Effect of fermentation temperature on the properties of exopolysaccharides and the acid gelation behavior for milk fermented by Streptococcus thermophilus strains DGCC7785 and St-143

Abstract

We investigated the effect of fermenting milk with 2 strains (DGCC7785 and St-143) of Streptococcus thermophilus, which are known to produce different types of exopolysaccharide (EPS) structures. The yields and physical properties of these ropy EPS were monitored during the fermentation of milk at different temperatures. We wanted to understand how these types of EPS properties affected yogurt gelation. Reconstituted skim milk was fermented at 33, 39, or 45°C until pH values reached 5.2, 4.9, 4.7, and 4.5. Molar mass of ropy EPS samples was determined using size exclusion chromatography coupled with multiangle laser light scattering. Rheological properties of fermented milk gels were analyzed using small-strain dynamic oscillatory measurements. In both strains, concentrations of ropy EPS increased during fermentation and at all temperatures. Fermentation times, by both strains, were shortest at 45°C and longest at 33°C. For both strains, molar mass of ropy EPS ranged from 2 to 4 × 10 g/mol during fermentation. A major proteinaceous contaminant that was co-isolated with the ropy EPS fraction by our isolation method was identified as a milk-derived phosphoglycoprotein PP3. Increase in fermentation temperature from 33 to 45°C significantly decreased the storage modulus values (from 170 to 41 Pa) for milk gelled by strain DGCC7785, whereas the gels made with St-143 had very low storage modulus values (11-17 Pa) regardless of fermentation temperatures. For both strains, the values of maximum loss tangent in the milk gels increased with fermentation temperature; the maximum loss tangent occurred at higher pH values when milk was fermented by strain DGCC7785. The specific type of EPS produced appeared to be responsible for the differences in yogurt texture rather than the concentration or molar mass of the EPS.

Use of Streptococcus thermophilus for the in situ production of γ-aminobutyric acid-enriched fermented milk

“…Production of GABA was monitored using HPLC. Notably, temperature was among the most influential factors affecting bacterial growth, consistent with previous observations that this factor affects the fermentation time of exopolysaccharide production in S. thermophilus (Khanal and Lucey, 2018). The rate of milk acidification is a highly important technological factor in the manufacturing of fermented milk.…”

Potentially lactic acid bacteria as an EPS producing starter from yellow sweet potato fermentation

“…Isnawati and Trimulyono's (2018) study showed that lactic acid bacteria were able to grow at a range of 4 to 50⁰C. The thermophilic lactic acid bacteria as an EPS producing were not surprising as reported by previous studies (Zhang et al 2011;Panthavee et al 2017;Khanal and Lucey 2018).…”

Investigation of physicochemical composition and microbial communities in traditionally fermented vrum from Inner Mongolia

“…Streptococcus was the predominant bacterial genus in FV5, with a relative abundance of 73.57%. Some of the bacterial genera we identified were commercially significant for the fermentation of dairy products (Krzyściak et al, 2013;Li et al, 2016;Khanal and Lucey, 2018). Acetobacter, Lactococcus, and Lactobacillus dominated in FV2, at 48.51, 20.83, and 29.58% relative abundance, respectively.…”