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    Comparative analysis of thermal and ultrasound inactivation of Lactobacillus acidophilus LA-5: Viability by flow cytometry and plate count and postbiotic functional properties
    (Elsevier, 2025) Muldur, Dogukan Yiltan; Erbay, Zafer; Yavas, Adem; Akan, Ecem
    Considering the potential of postbiotics to exert health effects similar to probiotics and the limited data available in the literature, this study aimed to evaluate the viability and functional properties of Lactobacillus acidophilus LA-5 under different heat and ultrasound treatment conditions. The probiotic microorganism L. acidophilus LA-5 was subjected to 16 different heat treatments (65 degrees C-95 degrees C, 5-90 min) and 16 different ultrasound treatments (98 mu m-320 mu m, 15-60 min). Cell damage levels (colony count and flow cytometry) and functional properties of the inactivated probiotics (postbiotics), including antimicrobial activity, probiotic-enhancing activity, and short-chain fatty acid (SCFA) production in Lacticaseibacillus casei 431 and Bifidobacterium culture media, were assessed. All heat treatments achieved complete inactivation, while only 9 ultrasound conditions were fully effective. In ultrasound-treated samples, flow cytometry and colony count results were inconsistent, suggesting possible formation of viable but non-culturable cells, complicating viability assessments. Heat-treated postbiotics significantly enhanced the growth of L. casei 431, achieving up to a 10.8-fold increase compared to the control (p < 0.05), while ultrasound-treated postbiotics showed minimal effect. The strongest antimicrobial activity was observed in heat-treated postbiotics, reducing Escherichia coli and Enterococcus faecalis populations by 14.6 % and 8.4 %, respectively, compared to 10.0 % and 4.0 % with ultrasound-treated samples. Both methods increased SCFA levels, with heat-treated postbiotics at 65 degrees C yielding the highest acetic and significantly elevated butyric acid concentrations (p < 0.05). These findings underscore the importance of selecting inactivation strategies tailored to desired postbiotic functions and highlight the need for complementary analyses and standardized criteria to ensure reproducibility and safety in postbiotic applications.
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    Öğe
    Thermal Versus Ultrasound Inactivation of Bifidobacterium animalis subsp. lactis BB-12: Functional Implications for Postbiotics
    (Springer, 2025) Marsak, Nimet; Akan, Ecem; Yavas, Adem; Erbay, Zafer
    This study evaluated the viability and functional properties of postbiotics derived from Bifidobacterium animalis subsp. lactis BB-12 following thermal and ultrasound processing. Sixteen processing conditions were tested, including heat treatments (65-95 degrees C for 5-90 min) and ultrasound amplitudes (98-320 mu m for 15-60 min). Postbiotics were assessed for antimicrobial activity, probiotic-stimulating effects on Lacticaseibacillus casei 431 and Bifidobacterium spp. cultures, and their capacity to enhance short-chain fatty acid (SCFA) production. Complete inactivation was achieved under all heat treatment conditions, whereas only 11 ultrasound conditions resulted in total loss of culturability, indicating greater microbial resistance at lower intensities or shorter exposures. Discrepancies between flow cytometry and colony counting in ultrasound-treated samples suggest the presence of viable but non-culturable cells (VBNC), highlighting the limitations of culture-based viability assessments, especially when assessing VBNC states. Postbiotics from heat-treatment showed significantly stronger probiotic-enhancing effects, with growth increases up to 2.9-fold for L. casei and 37.7-fold for Bifidobacterium spp. compared to controls, alongside greater antimicrobial activity, especially against Enterococcus faecalis. Both processing methods significantly increased SCFA levels (p < 0.05). In conclusion, it can be said that heat treatment was more effective than ultrasound in producing biologically active postbiotics from B. lactis BB-12. The enhanced functional properties observed in heat-inactivated preparations underscore thermal processing as a robust method for postbiotic production. These findings highlight the potential of heat-derived postbiotics as active bioingredients for microbiota-targeted functional foods and nutraceuticals. Further in vivo validation and standardization efforts are needed to fully demonstrate their therapeutic potential and support regulatory approval.