Methional is an

organic compound Some chemical authorities define an organic compound as a chemical compound that contains a carbon–hydrogen or carbon–carbon bond; others consider an organic compound to be any chemical compound that contains carbon. For example, carbon-co ...

with the formula CH₃SCH₂CH₂CHO. It is a colorless liquid that is a degradation product of

methionine Methionine (symbol Met or M) () is an essential amino acid in humans. As the precursor of other non-essential amino acids such as cysteine and taurine, versatile compounds such as SAM-e, and the important antioxidant glutathione, methionine play ...

. It is a notable flavor in potato-based snacks, namely potato chips, one of the most popular foods containing methional.Faith C. Belanger, Rong Di & Daphna Havkin-Frenkel (2009) Increasing the Methional Content in Potato through Biotechnology, Biotechnology in Flavor Production, 185-188, Traces of the compound can also be found in black tea and green tea based products. Methional contains both

aldehyde In organic chemistry, an aldehyde () (lat. ''al''cohol ''dehyd''rogenatum, dehydrogenated alcohol) is an organic compound containing a functional group with the structure . The functional group itself (without the "R" side chain) can be referred ...

and

thioether In organic chemistry, a sulfide (British English sulphide) or thioether is an organosulfur functional group with the connectivity as shown on right. Like many other sulfur-containing compounds, Volatile organic compound, volatile sulfides have ...

functional group In organic chemistry, a functional group is any substituent or moiety (chemistry), moiety in a molecule that causes the molecule's characteristic chemical reactions. The same functional group will undergo the same or similar chemical reactions r ...

s. It is readily soluble in alcohol solvents, including

propylene glycol Propylene glycol ( IUPAC name: propane-1,2-diol) is a viscous, colorless liquid. It is almost odorless and has a faintly sweet taste. Its chemical formula is CH3CH(OH)CH2OH. As it contains two alcohol groups, it is classified as a diol. An al ...

and

dipropylene glycol Dipropylene glycol is a mixture of three isomeric chemical compounds, 4-oxa-2,6-heptandiol, 2-(2-hydroxy-propoxy)-propan-1-ol, and 2-(2-hydroxy-1-methyl-ethoxy)-propan-1-ol. It is a colorless, nearly odorless liquid with a high boiling point and ...

Occurrence

In nature, methional is a thermally-induced volatile flavor compound. For instance, the heat-initiated Maillard reaction of reducing sugars and amino acids forms the initial basis of methional's composition. The formation of methional stems from the interaction of α-dicarbonyl compounds (intermediate products in the Maillard reaction) with

(Met) by the Strecker degradation reaction: :CH₃SCH₂CH₂(NH₂)CHCO₂H + O → CH₃SCH₂CH₂(HN=)CCO₂H + H₂O :CH₃SCH₂CH₂(HN=)CCO₂H + H₂O → CH₃SCH₂CH₂CHO + NH₃ + CO₂ Methional easily degrades into methanethiol, which then oxidizes into

dimethyl disulfide Dimethyl disulfide (DMDS) is an organic chemical compound with the molecular formula . It is a flammable liquid with an unpleasant, garlic-like odor resembling that of "leaking gas". The compound is colorless, although impure samples often appea ...

. Dimethyl disulfide is partly responsible for the "reactive sulfur" that contributes to the taste of potatoes. Furthermore, the methionine resulting from the Strecker degradation reaction produces alkyl

pyrazine Pyrazine is a heterocyclic aromatic organic compound with the chemical formula C4H4N2. It is a symmetrical molecule with point group D2h. Pyrazine is less basic than pyridine, pyridazine and pyrimidine. It is a ''"deliquescent crystal or wax-lik ...

s, which contribute to the flavors in roasted, toasted, or thermally processed foods. Due to the ease of its decomposition, a large portion of methional is lost during potato processing. Similarly, in the presence of

flavin mononucleotide Flavin mononucleotide (FMN), or riboflavin-5′-phosphate, is a biomolecule produced from riboflavin (vitamin B2) by the enzyme riboflavin kinase and functions as the prosthetic group of various oxidoreductases, including NADH dehydrogenase, as ...

(FMN) and light, methionine is nonenzymatically oxidized into methional,

ammonia Ammonia is an inorganic chemical compound of nitrogen and hydrogen with the chemical formula, formula . A Binary compounds of hydrogen, stable binary hydride and the simplest pnictogen hydride, ammonia is a colourless gas with a distinctive pu ...

, and

carbon dioxide Carbon dioxide is a chemical compound with the chemical formula . It is made up of molecules that each have one carbon atom covalent bond, covalently double bonded to two oxygen atoms. It is found in a gas state at room temperature and at norma ...

. :CH₃SCH₂CH₂(NH₂)CHCO₂H → CH₃SCH₂CH₂CHO + NH₃ + CO₂

Preparation and reactions

Methional is synthesized commercially by the reaction of

methanethiol Methanethiol (also known as methyl mercaptan) is an organosulfur compound with the chemical formula . It is a colorless gas with a distinctive putrid smell. In small amounts, it is pervasive in nature and found in certain foods, such as some n ...

and

acrolein Acrolein (systematic name: propenal) is the simplest unsaturated aldehyde. It is a colorless liquid with a foul and acrid aroma. The smell of burnt fat (as when cooking oil is heated to its smoke point) is caused by glycerol in the burning fat ...

. :CH₃SH + CH₂=CHCHO → CH₃SCH₂CH₂CHO Using the Strecker synthesis, methional is converted to methionine. For the purpose of animal feed supplements, enantiopure methionine is not required. Methional is a versatile reagent in organic chemistry.

Biological routes

Because of their high cost, methional or its precursor methionine are not added during potato processing. In order to intensify flavoring of heat-processed potato foods, biotechnological approaches are used to increase methionine levels, and thus methional levels, in potato foods. The enzyme

aminotransferase Transaminases or aminotransferases are enzymes that catalyze a transamination reaction between an amino acid and an α- keto acid. They are important in the synthesis of amino acids, which form proteins. Function and mechanism An amino acid c ...

acts on methionine to remove the amine and form an α-keto-γ-methylthiobutyric acid. As catalyzed by α-keto acid

decarboxylase Carboxy-lyases, also known as decarboxylases, are carbon–carbon lyases that add or remove a carboxyl group from organic compounds. These enzymes catalyze the decarboxylation of amino acids and alpha-keto acids. Classification and nomenclature ...

, this ketomethylthiobutyric acid converts to methional.María Del Carmen Martínez-Cuesta , Carmen Peláez & Teresa Requena (2013) Methionine Metabolism: Major Pathways and Enzymes Involved and Strategies for Control and Diversification of Volatile Sulfur Compounds in Cheese, Critical Reviews in Food Science and Nutrition, 53:4, 366-385. {{doi, 10.1080/10408398.2010.536918 :CH₃S(CH₂)₂CH(NH₂)CO₂H + O → CH₃S(CH₂)₂COCO₂H + NH₃ :CH₃S(CH₂)₂COCO₂H → CH₃S(CH₂)₂CHO + CO₂

References

Thioethers Flavors Aldehydes