Sustainable Valorization of Jackfruit Peel Waste: Bio‐Functional and Structural Characterization

Abstract

ABSTRACT

The sustainable utilization of agricultural waste holds immense promise in addressing environmental concerns and promoting resource efficiency. In this context, jackfruit (Artocarpus heterophyllus) peel waste emerges as a valuable yet underexplored resource. Therefore, this study aimed at the bio‐functional and structural characterization of A. heterophyllus peel waste for unlocking its potential for food applications. By using cutting‐edge and environmentally friendly technology, A. heterophyllus peel can be used as a bioresource (raw material) to obtain a variety of high‐value biocompounds, in line with the circular bioeconomy philosophy. In this work, we examined A. heterophyllus peel, from its chemical composition to its functional and biological characteristics. Proximate analysis of the A. heterophyllus peel revealed the presence of protein (1%) and fiber (21%) content. Microscopic imaging (scanning electron microscopy and transmission electron microscopy) provided a comprehensive visual depiction of the peel's surface structure that possesses a high heat stability with peak disintegration observed at 200°C–300°C that was detected by thermogravimetric analysis. The findings of phytochemical screenings reported the presence of various bioactive compounds, such as alkaloids, steroids, glycosides, and tannins. Notably, the peel exhibited inhibitory effects against several bacterial strains, including Alcaligenes faecalis, Staphylococcus aureus, and Escherichia coli in the antimicrobial analysis. Additionally, Fourier‐transform infrared spectroscopy analysis identified the presence of alcohols and phenols, while X‐ray diffraction data displayed characteristic diffraction peaks at 20°–25°. In conclusion, this study identified the potential utility of A. heterophyllus peel as a valuable source of phytochemical compounds, polyphenolic antioxidants, and the antimicrobial additives that can be used in wide agri‐food‐pharma industries.

Abbreviations

• DPPHPH
• 2,2-diphenyl-1-picrylhydrazyl
• FTIR
• Fourier-transform infrared spectroscopy
• SEM
• scanning electron microscopy
• TEM
• transmission electron microscopy
• TGA
• thermogravimetric analysis
• XRD
• X-ray diffraction

Introduction

Jackfruit (Artocarpus heterophyllus), a member of the Moraceae family, is found extensively throughout the world's tropical regions, including India, Bangladesh, Sri Lanka, the rainforests of the Philippines, Indonesia, Malaysia, and Australia. Between 70% and 80% of A. heterophyllus components are nonedible; roughly 60% are the outer rind, perianth, and center core, which are typically discarded (Brahma and Ray 2022). A. heterophyllus peel generally gets discarded, resulting in a loss of potential. The peel is not edible and is considered the waste component of the fruit, which is primarily used as fertilizer or disposed of Tran et al. (2021).

There are multiple studies on jackfruit peel, however not many research publications have been found that focus solely on the complete characterization of jackfruit peel. As a result, the research gains novelty and serves as the platform for future studies centered on the A. heterophyllus peel.

A. heterophyllus peel has been found to have a number of medicinal characteristics (Khan et al. 2023). A. heterophyllus peel includes polyphenolic compounds, dietary fiber, and cellulose, all of which are advantageous to a range of sectors and can be utilized to solve environmental issues (Sarangi et al. 2023). A. heterophyllus peel with its different beneficial components can be used in a variety of ways in the food sector as additives such as thickeners, emulsifiers, etc (Kalse and Swami 2022). It was found by Saurabh et al. (2023) that A. heterophyllus peel when treated with low temperature-based ultrasound-assisted extraction facilitates high-quality food-grade pectin with higher yield and functionality in a short duration. Similar treatments related to the extraction of pectin from A. heterophyllus peel employing pulsed electric field (Lal et al. 2021), radio frequency assisted extraction (Naik et al. 2020), and ultrasonic-microwave assisted extraction (Xu et al. 2018). Researchers discovered that A. heterophyllus peel extracts contain a higher level of total phenolic and flavonoid content than pulp and seed extracts. They discovered an overall of 53 components in the extract, which were consequently recognized through high-performance liquid chromatography coupled with quadrupole time-of-flight mass spectrometry, which involves 8 organic acids, 8 glycosides, 12 phenolic acids, 18 flavonoids, 3 oxylipins, and 4 other components (Zhang et al. 2017). Research on A. heterophyllus peel extracts identified ascorbic acid, polyphenols (catechin and chlorogenic acid), and β-carotene (Sharma et al. 2015). These phytochemicals can work as protectants against lipid oxidation or microbial growth furthermore, if these phytochemicals are used as a coating in meat, it can prevent any oxidative damage (Siddiqui et al. 2023). It can also be utilized as a raw material in other industries, such as cellulose, fibers, and colors. In the pharmaceutical sector, it can be employed as an encapsulating component for various drug delivery methods (Khedmat et al. 2020; Lu Zhang et al. 2017). Although, A. heterophyllus has been used in history to cure ailments, there is certain information gap in the research related to its medicinal properties. Not much research has been carried out that employ A. heterophyllus components as alternatives for pharmaceutical drugs or supplements. Other fruit peels have previously been studied for their nutritional value. However, considerable research has been undertaken on this waste component of this tropical fruit. Although, there is a presence of numerous studies related to the nutritional and structural characterization of A. heterophyllus peel there are certain fields or areas of research which is yet to be explored such as the employment of various green techniques to quantify the phytochemical components or extraction of those components. There is also less information about the types of A. heterophyllus found in various regions of the world which eventually affects the data found out by researchers since there is no solid data regarding the various types or genotypes of A. heterophyllus.

Therefore, the study aimed to characterize A. heterophyllus peel waste for nutritional composition, surface morphology, and bioactive compounds. Moreover, thermal stability and the antimicrobial properties of A. heterophyllus peel waste were studied. This study helps to find a sustainable source for numerous products such as cellulose, ethanol, bioactive chemicals, and antibacterial compounds.

Materials and Methods

Materials

To ensure homogeneity in the study, A. heterophyllus was selected based on uniform size and weight of around 5–6 kgs, 50–60 cm (diameter), namely of variety “Lakoocha or Monkey Jack” and were transferred to the lab in sealed pouches during the harvesting season of June–July. Sodium hypochlorite, sodium hydroxide and DPPH (2,2-diphenyl-1-picrylhydrazyl) were purchased from Sigma Aldrich Limited. All other chemicals used in the study were analytical reagent grade and procured from Sisco Research Laboratories Pvt. Ltd.

Sample Preparation

Before use, the A. heterophyllus peel was washed multiple times with tap water to eliminate dirt and other organic impurities. Each fruit yielded 600–800 g of peel (sliced), which is finally grinded to form powder of 200–300 g (plant: powder = 2.67:1–3:1) followed by drying at 60°C for 24 h. The peel was then ground into powdered form. The powder was then sieved using a 180-micron sieve and used for subsequent examination.

Proximate Composition

All the analysis was carried out using standard protocols set by the (AOAC 1990). Cellulose, hemicellulose and lignin estimation was performed using the method of (Trilokesh and Uppuluri 2019) utilizing sodium chlorite method. The powdered jackfruit peel was dewaxed with water and then extracted with ethanol in a Soxhlet system for 8 h. The dewaxed powder was bleached with 1.5% w/v sodium chlorite in water (1:25 g/mL), at 70°C for 2 h. The bleaching process was repeated four times until a white-colored holocellulose was generated, after which the hemicellulose was completely removed using alkali treatment. The cellulose was suspended in water at 60°C for 2 h to remove excess sodium hydroxide. The purified cellulose was filtered and dried.

Physical Properties

Tap bulk density was evaluated by placing A. heterophyllus peel powder into a 100 mL measuring cylinder and tapping until a consistent volume was attained (Jouki et al. 2021). The bulk density of samples was determined according to Equation (1). 1$\text{Bulk density }(\text{g}/{\text{cm}}^3)=\left[\frac{\text{Weight of sample }\left(\text{g}\right)}{\text{Volume of sample }\left({\text{cm}}^3\right)}\right]$

The true density was calculated by placing 1 g of A. heterophyllus peel powder into a cylinder containing toluene and measuring the rise in toluene level taking safety precautions like gloves and conducting the experiment in a non-flammable environment (Smita et al. 2019). The true density of samples was determined according to Equation (2). 2$\text{True density }(\text{g}/\text{mL})=\left[\frac{\text{Weight of sample }\left(\text{g}\right)}{\text{Volume of sample }\left(\text{mL}\right)}\right]$

The porosity of the sample was estimated using the relationship between the bulk and actual density of the powder (Smita et al. 2019). The porosity of samples was determined according to Equation (3). 3$\text{Porosity}(\%)=\left[\left(1-\frac{\text{Bulk density}}{\text{True density}}\right)\times 100\right]$

The angle of repose was calculated using the fixed funnel method, which includes letting the powder to move freely via a funnel fixed at a height, H, above the floor until the apex of the generated conical pile reaches the tip of the funnel (Müller et al. 2021). The average diameter (2R) of the powder cone's base is measured, and the angle of repose is determined using Equation (4). 4$\text{Angle of repose }(°)=\left[\left(\text{Tan }-\frac{\mathit{\text{H}}}{\mathit{\text{R}}}\right)\right]$where H is the Hausner ratio, calculated by the ratio of tap bulk density and loose bulk density.

A laser diffraction particle size analyzer (SALD-7500 nano Shimadzu) was used to measure particle sizes ranging from 0.007 to 800 μm (Gurak et al. 2014).

Swelling Index: According to the method described by Hassan et al. (2011), the peel powder (1 mg) was precisely weighed and transferred into a calibrated cylinder. Distilled water (10 mL) was then poured into the cylinder. After mixing, the mixture was incubated for 18 h at room temperature. The packed volume was then measured, and the swelling was computed using milliliters per gramme of peel powder.

Phytochemical Screening

The ethanolic extract of A. heterophyllus peel powder was prepared by making slight modifications to the procedure (Yamin et al. 2021). Dissolve 10 g of A. heterophyllus peel powder in 100 mL of distilled water and stir continuously for 5 min. The solution was left in the dark for 4 h at 4°C. The solution was then filtered using Whatman filter paper, then centrifuged at 4000 rpm for 15 min. The supernatant was collected to screen for various phenolic chemicals. The studies were carried out in duplicate. Adding 1 mL of Dragendorff's reagent to 2 mL of extract produced an orange-red precipitate, suggesting the presence of alkaloids (Kancherla et al. 2019). A vigorous shaking of the solution (5–10 mL extract + a drop of sodium carbonate) was performed for 15 min. The appearance of foam suggests the presence of saponins (Kancherla et al. 2019). Keller–Killiani's test: 2 mL of extract was treated with 1 mL of glacial acetic acid and a few drops of iron chloride (FeCl₃) solution. The concentrated sulfuric acid was cautiously poured from the side. The presence of cardiac glycosides is indicated by the production of bluish-green at the upper layer and reddish brown at the junction of two layers (Kancherla et al. 2019). Lieberman Burchard test: 1 mL of extract was combined with 2 mL of acetic anhydride and a few drops of strong sulfuric acid. Green coloration suggests the presence of steroids (Pooja and Gm 2016). Modified Borntrager's test: 1 mL extract was combined with 5 mL chloroform and agitated for 5 min. The extract was filtered and shaken with the same volume of 100% ammonia solution. A pink/violet/red color in the lower section indicates the presence of anthraquinones (Godlewska et al. 2023). 3 mL of 10% NaOH was mixed with 2 mL of extract. Formation of yellow color shows the presence of coumarins (Godlewska et al. 2023). Ferric chloride test: 5 mL of extract was mixed with 1 mL of 5% ferric chloride solution. The greenish-black coloring suggests the presence of phenols (Godlewska et al. 2023). Gelatin test: A 1% gelatin mixture comprising 10% sodium chloride solution was incorporated into 1 mL of extract. The physical appearance of the white precipitate shows the presence of tannins (Pooja and Gm 2016). Shinoda test: Magnesium powder when added to the extract along with dropwise addition of concentrated hydrochloric acid indicates a pink-tomato red color to confirm the presence of flavonoids (Pooja and Gm 2016). Two milliliters of extract when added to 2 mL of 2 M HCl and ammonia indicates the presence of anthocyanin upon the appearance of a blue-violet color (Gupta 2020).

Antioxidant Activity

The antioxidant activity of A. heterophyllus peel powder was tested using the DPPH (Yamin et al. 2021). The ethanolic extract of A. heterophyllus peel powder was mixed with 2 mL of a DPPH solution (0.2 mM in ethanol) and put in a dark atmosphere at room temperature (25°C ± 1°C) for 45 min. An ultraviolet spectrophotometer was used to determine the absorbance values at 517 nm. The antioxidant activity was determined as DPPH radical scavenging activity by using the following Equation (5): 5$\text{DPPH radical scavenging activity }(\%)=\left[\left(\frac{{\mathit{\text{A}}}_{\text{a}}-{\mathit{\text{A}}}_{\text{b}}}{{\mathit{\text{A}}}_{\text{a}}}\right)\times 100\right]$where A_a is the absorbance of the control and A_b is the absorbance of the peel extract.

Antimicrobial Activity

Strains of bacteria (5) were used in this study that is Alcaligenes faecalis, Staphylococcus aureus, Enterobacter aerogenes, Escherichia coli, Bacillus subtilis to study the antimicrobial activity by studying the zone of inhibition following the agar well diffusion method. MHA was used for the antimicrobial assay. Incubation was done for 24 h in 31°C using the method of (Yonghang et al. 2019). A (10 g) sample of A. heterophyllus peel powder was gathered, weighed, and placed in an individual thimble. After encapsulating the sample, ethanol and water were used as the solvent. The solvent was then applied to fully cover the thimble. Extracts were concentrated to dryness in a beaker using a rotary evaporator. The extracts were then tested for antibacterial activity. Antibacterial activity was assessed using agar well diffusion on Mueller–Hinton agar (MHA) against test microorganisms. After pouring 20 mL of sterilized MHA into sterile petri plates and solidifying, 100 μL of fresh culture of Test Bacteria (0.5 Mc-Farland standards) was swabbed on each plate. Bore 6 mm diameter wells in inoculated plates with a sterile cork borer. Load 100 mL of extracts into each well and incubate at 37°C for 24 h. After incubation, the diameter of the inhibitory zones around the well was measured.

The antimicrobial assay was conducted in triplicates for accurate findings. Two types of extracts were used that is distilled water-based peel extract and the ethanolic peel extract.

Structural Properties

Thermogravimetric Analysis (TGA)

TGA of A. heterophyllus peel powder was performed according to (Jancy et al. 2020). TGA was carried out on a 4000 (Perkin Elmer) to study the heating stability and degradation patterns of two cellulose variants using dynamic thermogravimetry. Each measurement used approximately 5 mg of the sample. Patterns were generated by heating the product to 800°C at a mean rate of 10°C/min while being placed in the presence of nitrogen having an average flow rate of 100 mL/min.

Transmission Electron Microscopy (TEM)

The physiological characteristics of A. heterophyllus peel powder influence its morphological frameworks, which change according on the treatments it gets. A. heterophyllus peel was studied using TEM analysis in a JEM-2100 PLUS (HR), JEOL with an accelerating voltage of 200 KV as performed by Jancy et al. (2020). Bright-field images were obtained in 10,000× magnification. The samples were prepared before analysis by taking fine powdered peel and suspending them in ethanol followed by 5 min ultrasonication and transferring into TEM grid followed by drying and transferring into the TEM sample holder for imaging.

Scanning Electron Microscopy (SEM)

SEM analysis of A. heterophyllus peel was conducted with a JEOL JSM 6701 F microscope and a 6 kV accelerating voltage. To lessen the electron charging effects, the specimen was attached to an aluminum stub and gold sputter as performed by Trilokesh and Uppuluri (2019).

X-Ray Diffraction (XRD)

XRD analysis is used on fruit peels to study the crystalline structure of the peel's components, primarily to identify the presence and relative amounts of crystalline materials like cellulose, hemicellulose, and lignin, which can be important in understanding the potential applications of the peel as a biomaterial, such as the development of adsorbents or other functional materials based on fruit waste. The crystallinity of A. heterophyllus peel powder was measured using XRD. The examination was conducted using an X-ray diffractometer (Bruker D8 Advance) with a scanning span of 5–60 (2θ) as performed by Trilokesh and Uppuluri (2019).

Fourier Transform Infrared Spectroscopy (FTIR)

FTIR analysis is used to identify and characterize the chemical composition of the peel, specifically the different functional groups present. This can reveal valuable information about the potential bioactive compounds, antioxidant properties, and overall chemical profile of the fruit peel, allowing researchers to explore its potential uses in various applications such as food additives, nutraceuticals, or waste utilization. The diffuse reflectance setting of a Spectrum One (Perkin Elmer, USA) instrument was used for determining the FTIR spectra of A. heterophyllus peel powder (2 mg) and dry KBr (200 mg) compressed into a 16 mm diameter mold as performed by Trilokesh and Uppuluri (2019).

Statistical Analysis

The experiments were independently repeated at least three times and the results were expressed as the mean ± standard deviation. Data analysis was performed using OriginPro 9.0 software where Tukey tests were performed at a significance level of p < 0.05.

Results and Discussion

Proximate Analysis

Table 1 depicts the proximate composition of A. heterophyllus peel powder. Protein content of 1% was comparable to other varieties of peel, such as apple, pineapple, pomegranate, and orange peels, which showed 0.25%, 0.17%, 0.17%, and 0.28%, respectively (Dias et al. 2020). However, the fiber content was less compared to the above-mentioned peels showing 53.14%, 11.66%, and 32.85% meanwhile orange peel had a lower fiber content as compared (Dias et al. 2020). A. heterophyllus peel contains high amount of cellulose, hemicellulose, and sugars (Table 1) which can be put into use in the conversion to ethanol. Studies have been carried out to convert cellulose to ethanol from various fruit peels/agricultural wastes such as sugarcane bagasse (Méndez et al. 2021), banana peels (Palacios et al. 2021), and pomegranate peels (Chaudhary et al. 2021). A. heterophyllus peel when taken as substrate using Saccharomyces cerevisiae synthesizes bioethanol (Yuvarani and Development 2017). Similar to A. heterophyllus peel, banana peel also has high fiber; thus, it was used as substrate to produce ethanol at high temperature and pH to obtain more yields of ethanol (Sarkar et al. 2022). Pineapple peel was also used for the production of bioethanol with a yield of 6 g/L from the fruit peels after fermentation of 48 h (Casabar et al. 2019). A. heterophyllous is particularly advantageous than sugarcane bagasse, pomegranate and banana peels because of the higher amount of extractable cellulose which is approximately 69% as compared to the sugarcane bagasse (40%–50%) (Mahmud and Anannya 2021), banana peels (7.5%–18%) (Mohd Jamil et al. 2022), and pomegranate peels (16%–22%) (Muhammad et al. 2023). Overall, it could be suitable for use in bioenergy generation, paper manufacturing, or other businesses that require plant-based raw materials.

Table 1 Proximate composition of A. heterophyllus peel powder.^a

Properties	Value (%)
Moisture content	3.42 ± 0.29
Protein	1.03 ± 0.44
Crude fiber	21.16 ± 1.22
Ash content	10.07 ± 0.38
Cellulose	69.1 ± 0.22
Hemicellulose	20.8 ± 0.45
Lignin	3.8 ± 0.38

Physical Properties

The physicochemical qualities of A. heterophyllus peel powder can help to determine its suitability in a variety of food-related applications. Table 2 shows the physical parameters of the peel powder.

Table 2 Physical properties of A. heterophyllus peel powder.

Properties	Value
Tap bulk density (g/cm3)	0.60 ± 0.016a
True density (g/mL)	0.66 ± 0.04a
Porosity	11.76 ± 0.61a
Angle of repose (°)	29.28 ± 0.7a
Hausner ratio (H)	0.67 ± 0.08a
Particle size (µm)	360.82 ± 29.72b
Swelling index (g/g)	14.6 ± 0.48a

The physical properties of the peel are used to monitor the overall powder quality and its usability for various purposes. Bulk density and porosity can normally show the flowability of the peel powder. The swelling index of A. heterophyllus peel powder in terms of its water absorbing capacity was studied. It showed an overall swelling index of 15 ± 0.07 g/g. Other types of peel such as potato peels showed a lower swelling index as compared that is 4.45 ± 0.22 g/g (Ben Jeddou et al. 2017). The swelling index of lemon peel powder was 2.5 mL/g as found out by Bakshi and Ananthanarayan (2022). The swelling index of pomelo peel powder was however more than A. heterophyllus peel powder showing 43% swelling capacity (Lei Zhang et al. 2020).

Phytochemical Screening

Various analyses involving the tests to check the presence of 10 different kinds of phytochemicals were performed. In Table 3, A. heterophyllus peel displays various phytochemicals that can be used in the food industry upon more in-depth research. This screening leads to a lot of quantitative analysis that can be done to look for sustainable alternatives. Sundarraj and Res (2018) detected the presence of carbohydrates, proteins, tannins, saponins, flavonoids, alkaloids, etc in A. heterophyllus peel. Valorization of A. heterophyllus peel has various prospects to focus on. The presence of various phytochemicals and antioxidants in the peel as detected by this current research work is an essential point of importance since recovery of bioactive components from peels is a cost-effective and environmentally friendly solution to repurpose waste meanwhile promoting sustainability. However, chemical treatments and energy-intensive recycling are examples of waste valorization methods that may have high environmental costs. In some circumstances, the environmental impact of valorizing technology may outweigh the advantages of waste diversion. Thus, it can be sustainable if the environmental footprint is thoroughly calculated.

Table 3 Phytochemicals in A. heterophyllus peel.^a

Compound	Presence
Alkaloid	+
Saponin	+
Glycosides	+
Steroids	+
Anthraquinone	−
Coumarins	−
Phenol	+
Tannin	+
Flavonoids	+
Anthocyanin	+

Other aspects such as the presence of pectin and calcium were found by Moorthy et al. (2017), which adds more value since pectin is an important food additive and is highly consumed. Lu Zhang et al. (2017) found a total of 53 compounds in A. heterophyllus peel, glycosides being high in number, it also emphasizes its potential to stand as a good hypoglycaemic agent. Adan et al. (2020) found a bunch of minerals such as potassium, sodium, calcium, magnesium, and zinc in peels which adds more emphasis on the potential of using A. heterophyllus peel as a raw ingredient as a good food additive etc.

Antioxidant Activity

The antioxidant activity of the ethanolic peel extract was tested using the DPPH scavenging ability assay. When concentration increased the DPPH activity gradually decreased. The antioxidant activity is shown in Table 4. The antioxidant activity decreases dramatically after 0.5 h, most likely due to degradation, consumption, or a decrease in the availability of active antioxidant molecules. Beyond 24 h, the activity stabilizes, indicating that the leftover antioxidants or their effects continue albeit at a decreased level. Antioxidant activity is rather steady between 0.5 and 120 h, with a slight reduction. Antioxidants neutralize free radicals (unstable molecules with unpaired electrons) by donating electrons or hydrogen atoms, stabilizing the radicals, and protecting cells. The decrease in the DPPH activity with increasing concentration demonstrates the scavenging ability of antioxidants found in jackfruit peel phytochemicals (Lobo et al. 2010).

Table 4 Antioxidant activity in terms of % inhibition.

Time (h)	Antioxidant activity (% inhibition)
0.5	85 ± 5a
24	80 ± 5a
48	80 ± 6a
120	78 ± 6a

From Table 4, it can be stated that jackfruit peel shows a DPPH radical scavenging potential of 80%–85%. If compared to other fruit peels, such as watermelon peel with a DPPH radical scavenging potential of 55.75% (Neglo et al. 2021), Citrus limetta peels—78.6% and lemon peels—93.1% (Saleem et al. 2023), kinnow mandarin peel—64.70%, banana peels—75% (Chaudhry et al. 2022). The reason behind the DPPH scavenging activity of A. heterophyllus peels is primarily due to their high concentration of phenolic compounds, like flavonoids and phenolic acids, which act as natural antioxidants capable of neutralizing free radicals by donating hydrogen atoms, thus exhibiting a strong ability to scavenge the DPPH radical in laboratory assays.

Antimicrobial Activity

The ethanolic and distilled water-based extracts were found to be effective against A. faecalis, S. aureus, and E. coli where maximum inhibition was shown by distilled water-based extract against E. coli thus stating a clear disposition of its potential against microbial strains. The ethanolic extract had lesser inhibition capability compared to distilled water extract this might be due to many factors, such as inaccurate ethanol percentage in extract or certain uncontrolled reactions between the sample and ethanol. Similar, behavior was seen in Cassia alata water extracts which showed better inhibition than the ethanolic extracts (Somchit et al. 2003). To the best of our knowledge, not much research work has been carried out to study the antimicrobial activity of A. heterophyllus peel. The antimicrobial activity of the peel extracts was studied by Adan et al. (2020) against Xanthomonas axonopodispv. manihotis (Xam) which showed good inhibition activity at an average of 4–6 mm. Similarly, In the work of Roy and Lingampeta (2014), the zones of inhibition varied from 20 to 30 mm, with the highest inhibition diameters seen against Klebsiella pneumoniae (30 mm) and Enterococcus faecalis (30 mm). Thus, it can be concluded that A. heterophyllus peel extract has great potential for usage as antimicrobial agents and can be included as an ingredient in various types of food packaging.

A. heterophyllus peel has also displayed antimicrobial activity against A. faecalis, S. aureus, and E. coli which helps in the prevention of traveler's diarrhea and other pathogenic infections (López-Vélez et al. 2022). Table 5 gives detailed data on the inhibition activity found in the ethanolic and distilled water extracts of A. heterophyllus peel; along with Figure 1 showing the images for the zone of inhibition for water extracts of peel. Similar antimicrobial effects were found in pomegranate peels (Al-Zoreky 2009). Extracts were studied for antimicrobial effects and many significant results were seen in peel extracts (Dubreuil 2020). This leads to the idea that A. heterophyllus peel can be employed in food preservation and pharmaceutical purposes if more thoroughly researched.

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Table 5 Antibacterial activity of A. heterophyllus peel extract against selected bacterial strains.^a

Microorganism	Zone of inhibition (mm)
Water extract	Ethanolic extract
Alcaligenes faecalis	0.5 ± 0.1a	0.4 ± 0.3b
Staphylococcus aureus	1.0 ± 0.5a	0.5 ± 0.6b
Enterobacter aerogenes	ND	ND
Escherichia coli	3.1 ± 0.4a	ND
Bacillus subtilis	ND	ND

Structural Properties

Thermal Analysis

Thermal degradation of A. heterophyllus peel was done to conduct a thermal analysis. TGA curve of the peel shows degradation in three steps; decomposition, evaporation, and reduction (Saadatkhah et al. 2020). Mass loss graphs from TGA crucible analysis show how a sample's weight changes with time or temperature. The curves frequently have discrete steps or peaks, each representing a separate thermal event in the material. The principle of TGA is to measure the changes in mass of a substance when it is continuously heated to elevated temperatures. There is an occurrence of initial weight loss between 30°C and 100°C. Each weight loss step during the thermal examination of the jackfruit peel correlates to particular chemical processes and components. The process involves evaporating moisture and volatiles (Stage 1), decomposing cellulose, hemicellulose, and lignin (Stage 2), and reducing char and minerals (Stage 3). This deep understanding is useful in applications such as charcoal manufacturing, bioenergy, and material recycling.

Similar patterns of weight loss were observed in other types of peel and a primary decomposition/degradation in the range of 289°C–367°C in the case of A. heterophyllus peel powder is observed (Figure 2). Meanwhile, orange peel showed the primary decomposition in the range of 200°C–300°C (Rathinavel and Saravanakumar 2021). In Kinnow peel powder, the primary weight loss occurs at the range of 230°C–510°C (Verma et al. 2022). In pomegranate peel powder, the primary weight loss is between 194°C and 334°C (Hashem et al. 2023). In the case of mangosteen peel powder, the decomposition occurs from 264°C to 388°C (Ahmad Mahir and Ismail 2017). The potential reason for the difference in primary degradation temperature is the difference in moisture content and prevalence of various volatile compounds. Moreover, the difference in cellulose, hemicellulose, and lignin causes the curve to differ in various types of peels. A high thermal stability assessment is better suited for food packaging due to its greater resilience (Rahman et al. 2024).

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TEM

Using TEM, the particle microstructure and peel surface geometry of the A. heterophyllus were determined. The bright-field TEM image of A. heterophyllus peel powder shows a particle range of 300–500 nm upon 10,000× magnification in Figure 3. In a bright-field TEM, the contrast is formed by differences in the electron beam intensity transmitted through the sample. The darker regions correspond to areas where electrons are scattered or absorbed more due to higher mass or thickness, while lighter regions correspond to less scattering or thinner areas. This aligns with the characteristics of the image. The image shows that the surface is irregular in shape with varied shapes. It might be due to the various components present in the peel powder. Similar results have been shown by Allwyn Sundarraj and Vasudevan Ranganathan (2018) where A. heterophyllus peel showed irregular surface and microstructure.

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SEM

SEM analysis was done to study the detailed microstructure of the A. heterophyllus peel powder. The microstructure of the peel appeared rougher, irregular, and ruptured which may be due to the presence of other sugar, proteins, fibers, and macromolecules. Figure 4 shows the various images captured based on the principle of SEM in case of A. heterophyllus peel powder in various magnifications such as 1, 10, 40, 2.82 K.X. There is also a display of various globular shapes in the images which suggests the presence of various types of globular proteins which has been validated by the initial proximate analysis (Kumar et al. 2021).

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XRD Analysis

In the above Figure 5, The XRD pattern shows several distinct peaks, indicating the presence of a crystalline phase.

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~16° 2θ: This peak could be associated with the (101) plane of cellulose, a common component of plant cell walls.

~22° 2θ: This peak is likely related to the (200) plane of cellulose.

The other peaks may correspond to different crystalline phases within the jackfruit peel, such as hemicellulose, pectin, or lignin. The presence of sharp peaks in the pattern suggests that the jackfruit peel contains crystalline structures, likely due to the presence of cellulose and other biopolymers. The diffraction pattern displayed peaks clearly at 2θ = 5.21°, 16.94°, 22.9°, 25.04°, and 59.57°. To gain a more comprehensive understanding of the material's structure, additional characterization techniques, such as FTIR, have been employed and are discussed in the subsequent section.

FTIR

The determined spectra of A. heterophyllus peel powder showed distinct absorption patterns that corresponded to particular functional groups. There is a significant rise in the graph as peaks displayed an incline till 3600 cm⁻¹.

Figure 6 shows various peaks in the range of 3600–3950 cm⁻¹ which corresponds to the stretching frequencies of O-H bonds (non-H bonded) implying the presence of alcohols, phenols which is similar to the results achieved by Resende et al. (2020). The strong band in the high energy region is caused by a high concentration of OH groups from lignin and hemicellulose that are present in significant amounts in A. heterophyllus peel. An absence of other functional groups was seen in the FTIR absorption band. A. heterophyllus peel does not show any peak in the range of 2220 and 2260 cm⁻¹ in the FTIR graph which proves the absence of cyanide groups suggesting that there are no toxic compounds in the sample (Yaradoddi et al. 2022). Similar results were seen in Ecballium elaterium peels where no cyanide peaks were detected (Felhi et al. 2017).

[IMAGE OMITTED. SEE PDF]

Conclusion and Future Prospects

In the present investigation, research work related to the characterization of A. heterophyllus peel powder was done and experimental observations suggested the high potential of the usage of A. heterophyllus peel as food additive as it contains many beneficial components such as alkaloids, glycosides, phenols, flavonoids, etc. Specifically, discussions have been made about the A. heterophyllus peel's chemical and physical properties, possible uses with additional value, and the restrictions on reusing the peel. It also showed high protein and fiber content which can be used for medicinal/pharmaceutical purposes. Antimicrobial studies also suggested the highly competent inhibition capability of A. heterophyllus peel against E. coli which can be used as a good additive in various kinds of food films, etc. TGA showed good thermal stability. Research results show that A. heterophyllus peel has the potential to include a variety of beneficial components, accentuating the importance of A. heterophyllus peel in terms of sustainability. However, the properties of A. heterophyllus peel might vary between various regions because of different weather/climates thereby limiting the current research. Thus, more research in this field can be done by future researchers to grasp a better comprehension of the peel's physical, chemical and morphological properties. Future research should prioritize these aspects, particularly by incorporating aspects such as variability studies, shelf life and in-vivo studies. Addressing these gaps will provide a more robust foundation for potential real-world applications and further validate the findings of this study. The current study examined a variety of elements of jackfruit peel to give readers with insight into the morphological, antimicrobial, and phytochemical aspects, as well as the overall powder qualities, while keeping sustainability in perspective. Its potential scalability and economic feasibility will lie in the region since it is mostly available in tropical or subtropical zones. Also, using jackfruit peel supports the concept of a circular economy, which converts agricultural waste into valuable products while reducing environmental impact.

Author Contributions

Rangina Brahma: conceptualization, methodology, software, data curation, investigation, validation, formal analysis, writing – original draft. Subhajit Ray: validation, supervision, visualization, project administration, resources, writing – review and editing. Prakash Kumar Nayak: validation, supervision, funding acquisition, visualization, project administration, resources, writing – review and editing. Kandi Shridhar: validation, supervision, funding acquisition, visualization, resources, writing – review and editing.

Acknowledgments

Ms. Rangina Brahma thanks the “National Fellowship and Scholarship for Higher Education of ST Students,” India for the research, authorship, and/or publication of this article. Also, authors are grateful to the Department of Food Engineering and Technology, Central Institute of Technology Kokrajhar and Institute of Advanced Study in Science and Technology (IASST) for the assistance in conducting the analyses. The authors received no specific funding for this work.

Ethics Statement

The plants utilized in this investigation were collected following local or national guidelines. Plant safety guidelines were meticulously adhered during the harvesting process. Plant cultivation/harvesting did not require any permissions or licenses because the plant part as a waste fraction employed in the current study are regularly cultivated and collected throughout the country. Moreover, no animal or human study was involved in this work.

Conflicts of Interest

The authors declare no conflicts of interest.

Data Availability Statement

All data underlying the results is available as part of the article.

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