Effect of Nigella sativa L. essential oil on oxidative stability and microbial growth of local white Feta cheese.

Controlling the development of pathogenic and spoilage microorganisms is critical for food manufacturers to preserve their products. Cheese provides favourable conditions for microbial growth and oxidative degradation due to the presence of water, fat, protein, and minerals. The present work thus aimed to determine the influence of Nigella sativa L. essential oil on microbial growth and oxidative stability of cheese made from fresh milk. The analysis of the chemical composition of N. sativa essential oil was performed by gas chromatography-mass spectrometry. The main compounds detected were 9,12- octadecadienoic acid (27.96%), cis-vaccenic acid (20.69%), 6-epi-shyobunol (7.08%), benzene, 1-methyl-3-(1-methylethyl)- (6.33%), n-hexadecanoic acid (3.86%), o-cymene (2.77%), and cis-4-methoxy thujane (2.71%). The antioxidant activity of N. sativa essential oil was calculated by the 2,2-diphenyl-1-picrylhydrazyl method with IC50 = 8.08 μg/mL. The microdilution test showed that the minimum inhibitory concentration (MIC) of N. sativa essential oil for all pathogens was 500 μg/mL, while the minimum bactericidal concentration (MBC) was 1,000 μg/mL for Staphylococcus aureus and Bacillus cereus, and 2,000 μg/mL for Escherichia coli and Pseudomonas aeruginosa. The physicochemical properties of the cheese showed that the addition of essential oil did not affect the dry matter, but increased the pH, decreased the % acidity, and decreased the peroxide value compared to the control sample (sample without essential oil). In addition, the essential oil reduced the bacterial and fungal counts of the cheese compared to the control sample, and affected the sensory characteristics of the cheese during the 90-day storage period. Results also showed that the addition of 0.5% essential oil of N. sativa not only prevented microbial growth and oxidative degradation, but also improved the taste and overall acceptability of cheese. [ABSTRACT FROM AUTHOR]