Biosynthesis of Plant-derived flavor compounds

1. Biosynthesis of Plant-derived flavor compounds By Dudsadee Uttapap

2. Biosynthesis of plant-derived flavor compounds References • 1. “Flavor Chemistry and Technology”, H.B. Heath, G. Reineccius, 1986. • 2.“Flavor Chemistry”, D.B. Min, http://class.fst.ohio-state.edu/fst820/default.htm • “Biosynthesis of plant-derived flavor compounds”, The Plant Journal (2008) 54, 712–732 • “Plant Biochemistry” http://www.uky.edu/~dhild/biochem/lecture.html

3. Flavor compounds Flavor molecules constitute a heterogeneous group of compounds, with straight-chain, branched-chain, aromatic and heteroaromatic backbones bearing diverse chemical groups such as hydroxyl, carbonyl, carboxyl, ester, lactone, amine, and thiol functions. More than 700 flavor chemicals have been identified and catalogued

4. Chemical synthesis VS Biosynthesis Most commercial flavorants are ‘nature identical’, which means that they are the chemical equivalent of natural flavors but are chemically synthesized, mostly from petroleum-derived precursors Bioproduction, including the extraction from natural sources, de novo microbial processes (fermentation), and bioconversion of natural precursors using micro-organisms or isolated enzymes

5. Biologicalfunctionsofplantvolatiles “associatedwithdefensiveandattractiveroles” • Compoundsemittedbyflowersmostprobablyservetoattractandguidepollinators • volatilesmightalsoprotectthecarbohydrate-richnectarbyinhibitingmicrobialgrowth. • vegetative plant tissue release volatiles following herbivore damage. Some of these substances attract arthropods that prey upon or parasitize the herbivores. • Volatiles also act as direct repellents or toxicants for herbivores and pathogens. • In fruits, volatile emission and accumulation facilitate seed dispersal by animals and insects. • vegetative tissues often produce and release many of the volatiles after their cells are disrupted. These volatile flavor compounds may exhibit anti-microbial activity.

6. R OCO Alcohols Esters Carbonyls Lactones Acids Phenols Aromatic compounds responsible for odor and flavor of fruits comprise; R-COO-R’ R-OH R-CHO R-CO-R’ R-COOH

7. Estimated world consumption of selected aroma chemicals in flavor and fragrance compositions

10. Calvin cycle

11. Amino acid synthesis N enters roots as NO3- or NH4+. The NH4+ is incorporated into amino acids in roots and leaves and the amino acids accumulate in proteins. The main if not sole function of some proteins is to provide a store of amino acids

12. Amino acid synthesis

16. Glycolysis

17. isoprenoid biosynthesis proceeds either via the "classical" or most well studied, mevalonate pathway (cytosolic) (for the synthesis of sterols, sesquiterpenes, triterpenoids) or via the non-mevalonate (1-deoxy-D-xylulose-5-phosphate, DXP) pathway for plastidic isoprenoids (carotenoids, phytol [side-chain of chlorophylls], plastoquinone, isoprene, monoterpenes and diterpenes).

20. Vegetable flavors develop when tissue damage occurs (Intact vegetable generally contains few volatiles) Fruit flavors are formed during brief ripening period Biosynthesis of flavors in vegetables and fruits

21. BIOGENESIS OF FRUIT AROMA develops entirely during ripening period of plant Minute quantities of lipids, CHO, protein (amino acids) are enzymatically converted to volatile flavors.

22. FRUIT FLAVOR COMPOUNDS

23. Carbohydrate Pyruvate Malonyl CoA Amino acid Acetyl CoA Fatty acid Shikimic acid Acetyl-CoA Terpene Mevalonyl CoA Cinnamic acid Biosynthesis of fruit volatiles

24. Furanones and pyrones “fruit constituents” Flavorants from carbohydrate metabolism Only a limited number of natural volatiles originate directly from carbohydrates without prior degradation of the carbon skeleton.

25. Furanones and pyrones Carbohydrate-derived flavor molecules, including 4-hydroxy-2,5-dimethyl-3(2H)-furanone (furaneol), 2,5-dimethyl-4-methoxy-3(2H)-furanone (methoxyfuraneol), 4-hydroxy-5-methyl-3(2H)-furanone (norfuraneol), 2-ethyl-4-hydroxy-5-methyl-3(2H)-furanone (homofuraneol), 4-hydroxy-2-methylene-5-methyl-3(2H)- furanone (HMMF) and 3-hydroxy-2-methyl-4H-pyran-4-on (maltol).

26. Glucose (6C) 2 Pyruvate (3C) CO2 -O2 -O2 +O2 Ethanol Lactate TCA Cycle Glycolysis Flavorants from carbohydrate metabolism

28. Terpenoids are enzymatically synthesized from acetyl CoA and pyruvate provided by the carbohydrate pools in plastids and the cytoplasm. Terpenoids constitute one of the most diverse families of natural products, with over 40 000 different structures of terpenoids Many of the terpenoids produced are non-volatile and are involved in important plant processes such as membrane structure (sterols), photosynthesis (chlorophyll side chains, carotenoids), redox chemistry (quinones) and growth regulation (gibberellins, abscisic acid, brassinosteroids) Flavorants from carbohydrate metabolism “the most interesting is terpene biosynthesis”

29. Important plant-derived volatile terpenoids.

30. Biosynthesis of Terpenes “isoprene is derived from acetyl-CoA”

31. Classification of Terpenes

32. Apocarotenoid formation Carotenoid substrates are oxidatively cleaved to yield the apocarotenoid derivatives (right).

33. Some of the volatile organic compounds in wine come from the grape's skin, or exocarp, while others come from the grape's flesh, or mesocarp. Organic acids give wine its tartness, and sugars give it sweetness. Terpenes provide floral or fruity flavors. Norisoprenoids impart a honeylike character. Thiols are the sulfur-based compounds behind complex wine aromas such as guava, passionfruit or grapefruit — but when thiols go wrong, they can make a wine taste "funky."

34. Lipids metabolic pathway for lipid biosynthesis plays a significant role in flavor formation. Alpha-, Beta-oxidation Oxidation via lipoxygenase products; acids, alcohols, diketones, ketones, esters of these compounds.

35. Oxidation via Lipoxygenase Lipoxygenase activity is believed to be the major source of volatiles in plants. Lipoxygenase enzymes (dioxygenase) catalyze reactions between O2 and polyunsaturated fatty acids Substrate: unsaturated fatty acid (linoleic and linolenic acids). Major products: volatile C6 and C9 aldehydes and alcohols

36. Linolenic acid-derived flavor molecules. AAT, alcohol acyl CoA transferase; ADH, alcohol dehydrogenase; AER, alkenal oxidoreductase; AOC, allene oxide cyclase; AOS, allene oxide synthase; HPL,hydroperoxide lyase; JMT, jasmonate methyltransferase; LOX, lipoxygenase; OPR, 12-oxo-phytodienoic acid reductase; 3Z,2E-EI, 3Z,2E-enal isomerase.

37. Fatty acid precursors (Tomato)

38. Palmitoyl-CoA (16:0) + Acetyl-CoA Myristoyl-CoA (14:0) • - and -oxidation of fatty acids the specific pathways in plants are not well understood

39. Formation of pear flavors via beta-oxidation

40. Lactones

41. Amino acid metabolism yields short chain aliphatic and aromatic alcohols, acids, carbonyls and esters They are the primary source of branched chain aliphatic flavor compounds Amino Acid Metabolism their pathways have been barely analyzed in plants.

43. amino acid precursors (Tomato)

44. Biosynthesis of amino acid-derived flavor compounds (a) Catabolism of branched-chain amino acids leading to methyl branched flavor compounds, and (b) postulated biosynthesis of sotolon. Formation of aldehyde (a) from amino acids requires the removal of both carboxyl and amino groups. The sequence of these removals is not fully known and could be the opposite to that shown or aldehyde could be formed in one step by aldehyde synthase

45. Starting amino acids: Tyrosine and phenylalanine products: phenolic/spicy in character

46. Shikimic acid formation

47. Vegetable Flavors

48. flavor again arises from major metabolic processes - e.g. Lipids, CHO & amino acids. the precursors, enzymes and end flavors are quite different from fruits. The role or importance of S compounds to vegetable flavor is quite significant. Vegetable flavors

49. Carbohydrate Fatty acid Amino acid Formation of flavor in vegetables

50. Genus Allium Enzymes produce volatiles from derivatives of cysteine (sulfoxides) Genus Brassica Enzymes produce volatiles from glucosinolates Vegetable Flavor Categories