Characterization of Headspace Volatile Flavor Compounds Formed During Kefir Production: APplication of Solid Phase MicroextractioN

Figures & data

Table 1 The time (min ± SD, n = 3) corresponding to the pH of sampling

pH of sampling	Time (min)
6.4	0 ± 0 ^a
6.2	25 ± 7
6.0	53 ± 4
5.8	83 ± 4
5.6	108 ± 3
5.4	136 ± 7
5.2	166 ± 10
5.0	198 ± 6
4.8	227 ± 5
4.6	258 ± 16
^aImmediately after inoculation.

Table 2 Linear retention indices, similarity, and FID peak area (%) of the representative volatile flavor compounds in kefir sample

No.	Compound	LRI ^a	Similarity	FID peak area (%)
1	Carbon dioxide	921	928	nd
2	Carbonyl sulfide	926	879	nd
3	Acetaldehyde	954	978	1.770
4	Unknown 1	1026	984	nd
5	Acetone	1143	834	3.674
6	Ethyl acetate	1371	956	8.951
7	2-Butanone	1439	963	31.682
8	Ethanol	1670	979	39.347
9	1,2-ethanediol, diacetate	1742	874	nd
10	2,3-Butanedione	1970	887	2.986
11	Hexan-2-one	1993	986	nd
12	2-Methylpropan-1-ol	2067	914	nd
13	Pentan-2-ol	2113	983	nd
14	1-Methoxy-2-propanol	2167	858	nd
15	Butan-1-ol	2263	862	nd
16	3-Methylbutan-1-ol	2306	982	nd
17	Ethyl butyrate	2495	898	5.535
18	Hexadecanoic acid, ethyl ester	2507	897	nd
19	Unknown 2	2519	883	nd
20	Heptan-2-ol	2538	964	0.002
21	Hexan-1-ol	2572	962	nd
22	Heptanoic acid, ethyl ester	2597	879	0.054
23	Dodecanoic acid, ethyl ester	2628	895	nd
24	Unknown 3	2647	926	nd
25	1-Propanol,2-methyl-	2663	992	0.0328
26	1-Butanol, 3-methyl-(s)	2679	849	nd
27	Octanal	2692	973	nd
28	3-Hydroxy-2-butanone	2708	889	3.239
29	Propionic acid, 2-hydroxy-,ethyl ester	2714	952	nd
30	2-Nonanone	2719	824	nd
31	Nonanal	2726	986	nd
32	Ethanol, 2-butoxy-	2732	929	nd
33	Acetic acid	2737	993	0.053
34	Propionic acid, 2-methyl-	2759	898	0.009
35	2,3-Butanediol	2783	837	0.035
36	Butanoic acid	2814	892	0.017
37	Unknown 4	2839	948	nd
38	Heptanoic acid	2861	958	nd
39	Octanoic acid	2875	973	nd
40	Benzoic acid	2943	827	nd
^aLinear Retention Indices for HP-Innowax column; nd: not detected.

Figure 1 Changes in ketones concentration released in headspace during kefir production. (A): 2-butanone; (B): acetone; (C): acetoin; and (D): diacetyl.

Figure 2 Changes in alcohol concentration released in headspace during kefir production.

Figure 3 Changes in esters concentration released in headspace during kefir production. (A): ethyl acetate; (B): ethyl butyrate.

Figure 4 Changes in aldehyde concentration released in headspace during kefir production.