Abstract

SummaryLactic acid bacteria are widely used for the fermentation of dairy products. While bacterial acidification rates, proteolytic activity and the production of exopolysaccharides are known to influence textural properties of fermented milk products, little is known about the role of the microbial surface on microbe–matrix interactions in dairy products. To investigate how alterations of the bacterial cell surface affect fermented milk properties, 25 isogenic Lactococcus lactis strains that differed with respect to surface charge, hydrophobicity, cell chaining, cell‐clumping, attachment to milk proteins, pili expression and EPS production were used to produce fermented milk. We show that overexpression of pili increases surface hydrophobicity of various strains from 3–19% to 94–99%. A profound effect of different cell surface properties was an altered spatial distribution of the cells in the fermented product. Aggregated cells tightly fill the cavities of the protein matrix, while chaining cells seem to be localized randomly. A positive correlation was found between pili overexpression and viscosity and gel hardness of fermented milk. Gel hardness also positively correlated with clumping of cells in the fermented milk. Viscosity of fermented milk was also higher when it was produced with cells with a chaining phenotype or with cells that overexpress exopolysaccharides. Our results show that alteration of cell surface morphology affects textural parameters of fermented milk and cell localization in the product. This is indicative of a cell surface‐dependent potential of bacterial cells as structure elements in fermented foods.

Highlights

  • Lactic acid bacteria (LAB) are Gram-positive bacteria that are generally regarded as safe (GRAS) and are used extensively in food and feed fermentations

  • One of the dominant attributes of LAB is the fact that they produce lactic acid as the main metabolic endproduct of fermentation, which leads to acidification and preservation of the fermented product

  • LAB can play a significant role in altering textural properties of the end-products through acidification, proteolytic activity or the production of extracellular polysaccharides (EPS; Smid and Kleerebezem, 2014)

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Summary

Introduction

Lactic acid bacteria (LAB) are Gram-positive bacteria that are generally regarded as safe (GRAS) and are used extensively in food and feed fermentations. They are found on mucosal surfaces of humans and animals (Stiles and Holzapfel, 1997; Leroy and De Vuyst, 2004). One of the dominant attributes of LAB is the fact that they produce lactic acid as the main metabolic endproduct of fermentation, which leads to acidification and preservation of the fermented product. One economically very important species of LAB, Lactococcus lactis, is used worldwide in the dairy industry for the production of quark, buttermilk and a huge variety of cheeses

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