Role of lactic acid bacteria on the yogurt flavour: A review

Figures & data

Table 1. List of flavour compounds, description, and odour thresholds identified in yogurts.

Flavour compounds^a	Description^b	Odour threshold(mg/kg)^c
Aldehydes
Acetaldehyde	Ethereal, fresh, green, pungent	0.0079–0.039
Propanal	Solvent, pungent	0.081–0.16
Butanal	Pungent, green	0.007–0.017
3-Methylbutanal	Cocoa, almond, green, malty, unripe, cocoa, malty	0.006
Hexanal	Green, cut-grass	0.0091
Octanal	Fat, soap, lemon, green	0.0009
Furfural	Bread, almond, sweet	0.77
Benzaldehyde	Almond, burnt sugar	1–4.6
Methional	Cooked potato	0.0002
Pentanal	Fruit, bread, sweet	0.022
2-Methylbutanal	Fermented	0.003
Heptanal	Green, sweet	0.06–0.55
Nonanal	Sweet, floral, citrus, grass-like	0.04
(E)-2-Nonenal	Green, fatty	0.0004
Decanal	Fatty	0.03
Undecanal	Fatty	0.01
Phenylacetaldehyde	Floral sweet	0.004
Ketones
Diacetyl	Buttery, creamy, vanilla	0.0011
Acetone	Sweet, fruity	0.832
Acetoin	Buttery	0.014
2-Propanone	Sweet, fruity	0.832
2-Butanone	Varnish-like, sweet, fruity	17–32
2-Pentanone	Sweet, fruity, cheesy	1.38
2,3-Pentanedione	Butter, vanilla, mild	0.02
2-Hexanone	Floral, fruity	0.56
2-Undecanone	Floral, rose-like, herbaceous	0.041–0.082
1-Nonen-3-one	Sweet,waxy	0.000000008
3-Penten-2-one	Sweet, fruity	1.2
2-Heptanone	Fruity, spicy	0.001–0.01
3-Octanone	Mushroom, fruity	0.028
Nonanone	Grassy-herbal, green-fruity, floral	0.041–0.082
2-Dodecanone	Sweet, waxy	0.042–0.083
3-Hexanone	Sweet, fruity	0.041–0.081
1-Octen-3-one	Mushroom-like, earthy, fruity	0.0005
Acids
Octanoic acid	Wax, soap, goat, musty, rancid, fruity	0.91–1.9
Propionic acid	Vinegar, pungent, sour milk	2
Acetic acid	Vinegar, pungent, acidic	25.59–26
Pentanoic acid	Sweat	0.28
Hexanoic acid	Pungent, rancid, flowery	1.8–1.84
Heptanoic acid		0.64–0.91
Decanoic acid	Rancid	0.13
Butanoic acid	Sharp, cheesy, rancid, sweaty, sour, putrid	1.40
Butyric acid	Rancid, cheese, sweat	1.40
3-Methylbutanoic acid	Rancid cheese, sweaty, putrid	0.1
Nonanoic acid	Green, fat	4.6–9.0
Formic acid	Pungent	1240–2440
Isovaleric acid	Rotten fruit, mild, sweaty, rancid, faecal, putrid, flowery	0.1
Isobutyric acid	Sweet, mild, rotten apple	0.05
Alcohols
1-Butanol	Fruity, alcoholic	4.33
2,3-Butanediol	Buttery	20–50
Methanol	Alcoholic	800–1200
1-Propanol	Alcoholic, pungent	5.7–7.8
2-Propanol	Alcoholic	40–78
Ethanol	Mild, ether	200
2-Heptanol	Earthy, oily	0.041–0.081
2-Butanol	Wine	3.3
2-Furanmethanol	Burnt, sweet, caramellic, brown	1.9–2.0
1-Penten-3-ol	Fish, pungent	0.4
1-Pentanol	Alcoholic, iodoform-like	0.12
3-Methyl-2-butenol	Sweet, fruity	0.25
3-Methylbutanol	Fusel, alcoholic, pungent, ethereal	3.06
1-Octen-3-ol	Mushroom-like	0.01
Guaiacol	Bacon, phenolic, smoked, spicy	0.02
Esters
Ethyl acetate	Solvent-like, fruity, pineapple	3.28–3.3
Methyl acetate	Ethereal and solvent-like, estery, fruity, winey	1.5–47
Butyl acetate	Pineapple	0.01–0.1
δ-Dodecalactone	Fruit, sweet	0.06
γ—Dodecalactone	Sweet, fruit, flower	0.007
Ethyl hexanoate	Apple peel, fruit	0.001
Ethyl butanoate	Fruity, sweet, banana	0.00018
Ethyl octanoate	Fruity, banana, apple	0.015
Aromatic hydrocarbons
Benzene	Aromatic	0.072
Toluene	Paint	0.024
Ethylbenzene	Phenol, spice	0.0024
1,3-Dimethylbenzene	Plastic	1.1
1,4-Dimethylbenzene	Leathery	1
Trimethylbenzene	Leathery	0.5
Hydrocarbon
Dichloromethane		5.6
Limonene	Lemon, orange	0.2
Ethenylbenzene	Balsamic, gasoline	0.0036
Heterocyclic
2-Methylthiophene	Sulphur	3
Pyrazine	Roasted	300
Methylpyrazine	Roasted	30
1 H-pyrrole	Sweet, warm, nutty, ethereal	20
Furans
Furan	Sweet	4.5–6
2-Methylfuran	Ethereal, acetone, chocolate	3.5–4
2-Pentylfuran	Green bean, butter	0.006
Sulphur compounds
Dimethyl sulphide	Intense, lactone-like, sulphurous, cabbage	0.01
Dimethyl disulphide	Boiled cabbage, cauliflower, garlic	0.0003
Dimethyl trisulphide	Sulphurous, faecal	0.01

^aFlavour compounds are from the following literature: Cheng,^[5] Routray & Mishra,^[8] Beshkova et al.^[58] and Thierry et al.^[20]

^bOdour descriptions are mainly sourced from the following website: http://flavornet.org/flavornet.html and http://www.thegoodscentscompany.com/

^cThresholds are mainly obtained from the literature which applied water as the matrix.^[91]

Figure 1. General metabolic pathways for the formation of the main flavour compounds of carbohydrate fermentation by LAB. The pathways are generated according to the following literature: Cheng,^[5] Thierry et al.^[20] and Tamime & Robinson.^[13] The main flavour compounds are in bold. Key enzymes: CL, citrate lyase; OAD, oxaloacetate decarboxylase; LDH, lactate dehydrogenase; PDC, pyruvate decarboxylase; ALS, α-acetolactate synthase; PFL, pyruvate formate lyase; PDH, pyruvate dehydrogenase; ACDH, acetaldehyde dehydrogenase; ADHE, alcohol dehydrogenase; ACK, acetate kinase; ALD, α-acetolactate decarboxylase; DR, diacetyl reductase; AR, acetoin reductase; Tppi, thiamine pyrophosphate.

Figure 2. General conversion pathways of proteins relevant for flavour formation by LAB. The pathways are generated according to the following literature: Smit et al.,^[17] Sadat-Mekmene et al.^[48] and Aleksandrzak-Piekarczyk et al.^[25].Key enzymes: CEP, cell envelope proteinase; PrtM, proteinase maturation protein; Opp, oligopeptide transporter; DtpT, ion-linked transporter for di-and tripeptides; Dpp, ATP-driven transporter for di-and tripeptides; Pep, peptidase; AT, aminotransferase; HycDH, hydroxyacid dehydrogenase; KaDH, α-keto acid dehydrogenase complex; PTA, phosphotransacylase; ACK, acyl kinase; KdcA, α-keto acid decarboxylase; AlcDH, alcohol dehydrogenase; AldDH, aldehyde dehydrogenase; EstA, esterase A.

Figure 3. General degradation pathways of lipids during milk fermentation by LAB. The pathways are generated according to the following literature: Cheng^[5] and Mcsweeney et al.^[45].

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