Abstract
Sub-lethal high-pressure homogenization treatments applied to Lactobacillus paracasei A13 demonstrated to be a useful strategy to enhance technological and functional properties without detrimental effects on the viability of this strain. Modification of membrane fatty acid composition is reported to be the main regulatory mechanisms adopted by probiotic lactobacilli to counteract high-pressure stress. This work is aimed to clarify and understand the relationship between the modification of membrane fatty acid composition and the expression of genes involved in fatty acid biosynthesis in Lactobacillus paracasei A13, before and after the application of different sub-lethal hyperbaric treatments. Our results showed that Lactobacillus paracasei A13 activated a series of reactions aimed to control and stabilize membrane fluidity in response to high-pressure homogenization treatments. In fact, the production of cyclic fatty acids was counterbalanced by the unsaturation and elongation of fatty acids. The gene expression data indicate an up-regulation of the genes accA, accC, fabD, fabH and fabZ after high-pressure homogenization treatment at 150 and 200 MPa, and of fabK and fabZ after a treatment at 200 MPa suggesting this regulation of the genes involved in fatty acids biosynthesis as an immediate response mechanism adopted by Lactobacillus paracasei A13 to high-pressure homogenization treatments to balance the membrane fluidity. Although further studies should be performed to clarify the modulation of phospholipids and glycoproteins biosynthesis since they play a crucial role in the functional properties of the probiotic strains, this study represents an important step towards understanding the response mechanisms of Lactobacillus paracasei A13 to sub-lethal high-pressure homogenization treatments.
Highlights
High-pressure homogenization (HPH) is one of the most promising alternatives to traditional thermal treatments for food preservation and product innovation due to the physico-chemical, structural changes following the treatment
HPH treated cells were characterized by increased concentrations of both saturated fatty acids (SFAs), such as C12:0, C13:0, C14:0, C16:0 and C18:0, and unsaturated fatty acids (UFAs) such as C16:1, C18:1 cis and C18:1 trans
Both SFA and UFA concentrations increased in almost all HPH treated cells, the ratio UFA/SFA reached its maximum score at 150 MPa
Summary
High-pressure homogenization (HPH) is one of the most promising alternatives to traditional thermal treatments for food preservation and product innovation due to the physico-chemical, structural changes following the treatment. The microbial inactivation caused by the application of HPH, affected by several factors and mainly by the physio-chemical features of the food matrix and the sensitiveness of different microorganisms, increases with the pressure level [12]. HPH treatments, at levels lower than 100 MPa (sublethal pressures), applied to microbial starter, co-starter or probiotic cultures of lactic acid bacteria (LAB) and yeasts, are reported to change their metabolic and enzymatic activities resulting in the production of probiotic fermented milks or cheeses with improved sensorial, technological, or functional properties. Sub-lethal HPH treatments applied to LAB demonstrated to be a useful strategy to regulate, in a strain-dependent manner, fermentation kinetics, proteolytic activities and volatile molecule profiles of starter cultures and non-starter LAB, without detrimental effects on their viability [4]. Concerning the probiotic features, sub-lethal HPH treatments improved acid and bile tolerances of Lactobacillus acidophilus LA-K [15] and enhanced some technological and functional properties of Lb. acidophilus 08, Lb. acidophilus DRU and Lb. paracasei A13 [16,17]
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