Investigations of antimicrobial lactic acid bacteria (PRB) functionalization in rice mill waste and berry pulp model systems,
by sonication for the formation of digestion-resistant starch and modeling of selected antimicrobially active microorganisms and pectic material (berry) matrices stabilized in rice bran medium while maintaining a stable structure and maximum viability of microorganisms at different temperatures.
Project funding:
Project is funded by EU Structural Funds according to the 2014–2020 Operational Programme for the European Union Funds’ Investments priority “Development of scientific competence of researchers, other researchers, students through practical scientific activities” under Measure No. 09.3.3-LMT-K-712.
Project results:
Results obtained:
1. The quantitative RS/BR ratio had a significant effect on the texture parameters of the analyzed immobilization systems as a function of treatment UG duration. The RS additive reduced the hardness and consistency of the gel and increased the cohesion (stickiness). The RS-BR system had the highest values ??of texture parameters, in which the ratio of components was 1: 1, and the optimal duration of mass processing at UG 40oC was 30 min.
2. The type of stabilizer had a significant effect on the texture and setting rate of RS-BR systems. The most stable gel texture was obtained using sodium alginate, which provided higher values ??of hardness and consistency compared to agar and xanthan. Also, gels prepared with alginate had the highest cure rate, while gels with agar and xanthan stalled more slowly.
3. In all cases, the addition of blueberry pulp (BR) increased the number of L. brevis LUHS173 cells by 10 to 50%, depending on the incubation time. The highest cell number (9.25 log CFU / ml) was reached after 12 h of fermentation in RS medium with 50% BR additive. For immobilization using P. pentosaceus LUHS100, the highest cell number was found after 12 h fermentation in UG-treated RS medium with 10% BR additive (9.25 log CFU/ml), and> 30% BR additive inhibited LUHS100 growth.
4. The antimicrobial activity of lactic acid bacteria depended on the fermentation time, the amount of BR additive and the PRB strain. In all cases, the addition of BR increased the antibacterial activity of PRB. BR 20?50% supplementation increased the antimicrobial activity of L. brevis LUHS173 from mild to moderate against all indicator microorganisms used in the study. Antimicrobial activity against E. coli, S. typhimurium, B. cereus and St. aureus was characterized by fermented samples of P. pentosaceus LUHS100 with 50% BR addition.
5. Storage time significantly affected the moisture loss of RS-RB gels. After 28 days of storage, the significant moisture losses in gels stored at 4oC averaged 8.2%, those stored at 18oC averaged 10.4%, and at the end of the storage period, moisture losses averaged 13.5 and 15%. Stability was observed in gels prepared with sodium alginate: moisture loss was found to be significantly lower, 6.6–7.8%, respectively, compared to agar and xanthan gels (17.6–20.2%).
6. The highest stability of PRB was found during the 35-day storage period in the RS-BR immobilization system stabilized with agar and alginate: the number of viable cells in these systems decreased on average by 6.2%. At the end of the storage period, no significant differences were found between the number of PRBs in the gels stored in temperature. The highest number of viable cells was found in alginate gels (mean 6.67 log CFU/g) stored at 4oC.
Recommendation:
The RS-BR model system, structured by high-intensity ultrasound for 30 min at 40oC, is suitable for immobilizing antimicrobial Lactobacillus brevis LUHS173, increasing their antimicrobial activity and maintaining stability: in stabilized sodium alginate RS-BR gels after 8 weeks of exposure to 4oC brevis cell count was set at 6.67 CFU/g.
Period of project implementation: 2019-10-15 - 2020-04-30
Project coordinator: Kaunas University of Technology
