Abstract
The following study was designed to explore antimicrobial properties of the by-product obtained in a hydro-distillation process of essential oil from Nepeta nuda L. We strived to develop a novel drink with antimicrobial self-preserving properties based on two components, N. nuda decoct and apple juice. By using 96-well plate microdilution assay it was shown that the N. nuda decoct has antimicrobial potential towards 8 bacterial and 6 fungal species, with the range of minimal inhibitory concentrations 10-300 mg/mL. By using actual food system, such as apple juice, in combination with and without short thermal treatment, we have shown that the decoct of N. nuda can inhibit the growth of food contaminant fungus Penicillium aurantiogriseum. It was determined that 3 volumes of decoct (500 mg/mL) and 22 volumes of apple juice should be mixed in order to obtain self-preserving drink resistant to P. aurantiogriseum contamination. Likewise, when thermal treatment (80 °C for 10 s) is included, self-preserving mixture of decoct and apple juice should be made in volume ratios 3:47, respectively. The designed product maintained the pleasant taste as determined by panelists during the sensorial evaluation. Chemical investigations (UHPLC-Orbitrap MS analysis) of N. nuda decoct showed that the most abundant compound was 1,5,9-epideoxyloganic acid (0.410 mg/g of dried decoct). Since N. nuda is traditionally used as a tea, we presented the novel formulation of the drink with antimicrobial properties based on the its decoct and apple juice.
Highlights
Apple juice is one of the most widely consumed juices due to its health beneficial and nutraceutical properties accompanied by a pleasant taste
Since N. nuda is traditionally used as a tea, we presented the novel formulation of the drink with antimicrobial properties based on the its decoct and apple juice
The other investigated species of bacteria such as Micrococcus flavus, Salmonella typhimurium, Enterobacter cloacae, Listeria monocytogenes, Staphylococcus aureus and Bacillus cereus showed the same reaction to inhibitory and bactericidal effect of the N. nuda decoct (MIC 10 mg/mL; minimum bactericidal concentration (MBC) 20 mg/mL)
Summary
Apple juice is one of the most widely consumed juices due to its health beneficial and nutraceutical properties accompanied by a pleasant taste. Juice quality and safe consumption rely on methods like refrigeration and addition of chemical preservatives to keep the product safe. Disease outbreaks, related to consumption of food contaminated with microorganisms, increased (Gayán et al, 2013). Pasteurization, sterilization and addition of synthetic antimicrobials can solve this issue and can change products’ characteristics like color, aroma, and vitamin content (Heinz et al, 2003). Heat treatment and addition of antimicrobial preservatives are frequently used tools to dispose of microorganisms and extend shelf life of foods and beverages (Gayán et al, 2013). There is a notable interest in using natural matrices as juice preservatives that would keep the product safe for use and extend its shelf-life
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