The processing waste of Jackfruit comprising of peel, rind, fibrous rags (perianth) and core was collected from local fruit markets of Greater Noida, Uttar Pradesh, India during harvesting season. Waste materials were collected from at least five local vendors and pooled together to obtain a representative composite sample. Equal quantities of peel, rind, fibrous rags, and core in a 1:1:1:1 (w/w) ratio were mixed and homogenized thoroughly before analysis. Equal proportions were used for the major fractions of jackfruit processing waste and to facilitate evaluation of the overall waste stream.

The collected biomass was thoroughly washed with tap water, then with distilled water to remove adhering dirt and extraneous matter. The cleaned material was air-dried at room temperature for 24 h and then oven-dried at 60°C for 48 h to reduce moisture content and facilitate grinding. The dried material was ground in a laboratory grinder and screened to a uniform particle size. The powdered samples were kept in sealed polyethylene containers at room temperature until further analysis.

It should be noted that the drying step at 60°C was performed for sample preparation and storage purposes. Moisture content was measured separately by standard AOAC methods by drying representative samples at 105°C to constant weight [22].

The proximate composition of jackfruit waste was determined as per standard AOAC methods [22]. All analyses were carried out in triplicate, and results are expressed as mean ± standard deviation.

The lignocellulosic composition of jackfruit waste was determined using the conventional detergent fibre system as described by Van Soest et al. [9]. Main fibre fractions were determined as neutral detergent fibre (NDF), acid detergent fibre (ADF) and acid detergent lignin (ADL). Samples were defatted during the crude fat extraction step prior to analysis to minimize interference from lipids and other extractives during fibre determination.

NDF determination was carried out under reflux in a neutral detergent solution at about 100°C for 60 min. The residue was filtered, washed with hot distilled water and then with acetone, dried to constant weight and weighed. ADF was subsequently determined from the NDF residue by acid detergent solution under reflux at approximately 100°C for 60 min. The product was filtered, washed, dried, and weighed. Heat-stable amylase was not used in NDF determination as jackfruit processing waste is not expected to contain sufficient starch to interfere with cell wall fibre estimation.

Determination of ADL: The ADF residue was treated with 72% sulphuric acid at room temperature for 3 h with occasional stirring. Then the residue was filtered, washed till acid-free, oven-dried, weighed, and finally ignited in a muffle furnace at 550°C. The acid detergent lignin content was determined by weight loss after ignition [9,10].

All fibre fractions were measured in triplicate and expressed on a dry weight basis.

NDF is the total cell wall fraction containing cellulose, hemicellulose and lignin, while ADF is composed mainly of cellulose and lignin. ADL is the fraction of acid-insoluble lignin [9,10].

The following equations calculate the structural carbohydrate fractions:

The primary NDF, ADF, and ADL values are reported alongside the derived cellulose, hemicellulose, and lignin contents to facilitate verification of the calculations and comparison with other lignocellulosic biomass studies [10,17].

It should be noted that the ADL method measures mainly acid-insoluble lignin and may underestimate the total lignin content because the acid-soluble lignin was not included in the determination [10].

Theoretical ethanol production potential of jackfruit waste from its cellulose and hemicellulose contents was estimated by using stoichiometric conversion factors commonly used for lignocellulosic biomass [23,24,25].

where 1.111 is the hydrolysis factor for conversion of cellulose to glucose, 1.136 is the hydrolysis factor for conversion of hemicellulose to fermentable pentose sugars, and 0.511 is the theoretical conversion factor of fermentable sugars to ethanol.

The corresponding ethanol volume was estimated using the density of ethanol (0.789 g mL^-1):

The calculated values represent the maximum theoretical yields under ideal hydrolysis and fermentation conditions and do not consider process losses. The theoretical yield was predicted only to indicate the potential of jackfruit waste as a lignocellulosic feedstock and does not imply experimentally validated ethanol production.

All analyses were done in triplicate (n = 3), and results are presented as mean ± standard deviation (SD). The reported standard deviations are for analytical replicates, not for biological variation between independent collection events.

This study did not involve human participants, animals, or clinical samples. Therefore, ethical approval was not required for this research.

Table 1 shows the proximate composition of jackfruit processing waste. Moisture content was 8.18 ± 0.28 g/100 g and ash content was 4.18 ± 0.24 g/100 g. The crude protein and crude fat contents were 8.50 ± 0.08 g/100 g and 3.10 ± 0.18 g/100 g, respectively. Crude fibre content was 13.50 ± 0.18 g/100 g. The available carbohydrate by difference was 62.54 g/100 g dry weight.

The measured components showed that the largest proportion of the biomass consisted of available carbohydrate. Table 1 summarizes the values obtained for moisture, ash, protein, fat and fibre.

The lignocellulosic composition of jackfruit processing waste is shown in Table 2. The cellulose content was 23.35 ± 0.68 g/100 g and the hemicellulose content was 25.50 ± 0.72 g/100 g. Lignin content was 18.32 ± 0.62 g/100 g.

The NDF, ADF and ADL obtained were 67.17 ± 1.17, 41.67 ± 0.92 and 18.32 ± 0.62 g/100 g, respectively. The calculated cellulose and hemicellulose values were in agreement with the measured detergent fibre fractions.

Based on the cellulose and hemicellulose contents determined in the present study, the theoretical ethanol production potential of jackfruit processing waste was estimated. The theoretical ethanol yield calculated was 28.06 g/100 g of dry biomass.

This yield, using the density of ethanol (0.789 g mL^-1), corresponds to approximately 35.56 mL of ethanol per 100 g dry biomass. The potential for ethanol production was estimated at about 356 L per ton of jackfruit processing waste on a dry biomass basis.

The estimated potential for ethanol production was ~356 L/tonne of jackfruit processing waste on dry biomass basis.

The lignocellulosic composition of jackfruit processing waste was compared with the selected agricultural and fruit biomasses reported in the literature (Table 3). The cellulose content of jackfruit processing waste (23.35%) was lower than the normal values reported for rice straw (32-47%), wheat straw (28-40%) and sugarcane bagasse (32-45%) which are the most studied feedstocks for lignocellulosic bioconversion [6,28]. However, the cellulose content was much higher than that reported for banana peel biomass (7.6-9.6%) [29]. The hemicellulose content (25.50%) was within the range reported for wheat straw and sugarcane bagasse, suggesting a significant fraction of potentially fermentable structural carbohydrates.

The lignin content of jackfruit processing waste (18.32%) was in the same range as the reported lignin content of wheat straw (15-22%) and within the reported range of lignin content of sugarcane bagasse (17-32%). The detected lignin content shows that pretreatment is required for efficient biochemical conversion. Lignin acts as a physical barrier to enzymatic access to cellulose and hemicellulose. However, the biomass is less recalcitrant than several conventional lignocellulosic feedstocks [30,31].

The major structural carbohydrate pool that can be potentially converted into biofuels, biochemicals, and other value-added products is the combined cellulose and hemicellulose fraction (48.85%). This value is lower than those reported for cereal straws and sugarcane bagasse, but is much higher than that reported for banana peel biomass. The findings indicate that jackfruit processing waste could be a moderate-quality lignocellulosic carbohydrate feedstock for bioconversion applications in the future.

Direct comparisons between studies should be made with caution as the composition of biomass can be influenced by cultivar, stage of maturity, geographical origin, seasonal variation, sample preparation procedures, analytical methodology and basis of reporting. Table 3 data are thus intended to provide a rough compositional context, not a strict statistical comparison of different biomass resources [18].

Since the comparative values presented in Table 3 were obtained from independent literature sources with different biomass origins, cultivars, geographical locations, sample preparation procedures, and analytical methodologies, direct statistical comparisons were not performed. Therefore, the literature values are provided only to establish compositional context and facilitate qualitative comparison with commonly studied lignocellulosic feedstocks.

The physicochemical properties of biomass are important for determining its suitability for storage, handling, and subsequent processing. The moisture content of jackfruit processing waste (8.18 g/100 g) was considerably lower than the 15-20% moisture level generally associated with increased microbial spoilage and deterioration during biomass storage [14,24]. Such low moisture content may improve storage stability and reduce the energy required for additional drying prior to thermochemical or biochemical conversion processes. Moisture content is considered an important parameter in biomass utilization because excessive moisture increases transportation costs, reduces thermal efficiency, and adversely affects storage stability [14,24].

The inorganic mineral content of biomass, ash, can impact processing performance in biochemical and thermochemical conversion. The ash content (4.18 g/100 g) was within the range generally reported for fruit-processing residues and remained below the approximately 10% level often associated with operational challenges such as slagging, fouling, and ash accumulation during thermal conversion processes [24,25]. Therefore, the ash content observed in the present study is unlikely to impose major limitations on biomass utilization, while still contributing mineral nutrients that may support biological conversion processes such as composting and anaerobic digestion [15,32]. The crude protein and crude fat contents indicate the presence of organic constituents with nutritional value in jack fruit processing waste. Although these components are not targeted for lignocellulosic bioconversion, they may contribute positively to microbial growth in biological treatment processes such as composting and anaerobic digestion [15,32]. The available carbohydrate fraction was the highest fraction of the biomass, indicating the abundance of carbohydrate-based materials in jackfruit residues. This agrees with the high carbohydrate content in many fruit processing by-products reported in the literature [2,33].

The crude fibre value determined in the present investigation was lower than the sum of structural carbohydrate fractions determined by detergent fibre analysis. This difference is expected because the traditional method for crude fibre removes fractions of hemicellulose and cellulose during acid and alkali digestion, thus underestimating the real structural carbohydrate content of lignocellulosic biomass [9,18]. The detergent fiber analysis thus gives a more realistic picture of the biomass composition for bioresource application.

The cellulose, hemicellulose, and lignin contents obtained in this study indicate that jackfruit processing waste is rich in structural carbohydrates. Cellulose and hemicellulose, which can make up to nearly half of the dry biomass, indicate a rich reserve of fermentable carbohydrates that could be potentially converted into biofuels and biochemicals through suitable pretreatment and hydrolysis processes [8,13,23].

Cellulose is mostly known as the primary polysaccharide from which fermentable sugars are obtained, while hemicellulose provides additional carbohydrate fractions that can improve the overall efficiency of biomass conversion [11,30]. Thus, the cellulose and hemicellulose contents reported in the present study indicate that jackfruit processing waste could be a potential feedstock for application in lignocellulosic biorefineries. Similar observations have been reported for several fruit processing residues and agricultural by-products studied for bioethanol production and other value-added applications [15,16,32]. It should be noted that the lignin content reported in the present study was determined using the acid detergent lignin (ADL) method, which primarily measures acid-insoluble lignin. Therefore, the total lignin content of jackfruit processing waste may be slightly higher than the reported value due to the presence of acid-soluble lignin fractions that were not quantified in the present investigation [9].

Lignin content is an important parameter affecting biomass recalcitrance as it forms a protective matrix around the structural carbohydrates and limits enzyme accessibility during hydrolysis [30,34]. The lignin content of this study suggests the need for pretreatment for effective biochemical conversion. Published studies have shown that increasing lignin content generally reduces enzymatic saccharification efficiency because lignin restricts enzyme accessibility to structural carbohydrates and promotes non-productive enzyme adsorption [30,32]. Various pretreatment methods such as dilute acid, alkaline, steam explosion, and biological treatments have been reported to enhance the accessibility of cellulose and hemicellulose in lignocellulosic feedstocks with comparable lignin contents [7,12,34,35].

Apart from the production of biofuel, the composition of jackfruit processing waste also indicates the possibility of recovery of cellulose-rich materials. Several studies have demonstrated the extraction of cellulose and nanocellulose from jackfruit peel and other waste products from fruit processing for biodegradable materials and sustainable packaging systems [4,13,17,20]. The present work further proposes to investigate such value-added applications with high cellulose content.

The theoretical ethanol yield based on the measured contents of cellulose and hemicellulose provides an initial indication of the bioconversion potential of the waste from jackfruit processing. The calculated yield represents the maximum quantity of ethanol obtainable from a specific feedstock under ideal hydrolysis and fermentation conditions and thus serves as a useful benchmark for evaluating the feedstock’s suitability [23,25,28].

It should be noted that actual ethanol yields are usually lower than theoretical values due to incomplete hydrolysis, sugar degradation, inefficient microorganisms, and process inefficiencies during fermentation [28,30,31]. However, the estimated yield obtained in the present study indicates that the jackfruit processing waste contains sufficient structural carbohydrates to be further explored as a potential lignocellulosic bioethanol feedstock. Similarly, studies on fruit-derived biomass and agricultural residues have shown the potential of carbohydrate-rich feedstocks as a promising substrate for second-generation bioethanol production following appropriate pretreatment strategies [25,28,32].

Apart from bioethanol production, the carbohydrate-rich composition of jackfruit waste can also be used in other biological conversion processes such as anaerobic digestion, composting, and the production of platform biochemicals. Thus, the potential utilization of this biomass should not be limited to ethanol production but can be extended to a broader range of biorefinery applications [1,15,29].

The present study was limited to physicochemical and lignocellulosic characterization of jackfruit processing waste from one geographic region. Values are for the composite sample analysed and may vary with cultivar, season, and source of collection. Moreover, the bioethanol production potential in this study was estimated using theoretical calculations from compositional data and was not experimentally validated by hydrolysis or fermentation studies. The next step should be the experimental evaluation of the biomass conversion pathways and the optimization of the processes.