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A pinboard by
A S M Mainul Hasan

I am a researcher having very good skills and knowledge in the field of Molecular Plant Genetics.

My research interests are mainly focused on understanding the underlying molecular mechanism driving different quality and resistant traits in plants. Due to the climate change aspect in recent years, I have eagerness about scientific topics in developmental biology as well.

PINBOARD SUMMARY

Consumer preference is crucial for designing chemical and genetics studies involving fruit flavour.

Flavour could be regarded as combination of senses which are integrated in our brain to inform us about the type of food that we are eating. Determination of flavour is dependent on receptors that perceive taste and smell. Five different types of receptors in our mouth regulate taste which quantify the amount of sweet, sour, salt, bitter and umami present in a food. On the other hand, a large number of olfactory receptors present in the nose assist in perceiving smell by recognizing various volatiles (organic compounds that transforms into gas phase due to high vapor pressure under room temperature).

Different chemicals that interact with taste and smell associated receptors in human body are components of fruit flavor. Such chemicals primarily include various sugars such as glucose, sucrose, fructose and sorbitol which are present in high amount in a range of fruits when they ripe. Besides, various acids such as citrate, malate and ascorbate contribute towards flavour. Likewise, a range of volatiles are present in different fruits that plays role in governing the ultimate flavour. For instance, tomato, apple and kiwifruit carries more than 400, 300 and 80 volatiles respectively. Within the human body, certain receptors could recognize a number of volatiles whereas certain volatiles could be perceived by various receptors. Human odour threshold is dependent on optimum level of volatiles, and negative influence upon flavour by a particular volatile could be exerted if this threshold is crossed.

The favour phenotype is very difficult to study for molecular plant geneticists because chemical composition of fruit flavor varies widely and is regulated by many genes (polygenic), environment and agronomic practices. Identification of genes that regulate the synthesis of key flavors chemicals is important to produce plant varieties that are not just disease resistant and high yielding, rather also possess appropriate flavour. Recent development in genome sequencing platform has given a significant boost in molecular genetics based research in this direction. In tomato, a gene locus mediating synthesis of three key phenylalanine derived volatiles have been discovered. In strawberry, identification of a gene called ANTHRANILIC ACID METHYL TRANSFERASE (AAMT) is considered to be important in restoring a key flavour related volatile, methyl anthranilate (MA). In another study, genes responsible for the synthesis of a type of volatile called cucurbitacins which contribute to bitterness in cucumber, melon and watermelon was identified through genomics studies.

Most commonly, the production of fruit is determined by priority of the producer which in turn depend on total cost related to yield, pest management, harvesting and post-harvesting procedures. The end users, i.e., customers are usually kept out in this process even though certain consumer liking rating are being carried out to a certain degree. However, the road ahead lies in developing strategies that involve consumer preference studies, thereby determining which flavor they like or dislike and then undertake relevant sensory and chemical analysis followed by deciphering the underlying genetic process that regulate the respective flavour. This should ultimately lead to introgression of the identified genes via molecular breeding into existing commercial fruit varieties.

8 ITEMS PINNED

Chemical Studies of Yellow Tamarillo (Solanum betaceum Cav.) Fruit Flavor by Using a Molecular Sensory Approach.

Abstract: The odor-active volatile compounds of yellow tamarillo fruit (S. betaceum Cav.) were identified and quantified by using a sensomics approach, combining a gentle volatile extraction (solvent-assisted flavor evaporation (SAFE)), gas chromatography-mass spectrometry (GC-MS), and sensory analyses (gas chromatography-olfactometry (GC-O) and aroma extract dilution analysis (AEDA)). The medium-term purpose of this work is to evaluate the change of odor-active volatiles during processing. Thus, (Z)-3-hexenal, hexanal, and ethyl butanoate were identified as key aroma compounds of yellow tamarillo. The C₆-aliphatic compounds, aliphatic esters, and terpenols were characterized as the volatiles responsible for the herbal-green, fruity, and fresh-mint odor notes of this variety, respectively. Additionally, one non-volatile compound contributing to the residual bitter taste of this fruit was isolated by a bioguided (taste sensory analyses) fractionation. The freeze-dried fruit was sequentially liquid-liquid partitioned with solvents of different polarity, and then the ethyl acetate fraction was submitted to size exclusion chromatography. Then, its structure was elucidated as rosmarinic acid, by using common spectroscopic methods (mass spectrometry (MS) and nuclear magnetic resonance (NMR)). The amount of rosmarinic acid was quantified as 46.17 ± 1.20 mg/100 g of dried fruit, by the external standard method. Its bitter taste threshold value was determined by using the 3AFC (alternative forced choice) method to be 37.00 ± 1.25 mg/L.

Pub.: 22 Dec '16, Pinned: 08 Jul '18

Gain and loss of fruit flavor compounds produced by wild and cultivated strawberry species.

Abstract: The blends of flavor compounds produced by fruits serve as biological perfumes used to attract living creatures, including humans. They include hundreds of metabolites and vary in their characteristic fruit flavor composition. The molecular mechanisms by which fruit flavor and aroma compounds are gained and lost during evolution and domestication are largely unknown. Here, we report on processes that may have been responsible for the evolution of diversity in strawberry (Fragaria spp) fruit flavor components. Whereas the terpenoid profile of cultivated strawberry species is dominated by the monoterpene linalool and the sesquiterpene nerolidol, fruit of wild strawberry species emit mainly olefinic monoterpenes and myrtenyl acetate, which are not found in the cultivated species. We used cDNA microarray analysis to identify the F. ananassa Nerolidol Synthase1 (FaNES1) gene in cultivated strawberry and showed that the recombinant FaNES1 enzyme produced in Escherichia coli cells is capable of generating both linalool and nerolidol when supplied with geranyl diphosphate (GPP) or farnesyl diphosphate (FPP), respectively. Characterization of additional genes that are very similar to FaNES1 from both the wild and cultivated strawberry species (FaNES2 and F. vesca NES1) showed that only FaNES1 is exclusively present and highly expressed in the fruit of cultivated (octaploid) varieties. It encodes a protein truncated at its N terminus. Green fluorescent protein localization experiments suggest that a change in subcellular localization led to the FaNES1 enzyme encountering both GPP and FPP, allowing it to produce linalool and nerolidol. Conversely, an insertional mutation affected the expression of a terpene synthase gene that differs from that in the cultivated species (termed F. ananassa Pinene Synthase). It encodes an enzyme capable of catalyzing the biosynthesis of the typical wild species monoterpenes, such as alpha-pinene and beta-myrcene, and caused the loss of these compounds in the cultivated strawberries. The loss of alpha-pinene also further influenced the fruit flavor profile because it was no longer available as a substrate for the production of the downstream compounds myrtenol and myrtenyl acetate. This phenomenon was demonstrated by cloning and characterizing a cytochrome P450 gene (Pinene Hydroxylase) that encodes the enzyme catalyzing the C10 hydroxylation of alpha-pinene to myrtenol. The findings shed light on the molecular evolutionary mechanisms resulting in different flavor profiles that are eventually selected for in domesticated species.

Pub.: 04 Nov '04, Pinned: 08 Jul '18

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

Abstract: 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.

Pub.: 31 Aug '13, Pinned: 08 Jul '18