Adaptation of Lactobacillus acidophilus to Thermal Stress Yields a Thermotolerant Variant Which Also Exhibits Improved Survival at pH 2

Abstract

Loss in probiotic viability upon exposure to stressful storage and transport conditions has plagued the probiotic market worldwide. Lactobacillus acidophilus is an important probiotic that is added to various functional foods. It is known to be fairly labile and susceptible to temperature variations that it encounters during processing and storage which increases production cost. It has been repeatedly demonstrated that pre-exposure to sub-lethal doses of stress, particularly, temperature and pH, leads to improved survival of various probiotics when they subsequently encounter the same stress of a much greater magnitude. Attempts to adapt L. acidophilus to temperatures as high as 65 °C to arrive at a thermotolerant variant have not been reported previously. To improve viability at elevated temperatures, we gradually adapted the L. acidophilus NCFM strain to survival at 65 °C for 40 min. Following adaptation, the variant showed a 2-log greater survival compared to wild-type at 65 °C. Interestingly, this thermotolerant variant also demonstrated a 2-log greater stability compared to wild-type at pH 2.0. The improved pH and temperature stress tolerance exhibited by this variant remained unaltered even when the strain was lyophilized. Moreover, the thermotolerant variant demonstrated improved stability compared to wild-type when stored for up to a week at 37 and 42 °C. Probiotic properties of the variant such as adherence to epithelial cells and antibacterial activity remained unaltered. This strain can potentially help address the issue of significant loss in viable cell counts of L. acidophilus which is typically encountered during probiotic manufacture and storage.

Stress adaptation and cross-protection of Lactobacillus plantarum KLDS 1.0628

“…adaptation did little to enhance the acid tolerance, which is similar to the results reported by Chen et al (2017) and is different from Kulkarni et al (2018). The results illustrated that acid adaptation can be used as a potential strategy to improve cell survival in response to multiple lethal stresses.…”

Lactobacillus , Bifidobacterium and Lactococcus response to environmental stress: Mechanisms and application of cross‐protection to improve resistance against freeze‐drying

“…One of the stress responses of LAB is heat-related stress (Chang-Ho et al, 2015). Kulkarni et al (2018) reported that Lactobacillus acidophilus could survive at 65℃ for 40 min and exhibited a positive correlation between the synthesis and induction of heat shock proteins (HSPs). The up-regulation of HSPs, including the chaperonins (DnaK and GroEL) and cofactors (GroES), is the main adaptation for the enhanced heat resistance of LAB.…”

Complete Genome Sequence of the Newly Developed Lactobacillus acidophilus Strain With Improved Thermal Adaptability

“…We have demonstrated that the newly developed L. acidophilus EG008 strain had better thermal resistance than wild type at high temperatures of 65-75 • C (Figure 2B). Recently, studies on the development of EG008 strains using ALE have been conducted (Kulkarni et al, 2018;Min et al, 2020), but most of the experiments were performed at temperatures below 65 • C to ensure applicability in LTST pasteurization (Vaudagna et al, 2002). Therefore, the EG008 strain developed in this study is expected to be utilized for HTST pasteurization, which sterilizes at a relatively high temperature.…”

“…In another study, the thermal resistance of L. acidophilus LA1-1 was measured at 37-58 • C (Kim et al, 2001). There have also been attempts to develop L. acidophilus EG008 strains using ALE such as L. acidophilus NCFM at 65 • C (Kulkarni et al, 2018) and Lactiplantibacillus plantarum Lp 998 at 45-55 • C (Ferrando et al, 2015).…”