Bioactive metal oxide nanoparticles from some common fruit wastes and Euphorbia condylocarpa plant

Abstract For the first time, the potential of orange and banana peels as fruit wastes was evaluated in contrast with Euphorbia condylocarpa as a widely distributed medicinal plant of Kurdistan, Iran, for biosynthesis of Fe3O4, CuO, ZnO, and TiO2 NPs. The extracts of the green sources were assessed to monitor the bioreducing phytochemicals inside them using the UV‐Vis spectrophotometer. Moreover, the obtained green nanoparticles were identified using the micrograph and diffractogram techniques to show their size, shape, and morphology. Also, the antibacterial activities of the green NPs were investigated against common pathogenic bacteria of Pseudomonas aureus, Staphylococcus aureus, Escherichia coli, and Klebsiella pneumoniae.

Medicinal effects of fruit as the simplest form of functional foods and their extracts obtained from fresh tissues, residual parts, and wastes caused to their application in various sectors, like cosmetics, pharmaceuticals, and food industries due to high amounts of bioactive compounds (Baiano, 2014;Drosou, Kyriakopoulou, Bimpilas, Tsimogiannis, & Krokida, 2015;Filip, Pavlić, Vidović, Vladić, & Zeković, 2017). In fact, fruits are valuable source of secondary metabolites with a wide range of applications which their intake helps in overall health improvement. Residues consist of fruit skin/peels, sugarcane bagasse, residual part, and seeds are among the major sources of municipal solid waste and bioactive phytochemicals rich in antioxidant compounds apart from dietary fiber, minerals, phenolic compounds, carotenoids, tannins, vitamin C, and dietary fiber. In some cases, analysis of fruit wastes revealed that the total polyphenol and flavonoid contents are much higher in the fruit wastes from peel and seeds as compared to the edible part of fruit of mangoes, lemons, oranges, and grapes. There is growing interest of consumers toward citrus fruit antioxidant-rich compounds (e.g., ascorbic acid) and essential oils for their effects on human health promotion and disease risk reduction (Nobre, Palavra, Pessoa, & Mendes, 2009;Šeregelj et al., 2018).
The Euphorbiaceae (spurge) are a large family of flowering plants observed in tropical and nontropical areas as herbs, shrubs, or trees. In most cases, a milky and poisonous latex is a characteristic of the plants of this family. The plants of these family are a very rich source of bioactive phytochemicals such as terpenoids, flavonoids, alkaloids, tannins, phenolic acids, and porphyrins. In addition of the rich phytochemical content of this family, their latex is used as a laxative in folk medicine (Maryami, Nasrollahzadeh, Mehdipour, & Sajadi, 2017;Nasrollahzadeh, Atarod, & Sajadi, 2017;Sajadi, Nasrollahzadeh, & Maham, 2016). The huge variety of phytochemical content of the family revealed its effective remedy for many diseases like antidiarrhea, antioxidant, antibacterial, antidiabetic, and anti-inflammation diseases (Jassbi et al., 2006;Rizk, 1987). During this study, we employed the Euphorbia condylocarpa aqueous extract as reducing and stabilizing agent for phytosynthesis of some metal oxide nanoparticles and investigation of their bioactivity characteristics with the same nanostructures synthesized by using some common fruit wastes.

| Instrumentations
All used chemicals were of Merck purity. XRD analysis was carried out using Panalytical X'Pert 3 Powder using Cu Kα radiation equipped with a diffractometer system X'Pert Pro. The diffraction pattern was recorded for 2θ from 5 to 80° and a 2θ step scan of 0.010° was used, counting for 0.5 s at every step. The voltage and current of the generator were set at 45 kV and 40 mA, respectively. The prepared nanomaterials coated with gold using coater machine, then particles morphology was investigated using FEI (Quanta 450) scanning electron microscopy equipped with Quantax EDS-XFlash 6/10 microanalyzer for detecting chemical composition of the prepared nanomaterials. UV-visible spectral analysis was recorded on a double-beam spectrophotometer (Super Aquarius) to monitor the antioxidant extracts of the employed green sources.

| Fruit waste and plant material
The whole E. condylocarpa plant was collected from Sarshive Region in Saqqez city of Iranian Kurdistan, Figure 1. Fruit wastes were collected from the residual of wasted parts of fruits after daily consumption.

| Preparation of extracts
20 g root powders of E. condylocarpa was mixed to 100 ml distilled water at 85°C for 30 min while stirring on magnetite heater. Then, the mixture was centrifuged at 7,000 rpm and supernatant separated as extract. In case of obtaining the extract of fruit wastes including banana and orange peels, the procedure was the same.

| Green synthesis of Fe 3 O 4 , CuO, ZnO, and
TiO 2 NPs 0.5 g FeCl 2 and 1 g FeCl 3 (in case of CuO, ZnO, and TiO 2 NPs, the amount of salts was 0.5 g CuCl 2 .2H 2 O, 0.8 g ZnCl 2, and 0.5 g TiO(OH) 2 ) were mixed with 20 ml E. condylocarpa extract (in case of banana and orange peel wastes, the amount of employed extract F I G U R E 1 The image of E. condylocarpa plant was the same) at pH 9 (as adjusted using Na 2 CO 3 ) while stirring at 80 ºC for 5 hr (in case of CuO, ZnO, and TiO 2 , the time was 2, 1.5, and 2.5 hr, respectively) as the completion time of the reaction under reflux conditions. Of course, the time of changing the color of the mixture for each nanoparticle originated from different green sources demonstrating the SPR (surface plasmon resonance) signals and starting the formation of nanoparticles is different.
The obtained precipitates from each case were separated using filtration, washed with 60% hydroethanolic solution to remove the impurities, and then dried and kept to further investigations, Scheme 1.

| Anti-bacterial activity of green-synthesized nanoparticles
The disk diffusion method was employed to assess the antipatho-

| RE SULTS AND D ISCUSS I ON
Plants and majority of edible fruits as biofactories contain a diverse type of bioactive secondary metabolites. Besides them, it has been revealed that fruit wastes are precise sources of phytochemicals as which the total polyphenol and flavonoid contents of some fruit wastes are higher than the consumable parts of the fruit. Therefore, in this study we focus on using the banana and orange wastes potential for synthesis of bioactive nanoparticles and comparison of them with the same nanostructures produced by powerful antioxidant extract of Euphorbia condylocarpa plant.

| UV-visible monitoring of the aqueous extracts from E. condylocarpa plant, banana, and orange peels
The UV-Vis spectra of each aqueous extracts of E. condylocarpa plant and banana and orange peels as real samples of fruit wastes show the potential of these extracts for biosynthesis of nanoparticles as they have signals at the range of 220-270 nm and also 315-370 nm assigned to the benzoyl and cinnamoyl rings of phenolic antioxidants, respectively. Although according to the UV-vis spectra of the samples, the intensity of the plant and orange extract signals probably indicates the higher concentration of these antioxidant systems in their extracts. Generally, based on this analysis they are very good bioreducing sources to green synthesis of nanoparticles, Figure 2.

| Identification of the green-synthesized nanoparticles
The green-synthesized nanostructures using E. condylocarpa plant and also orange and banana fruit wastes were identified using the micrograph (SEM and EDS) and X-ray diffraction techniques. The  (Table 1).

| Antimicrobial activity
The antibacterial activity of green-synthesized NPs was subjected to test with common pathogenic bacteria of Pseudomonas aureus, Staphylococcus aureus, Escherichia coli, and Klebsiella pneumoniae.
The chloramphenicol was used as positive control to carefully evaluate the antibacterial activities. The inhibition zone for all types of nanoparticles fabricated by E. condylocarpa, orange peel, and banana peel sources were shown in Figure 6. The inhibition zone diameters of all samples are recorded in Table 2.
The antibacterial activities of green-synthesized NPs against some of the most common pathogenic bacteria revealed a potent bioactivity for most of them. Among the green NPs, those synthesized by E. condylocarpa as a green source generally showed more antibacterial activity than the NPs fabricated by the orange and banana peels. Also, for the TiO 2 NPs synthesized by banana peel, the inhibition zones (mm) for all types of bacteria are even more than chloramphenicol as positive control (38 mm

| CON CLUS IONS
In this study, the ability of Euphorbia condylocarpa plant, and orange and banana peels as fruit wastes and reducing agents were examined to biosynthesis of a series of the same nanoparticles of

ACK N OWLED G M ENT
The authors are grateful to Soran University and University of Maragheh for partial support of this work.

CO N FLI C T O F I NTE R E S T
The authors declare that they do not have any conflict of interest.

E TH I C A L A PPROVA L
This study does not involve any human or animal testing.

O RCI D
S. Mohammad Sajadi https://orcid.org/0000-0001-8284-5178 TA B L E 2 The inhibition zone of green-synthesized NPs using various green sources against common pathogenic bacteria