Abstract
The anti-yeast activity of oil-in-water encapsulated nanoemulsion containing individual or a combination of the three essential oils of Tasmanian pepper leaf (Tasmannia lanceolata), lemon myrtle (Backhousia citriodora), and anise myrtle (Syzygium anisatum) against weak-acid resistant Zygosaccharomyces bailii in clear apple juice was investigated. The effectiveness of the shelf-life extension of Z. bailii-spiked (1 × 103 CFU/mL) clear apple juice was evaluated and compared between natural (essential oils) and synthetic (sodium benzoate) antimicrobial agents. Essential oils showed an immediate reduction in the Z. bailii cell population at day-0 and exerted a fungicidal activity at day-4 of storage, with no further noticeable growth at the end of the experiment (day-28). At lower concentrations, Tasmanian pepper leaf oil of 0.0025% had >6 log CFU/mL at day-12 of storage. For lemon myrtle essential oils, the yeast population reached >6 log CFU/mL at day-24 and day-20 for concentrations of 0.02% and 0.01%, respectively. The fungicidal activity of Tasmanian pepper leaf oil reduced from 0.005% to 0.0025% v/v when mixed at a ratio of 1:1 with anise myrtle oil. The results of the present study suggest that these three native Australian herbs have the potential to be used in the beverage industry by controlling Zygosaccharomyces bailii in clear apple juice products.
Highlights
Controlling the growth of food spoilage causing microorganisms is mainly achieved by the use of synthetic preservatives; they have been linked to negative health effects such as carcinogenicity, acute toxicity, teratogenicity, attention deficit hyperactivity disorder, asthma, and allergy, and to environmental pollution due to their slow degradation [1,2,3,4,5]
Sodium benzoate is soluble in water and converted into benzoic acid once dissolved in water, which becomes undissociated to its protonated acid form (–COOH) at a low pH; once it has entered into the microbial cells, reaching the neutral pH of the cellular cytosol, it dissociates, producing an anion (–COO−) and releasing a proton (H+) inside the cell [26]
Nanoemulsion technology could be utilized to reduce the size of essential oil particles to nanoscale and, with the aid of surfactant, to allow essential oils to be effectively dissolved in liquid while time maintaining their antimicrobial activity in liquid
Summary
Controlling the growth of food spoilage causing microorganisms is mainly achieved by the use of synthetic preservatives; they have been linked to negative health effects such as carcinogenicity, acute toxicity, teratogenicity, attention deficit hyperactivity disorder, asthma, and allergy, and to environmental pollution due to their slow degradation [1,2,3,4,5]. With the current status of limiting the use of synthetic preservatives in food products, it has become a challenge for the beverage industry to increase the dosage of weak-acid preservatives to control the growth of resistant yeasts. This provides an opportunity for plant essential oils to be used as a natural source of antimicrobial agents in beverage products. Plant essential oils are gaining much attention for their use as an alternative solution to control the growth of weak-acid resistant yeast and, at the same time, satisfying modern consumers by the application of natural antimicrobial agents in food products instead of synthetic preservatives [35,36,37]. Nanoemulsion technology could be utilized to reduce the size of essential oil particles to nanoscale and, with the aid of surfactant, to allow essential oils to be effectively dissolved in liquid while time maintaining their antimicrobial activity in liquid
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