increased significantly (P < 0.05), except methyl butanoate, which always showed higher levels in untreated strawberries. In contrast to aroma compounds, the change in the concentration of flavonols (i.e. myricetin, quercetin and kaempferol) was not significant in MJ-treated strawberries. Considering the health-promoting activity of these compounds, further investigations on the experimental conditions related to the treatment are required to control flavonol bioformation by means of MJ. CONCLUSION The exogenous application of MJ vapour to strawberry enhances, in general, the production of the most relevant aroma-active compounds. On the contrary, MJ treatment does not appear to influence the levels of myricetin, quercetin and kaempferol. Thus postharvest MJ treatment is proposed as an approach to obtain improved strawberry fruits in terms of sensory quality and health-promoting properties.

In vitro fermentation of juçara pulp (Euterpe edulis) by human colonic microbiota.

This study was carried out to investigate the potential fermentation properties of juçara pulp, using pH-controlled anaerobic batch cultures reflective of the distal region of the human large intestine. Effects upon major groups of the microbiota were monitored over 24h incubations by fluorescence in situ hybridisation (FISH). Short-chain fatty acids (SCFA) were measured by HPLC. Phenolic compounds, during an in vitro simulated digestion and fermentation, were also analysed. Juçara pulp can modulate the intestinal microbiota in vitro, promoting changes in the relevant microbial populations and shifts in the production of SCFA. Fermentation of juçara pulp resulted in a significant increase in numbers of bifidobacteria after a 24h fermentation compared to a negative control. After in vitro digestion, 46% of total phenolic content still remained. This is the first study reporting the potential prebiotic effect of juçara pulp; however, human studies are necessary to prove its efficacy.

Enantioselective isolation of methyl jasmonate using permethyl-β-cyclodextrin HPLC

A method based on the use of HPLC for the enantioselective resolution of the four stereoisomers of methyl jasmonate (MJ) with no need for the previous formation of the diastereoisomers is developed. To that end, a Nucleodex-beta-PM column as well as an optimization process considering different flow rates and mobile phase compositions were required. As a result, 0.8 mL/min and 55:45 methanol/water composition were the conditions selected to carry out the separation of the stereoisomers. Isolation of pure (-)- and (+)-MJ was accomplished by collecting the HPLC fractions corresponding to their elution time. SPE was subsequently used to concentrate and change the solvent of the HPLC fractions collected. Chiral GC and polarimetry were additionally employed to evaluate the purity and optical rotation, respectively, of the enantiomers separated. The results found in this study are particularly relevant considering that MJ stereoisomers are not commercially available.

Development of a method based on on-line reversed phase liquid chromatography and gas chromatography coupled by means of an adsorption-desorption interface for the analysis of selected chiral volatile compounds in methyl jasmonate treated strawberries

A method based on the use of the through oven transfer adsorption-desorption (TOTAD) interface in on-line coupling between reversed phase liquid chromatography and gas chromatography (RPLC-GC) for the determination of chiral volatile compounds was developed. In particular, the method was applied to the study of the influence of methyl jasmonate (MJ) treatment on the production and enantiomeric composition of selected aroma compounds in strawberry. The compounds studied were ethyl 2-methylbutanoate, linalool and 4-hydroxy-2,5-dimethyl-3(2H)-furanone (i.e. furaneol), which were examined on days 3, 6 and 9 after treatment. The method developed resulted in relative standard deviations (RSDs) of 21.6%, 8.1% and 9.8% and limits of detection (LD) of 0.04, 0.07 and 0.02mg/l for ethyl 2-methylbutanoate, linalool and furaneol, respectively. The application of the RPLC-TOTAD-GC method allowed higher levels of ethyl 2-methylbutanoate, linalool and furaneol to be detected, particularly after 9 days of treatment. Besides, MJ demonstrated to affect the enantiomeric distribution of ethyl 2-methylbutanoate. On the contrary, the enantiomeric composition of linalool and furaneol kept constant in both control and MJ-treated strawberries throughout the study. These results are discussed.

Through oven transfer adsorption–desorption interface for the analysis of methyl jasmonate in aromatic samples by on‐line RPLC‐GC

A fully automated method for the determination of medium volatility compounds in aromatic samples was developed. Specifically, the determination of methyl jasmonate in jasmine fragrances was performed by using the through oven transfer adsorption-desorption (TOTAD) interface for the on-line coupling between RPLC-GC. A study of the most relevant variables involved in the performance of the TOTAD interface for medium volatility compounds was carried out by testing different values of helium flow (100, 300, 400, and 500 mL/min), transfer speed (0.1, 0.3, 0.5, and 2.0 mL/min), and methanol/water percentages (86:14, 85:15, 83:17, 80:20, and 70:30). The method developed provided satisfactory repeatability (RSD for retention times of 0.15% and for peak areas of 9.4%) and recovery (71%) as well as excellent LOD (0.01 mg/L) for methyl jasmonate in commercial jasmine essence under the experimental conditions selected as optimum. Additional advantages of the automated RPLC-TOTAD-GC method proposed in the present work are its rapidness, reliability, and the possibility of directly introducing the sample with no further pretreatment.

Use of absorbent materials in on-line coupled reversed-phase liquid chromatography–gas chromatography via the through oven transfer adsorption desorption interface

The use of absorbents as retaining materials in the through oven transfer adsorption desorption interface (TOTAD) of an on-line coupled reversed-phase liquid chromatography-gas chromatography system (RPLC-GC) is proposed for the first time. A comparative study of an adsorbent (Tenax TA) and two absorbents, namely polydimethylsiloxane and poly(50% phenyl/50% methylsiloxane) is performed to establish the best experimental conditions for the automated and simultaneous determination of 15 organophosphorus and organochlorine pesticide residues in olive oil. The proposed method provides satisfactory repeatability (RSDs lower, in general, than 8.5%) and sensitivity (limits of detection ranging from 0.6 to 81.9 microg/L) for the investigated compounds.

Isolation of the four methyl jasmonate stereoisomers and their effects on selected chiral volatile compounds in red raspberries.

The four stereoisomers present in a commercial sample of methyl jasmonate (MJ) were isolated at semi-preparative scale by HPLC, using a permethylated β-cyclodextrin column. This allowed the baseline resolution and collection of both major (methyl jasmonates) and minor (epi-methyl jasmonates) stereoisomers. When 1.5 mL of a 5mg per mL MJ solution were injected, isolated amounts were 3.56 mg for (-) and (+)-methyl jasmonates, with respective purities of 96.1% and 99.9%, and 0.18 mg for (-)- and (+)-epi-methyl jasmonates, with 98.6% and 91.6% respective purities. The post-harvest treatment of red raspberry fruits with the pure methyl jasmonate stereoisomers isolated proved that (-)-epi-MJ either promotes the bioformation of (+)-limonene or inhibits that of (-)-limonene to a greater extent than the other three MJ stereoisomers, while the biosynthesis of the (+)-enantiomer of α-ionone is favoured equally, whichever MJ stereoisomer used. The results obtained in the present study might be used to obtain food products with improved sensory characteristics.

Phenylalanine ammonia-lyase, flavanone 3β-hydroxylase and flavonol synthase enzyme activity by a new in vitro assay method in berry fruits.

An HPLC method for the determination of phenylalanine ammonia-lyase, flavanone 3β-hydroxylase and flavonol synthase enzyme activity is proposed. This method is based on the determination of the compounds produced and consumed on the enzymatic reaction in just one chromatographic analysis. Optimisation of the method considered kinetic studies to establish the incubation time to perform the assay. The method here described proved to be an interesting approach to measure the activities of the three enzymes simultaneously increasing the rapidity, selectivity and sensitivity over other exiting methods. The enzyme activity method developed was applied to strawberry, raspberry, blackberry, redcurrant and blackcurrant fruits.

Exogenous methyl jasmonate diminishes the formation of lipid‐derived compounds in boiled potato (Solanum tuberosum L.)

BACKGROUND During potato storage the tubers tend to develop off-flavours, mainly due to lipid-derived aldehydes, whose formation is increased after boiling or processing. This may become a problem when boiled or precooked potatoes are used. Methyl jasmonate (MJ) is a phytohormone capable of modifying plant and food composition. The aim of this work was to control the formation of off-flavours in different cultivars of raw potato during storage by MJ treatment. RESULTS The use of Carbowax 20M as support in MJ emulsion resulted in significantly (P < 0.05) lower levels of lipid-derived compounds than the use of lanolin. Levels of the lipid-derived aldehydes propanal, hep-2-enal, nonanal, oct-2-enal and hexanal, although dependent on variety, generally decreased significantly (P < 0.05) after treatment with MJ/Carbowax 20M emulsion. Sugar-derived compounds such as pyridine and furfural, however, were not affected by this treatment. CONCLUSION Treatment with MJ/Carbowax 20M can be used to diminish the formation of off-flavours in boiled potato. However, this treatment is not useful to avoid the sweetening caused by sugar-derived products. Additional advantages of exogenous MJ are a delay in the appearance of sprouting and aging and hence prolongation of the storage life of potato tubers.

Effect of postharvest methyl jasmonate treatment on fatty acid composition and phenolic acid content in olive fruits during storage.

BACKGROUND The nutritional effects of both table olives and olive oil are attributed not only to their fatty acids but also to antioxidant phenolics such as phenolic acids. Delays in oil processing usually result in undesirable oxidation and hydrolysis processes leading to formation of free fatty acids. These alterations create the need to process oil immediately after olive harvest. However, phenolic content decreases drastically during olive storage resulting in lower quality oil. In the present study we propose postharvest methyl jasmonate treatment as a mean to avoid changes in fatty acid composition and losses of phenolic acids during olive storage. RESULTS Contents of fatty acids and phenolic acids were estimated in methyl jasmonate treated olives throughout 30-day storage, as compared with those of untreated olives. Significant decreases of saturated fatty acids were observed in treated samples whereas increases of oleic, linoleic and linolenic acids were respectively measured (i.e. from 50.8% to 64.5%, from 7.2% to 9.1% and from 1.5% to 9.3%). Also, phenolic acid contents increased significantly in treated olives. Particularly, increases of gallic acid from 1.35 to 6.29 mg kg-1 , chlorogenic acid from 9.18 to 16.21 mg kg-1 , vanillic acid from 9.61 to 16.99 mg kg-1 , caffeic acid from 5.12 to 12.55 mg kg-1 , p-coumaric acid from 0.96 to 5.31 mg kg-1 and ferulic acid from 4.05 to 10.43 mg kg-1 were obtained. CONCLUSION Methyl jasmonate treatment is proposed as an alternative postharvest technique to traditional methods to guarantee olive oil quality when oil processing is delayed and olive fruits have to necessarily to be stored.