228 ◾ Fundamental Food Microbiology
effectively inactivated Listeria monocytogenes in a model food system. 23 Nanofibers are made of
poly (d,l-lactide) and polyethylene oxide dissolved in N,N-dimethylformamide and are used for
delivery of several bacteriocins.
Safety Concerns with nanotechnology 20,24
The physicochemical properties of engineered nanomaterials (ENMs) that may be altered as compared to bulk materials include optical property, catalytic activity, surface property, mechanical
strength, increased stability, altered reactivity, improved functionality, and adsorption potential.
Hence, there is a potential for increased systemic bioavailability to organs and tissues. Furthermore,
solubility and biopersistence are other concerns. The application of nanotechnology in food has
focused on the uncertainties and unknowns and lack of toxicological data. Even though many of
the biomaterials used in food application (encapsulation) are GRAS listed, yet chemical or physical modification of such molecules may alter their physicochemical properties; thus their safety
aspects should be thoroughly examined before food use. Recently a detailed guideline has been
developed by European scientists to assess the safety of ENMs in food employing a systemic tiered
approach. This is divided into five key steps: 24 (1) characterization of bulk materials from which
the ENM is derived; (2) characterization of the physicochemical properties of ENMs; (3) identification of ENMs requiring focused toxicological assessments; (4) toxicological assessment (adsorption, distribution to tissues and organs, metabolism and excretion, and cellular interaction, that
is, cytotoxicity, inflammation, oxidative stress and genotoxicity); and (5) safety evaluation of the
ENM as used in its intended food matrix.
Yeast Metabolites as Preservatives
Certain yeasts, including strains of Saccharomyces cerevisiae, produce several proteins that have
limited antimicrobial properties. 25 These proteins (designated as killer toxins or zymocins) can,
through genetic manipulation, be altered to have a wider antimicrobial spectrum, especially
against fungi. However, very few studies are currently being conducted in this area.
Several yeast isolates normally present on the surface of fruits and vegetables are reported to
prevent spoilage of the produce by molds. Some of the inhibitory compounds are small proteins,
whereas others are enzymes. Cells of one such yeast isolate was found to adhere tightly with the
mold mycelia and produce β-gluconase, which degrades the cell wall of the molds and kills them.
Because many of these yeasts are normally present in fruits and vegetables that are eaten raw, they
are not considered pathogenic, and thus can be used in place of fungicides to enhance the preservation of fruits and vegetables. 26
Conclusion
Food-grade bacteria and yeasts produce different antimicrobial compounds, such as organic acids,
diacetyl, H 2 O 2 , reuterine, bacteriocins, and enzymes, that have bacteriostatic, bactericidal, fungistatic, and fungicidal action against microorganisms involved in food spoilage and food-borne diseases. They differ in the mode of antimicrobial action. Because they are from safe microorganisms,
effectively inactivated Listeria monocytogenes in a model food system. 23 Nanofibers are made of
poly (d,l-lactide) and polyethylene oxide dissolved in N,N-dimethylformamide and are used for
delivery of several bacteriocins.
Safety Concerns with nanotechnology 20,24
The physicochemical properties of engineered nanomaterials (ENMs) that may be altered as compared to bulk materials include optical property, catalytic activity, surface property, mechanical
strength, increased stability, altered reactivity, improved functionality, and adsorption potential.
Hence, there is a potential for increased systemic bioavailability to organs and tissues. Furthermore,
solubility and biopersistence are other concerns. The application of nanotechnology in food has
focused on the uncertainties and unknowns and lack of toxicological data. Even though many of
the biomaterials used in food application (encapsulation) are GRAS listed, yet chemical or physical modification of such molecules may alter their physicochemical properties; thus their safety
aspects should be thoroughly examined before food use. Recently a detailed guideline has been
developed by European scientists to assess the safety of ENMs in food employing a systemic tiered
approach. This is divided into five key steps: 24 (1) characterization of bulk materials from which
the ENM is derived; (2) characterization of the physicochemical properties of ENMs; (3) identification of ENMs requiring focused toxicological assessments; (4) toxicological assessment (adsorption, distribution to tissues and organs, metabolism and excretion, and cellular interaction, that
is, cytotoxicity, inflammation, oxidative stress and genotoxicity); and (5) safety evaluation of the
ENM as used in its intended food matrix.
Yeast Metabolites as Preservatives
Certain yeasts, including strains of Saccharomyces cerevisiae, produce several proteins that have
limited antimicrobial properties. 25 These proteins (designated as killer toxins or zymocins) can,
through genetic manipulation, be altered to have a wider antimicrobial spectrum, especially
against fungi. However, very few studies are currently being conducted in this area.
Several yeast isolates normally present on the surface of fruits and vegetables are reported to
prevent spoilage of the produce by molds. Some of the inhibitory compounds are small proteins,
whereas others are enzymes. Cells of one such yeast isolate was found to adhere tightly with the
mold mycelia and produce β-gluconase, which degrades the cell wall of the molds and kills them.
Because many of these yeasts are normally present in fruits and vegetables that are eaten raw, they
are not considered pathogenic, and thus can be used in place of fungicides to enhance the preservation of fruits and vegetables. 26
Conclusion
Food-grade bacteria and yeasts produce different antimicrobial compounds, such as organic acids,
diacetyl, H 2 O 2 , reuterine, bacteriocins, and enzymes, that have bacteriostatic, bactericidal, fungistatic, and fungicidal action against microorganisms involved in food spoilage and food-borne diseases. They differ in the mode of antimicrobial action. Because they are from safe microorganisms,