3 Novel Technologies in Food Nanobiotechnology
3.3 Green Synthesis of Inorganic Nanoparticles
magnetic particles are magnetite (Fe3O4) and maghemite (γ-Fe2O3). Magnetic nano-systems combining enzymes are one of the fastest growing areas of biotechnology research. A graphical overview of several types of MNP architectures with different core-shell arrangements is depicted in Fig. 3.2. The size of MNPs can vary from a few nm to several hundred nm in some condensed NP assemblies which exhibit diverse structural shapes (Vaghari et al. 2016). Some of immobilized enzymes onto MNPs are listed in Table 3.2.
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bulk state, metallic NPs exhibit unusual chemical, physical, biological, optical and thermal properties due to their high surface area to volume ratio. Therefore, these unique properties make NPs favorable for many different applications such as pack-aging, nanosensors and new antibiotics generation (Mohammadlou et al. 2016).
Generally, metal NPs can be produced using the top-down (physical) and up (chemical and biological) methodologies. Figure 3.3 indicates all top-down and bottom-up techniques used to synthesize metal NPs. The chemical synthesis methods are simple and easily controlled. However, they generate toxicity due to unwanted
Fig. 3.2 General types of MNP arrangements with polymers, molecules and inorganic nanopar-ticles (Vaghari et al. 2016)
3.3 Green Synthesis of Inorganic Nanoparticles
harmful interactions with biological systems. Furthermore, in the chemical synthesis method, chemical reductants, such as sodium borohydride, and stabilizers, such as Polyvinylpyrrolidone, are widely used and their residual in the final products limit the applications of the fabricated NPs in medicine and food areas. Generally, metal NP synthesis has three steps, namely nucleation (by reducing the metal ions into the ele-ments), growth of nucleuses and stabilizing of the formed NPs. Figure 3.4 shows the three steps of the silver NPs formation. Numerous physical methods (e.g.
sonochemi-Table 3.2 Some of the immobilized enzymes onto the MNPs (Vaghari et al. 2016)
Enzyme Magnetic carrier
NPs preparation
method Immobilization method Alkaline phosphatase Fe3O4 Co-precipitation Cross-linking
α-Amylase Fe3O4 @ cellulose Co-precipitation Covalent attachment
Cellulase Carboxylic acid
functionalized Fe3O4
Co-precipitation Cross-linking
Cholesterol oxidase Gama-Fe2O3 @ SiO2
@ APES
Co-precipitation Cross-linking D-Amino acid oxidase
from Rhodosporidium toruloides
Fe3O4 @ APES Co-precipitation Cross-linking
Esterase Fe3O4 @ APES Co-precipitating Cross-linking Glucose oxidase Amino-modified
CoFe2O4 @ SiO2
Co-precipitation Cross-linking β-glucosidase Agarose-Fe3O4-ECH-
IDA-Co2+
Co-precipitation Metal ion affinity β-glucosidase Sodium citrate coated
Fe3O4
Co-precipitation Cross-linking Lipase from Aspergillus
niger
Chitosan-coated Fe3O4 – Covalent binding Lipase from Candida
rugosa ɣ-Fe2O3 –
Lipase from Semi tinmarcescens
Aldehyde- functionalized Fe3O4 @ APES
Co-precipitation –
Lipase from Thermomyces lanuginosa
Aminofunctionalized Fe3O4
Co-precipitation Covalent binding
Papain Fe3O4 @ SiO2 Co-precipitation, Sol-gel
–
Trypsin Amine-functionalized
Fe3O4 nanoparticles
– Cross-linking
Chitosanase Fe3O4 @ amylose – Physical-adsorption and
multipoint covalent bonding
Pectinase AOT-Fe3O4 – Co-precipitation
Note: APES: 3-aminopropyltriethoxysilane, AOT: Docusate sodium salt
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cal, ultrasound irradiation, ultraviolet (UV) irradiation, microwave and hydrothermal) have been applied to synthesize NPs. However, these techniques are expensive and unsustainable (Eskandari-Nojehdehi et al. 2016).
Metal NP synthesis using microorganisms such as bacteria, fungi, yeast and acti-nomycetes has immense potential and is an environmentally friendly process. Extracts from microorganisms, including enzymes, proteins, amino acids, polysaccharides and vitamins, may take part in NP synthesis as both reducing and capping agents. It seems that microorganisms have the potential to immobilize NPs by providing a vis-cous medium which, in turn, prevents their aggregation. Recently, these microorgan-isms have been known as possible eco-friendly nano-factories. Several studies have been reported successful on biological synthesis of silver NPs using microorganisms including Verticillium sp., Aspergillus fumigatus, Aeromonas sp., Klebsiella
pneumo-Fig. 3.3 Top-down and bottom-up techniques used to synthesize of metal NPs (Mohammadlou et al. 2016)
3.3 Green Synthesis of Inorganic Nanoparticles
nia, Escherichia coli, Enterobacter cloacae (Enterobacteriaceae), Aspergillus flavus and Bacillus subtilis (Mohammadlou et al. 2016).
Various plant metabolites, including terpenoids, polyphenols, sugars, alkaloids, phenolic acids and proteins play an important role in the bioreduction of metal ions to form NPs. Terpenoids are a group of diverse organic polymers synthesized in plants from five-carbon isoprene units which display strong antioxidant activity.
Flavonoids are a large group of polyphenolic compounds that comprise several classes including anthocyanins, isoflavonoids, flavonols, chalcones, flavones, and flavanones, which can actively chelate and reduce metal ions into nanoparticles.
Various functional groups of flavonoids are capable of forming NPs. Table 3.3 shows different bioreductant of numerous plants which have been used in the syn-thesis of metal NPs.
Metal NPs have a high surface energy, making them less stable. Therefore, resulting NPs aggregate and prefer to acquire a more stable morphology such as a truncated triangle to minimize their Gibbs free energy. Plant hydrocarbons, such as nonacosane and heptacosane, have a positive effect on stabilization of the formed NPs. In fact, the carbonyl group of amino acid, such as lysine, cysteine, arginine, and methionine residues and proteins has the potential to bind metal ions to form nanoparticles (e.g. capping of NPs) and to prevent agglomeration and thereby stabi-lize the medium (Ahmadi et al. 2018a; Mohammadlou et al. 2017). Table 3.4 indi-cates some of our previous studies on green synthesis of metal and metal oxide NPs using plant extracts and microorganisms.
Fig. 3.4 Silver NPs formation steps (Mohammadlou et al. 2016)
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Table 3.3 Plants and their bioreductants (Mohammadlou et al. 2016)
Plant Bioreductant molecules
Jatropha curcas Proteins
Carica papaya Hydroxyflavones and catechins
Ocimum sanctum Phenolic and flavonoid compounds, proteins, ascorbic acid, Gallic acid Desmodium triflorum Water-soluble antioxidative agents like ascorbic acids
Rosa rugosa Carboxylate content, amine groups
Chenopodium album Aldehyde, alkaloids, apocarotenoids, flavonoids Acalypha indica Flavonoids
Sesuvium portulacastrum
Proteins, flavones and terpenoids Hibiscus rosa sinensis Carboxylate ion groups Achyranthes aspera Polyols
Citrus sinensis Vitamin C, flavonoids, acids and volatile oils Mentha piperita Menthol
Citrullus colocynthis Polyphenols with aromatic ring and bound amide region Anacardium
occidentale
Polyols and proteins Zingiber officinale Alkanoids, flavonoids Piper betle Proteins
Solanum xanthocarpum
Phenolics, alkaloids and sugars Glycyrrhiza glabra Flavonoids, terpenoids, thiamine Piper nigrum Proteins
Trianthema decandra Hydroxyflavones and catechins Dioscorea bulbifera Polyphenols or flavonoids
Elettaria cardamomum Alcohols, carboxylic, acids, ethers, esters and aliphatic amines Leonuri herba Polyphenols and hydroxyl groups
Morinda pubescens Hydroxyflavones, catechins Olibanum Hydroxyl, carbonyl
Annona squamosa Sugars (aldoses) and terpenoids Piper betle Proteins
Plumeria rubra Proteins Hydrilla verticillata Proteins
Lantana camara Carbohydrates, glycosides and flavonoids Andrographis
paniculata
Hydroxyflavones catechins
Annona squamosa Glycoside, alkaloids, saponins, flavonoids, tannins, carbohydrates, proteins, phenolic compounds, phytosterols, and amino acids Malva parviflora Proteins
Hibiscus cannabinus Ascorbic acid Castor oil, Khat and
Sun flower
Proteins, phenols and flavonoids, terpenoids Artocarpus
heterophyllus
Amino acids, amides group
(continued)