Flavor chemistry of butter culture

Graduation date: 1965Numerous investigations have been made on the contribution of\ud butter cultures to the flavor of cultured cream butter, but production\ud of uniform cultured cream butter has not been possible in industry.\ud Therefore, it was desirable to investigate in detail the qualitative\ud and quantitative chemistry of the flavor of high quality butter cultures,\ud and to examine more closely some of the aspects of flavor\ud production by butter culture organisms.\ud Volatile flavor components of high quality butter culture and\ud control heated milk were isolated from intact samples by means of\ud a specially designed low-temperature, reduced-pressure steam distillation\ud apparatus. Most of the flavor compounds present in the resulting\ud distillate fractions were tentatively identified by gas chromatographic\ud relative retention time data. Flavor concentrates obtained\ud by ethyl ether extractions of aqueous distillates were also separated by temperature-programmed, capillary column gas chromatography,\ud and the effluent from the capillary column was analyzed by a fast-\ud scan mass spectrometer. Many of the flavor compounds in the flavor\ud concentrates were positively identified by correlation of mass spectral\ud and gas chromatographic data. In addition, supporting evidence\ud for the identification of some flavor components was obtained through\ud the use of qualitative functional group reagents, derivatives and headspace\ud gas chromatography.\ud Compounds that were positively identified in butter culture include\ud ethanol, acetone, ethyl formate, methyl acetate, acetaldehyde,\ud diacetyl, ethyl acetate, dimethyl sulfide, butanone, 2-butanol,\ud methyl butyrate, ethyl butyrate, methane, methyl chloride, carbon\ud dioxide and methanol; also included were 2-pentanone, 2-heptanone,\ud acetoin, formic acid, acetic acid, lactic acid, 2-furfural, 2-furfurol,\ud methyl hexanoate, ethyl hexanoate, 2-nonanone, 2-undecanone,\ud methyl octanoate and ethyl octanoate. Compounds that were tentatively\ud identified in butter culture include hydrogen sulfide, methyl\ud mercaptan, n-butanal, n-butanol, 2-hexanone, n-pentanal, n-pentanol,\ud 2-mercaptoethanol, n-butyl formate, n-butyl acetate,\ud 2-methylbutanal, 3-methylbutanal, methylpropanal, methyl heptanoate,\ud n-octanal, 2-tridecanone, methyl benzoate, methyl nonanoate,\ud ethyl nonanoate, ethyl decanoate, methyl dodecanoate, ethyl dodecanoate,\ud delta-octalactone and delta-decalactone.\ud Compounds that were positively identified in control heated milk\ud include acetaldehyde, ethyl formate, ethyl acetate, 2-heptanone,\ud 2-furfural, 2-furfurol, 2-nonanone, 2-undecanone, ethyl octanoate\ud and methyl decanoate. Compounds that were tentatively identified in\ud control heated milk include dimethyl sulfide, hydrogen sulfide, ammonia,\ud methyl mercaptan, methyl acetate, acetone, methanol, butanone,\ud butanal, n-butanol, methyl butyrate, ethyl butyrate, 2-pentanone,\ud 2-hexanone, 2-mercaptoethanol, 2-furfuryl acetate, ethyl\ud hexanoate, methyl heptanoate, 2-tridecanone, ethyl decanoate, ethyl\ud dodecanoate, delta-octalactone and delta-decalactone. The data indicated\ud that the qualitative flavor composition of control heated milk\ud and butter culture were very similar. Diacetyl, ethanol, 2-butanol\ud and acetic acid were noted to be consistently absent in the data for\ud the control heated milk. Other compounds were not observed in the\ud heated milk fractions, but were also absent from some of the culture\ud fractions. This was attributed to their presence in low concentrations,\ud chemical instability or inefficient recovery.\ud A modified 3-methyl-2-benzothiazolone hydrazone spectrophotometric\ud procedure was adapted for the determination of acetaldehyde\ud produced in lactic starter cultures. The procedure was applied in\ud conjunction with diacetyl measurements in studying single- and\ud mixed-strain lactic cultures. The diacetyl to acetaldehyde ratio was\ud found to be approximately 4:1 in desirably flavored mixed-strain butter cultures. When the ratio of the two compounds was lower\ud than 3:1 a green flavor was observed. Acetaldehyde utilization at\ud 21°C by Leuconostoc citrovorum 91404 was very rapid in both acidified\ud (pH 4.5) and non-acidified (pH 6.5) milk cultures. The addition\ud of five p.p.m. of acetaldehyde to non-acidified milk media prior to\ud inoculation greatly enhanced growth of L. citrovorum 91404 during\ud incubation at 21°C. Combinations of single-strain organisms demonstrated\ud that the green flavor defect can result from excess numbers\ud of Streptococcus lactis or Streptococcus diacetilactis in relation\ud to the L. citrovorum population.\ud Diacetyl, dimethyl sulfide, acetaldehyde, acetic acid and carbon\ud dioxide were found to be "key" compounds in natural butter culture\ud flavor. Optimum levels of these compounds in butter culture were\ud ascertained by chemical or flavor panel evaluations. On the basis of\ud these determinations, a synthetic butter culture prepared with heated\ud whole milk and delta-gluconolactone (final pH 4.65) was flavored with\ud 2.0 p.p.m. of diacetyl, 0.5 p.p.m. of acetaldehyde, 1250 p.p.m. of\ud acetic acid, 25.0 p.p.b. of dimethyl sulfide and a small amount of\ud sodium bicarbonate for production of carbon dioxide. The resulting\ud synthetic butter culture exhibited the typical aroma, flavor and body\ud characteristics found in natural high quality butter cultures, except\ud that the delta-gluconolactone was found to contribute an astringent\ud flavor