Jackfruit (Artocarpus heterophyllus Lam.), a member of the family Moraceae and the state fruit of Kerala, India - its primary centre of origin in the Western Ghats - is also the national fruit of Bangladesh (Nair et al., 2021). As the largest tree-borne fruit, it is widely cultivated across South and Southeast Asia, sub-Saharan Africa and tropical America, with India leading global production at over 1.4 million tonnes annually (FAOSTAT, 2023). Valued for its carbohydrates, vitamins A and C, potassium, dietary fibre and growing recognition as a sustainable plant-based meat alternative (Swami et al., 2012; Ranasinghe et al., 2019), jackfruit also exhibits considerable inter-genotypic variability in morphometric and biochemical traits that significantly influences fruit quality and processing potential (Kavya et al., 2019; Gomez et al., 2024).
       
Despite its nutritional and economic significance, jackfruit processing is characterised by a high non-edible fraction burden. Its complex architecture - comprising an outer spiny pericarp (rind), central fibrous core and rachis, arils embedded in fibrous perianth tissue and large seeds enclosed by a thin membranous seed coat - results in non-edible fractions accounting for approximately 60-75% of total fruit mass (Hossain et al., 2022). These generate substantial agro-industrial by-product streams that remain largely underutilised. The rind, as the most voluminous non-edible component, is a documented source of pectin (8-18% dry weight basis), flavonoids and dietary fibre (Leong, 2016) and has been reported to yield nutrient-rich flour with considerable value-addition potential (Tharani and Divakar, 2026). Jackfruit seeds similarly contain commercially extractable starch (~22-26% dry weight) and protein (~6-10%) (Mukprasirt and Sajjaanantakul, 2004).
       
Kerala hosts exceptional jackfruit cultivar diversity, with locally evolved selections exhibiting wide variation in morphological profile, flesh texture (Varikka and Koozha types), fruit size, flavour and post-harvest behaviour (KAU, 2016). Systematic morphometric and gravimetric characterisation of these cultivars is prerequisite to establishing cultivar-specific baselines for post-harvest decision-making, processing technology design and valorisation strategy development (Baliga et al., 2011; Jagadeesh et al., 2007). While recent studies from Karnataka (Natta et al., 2025; Valeeta et al., 2023) and other regions have documented significant inter-cultivar variation in fruit and flake quality traits, fraction-wise mass balance data for Kerala’s germplasm remain sparse. Accordingly, the present study aimed to: (i) characterise five Kerala jackfruit cultivars for whole-fruit morphometric dimensions; (ii) quantify fraction-wise mass distribution (rind, core-rachis, edible aril, seed and perigones/rag); (iii) compute edible and non-edible yield indices (ERI and NFI) to identify cultivar-level differences in processing efficiency; (iv) assess bulb quality parameters (TSS, pH and CIE colorimetric values); and (v) establish baseline data on non-edible by-product volumes to guide future valorisation research, particularly for pectin extraction.

Plant material and experimental site
 
The study was conducted at the College of Agriculture, Vellayani, Kerala Agricultural University (KAU), Kerala, India, from November 2024 to June 2025. Five jackfruit (Artocarpus heterophyllus Lam.) cultivars were selected to represent the principal cultivar groups present in Kerala, comprising one KAU-released variety (Muttom Varikka) and four locally evolved selections from different agroclimatic zones. Details of cultivar identity, classification and source of origin are presented in Table 1.


       
For each cultivar, three mature, sound fruits were harvested at commercial maturity from designated orchard blocks and farmer fields. Harvest maturity was determined using a combination of non-destructive indices: Development of a yellowish-green skin colour, softening of spine tips, emanation of a characteristic aromatic odour, a hollow sound on tapping and ease of spine separation upon gentle pressure - criteria consistent with those recommended by KAU for jackfruit harvest (KAU, 2016). Fruits exhibiting physical injury, disease symptoms or abnormal morphology were excluded. All harvested fruits were transported to the laboratory within two hours of harvest and processed on the same day to minimise post-harvest physiological changes.
 
Morphometric measurements
 
The weight of the whole fruit was recorded using a digital platform balance (readability ±1 g). External morphometric dimensions were measured on intact, uncut fruits before dissection. Fruit length (cm) was measured from the base of the peduncle attachment to the fruit apex; fruit breadth (cm) was taken as the maximum equatorial diameter; and fruit girth (cm) was measured as the circumference at the equatorial plane using a flexible measuring tape. The shape index (SI) was calculated as the ratio of fruit length to fruit breadth (SI = L/B); values greater than 1.0 indicate oblong (elongated) fruits, while values approaching 1.0 indicate round or globose forms (Jagadeesh et al., 2007). A complete list of all morphometric, gravimetric and derived parameters, along with units and measurement methods, is presented in Table 2.


 
Fruit fractionation and fraction-wise weight determination
 
Fruits were dissected on a clean stainless-steel dissection table under standard laboratory conditions using sharp, pre-sterilised stainless-steel knives. Each fruit was carefully and systematically dissected to separate seven discrete fractions, each collected in individually pre-weighed trays and weighed using a digital balance (readability±0.1 g): (i) outer rind (hard spiny exocarp); (ii) inner rind (spongy white mesocarp); (iii) core-rachis (central fibrous axis and all rachis branches); (iv) rag/perigones (fibrous perianth tissue surrounding the bulbs); (v) edible bulb (fleshy perianth, seedless); (vi) seed; and (vii) seed-coat/perianth membrane (thin membranous layer enclosing each seed). The total rind weight was obtained by summing the outer and inner rind fractions.
       
Fraction-wise yield was expressed as a percentage of total fresh fruit weight (%FW). The edible fraction comprised the bulb and seed, while the non-edible fraction included the outer rind, inner rind, core-rachis, rag and seed-coat membrane. The following derived indices were computed:

 
ERI and NFI were defined such that their sum approximated 100% of total fruit weight, with minor deviations attributed to dissection handling losses.
 
Assessment of quality attributes
 
Total soluble solids (TSS) were determined using a hand-held refractometer calibrated with distilled water before measurement. A single drop of fresh juice, extracted from three representative arils per fruit per replication, was placed on the prism and TSS was recorded as oBrix at ambient laboratory temperature. The pH was measured using a calibrated digital pH meter (Model MK-VI, Siltronic’s India Pvt. Ltd., India) standardised with reference buffer solutions of pH 4.0 and 7.0 before each measurement session. The colour of jackfruit bulbs was measured instrumentally using a colorimeter (Hunter Lab, Hunter Associates Laboratory Inc., USA) and expressed in the CIE L*, a*, b* colour space system. The instrument was calibrated with a certified white reference tile before analysis and all measurements were taken under defined standard illumination conditions. Munsell colour chart notation was recorded as a supplementary qualitative descriptor. Bulb firmness and texture were assessed by a trained sensory panel of fifteen evaluators using a structured descriptive scale of 1 to 5 (1 = very soft; 5 = very firm/crisp). Each evaluator assessed samples independently and the final classification was based on the consensus score (Table 3).


 
Statistical analysis
 
Three fruits per cultivar were used as replications, giving a total of 15 experimental units (5 cultivars × 3 replications). All data are expressed as mean ± standard deviation (SD) (n = 3) per cultivar. One-way analysis of variance (ANOVA) was performed independently for each measured parameter to assess the significance of inter-cultivar variation. Mean separation was carried out using Duncan’s Multiple Range Test (DMRT) at the 5% level of significance (p< 0.05) when the F-test was significant. Means within a column followed by different lowercase letters are significantly different at p<0.05. The standard error of the mean (SEm±) and the critical difference (CD) at p≤0.05 are reported for all parameters. Pearson’s product-moment correlation analysis was performed to determine the linear relationships between whole-fruit weight and each of the morphometric dimensions (length, breadth) and major fraction weights (bulb, seed, rind, core-rachis, rag). Correlations with |r|≤0.70 were considered strong, 0.40-0.69 moderate and < 0.40 weak. All statistical analyses were performed using IBM SPSS Statistics (Version 26.0) and Microsoft Excel 2019.

Whole-fruit weight and external morphometric dimensions
 
Whole-fruit weight and shape index showed significant inter-cultivar variation (p<0.05), as presented in Table 4. Fruit weight ranged from 5.83±0.21 kg in Koozha (C2) to 11.33±2.30 kg in Chembarathi Varikka (C3), reflecting the wide genetic diversity in fruit size among the evaluated cultivars. Chembarathi Varikka (C3) was the heaviest cultivar (group a), while Koozha (C2) was the lightest (group c). Pullichira Jack (C1), Muttom Varikka (C4) and Honey Dew (C5) formed an intermediate group (group b), with weights of 8.49, 7.57 and 6.83 kg, respectively. These data are consistent with the broad size range reported for Indian jackfruit accessions, where fruit weight has been documented to vary from 2.5 to over 25 kg depending on genotype (Jagadeesh et al., 2007; Natta et al., 2025).


       
In contrast, fruit length (range: 40.33-48.33 cm), breadth (range: 22.50-27.83 cm) and girth (range: 69.10-85.17 cm) did not differ significantly among cultivars (all NS, Table 4), indicating that while cultivars diverge substantially in total mass, their external linear and circumferential dimensions overlap considerably within the variability of a small replication set (n = 3). The high standard deviations observed for these parameters - particularly for Koozha (girth SD = 14.16 cm) - reflect the inherent morphological variability within individual cultivars and underscore the limitation of n = 3 in resolving linear dimension differences among cultivars that may be naturally variable in shape.
       
The shape index (SI) was significant (F = 52.56, p<0.01). Muttom Varikka (2.01±0.05) and Honey Dew (1.96 ±0.02) recorded the highest SI values (group a), indicating distinctly more elongated fruit morphology. Pullichira Jack (1.73±0.05) and Koozha (1.69±0.05) formed group b, while Chembarathi Varikka (1.64±0.01) was the most compact cultivar (group c). These values fall within the range of 1.5-2.3 reported for jackfruit accessions (Jagadeesh et al., 2007; Natta et al., 2025), confirming that SI is a cultivar-discriminating morphometric trait of practical utility for grading, packing and transport efficiency assessments.
 
Correlation analysis among morphometric and fraction-weight traits
 
Pearson’s correlation analysis among fruit weight, morphometric dimensions and major fraction weights is presented in Table 5. Fruit weight exhibited strong positive correlations with fruit length (r = 0.86, p<0.01) and fruit breadth (r = 0.82, p<0.01), indicating that larger fruits are generally more elongated and broader. These relationships highlight the potential of non-destructive external dimensions as reliable predictors of fruit mass for grading and sorting, consistent with reports on Karnataka accessions (Natta et al., 2025) and Ugandan germplasm (Gwokyalya et al., 2024). Moderate positive correlations were recorded between fruit weight and bulb weight (r = 0.78, p<0.05) and seed weight (r = 0.74, p<0.05), suggesting that increases in fruit size are associated with higher edible biomass, though not in direct proportion, possibly due to the contribution of structural components. Rind, core-rachis and rag fractions showed comparatively weaker correlations with fruit weight (r = 0.65, 0.60 and 0.58, respectively), indicating a relatively consistent distribution of non-edible components across fruit sizes. Among inter-fraction relationships, bulb weight was positively correlated with seed weight (r = 0.76, p<0.05), suggesting coordinated development of edible tissues. Rind weight showed a significant association with core–rachis weight (r = 0.70, p<0.05), reflecting structural interdependence within the fruit.


 
Fraction-wise mass distribution - non-edible fractions
 
The fraction-wise gravimetric composition of the five cultivars is presented in Table 6. The total rind fraction was the dominant non-edible component across all cultivars, ranging from 21.88±1.23% (C1, Pullichira Jack) to 44.00±1.63% (C3, Chembarathi Varikka). The exceptionally high rind fraction of C3 - which substantially exceeds the 20-35% range commonly reported for jackfruit pericarp (Hossain et al., 2022; Gayatri et al., 2020) - is likely an intrinsic characteristic of this homestead cultivar, possibly associated with a thicker and more protective pericarp structure that may have been selectively favoured for improved transport tolerance in traditionally unprocessed, whole-fruit marketing contexts. From a valorisation standpoint, this exceptionally high rind fraction positions Chembarathi Varikka as the most advantageous raw material source for rind-derived value-added products, including pectin and dietary fibre.


       
A notable finding from the present study is the substantially elevated rag (perigones) fraction in Pullichira Jack (11.73±0.98%, group b) and particularly in Koozha (16.05±0.49%, group a), compared to the remaining three cultivars, which recorded approximately 5% rag (group c). This pattern suggests that koozha-type jackfruit - characterised by softer, less defined arils - may possess a more extensively developed fibrous perianth architecture. The practical consequence of this high rag fraction in Koozha is a substantially greater fibrous by-product stream per unit of edible output. This aspect warrants attention in the design of cultivar-specific processing lines.
       
Core-rachis fraction ranged from 6.00±0.00% (C4, Muttom Varikka) to 8.80±0.31% (C2, Koozha), consistent with previously reported ranges for this fruit component. The seed-coat/perianth membrane fraction increased progressively from C1 (4.40%) and C2 (5.26%) through C3 (8.98%) and C4 (10.57%) to C5 (14.67%), with Honey Dew recording the highest value (group a). This gradient likely reflects differences in the number and size of seeds across cultivars, as larger and more numerous seeds would correspondingly bear a greater total membranous envelope. The NFI ranged from 46.46±2.36% (C1, Pullichira Jack) to 65.47±0.05% (C3, Chembarathi Varikka), confirming that non-edible fractions constitute a substantial proportion of total fresh fruit weight across all evaluated cultivars, underscoring the critical need for integrated valorisation pipelines targeting rind, seed-coat membrane, core-rachis and rag recovery (Nair et al., 2021; Yang et al., 2023).
 
Edible fraction, yield indices and quality attributes
 
The edible fraction composition and associated quality parameters are presented in Table 7. Bulb percentage (fleshy perianth, seedless) ranged from 28.70±1.97% (C2, Koozha, group b) to 40.33±0.58% (C4, Muttom Varikka, group a). The Edible Recovery Index (ERI), which encompasses both bulb and seed fractions, ranged from 34.53±0.05% (C3, Chembarathi Varikka) to 53.54±2.36% (C1, Pullichira Jack). Pullichira Jack (C1) and Muttom Varikka (C4) were statistically equivalent in ERI (both groups: 53.54% and 51.13%, respectively), recording the highest total edible biomass utilisation among the five cultivars. This equivalence is noteworthy because C1 achieves its high ERI primarily through an exceptionally large seed fraction (16.88±4.20%, group a - the highest among all cultivars), whereas C4 derives its high ERI from superior bulb development (40.33% bulb fraction). These contrasting mechanisms of edible fraction accumulation - seed-driven in C1 versus bulb-driven in C4 - have distinct practical implications: C4 (Muttom Varikka) is superior for fresh bulb yield and processing efficiency, while C1 (Pullichira Jack) presents a seed-rich profile warranting separate valorisation as a starch and protein source (Mukprasirt and Sajjaanantakul, 2004).


       
The seed fraction of Koozha (C2) was 12.80±0.38%, substantially higher than commonly reported values for koozha-type jackfruit, which are generally characterised by smaller, fewer seeds. Chembarathi Varikka (C3) recorded the lowest seed fraction (4.53±0.05%, group c), suggesting that despite its firm varikka-type flesh, this cultivar invests relatively little biomass in seed development - a characteristic that may be of value for cultivars targeted at fresh processing where large seeds are considered a disadvantage. The large SD observed for C1 seed fraction (±4.20%) reflects substantial variation in seed allocation across its three replications and is partly attributable to the high natural variability in seed number and size in this locally selected, non-standardised genotype.
       
TSS values ranged from 23.20 ^oBrix (C3) to 29.13 ^oBrix (C5) and pH values ranged from 5.03 to 5.30 across cultivars. Although Honey Dew and Muttom Varikka recorded numerically higher TSS values, consistent with their reputation as premium dessert-type cultivars, the inter-cultivar differences in TSS were not statistically significant (F = 3.198, NS). This non-significance is attributable to the high within-cultivar variability in TSS (SD ±2.10-2.55 oBrix) relative to the between-cultivar differences, in the context of the small replication number (n = 3). Similarly, pH did not differ significantly among cultivars (F = 0.886, NS). These findings are consistent with the reported range of 20-30 ^oBrix and pH 4.9–5.6 for ripe jackfruit pulp (Ranasinghe et al., 2019; Hossain et al., 2022; Ramachandra et al., 2022) and indicate that while trends in sweetness are apparent, confirmation of cultivar-level TSS differences would require a larger replication set to achieve adequate statistical power.
 
CIE L*, a*, b* colorimetric characterisation of jackfruit bulbs
 
CIE colorimetric analysis revealed striking and statistically significant inter-cultivar differences in all three colour parameters (L*, a* and b*), as presented in Table 8. Pullichira Jack (C1) exhibited a uniquely distinctive creamy white/off-white bulb colour characterised by a very high L* value (82.27±1.61, group a), indicating the highest lightness among all cultivars. Its near-zero a* (1.17±0.25, group d) and exceptionally low b* (10.63±1.05, group e) are consistent with a predominantly achromatic, low-carotenoid colour profile. This colouration, which is uncommon among varikka-type jackfruit cultivars - which are typically associated with yellow-to-golden bulb pigmentation - suggests that C1 possesses either a markedly reduced capacity for carotenoid biosynthesis or enhanced carotenoid catabolism in ripening arils. The fact that C1 is classified as a varikka-type (firm-flesh) cultivar yet displays markedly lower b* values than all other varikka-type entries (C3: 52.50, C4: 55.43, C5: 58.23) conclusively demonstrates that flesh texture type and carotenoid-driven yellow pigmentation are independently inherited phenotypic traits and do not co-segregate within the varikka classification.


       
Honey Dew (C5) exhibited the brightest golden-yellow colour, recording the highest b* value (58.23±1.26, group a) and the highest L* among the yellow-pigmented cultivars (71.47±1.37, group b), indicating a luminous, saturated yellow hue. The 5.5-fold difference in b* values between C1 (10.63) and C5 (58.23) represents the most pronounced inter-cultivar colorimetric contrast observed and identifies b* as the primary discriminating colorimetric parameter among these cultivars, consistent with Natta et al., (2025). A progressive and statistically significant increase in b* was observed from C2 (47.27) through C3 (52.50) and C4 (55.43) to C5 (58.23), with each cultivar occupying a distinct DMRT group (d, c, b and a, respectively), reflecting a continuous gradient of carotenoid accumulation independent of flesh-type classification.
       
For the a* (red-green axis), Chembarathi Varikka (C3) recorded the highest value (11.37± 0.45, group a), indicating the greatest redness component, while Muttom Varikka (C4) and Honey Dew (C5) formed a common group b (10.20 and 9.57, respectively). Koozha (C2) was intermediate (8.50, group c) and Pullichira Jack (C1) was distinctly the lowest (1.17, group d), consistent with its near-achromatic colour profile. The Munsell notations recorded (Table 8) provide supplementary qualitative validation of the instrumental CIE values and are presented as descriptive reference data.
 
Implications for post-harvest valorisation
 
The present dataset has direct and quantifiable implications for jackfruit processing system design and by-product valorisation. With non-edible fractions constituting 46.46-65.47% of fresh fruit weight, even modest processing volumes generate substantial biomass streams. A hypothetical unit processing one tonne of jackfruit per day would yield approximately 219-440 kg of rind, 60-88 kg of core-rachis, 50-161 kg of rag and 44-147 kg of seed-coat membrane - totalling 465-655 kg of non-edible biomass per tonne processed. The rind stream alone justifies a dedicated pectin or dietary fibre extraction operation at this scale, given its documented pectin content (Leong, 2016), while the residual biomass including rind, core and undeveloped perigones also holds demonstrated potential for fermented value-added product development (Bensi and Divakar, 2026) and the considerable inter-cultivar variation in rind-related traits observed here aligns with previous reports on indigenous jackfruit variability (Hazarika et al., 2025).
       
The seed fraction, classified as part of the edible biomass (ERI) in the present study, ranged from 4.53% (C3) to 16.88% (C1) of fruit weight. Seeds are a well-documented source of starch (~22-26% dry weight) and protein (~6-10%), both commercially valorisable (Mukprasirt and Sajjaanantakul, 2004; Nair et al., 2021). Cultivars with high seed fractions - notably Pullichira Jack (C1) - may be strategically processed to direct seeds towards starch or flour extraction, simultaneously maximising edible recovery and industrial value. The wide cultivar-dependent variation in fraction yields underscores that mass-balance inputs for biorefinery cascade modelling (Yang et al., 2023) must be parameterised at the cultivar level rather than derived from generic species-wide estimates.

Five Kerala jackfruit cultivars, Pullichira Jack, Koozha, Chembarathi Varikka, Muttom Varikka and Honey Dew, representing one koozha-type (Koozha) and four varikka-type genotypes, were comprehensively evaluated for whole-fruit morphometric dimensions, fraction-wise mass distribution and bulb quality attributes. Significant inter-cultivar variation was observed for fruit weight, shape index, all non-edible fraction components (rind, core-rachis, rag, seed-coat membrane), edible fraction parameters (bulb weight, bulb percentage, ERI, seed percentage) and all CIE colorimetric parameters (p<0.05 to p<0.01). Fruit length, breadth, girth, TSS and pH did not differ significantly among cultivars under the conditions of the present study.

Fruit weight ranged from 5.83 kg (Koozha) to 11.33 kg (Chembarathi Varikka). Morphometric dimensions showed strong positive correlations with fruit weight (length: r = 0.86; breadth: r = 0.82), confirming their utility as non-destructive size estimators. Pullichira Jack and Muttom Varikka recorded the highest and statistically equivalent Edible Recovery Index (53.54% and 51.13%, respectively), though through contrasting mechanisms - seed-driven in Pullichira Jack and bulb-driven in Muttom Varikka. Chembarathi Varikka exhibited the lowest ERI (34.53%) but the highest total rind fraction (44.00%), positioning it as the most promising source of rind-derived by-products for pectin and fibre extraction. Non-edible fractions collectively constituted 46.46-65.47% of total fruit weight, with the rind as the dominant non-edible stream across all cultivars. Pullichira Jack exhibited a unique creamy white bulb colour (b* = 10.63) despite its varikka-type classification, demonstrating that flesh texture type and carotenoid pigmentation are independently inherited traits. These results establish a comprehensive, quantitative, cultivar-specific baseline for post-harvest processing decisions and valorisation pipeline design in the Kerala jackfruit sector and contribute new morphometric and gravimetric data on Kerala germplasm to the scientific literature.

The authors sincerely thank Dr Suma Divakar, Research guide, for constant encouragement and support. They also acknowledge Kerala Agricultural University (KAU), College of Agriculture Vellayani, FSRS Kollam and KVK Kollam for providing experimental facilities and access to orchard blocks. The technical assistance of the laboratory and farm staff at FSRS Kollam, KVK Kollam, District Agricultural Farm Anchal and the collaborating farmers is gratefully acknowledged. The contributions of the sensory panel evaluators for bulb quality assessment are also acknowledged.
 
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Disclaimers
 
The views and conclusions expressed in this article are solely those of the authors and do not necessarily represent the views of their affiliated institutions. The authors are responsible for the accuracy and completeness of the information provided, but do not accept any liability for any direct or indirect losses resulting from the use of this content.

The authors declare that there are no conflicts of interest regarding the publication of this article. No funding or sponsorship influenced the design of the study, data collection, analysis, decision to publish, or preparation of the manuscript.