In this article, several applications of nanomaterials in food packaging and food safety are reviewed, including: polymer/clay nanocomposites as high barrier packaging materials, silver nanoparticles as potent antimicrobial agents, and nanosensors and nanomaterial-based assays for the detection of food-relevant analytes (gasses, small organic molecules and food-borne pathogens). In addition to covering the technical aspects of these topics, the current commercial status and understanding of health implications of these technologies are also discussed. These applications were chosen because they do not involve direct addition of nanoparticles to consumed foods, and thus are more likely to be marketed to the public in the short term.

Applications of nanotechnology in food packaging and food safety: Barrier materials, antimicrobials and sensors

Bio-nanocomposites for food packaging applications

The structure

Fish gelatin: properties, challenges, and prospects as an alternative to mammalian gelatins

Foreword. Preface. Introduction. The Framework of Population Balances. Birth and Death Functions. The Solution of Population Balance Equations. Similarity Behavior of Population Balance Equations. Inverse Problems in Population Balances. The Statistical Foundation of Population Balances. Index.

Population Balances: Theory and Applications to Particulate Systems in Engineering

Emulsions are dispersions of one liquid into the second immiscible liquid in the form of fine droplets. Emulsions can be classified as either oil-in-water or water-in-oil emulsions depending on whether oil or water is the dispersed phase. Milk, cream and sauces are some examples of oil-in-water emulsions whereas butter and margarine are examples of water-in-oil emulsions. This chapter discusses the physical principles that are involved in the formation and stability of food emulsions. Prediction of droplet size distribution for food emulsions that are formed in colloid mill (predominantly by shear) and high pressure homogenizer (predominantly by turbulence) in terms of operating conditions in these equipments is discussed. The fluid mechanics of droplet breakage and coalescence in shear and turbulence are discussed and applied to the formation of food emulsions and to the prediction of drop size. The role of proteins and surfactants on the stability of emulsions is discussed. The effect of interfacial dilatational and shear elasticity on thin film stability and drop coalescence is described. Some recent results of a new technique, layer by layer deposition, to improve the shelf life of emulsions by using alternate layers of proteins and polysaccharides is presented. Thermodynamics and phase behavior of microemulsions and its application to food is discussed.

Guidelines for Processing Emulsion-Based Foods

Since antimicrobial peptides kill bacteria by pore formation in cell membranes, transient pores formed by low power ultrasonication should result in enhancement of antimicrobial activity. Because of its relatively gentle action, low intensity ultrasound is expected to have no adverse effect on food texture. Experiments were conducted for deactivation of pure culture of L. monocytogenes using a model system of naturally occurring antimicrobial peptide (AMP) melittin in the absence as well as in the presence of ultrasonication. In the absence of AMP melittin, ultrasonication has very small effect on cell density upto a power level of 40 W. However, at a higher power level of 60 W, a dramatic decrease in cell density was observed which implied cell lysis. At low AMP concentration, low power ultrasonication did not improve the antimicrobial activity. At high AMP concentrations, however, AMP was found to completely inactivate L. monocytogenes. The synergistic effect of AMP with ultrasonication was found to be the maximum at AMP concentration of 0.78 μg/ml of melittin. A dramatic decrease in 2 orders of magnitude in cell density was observed for ultrasonication in the presence of 0.78 μg/ml of melittin compared to either ultrasonication alone or AMP action alone.

Synergistic effect of low power ultrasonication on antimicrobial activity of melittin against Listeria monocytogenes

A mechanistic model for swelling kinetics of waxy maize starch suspension

The dynamics of adsorption of commercial samples of α-lactalbumin and β-lactoglobulin was investigated through the measurement of dynamic surface pressure and surface concentration via a radiotracer method. An unusual two-step adsorption behavior was observed for both proteins at low concentration which was believed to be due to the presence of a surface active contaminant. This hypothesis was tested by comparing the native whey protein samples with those purified with charcoal extraction. Analysis of the charcoal extract by thin-layer chromatography revealed the presence of contaminating free fatty acid and triglycerides in the commercial samples. β-Lactoglobulin was found to contain a higher concentration of these contaminants than α-lactalbumin. Extraction by charcoal was found not to modify the protein structure with respect to their near-and far-UV circular dichroism spectra. The presence of contaminant resulted in a higher steady-state surface pressure for β-lactoglobulin, but the protein was not displaced from the interface. On the other hand, the presence of a low concentration of surfactant was sufficient to decrease the steady-state surface concentration of α-lactalbumin due to the displacement of the protein from the interface by the lipids.

Effect of contaminant on adsorption of whey proteins at the air-water interface

A surface equation of state for globular proteins at the air-water interface accounting for the structure of the protein molecule, its degree of unfolding, and segment-segment, segment-solvent, and electrostatic interactions is proposed. The proposed lattice model employs the simplifying assumption that all the adsorbed segments are present in the form of trains. Results obtained by fitting the equation of state to the experimental data indicate that the average degree of unfolding of bovine serum albumin (BSA) is greater than that of lysozyme. The number of segments adsorbed per molecule of BSA is found to vary linearly with the surface concentration, whereas the segments of lysozyme adsorbed at the interface are fairly independent of surface concentration. The segment-solvent interactions of the adsorbed segments of BSA and lysozyme are found to be unfavorable (χ > 0.5) due to the exposure of hydrophobic functional groups resulting from unfolding. The maximum surface pressure and surface concentration for monolayer coverage are highest at pI and their predicted variation with pH is in good agreement with the experimental data.

Ganesan Narsimhan

Papers

Guidelines for Processing Emulsion-Based Foods

Synergistic effect of low power ultrasonication on antimicrobial activity of melittin against Listeria monocytogenes

A mechanistic model for swelling kinetics of waxy maize starch suspension

Effect of contaminant on adsorption of whey proteins at the air-water interface

A surface equation of state for globular proteins at the air-water interface