Isoamyl Acetate Research Articles

The Influence of Pichia kluyveri Addition on the Aroma Profile of a Kombucha Tea Fermentation.

Traditional kombucha is a functional tea-based drink that has gained attention as a low or non-alcoholic beverage. The fermentation is conducted by a community of different microorganisms, collectively called SCOBY (Symbiotic Culture of Bacteria and Yeast) and typically consists of different acetic acid bacteria and fermenting yeast, and in some cases lactic acid bacteria that would convert the sugars into organic acids-mostly acetic acid. In this study, the effect of including a Pichia kluyveri starter culture in a kombucha fermentation was investigated. P. kluyveri additions led to a quicker accumulation of acetic acid along with the production of several acetate esters including isoamyl acetate and 2-phenethyl acetate. A subsequent tasting also noted a significant increase in the fruitiness of the kombucha. The significant contribution to the aroma content shows the promise of this yeast in future microbial formulations for kombucha fermentations.

Influence of ethanol content on the detection of volatile components in Huangjiu

Huangjiu (Chinese rice wine) is a traditional Chinese fermented wine with a unique flavor. The components of this wine are complex, and the ethanol content of different Huangjiu preparations varies greatly. In this study, changes in the chromatographic peak areas of the volatile components of Huangjiu samples with different ethanol contents were measured using headspace-gas chromatography (HS-GC). The influence of ethanol on the quantitative detection of different volatile components of Huangjiu at gas-liquid equilibrium was also analyzed. When the ethanol content of Huangjiu was in the range of 10%-19% vol, the peak areas of 16 volatile components (i. e., sec-butanol, n-propanol, isobutanol, n-butanol, isoamyl alcohol, β-phenyl-ethanol, acetaldehyde, isovaleraldehyde, benzaldehyde, ethyl formate, ethyl acetate, isobutyl acetate, isoamyl acetate, ethyl hexanoate, ethyl lactate, and diethyl succinate) were negatively correlated with the ethanol content. Increases in the ethanol content of the liquor changed the gas-liquid equilibrium of most other trace volatile components. In addition, only the peak area of acetal was positively correlated with ethanol content. The content of acetal in Huangjiu was affected by the alcohol content, and its decomposition reaction occurred along with the dilution process. The influence coefficient of ethanol content on the peak area of the above compounds ranged from -12.4% to 4.9%. The vapor pressure of most volatile components decreased with increasing ethanol content, and different components were affected in different ways. Compared with those of other components, the peak areas of methanol, furfural, and acetic acid were less affected by the ethanol content. These components were also affected by other factors, such as ionization and chemical reactions occurring during the dilution process. When different wine samples were adjusted to the same ethanol content, the concentration of volatile components in these samples became proportional to the total chromatographic peak area and the influence of the matrix effect of ethanol on the quantitative analysis was effectively eliminated. Thus, when researchers use pretreatment methods based on the principle of gas-liquid balance to carry out the quantitative detection of flavor components, they should adjust different rice wine samples to the same alcohol content to effectively control the matrix effect caused by differences in ethanol content and achieve accurate quantitative analysis.

Evaluation of volatile compound profiles and sensory properties of dark and pale beers fermented by different strains of brewing yeast

To evaluate the differences in the volatile compound profile of dark and pale beers fermented by different strains of brewer's yeast, gas chromatography with flame ionization detection and gas chromatography mass spectrometry analysis of eight beers was carried out. The prevalent group of compounds in all the beers analysed were alcohols (56.41–72.17%), followed by esters (14.58–20.82%), aldehydes (8.35–20.52%), terpenes and terpenoids (1.22–6.57%) and ketones (0.42–1.00%). The dominant higher alcohols were 2-methylpropan-1-ol, 3-methylbutanol, phenethyl alcohol, among aldehydes furfural, decanal, nonanal, and among esters ethyl acetate, phenylethyl acetate and isoamyl acetate. Beers fermented by the top-fermenting yeast Saccharomyces cerevisiae var. diastaticus had the highest volatile content. The addition of dark malt in wort production process had no effect on the total content of volatiles, but for some beers it caused changes in the total content of esters, terpenes and terpenoids. Variations in the total volatile content between beers fermented by different yeast strains are mainly due to esters and alcohols identified. Sensory analysis of beers allowed us to identify the characteristics affected by the addition of dark speciality malts in the production of wort and yeast strains used in the fermentation process.

Effects of fermentation on flavor and antioxidant activity in ginkgo rice wine

Ginkgo seed is a kind of food and medicine homologous goods. It is a feasible method to use Saccharomyces cerevisiae and Non-Saccharomyces yeast to ferment ginkgo rice wine (GRW) to remove the bitter taste and retain the biological activity. In order to better explore the formation of the unique flavor and taste of GRW, the volatile flavor compounds and sensory properties of GRWs fermented at different time were analyzed by GC-MS, GC-IMS and electronic sensory evaluation techniques. In addition, the changes of phenols in GRW were determined by LC-MS, and the antioxidant activity was dynamically monitored. GC-MS analysis showed the content of ethyl laurate, isoamyl acetate, ethyl heptanoate, 1-pentanol, ethanol and 1-propanol increased significantly with the progress of fermentation, among which ethyl acetate (OAV = 23.0), ethyl heptanoate (OAV = 44.4) and isoamyl acetate (OAV = 34.7) were the key flavor compounds of GRW at 60 h. GC-IMS analysis suggested some alcohols and ketones were significantly enriched at 60 h, including 2-pentanone, acetone, 1-butanol, 1-hexanol. Electronic sensory technology showed GRW at 60 h had strong mellow and fruity aroma due to benzoic acid, butyric acid and 2-methylbutyric acid. The bitterness and umami intensity in GRW gradually decreased, while the astringency and aftertaste increased. Furthermore, LC-MS results indicated the types of phenols increased, including quinic acid, shikimic acid, sorbic acid, etc., which significantly improved the antioxidant activity of GRW. Together, the flavor quality and biological activity of GRW had been effectively improved through microbial fermentation, which indicated that GRW had potential market prospects.

Revelation of volatile contributions in green teas with different aroma types by GC–MS and GC–IMS

Aroma types of green teas associate with their commercial prices and consumer acceptance, mainly including floral-like (HX), chestnut-like (LX), and fresh (QX) aromas. However, the volatile differences and specificities in these aroma types are still unclear. Herein, Taiping Houkui green teas with HX, LX, and QX aromas were processed separately with the same fresh tea leaves. Ninety-four and seventy-eight volatiles were detected and identified by headspace solid-phase microextraction gas chromatography–mass spectrometry (HS–SPME–GC–MS) and headspace gas chromatography–ion mobility spectrometry (HS–GC–IMS), respectively. Candidate differential volatiles among the tea samples were determined by the variable importance in projection (VIP) of the partial least squares–discriminant analysis (PLS–DA) and were further confirmed by the relative odor activity value (ROAV) and odor description. The volatiles 1-hexanol, linalool oxide (furanoid), linalool, geraniol, (E)-β-ionone, isoamyl acetate, and 2-methylpropanal enriched in HX and contributed to the floral-like aroma, while 3-methylbutanal, 2-ethyl-1-hexanol, indole, β-damascone, and cedrol enriched in LX and contributed to the chestnut-like aroma. This study reveals the specificities and contributions of volatiles in green teas with different aromas, thus providing new insights into the molecular basis of different flavored teas, benefiting for their precision processing and targeted quality control.

Metschnikowia pulcherrima as biocontrol agent and wine aroma enhancer in combination with a native Saccharomycescerevisiae

One of the main objectives for a sustainable winemaking process is the reduction of the use of sulfur dioxide. In this regard, non-Saccharomyces wine yeasts are proposed as biocontrol agent in different steps of wine production chain. Here, a selected strain of Metschnikowia pulcherrima (DiSVA 269) and a native Saccharomyces cerevisiae low sulfite producer strain (DiSVA 708) were investigated. After preliminary laboratory trials, winemaking process at industrial level showed an effective biocontrol action (reduction of c.a. 1 Log order of wild yeasts) of M. pulcherrima inoculated at prefermentative stage in cold clarification (48 h at 10 °C) and during the subsequent fermentation process. The combination of M. pulcherrima/S. cerevisiae led a distinctive aromatic profile of wines both in laboratory and winery trials with a significant enhancement of ethyl butyrate, ethyl hexanoate, isoamyl acetate and β-phenyl ethanol. Moreover the use of the two selected strains was the best combination to enhance volatile thiols (3-mercaptohexan-1-ol and 3-mercaptoexil acetate) that well correlate with the sensory analysis (tropical fruits). The overall results indicate that the combined use of M. pulcherrima DiSVA 269 and native S. cerevisiae DiSVA 708 led a biocontrol action and an improvement of aromatic and sensorial profile of wine with low SO2 content.

Early transcriptional response of Saccharomyces cerevisiae in mixed culture with Torulaspora delbrueckii in cherry wine

Mixed culture by Saccharomyces cerevisiae and Torulaspora delbrueckii has been proposed for the production of wine with improved aroma, but the yeast-yeast interactive mechanism still needs in-depth elucidation. This study compared the transcriptome responses of S. cerevisiae in single and mixed fermentations with T. delbrueckii, in the initial stages of cherry wine fermentation, in order to disclose the possible relationship between aroma synthesis and gene expression. Transcriptome profiling showed a total of 446 and 186 differentially expressed genes were detected in S. cerevisiae and T. delbrueckii, respectively, and several metabolic pathways such as glucose, lipid and amino acid metabolisms were observed with variations. For aroma, a total of 35 volatile compounds were identified by HS-GC-IMS, and mixed fermentation prominently enhanced the syntheses of most esters including propyl acetate, 2-methylpropyl acetate, isoamyl acetate and 2-methylbutyl acetate. By integrating the transcriptomic and volatile results, we propose that ILV5, BATs, PDCs, ADHs, ALDs, ACS1, ACC1 and ARO10 genes are possibly the decisive genes in S. cerevisiae, which showed significant variations following S. cerevisiae's adaptive responses in mixed culture and associated with the formation of certain aldehydes, alcohols and esters in cherry wine.

Semiochemicals produced by fungal bark beetle symbiont Endoconidiophora rufipennis and the discovery of an anti-attractant for Ips typographus.

Bark beetles vector symbiotic fungal species into their host trees during mass attacks. The symbiotic relationship with blue stain fungi of the Ascomycetes, including genera of Endoconidiophora (syn. = Ceratocystis), promotes successful establishment whereby the microbes help to overcome the host trees' defence and degrade toxic resins. This is the first study to evaluate both the volatile emissions from an insect-associated blue stain fungus over time and the insect response in a field trapping experiment. Volatile emissions from isolates of Endoconidiophora rufipennis (ER) were collected by solid-phase microextraction (SPME) and analysed by gas chromatography-mass spectroscopy (GC-MS) over a period of 30 days. This virulent North American fungus is closely related to E. polonica, a symbiotic fungus known from Eurasian spruce bark beetle Ips typographus.Nine volatiles were emitted by ER in substantial amounts: isoamyl acetate, sulcatone, 2-phenethyl acetate, geranyl acetone, geranyl acetate, citronellyl acetate, (R)- and (S)-sulcatol, and (R)-sulcatol acetate. A late peaking compound was geranyl acetone. In the field trapping experiment, three of the fungal volatiles (geranyl acetone, 2-phenethyl acetate and sulcatone) were tested in combination with a synthetic aggregation pheromone for I. typographus. Traps with geranyl acetone attracted lower numbers of I. typographus compared to traps with 2-phenethyl acetate, sulcatone or the pheromone alone as a control. The results showed that geranyl acetone acts as an anti-attractant and may act naturally on I. typographus as a cue from an associated fungus to signal an overexploited host.

Modelling the transfer and degradation kinetics of aroma compounds from liquid media into coffee beans during simulated wet processing conditions

Models of increasing complexity were developed to identify and represent mechanisms affecting the evolution of the concentration of 3 aroma compounds (2-phenylethanol, isoamyl acetate and butanal) usually produced by yeasts and transferred to coffee beans during the fermentation. Model parameters were identified from simulated wet treatment performed with four media (M1: dehulled beans, M2: demucilaginated beans, M3: depulped beans, M4: depulped beans with yeast), at 25 °C using labeled aroma compounds. The transfer of 2-phenylethanol was well described by a model including evolving resistance over time (R 2 = 0.98) while the accumulation of isoamyl acetate and butanal was better described by a model including two first order reactions in parallel (r 2 = 0.87–0.66 and r 2 = 0.80–0.67, respectively). The model development contributed to understand several mechanisms involved during fermentation such as the evolutive parchment resistance and the complex degradation reactions that take place simultaneously and have a significant impact on the compounds transfer. • Dynamic modelling of the transfer kinetics of aroma compounds in coffee beans. • Identification of complex mechanisms related to layer resistance and reactions. • Accurate prediction of the transfer of higher alcohols.

Analysis of the Formation of Characteristic Aroma Compounds by Amino Acid Metabolic Pathways during Fermentation with Saccharomyces cerevisiae.

Amino acid metabolic pathways can have profound impacts on the activities of key enzymes in the biosynthesis of specific aroma compounds during yeast fermentation. Aroma compounds, pyruvic acid and glucose were monitored in relation to the key enzymes of leucine aminotransferase (LTR), phenylalanine aminotransferase (PAL), pyruvate kinase (PK) and acetyl-CoA in the amino acid metabolic pathways during the fermentation of simulated juice systems with added amino acids in order to explore the formation of characteristic aroma compounds. The addition of L-phenylalanine or L-leucine to the simulated juice systems significantly improved the activities of PK, PAL and LTR, and the content of acetyl-CoA, and significantly increased the concentrations of phenylethyl alcohol, octanoic acid, isoamyl acetate, phenylethyl acetate, ethyl hexanoate and ethyl caprylate during fermentation. Correlation analysis showed that there was a significant positive correlation between PAL, LTR, PK and acetyl-CoA and pyruvic acid formation. Path analysis revealed that the addition of amino acids affected the metabolism of pyruvate to alcohols, acids and esters to some extent.

Identifying markers volatiles in Brazilian virgin oil by multiple headspace solid-phase microextraction, and chemometrics tools

A protocol was optimized to determine the volatile profile from monovarietal virgin olive oil (VOO) by multiple headspace solid-phase microextraction (MHS-SPME) followed by gas chromatography-mass spectrometry (GC–MS) analysis. For this, a Plackett-Burman (PB) and central composite rotational designs (CCRD) were used to define the best condition of extraction. Moreover, fatty acids profile and principal component analysis (PCA) was used to identify markers among the cultivars. The amount of 0.1 g of sample was enough to express the volatile composition of the olive oils by MHS-SPME. Volatile compounds [nonanal, (Z)-3-Hexen-1-ol, (Z)-3-Hexenyl Acetate, Hexyl Acetate, 3-Methylbutyl Acetate, (E)-2-Hexen-1-ol, (E)-2-Hexenyl Acetate] and fatty acids [C17:1, C18, C18:1, C18:2] were those reported such as the markers in the varieties of olive oils. The PCA analysis allowed the classification of the most representative volatiles and fatty acids for each cultivar. Through two principal components was possible to obtain 81.9% of explanation of the variance of the compounds. The compounds were quantified using a validated method. The MHS-SPME combined with multivariate analysis showed a promising tool to identify markers and for the discrimination of olive oil varieties.

Characterization of the Aroma Profile of Commercial Prosecco Sparkling Wines

In this work, the aromatic characterization of commercially available Prosecco wines with a price range between EUR 7 and 13 was carried out. These wines came from three different areas of origin: Valdobbiadene, Asolo and Treviso. Seventy volatile compounds were identified and quantified in the wines. Quantitatively, the wines were mainly characterized by compounds of fermentation origin (alcohols, acids, esters), and C6-alcohols, and to a lesser extent, terpenes, low molecular weight volatile sulfur compounds (VSC), and benzenoids. To determine their impact on the aroma of Prosecco wine, the respective OAVs were calculated. The molecules with higher OAV were ethyl hexanoate, isoamyl acetate, and β-damascenone. More generally, esters, responsible for fruity notes, seemed to play a major role in the aroma of Prosecco wine. Investigation into the possible effect of different production zones indicated 16 significantly different compounds accounting for differences between the various areas of origin of the wines, being mostly VSC, esters and C6-alcohols. A sensory evaluation through a sorting task highlighted the formation of clusters; wine samples were divided into two main groups partially attributable to the areas of origin. From a chemical point of view, cluster A was richer in esters, while cluster B had, on average, higher concentrations of compounds associated with wine aging such as cyclic terpenes, norisoprenoids (TDN and vitispirane), and VSC.

Research on flavor characteristics of beef cooked in tomato sour soup by gas chromatography-ion mobility spectrometry and electronic nose

Tomato sour soup beef (TSSB), which is beef cooked with tomato sour soup (TSS), is nutritious and tastes “meaty and sour”, however, effect on beef flavor characteristics at the molecular level remains unclear. Gas chromatography-ion mobility spectrometry (GC-IMS), in combination with an electronic nose, was used to determine flavor differences with cooking time. A total of 74 volatile flavor compounds (VFCs) was identified by GC-IMS. In TSSB, relative contents of esters, alcohols, ketones and acids increased, whereas aldehydes decreased, relative to control cooked beef. E-nose analysis found differences in aroma characteristics of TSSB at different stages of cooking. Sensory analysis showed that TSSB had improved taste and flavor. A total of 24 VFCs was identified by orthogonal partial least squares discriminant analysis (OPLS-DA), of which 2-methyl propionate ethyl ester, isoamyl acetate, isobutyl butanoate, isoamyl butanoate, propionate, benzaldehyde and 2-butanone (D) were the characteristic VFCs of TSSB. Correlation analysis indicated that lactic, citric and succinic acids were positively correlated with ethyl 2-methylpropanoate, isoamyl acetate, isopentyl butanoate, isobutyl butanoate, benzaldehyde and 2-butanone (D). Cooking beef in TSS decreased the relative content of aldehydes and increased that of esters, alcohols, ketones and acids, further improving the flavor and sensory quality of the beef.

Discovering Aethina tumida responses to attractant and repellent molecules: A potential basis for future management strategies

Small hive beetle (Aethina tumida) management has been highly dependent upon chemical and mechanical control over the past two decades; however, many of these methods have not been consistently effective or safe for European honey bee (Apis mellifera) colonies. Here we explore the behavioral and physiological effects of the attractants isopentyl acetate and pollen patty upon A. tumida adults, and also investigate the mixture of attractants with repellent compounds, which were previously untested against A. tumida. Electroantennograms established sensitivity of A. tumida antennae to both attractants and all repellents with the exception of DEET, with antennae displaying greatest sensitivity to the repellent pyrrolidine. A walking-response olfactometer, designed specifically for A. tumida, was used for all behavioral experiments. It was found that both pollen patty and isopentyl acetate were attractive to A. tumida adults; conversely, mixes of attractants and repellent volatiles led to less attraction or avoidance of what was previously a significantly attractive source. Of all repellents tested, pyrrolidine was found to be the most repelling molecule, with significant avoidance of the attractive source at a 10 mg treatment of pyrrolidine. The results of this study indicate that, at the behavioral level, the repellent compounds pyrrolidine and 1,4-dimethylpiperazine resulted in a negative preference index indicating a repellent behavioral response. By strategically implementing a repellent source in an apiary environment, A. tumida adults could be deterred from entering and invading hives.

Geosmin suppresses defensive behaviour and elicits unusual neural responses in honey bees

Geosmin is an odorant produced by bacteria in moist soil. It has been found to be extraordinarily relevant to some insects, but the reasons for this are not yet fully understood. Here we report the first tests of the effect of geosmin on honey bees. A stinging assay showed that the defensive behaviour elicited by the bee’s alarm pheromone component isoamyl acetate (IAA) is strongly suppressed by geosmin. Surprisingly, the suppression is, however, only present at very low geosmin concentrations, and disappears at higher concentrations. We investigated the underlying mechanisms at the level of the olfactory receptor neurons by means of electroantennography, finding the responses to mixtures of geosmin and IAA to be lower than to pure IAA, suggesting an interaction of both compounds at the olfactory receptor level. Calcium imaging of the antennal lobe (AL) revealed that neuronal responses to geosmin decreased with increasing concentration, correlating well with the observed behaviour. Computational modelling of odour transduction and coding in the AL suggests that a broader activation of olfactory receptor types by geosmin in combination with lateral inhibition could lead to the observed non-monotonic increasing–decreasing responses to geosmin and thus underlie the specificity of the behavioural response to low geosmin concentrations.

Analysis of volatile compounds production kinetics: A study of the impact of nitrogen addition and temperature during alcoholic fermentation.

Among the different compounds present in the must, nitrogen is an essential nutrient for the management of fermentation kinetics, also playing a major role in the synthesis of fermentative aromas. Fermentation temperature is yet another variable that affects fermentation duration and the production of fermentative aromas in wine. The main objective of this study was thus to evaluate the combined effects of nitrogen addition-at the start of the fermentation process or during the stationary phase-at different fermentation temperatures on both fermentation kinetics and aroma synthesis kinetics. To study the impact of these three parameters simultaneously, we used an innovative transdisciplinary approach associating an online GC-MS system with an original modeling approach: a Box-Behnken experimental design combined with response surface modeling and GAM modeling. Our results indicated that all three factors studied had significant effects on fermentation and aroma production kinetics. These parameters did not impact in the same way the different families of volatile compounds. At first, obtained data showed that reduction of ester accumulation in the liquid phase at high temperature was mainly due to important losses by evaporation but also to modifications of yeast metabolic capabilities to synthetize these compounds. In a noticeable way, optimal temperature changed for liquid accumulation of the two classes of esters-23°C for acetate ester and 18°C for ethyl esters-because biological impact of temperature was different for the two chemical families. Moreover, the study of these three factors simultaneously allowed us to show that propanol is not only a marker of the presence of assimilable nitrogen in the medium but above all a marker of cellular activity. Finally, this work enabled us to gain a deeper understanding of yeast metabolism regulation. It also underlines the possibility to refine the organoleptic profile of a wine by targeting the ideal combination of fermentation temperature with initial and added nitrogen concentrations. Such observation was particularly true for isoamyl acetate for which interactions between the three factors were very strong.

Volatiles produced by symbiotic yeasts improve trap catches of Carpophilus davidsoni (Coleoptera: Nitidulidae): an important pest of stone fruits in Australia.

Carpophilus davidsoni (Dobson) is an important pest of Australian stone fruit. Current management practices for this beetle include the use of a trap that contains an attractant lure comprised of aggregation pheromones and a 'co-attractant' mixture of volatiles from fruit juice fermented using Baker's yeast, Saccharomyces cerevisiae (Hansen). We explored whether volatiles from yeasts Pichia kluyveri (Bedford) and Hanseniaspora guilliermondii (Pijper), which are closely associated with C. davidsoni in nature, might improve the effectiveness of the co-attractant. Field trials using live yeast cultures revealed that P. kluyveri trapped higher numbers of C. davidsoni compared to H. guilliermondii, and comparative GC-MS of volatile emissions of the two yeasts led to the selection of isoamyl acetate and 2-phenylethyl acetate for further investigation. In subsequent field trials, trap catches of C. davidsoni were significantly increased when 2-phenylethyl acetate was added to the co-attractant, compared to when isoamyl acetate was added, or both isoamyl acetate and 2-phenylethyl acetate. We also tested different concentrations of ethyl acetate in the co-attractant (the only ester in the original lure) and found contrasting results in cage bioassays and field trails. Our study demonstrates how exploring volatile emissions from microbes that are ecologically associated with insect pests can result in more potent lures for use in integrated pest management strategies. Results from laboratory bioassays screening volatile compounds should be treated with caution when making inferences regarding attraction under field conditions.

Aroma characterization and in vitro antihypertensive activity of Amazonian Camu-camu ( Myrciaria dubia) fruit

The Amazonian fruit known as camu-camu (Myrciaria dubia) has recently attracted attention due to its sensory and biofunctional properties. A sensomics methodology was used to identify the odour-active volatiles of the whole fruit (pulp and peel) by using solvent-assisted flavour evaporation (SAFE), analysis by gas chromatography-mass spectrometry (GC-MS), and gas chromatography-olfactometry (GC-O), and sensory evaluation (aroma extract dilution analysis (AEDA)) techniques. Four odour-active volatile compounds were reported at concentrations above the odour-activity values: isoamyl acetate, α-pinene, limonene, and β-caryophyllene. Recombination aroma testing further verified that the compounds contributed to the fruity, herbal, citrus, and woody notes of the M. dubia fruit. Furthermore, the fruit in vitro ACE-I inhibition activity was 39.48 ± 12.09 % (at 50 mg/mL, using lisinopril as positive control), showing a potential use as a functional food.

Defense Behavior of Honeybee Apis mellifera L. Hives: A Review

Al-Etby, M.A.A.W. 2023. Defense Behavior of Honeybee Apis mellifera L. Hives: A Review. Arab Journal of Plant Protection, 41(1): 85-92. https://doi.org/10.22268/AJPP-41.1.085092 Beekeeping is an important agricultural activity that contributes to increasing agricultural production. Therefore, it has received a lot of attention through the ages. Despite this importance, it is still facing many problems in all countries especially in Iraq. One of the obstacles of honeybee industry development is the aggressive behavior of this beneficial insect. This review examined the complex integration of external stimuli, reactions, and response to olfactory, visual, and mechanical signals. It was concluded that the strength of the colony, its queen health, her production of eggs, and the abundance of food sources, all have a role in determining the aggressiveness of bees. The physiological explanation of this behavior is the secretion of alarming pheromone, isopentyl acetate, which leads to an increase in the level of serotonin and dopamine in the brains of bee workers. Moreover, the location of the olfactory and visual receptors, and the number of sensory cells in the antennae, which varies according to honeybee races, resulted in a complex response of defensive reactions that include guarding, recruiting, alerting, attracting, culminating, biting, stinging, and pursuing. Keywords: Defense behavior, aggressiveness, venom gland, alarm pheromones, honeybees.

Effect of DAP and glutamine supplementation on sulfur-containing volatiles and sensory properties of Chardonnay wine fermented with Saccharomyces cerevisiae yeast.

Volatile compounds in wine have a critical impact on the consumers' senses. In this study, the effect of diammonium phosphate (DAP) and glutamine on sulfur-containing volatiles and sensory properties of Chardonnay wine fermented with Saccharomyces cerevisiae yeast were evaluated. Fermentation kinetics was determined by monitoring reducing sugar consumption rates during fermentation. The volatile profile of wines was analyzed by headspace solid phase microextraction (HS-SPME) coupled with gas-chromatography-mass spectrometry (GC-MS). The volatile sulfur compounds (VSCs) were analyzed by HS-SPME-GC-MS/MS. Flavor attributes of wines were assessed by a sensory panel with quantitative descriptive analysis. A total of 53 volatiles, including 6 VSCs, were identified and quantified in the Chardonnay wine. The results suggested that glutamine supplementation at the beginning of fermentation could help to initiate fermentation earlier and promote the formation of isoamyl acetate, phenethyl acetate, ethyl nonanoate, methyl decanoate, diethyl succinate and phenethyl alcohol, isobutanol, while DAP supplementation had no obvious effect on the volatile composition of the resulting wine and fermentation kinetics. PRACTICAL APPLICATION: Suitable nitrogen source is helpful to a healthy fermentation, and can also prevent the off-flavor and regulate aroma profile of wine. This study provides insights on the volatile and sensory characteristics of Chardonnay wines affected by different nitrogen source addition.