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. 2022 Aug 27;11(17):2607.
doi: 10.3390/foods11172607.

Distribution and Quantification of Lactic Acid Enantiomers in Baijiu

Hao Xu  1 , Shuyi Qiu  1 , Yifeng Dai  1   2 , Yuangen Wu  1 , Xiangyong Zeng  1
Affiliations

Distribution and Quantification of Lactic Acid Enantiomers in Baijiu

Hao Xu et al. Foods. .

Abstract

Enantiomers of lactic acid were investigated in Baijiu, including soy sauce aroma-type Baijiu (SSB), strong aroma-type Baijiu (STB), and light aroma-type Baijiu (LTB), via high-performance liquid chromatography with a chiral separation column. The natural concentration and enantiomeric distribution of lactic acid were studied, and their contribution to the flavor of Chinese Baijiu was evaluated based on recognition threshold. The results showed that there were significant differences in the content of lactic acid and the ratio of enantiomeric isomers among different aroma types and storage year. In SSB, the concentrations of D-lactic acid and L-lactic acid were higher, with the highest concentrations of 1985.58 ± 11.34 mg/L and 975.31 ± 14.03 mg/L, respectively. In STB, the highest concentrations of D-lactic acid and L-lactic acid were 1048.00 ± 11.46 mg/L and 939.83 ± 0.23 mg/L, respectively. In LTB, the highest concentrations of D-lactic acid and L-lactic acid were 760.90 ± 9.45 mg/L and 558.33 ± 3.06 mg/L, respectively. The average D/L enantiomeric ratios were 78:22 ± 16.16 and 80:20 ± 9.72 in the Commercial Baijiu products of SSB and STB, respectively. The average D/L enantiomeric ratio in LTB was 90:10 ± 6.08. D-lactic acid in JSHS vintage Baijiu showed a wave variation with aging, while L-lactic acid gradually increased during aging, and the average D/L enantiomeric ratio was 76:24 ± 4.26. The concentration of D-lactic acid in XJCT vintage Baijiu also showed a wave variation with aging, and the concentration of L-lactic acid tended to be stable during aging, with an average D/L enantiomeric ratio of 88:12 ± 2.80. The content of the two configurations of lactic acid in the LZLJ vintage Baijiu showed a decreasing trend during aging, with an average D/L enantiomeric ratio of 60:40 ± 11.99. The recognition threshold of D-lactic acid in 46% ethanol solution was 194.18 mg/L with sour taste; while the L-lactic acid was 98.19 mg/L with sour taste. The recognition threshold of L-lactic acid was about half that of D-lactic acid, indicating that L-lactic acid has a stronger sour taste. The taste activity values (TAVs) of D-lactic acid and L-lactic acid were greater than 1 in most of the Baijiu samples, and the TAV of D-lactic acid was greater than that of L-lactic acid. The study showed that the lactic acid enantiomers contributed to the taste perception of Baijiu in most of the samples, and D-lactic acid contributed more to the Baijiu taste than L-lactic acid.

Keywords: Baijiu; D-lactic acid; HPLC; L-lactic acid; TAVs; chiral; threshold.

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Conflict of interest statement

The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.

Figures

Figure 1
Figure 1
(a) D-lactic acid (CAS: 10326-41-7); (b) L-lactic acid (CAS: 79-33-4).
Figure 2
Figure 2
Separation of lactic acid isomers in Baijiu samples. (a): lactic acid standard, (b): MT43 Baijiu sample spectrum, (c): WLY Baijiu sample spectrum. (d): LBFJ Baijiu sample spectrum.
Figure 3
Figure 3
Box plots of D-lactic acid and L-lactic acid contents in SSB (a), STB (b), and LTB (c). t-test: NS (not significant, p > 0.05); ***: p < 0.001.
Figure 4
Figure 4
(a,b) Box plots of D-lactic acid and L-lactic acid contents in three aromatic Baijiu (SSB, STB, and LTB). t-test: NS (not significant, p > 0.05); *: 0.01 < p < 0.05 and ***: p < 0.001.
Figure 5
Figure 5
(a,b) Box plots of D-lactic acid and L-lactic acid contents in three different types of Baijiu (Commercial Baijiu products, JSHSJ, XJCTJ) in SSB; (c,d) box plots of D-lactic acid and L-lactic acid contents in two different types of Baijiu (Commercial Baijiu products, LZLJ) in STB. t-test: NS (not significant, p > 0.05); *: 0.01 < p < 0.05; **: 0.001 < p < 0.01; and ***: p < 0.001.
Figure 6
Figure 6
(a–c) Histograms of D-lactic acid and L-lactic acid in soy sauce aroma-type vintage Baijiu (JSHS, XJCT) and strong aroma-type vintage Baijiu (LZLJ).
Figure 7
Figure 7
(a) Principal component analysis of lactic acid enantiomers in Baijiu samples, A: SSB; B: STB; C: LTB; (b) heatmap analysis of lactic acid enantiomers in Baijiu.
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