High-throughput screening for texturingLactococcusstrains

Abstract

In the food industry, lactic acid bacteria (LAB) are used in dairy fermentations, extending the shelf life by lowering the pH and also affecting taste and texture of the fermented milk. The texture of fermented milk is an important quality parameter, affecting consumer acceptance. Finding LAB providing desired texture of a product is time consuming and laborious when using standard methods for measuring texture, e.g. rheology measurements. Screening of 986 Lactococcus lactis strains resulted in few strains with the ability to enhance texture, demonstrating the necessity of implementation of high-throughput screening methods. A high-throughput screening assay was developed, combining small-scale 96-well microtiter plates and pressure measurements during liquid handling, e.g. aspiration, to find strains that give good texture in fermented milk. Only about 1% of the strains were found to enhance milk texture. Two of the texturing strains belong to L. lactis subsp. lactis, which are the first texturing strains from this subsp. reported. Mining for eps gene clusters responsible for exocellular polysaccharide production was performed, as polysaccharide production can contribute positively to fermented milk texture. Comparative genomics approach revealed four types of texturing L. lactis strains with diverse eps gene clusters.

Clustering of Streptococcus thermophilus Strains to Establish a Relation between Exopolysaccharide Characteristics and Gel Properties of Acidified Milk

“…Monomer composition was also used by Mozzi et al [13] to distinguish between EPS producers of different species. Recently, there has been an increasing interest in identifying the relationship between gene clusters and textural properties [10,29,30].…”

Use of Cell Envelope Targeting Antibiotics and Antimicrobial Agents as a Powerful Tool to Select for Lactic Acid Bacteria Strains With Improved Texturizing Ability in Milk Fermentations

“…DCS and AMP resistant derivatives, showing improved rheological properties, were identified as having reduced whey syneresis and perceived improved texture when grown in milk compared to the parent strain ( Kibenich et al, 2012 ). While to identify the fosfomycin, vancomycin, and triclosan resistant derivatives with improved texturizing properties, the selected isolates were grown to saturation in broth and inoculated 1% vol/vol into 96-well deep-well plates containing 1.8 ml/well B-milk including the pH indicators bromocresol purple and bromocresol green ( Poulsen et al, 2019 ). After fermentation at 37°C, the texturizing properties of the derivatives were assessed using the TADM-based method described in Poulsen et al (2019) .…”

“…While to identify the fosfomycin, vancomycin, and triclosan resistant derivatives with improved texturizing properties, the selected isolates were grown to saturation in broth and inoculated 1% vol/vol into 96well deep-well plates containing 1.8 ml/well B-milk including the pH indicators bromocresol purple and bromocresol green (Poulsen et al, 2019). After fermentation at 37 • C, the texturizing properties of the derivatives were assessed using the TADMbased method described in Poulsen et al (2019). Finally, the most interesting candidates from all selections were grown to saturation in the appropriate broth and inoculated 1% vol/vol into 200 ml full fat milk and then fermented overnight at 40 • C. The milk used for rheology measurement was added 2% whey protein to standardize the protein content of the milk.…”

Gene-Trait Matching and Prevalence of Nisin Tolerance Systems in Lactococus lactis

“…One hundred and fifty microliter of each of the 710 inoculated milk samples were then mixed with 50 µl of one of the two CFS types described above, resulting in a final nisin A concentration of 0.0 or 1.5 µg ml −1 , and incubated for 18 h at 30 • C on flatbed scanners (HP ScanJet G4010) to obtain HUE-values every 6 min. Acidification profiles were obtained by converting HUE-values into pH values as described previously (Poulsen et al, 2019). Experiments with CFS from Wg2 and ATCC 11454 were always run in parallel and the experiments were performed in triplicates: one technical and two biological replicates.…”