Aroma Volatile Production Research Articles

Effects of enzymatic reaction on the generation of key aroma volatiles in shiitake mushroom at different cultivation substrates.

Aroma is an important factor affecting mushroom character and quality. According to the different reaction pathway, the key aroma metabolites (sulfur and eight‐carbon volatiles) formation can be classified into enzymatic reactions and nonenzymatic reactions. Aroma volatiles are generated from precursors via the biocatalytic activities of various synthases during the growth stages of shiitake mushrooms. Understanding the specific relationships between the key aroma metabolites and their synthases is key to improving shiitake mushroom quality. At the same time, to reduce forest logging and burning of agricultural by‐products in farmland, agricultural by‐products have been applied to shiitake mushroom cultivation. Nevertheless, how to further improve the production of aroma volatiles in mushroom cultivated with agricultural waste is still a challenge. In order to understand the biosynthesis of volatiles via enzymatic reactions and screen the agricultural by‐products that can improve the production of aroma volatiles in mushroom cultivation, the mechanism of producing aroma volatiles needs to be further elucidated. In this study, the activities and gene expression levels of the key synthases involved in volatile metabolism, the contents of key aroma volatiles, and the correlations between related synthetase, volatiles, and cultivation substrate (CS) were investigated. Network models for visualizing the links between synthetase, volatiles, and CSs were built through partial least squares (PLS) regression analysis. The correlation coefficients among three related synthetase and enzymatic gene expression were high, and the combined effects of multiple synthetase promoted the production of volatiles. PLS analysis showed that the corncob and corn meal were more related to the production of volatiles and synthetase gene expression, and they can be added to the CSs as flavor promoting substances. The enrichment of key aroma volatiles in shiitake mushroom cultivated by the gradient of 20% corn meal combination CS was noticeable.

Pre-storage application of 1-methylcyclopropene does not affect the flavour of ‘Conference’ pears ripened after 8 months of commercial-standard controlled atmosphere storage

Postharvest 1-methylcyclopropene (1-MCP) applications are commercially used on ‘Conference’ pears to obtain an improved fruit quality after storage for up to 11 months. Treatment with 1-MCP may result in firmer and greener fruit at the end of storage. During subsequent shelf life, 1-MCP treated pears may show slower ripening, including a reduced rate of softening and a reduced production of aroma volatiles. The lower levels of aroma volatiles and consumer complaints of reduced flavour suggest that flavour is negatively affected by 1-MCP treatments, which has raised concern within in the Dutch fruit industry.In the present study, the effect of pre-storage 1-MCP treatment on post-storage ripening and flavour perception was studied. Untreated and 1-MCP-treated pears (325 nL L−1) were stored for 8 months at -0.8 °C under controlled atmosphere conditions of 3 kPa O2 and 0.6 kPa CO2 according to commercially used protocols. At day 7 and 9 of the subsequent shelf life at 10 °C, 1-MCP-treated fruit showed decreased yellowing and ethylene production, whereas firmness was similar to that of untreated fruit. The production of aroma volatiles was significantly reduced in 1-MCP-treated fruit; this was especially observed for different acetate esters, ethanol and butanol. Despite the reduction in aroma volatiles, a consumer panel could not distinguish (in a Tetrad test) between samples from untreated and 1-MCP-treated fruit with similar firmness. This indicates that the important aroma volatiles, although reduced in abundance, were still above threshold levels and did not affect overall flavour perception. We conclude that 1-MCP does not affect flavour when pears within equal firmness classes are compared.

Brewing potential of the wild yeast species Saccharomyces paradoxus

Saccharomyces paradoxus is commonly isolated from environmental samples in Northern Europe and North America, but is rarely found associated with fermentation. However, as novelty has become a selling point in beer markets, interest toward non-conventional and local yeasts is increasing. Here, we report the first comprehensive investigation of the brewing potential of the species. Eight wild strains of S. paradoxus were isolated from oak trees growing naturally in Finland, screened in a series of fermentation trials and the most promising strain was selected for lager beer brewing at pilot scale (40 l). Yeasts were evaluated according to their ability to utilize wort sugars, their production of flavour-active aroma volatiles, diacetyl and organic acids, and sensorial quality of beers produced. All strains could assimilate maltose but this occurred after a considerable lag phase. Once adapted, most wild strains reached attenuation rates close to 70%. Adaptation to maltose could be maintained by re-pitching and with appropriate handling of the adapted yeast. Fermentation at 15 °C with the best performing strain was completed in 17 days. Maltose was consumed as efficiently as with a reference lager yeast, but no maltotriose use was observed. Bottled beers were evaluated by a trained sensory panel, and were generally rated as good as, or better than, reference beers. S. paradoxus beers were considered full-bodied and had a relatively clean flavour profile despite the presence of the clove-like 4-vinyl guaiacol. In conclusion, S. paradoxus exhibits a number of traits relevant to brewing, and with appropriate handling could be applied industrially.

Effect of Thidiazuron on Terpene Volatile Constituents and Terpenoid Biosynthesis Pathway Gene Expression of Shine Muscat (Vitis labrusca × V. vinifera) Grape Berries.

Volatile compounds are considered to be essential for the flavor and aroma quality of grapes. Thidiazuron (TDZ) is a commonly used growth regulator in grape cultivation that stimulates larger berries and prevents fruit drop. This study was conducted to investigate the effect of TDZ on the production of aroma volatiles and to identify the key genes involved in the terpene biosynthesis pathways that are affected by this compound. Treatment with TDZ had a negative effect on the concentration of volatile compounds, especially on monoterpenes, which likely impacts the sensory characteristics of the fruit. The expression analysis of genes related to the monoterpenoid biosynthesis pathways confirmed that treatment with TDZ negatively regulated the key genes DXS1, DXS3, DXR, HDR, VvPNGer and VvPNlinNer1. Specifically, the expression levels of the aforementioned genes were down-regulated in almost all berry development stages in the TDZ-treated samples. The novel results from the present study can be used to aid in the development of food products which maintain the flavor quality and sensory characteristics of grape. Furthermore, these findings can provide the theoretical basis that can help to optimize the utilization of TDZ for the field production of grapes at a commercial scale.

Novel microRNAs regulating ripening-associated processes in banana fruit

MicroRNAs (miRNAs) modulate gene expression and regulate various physiological and developmental processes in plants. During fruit ripening phase, several physiological and biochemical variations take place resulting changes in colour and texture, softening and production of aroma volatiles. A number of pathways leading to cell wall hydrolysis, ethylene signaling, biosynthesis of fatty acids, esters and a number of secondary plant products play important role during fruit ripening. However, detailed analysis of various processes regulated by miRNAs has not been studied in detailed in a number of fruits. In this study, we sequenced small RNA libraries from ripe and un-ripe fruit of Banana (Musa acuminata), an important and staple food crop, to identify miRNAs regulating fruit ripening. Our analysis identified a number of novel miRNAs which are differentially expressed during fruit ripening. These novel miRNAs were analyzed for their precursors, chromosome localization and targets. Some of these miRNAs were identified to target genes involved in miRNA biogenesis, fruit softening and aroma biosynthesis. This study advances our knowledges in the area of fruit ripening process regulated by miRNAs.

Low Temperature Storage Stimulates Fruit Softening and Sugar Accumulation Without Ethylene and Aroma Volatile Production in Kiwifruit.

Fruit ripening in response to propylene (an ethylene analog), 1-methylcyclopropene (1-MCP, an ethylene action inhibitor), and low temperature (5°C) treatments was characterized in “Kosui” kiwifruit (Actinidia rufa × A. chinensis). Propylene treatment induced ethylene production, with increased expression levels of 1-aminocyclopropane-1-carboxylic acid (ACC) synthase 1 (AcACS1) and ACC oxidase 2 (AcACO2), and rapid fruit softening together with increased expression levels of polygalacturonase (AcPG) and expansin 1 (AcEXP1) within 5 days (d). Fruit soluble solids concentration (SSC) and contents of sucrose, glucose, and fructose together with the expression levels of β-amylase 1 (Acβ-AMY1), Acβ-AMY2, and invertase (AcINV3-1) increased rapidly after 5 d exposure to propylene. Furthermore, propylene exposure for 5 d was sufficient to induce the production of key aroma volatile compounds, ethyl- and methyl butanoate, accompanied with increased expression levels of alcohol acyl transferase (AcAAT). Application of 1-MCP at the start of the experiment, followed by continuous exposure to propylene, significantly delayed fruit softening, changes in SSC and sugars, and strongly suppressed the production of ethylene, aroma volatiles, and expression of associated genes. During storage, fruit softening, SSC and sugar increase, and increased expression of genes associated with cell wall modification and carbohydrate metabolism were registered without detectable ethylene production; however, these changes occurred faster at 5°C compared to 22°C. Interestingly, ethyl and methyl butanoate as well as AcAAT expression were undetectable in kiwifruit during storage, while they were rescued by post-storage propylene exposure, indicating that the production of aroma volatile compounds is strongly ethylene-dependent. Transcript levels of a NAC-related transcription factor (TF), AcNAC3, increased in response to both propylene and low temperature treatments, while AcNAC5 was exclusively up-regulated by propylene. By contrast, transcript levels of a MADS-box TF, AcMADS2, exclusively increased in response to low temperature. The above findings indicate that kiwifruit ripening is inducible by either ethylene or low temperature signals. However, fruit ripened by low temperature were deficient in ethylene-dependent aroma volatiles, suggesting that ethylene signaling is non-functional during low temperature-modulated ripening in kiwifruit. These data provide further evidence that ethylene-dependent and low temperature-modulated ripening in kiwifruit involve different regulatory mechanisms.

Induced Ripening Agents and Their Effect on Fruit Quality of Banana

Ripening is a genetically programmed highly coordinated irreversible phenomenon which includes many biochemical changes including tissue softening, pigment changes, aroma and flavour volatile production, reduction in astringency, and many others. Banana is one of mostly consumed fruit crops in the world. Since banana is a climactic fruit, induced ripening is essential in commercial scale banana cultivation and distribution to assure good flavour, texture, and uniform peel colour. Ethylene gas, acetylene gas liberated from calcium carbide, and ethephon are some of the commercial ripening agents used successfully in the trade and they have been widely studied for their effectiveness on initiating and accelerating the ripening process and their effect on fruit quality and health related issues. Lauryl alcohol was also shown as a ripening agent for bananas. Most studies suggest that there is no difference in biochemical composition and sensory quality in bananas treated with chemicals that induce ripening from naturally ripened bananas. However volatile profiles of artificially ripened bananas were shown to be considerably different from naturally ripened bananas in some studies. This review discusses induced ripening agents and their effect on fruit quality of bananas.

Canopy attachment position influences metabolism and peel constituency of European pear fruit

BackgroundInconsistent pear fruit ripening resulting from variable harvest maturity within tree canopies can contribute to postharvest losses through senescence and spoilage that would otherwise be effectively managed using crop protectant and storage regimes. Because those inconsistencies are likely based on metabolic differences, non-targeted metabolic profiling peel of ‘d’Anjou’ pears harvested from the external or internal canopy was used to determine the breadth of difference and link metabolites with canopy position during long-term controlled atmosphere storage.ResultsDifferences were widespread, encompassing everything from expected distinctions in flavonol glycoside levels between peel of fruit from external and internal canopy positions to increased aroma volatile production and sucrose hydrolysis with ripening. Some of the most substantial differences were in levels of triterpene and phenolic peel cuticle components among which acyl esters of ursolic acid and fatty acyl esters of p-coumaryl alcohol were higher in the cuticle of fruit from external tree positions, and acyl esters of α-amyrin were elevated in peel of fruit from internal positions. Possibly the most substantial dissimilarities were those that were directly related to fruit quality. Phytosterol conjugates and sesquiterpenes related to elevated superficial scald risk were higher in pears from external positions which were to be potentially rendered unmarketable by superficial scald. Other metabolites associated with fruit aroma and flavor became more prevalent in external fruit peel as ripening progressed and, likewise, with differential soluble solids and ethylene levels, suggesting the final product not only ripens differentially but the final fruit quality following ripening is actually different based on the tree position.ConclusionsGiven the impact tree position appears to have on the most intrinsic aspects of ripening and quality, every supply chain management strategy would likely lead to diverse storage outcomes among fruit from most orchards, especially those with large canopies. Metabolites consistently associated with peel of fruit from a particular canopy position may provide targets for non-destructive pre-storage sorting used to reduce losses contributed by this inconsistency.

Effects of 1-MCP in combination with Ca application on aroma volatiles production and softening of ‘Fuji’ apple fruit

Abstract 1-Methylcyclopropene (1-MCP) can maintain the physical quality of climacteric fruits, such as apple and pear, but inhibit aroma volatile production and fruit flavor. In this study, the effects of calcium (Ca) in combination with 0.6 and 1.0 μL L−1 1-MCP on flesh firmness and aroma volatiles has been investigated on ‘Fuji’ apples stored at room temperature. Results from electronic nose detection and texture evaluation showed that 1-MCP of reduced concentration (0.6 μLL−1), but not 1.0 μL L−1, presented an interactive effect with Ca application on promoting volatile emission and reducing softening. The amount of branched and straight esters and total aroma volatiles, as well as related enzymes including aromatase-related acyltransferase (AAT), alcohol dehydrogenase (ADH), and pyruvate decarboxylase (PDC), were significantly higher in fruit treated with (1-MCP 0.6 + Ca) than 1-MCP 1.0 after 50 and 100 days storage. There was no significant difference between two treatments of (1-MCP 0.6 + Ca) and 1-MCP 1.0 in maintaining fruit firmness. Fruit treated with (1-MCP 0.6 + Ca) had higher aroma quality than 1-MCP 1.0 according to sensory evaluation, but showed no significant difference in terms of texture quality. In conclusion, 1-MCP of reduced concentration combined with Ca treatment had synergetic effect on the aroma formation and softening inhibition of apple fruit, resulting in advanced sensory quality.

Overexpression of mango alcohol dehydrogenase (MiADH1) mimics hypoxia in transgenic tomato and alters fruit flavor components

Plant alcohols and aldehydes are produced by the action of alcohol dehydrogenases (ADH) and play an important role during fruit ripening and aroma production. Alcohols are not only produced in different tissues at different stages of plant development but are also products of the fermentative pathway which gets activated by different stresses, including hypoxia. The ADH gene is a well-established marker for hypoxic response as well as plant aroma. In a previous report we have identified and characterized three ADHs (MiADH1, 2, 3) from Dashehari mango. MiADH1 was found to be fruit specific and was upregulated by ethylene and ABA, suggesting a role in fruit aroma volatile production. In order to functionally characterize MiADH1, transgenic tomato plants were developed under the control of the constitutive (CaMV35S) promoter. Transgenic tomato fruit expressing MiADH1 gene showed a change in the levels of several alcohols and aldehydes related to flavor in comparison to the control. The change in aroma and volatiles compounds was more prominent during the ripe stage as compared to unripe and mid-ripe stages of tomato fruit. The transgenic tomato plants also produced adventitious roots. Our results suggest that the overexpression of MiADH1 in tomato plants induced the fermentative pathway in roots, and mimicked hypoxic response by development of adventitious roots from the stem as an adaptive mechanism.

Solid-state fermentative production of aroma esters by Myroides sp. ZB35 and its complete genome sequence

Consumers prefer biotechnological food products with high nutritional values and good flavors. Solid-state fermentation is a commonly used technique with a long history. In the present study, Myroides sp. ZB35 was used in solid-state fermentative production of aroma volatiles on a rice medium. Using the headspace solid phase microextraction coupled with gas chromatography–mass spectrometry technique and authentic standards, 22 esters with molecular weight ranging from 102 to 172 were identified. At 192h, the esters reached a total concentration of 1774μg/kg. Subsequently, the complete genome of ZB35 was sequenced using the PacBio RS II platform. ZB35 has a single circular chromosome of 4,065,010bp with a GC content of 34.1% and six putative novel esterase genes were found. ZB35 is the first bacterium here discovered being capable of producing so many kinds of aroma esters. The data revealed here would provide helpful information for further developing this strain as a promising source of aroma esters relevant in food and fragrance industries and the source of novel enzymes with potential usages.

Comparative study of the effects of black or white hail nets on the fruit quality of ‘Golden Delicious’ apples

Introduction. The use of hail nets to protect apples during development and maturation on the tree is very common in Mexico. This practice can cause changes in fruit quality and aroma composition. The effects of the hail net color on the quality and aroma volatile production of apple cultivated in Chihuahua, Mexico, were evaluated. Materials and methods. ‘Golden Delicious’ apple trees were covered with white or black hail nets. Apple samples were harvested weekly from August to early October, and analyzed for weight, axial and equatorial diameters, color (°Hue), firmness, total soluble solids (TSS), acidity, ethylene production (EC), and aroma volatile composition. The photosynthetically available radiation (PAR) was measured every ten days under each hail net and outside. Results and discussion. Apple quality was affected by hail net color. Black hail nets delayed maturation and quality development of apples by one week when compared with white hail nets. The PAR values were 18% lower under black nets than under white nets. Quality parameters at commercial harvest (162 days after full bloom) showed that white-net apples presented 7% lower firmness, 11.1% less acidity, 8.3% higher TSS and a more developed yellow color, when compared with black-net apples. In addition, white-net apples presented higher contents of the main aroma compounds (in μg L-1 ) 1-hexanol (8.09 vs. 4.38), 2-methyl-1-butanol (6.24 vs. 2.65), and 2-methyl-butyl acetate (0.47 vs. 0.16). At the same maturity stage (beginning of the climacteric rise), no difference was found between white- and black-net apples in TSS, acidity, firmness and aromatic compounds. Conclusion. Hail net functionality goes beyond protecting orchards from hail damage; hail net color affects the apple maturation rate, quality and aroma volatile production.

γ-Irradiation effects on appearance and aroma of ‘Kensington Pride’ mango fruit

γ-Irradiation doses of 0.5 (target) and 1.0 (high) kGy were applied as insect disinfestation treatments to 'Kensington Pride' mango fruit. The effects of these treatments on fruit physicochemical properties and aroma volatile production were investigated and compared to non-irradiated controls. There were no significant effects of the irradiation treatments on flesh total soluble solids content. However, the loss of green skin colour usually associated with fruit ripening was inhibited by irradiation at both 0.5 and 1.0 kGy by approximately 32 and 52%, respectively, relative to non-irradiated fruit. Fruit exposed to 0.5 and 1.0 kGy exhibited a 58 and 80% reduction in emission of a-terpinolene volatiles, respectively. Thus, γ-irradiation at 0.5 and 1.0 kGy can have an adverse effect on 'Kensington Pride' mango fruit aroma volatile production and skin colouration.

CONTROLLED ATMOSPHERE STORAGE OF MANGO FRUIT: CHALLENGES AND THRUSTS AND ITS IMPLICATIONS IN INTERNATIONAL MANGO TRADE

The highly perishable nature of mango fruit and its susceptibility to chilling injury (CI) when stored below 13°C limits its international trade. Cold storage of mango at 12-13°C is successful only for 2-3 weeks coupled with substantial losses in fruit quality. Cold storage limits the use of sea freight which is usually more economical and eco-friendly than air freight. Controlled atmosphere (CA) storage usually involves regulating the concentration of oxygen (O2) and carbon dioxide (CO2) using nitrogen, storage temperature, as well as relative humidity in the storage environment. CA in combination with an optimum storage temperature has been reported to prolong the storage life and maintain fruit quality including aroma volatiles in mango fruit depending upon the cultivar. Fruit quality is an important factor in influencing consumer preferences in international and domestic markets. CA storage seems to be promising in extending storage life, maintaining quality of mango fruit consequently offers opportunities to export mangoes to distant markets using sea freight. This overview paper will focus on fundamental and applied aspects of CA storage of mango fruit and its implications in facilitating international trade. Some research work has been reported on optimising CA conditions for different cultivars of mango as the CA requirements of mangoes vary among cultivars and inappropriate CA conditions adversely affect quality of ripe mango fruit. CA comprising of low O2 concentrations (<2%) has been reported to accumulate ethanol and adversely affect fruit quality of ‘Tommy Atkins’ and ‘Delta R2E2’ cultivars of mango. My research group has been exploring the effects of CA on extending storage life, maintaining fruit quality including aroma volatiles production in mango fruit for more than a decade. CA storage comprising 3% O2 in combination with 6% CO2 at 13°C proved to be beneficial for extending the storage life of the Australian mango cultivars ‘Kensington Pride’ and ‘R2E2’ by up to six weeks, with good fruit quality and maintaining a high concentration of the major volatile compounds responsible for the aroma of ripe mangoes. The applications of CA in preventing CI, postharvest diseases and insect disinfestations will also be discussed. The faster rate of expansion of mango production, its international trade, short shelf life, and higher susceptibility to CI, postharvest diseases, as well as consumer demand for superb quality are major challenges in extending storage life of mango fruit and their implications in international trade. CA storage offers a great potential in extending storage life of mango which enable to employ sea freight for wider distribution of mango fruit in the distant international markets in a very cost effective manner. A specific composition of O2 and CO2 in CA which extends the storage life of mango fruit is cultivar dependent and is yet inconclusive. Moreover, to minimise the negative effects of CA storage in mango such as fruit softening, poor colour development and higher titratable acidity (TA), reduced aroma and flavour are major research gaps yet to be addressed by the research in the future. CA storage offers an attractive alternative for ameliorating CI, controlling of postharvest diseases and pests in combination with preharvest technology. A holistic approach to meet market requirements considering mango production, postharvest handling including CA storage and supply chain is prerequisite for promoting international trade of mango.

Biodegradation of C5-C 8 fatty acids and production of aroma volatiles by Myroides sp. ZB35 isolated from activated sludge.

In the effluents of a biologically treated wastewater from a heavy oil-refining plant, C5-C8 fatty acids including pentanoic acid, hexanoic acid, heptanoic acid, octanoic acid, and 2-methylbutanoic acid are often detected. As these residual fatty acids can cause further air and water pollution, a new Myroides isolate ZB35 from activated sludge was explored to degrade these C5-C8 fatty acids in this study. It was found that the biodegradation process involved a lag phase that became prolonged with increasing acyl chain length when the fatty acids were individually fed to this strain. However, when fed as a mixture, the ones with longer acyl chains were found to become more quickly assimilated. The branched 2-methylbutanoic acid was always the last one to be depleted among the five fatty acids under both conditions. Metabolite analysis revealed one possible origin of short chain fatty acids in the biologically treated wastewater. Aroma volatiles including 2-methylbutyl isovalerate, isoamyl 2-methylbutanoate, isoamyl isovalerate, and 2-methylbutyl 2-methylbutanoate were subsequently identified from ZB35 extracts, linking the source of the fruity odor to these esters excreted by Myroides species. To our best knowledge, this is the first finding of these aroma esters in bacteria. From a biotechnological viewpoint, this study has revealed the potential of Myroides species as a promising source of aroma esters attractive for food and fragrance industries.

Identification of lipoxygenase (LOX) genes putatively involved in fruit flavour formation in apple (Malus × domestica)

Lipoxygenases (LOXs) are non-heme iron-containing enzymes that catalyse the dioxygenation of polyunsaturated fatty acids. The resulting hydroperoxides are further metabolized into biologically active oxylipins including jasmonic acid and green leaf volatiles (GLV) such as C6-aldehydes and C6-alcohols. LOXs are also known to play a decisive role in the production of volatiles that influence the flavour and aroma of fruits and vegetables. To obtain an overview of the inventory of the apple LOX gene family, the published Golden Delicious genome was mined for LOX coding sequences. In total, 23 putative functional LOX genes were identified and used for the construction of a phylogenetic tree. Two sub-trees were found which differentiate the LOX sequences into type 1- and type 2-LOXs. Their chromosomal locations were assigned to the predicted chromosomes of the assembled Golden Delicious genome sequence. Single LOX genes as well as clusters consisting of up to four genes were detected on apple chromosomes 2, 4, 5, 6, 7, 9, 11, 12, 13 and 16. LOX gene clusters on chromosomes 2 and 7, and on 4 and 12, respectively, indicated duplicated genome regions with high homology, which supports previous hypotheses of an ancient genome-wide duplication event in Malus. By using a PCR-based strategy, eight genes belonging to both type 1- and type 2-LOXs with altogether 30 full-length sequences were cloned. Several putative LOX alleles were detected within the same and among different apple cultivars. Two parental genetic maps available for ‘Discovery’ and ‘Prima’ were used for a quantitative trait locus (QTL) mapping experiment of apple volatile compounds known to be produced by the LOX biosynthetic pathway. The QTL detection resulted in a total number of 15 QTLs for eight volatiles (esters and the aldehyde hexanal) which were located on chromosomes 2, 7, 9 and 12 determined in silico as carriers of at least one LOX gene. To examine the putative roles of apple LOX genes in fruit volatile production, the spatial and temporal expression patterns were analysed by RT-PCR-based transcription analyses of apple leaf and fruit tissues. Two genes, MdLOX1a and MdLOX5e, were identified as candidate genes to be involved in fruit aroma volatile production in apple. The genetic association of QTLs found for the GLV hexanal at the top of chromosome 7, three clustered MdLOX5 genes with a putative 13-LOX function and published apple aphid resistance factors located all in the same region of chromosome 7 indicate that a lipoxygenase action might be involved in Malus aphid resistance reactions.

Putative role of cytokinin in differential ethylene response of two lines of antisense ACC oxidase cantaloupe melons

Two transgenic lines of ‘Cantaloupe’ melon derived from the same wild type genotype were previously generated using ACC oxidase antisense constructs from melon (pMEL1AS) and apple (pAP4AS). Both lines yielded fruit with reduced ethylene production and low ACC oxidase (ACCO) expression. ACCO antisense fruit also exhibited lower expression of ACC synthase genes, ACCS1 and ACCS3, indicating that these genes are positively regulated by ethylene and participate in the autocatalytic ethylene production process. In contrast, a higher expression of ACCS5 was observed in antisense lines when compared to the wild type indicating a negative feedback regulation of ACCS5 by ethylene. Fruit of both transformed lines exhibited delayed ripening and reduction in ester volatile production but differed in their response to exogenous ethylene supply. While postharvest ethylene application fully restored the ripening process in pMEL1AS melon, it only restored flesh softening of pAP4AS melon but not rind color change or aroma volatile production. Up-regulation of lipoxygenase pathway associated genes (hydroxyperoxide lyase, lipoxygenase, and alcohol acyl transferases 1, 3 and 4) occurred in ethylene-treated pMEL1AS fruit but not in pAP4AS melons. Polygalacturonase1 gene transcript accumulation increased in pMEL1AS and pAP4AS fruit upon ethylene supply. Zeatin and zeatin riboside content of roots and fruit (rind and flesh) of pAP4AS plants were 5-fold higher than the wild type and pMEL1AS counterparts. Higher relative transcript accumulation of a gene involved in the cytokinin synthesis and a gene involved in cytokinin response were also found in the roots and fruit of pAP4AS. In addition, polyamines, which are known to reduce sensitivity to ethylene, remained unchanged in all fruit. Collectively the results suggest a putative role for the increased endogenous cytokinin content in counteracting ethylene action in some aspects of the fruit ripening process.

CONTROLLED ATMOSPHERE STORAGE OF MANGO FRUIT - AN OVERVIEW

Highly perishable nature of mango fruit and its susceptibility to chilling injury when stored below 13°C limits its international trade. Cold storage of mango at 12-13°C is successful only for 2-3 weeks coupled with substantial losses in fruit quality. Controlled atmosphere (CA) in combination with an optimum storage temperature has been reported to prolong the storage life and maintain fruit quality including aroma volatiles in mango fruit depending upon cultivar. Fruit quality is an important factor in influencing consumer preferences in international and domestic markets. This paper will focus on fundamental and applied aspects of CA storage of mango fruit and its implications in facilitating international trade. Various researchers have attempted to optimise CA conditions for different cultivars of mango as the CA requirements of mangoes vary among cultivars and inappropriate CA conditions adversely affect quality of ripe mango fruit. CA comprising of low O2 concentrations (<2%) has been reported to accumulate ethanol and adversely affect fruit quality of 'Tommy Atkins' and 'Delta R2E2' mangoes. For about a decade, my research group has been exploring the effects of CA on extending storage life, maintaining fruit quality including aroma volatiles production in mango fruit. CA storage comprising 3% O2 in combination with 6% CO2 at 13°C seems to be promising for extending the storage life of the Australian mango cultivars 'Kensington Pride' (KP) and 'R2E2' up to six weeks, with good fruit quality and maintaining a high concentration of the major volatile compounds responsible for the aroma of ripe mangoes. The applications of CA in preventing chilling injury, postharvest diseases and insect disinfestations have also been discussed.

Determination of Aroma Volatiles in Mango Fruit Cv.Amrapalias Affected During Storage Under Rapid Control Atmosphere Conditions using Liquid Nitrogen

Green mature “amrapali” mango fruits were stored at 12 ± 0.2°C under rapid controlled atmosphere (RCA) with various combinations of two levels of oxygen (2 or 5%) and 3 levels of carbon dioxide (4, 6 or 8%) to investigate the effect of RCA on the production of aroma volatiles both in the raw fruit and after ripening at 21°C for 5 days. The RCA conditions were established by flushing calculated amounts of liquid nitrogen (LN2) into the storage chamber. Whole fruit samples were removed from storage at weekly intervals and analysed for volatiles with a headspace purge and trap system. Terpene hydrocarbons were found to be the dominant group for the raw fruits while esters were the major component of the volatiles for the ripe fruit. Production of aroma volatiles on ripening was found to be higher in the freshly harvested fruit, with lower level of O2 and elevated level of CO2 inhibiting production of volatiles especially for hydrocarbons and esters. Mathematical equations using polynomial regression were found to closely predict the values of total aroma volatile classes. The RCA stored ripened fruits were found to be sensorily acceptable, even though it scored lower compared to control fruits, the difference was not significant.

VARIABILITY IN WAXING-INDUCED ETHANOL AND AROMA VOLATILE PRODUCTION AMONG MANDARIN GENOTYPES

VARIABILITY IN WAXING-INDUCED ETHANOL AND AROMA VOLATILE PRODUCTION AMONG MANDARIN GENOTYPES