An alternative solution against mould spoilage problem in tomato paste: Lyophilised postbiotic addition

The aim of this thesis was to test the antifungal and antiaflatoxigenic activity of lyophilised postbiotics against the mould spoilage problem on the surface of tomato paste and to determine the molecules and compounds that contribute to this effect. For this purpose, the chemical composition, in vitro antifungal activity and antioxidant capacity of the postbiotic obtained from Lactiplantibacillus plantarum ATCC 14917 strain were determined. A total of 5 different organic acids, 22 polyphenolic compounds, 12 free fatty acids, 21 free amino acids, and 67 volatile compounds were identified in the postbiotic. Furthermore, the postbiotic displayed a strong antioxidant capacity, as evidenced by the DPPH (30353.66 ± 0.01 mg TEAC/kg), ABTS (13427.84 ± 0.05 mg TEAC/kg) and FRAP (8630.6 ± 0.01 mM FE/kg) assays. In vitro antifungal activity tests showed that the minimum inhibitory and fungicidal concentrations of the postbiotic against Aspergillus parasiticus NRRL 2999 were found to be 12.5 and 100 mg/mL, respectively, and 10 mg of the postbiotic exhibited an inhibition zone of 16.47 mm. In addition, the tomato pastes were experimentally inoculated with the mould at 105 cfu/g. The postbiotics were added at 4, 6 and 8-folds of the MIC value (MIC × 4, MIC × 6, MIC × 8) and physical, chemical and microbiological changes were monitored during the 45-day storage period at 4 °C. Compared to the group without postbiotic addition (control), the addition of lyophilised postbiotic inhibited A. parasitucus and the number of the moulds in the MIC × 8 group was below the detection limit on day 45 (p˂0.05). Total mesophilic aerobic, psychrotrophic, lactic acid and sulphite-reducing bacteria were found to be significantly lower in the postbiotic-added groups in comparison to the control group (p˂0.05). In contrast, pH, colour, and titratable acidity did not change significantly during storage in all groups (p˃0.05). It was also found that depending on the concentration postbiotics significantly reduced the amount of aflatoxin B1, B2, G1 and G2 by binding (p˂0.05). In conclusion, the addition of lyophilized postbiotics to tomato paste showed potent antifungal and anti-aflatoxigenic effects without significantly altering the physicochemical properties and contributed to improving the microbiological quality of the paste.