Heat Treatment of Fibers Used as Growth Supplement for Lactobacillus acidophilus and Lactobacillus rhamnosus

The interaction between humans and microbes that colonize the human body has been a topic of great interest among the scientific community in recent years. Furthermore, the relationship between these probiotic bacteria and the use of prebiotics has also gained attention. The most common prebiotics used in human nutrition are fibers; therefore, learning how fibers can affect the growth of probiotics is a priority. Furthermore, fiber supplementation has been proven beneficial and recommended by the American Heart Association. However, fiber consumption has not increased substantially over the last few decades. Therefore, finding a new benefit of fiber consumption may result in improved intake. We have previously shown that supplementing growth media with different fibers (prebiotics) can stimulate the growth of Lactobacilli. However, some of the supplemented fibers did not stimulated growth as expected. Therefore, it was hypothesized that heat‐treating the fibers before exposure to the bacteria would improve their availability, which would improve bacterial growth. To test this hypothesis, L. acidophilus ( LA , ATCC 4356™) and L. rhamnosus ( LR , ATCC® 53103™) were used as the bacterial inoculum grown on MRS (de Man, Rogosa and Sharpe) broth supplemented with different fiber. Four different fibers (inulin, fructoligosaccharide ‐FOS, psillyum, and β‐glucan) were used in the study mixed in the media at a concentration of 1%. Fibers were added to the broth before autoclaving for sterilization and heat treatment. After inoculation, tubes were incubated at 37 °C in microaerophilic environment for 24 h, then plated onto the MRS agar plates and grown for 48–72 h at 37°C in microaerophilic environment. Colonies were counted and expressed in colony forming units (CFU). Data of our previous study was used for comparison. The pH of the broth was measured and compared between treatments and bacteria. After statistical analysis, psyllium and β‐glucan supplementation significantly increased the growth of LR (p=0.02) after the heating process. LR growth was significantly higher than LA both in the current study (8.8 vs. 7 log CFU/ml, p<0.001) and in the previous (9 vs. 7.5 log CFU/ml, p<0.001). After the data was compared to the previous study (without heat treatment), on average LA (7.5 vs. 7 log CFU/ml, p=0.0361) as well as LR (9 vs. 8.8 log CFU/ml, p=0.0213) showed significantly higher populations without heat‐treating the fibers. pH reduced significantly after growth in all treatments, but it was significantly lower for LR than for LA (4.2 vs. 5.3, p<0.001). In conclusion, LA is a more fastidious organism compared to LR , which might account for the lack of improvement in growth after fiber supplementation. The pH of the medium decreased after growth, but it was not influenced by the treatments. Even though the treatment effect was not as significant compared to the previous study, LR was still influenced by fiber supplementation, in which for the second time, psyllium showed to improve LR growth. Therefore, after the comparison of the two experiments, heating treatment did not improve the use of supplemented fiber as predicted. Lastly, more studies are needed to elucidate how bacterial cells react when exposed to higher fiber concentrations. Support or Funding Information This research project was funded by the seed grant of the Adventist University of Health Sciences.