**4.1 Organic acids (OA)**

High-moisture grains are prone to deterioration during storage if moisture exceeds 14%. For this reason, in the 1970s, chemicals were used to preserve high moisture grains. Propionic acid was used alone (applied worldwide) or in combination with acetic acid, isobutyric acid. Formaldehyde was mostly used in Europe to inhibit the growth of mold and bacteria in outdoor storage of grains. However, when galvanized steel equipment are used to store acid treated grains, extreme corrosion occurred. Thus, lining the bins with oil was recommended. The combinations of propionic acid and sodium benzoate curbed the issue of corrosion, and less harmful compared to pure propionic acid [114–116]. Coating the bins with silver nanoparticle protective paints [117] could prevent corrosion and exert fungicidal activities.


**111**

**4.2 Drying**

for small-scale farmers.

viability, as well as economic losses [122, 128].

**4.3 Chlorine and hypochlorite**

*The Potential Application of Nanoparticles on Grains during Storage: Part 1 – An Overview…*

used to inhibit the growth of microorganisms on the product.

OA can increase moisture content and penetrate the endosperm, thus alter the functionality of the grains [118, 119]. It could also modify the nutritional composition of the stored grain, consequently decreasing the quantity and quality of nutrients. The combination of organic acids, such as propionic, sorbic, and acetic acids, as well as their salts, had antimould activities, which extended the shelf life of bakery products [36]. Similarly, calcium propionate (0.003%), potassium sorbate (0.03%), and sodium benzoate (0.3%) suppressed the growth and mycotoxin production in *Eurotium, Aspergillus* and *Penicillium*. However, the author claimed that aw and pH contributed to the effectiveness of the compounds and should therefore be carefully considered during application [115]. High sorbate concentration altered the sensorial properties of food [120]; therefore, the concentration used is crucial to maintain grain quality after storage. Propionic acid and its salts exhibited antimicrobial effect against *Bacillus* spp., and was ascribed to their high MW fatty acids [120]. Valerio et al. [121] tested the antifungal activities of organic acids synthesized by lactic acid bacteria (LAB) isolated from a semolina ecosystem. The results showed that all the acids produce by the LAB had inhibitory effects on the test species (*Penicillium roqueforti*, *A. niger*, and *Endomyces fibuligera*). This approach could be classified as biopreservation since the metabolites of living organisms were

According to [122], drying is the phase of postharvest processing during which grains are dried to achieve low MC, thereby guaranteeing safe storage (<0.70 aw). The MC of adequately dried grains ranged within 10–14%. Russ and coworkers [123] reported that at higher MC, residue of fermentable sugars and other nutrients predispose grains to microbial colonization, resulting in rapid deterioration. Thus, a productive drying process warrants the reduction of moisture, thereby lowering the pH and creating an uninhabitable environment for the germination and proliferation of a microorganism. Dried grains should be allowed to cool before bagging because heat generated during drying could cause a warm spot. Earlier works [36] reported that warm spot in grains support fungal growth, resulting in contamination of grain by mycotoxins. Kumar and coworkers [124] reviewed a paper on heat convection solar drying systems. Some of the techniques described could be employed when drying grains. The low-cost material utilized in manufacturing these dryers, coupled with user friendly, make them ideal for large scale drying, even

Different drying methods have been described: (1) high temperature or heated air-drying; (2) low-temperature air-drying; (3) combined air-drying; (4) dry ration and in-storage cooling method (an alternative to in-dryer cooling) [125, 126]. The expensive nature (cost of power) of artificial drying makes it unpopular, couple with the technicalities involved. For instance, in Russia, sun drying becomes insufficient due to the high MC (i.e., in St Petersburg, Yekaterinburg, etc.); thus, it is impossible to achieve uniform drying of grains. In Africa, sun drying is efficient and effective since there is almost 13-h of sun during the dry season [127]. Applying excessive temperatures (using artificial means) can lead to grains cracking, loss of

Chlorine dioxide (ClO2) has biocidal activities due to its oxidizing capacity (strong oxidant), and is widely used for decontamination. It is used both in its gaseous and aqueous forms to sanitize food and, exert potent biocidal activity against

*DOI: http://dx.doi.org/10.5772/intechopen.91005*

### **Table 1.**

*Some conventional approaches of grains preservation.*

*The Potential Application of Nanoparticles on Grains during Storage: Part 1 – An Overview… DOI: http://dx.doi.org/10.5772/intechopen.91005*

OA can increase moisture content and penetrate the endosperm, thus alter the functionality of the grains [118, 119]. It could also modify the nutritional composition of the stored grain, consequently decreasing the quantity and quality of nutrients. The combination of organic acids, such as propionic, sorbic, and acetic acids, as well as their salts, had antimould activities, which extended the shelf life of bakery products [36]. Similarly, calcium propionate (0.003%), potassium sorbate (0.03%), and sodium benzoate (0.3%) suppressed the growth and mycotoxin production in *Eurotium, Aspergillus* and *Penicillium*. However, the author claimed that aw and pH contributed to the effectiveness of the compounds and should therefore be carefully considered during application [115]. High sorbate concentration altered the sensorial properties of food [120]; therefore, the concentration used is crucial to maintain grain quality after storage. Propionic acid and its salts exhibited antimicrobial effect against *Bacillus* spp., and was ascribed to their high MW fatty acids [120]. Valerio et al. [121] tested the antifungal activities of organic acids synthesized by lactic acid bacteria (LAB) isolated from a semolina ecosystem. The results showed that all the acids produce by the LAB had inhibitory effects on the test species (*Penicillium roqueforti*, *A. niger*, and *Endomyces fibuligera*). This approach could be classified as biopreservation since the metabolites of living organisms were used to inhibit the growth of microorganisms on the product.

#### **4.2 Drying**

*Mycotoxins and Food Safety*

good sources [95, 98–101].

**contamination**

**4.1 Organic acids (OA)**

below.

[4, 102, 103]

and other foods. However, sampling methods, extraction, and the instrument used could alter mycotoxin quantification. In response, Rahmani et al. [95] compiled a

The impact of the sampling on sample preparation and analytical instrument contribute to the total variance during the analysis of ochratoxin A (OTA) in flour and aflatoxinB1 (AFB1) in oats was recently reported. The authors suggested that increasing sample weight (size) could potentially reduce the high heterogeneity encountered [96, 97]. For efficient extraction, methods of detection and quantification of mycotoxins, the reader(s) are referred to the following

good comprehensive review to address the challenges mentioned above.

**4. Some conventional methods of controlling grains microbial** 

Contamination of stored grains by fungi mycotoxins has resulted in economic losses of food products, which could have been used to feed the less privileged (i.e., refugees, natural disaster victims, etc.). Therefore, preservation of grains during storage is necessary to maintain food security. Moreover, with the growing population of the world, more food will be required to feed folks. Some conventional approaches used in preserving grains are listed in **Table 1** besides those described

High-moisture grains are prone to deterioration during storage if moisture exceeds

Debranning • Not entirely suitable for wheat due to the crease on the wheat kernels.

• Limited to highly vented packages or open-top containers.

• Whole-grain demand in the market.

[111–113] Irradiation • Can negatively modify the quality and technological properties of cereals and cereal products

• Direct negative impact on human health. • Increasing resistance against pesticides. [107–110] Ozone • The cost of treatment can be relatively high due to complex technology.

14%. For this reason, in the 1970s, chemicals were used to preserve high moisture grains. Propionic acid was used alone (applied worldwide) or in combination with acetic acid, isobutyric acid. Formaldehyde was mostly used in Europe to inhibit the growth of mold and bacteria in outdoor storage of grains. However, when galvanized steel equipment are used to store acid treated grains, extreme corrosion occurred. Thus, lining the bins with oil was recommended. The combinations of propionic acid and sodium benzoate curbed the issue of corrosion, and less harmful compared to pure propionic acid [114–116]. Coating the bins with silver nanoparticle protective paints

[117] could prevent corrosion and exert fungicidal activities.

[104–106] Pesticides • High environmental impacts.

**Reference Methods Limitations**

*Modified with permission from ref. 4496530764014 [122].*

*Some conventional approaches of grains preservation.*

**110**

**Table 1.**

According to [122], drying is the phase of postharvest processing during which grains are dried to achieve low MC, thereby guaranteeing safe storage (<0.70 aw). The MC of adequately dried grains ranged within 10–14%. Russ and coworkers [123] reported that at higher MC, residue of fermentable sugars and other nutrients predispose grains to microbial colonization, resulting in rapid deterioration. Thus, a productive drying process warrants the reduction of moisture, thereby lowering the pH and creating an uninhabitable environment for the germination and proliferation of a microorganism. Dried grains should be allowed to cool before bagging because heat generated during drying could cause a warm spot. Earlier works [36] reported that warm spot in grains support fungal growth, resulting in contamination of grain by mycotoxins. Kumar and coworkers [124] reviewed a paper on heat convection solar drying systems. Some of the techniques described could be employed when drying grains. The low-cost material utilized in manufacturing these dryers, coupled with user friendly, make them ideal for large scale drying, even for small-scale farmers.

Different drying methods have been described: (1) high temperature or heated air-drying; (2) low-temperature air-drying; (3) combined air-drying; (4) dry ration and in-storage cooling method (an alternative to in-dryer cooling) [125, 126].

The expensive nature (cost of power) of artificial drying makes it unpopular, couple with the technicalities involved. For instance, in Russia, sun drying becomes insufficient due to the high MC (i.e., in St Petersburg, Yekaterinburg, etc.); thus, it is impossible to achieve uniform drying of grains. In Africa, sun drying is efficient and effective since there is almost 13-h of sun during the dry season [127]. Applying excessive temperatures (using artificial means) can lead to grains cracking, loss of viability, as well as economic losses [122, 128].

#### **4.3 Chlorine and hypochlorite**

Chlorine dioxide (ClO2) has biocidal activities due to its oxidizing capacity (strong oxidant), and is widely used for decontamination. It is used both in its gaseous and aqueous forms to sanitize food and, exert potent biocidal activity against

bacteria, yeasts, and molds [129–133]. All bacteria and their spores in a hospital room were reported killed/inactivate by ClO2 gas [134].

Poliovirus was found to have been inhibited due to the application of ClO2, which interreacted with the viral RNA and damaged the genome's ability to act as a template for RNA synthesis [135]. Aqueous ClO2 was documented to have significantly enhanced the inactivation of *F. graminearum* on wheat at high concentration, (15 mg/L) compared to lower levels (5 and 10 mg/L) [131]. Inexpensive, less corrosive, the ease with which it mixes with air, rapid diffusion, and being easy to use are some merits associated with this method. However, it can produce toxic by-products and interfere with the flavor compounds in the grains. It also requires expensive onsite generation [136–139]. Chlorine solution (0.4%) was ineffective against highly contaminated grains [140, 141]. The reason could be the colonies were mature and had thicker peptidoglycan, hence, the chlorine could not penetrate the cells to reach the genetic material. Another hypothesis could be that the concentration was not enough to destabilize cell and react with the amino acids. Sun and collaborators [133] documented that coupling aqueous sanitizer with gaseous ClO2 enhanced the decontamination of foodborne and plant pathogens. It also improved the safety, quality, and sensory properties of products (fruits and vegetables). Nevertheless, higher concentrations may cause bleaching or browning.

## **5. Nanoparticles**

The term 'nano' is a Greek word for dwarf, and a nanometer (nm) is 1-billionth of a meter. Nanotechnology has been in existence for decades now, and not an invention of the twentieth century. Nanomaterials and nanoparticles (NPs) are materials that have at least one dimension on the nanoscale (1–100 nm) or whose basic unit in the three-dimensional space is in this range. NPs have a more comprehensive range of applications in food science and technology, drug delivery, biomedical engineering, tissue engineering, textile industry, environment, electronics, agriculture, etc. [10, 142–145]. Nanoparticles are classified as organic (also known as nanocapsules) and inorganic.

Organic NPs act as core shells to shield sensitive bioactive ingredient such as carotenoids [146] against environmental factors, thereby enhancing their bioavailability for safer delivery [10, 147]. Nanoprecipitation, emulsion-diffusion, double emulsification, emulsion-coacervation, polymer coating, etc. are examples of organic NPs [148]. All these techniques are used to prepare the core materials (β-carotene, probiotic bacteria, folic acid, omega fatty acid, protease enzymes, etc.) for encapsulation. Fluorescent organic NPs have recently been used to develop nanosensors [149] which are used to detect contaminants and other foodborne pathogens as well as in bioremediation [150].

Inorganic NPs have attracted the attention of researchers in the last two decades due to their multiple antimicrobial activities (antifungal or antiviral) coupled with the pronouncement from Food Safety Authority that these NPs are safe and do not affect humans/consumers in any way [151–153]. Silver, silica, and titanium dioxide NPs are the main NPs used in the agri-food industries [154].

#### **5.1 Silver nanoparticles (AgNPs)**

Several studies have confirmed the potent biocidal effects of silver nanoparticles (AgNPs) towards fungi [155–158]. Due to their peculiar properties (i.e., optical,

**113**

*The Potential Application of Nanoparticles on Grains during Storage: Part 1 – An Overview…*

electrical, and thermal, and biological properties), AgNPs have been used in several applications: as biocidal agents; medical device coatings; optical sensors; in cosmetics; in the food industry (food products); in diagnostics, orthopedics, drug delivery; as anticancer agents and have greatly enhanced the tumor-killing effects of anticancer drugs [158–163]. Healthcare products, such as scaffolding, burn dressings, water purification systems, and medical devices are manufactured using AgNPs [164, 165]. It was reported that 10 μg/mL AgNPs completely inhibited

reducing sugars and proteins forced respiratory chain dehydrogenases into an inactive state, suggesting that AgNPs penetrated the bacterial cell membrane with high efficiency and could therefore be used in the manufacturing of drugs used against bacterial diseases [158]. AgNPs extracted from *Pistacia atlantica* were effective against important clinical pathogens [166]. AgNPs synthesized (green AgNPs) from the leaf of CRCP (medicinal plant) was utilized against multidrug-resistant (MDR)

infections. 80 mg/mL AgNPs was reported effective against, *S. aureus* and CoNS isolates but had little effects on *P. aeruginosa*. However, 100-120 mg/mL AgNPs completely inhibited *P. aeruginosa* [153]. These findings shows that the concentration of AgNPs utilize is critical therefore should carefully be considered during

The fungicidal activities of AgNPs are documented in many studies [13, 152, 160, 167–170]. Six fungal species (*Aspergillus fumigatus*, *Penicillium brevicompactum*, *Cladosporium cladosporoides*, *Mortierella alpina*, *Chaetomium globosum*, and *Stachybotrys chartarum*) isolated from an indoor environment were used to test the antifungal activity of AgNPs. The results revealed that the presence of AgNPs in concentrations of 30–200 mg/L significantly inhibited or decreased the growth of all the fungi species except *Mortierella* species, which were insensitive to the AgNPs but instead metabolized the AgNPs for its own benefit (the presence of AgNPs in agar substrates significantly enhanced *Mortierella* growth rate) [152]. AgNPs and a conventional antifungal agent, Amphotericin B (for a positive test), were tested against *Saccharomyces cerevisiae* (KCTC 7296), *Trichosporon beigelii* (KCTC 7707), and *Candida albicans* (ATCC 90028). The AgNPs exhibited a minimum inhibition concentration (MIC) value of 2 μg/mL, similar to the positive control [155]. AgNPs was found to effectively suppress growth and AFB1 production in *A. parasiticus* (**Figure 1**) [171]. In a similar study, the addition of AgNP HA1N, AgNP HA2N, and AgNP EH resulted in 88.2%, 67.7% and 83.5% reduction of AFB1 synthesized by *A. flavus* [172]. Also, the fungicidal activity of *Capsicum annuum* L. was recently reported [173]. The active ingredient could be isolated and encapsulated in NPs, which may exhibit potent inhibitory activities against

The potent antimicrobial activity of AgNPs has attracted global attention, hence its application in multiple fields (i.e., food industries, medicine, textile industries, etc.). However, the exact mechanistic action is still not clear, because the mechanism depends on the type of microorganism (i.e., bacteria, fungi, etc.) involved and, since different organisms possess different cell structure, the mechanistic action differ. Several researchers have tried to understand the antimicrobial effects of AgNPs using various model microorganisms, e.g., *E. coli* [158, 174, 175], *P. aeruginosa, S. aureus* [175], *V*. *cholera* [174, 176], *S. cerevisiae* [177, 178] and *S*. *typhi* [174]. Other groups [179, 180] have also worked on fungi. Mitochondrial dysfunction predispose cells for easier penetration by AgNPs via diffusion and endocytosis. The efficiency of

CFU/mL *E. coli* ATCC 8739 cells in liquid medium. The leakage of

CFU each) from post-surgical wound

*DOI: http://dx.doi.org/10.5772/intechopen.91005*

*P. aeruginosa*, *S. aureus* and CoNS isolates (106

the growth of 107

application.

storage pest and microorganism.

*5.1.1 Mechanistic action of AgNPs biocidal activities* 

### *The Potential Application of Nanoparticles on Grains during Storage: Part 1 – An Overview… DOI: http://dx.doi.org/10.5772/intechopen.91005*

electrical, and thermal, and biological properties), AgNPs have been used in several applications: as biocidal agents; medical device coatings; optical sensors; in cosmetics; in the food industry (food products); in diagnostics, orthopedics, drug delivery; as anticancer agents and have greatly enhanced the tumor-killing effects of anticancer drugs [158–163]. Healthcare products, such as scaffolding, burn dressings, water purification systems, and medical devices are manufactured using AgNPs [164, 165]. It was reported that 10 μg/mL AgNPs completely inhibited the growth of 107 CFU/mL *E. coli* ATCC 8739 cells in liquid medium. The leakage of reducing sugars and proteins forced respiratory chain dehydrogenases into an inactive state, suggesting that AgNPs penetrated the bacterial cell membrane with high efficiency and could therefore be used in the manufacturing of drugs used against bacterial diseases [158]. AgNPs extracted from *Pistacia atlantica* were effective against important clinical pathogens [166]. AgNPs synthesized (green AgNPs) from the leaf of CRCP (medicinal plant) was utilized against multidrug-resistant (MDR) *P. aeruginosa*, *S. aureus* and CoNS isolates (106 CFU each) from post-surgical wound infections. 80 mg/mL AgNPs was reported effective against, *S. aureus* and CoNS isolates but had little effects on *P. aeruginosa*. However, 100-120 mg/mL AgNPs completely inhibited *P. aeruginosa* [153]. These findings shows that the concentration of AgNPs utilize is critical therefore should carefully be considered during application.

The fungicidal activities of AgNPs are documented in many studies [13, 152, 160, 167–170]. Six fungal species (*Aspergillus fumigatus*, *Penicillium brevicompactum*, *Cladosporium cladosporoides*, *Mortierella alpina*, *Chaetomium globosum*, and *Stachybotrys chartarum*) isolated from an indoor environment were used to test the antifungal activity of AgNPs. The results revealed that the presence of AgNPs in concentrations of 30–200 mg/L significantly inhibited or decreased the growth of all the fungi species except *Mortierella* species, which were insensitive to the AgNPs but instead metabolized the AgNPs for its own benefit (the presence of AgNPs in agar substrates significantly enhanced *Mortierella* growth rate) [152]. AgNPs and a conventional antifungal agent, Amphotericin B (for a positive test), were tested against *Saccharomyces cerevisiae* (KCTC 7296), *Trichosporon beigelii* (KCTC 7707), and *Candida albicans* (ATCC 90028). The AgNPs exhibited a minimum inhibition concentration (MIC) value of 2 μg/mL, similar to the positive control [155]. AgNPs was found to effectively suppress growth and AFB1 production in *A. parasiticus* (**Figure 1**) [171]. In a similar study, the addition of AgNP HA1N, AgNP HA2N, and AgNP EH resulted in 88.2%, 67.7% and 83.5% reduction of AFB1 synthesized by *A. flavus* [172]. Also, the fungicidal activity of *Capsicum annuum* L. was recently reported [173]. The active ingredient could be isolated and encapsulated in NPs, which may exhibit potent inhibitory activities against storage pest and microorganism.

### *5.1.1 Mechanistic action of AgNPs biocidal activities*

The potent antimicrobial activity of AgNPs has attracted global attention, hence its application in multiple fields (i.e., food industries, medicine, textile industries, etc.). However, the exact mechanistic action is still not clear, because the mechanism depends on the type of microorganism (i.e., bacteria, fungi, etc.) involved and, since different organisms possess different cell structure, the mechanistic action differ. Several researchers have tried to understand the antimicrobial effects of AgNPs using various model microorganisms, e.g., *E. coli* [158, 174, 175], *P. aeruginosa, S. aureus* [175], *V*. *cholera* [174, 176], *S. cerevisiae* [177, 178] and *S*. *typhi* [174]. Other groups [179, 180] have also worked on fungi. Mitochondrial dysfunction predispose cells for easier penetration by AgNPs via diffusion and endocytosis. The efficiency of

*Mycotoxins and Food Safety*

browning.

**5. Nanoparticles**

as nanocapsules) and inorganic.

pathogens as well as in bioremediation [150].

**5.1 Silver nanoparticles (AgNPs)**

NPs are the main NPs used in the agri-food industries [154].

bacteria, yeasts, and molds [129–133]. All bacteria and their spores in a hospital

Poliovirus was found to have been inhibited due to the application of ClO2, which interreacted with the viral RNA and damaged the genome's ability to act as a template for RNA synthesis [135]. Aqueous ClO2 was documented to have significantly enhanced the inactivation of *F. graminearum* on wheat at high concentration, (15 mg/L) compared to lower levels (5 and 10 mg/L) [131]. Inexpensive, less corrosive, the ease with which it mixes with air, rapid diffusion, and being easy to use are some merits associated with this method. However, it can produce toxic by-products and interfere with the flavor compounds in the grains. It also requires expensive onsite generation [136–139]. Chlorine solution (0.4%) was ineffective against highly contaminated grains [140, 141]. The reason could be the colonies were mature and had thicker peptidoglycan, hence, the chlorine could not penetrate the cells to reach the genetic material. Another hypothesis could be that the concentration was not enough to destabilize cell and react with the amino acids. Sun and collaborators [133] documented that coupling aqueous sanitizer with gaseous ClO2 enhanced the decontamination of foodborne and plant pathogens. It also improved the safety, quality, and sensory properties of products (fruits and vegetables). Nevertheless, higher concentrations may cause bleaching or

The term 'nano' is a Greek word for dwarf, and a nanometer (nm) is 1-billionth

Organic NPs act as core shells to shield sensitive bioactive ingredient such as carotenoids [146] against environmental factors, thereby enhancing their bioavailability for safer delivery [10, 147]. Nanoprecipitation, emulsion-diffusion, double emulsification, emulsion-coacervation, polymer coating, etc. are examples of organic NPs [148]. All these techniques are used to prepare the core materials (β-carotene, probiotic bacteria, folic acid, omega fatty acid, protease enzymes, etc.) for encapsulation. Fluorescent organic NPs have recently been used to develop nanosensors [149] which are used to detect contaminants and other foodborne

Inorganic NPs have attracted the attention of researchers in the last two decades due to their multiple antimicrobial activities (antifungal or antiviral) coupled with the pronouncement from Food Safety Authority that these NPs are safe and do not affect humans/consumers in any way [151–153]. Silver, silica, and titanium dioxide

Several studies have confirmed the potent biocidal effects of silver nanoparticles (AgNPs) towards fungi [155–158]. Due to their peculiar properties (i.e., optical,

of a meter. Nanotechnology has been in existence for decades now, and not an invention of the twentieth century. Nanomaterials and nanoparticles (NPs) are materials that have at least one dimension on the nanoscale (1–100 nm) or whose basic unit in the three-dimensional space is in this range. NPs have a more comprehensive range of applications in food science and technology, drug delivery, biomedical engineering, tissue engineering, textile industry, environment, electronics, agriculture, etc. [10, 142–145]. Nanoparticles are classified as organic (also known

room were reported killed/inactivate by ClO2 gas [134].

**112**

#### **Figure 1.**

*Inhibition of aflatoxin B1 production at different concentration of AgNPs. Modified with permission from © Iranian Journal of Medical Sciences [171].*

AgNPs uptake by skin keratinocytes depends on the size, shape, pH, zeta potential, and incubation time. Smaller (<5 nm) NPs are more toxic than the larger ones. This could be ascribed to the secure attachment and penetration of the smaller NPs compared to the larger NPs, which requires larger pores to penetrate, into the cell membrane and internalized. AgNPs were able to attach and penetrate cell membrane causing toxicity in *Caenorhabditis elegans*. Ag0 can interact with molecular oxygen, as well as with other redox-active compounds to produce ionic silver, which then further interact with environmental factors to yield Ag+ [181–186]. AgNPs ranging from less than 10 nm can inhibit *E. coli* and *P. aeruginosa* due to their potent biocidal activities [187, 188]. Certain viruses were unable to bind to their host cells due to the presence of AgNPs of 1–10 nm, thus starving them to death [189]. Concerning shapes, Pal et al. [190] reported that triangular AgNPs were found to be effective compared to rod and sphere AgNPs. The biocidal efficiency of AgNPs is related to Ag+ , which interact with biological macromolecules (proteins, carbohydrates, nucleic acids, and lipids). When AgNPs adhere to the surface of the cell, it automatically alters membrane properties, undermining the fluidity of the cell. AgNPs can degrade lipopolysaccharide molecules causing them to accumulate inside membrane by forming "pits", thereby increasing membrane permeability [191]. According to reports Ag+ can inhibit phosphate uptake, resulting in the efflux of phosphate, mannitol, succinate, glutamine, and proline from the cell [192–198].

The minimal bactericidal concentration (MBC) of AgNPs on Gram (+) bacteria was 32 times higher compared to Gram (−) cells [199]. Thus, the sensitivity of the cell wall depends on the class of microorganisms. Research [174] also demonstrated that AgNPs can interact with bacterial cell membranes. Furthermore, the AgNPs found inside the cells are the same sizes as the ones interacting with the membrane, therefore providing more evidence to support the theory that particles that interact with the membrane penetrated into the bacteria.

Several studies [176, 200, 201] have reported that the positive charge of AgNPs is crucial for its antimicrobial activity through the electrostatic attraction with the negatively charged cell membrane of the microorganism.

The permeability of the cell membrane was altered after treatment with AgNPs, resulting in the leaking of reducing sugars and proteins which induced respiratory chain dehydrogenases into inactive state. The amount of reducing sugars leaked after 2 h was 102.5 and 30 μg/mg per bacterial dry weight in the treated and the control cells, respectively. While the activity of respiratory chain dehydrogenases

**115**

H2O2 and OH•

*The Potential Application of Nanoparticles on Grains during Storage: Part 1 – An Overview…*

of positive control increased at 37 ± 2, nearly no change was observed in negative control cells. Furthermore, the enzymatic activity of cells treated with 5 μg/ mL AgNPs decreased [158]. The survival rate of bacterial species decreased with increase in the adsorption of AgNPs. Additionally, the adsorption and toxicity of AgNPs on *P. aeruginosa*, *M. luteus*, *B. subtilis*, *B*. *barbaricus*, and *K*. *pneumonia* was optimum at pH 5, NaCl concentration of <0.5 M. A manifestation of less toxicity was noticed at pH 9 and NaCl concentration >0.5 M, indicating that the environmental pH under which the microorganism grows plays a crucial role in either protecting or exposing it to rapid interaction with the AgNPs [185]. The ability of AgNPs to bind, interact, deform, and induce DNA damage was documented [181, 202–204]. Hackenberg and coworkers [203] used comet assay and chromosomal aberration (CA), a method previously recommended by [205], to determine the damage AgNPs inflict on DNA. In both methods, maximum damage to human mesenchymal stem cells occurred less than an hour after treatment (0.1 μg/mL). Circular dichroism spectra analysis of treated calf thymus DNA revealed that AgNPs interacted and formed a new complex with the double-helical DNA, then induced an alteration of non-planar and change the orientations of DNA bases which act as an intercalator, increasing the stability of DNA which in turn increase the Tm value of the DNA [202]. A researcher [206] suggested that AgNPs can interact with nucleic acids by forming bonds with pyrimidine bases, thus condensing DNA and inhibiting replication. In a recent study, Li et al. [207] showed that citrate-AgNPs (C-AgNP20) induced different cytomorphological alterations and intracellular distributions in cetacean (bottlenose dolphins (*Tursiops truncatus*)) polymorphonuclear cells (cPMNs) and peripheral blood mononuclear cells (cPBMCs). High dose (10 and 50 μg/mL) of C-AgNP20 triggered apoptosis in cPMNs and cPBMCs (induced cytotoxicity). Additionally, the functional activities of cPMNs (phagocytosis and respiratory burst) and cPBMCs (proliferative activity) were negatively altered at sub-lethal dose of 0.1 and 1 μg/mL. AgNPs induced structural damage to cell wall, intracellular proteins (enzymes), and organelles, leading to the disruption or the collapse of metabolic processes, like antioxidant

defense mechanisms, thereby inhibiting growth [177, 178].

peroxide (H2O2), superoxide anion (O2<sup>−</sup>

in cells, resulting in genotoxic effects.

The cellular oxidative stress in microbes was enhanced by increasing the concentra-

), hydroxyl radical (OH•

, respectively [214–216]. Apoptosis and cell membrane damage were

), hypochlorous acid

tion of Ag (+) ions [206]. Several reports [208–213] have highlighted the potential antiviral, antifungal, and antibacterial activities of AgNPs and was ascribed to its ability to generate enough reactive oxygen species (ROS), free radicals (i.e., hydrogen

(HOCl)) and singlet oxygen. During mitochondrial oxidative phosphorylation, ROS are produced. Moreover, nicotinamide adenine dinucleotide phosphate (NADPH) oxidase catalyzes series of reactions where molecular oxygen (O2) is reduced to O2•. With dismutation and metal-catalyzed Fenton reaction, the O2• is further reduced to

induced by ROS, leaving the cells incapable of regulating transport through the plasma membrane, resulting in cell death [217–220]. A research group [221], evaluated the effects of ROS against *S. aureus* and *E. coli*. The results showed the inactivation of lactate dehydrogenase and protein denaturation in both test organisms. Membranal damage allowed influx of calcium, thus inducing intracellular calcium overload, further doubling ROS generation and mitochondrial membrane potential variation [222]. The overproduction of ROS was reported to have interfered with ATP synthesis, leading to DNA damage [223]. Free radicals and ROS (an excessive amount) can inflict damage/stress on the mitochondrial membrane, causing necrosis, peroxidation of lipids, proteins, and DNA damage [206, 224, 225]. According to [184, 225], elevated levels of ROS can stress the endoplasmic reticula and deactivate antioxidant enzymes

*DOI: http://dx.doi.org/10.5772/intechopen.91005*

#### *The Potential Application of Nanoparticles on Grains during Storage: Part 1 – An Overview… DOI: http://dx.doi.org/10.5772/intechopen.91005*

of positive control increased at 37 ± 2, nearly no change was observed in negative control cells. Furthermore, the enzymatic activity of cells treated with 5 μg/ mL AgNPs decreased [158]. The survival rate of bacterial species decreased with increase in the adsorption of AgNPs. Additionally, the adsorption and toxicity of AgNPs on *P. aeruginosa*, *M. luteus*, *B. subtilis*, *B*. *barbaricus*, and *K*. *pneumonia* was optimum at pH 5, NaCl concentration of <0.5 M. A manifestation of less toxicity was noticed at pH 9 and NaCl concentration >0.5 M, indicating that the environmental pH under which the microorganism grows plays a crucial role in either protecting or exposing it to rapid interaction with the AgNPs [185]. The ability of AgNPs to bind, interact, deform, and induce DNA damage was documented [181, 202–204]. Hackenberg and coworkers [203] used comet assay and chromosomal aberration (CA), a method previously recommended by [205], to determine the damage AgNPs inflict on DNA. In both methods, maximum damage to human mesenchymal stem cells occurred less than an hour after treatment (0.1 μg/mL). Circular dichroism spectra analysis of treated calf thymus DNA revealed that AgNPs interacted and formed a new complex with the double-helical DNA, then induced an alteration of non-planar and change the orientations of DNA bases which act as an intercalator, increasing the stability of DNA which in turn increase the Tm value of the DNA [202]. A researcher [206] suggested that AgNPs can interact with nucleic acids by forming bonds with pyrimidine bases, thus condensing DNA and inhibiting replication. In a recent study, Li et al. [207] showed that citrate-AgNPs (C-AgNP20) induced different cytomorphological alterations and intracellular distributions in cetacean (bottlenose dolphins (*Tursiops truncatus*)) polymorphonuclear cells (cPMNs) and peripheral blood mononuclear cells (cPBMCs). High dose (10 and 50 μg/mL) of C-AgNP20 triggered apoptosis in cPMNs and cPBMCs (induced cytotoxicity). Additionally, the functional activities of cPMNs (phagocytosis and respiratory burst) and cPBMCs (proliferative activity) were negatively altered at sub-lethal dose of 0.1 and 1 μg/mL. AgNPs induced structural damage to cell wall, intracellular proteins (enzymes), and organelles, leading to the disruption or the collapse of metabolic processes, like antioxidant defense mechanisms, thereby inhibiting growth [177, 178].

The cellular oxidative stress in microbes was enhanced by increasing the concentration of Ag (+) ions [206]. Several reports [208–213] have highlighted the potential antiviral, antifungal, and antibacterial activities of AgNPs and was ascribed to its ability to generate enough reactive oxygen species (ROS), free radicals (i.e., hydrogen peroxide (H2O2), superoxide anion (O2<sup>−</sup> ), hydroxyl radical (OH• ), hypochlorous acid (HOCl)) and singlet oxygen. During mitochondrial oxidative phosphorylation, ROS are produced. Moreover, nicotinamide adenine dinucleotide phosphate (NADPH) oxidase catalyzes series of reactions where molecular oxygen (O2) is reduced to O2•. With dismutation and metal-catalyzed Fenton reaction, the O2• is further reduced to H2O2 and OH• , respectively [214–216]. Apoptosis and cell membrane damage were induced by ROS, leaving the cells incapable of regulating transport through the plasma membrane, resulting in cell death [217–220]. A research group [221], evaluated the effects of ROS against *S. aureus* and *E. coli*. The results showed the inactivation of lactate dehydrogenase and protein denaturation in both test organisms. Membranal damage allowed influx of calcium, thus inducing intracellular calcium overload, further doubling ROS generation and mitochondrial membrane potential variation [222]. The overproduction of ROS was reported to have interfered with ATP synthesis, leading to DNA damage [223]. Free radicals and ROS (an excessive amount) can inflict damage/stress on the mitochondrial membrane, causing necrosis, peroxidation of lipids, proteins, and DNA damage [206, 224, 225]. According to [184, 225], elevated levels of ROS can stress the endoplasmic reticula and deactivate antioxidant enzymes in cells, resulting in genotoxic effects.

*Mycotoxins and Food Safety*

ity in *Caenorhabditis elegans*. Ag0

*© Iranian Journal of Medical Sciences [171].*

**Figure 1.**

environmental factors to yield Ag+

[191]. According to reports Ag+

biocidal efficiency of AgNPs is related to Ag+

with the membrane penetrated into the bacteria.

negatively charged cell membrane of the microorganism.

AgNPs uptake by skin keratinocytes depends on the size, shape, pH, zeta potential, and incubation time. Smaller (<5 nm) NPs are more toxic than the larger ones. This could be ascribed to the secure attachment and penetration of the smaller NPs compared to the larger NPs, which requires larger pores to penetrate, into the cell membrane and internalized. AgNPs were able to attach and penetrate cell membrane causing toxic-

*Inhibition of aflatoxin B1 production at different concentration of AgNPs. Modified with permission from* 

other redox-active compounds to produce ionic silver, which then further interact with

inhibit *E. coli* and *P. aeruginosa* due to their potent biocidal activities [187, 188]. Certain viruses were unable to bind to their host cells due to the presence of AgNPs of 1–10 nm, thus starving them to death [189]. Concerning shapes, Pal et al. [190] reported that triangular AgNPs were found to be effective compared to rod and sphere AgNPs. The

ecules (proteins, carbohydrates, nucleic acids, and lipids). When AgNPs adhere to the surface of the cell, it automatically alters membrane properties, undermining the fluidity of the cell. AgNPs can degrade lipopolysaccharide molecules causing them to accumulate inside membrane by forming "pits", thereby increasing membrane permeability

The minimal bactericidal concentration (MBC) of AgNPs on Gram (+) bacteria was 32 times higher compared to Gram (−) cells [199]. Thus, the sensitivity of the cell wall depends on the class of microorganisms. Research [174] also demonstrated that AgNPs can interact with bacterial cell membranes. Furthermore, the AgNPs found inside the cells are the same sizes as the ones interacting with the membrane, therefore providing more evidence to support the theory that particles that interact

Several studies [176, 200, 201] have reported that the positive charge of AgNPs is crucial for its antimicrobial activity through the electrostatic attraction with the

The permeability of the cell membrane was altered after treatment with AgNPs, resulting in the leaking of reducing sugars and proteins which induced respiratory chain dehydrogenases into inactive state. The amount of reducing sugars leaked after 2 h was 102.5 and 30 μg/mg per bacterial dry weight in the treated and the control cells, respectively. While the activity of respiratory chain dehydrogenases

phosphate, mannitol, succinate, glutamine, and proline from the cell [192–198].

can interact with molecular oxygen, as well as with

[181–186]. AgNPs ranging from less than 10 nm can

can inhibit phosphate uptake, resulting in the efflux of

, which interact with biological macromol-

**114**

It has been discovered that OH• , interacted with constituents of DNA, which led to the breakage of DNA single-strands via the formation of 8-hydroxyl-2′ deoxyguanosine (8-OHdG) DNA adduct [226, 227]. In vivo studies have shown that AgNPs influenced the activity of chicken oxidative stress enzymes [228]. AgNP treatment induced a pronounced ROS in *P. aeruginosa* compared to AgNO3. The expression levels of ROS related proteins (PA4133, Hmp, KatA, CcoP2, SodB, CcpA, RibC, EtfA, and PiuC) were specifically regulated after exposure to AgNPs in concentration and time-related modes. Cells treated with AgNO3 did not show any perturbation in intracellular ROS generation at low levels, which supports the existing theory that oxidative stress is triggered solely by AgNPs at their corresponding concentrations [229]. As reported by [220], the biocidal activities of Ag+ could also be attributed to its interactions with the thiol-related compounds found in the respiratory enzymes of cells, resulting in cell death. A researcher [230] proposed a theory using Ag with cellular energy production. Essential proteins of prokaryotes and eukaryotes located on the cell exterior and interior (mitochondrial organelles), respectively, deactivated after coming in contact with AgNPs. However, the interior components (mitochondrial proteins) required higher concentrations and much smaller AgNPs before they are rendered inactive, because the cellular membrane acted as a diffusion barrier. Moreover, the eukaryotes possessed numerous biological energy conservation system due it extensive mitochondria when compared to the prokaryotes, thereby predisposing the latter cells to AgNP interaction, hampering cell respiration, which led to cell death.
