Abstract
Applying sub-lethal levels of high-pressure homogenization (HPH) to lactic acid bacteria has been proposed as a method of enhancing some of their functional properties. Because the principal targets of HPH are the cell-surface structures, the aim of this study was to examine the effect of sub-lethal HPH treatment on the outermost cellular structures and the proteomic profiles of two known probiotic bacterial strains. Moreover, the effect of HPH treatment on the metabolism of probiotic cells within a dairy product during its refrigerated storage was investigated using SPME-GC-MS. Transmission electron microscopy was used to examine the microstructural changes in the outermost cellular structures due to HPH treatment. These alterations may be involved in the changes in some of the technological and functional properties of the strains that were observed after pressure treatment. Moreover, the proteomic profiles of the probiotic strains treated with HPH and incubated at 37°C for various periods showed different peptide patterns compared with those of the untreated cells. In addition, there were differences in the peaks that were observed in the low-mass spectral region (2000–3000 Da) of the spectral profiles of the control and treated samples. Due to pressure treatment, the volatile-molecule profiles of buttermilk inoculated with treated or control cells and stored at 4°C for 30 days exhibited overall changes in the aroma profile and in the production of molecules that improved its sensory profile, although the two different species imparted specific fingerprints to the product. The results of this study will contribute to understanding the changes that occur in the outermost cellular structures and the metabolism of LAB in response to HPH treatment. The findings of this investigation may contribute to elucidating the relationships between these changes and the alterations of the technological and functional properties of LAB induced by pressure treatment.
Highlights
There has been increasing interest in the potential of applying techniques such as pulsed electric field (PEF), highhydrostatic pressure (HHP), or high-pressure homogenization (HPH) to enhance the survival rate of probiotic strains or to modify their overall functionality in a positive manner
Considering that some probiotic properties are associated with the bacterial cell wall, which is the principal target of HPH, the aim of this study was to evaluate the effect of sublethal HPH treatment on the outermost structures of two strains endowed with probiotic features (Lactobacillus acidophilus DRU and Lactobacillus paracasei A13) using transmission electron microscopy (TEM)
It was demonstrated that HPH treatment at 50 MPa enhanced certain probiotic properties of lactic acid bacteria (LAB) and changed the fatty acid composition of the cell membrane as response to the sub-lethal stress applied (Tabanelli et al, 2013, 2014)
Summary
There has been increasing interest in the potential of applying techniques such as pulsed electric field (PEF), highhydrostatic pressure (HHP), or high-pressure homogenization (HPH) to enhance the survival rate of probiotic strains or to modify their overall functionality in a positive manner. Sub-lethal HPH treatment improved the acid tolerance and bile tolerance of L. acidophilus LA-K (Muramalla and Aryana, 2011) and enhanced some of the biological and functional properties of known probiotic strains both in vitro and in vivo, and in mice, trials (Tabanelli et al, 2013, 2014) The latter authors demonstrated that an HPH treatment applied at 50 MPa modulated the hydrophobicity and auto-aggregation of the treated strains in vitro and modified their interaction with the small-intestinal structures of BALB mice. Some authors showed that modulating the membrane fatty-acid composition in response to environmental conditions affected the cell-surface hydrophobicity and adhesive ability of bacterial strains and, their functional features (Kirjavainen et al, 1998; Kankaanpää et al, 2001, 2004)
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