Volatiles and primary metabolites profiling in two Hibiscus sabdariffa (roselle) cultivars via headspace SPME-GC-MS and chemometrics

Hibiscus sabdariffa (roselle) is a plant of considerable commercial importance worldwide as functional food due to its organic acids, mucilage, anthocyanins, macro and micro-nutrients content. Although Hibiscus flowers are emerging as very competitive targets for phytochemical studies, very little is known about their volatile composition and or aroma, such knowledge can be suspected to be relevant for understanding its olfactory and taste properties. To provide insight into Hibiscus flower aroma composition and for its future use in food and or pharmaceutical industry, volatile constituents from 2 cultivars grown in Egypt, viz. Aswan and Sudan-1 were profiled using solid-phase microextraction (SPME) coupled to GCMS. A total of 104 volatiles were identified with sugar and fatty acid derived volatiles amounting for the major volatile classes. To reveal for cultivar effect on volatile composition in an untargeted manner, multivariate data analysis was applied. Orthogonal projection to latent structures-discriminant analysis (OPLS-DA) revealed for 1-octen-3-ol versus furfural/acetic acid enrichment in Aswan and Sudan-1 cvs., respectively. Primary metabolites contributing to roselle taste and nutritional value viz. sugars and organic acids were profiled using GC-MS after silylation. The impact of probiotic bacteria on roselle infusion aroma profile was further assessed and revealed for the increase in furfural production with Lactobacillus plantarum inoculation and without affecting its anthocyanin content. This study provides the most complete map for volatiles, sugars and organic acids distribution in two Hibiscus flower cultivars and its fermented product.     

Characterization of volatile organic compounds released by granivorous insects in stored wheat

Identification of the volatile organic compounds released by insects can be used to detect insects in stored grains. An attempt was made to identify the volatile organic compounds released by Tribolium castaneum (red flour beetle) and Cryptolestes ferrugineus (rusty grain beetle) by headspace analysis. Feasibility of the automatic headspace sampler in headspace analysis was found to be positive. The amount of volatiles produced by T. castaneum adults increased with an increase in insect density. The concentration of methyl-1,4-benzoquinone; ethyl-1,4-benzoquinone; and 1-tridecene released by ten adult insects were: 8.5, 9.1 and 10.6 μg/100 μL compared to 7, 8 and 4.2 μg/100 μL for five adult insects. Extreme high or low temperature leading to death produced very high amounts of volatiles compared to insects kept at 35 °C. The larvae of the T. castaneum insects did not produce any volatiles at ambient condition or at extreme cold or hot condition. The C. ferrugineus adults did not produce any detectable amount of volatiles even at very high insect density after up to 3 days. The results of the combination of T. castaneum and C. ferrugineus insects gave the same volatile compounds as produced by T. castaneum insects alone.     

A comparative study of the phenolic compounds and the in vitro antioxidant activity of different Brazilian teas using multivariate statistical techniques

A total of 51 Brazilian teas from the species Camellia sinensis, Peumus boldus, Matricaria recutita, Baccharis trimera, Cymbopogon citratus, Pimpinella anisum, Mentha piperita, and Ilex paraguariensis were analyzed in terms of phenolic compounds, color and in vitro antioxidant capacity using ferric reducing antioxidant power (FRAP) and 1,1-diphenyl-2-picrylhydrazyl (DPPH) assays. Data were processed using principal component analysis (PCA), hierarchical cluster analysis (HCA) and linear discriminant analysis (LDA). Significant (P < 0.01) correlations between antioxidant activity measured by DPPH and FRAP assays with the total phenolic compounds (r = 0.87; r = 0.90, respectively) and flavonoids (r = 0.79; r = 0.77, respectively) were attained. The compounds that displayed significant (P < 0.05) correlations with the antioxidant activity were gallic acid, catechin, epicatechin, procyanidin B2, quercetrin, and caffeine. PCA was a suitable approach to check for similarities among tea samples, explaining up to 50% of data variability. Four groups were suggested using HCA, in which cluster 3 showed the highest content of total phenolic compounds, flavonoids, antioxidant activity, gallic acid, and caffeine. All samples included in this group were from C. sinensis. The overall classification capacity obtained by LDA was 82.00%, in which 100% of samples from I. paraguariensis, C. citratus, M. recutita, and P. boldus were adroitly classified, while 60% of teas from P. anisum, 80% of M. piperita teas, and 88.24% of C. sinensis teas were correctly classified.     

Characterisation of volatile and non-volatile metabolites in etiolated leaves of tea (Camellia sinensis) plants in the dark

Aroma is an essential factor affecting the quality of tea (Camellia sinensis) products. While changes of volatile compounds during tea manufacturing have been intensively studied, the effect of environmental factors on volatile contents of fresh tea leaves has received less attention. We found that C. sinensis var. Yabukita kept in darkness by shading treatment for 3 weeks developed etiolated leaves with significantly increased levels of volatiles, especially volatile phenylpropanoids/benzenoids (VPBs). Upstream metabolites of VPBs, in particular shikimic acid, prephenic acid, and phenylpyruvic acid, showed lower levels in dark treated than in control leaves, whereas the contents of most amino acids including l-phenylalanine, a key precursor of VPBs, were significantly enhanced. In addition, analysis by ultra performance liquid chromatography-time of flight mass spectrometry, capillary electrophoresis–time of flight mass spectrometry, high performance liquid chromatography, and gas chromatography–mass spectrometry indicated that volatile and non-volatile metabolite profiles differed significantly between dark treated and untreated leaves.     

Variations of volatile flavour compounds in Cordyceps militaris chicken soup after enzymolysis pretreatment by SPME combined with GC-MS,GC × GC-TOF MS and GC-IMS

Cordyceps militaris chicken soup has always been one of the most popular Chinese-style soups due to its high nutritional value and special flavour. In the present work, C. militaris chicken soup was stewed after enzymolysis pretreatment. Several advanced techniques including GC-MS, GC × GC-TOF MS and GC-IMS were utilised to investigate the volatiles of as-prepared C. militaris chicken soup. GC-MS and GC  ×GC-TOF MS analysis indicated that contents and kinds of the main compounds especially aldehydes and esters which have fatty and sweet aroma in C. militaris chicken soup were increased after enzymolysis process. GC-IMS results demonstrated that some volatile substances in chicken soup disappeared with the addition of C. militaris and concentrations of some volatile substances were increased after enzymolysis process. Enzymolysis pretreatment was confirmed to be an effective way to enhance the soluble protein dissolution rate and volatile flavour compounds of C. militaris chicken soup.     

Response of moth Plodia interpunctella to volatiles of fungus-infected and uninfected wheat grain

The aim of the study was to reveal volatile organic compounds (VOCs) produced by wheat grain, both before and after fungi infestation, which evoke reactions in Indian meal moth, Plodia interpunctella (Hübner) (Lepidoptera: Pyralidae), mated females. Solid phase micro-extraction (SPME) technique was used to collect volatiles and gas-chromatography, mass spectrometry (GC-FID/EAD, GC-MS) analysis and synthetic standards were applied to reveal and identify active compounds. Olfactory receptors of P. interpunctella females responded to five VOCs: 1-hexanol, nonanal, phenylacetaldehyde and 4-oxophorone (emitted by fungi-uninfected grain), and 3-methyl-1-butanol (emitted by fungi-infected grain). Behavioral tests carried out in olfactometers revealed attractive property of 1-hexanol and nonanal at low concentrations and repellent properties of 4-oxoisophorone to mated P. interpunctella females. Phenylacetaldehyde was neither an attractive nor repellent. 3-Methyl-1-butanol acted as an attractant at low concentrations and as repellent at higher ones. The latter compound could serve as a kairomone and allomone due to its different effects on behavior at higher and lower concentration.     

Effect of accumulated temperature on flavour and microbial diversity of japonica rice during storage

Storage temperature is closely related to rice grain quality in granaries. The purpose of this study was to determine the relationship between the microbial community and volatile components with the different accumulated temperature changes in japonica rice storage granaries NO. 37, NO. 38 and NO. 40 every two months from February to September. In the three granaries, the accumulated temperature during storage continued to increase, but the mould counts first increased and then decreased. When the accumulated temperature was 650–1000 °C·d, the quantity of mould reached its maximum. The content of volatile components such as ketones, alcohols, sulphur compounds and acids measured by the electronic nose increased significantly. Illumina high-throughput sequencing revealed that as the accumulated temperature reached 650–1000 °C·d, the fungi community richness and diversity were higher than at other accumulated temperatures in the three granaries. In addition, at the fungal genus level, unclassified_Hypocreales, Papiliotrema, Bulleromyces, Sarocladium, Dioszegia and unclassified_Ustilaginaceae had an obvious correlation with the volatile hydrocarbons and alcohols (p < 0.05) measured by gas chromatography mass spectrometry (GC-MS). After screening the dominant strains, we found that the volatile hydrocarbons were mainly from Papiliotrema_fuscus, Pleosporales_sp, Alternaria_sp, Phaeosphaeria_microscopica, Bulleromyces_spand and Erythrobasidium_hasegawianum. Therefore, the accumulated temperature of 650–1000 °C•d over two months can be used as an indicator for rapid moulds growth. Furthermore, the volatile compound content reflects the extent of fungal activity and can be used as a reference for monitoring rice quality and consumption safety.     

Effects of the origins of Botrytis cinerea on earthy aromas from grape broth media further inoculated with Penicillium expansum

Earthy “off” aromas from wine and grape juice are highly detrimental to the production of quality grape products. These volatile compounds are produced on grapes by Botrytis cinerea, Penicillium expansum and/or a combination of P. expansum and B. cinerea strains. B. cinerea strains were isolated from different (a) vineyards in Spain and Portugal, (b) grape varieties (c) bunches (i.e., sound and botrytized) and (d) positions in the botrytized bunch (i.e., interior or exterior). A novel Headspace-Phase Microextraction (SPME) followed by Gas Chromatrography/Mass Spectrometry (GC-MS) dedicated to analyze geosmin, methylisoborneol (MIB), 1-octen-3-ol, fenchone and fenchol in grape broth medium was used. Approximately 50% of the B. cinerea strains induced detectable geosmin. One strain accumulated significant amounts of anisoles, demonstrating that this contamination might already occur in the vineyard. Strains from the interior of Cainho grape bunches induced more geosmin and hence it may be possible to reduce this volatile in wine by avoiding using these grapes in case of B. cinerea attack.     

Method for the static headspace analysis of carrot volatiles

A static headspace analysis/gas chromatography/mass spectrometry (SHA/GC/MS) method was developed to analyse the volatile composition of raw (seven different varieties), stored and cooked carrot samples. A total of 35 different volatile compounds were identified in carrots. Of these, trans-ocimene, 2,5-dimethyl styrene, camphor, borneol, α-santalene, α-selinene, γ-elemene and α-zingiberene in raw carrots and propanol in stored carrots were identified for the first time. Major volatile compounds identified in raw carrots were α-pinene, sabinene, myrcene, limonene, γ-terpinene, terpinolene, β-caryophyllene and γ-bisabolene. Mono-and sesquiterpenes accounted for about 97% of the total volatiles identified. Sizeable varietal differences (p<0.01) were observed. Carrot volatiles did not change appreciably during the 28 day storage period at 5, 25 and 35°C, except propanol that showed exponential increases at higher temperatures. No propanol was detected in fresh raw carrots. Cooking resulted in 88.6, 93.0 and 95.5% loss in total volatiles after cooking times of 10, 20 and 30 min, respectively.     

Effects of the volatile organic compounds produced by Enterococcus spp. strains isolated from maize grain silos on Fusarium verticillioides growth and fumonisin B1 production

Fusarium verticillioides is a phytopathogenic fungus that can contaminate maize grain silos and result in important losses in the post-harvest product. The objective of this work was to investigate the effects of volatile organic compounds produced by four lactic acid bacterial strains isolated from maize grain silos on F. verticillioides M3125 growth and fumonisin B₁ (FB₁) production. The bacterial isolates 55 and 49 were identified as Enterococcus faecium and M4A and M4G as Enterococcus casseliflavus. The fungal growth was inhibited by 33.33% by the volatiles released by the M4A strain and by approximately 10% by the volatiles emitted by the 55 and 49 strains. The volatiles produced by the M4A strain also significantly reduced (88.75%) FB₁ biosynthesis. The gas chromatography–mass spectrometer analysis identified 21 volatile organic compounds, with diacetyl, acetic acid and acetoin being the main volatiles emitted by the four bacterial strains. Acetoin was the volatile produced in the highest proportion by the four strains, with M4A generating the highest proportion of diacetyl (35.11%). Diacetyl and acetic acid completely inhibited fungal growth at concentrations of 0.3 and 1 mM, respectively, while acetoin promoted fungal growth. Only acetoin significantly reduced FB₁ production. These results showed that diacetyl was the main compound involved in fungal inhibition, while the effect on FB₁ production could have been due to the combination of the volatile organic compounds produced by the M4A strain. In conclusion, the volatiles emitted by the E. casseliflavus M4A strain could be a promising tool for the biocontrol of F. verticillioides in storage maize grain silos.     

Contents of lovastatin, γ-aminobutyric acid and ergothioneine in mushroom fruiting bodies and mycelia

Lovastatin, γ-aminobutyric acid (GABA) and ergothioneine were analysed in mushrooms. Among fruiting bodies, Pleurotus ostreatus (Japan) and Agaricus bisporus contained the highest amount of lovastatin (606.5 and 565.4 mg/kg, respectively) whereas among mycelia, Cordyceps sinensis and Antrodia salmonea contained the highest (1365 and 1032 mg/kg, respectively). Among fruiting bodies, Flammulina velutipes and Boletus edulis contained the highest amount of GABA (229.7 and 202.1 mg/kg, respectively) whereas among mycelia, Cordyceps cicadae, C. sinensis and Agaricus blazei contained the highest (254.9, 220.5 and 200.4 mg/kg, respectively). Among fruiting bodies, Pleurotus citrinopileatus, P. ostreatus (Korea), P. ostreatus (Taiwan) and Pleurotus salmoneostramineus contained the highest amount of ergothioneine (2850.7, 1829.4, 1458.4 and 1245.0 mg/kg, respectively) whereas among mycelia, Pleurotus eryngii contained the highest (1514.6 mg/kg). Ergothioneine was detected in all samples. However, the Pleurotus genus contained considerably high amount of ergothioneine. Overall, these results might be related to their beneficial effects.     

Glycine max (L.) Merr., Vigna radiata L. and Medicago sativa L. sprouts: A natural source of bioactive compounds

The consumption of sprouts, common in Asia, has been growing in western countries, once they are a natural healthy food and considered as a valuable dietary supplement. Comparing with their mature counterparts, sprouts are usually richer in health-promoting phytochemicals. So, the nutritional composition and the biological potential of widely consumed sprouts of three species – Glycine max (L.) Merr., Vigna radiata L. and Medicago sativa L. – were compared for the first time. Phenolic compounds and phytosterols were analyzed by HPLC–DAD and organic acids by HPLC–UV. The volatile profile was determined by HS-SPME/GC–IT/MS. Fourteen phenolic compounds (including four isoflavones), three sterols one triterpene, sixteen fatty acids, seven organic acids and thirty volatile compounds were determined. The antioxidant activity was assessed against DPPH^?, superoxide and nitric oxide radicals. G. max sprouts were the most active against DPPH^? (IC₅₀ = 1.337 mg/mL), while those of M. sativa were the most effective against superoxide and nitric oxide radicals (IC₅₀ = 67 μg/mL and IC₅₀ = 426 μg/mL, respectively). Data provide evidence of great similarities between G. max and M. sativa sprouts, both being rich in phenolic compounds, fatty acids and volatiles, and exhibiting better antioxidant activity. On the other hand, V. radiata showed higher amounts of sterols, triterpenes and organic acids. In this study it was found that the sprouts are a good source of bioactive compounds in our diet with health-promoting antioxidants.     

Toxicity of carbon dioxide to drugstore beetle Stegobium paniceum and cigarette beetle Lasioderma serricorne

Mortality and sub-lethal effects of carbon dioxide (CO₂) against Stegobium paniceum and Lasioderma serricorne were studied. All life stages of S. paniceum were relatively more susceptible than those of L. serricorne. In both species, the pupal stage was the most tolerant followed by larva, egg and adult. The influence of changing CO₂ concentrations (stepwise increase or stepwise decrease) in comparison with constant CO₂ concentration on the mortality responses of adults of S. paniceum and L. serricorne at fixed Ct products was also examined. Both changing concentrations of CO₂ were more effective than constant concentration and the effect was more pronounced in S. paniceum. CO₂, at LD₅₀ doses, prolonged the developmental period of the survivors in both species. Treatment of adults caused a significant reduction in progeny production indicating an adverse effect on the multiplication potential of the survivors.     

Stored-product insects in botanical warehouses

Insect pests infesting six stored botanicals were sampled monthly in two Egyptian warehouses over 12 months. The plants sampled were; roselle (Hibiscus sabdariffa), mogat (Glossostemon bruguieri), coriander (Coriandrum sativum), anise (Pimpinella anisum), chamomile (Matricaria chamomilla) and marjoram (Origanum majorana). The warehouses were located in northern Egypt in Mansoura and Bilqas. Lasioderma serricorne and Stegobium paniceum were the most common insect pests in warehouses. The beetles Tribolium castaneum, Tribolium confusum, Trogoderma granarium and Cryptolestes ferrugineus had lower and similar levels of infestation. The moths, Plodia interpunctella and Sitotroga cerealella, had the lowest infestation levels. There were small differences in infestation by the most common insects, L. serricorne and S. paniceum, among the six botanicals. In general, M. chamomilla and O. majorana had the lowest level of infestation. The other plants, H. sabdariffa and C. sativum had higher levels of infestation. The warehouse in Bilqas had higher populations than the warehouse in Mansoura. In Bilqas, the temperature and relative humidity were slightly higher and the warehouse was older and had open windows, factors that may have contributed to higher insect infestations.     

Contribution of coagulant and native microflora to the volatile-free fatty acid profile of an artisanal cheese

The contributions of the coagulant Cynara cardunculus and of the microflora of raw milk to the volatile-free fatty acid profile of Serra da Estrela cheese were evaluated. The experimental design included both a model system and, dual cheeses. The study in the model system showed that isovaleric acid was the predominant volatile compound after 7 d of ripening. The systems inoculated with Enterococcus faecium produced the highest amount of this volatile (ca. 135.8 mg kg⁻¹ curd), while those inoculated with Lactobacillus plantarum produced the least (21.4 mg kg⁻¹ curd); Lactococcus lactis produced moderate amounts (ca. 34.2 mg kg⁻¹ curd) but a total amount of volatile-free fatty acids similar to those found in control samples. This is considered advantageous since this volatile fatty acid confers a harsh, piquant, mature flavour to cheese, coupled with the realisation that excess volatiles may result in off-flavours. The addition of cultures in experimental cheeses helped reduce ripening time to about one half. Inclusion of Lb. plantarum led to cheeses containing the highest amounts of volatiles, and exhibiting an aroma closest to that of typical Serra da Estrela cheese.     

Development of a Rapid Discrimination Tool for <Emphasis Type="Italic">Luzhou-flavor</Emphasis> Pit Mud Classification by the Kohonen Artificial Neural Network Model

Understanding the volatile composition of pit mud (PM) samples and discriminating these samples has become a highly necessary task, owing to the fact that volatile profiling of PM can significantly affect Chinese Luzhou-flavor liquor quality. In this study, the volatile constitutions of 13 Luzhou-flavor liquor PM samples from four typical producing regions were investigated by gas chromatography–mass spectrometry (GC-MS). Owing to their high concentrations, compounds such as ethyl hexanoate, butyric acid, hexanoic acid, ethyl pentadecanoate, ethyl palmitate, ethyl (9E)-9-octadecenoate, ethyl (9E,12E)-9,12-octadecadienoate, and palmitic acid were considered to be predominant volatiles. A promising artificial neural network model, the Kohonen self-organizing map (SOM), was applied to rapidly discriminate the PM samples in terms of differences based on the quantitative information of volatile compounds. After Kohonen SOM training, 13 distinct clusters, corresponding to PM samples, were clearly visualized on a uniform distance matrix (U-matrix). The influence of volatile compounds on the classification of the PM could be displayed using component panels, which can give quantitative insight. GC-MS coupled with the Kohonen SOM model not only presented the volatile constitution of PM but also provided promising information for discrimination between different PM samples, even in other fermented foods.     

Sensor analyses of volatile components derived from earth-almond Cyperus esculentus L. and carob Ceratonia siliqua L.

The Aroma Scanner A32?S, which mimics the human olfactory system, is based on conducting polymer sensor technology. The design of this electronic nose (capable of detecting and recognizing odours) is described. Two different products, earth-almond and carob (raw, and roasted for different lengths of time), were analysed by means of this electronic nose and by gas chromatography-mass spectrometry (GC-MS), in order to establish a basis of comparison between the two methods. After having analysed and compared the results obtained from both products, the Aroma Scanner was found to be a suitable method for monitoring the earth-almond roasting process, but not so effective at controlling carob roasting, as the correlation between sensor and GC-MS data was lower in the case of carob (R ²=0.74) than with earth-almond (R ²=0.98). This may be due to the inherent nature of the sample, as well as to the choice of signal processing technique. Therefore, the Aroma Scanner A32?S can be used as an efficient tool complementary to GC-MS analyses in recognizing aroma components of different products if the values concerning the volatiles formed in the roasting process do not appear very close to each other (Euclidean distance ≥0.5).     

Sensory characteristics of spoilage and volatile compounds associated with bacteria isolated from cooked and peeled tropical shrimps using SPME-GC-MS analysis

The spoilage potential of six bacterial species isolated from cooked and peeled tropical shrimps (Brochothrix thermosphacta, Serratia liquefaciens-like, Carnobacterium maltaromaticum, Carnobacterium divergens, Carnobacterium alterfunditum-like and Vagococcus penaei sp. nov.) was evaluated. The bacteria were inoculated into shrimps, packaged in a modified atmosphere and stored for 27 days at 8 °C. Twice a week, microbial growth, as well as chemical and sensory changes, were monitored during the storage period. The bacteria mainly involved in shrimp spoilage were B. thermosphacta, S. liquefaciens-like and C. maltaromaticum whose main characteristic odours were cheese-sour, cabbage-amine and cheese-sour-butter, respectively. The volatile fraction of the inoculated shrimp samples was analysed by solid-phase microextraction (SPME) and gas chromatography coupled to mass spectrometry (GC-MS). This method showed that the characteristic odours were most likely induced by the production of volatile compounds such as 3-methyl-1-butanal, 2,3-butanedione, 2-methyl-1-butanal, 2,3-heptanedione and trimethylamine.