Elimination of detached Listeria monocytogenes from the biofilm on stainless steel surfaces during milk and cheese processing using natural plant extracts.

Bacterial cells can form biofilm on food contact surfaces, becoming a source of food contamination with profound health implications. The current study aimed to determine some Egyptian medicinal plants antibacterial and antibiofilm effects against foodborne bacterial strains in milk plants. Results indicated that four ethanolic plant extracts, Cinnamon (Cinnamomum verum), Chamomile (Matricaria chamomilla), Marigold (Calendula officinalis), and Sage (Salvia officinalis), had antibacterial (12.0-26.5 mm of inhibition zone diameter) and antibiofilm (10-99%) activities against Staphylococcus aureus, Bacillus cereus, Listeria monocytogenes and Salmonella Typhimurium. The tested extracts had minimum inhibitory concentration values between 0.14 and 2.50 mg/ml and minimum bactericidal concentration values between 0.14 and 12.50 mg/ml. L. monocytogenes was more sensitive for all tested ethanolic extracts; Sage and Cinnamon showed a bacteriocidal effect, while Chamomile and Marigold were bacteriostatic. The ethanolic extracts mixture from Chamomile, Sage, and Cinnamon was chosen for its antibiofilm activity against L. monocytogenes using L-optimal mixture design. Gas chromatography and mass spectrometry analysis showed that this mixture contained 12 chemical compounds, where 2-Propenal,3-phenyl- had the maximum area % (34.82%). At concentrations up to 500 µg/ml, it had no cytotoxicity in the normal Vero cell line, and the IC50 value was 671.76 ± 9.03 µg/ml. Also, this mixture showed the most significant antibacterial effect against detached L. monocytogenes cells from formed biofilm in stainless steel milk tanks. At the same time, white soft cheese fortified with this mixture was significantly accepted overall for the panelist (92.2 ± 2.7) than other cheese samples, including the control group.

Characterization and application of tannase and gallic acid produced by co-fungi of Aspergillus niger and Trichoderma viride utilizing agro-residues substrates.

Bioconversion using fungi, as natural factory of many applicable bioactive compounds, as enzymes utilizing agro-residue substrates as a solid, abundant, low-cost growth and enzyme production media. This study characterized and applied a tannase enzyme (308 U/mg) from Aspergillus niger A8 + Trichoderma viride co-cultures utilizing pomegranate peels. The partially purified enzyme showed maximal relative activity at 37-65 °C for 10 min and kinetics of thermal inactivation energy at a high point at 60 °C for 0.040/min. The half-life was 37 °C for 58.6 min, temperature coefficient Q10 of tannase was maximal for 1.38 between 40 and 50 °C, and the activation energy was 17.42 kJ/mol. The enzyme activity peaked in the pH range of 4-8, and the maximum relative activity (100.6%) for tannase was achieved at pH 6. The Km and Vmax values for purified enzymes using tannic acid were 7.3 mg/mL and 3333.33 U/mL, respectively. The enzyme reduced the total tannin content in all tannin-rich substrates after 12h. The gallic acid (GA) had total phenols of 77.75 ppm and antioxidant activity of 82.91%. It was observed that the GA as antimicrobial influencer exhibited the largest inhibitory zone diameter (IZD) of 31 ± 1.0 mm against Pseudomonas aeruginosa ATCC27853. The GA minimum inhibitory concentration value was ranged from 7770.0-121.41 µg/mL. The obtained GA showed a bactericidal effect against all bacterial strains except Shigella sonnei DSM5570 and Salmonella typhi DSM17058, which showed bacteriostatic behavior.