Barrier Properties

Barrier property is one of the key parameters in selecting the packaging material for food packaging applications. Barrier properties denote permeability of gases such as oxygen, carbon dioxide, and dinitrogen; water vapor; and aroma compounds which determine the quality of the food. For instance, permeability to oxygen facilitates degradation through mechanisms such as corrosive phenomena, oxidations, and the modification of organoleptic properties (Lopez et al., 2015). Knowledge of the diffu- sion/permeation behaviors of these molecules through packaging material is necessary for designing novel packaging material. The diffusion of gas/water vapour across packaging film is influenced by the following factors (Siracusa, 2012):

  • • Film structure
  • • Film permeability properties to a specific substance
  • • Physical properties of the film such as thickness and area
  • • Conditions of the packaging material and the environment (temperature)
  • • Difference in pressure and concentration gradient across the film

Kinetic Model for the Analysis of the Antimicrobial Activity of Nanoparticles

Various studies have been carried out in terms of the antimicrobial property of NPs. Several metal NPs, such as silver, copper, zinc, carbon, and iron, either generated naturally or created artificially, have been used. Of the metals used, silver is the most extensively used metal in the form of NP for various functions on such being the antimicrobial property. Since ancient Greece, silver has been known for its effectiveness in cases of microbial activity, as it is effective in case of all microbes were basic antibiotics fail to action (Panacek et al., 2006; Beyth et al., 2015; Nallamuthu et al., 2013). NPs heavily depend on various physical factors such as the form of its availability and the dimension of the NP (Panacek et al., 2006). As stated, mainly particles with smaller dimensions in terms of diameter are comparatively more effective than those with larger diameters (Beyth et al., 2015). Based on various understandings in terms of growth of microbes, it can be either stated as the death or birth of microbes in any order to understand the basic effect of microbial load in any scenario (Pearl, 1927). Metal NPs can be synthesized using the various organic and chemical methods by reducing other compounds of metals. According to these generations of NP, the

NPs can be termed as organic and engineered NPs, respectively (Dinesh et al., 2012; Kheybari et al., 2010).

Almost all NPs are generally produced using a compound of metals and then reducing it to elemental NPs. In this scenario, bacteria play an important role in producing NPs; as stated by Klaus et al. (1999) and Joerger et al. (2000), bacteria named Pseudomonas stutzeri are capable of reducing the nitrate of silver in an aqueous solution of NPs in range of 2 to 200 nm. In contrast, engineered NPs are produced using the same techniques but with chemicals that act as reducing agents, such as sodium borohydride (NaBH4), ascorbate, and citrate (Panacek et al., 2006). The engineered NP synthesized by man have a specific characteristic property in term of size, properties and behaviors.

Effect of Particle and Size Determination

Various sizes have different effects on microbes, thus changing the attributes of action as antimicrobial agents. The most proliferated use of silver as an antimicrobial agent is documented by various researchers, who also mention various sizes and their consequential effect and mode of action. Whereas silver can range from 4 to 22 nm in particle size, which has various modes of action such as attaching to bacterial membrane and forming protein complexes, thus leading to lysis of the overall cell, or binding to the membrane, thus eventually rupturing the membrane to cause lysis of the cell (Sondi and Salopek-Sondi, 2004; Prema and Raju, 2009), in the case of gold-and- silver compounds, they can be as big as 209 nm, targeting the cell wall by creating a depression into it and causing the release of silver ions as NPs that attach to various elements, thus retarding the metabolic activity. In the case of gallium and zinc, they have a range of 28 to 305 nm and 12 to 2000 nm, respectively, in size in which zinc occurs in the form of an oxide, thus targeting cytokines and eliminating them from the system. Other NPs can be of manganese and titanium, both occurring in their oxide form, in a size range of 11 to 130 nm and mainly acting to oxidization of protein or preventing surface adhesion of the bacterial cell to the wall, thus preventing growth.

Various models can be utilized to determine the particle size of NPs whether synthesized organically or chemically. For calculation of particle size, the Scherrer equation can be used.

The particle size in case of an iron oxide NP (IONP) can be determined by the following equation:

where

К is the proportionality coefficient (in case of IONP it can be taken as 0.9),

X is the wavelength of X-ray for the X-ray diffraction (XRD) equipment,

(3 is defined as the full width at half maximum (FWHM) in term of radians, and 0 is termed as Braggs angle.

The preceding equation can be used in terms of calculation of particle size using XRD data generated by using X’ pert high score software with the option of search and match (Arakha et al., 2015). As per the research done by Ramani et al. (2012), which suggested that the particle size obtained using the Scherrer equation increased if there is an increase in the concentration of tri-n-propylamine during the synthesis of ZnONP using zinc acetate dihydrate to overcome the condition of increasing size, a modification was made in term of Scherrer equation by adding a lattice strain in consideration and then calculating the particle size by a Williamson-Hall plot followed by the application of the formula

where

P is the FWHM intensity of the diffraction line,

L is the crystallite size, e is the synthesized structure lattice strain.

К is the shape factor (in case of ZnO shape factor is 0.89), and X is the wavelength of the CuKa (1.54 A).

 
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