Extraction of postbiotics from lactobacillus acidophilus by using heat treatment and ultrasound

Probiotics are microorganisms that provide health benefits to the host when taken in sufficient amounts in viable form. However, due to storage problems and theoretical health concerns arising from the fact that these microorganisms are alive, studies have been conducted on postbiotics obtained by inactivating these microorganisms and it has been observed that postbiotics can mimic the benefits that probiotics provide. In this thesis study, the effects of inactivating the selected probiotic microorganism (Lactobacillus acidophilus) using thermal and ultrasound treatment on postbiotic properties were examined. Postbiotics were produced under 16 different temperature-duration conditions (65 °C-95 °C temperature and 5-90 minutes) during thermal treatment, and it was determined that probiotics were inactivated under all thermal treatment conditions. It was found that ultrasound treatment at a constant frequency (20 kHz) with varying amplitude (98 µm-320 µm range) and duration (15-60 minutes range) was effective in the inactivation of probiotics, though inactivation was not achieved under all conditions. Probiotic inactivation was achieved at amplitude/duration combinations of 98 µm at 30, 45, and 60 minutes, 172 µm at 30, 45, and 60 minutes, 246 µm at 45 and 60 minutes, and 320 µm at 60 minutes during ultrasound treatment, and it was observed that inactivation was more effective at lower amplitudes compared to higher amplitudes. To investigate whether the produced postbiotics have enhancing activities on probiotics, a probiotic environment consisting of Lacticaseibacillus casei and a Bifidobacterium culture mixture was selected. The probiotic-enhancing activity of the postbiotics which were inactivated by thermal treatment was found to be higher activity compared to those inactivated by ultrasound. It was observed that, with the addition of postbiotics, inactivated by thermal treatment, particularly affecting L. casei and significantly increasing the probiotic count (up to 10.77-fold increase). The postbiotics produced by thermal treatment also provided up to a 3.54-fold increase in the Bifidobacterium culture. However, with postbiotics produced by ultrasound, depending on the production conditions, very low levels of increase (0.40%) or even decreases (-0.23%) were observed. It was determined that the antimicrobial activity of postbiotics produced at low temperature and short duration during thermal treatment provide higher activity compared to the antimicrobial activity of postbiotics produced by ultrasound, causing a reduction of 14.58% on E. coli and 8.37% on E. faecalis. It was observed that antimicrobial activity decreased with increasing temperature and duration during postbiotic production. The antimicrobial activity of postbiotics produced by ultrasound caused a reduction of 10.04% on E. coli and 3.96% on E. faecalis. Additionally, it was observed that when postbiotics produced by both inactivation methods were added to the probiotic environment, the production of short-chain fatty acids in the environment was significantly increased. Keywords: Inactivation, Microbiota, Microorganisms, Postbiotic, Probiotic