| Abstract [eng] |
Bioactive immobilization systems are a new technology concept that aids in the production of functional foods in which bioactive components are present in the immobilizing material or are immobilized to create a safe food product with specific properties. The aim of the project was to immobilize lactic acid bacteria with antimicrobial properties in the matrix of rice bran and lingonberry press cake, ensuring the highest bioactivity and stability of microorganisms during storage and release under simulated digestive conditions. The objectives of the project - to determine the conditions of ultrasound treatment (US) of rice bran (RB) for efficient production of resistant starch (RS), and evaluate the influence of US, lingonberry press cake (BR) additive and stabilizers on the viability and antimicrobial activity of selected antimicrobial PRBs. Also, the evaluation of the stability of RB-BR gel-type matrices and immobilized PRB during storage and their release under simulated digestive conditions was carried out. Results showed that the optimal conditions for US treatment (850 kHz) for efficient RS formation in rice bran were as follows: power 2 W/cm2; duration 20 min., temperature 40 °C. Under these conditions, a quantity of 11,79 mg/100 g of RS can be obtained. US treatment of RB and the addition of BR of 10‒50 % increased the number of tested LAB on average by 11%, and improved their antimicrobial activity. The metabolites of L. brevis LUHS173 and P. pentosaceus LUHS100 (5 and 4 inhibited pathogens from 5 in total) had the highest antimicrobial activity against the five tested indicator microorganisms. The most stable RS-BR gel texture was obtained using sodium alginate (hardness and consistency values, 5.2 N and 27.8 Ns, respectively) compared to agar and xanthan gum (3 N and 13.9 N*s, respectively). It was found that the storage time and temperature, and type of stabilizer had a significant effect (p<0.05) on the stability of RS-BR gels and the viability of immobilized LAB. The largest decrease in cell number at the end of the storage period was observed in the RS-BR gel with xanthan gum (2.46 log CFU/g), and the most stable cells were maintained after immobilization in the alginate gel (change of 0.76 log CFU/g). The stability of immobilized LABs under simulated digestive conditions was significantly affected by the medium and the stabilizer used. Gels with agar had the lowest stability in this medium (average number of cells released from the gel was 7.35 log CFU/ml, and gels with alginate were of the highest stability (number of cells released in the medium was 4.03 log CFU/ml). medium (pH 7.5), the number of viable cells released averaged 9%, and the lowest stability in this medium was found in gels with xanthan (average 4.38 log CFU ml). In summary, it can be concluded that brown rice bran with a higher content of resistant starch and a lingonberry pulp matrix can ensure the stability of immobilized LAB, protecting against environmental influences during storage (the number of remaining cells in the gel averaged 6.01 log CFU/g) and rapid degradation under digestive conditions, thus ensuring their uniform release, having a potential positive effect on health. |
