5.1.3. Microwave-Assisted Extraction

Microwave-assisted extraction (MAE) is a powerful alternative method for extracting bioactive compounds from FW. It is mainly used for extraction because it reduces solvent usage, energy consumption, extraction times, heating rates and increases extraction efficiency and selectivity, resulting in quality target products [148]. Many studies were conducted using MAE methods on FVW and FVB, including longan seed [149], tomato peel waste [150], apple pomace [151], banana peel [152], pitaya fruit peel [130,153], passion fruit peel [130], lemon peel, mandarin peel, and kiwi peel [154]; thus, MAE is mostly used to extract pectin from fruit waste. This approach has been used to extract high-quality pectin with biomasses such as mango peels [155], citrus mandarin peels [156], fig skin [157], orange peel, apple pomace, mango peel, carrot pulp [158], pumpkin biomass [148], and banana peels [159]. The study conducted by Zin et al. [160] showed that the highest microwave power used on the fruit waste (sour cherry pomace) was 700 W. Other biochemical compounds can also be obtained using this technique, such as antioxidants from black carrot pomace [161], pitaya peel [153], and mango seed kernels [162]; flavonoids from Jocote

pomace [163]; anthocyanins from grape juice waste [164] and sour cherry pomace [165]; and essential oil from lemon peels waste [166]. Casas et al. [167] also showed the potential of cocoa butter produced from mango kernel butter by extracting discarded seed kernels. Table 6 shows the summary conditions used for optimal bioactive compound extraction in recent studies on FVW.

For optimum yield extraction of the targeted compound, focused microwave-assisted extraction is preferred to conventional or household microwave ovens, as the parameters, namely the pressure and temperature, can be monitored [163]. A previous study showed that the combination of MAE with other methods could help produce high-yield compounds. Sequential ultrasound-microwave assisted extraction (UMAE) of fig skin extract resulted in higher pectin yield ~14.0%, with citric acid used as the solvents. Brönsted acidic– ionic liquid-based ultrasound-microwave synergistic extraction (BUME) from pomelo peels achieved the highest pectin yield of 328.64 ± 4.19 mg/g with optimum conditions involving 10 mM [HO3S(CH2)4mim]HSO<sup>4</sup> solvent, 15 min of extraction time, 360 W of microwave irradiation power, and 27 mL/g liquid–solid ratio compared as compared to MAE (210.39 ± 5.82 mg/g).

Utama-Ang et al. [168] studied MAE of dried ginger and developed a rice-based edible film containing ginger extract. The optimal MAE conditions were determined to be 400 W microwave power and one minute extraction time. At high temperatures and microwave power, 6-gingerol dehydrates water (H2O) from its structure, resulting in the formation of 6-shogaol4. Microwave power accelerated the retro-aldol reaction of 6-gingerol, and it is suggested that zingerone constituents be generated with aldehyde to deliver the products. The optimized extract showed good results in terms of the levels of total phenolic compounds (198.2 ± 0.7 mg GAE/g); antioxidant activity as measured by DPPH (91.4 ± 0.6% inhibition), ABTS (106.4 ± 3.1 mgTE/g), and FRAP (304.6 ± 5.5 mgTE/g); and bioactive compounds, including 6-gingerol (71.5 ± 3.6 mg/g), 6-shogaol (12.5 ± 1.0 mg/g), paradol (23.1 ± 1.1 mg/g), and zingerone (5.0 ± 0.3 mg/g).

In contrast, industrial potato peel by-products allowed greater antioxidant extraction yields than in combinations with ultrasound treatment [169]. Radiofrequency-assisted extraction (RFAE) with a frequency range of 1 to 300 MHz is another method used in dielectric heating as compared to microwave-assisted extraction (300 to 3000 MHz) in electromagnetic field-based thermal processes. An analysis discovered that the optimum conditions for RFAE were similar to MAE for pectin extraction from apple pomace. Still, the physicochemical properties (DE, GA, color values, and thermal stability) of apple pomace showed better RFAE pectin values [151].

**Table 6.** Progress studies of FVW in the application of microwave-assisted extraction.



#### **Table 6.** *Cont.*

**Table 7.** Progress studies of FVW involving pressurized liquid extraction.


Cejudo-Bastante et al. [178] investigated the extraction process used in developing bioactive jute-fiber-based food packaging using pressurized liquid extraction (PLE) and enhanced solvent extraction (ESE) techniques. The extraction yield and antioxidant capacity levels of the red grape pomace extract (RGPE) obtained using ESE and PLE were compared under varying pressure (10 and 20 MPa), temperatures (55–70 ◦C), and co-solvent (C2H5OH

or C2H5OH:H2O) conditions. They discovered that the PLE technique produced the most bioactive extract with 20 MPa, 55 ◦C, and one hour residence time using C2H5OH:H2O (1:1 *v*/*v*), providing antibacterial capacity against *Escherichia coli*, *Staphylococcus aureus*, and *Pseudomonas aeruginosa*.

#### 5.1.4. Subcritical Water Extraction

Compared to conventional extraction procedures, sub-critical water extraction (SWE) is a green extraction technology that yields superior quality extraction products and is cost-effective with a short extraction or treatment time [179–182]. SWE is also known as pressurized hot water or superheated water extraction, as it uses water at temperatures between 100 ◦C and 374 ◦C (critical temperature) and at pressures of up to 22.1 MPa (greater than vapor saturation) to keep the water molecules in a liquid state throughout the process [183]. Water is a polar solvent with a dielectric constant (ε) of 79.9 and a density of 1000 kg/m<sup>3</sup> [184,185]. When water is heated to higher temperatures, its hydrogen bonds break down, resulting in a drop in its dielectric constant (ε), demonstrating water's ability to act as a material reaction medium. Water has a density of 79.9% at ambient temperature and atmospheric pressure. Water may be lowered to 27–32.5% while remaining in liquid form by increasing the temperature to 250 ◦C and increasing the pressure to 5 MPa. Water has a similar density to methanol (32.5%) and ethanol (27%) at ambient temperature [186,187]. The latter enables water to interact with polar compounds, lowering the binding force and allowing substances to dissolve in water at greater temperatures and pressures.

The ionic constant of water (Kw) increases with increases in the reaction temperature according to Pourali et al. [188], and is nearly three times greater than at room temperature. Water's reactivity increases as the concentrations of H<sup>+</sup> and OH– in the aqueous medium increase, causing it to act as an acid or base catalyst that is appropriate for hydrolysis reactions. Organic waste can, thus, be hydrolyzed and the necessary components contained inside can be removed using sub-critical water treatment [189]. Sub-critical water treatment is an environmentally favorable procedure because no chemical solvent is required. As a result, less effluent is created. Table 8 shows several examples of the application of SWE on FVW.


**Table 8.** Progress studies of FVW involving sub-critical water extraction.

The extraction mechanism of SWE begins with solute desorption under elevated pressure and temperature, followed by the diffusion of extracted chemicals into the solvent. Finally, the extracted solutions are eluted from the extraction cell and transferred to a collection container [195,196].

Several process parameters influence the extraction efficiency of SWE, including the reaction temperature, pressure, reaction duration, solid-to-water ratio, sample particle size, pH, solute properties, and surfactant addition [197]; however, the reaction temperature, reaction duration, and solid-to-water ratio have the greatest influence on the SWE process. Because the viscosity and surface tension of the extraction solvent diminish with increasing temperature, Thani et al. [198] discovered that increasing the treatment temperature enhances the mass transfer rate and solubility of bioactive chemicals; however, if the temperature is raised above a certain point, the selected chemicals may degrade. As a result, the closely associated process temperature and duration should be optimized for each unique situation and are highly reliant on the desired product's qualities.

Ho et al. [199] investigated the influences of *P. palatiferum* freeze-dried powder (PFP) using SWE on the antioxidant activities and physical properties of gelatin–sodium alginate (GSA)-based films. *P. palatiferum* (Nees) Radlk. leaves were extracted with subcritical water, which increased the total phenolic content (TPC) and antioxidant activity as the PFP concentrations increased. The increase in antioxidant activity occurred in parallel with TPC. The antioxidant activity was attributed to the phenolic compounds [200] and gelatin–sodium alginate [201]. In addition to TPC, *P. palatiferum* leaves also contained a variety of other compounds, including protein, saponin, total sugar, and phytosterol [202], all of which can contribute to the antioxidant activity of GSA-based films.

Mohd Thani et al. [203] conducted an exhaustive review on SWE of sugar from FW. Monosaccharides and oligosaccharides are important carbohydrate molecules that can be hydrolyzed from FW. Sugar extraction from bakery waste, for example, is an effective way of valorizing this type of FW [198]. The leftover croissants had the most fructose and glucose at 4.74 and 3.76 mg/g substrate, respectively [198]; however, the sugar yield increased to a maximum value following SWE and then steadily decreased over time, whereas the yield of the degradation products increased over time [204,205].

Additionally, SWE can be successfully employed to extract antioxidant-rich extracts from yarrow by-products. The obtained extracts are rich in total phenols and flavonoids and have high antioxidant activity [206]. Oilseed cake extracts derived using subcritical water show a significant amount of promise for application in the fortification of various food goods and cosmetics. Depending on the type of oilseed, specific components such as the flavor amino acids aspartic acid, glutamic acid, and alanine can be extracted. This biowaste's favorable chemical composition and high nutritional content provide it with high utilization potential [207]. The most significant yield of phenolic compounds (4855 mg/100 g dry weight) was obtained using subcritical water extraction from pomegranate seed remnants [208]. Similar results were obtained for phenolics in white wine grape pomace [209] and peach palm by-products [210].

#### *5.2. Non-Thermal Extraction*

Each non-thermal extraction process has its own set of advantages and disadvantages, as summarized in Table 9. Several factors must be considered to obtain the best results when extracting phenolic compounds from FVW. The operation's success depends on the understanding of the nature of the target compounds, source materials, and waste matrices. Additionally, the process type and operating parameters used in the recovery process are critical determinants of the yield and quality of the recovered chemicals. The FVW matrix, the materials' physicochemical properties, and the type of compounds extracted may affect the chosen approach. Conventional extraction processes with low yields require longer extraction times, large amounts of energy, and significant capital investment. Due to the difficulties associated with achieving high-purity target compounds, conventional technologies are regarded as inadequate compared to the emerging non-conventional approaches, such as ultrasound-assisted, HPP, and PEF.


**Table 9.** Comparison of innovative extraction methods.

When combined with a properly chosen extraction method, media, and optimized parameters, these technologies have been shown to increase the yield of specific chemicals from FVW while minimizing carbon footprints [220]. Although selective for lipophilic and volatile compounds such as fats and oils, certain methods such as SFE utilize CO2; thus, co-solvents are indicated to boost extract purity. As such, green extraction media should be thoroughly evaluated prior to extraction, especially when the desired chemicals are food-grade. In order to turn the FVW problem into a solution for recovering the valuable qualities of bioactive substances that are now being wasted, more research is required.

As such, this sub-section will focus on the innovative technologies used to extract bioactive compounds from FVW and will be limited to notable articles published in the previous decade.

#### 5.2.1. High-Pressure Processing

High-pressure processing (HPP) is commonly used to produce commercially available commodities such as minimally processed fruit juices, guacamole, jellies, dips, salsas, meat and poultry, seafood, and ready-to-eat meals [221,222]. Pasteurization at high pressures ranging from 400 to 600 MPa and temperatures ranging from 20 to 70 ◦C is a common industrial process. On the other hand, high-pressure sterilization at pressures greater than 600 MPa and temperatures ranging from 90 to 120 ◦C is more commonly used to eliminate resistant food enzymes, bacteria, and spoilage spores [223,224]. In addition, this technology is being researched for various applications, such as reducing allergenicity in meals, inactivating fruit and vegetable enzymes, and valorizing food matrices. High pressure benefits both fresh produce and FW by-products [225,226]. High-pressure extraction and infusion technologies, for example, may show promise for agricultural and FW valorization.

High-pressure treatment is a green method for extracting bioactive compounds from agricultural commodities. Flavonoids, polyphenols, ginsenosides, anthocyanins, lycopene, caffeine, salidroside, corilagin, and momordicosides are bioactive compounds that have varying polarity levels [226,227]. The steps in specific bioactive compound extraction methods are breaking down plant cell walls to free intracellular molecules, isolating the bioactive compounds from auxiliary components, and purifying them [228]. High-pressure extraction improves the bioactive and heat-sensitive chemical extraction processes while requiring less time and energy [226].

Plant tissues, cellular membranes, and organelles are disrupted, allowing the solvent to enter the cell and dissolve the bioactive compounds [211]. The mass transfer rate is directly proportional to the applied pressure because solubility increases with pressure [229]. As a result, high-pressure treatments improve extraction rates and the availability of bioactive molecules, particularly from difficult-to-release matrices. Pressure has been shown to reduce intracellular pH [230], which aids in the extraction of acylated anthocyanins because they are more stable at low pH [231]. High-pressure treatments also reduce the dielectric constant of water and solvents, which aids in releasing phenolic compounds and the most stable anthocyanins in acylated form, which is less polar [231].

#### 5.2.2. Supercritical Fluid Extraction (SFE)

Supercritical fluid extraction (SFE) is another non-conventional extraction method that obeys the principle of the Green Extraction of Natural Products (second principle) [232]. This is due to the use of supercritical fluids such as CO2, which can reduce the solvent consumption and amount of waste [233]. SFE operates at temperatures and pressures above the critical points of the solvents used, whereby gas and liquid exist as separate phases. These fluids exhibit the properties of the liquid (density and salvation power) and gas (viscosity, diffusion, and surface tension), facilitating higher extraction yield within a short time [234].

Compounds that are soluble in CO2, such as oil, fatty acids, carotenoids, and tocopherols, have benefited from the low critical temperature (31 ◦C) and pressure (7.4 MPa) of CO<sup>2</sup> [232]; however, due to CO2's low polarity, co-solvents (methanol, ethanol, dichloromethane, acetone, ethylene glycol, water) are sometimes required to extract polar molecules from water-rich FVW [235]. These co-solvents are used to change the polarity of CO2, improve its solvating power, and increase the extraction efficiency by reducing interactions between analytes and plant cell matrices [216].

The sample particle size, temperature, pressure, time, co-solvents, solvent-to-solid ratio, and processing before extraction are important SFE operational factors [216]. Pressure and temperature are essential elements in SFE, and adjusting them is critical to achieve optimal yield and economic performance. The performance of SFE is strongly temperaturedependent, as increasing temperature reduces the solvent density, lowering the yield, while increasing the solute vapor pressure increases the yield; however, temperatures that are too high can damage fragile molecules such as carotenoids, altering their structure and bioactivity [236]. Pressure, on the other hand, causes the fluid density to increase as

the pressure increases so that the extraction yield improves. In general, high pressure, temperature, and flow rate maximize polyphenol extraction in FVW.

Despite its many benefits, SFE has some drawbacks, including limited solvent diffusibility into the matrix, prolonged extraction times, high pressure requirements, costly infrastructure, inconsistency, and lack of repeatability during continuous processes [234]. Furthermore, even with identical chemicals, SFE process conditions can differ amongst plant matrices. Pre-treatments such as lyophilization, micronization, maceration, and decoction often impact the final extraction yields and compositions; thus, before using SFE for bioactive extraction, it is imperative that the appropriate operating conditions and pre-treatment are thoroughly investigated.

#### 5.2.3. Pulsed Electric Field (PEF)

PEF has been gaining traction for FW recycling and by-products due to its ability to extract valuable ingredients [237]. It is able to decrease energy costs, improve the extraction yield, lessen the degradation of heat-sensitive substances, and purify the extraction process with no environmental impacts [238]. In the PEF process, which occurs at ambient temperatures (20–25 ◦C), the sample is positioned in the middle of two or more electrodes before being exposed to high-voltage electric field pulses for short processing times with repeated frequency. This results in high electric field strengths (EFS) in batch mode of 100–300 V/cm and in continuous mode of 20–80 kV/cm [239].

PEF works by breaking down the structure of plant cell membranes with a high electric field. Due to their dipole nature, the electric charge separates the molecules of plant cell membranes. Because charged molecules repel each other, the pores on the weak sides of the membranes expand, causing permeability [240]. This electroporation or electropermeabilization element allows targeted chemical release from plant matrices [235]. For delicate plant tissues (e.g., pericarp or mesocarp of few fruits), a voltage of 0.1 to 10 kV/cm is sufficient, although for robust materials (e.g., seeds), a voltage of 10 to 20 kV/cm is required [241]. Another benefit of a low EFS (500–1000 V/cm) is the ability of the system to keep the temperature low [242]; thus, PEF reduces heat-labile chemical degradation [243].

The efficiency of PEF-assisted extraction is dependent on the PEF system configuration and extraction parameters. The intensity of the electric fields applied to the processed material is related to the electrode gap, the delivered voltage, the electrode geometry, and their placement in the reactor. Additionally, the extraction yield can be improved by considering the pulse width, number of pulses, treatment time, and total specific energy (kJ/kg). The physicochemical aspects of the treated matrix (size, shape, electric conductivity, cell structure, and membrane characteristics) and nature and cell location of the targeted molecules being extracted can also influence the extraction yield [218].

The EFS affects the physical properties of the targeted molecules, such as their diffusivity, surface tension, viscosity, and solubility [244]. The electric fields must be dispersed consistently across the treatment chamber. There are many waveforms that can be used to deliver electric field energy. In PEF extraction, high-energy exponential square wave pulses are typically used. Due to strong energy transfer in the plant cell matrix, boosting EFS also increases the chemical extraction. The treatment temperature also impacts the PEF extraction process [245], which is commonly conducted at room temperature; however, a high voltage electric field or inefficient delivery pump may increase the overall energy and sample temperature. Higher temperatures may reduce the solvent viscosity, affecting extraction. The treatment time (pulse numbers and width) and solvent selection are equally critical in assessing the PEF performance [128]. An increase in solvent conductivity allows for faster electroporation of the cell membrane. It also aids in mass transfer and increases the extraction rate due to its high solubility in the solvent [246].

Further applications of PEF extraction should be explored; however, the high investment cost is the major hindrance to this technology being widely employed in industry. Nevertheless, its principal benefits outweigh conventional extraction methods; namely, improved extraction yields with minimal thermal degradation while reducing the extraction

time, temperature, and solvent usage, subsequently lowering the energy consumption and environmental effects.

#### 5.2.4. Ultrasound-Assisted Extraction (UAE)

Ultrasound-assisted extraction (UAE) is an established extraction method that has been successfully employed to extract polyphenols, carotenoids, volatiles, and polysaccharides from various FVW [117,247–251]. This approach reduces the extraction time (saving energy) and solvent usage while increasing the bioactive component yield from FVW. It is also one of the most common green extraction methods because it is fast and straightforward. UAE utilizes mechanical waves from 20 to 100 kHz [252]. These waves are composed of compression and rarefaction cycles that can travel through any media, displacing and dislodging the treated FVW cell matrix. The cavitation bubbles implode forcefully at the end of the rarefaction cycle, releasing tremendous amounts of energy at temperatures up to 5000 K and pressures up to 50 MPa [253]. The collapsing cavitation bubbles will cause microjets, fragmentation due to rapid interparticle collision, localized erosion, pore creation, shear forces, enhanced absorption, and enhanced swelling index values in the treated plant cells. Reduced particle size, higher surface area, and high mass transfer rates in the border layer of the solid matrix contribute to the solubilization of bioactive components [254]; thus, by improving the mass transfer between the plant cells and solvent, UAE can improve extraction. Despite the considerable energy produced by collapsed cavitation bubbles, the timeframe for these processes is too short to affect the overall system; hence, UAE is the ideal method to extract heat-sensitive compounds [255].

Combining two or more operating factors (frequency, power, duty cycle, temperature, solvent type, and extraction time) creates synergistic effects [256]; thus, determining the extraction kinetics is critical to optimizing extraction times and lowering energy use. In experiments involving sonoporation, capillarity, and detexturization in plant cells, frequency has been shown to have a significant impact on the bioactive chemical yield and characteristics [257]. Low-frequency, high-intensity ultrasound produces strong shear and mechanical forces that are desirable in the extraction process, whereas high-frequency, low-power density ultrasound produces a large number of reactive radicals [247,249,258].

Low frequency is preferred due to large cavitation effects that diminish with ultrasound frequency. Extraction with more than 20 kHz energy affects the physicochemical properties of phytochemicals, causing chemical deterioration and free radical production [259]. Using response surface methods, González-Centeno et al. [248] determined that 40 kHz was most successful in extracting phenolics from grape pomace. The yields were high at both low and high frequencies but low at intermediate frequencies for all examined responses.

The power levels used for UAE bioactives from FVW vary depending on the component to be extracted and the plant matrix chosen for extraction [254]; however, UAE power is inversely proportional to the cavitation bubbles generated within the solvent or solid media. This relationship is significant because as cavitation bubbles collapse, they increase the contact area between the solid and solvent, the shear forces causing turbulence behavior, and ultimately cell wall rupture and solvent penetration. Although increasing the power increases the extraction yield, it should only be increased to a point where the cavitation effects do not diminish. The influence of power on yield also depends on other extraction parameters such as the temperature and solvent extraction time. Achat et al. [260] discovered that the UAE power (60 W) and solvent temperature (olive oil, 16 ◦C) had significant impacts on oleuropein extraction, with TPC extraction increasing by 53% (414 mg oleuropein eq./100 g). The maximum TPC extraction yield (30.7 mg GAE/g) was achieved by Martínez-Patiño et al. [261] using high amplitude percentages (70%) and extended ultrasonication periods (15 min); however, elevated temperatures (>75 ◦C) were reached at the end of the experiment, perhaps restricting the extraction yield.

The combined impacts of the sample particle size, solvent-to-solid ratio, pH, temperature, and extraction time on the yields of targeted bioactive chemicals should not be

underestimated. More surface area means a higher yield, especially when combined with a higher reaction temperature and the correct solvent-to-solid ratio. The bigger concentration difference improves the solute diffusivity and solubility in the solvent, enhancing extraction [254]. Pectin recovery is high when the pH is low. Insoluble pectin is hydrolyzed into soluble pectin, and the molecular weight of the pectin is reduced, boosting dissolution into the surrounding medium and recovery [262]. The effect of increased sonication time on yield is similar to the effects from increasing the power and temperature. Longer exposure times and higher power input speed up the disintegration of dissolved pectin, producing simpler monosaccharides. According to Wang et al. [262] and Xu et al. [263], increasing the extraction time and decreasing the power intensity (lower energy expenditure) did not improve the pectin extraction yield in grapefruit peels.

It is essential to screen the optimal operating parameters that may help boost the extraction of the targeted chemicals and may further optimize the settings used in prior studies. Furthermore, secondary contamination from the UAE probe should be considered when extracting bioactive chemicals from FVW.

#### **6. Conclusions and Future Perspectives**

Fruit and vegetable wastes (FVW) from the food bioprocessing industry result in environmental pollution; however, these wastes can be valuable sources of polymer materials. This review focuses on recent advances in biocomposites, active packaging, and by-products and the innovative technologies used for bioactive compound extraction. The mechanical, thermal, antibacterial, and physicochemical properties of FVW-based biocomposites have recently shown improvement. Common matrices used for biocomposites are PLA and PP. Additionally, pectin is an extracted compound used in the polymeric matrix, and the films produced are both active and biodegradable. Additionally, blueberry, sweet potato, and black chokeberry dyes and pigments are added to the films as pH indicators to trace and monitor food freshness throughout storage. To extract bioactive compounds from FVW, various techniques are used, including thermal extraction. Traditional methods (conventional and Soxhlet heating extractions) and new emerging methods (pressurized liquid extraction, subcritical water extraction, and microwave-assisted extraction) have been reviewed in this paper. As a result of the reduced use of organic solvents in the extraction procedures, these well-developed and established methods have been recognized as green technology methods.

While the use of FVW has the potential to improve polymer properties, it is critical to maintain the low-cost benefits of using FVW while also maintaining the mechanical and thermal properties. Surface treatments with biopolymers or fibers improve these properties but are more expensive. The high temperatures involved in such processes may reduce the quality of the resulting bioactive compounds. The value of FVW for use in biocomposites is expected to grow for both industry and research applications due to global waste concerns. Additionally, the vast majority of FVW-based research has been conducted at the bench scale. The next level of valorization of FVW should be scaling up this process to the industrial level. Overall, the growth of FVW-based polymer materials has been rapid, and their applications in active packaging, biocomposites, by-products, and recent technologies for the extraction of bioactive compounds mean they appear to have a promising future in the coming years.

**Author Contributions:** Conceptualization, M.S.M.B. and N.N.A.K.S.; validation, A.S. and M.Z.M.N.; writing—original draft preparation, M.S.M.B., N.N.A.K.S., A.S., I.S.M.A.T., M.Z.M.N., S.H.A., N.H.A.G. and F.S.M.S.; supervision, N.N.A.K.S. and M.S.M.B.; project administration, M.S.M.B. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** The data presented in this study are available on request from the corresponding author.

**Acknowledgments:** The authors gratefully acknowledge the technical and financial support from the Universiti Putra Malaysia (UPM).

**Conflicts of Interest:** The authors declare no conflict of interest.
