Essential oils derived from plants have been recognized for decades to exhibit biological activities, including antioxidant, anticancer, and antimicrobial attributes. Antimicrobial activities of these natural plant materials have been intensively explored in recent years, mainly in response to the overwhelming concern of consumers over the safety of synthetic food additives. Gram-negative organisms are believed to be slightly less sensitive to essential oils than Gram-positive bacteria. Generally, a higher concentration is required to obtain the same efficacy in foods than in synthetic media. The combinations of different types of essential oils or with other food additives have been found to potentially exhibit synergistic if not additive effects. This suggests a cost-efficient and wholesome alternative to both food industry and consumers, at the same time adhering to the hurdle technology in inhibiting proliferation of foodborne pathogens. This review aims to examine the conventional methods commonly used for assessment of antimicrobial activities of essential oils and phytochemicals, the use of these substances as antimicrobials in food products, factors that affect their efficacy, synergism between components or with available food preservatives as well as the challenges and future directions of using essential oils and phytochemicals as natural food preservatives.

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Light-emitting diodes (LEDs) possess unique properties that are highly suitable for several operations in the food industry. Such properties include low radiant heat emissions; high emissions of monochromatic light; electrical, luminous, and photon efficiency; long life expectancy, flexibility, and mechanical robustness. Therefore, they reduce thermal damage and degradation in crops and foods and are suitable in cold-storage applications. Control over spectral composition of emitted light results in increased yields and nutritive content of horticultural or agricultural produce. Recently, LEDs have been shown to preserve or enhance the nutritive quality of foods in the postharvest stage, as well as manipulate the ripening of fruits, and reduce fungal infections. LEDs can be used together with photosensitizers or photocatalysts to inactivate pathogenic bacteria in food. UV LEDs, which are rapidly being developed, can also effectively inactivate pathogens and preserve food in postharvest stages. Therefore, LEDs provide a nonthermal means of keeping food safe without using chemical sanitizers or additives, and do not accelerate bacterial resistance. This article provides a review of the technology of LEDs and their role in food production, postharvest preservation, and in microbiological safety. Several challenges and limitations are identified for further investigation, including the difficulty in optimizing LED lighting regimens for plant growth and postharvest storage, as well as the sensory quality and acceptability of foods stored or processed under LED lighting. Nevertheless, LED technology presents a worthy alternative to current norms in lighting for the growth and storage of safe and nutritious food.

The influence of adaptation to pH (from pH 5.0 to 9.0) on membrane lipid composition, verotoxin concentration, and resistance to acidic conditions in simulated gastric fluid (SGF) (pH 1.5, 37°C) was determined for Escherichia coli O157:H7 (HEC, ATCC 43895), an rpoS-deficient mutant of ATCC 43895 (HEC-RM, FRIK 816-3), and nonpathogenic E. coli (NPEC, ATCC 25922). Regardless of the strain, D values (in SGF) of acid-adapted cells were higher than those of non-acid-adapted cells, with HEC adapted at pH 5.0 having the greatest D value, i.e., 25.6 min. Acid adaptation increased the amounts of palmitic acid (C16:0) and decreased cis-vaccenic acid (C18:17c) in the membrane lipids of all strains. The ratio of cis-vaccenic acid to palmitic acid increased at acidic pH, causing a decrease in membrane fluidity. HEC adapted to pH 8.3 and HEC-RM adapted to pH 7.3 exhibited the greatest verotoxin concentrations (2,470 and 1,460 ng/ml, respectively) at approximately 10 8 CFU/ml. In addition, the ratio of extracellular to intracellular verotoxin concentration decreased at acidic pH, possibly due to the decrease of membrane fluidity. These results suggest that while the rpoS gene does not influence acid resistance in acid-adapted cells it does confer decreased membrane fluidity, which may increase acid resistance and decrease verotoxin secretion.

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