Impact of Lacticaseibacillus rhamnosus GG on the Emulsion Stability of Raw Milk.

Raphael Dos Santos Morais,Joël Scher,Jennifer Burgain,Claire Gaiani,Dominique Dumas,Frederic Borges,Sarah Barrau,Loubiana Cvetkovska-Ben Mohamed,Nicolas Louvet

doi:10.3390/foods10050991

Abstract

Lactic acid bacteria (LAB) have been studied for several decades to understand and determine their mechanism and interaction within the matrix into which they are introduced. This study aimed to determine the spatial distribution of Lacticaseibacillus rhamnosus GG (LGG) in a dairy matrix and to decipher its behaviour towards milk components, especially fat globules. Two strains of this widely studied bacterium with expected probiotic effects were used: LGG WT with pili on the cell surface and its pili-depleted mutant—LGG ΔspaCBA—in order to determine the involvement of these filamentous proteins. In this work, it was shown that LGG ΔspaCBA was able to limit creaming with a greater impact than the wild-type counterpart. Moreover, confocal imaging evidenced a preferential microbial distribution as aggregates for LGG WT, while the pili-depleted strain tended to be homogenously distributed and found as individual chains. The observed differences in creaming are attributed to the indirect implication of SpaCBA pili. Indeed, the bacteria-to-bacteria interaction surpassed the bacteria-to-matrix interaction, reducing the bacterial surface exposed to raw milk. Conversely, LGG ΔspaCBA may form a physical barrier responsible for preventing milk fat globules from rising to the surface.

Highlights

Milk is used to design secondary products, such as yogurts or cheese
In the absence of bacteria, the backscattering intensity increased on the top of the sample (60–70 mm), which is the result of fat globule accumulation due to creaming
With regard to the addition of Lacticaseibacillus rhamnosus GG (LGG) to raw milk (Figure 1B,C), it can be observed that the addition of bacteria to raw milk tends to attenuate natural creaming by limiting the rising of fat globules to the surface

Summary

Introduction

Milk is used to design secondary products, such as yogurts or cheese. It is a complex colloidal system whose main constituents are water, fat in the form of fat globules, proteins, lactose and minerals [1]. Milk is an oil-in-water emulsion composed of 90% water presenting a supramolecular organization with fat globules (diameters ranging from 1 to 10 μm) surrounded by the milk fat globule membrane (MFGM), which has a high polar lipid and protein content [2] This emulsion may become unstable due to physical instability, i.e., a change in the spatial arrangement or size distribution of the fat globules, such as creaming, flocculation or coalescence [3,4]. Natural creaming occurs when the native fat globules present in non-agitated raw milk rise to the surface and form a concentrated layer at the top of the sample, with no change in the droplet size distribution [6]. Since raw milk is known to be naturally unstable, the role of LGG on emulsion stability was evaluated

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