Quantitative analysis of the lactic acid and acetaldehyde produced by Streptococcus thermophilus and Lactobacillus bulgaricus strains isolated from traditional Turkish yogurts using HPLC

Abstract

The present study was conducted to evaluate the lactic acid- and acetaldehyde-producing abilities of lactic acid bacterial species isolated from traditionally manufactured Turkish yogurts using HPLC. The lactic acid bacterial species purified from the yogurts were the 2 most widely used species in industrial yogurt production: Streptococcus thermophilus and Lactobacillus bulgaricus. These bacteria have the ability to ferment hexose sugars homofermentatively to generate lactic acid and some carbonyl compounds, such as acetaldehyde through pyruvate metabolism. The levels of the compounds produced during fermentation influence the texture and the flavor of the yogurt and are themselves influenced by the chemical composition of the milk, processing conditions, and the metabolic activity of the starter culture. In the study, morphological, biochemical, and molecular characteristics were employed to identify the bacteria obtained from homemade yogurts produced in different regions of Turkey. A collection of 91 Strep. thermophilus and 35 L. bulgaricus strains were investigated for their lactic acid- and acetaldehyde-formation capabilities in various media such as cow milk, LM17 agar, and aerobic-anaerobic SM17 agar or de Man, Rogosa, and Sharpe agar. The amounts of the metabolites generated by each strain in all conditions were quantified by HPLC. The levels were found to vary depending on the species, the strain, and the growth conditions used. Whereas lactic acid production ranged between 0 and 77.9 mg/kg for Strep. thermophilus strains, it ranged from 0 to 103.5 mg/kg for L. bulgaricus. Correspondingly, the ability to generate acetaldehyde ranged from 0 to 105.9 mg/kg in Strep. thermophilus and from 0 to 126.9 mg/kg in L. bulgaricus. Our study constitutes the first attempt to determine characteristics of the wild strains isolated from traditional Turkish yogurts, and the approach presented here, which reveals the differences in metabolite production abilities of the wild lactic acid bacteria strains, holds the potential for the selection of the most desirable strains to be used as starters in commercial yogurt manufacture in the future.

Isolation and identification of exopolysaccharide producer lactic acid bacteria from Turkish yogurt

“…Both L. delbrueckii subsp. bulgaricus and S. thermophilus strains were isolated from traditional yogurt samples as potential starter cultures similar to the previous studies (Aslim, Beyatli, & Yuksekdag, ; Aslim, Onal, & Beyatli, ; Boke, Aslim, & Alp, ; Dertli, ; Gezginc, Topcal, Comertpay, & Akyol, ), and the number of distinct S. thermophilus strains was higher than that of L. delbrueckii subsp. bulgaricus .…”

Cloning and Overexpression of the als, pflA, and adhB Genes in Streptococcus thermophilus and Their Effects on Metabolite Formation

“…These metabolites can be purified for the industrial use. Additionally, some wild S. thermophilus strains [14] can be transformed with these created constructs in order to see the effects of overexpression on metabolite formation.…”

Inferring the role of microorganisms in water kefir fermentations

“…Lactic acid was determined using HPLC, as previously described (Gezginc et al ., ), on a Varian 920‐LC HPLC apparatus and a C18 column. The absorbance was detected at a wavelength of 214 nm and a temperature of 30 °C.…”