|Abstract or Summary
- Numerous attempts have been made to identify the flavor
compounds in Blue cheese, however, duplication of Blue cheese
flavor has not yet been accomplished. Therefore, it was desirable
to make a qualitative and quantitative investigation of Blue
cheese flavor compounds and to study the effect of certain microorganisms
on Blue cheese flavor.
The aroma fraction of Blue cheese was isolated by centrifugation
of the cheese and molecular distillation of the recovered
fat. The volatiles were separated by gas chromatography on
packed columns containing polar and nonpolar phases and by temperature
programmed capillary column gas chromatography. Relative
retention time data and fast scan mass spectral analysis of the
capillary column effluent were used to identify compounds in the
aroma fraction. Compounds positively identified were as follows:
2-pentanone, 2-hexanone, 2-heptanone, 2-octanone, 2-nonanone,
2-decanone, 2-undecanone, 2-tridecanone, 2-propanol, 2-pentanol, 2-heptanol, 2-octanol, 2-nonanol, methyl butanoate, methyl hexanote,
methyl octanoate, methyl decanoate, methyl dodecanoate, ethyl formate,
ethyl acetate, ethyl butanoate, ethyl hexanoate, ethyl octanoate,
ethyl decanoate, ethanal, 3-methyl butanal, 2-methyl butanol, 3-methyl
butanol, 1-pentanol, benzene, and toluene.
Tentatively identified compounds included acetone, delta-octalactone,
delta-decalactone, methyl acetate, isopropyl hexanoate,
3-methylbutyl butanoate, pentyl hexanoate, ethyl-2-methylnonanoate,
isopropyl decanoate, furfural, 2-methyl propanal, methanol, ethanol,
2-phenylethanol, cresyl methyl ether, dimethylcyclohexane, diacetyl,
methyl mercaptan, and hydrogen sulfide.
A combination of liquid-liquid column chromatography and gas-liquid
chromatography was utilized to quantitate the major free fatty
acids in Blue and Roquefort cheese samples. The average concentration
(mg acid/kg cheese) in three Blue cheese samples was as
follows: 2:0, 826; 4:0, 1, 448; 6:0, 909; 8:0, 771; 10:0, 1,318; 12:0,
1,588; 14:0, 5,856; 16:0, 12,789; 18:0, 4,243; 18:1, 12,455; 18:2,
1,072; 18:3, 987. Roquefort cheese was found to be proportionately
more abundant in 8:0 and 10:0 acids and low in 4:0 acid compared to
Blue cheese. No formic, propionic, or isovaleric acid was detected
in any of the cheeses tested.
A quantitative procedure involving adsorption chromatography,
liquid-liquid chromatography and absorption spectrophotometry was used to isolate and measure the concentration of the C₃, C₅, C₇,
C₉, and C₁₁ methyl ketones in the fat of Blue and Roquefort cheese.
The average methyl ketone concentration (micromoles ketone/10 g
cheese fat) of five Blue cheese samples was as follows: acetone,
1.7; 2-pentanone, 5.9; 2-heptanone, 11.2; 2-nonanone, 9.3; 2-undecanone,
2. 4. Considerable variation in ketone concentration was noted
between samples, but no consistent differences were observed between
Blue and Roquefort cheese. One Roquefort sample contained
no acetone. The annount of ketone formed during cheese curing does
not depend directly on the amount of available fatty acid precursor.
There appears to be a selective conversion of the 8:0, and to a lesser
extent the 6:0 and 10:0, fatty acids to methyl ketones by the Penicillium
The concentration of the C₅, C₇, and C₉ secondary alcohols
was determined in the same cheeses used for ketone analysis. The
previously measured ketones acted as internal standards and facilitated
a semi-quantitative calculation of alcohol concentrations from
peak areas of gas chrorriatograms. The average alcohol concentration
(micromoles alcohol/10 g cheese fat) in five Blue cheese samples
was as follows: 2-pentanol, 0. 3; 2-heptanol, 2. 1; 2-nonanol,
0. 8. The alcohols were present in approximately the same ratios
as their methyl ketone analogs, but at much lower concentrations.
A synthetic Blue cheese flavor was prepared using a blend of butterfat, dry curd cottage cheese, cream, and salt as a base.
The most typical flavor was obtained using the following' compounds:
the 2:0, 4:0, 6:0, and 8:0 fatty acids at two-thirds the average concentration
found in cheese; twice the average concentration of the
C₃, C₅, C₇, C₉, and C₁₁ methyl ketones and C₅, C₇, and C₉ secondary
alcohols found in cheese: 2.0 mg/kg of base of 2-phenylethanol;
1.5 mg/kg of base of ethyl butanoate; 6.0 mg/kg of base of both methyl
hexanoate and methyl octanoate. Incorporation of higher acids
caused a soapy flavor. The presence of 2-phenylethanol and the esters
was judged as very important in duplicating Blue cheese flavor.
The mycelia of Penicillium roqueforti appear to be more active
in the reduction of methyl ketones to secondary alcohols than the
spores. Yeasts associated with Blue cheese are capable of reducing
methyl ketones to secondary alcohols. Yeasts also may play a role
in Blue cheese flavor by producing ethanol and other alcohols and