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Review

Kiwifruit Peelability (Actinidia spp.): A Review

by
Beibei Qi
1,2,
Peng Li
2,
Jiewei Li
2,
Manrong Zha
3,* and
Faming Wang
2,*
1
College of Agriculture, Guangxi University, Nanning 530004, China
2
Guangxi Key Laboratory of Functional Phytochemicals Research and Utilization, Guangxi Institute of Botany, Chinese Academy of Sciences, Guilin 541006, China
3
Key Laboratory of Plant Resources Conservation and Utilization, College of Life Sciences, Jishou University, Jishou 416000, China
*
Authors to whom correspondence should be addressed.
Horticulturae 2025, 11(8), 927; https://doi.org/10.3390/horticulturae11080927
Submission received: 13 June 2025 / Revised: 30 July 2025 / Accepted: 3 August 2025 / Published: 6 August 2025
(This article belongs to the Section Fruit Production Systems)
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Abstract

Kiwifruit (Actinidia spp.) is a globally important economic fruit with high nutritional value. Fruit peelability, defined as the mechanical ease of separating the peel from the fruit flesh, is a critical quality trait influencing consumer experience and market competitiveness and has emerged as a critical breeding target in fruit crop improvement programs. The present review systematically synthesized existing studies on kiwifruit peelability, and focused on its evolutionary trajectory, genotypic divergence, quantitative evaluation, possible underlying mechanisms, and artificial manipulation strategies. Kiwifruit peelability research has advanced from early exploratory studies in New Zealand (2010s) to systematic investigations in China (2020s), with milestones including the development of evaluation metrics and the identification of genetic resources. Genotypic variation exists among kiwifruit genera. Several Actinidia eriantha accessions and the novel Actinidia longicarpa cultivar ‘Guifei’ exhibit superior peelability, whereas most commercial Actinidia chinensis and Actinidia deliciosa cultivars exhibit poor peelability. Quantitative evaluation highlights the need for standardized metrics, with “skin-flesh adhesion force” and “peel toughness” proposed as robust, instrument-quantifiable indicators to minimize operational variability. Mechanistically, peelability is speculated to be governed by cell wall polysaccharide metabolism and phytohormone signaling networks. Pectin degradation and differential distribution during fruit development form critical “peeling zones”, whereas ethylene, abscisic acid, and indoleacetic acid may regulate cell wall remodeling and softening, collectively influencing skin-flesh adhesion. Owing to the scarcity of easy-to-peel kiwifruit cultivars, artificial manipulation methods, including manual peeling benchmarking, lye treatment, and thermal peeling, can be employed to further optimize kiwifruit peelability. Currently, shortcomings include incomplete genotype-phenotype characterization, limited availability of easy-peeling germplasms, and a fragmented understanding of the underlying mechanisms. Future research should focus on methodological innovation, germplasm development, and the elucidation of relevant mechanisms.

1. Introduction

Kiwifruit (Actinidia spp.), a deciduous woody vine belonging to the Actinidiaceae family, has gained global recognition for its exceptional nutritional composition, particularly its high vitamin C content, antioxidant capacity, and cardiometabolic benefits, such as hypolipidemic and immunomodulatory properties [1]. With rising living standards and evolving consumer preferences, quality expectations for fruits have expanded beyond basic nutritional and sensory attributes, e.g., flesh texture, acidity levels, and aroma profile, to encompass practical considerations such as postharvest storage longevity, visual freshness [2], and ease of peeling, which significantly influence purchasing decisions.
Previous research has focused predominantly on improving the nutritional composition, sensory qualities, and pericarp pigmentation of kiwifruit [1]. However, kiwifruit peelability, a critical quality determinant affecting consumer experience and market competitiveness, is substantially understudied. Fruits with easy-peeling characteristics present significant advantages in terms of convenience and hygiene. The commercial success of easy-peeling citrus cultivars in Chinese markets [3] highlights the economic potential of optimizing peelability. Contemporary market analyses reveal a pronounced consumer preference for fruits with either edible skins (e.g., apples and grapes) or readily separable peels (e.g., bananas) at the expense of species requiring substantial peeling effort, such as kiwifruit.
As one of the most successfully domesticated fruit crops of the 20th century, kiwifruit has achieved substantial advancements in conventional quality parameters, such as flavor profiles, yield potential, and postharvest storage capacity [4,5], making peelability optimization a critical frontier for continued market expansion, particularly with respect to consumer demand for convenience and hygiene. Consequently, peelability has emerged as a pivotal breeding target in global fruit crop improvement programs [6], especially for commercial kiwifruit cultivars. Notably, while certain wild relatives, such as Actinidia arguta, exhibit a smooth, trichome-free pericarp that permits direct consumption following simple rinsing [7]; however, their commercial cultivation is limited due to their small fruit size. Alongside the development of peelable cultivars, enhancing skin edibility represents another important strategy to improve fruit utilization and consumer acceptance.
The current review concentrates on mainstream commercial kiwifruit cultivars that necessitate manual peeling. We systematically synthesize the current knowledge of the physiological and molecular determinants underpinning kiwifruit peelability while analyzing emerging trends in peelability assessment methodologies and breeding strategies. The objective of this study is to establish a conceptual framework for understanding peelability mechanisms and identifying germplasm resources with favorable peeling characteristics and, thus, inform the development of next-generation kiwifruit cultivars, which will contribute to increasing global market competitiveness through improved consumption convenience while creating new export opportunities in premium fresh fruit markets.

2. Survey Methodology

A set of scientific papers (n = 560) were retrieved from two academic databases, the China National Knowledge Infrastructure (the largest Chinese academic journal database) and Web of Science, using four search terms, i.e., “猕猴桃剥皮/软化” and “kiwifruit peelability/softening”, respectively, covering publications from 1992 to 2025. The terms “softening” and “软化” were incorporated as it embodies the fundamental requirement for fruit peeling, which necessitates sufficient softness and ripeness. The titles, abstracts, and keywords of the retrieved papers were subsequently screened to assess their relevance. Additionally, several representative studies on the peelability of citrus, banana, loquat, and grape, etc., were also referred. Ultimately, 58 papers were selected for a systematic review focused on research evolution, genotypic divergence, quantitative assessment methods, possible underlying mechanisms, and artificial regulation strategies for kiwifruit peelability.

3. Research Evolution in Kiwifruit Peelability Studies

The scientific exploration of kiwifruit peelability has progressed through two phases: early exploratory research in New Zealand in approximately 2010 and recent systematic investigations in China in approximately 2020. Initial breakthroughs emerged from New Zealand’s horticultural research community, where pioneering studies established fundamental evaluation methodologies. Hallett and Sutherland (2007) [8] first identified genetic determinants of peelability variations within the Actinidia genus, particularly highlighting the exceptional peeling characteristics of Actinidia eriantha. Subsequently, Atkinson et al. (2009) [9] formally proposed peelability enhancement as a strategic breeding objective for commercial kiwifruit cultivars. Methodological advancements followed those of Harker et al. (2011) [10], who pioneered the application of triaxial quantitative metrics, e.g., “skin-flesh adhesion”, “skin compliance in tension”, and “skin tearing”.
The current research paradigm involving kiwifruit peelability, which was revitalized by Chinese research institutions, including Jiangxi Agricultural University and Guangxi Institute of Botany (Chinese Academy of Sciences), has expanded to encompass phenotypic characterization, molecular mechanisms and new cultivar breeding. For example, Huang et al. (2024) [11] conducted a comprehensive evaluation of 25 kiwifruit genotypes across various genera (Actinidia chinensis var. chinensis, Actinidia chinensis var. deliciosa, and Actinidia eriantha), employing a multiparameter assessment system integrating the “peeling number” “peeling degree” and “peeling force”. Tao et al. (2024) [12] elucidated the metabolic and transcriptional regulatory networks underlying peelability through integrated omics analysis, revealing key secondary metabolite pathways and cell wall modification genes in Actinidia eriantha. A new elite easy-peeling cultivar was released by the Guangxi Institute of Botany [13].
Despite these advancements, critical knowledge gaps persist in peelability research. Current limitations include (i) incomplete understanding of genotype-phenotype relationships within the Actinidia genus, (ii) insufficient characterization of the cellular and molecular determinants of peeling mechanics, and (iii) a scarcity of commercially viable easy-peeling germplasms. Addressing these challenges requires coordinated efforts in germplasm screening, molecular breeding optimization, and the development of standardized peelability evaluation protocols to facilitate the creation of novel kiwifruit cultivars with enhanced peeling characteristics.

4. Genotypic Divergences in Kiwifruit Peelability

Variations in peelability exist across the Actinidia genus (Table 1). Commercial Chinese cultivars, particularly Actinidia chinensis var. chinensis and Actinidia chinensis var. deliciosa, exhibit poor peeling performance characterized by discontinuous detachment patterns, irregular residual peel fragmentation, disorganized peel-flesh interface separation, and mechanical flesh damage, revealing features of difficult-peeling genotypes [11]. In contrast, Actinidia eriantha accessions such as ‘Ganmi 6’ and ‘White’ demonstrate superior peelability through reduced peeling steps, cohesive interfacial separation, and distinct tissue boundary formation [11,14]. Hybrid progenies derived from Actinidia eriantha × Actinidia chinensis var. deliciosa crosses partially inherit these advantageous peeling traits [8]. Currently, most wild populations of Actinidia eriantha in China are underutilized due to inherent biological constraints, characterized by small fruit size, dense epidermal trichomes, and limited commercial viability [15,16], and serve primarily as genetic reservoirs for improving fruit peelability [9].
Notably, an elite easy-peeling cultivar, ‘Guifei’ (CNA20171342.2), which is derived from the genus Actinidia longicarpa, was released by our team [13]. The cultivar ‘Guifei’ achieves complete epicarp removal via a single continuous peeling motion, which produces an intact peel morphology with zero tearing incidence while preserving pristine flesh integrity. To our knowledge, ‘Guifei’ represents both the most peelable kiwifruit cultivar documented to date and the first Chinese-bred easy-peeling cultivar that does not belong to the Actinidia eriantha genus. With an average fruit mass of 38.3 g, the cultivar ‘Guifei’ combines distinctive organoleptic properties (refreshing flavor profile) with exceptional biochemical attributes, notably, a vitamin C concentration of 2.4 g kg−1, which is 2~3-fold greater than that of commercial cultivars such as ‘Hongyang’ (Actinidia chinensis var. chinensis) and ‘Hayward’ (Actinidia chinensis var. deliciosa) [13]. These combined peelability advantages and nutritional merits enhance the market competitiveness of ‘Guifei’ and establish it as a model system for mechanistically investigating peelability determinants in kiwifruit. While the exceptional peelability of ‘Guifei’ was noted upon its introduction, few follow-up studies examining the underlying mechanisms of this trait have been published. This highlights a significant research gap, as its unique genetic background may offer novel insights into peelability-related traits.
The highly peelable cultivar ‘Guifei’ exhibits relatively high tensile tension and hardness, coupled with low gumminess, which collectively contribute to its favorable peelability. For the easily peelable Actinidia eriantha genus, represented by cultivar ‘Ganlv1’, the peel firmness and toughness are significantly lower than those of hard-to-peel cultivars, accompanied by a reduced number of subepidermal sclerenchyma cell layers. The cultivar ‘Ganlv1’ exhibits increased activities of β-galactosidase, pectinase, and cellulase, which facilitate accelerated degradation of cell wall components during fruit ripening [12]. The combined effects of peel texture characteristics, cell wall metabolic processes, anatomical structures, and gene expression patterns collectively confer the easy peelability trait to cultivar ‘Ganlv1’. In contrast, poor peelability in cultivars such as cultivar ‘Hayward’ is associated primarily with substantial flesh damage resulting from cell rupture rather than natural intercellular debonding. The poor peelability of cultivar ‘Hayward’ is determined by its thick-walled cellular structure, specific pectin distribution patterns, etc. [8].

5. Quantitative Evaluation of Kiwifruit Peelability

Fruit peelability is a biomechanically continuous process governed by composite force interactions. Current evaluation frameworks for kiwifruit peelability can be evaluated in terms of four aspects: (i) peel tearing force, which is the force needed to tear the peel [11]; (ii) skin-flesh adhesion, which is the force needed to separate the adhered peel from the flesh and the cleanliness of peel removal, which should be emphasized because it introduces perfect peeling performance [8]; (iii) peel tension, which is the force needed to cause the peel to rupture during the peeling process [10]; and (iv) peeling frequency, which is defined as the number of peeling times needed for complete separation of the peel from fruit flesh [9]. While the peeling frequency and peeling force remain predominant metrics, critical methodological limitations persist [11]. Empirically, the peel frequency significantly depends on size because larger fruits (greater surface area) inherently require more peeling operations than their smaller counterparts within the same genotype. Crucially, this size-related artifact does not intrinsically reflect superior peelability in smaller fruits, as peeling counts may be influenced by fruit dimensions. Furthermore, operator-induced variability in manual peeling techniques (e.g., pulling angle and force application rate) introduces substantial experimental noise for evaluating peeling counts.
The complexity of peelability necessitates multidimensional assessment protocols. Citrus research provides precedent through standardized instrumental metrics, i.e., penetration resistance and the skin-flesh adhesion force [3], which eliminate operational biases. Given their comparatively thinner epicarp, the penetration resistance of kiwifruit is negligible. Thus, optimizing kiwifruit peelability should focus on two key characteristics: high peel toughness and low skin-flesh adhesion [12]. Our experimental data indicate that genotypes enabling single-operation peel removal (e.g., cultivar ‘guifei’) exhibit both exceptional peel tensile strength and minimal adhesion forces (Figure 1). Methodological advancements highlight the superiority of instrumental quantification over manual assessments [11]. The use of peel toughness, which can be measured via single texture analyzer determination [19], is more reliable than the use of peeling frequency protocols, which require laborious fruit size standardization. We, therefore, propose a standardized evaluation framework comprising (i) the skin-flesh adhesion force and (ii) the peel toughness. The two proposed parameters enable quantitative standardization across genotypes while minimizing operational variability, which is critical for both germplasm screening and mechanistic studies of peelability determinants (Figure 1).

6. Possible Mechanisms of Peelability in Kiwifruit

6.1. Speculative Mechanisms Underlying Cell Wall Polysaccharide Regulation

Cell wall polysaccharides (pectin, hemicellulose, and cellulose) play critical roles in determining the viscosity and mechanical strength of cells in both the peel and pulp tissues of fruits [20]. Kiwifruit softening results mainly from cell wall breakdown and weakened intercellular adhesion. During fruit ripening and softening, degradation and depolymerization of these polysaccharides drive ultrastructural remodeling of cell walls, primarily through sequential processes such as pectin de-esterification, long-chain depolymerization, hemicellulose breakdown into monosaccharides (e.g., glucose and xylose), and cellulose dissolution [21,22,23,24], which collectively influence two key parameters, i.e., the “skin-flesh adhesion force” and “peel toughness”, and may regulate kiwifruit peelability.
Existing studies have explored kiwifruit peelability from two main perspectives. (i) Cell wall composition. The peelability of Actinidia eriantha (easy peeling) is correlated with cell wall polysaccharide degradation during fruit ripening, where the activities of β-galactosidase and pectinase are critical determinants [12]. Similarly, in grape berries, peelability exhibits a negative correlation with cell wall polysaccharide content and a positive correlation with the activity of relevant cell wall-degrading enzymes [25]. A recent study by Lin et al. (2024) [26] revealed that the T6P-SnRK1-TOR-starch metabolism pathway plays a regulatory role in postharvest fruit ripening, potentially influencing kiwifruit peelability. (ii) Collenchymatous cell layer structure. The peelability of Actinidia eriantha is associated with a “peeling zone” at the peel-pulp interface [8]. Easy-peeling cultivars exhibit steep pectin distribution gradients that form distinct interfaces [10], whereas difficult-peeling cultivars possess significantly thicker collenchymatous cell layers, requiring greater tearing force [10]. However, studies on Actinidia chinensis cultivars revealed that peelability does not depend on morphological peeling zones but may instead arise from mechanically discontinuous zones formed by differential cell wall modifications between the peel and pulp [27]. Currently, the understanding of the mechanisms of kiwifruit peelability remains fragmented and unsystematic, with discrepancies in scholarly findings potentially linked to variations in tested cultivars [12]. For instance, while differences in polysaccharide distribution across peel layers represent a compelling hypothesis, direct biochemical evidence remains to be experimentally validated. Future studies employing advanced polysaccharide profiling techniques will be necessary to substantiate this hypothesis.
A series of correlative studies have established a mechanistic link between pectin biology and fruit softening/firmness in tomato, banana, and loquat cultivars [28,29,30,31]. In mandarin cultivars, pectin/pectinase is closely related to mandarin peelability; pectin lyase genes (Ciclev10004783m.g, Ciclev10020423m.g and Ciclev10031429m.g) have been highlighted as potential regulators of peelability, and pectinase has been proposed as a target for peelability-oriented breeding of citrus [32]. It is well established that cell wall polysaccharides (e.g., pectin and hemicellulose) form the material basis for peel quality. On the one hand, as fundamental cell wall components, pectin and hemicellulose directly modulate adhesion between pulp and peel [3,6]; on the other hand, pectin acts as an intercellular glue, with its distribution pattern dictating cell structure, and localized pectin degradation results in critical “peeling zones” that facilitate easy detachment [8].
Our preliminary study revealed significant correlations between pectin metabolism (and related enzyme activities) and key peeling traits (e.g., skin-flesh adhesion force and peel toughness) in kiwifruit. Several pectin metabolism-regulating genes potentially associated with fruit peeling traits in Actinidia eriantha have been identified, with AeGAE6, AebHLH35-like, and AeBGAL5 emerging as primary candidates influencing peelability [12]. The selection of germplasms with specific pectin distribution patterns could enable the breeding of kiwifruit cultivars with both protective and easy-peeling properties [8]. Collectively, these observations suggest that pectin may play a role in governing kiwifruit peelability, although further empirical validation is needed to substantiate this hypothesis. The results from genetic manipulation and biomechanical modeling will be critical for strengthening causal claims.
The fruit growth of kiwifruit exhibits an ‘S’ curve pattern. According to the plant phenological period system, Richardson et al. (2011) [33] categorized the fruit development period of kiwifruit into three phases: the cell division phase, the fruit expansion phase, and the fruit ripening phase. Currently, research on the peelability of kiwifruit focuses on the morphological, physical, and chemical properties of the cortical pulp tissue during the ripening phase [12,27]. The polysaccharide substances increase exponentially during the fruit expansion phase, which acts as the material foundation for the formation of the components and structure of the cell wall and potentially impacts the peeling characteristics of the fruit.
Nevertheless, the correlation between polysaccharide substances and peelability during the fruit expansion period of kiwifruit remains ambiguous. During the young fruit stage of citrus, the application of calcium fertilizer modulates pectin and thereby influences the pericarp hardness [34] and fruit peelability. The synthesis of fruit polysaccharides commences during the fruit expansion phase, and a particular degradation process is initiated during the ripening phase. The differential metabolism of diverse polysaccharide substances at different stages affects the composition and structure of the peel and pulp of kiwifruit, ultimately affecting the peeling performance of kiwifruit. We hypothesize that the material that affects the peelability of kiwifruit is formed during the fruit expansion phase and that this trait manifests during the postharvest ripening phase.

6.2. Putative Indirect Pathways Through the Phytohormone Signaling Network

Fruit softening is intricately orchestrated by phytohormones through the modulation of cell wall metabolism and structural development [26,27,35] and ultimately affects kiwifruit peelability. For instance, as a ripening hormone, ethylene (ETH) plays a dominant role in postharvest kiwifruit softening and may directly affect peelability [35,36]. The abscisic acid (ABA)-cytokinin-ETH-cell wall degradation pathway plays a regulatory role in postharvest fruit ripening, potentially influencing kiwifruit peelability [26]. Phytohormones may increase cell wall degradation by activating pectin methylesterase or polygalacturonase expression, weakening the skin-flesh interface and facilitating peeling [23,37,38,39]. This review synthesizes evidence regarding hormone-driven changes in cell wall polysaccharide metabolism and cell layer structure, which known to influence fruit firmness, peel detachment force, and peel toughness, thereby providing insights into the putative hormonal mechanisms governing kiwifruit peelability, which require further experimental validation.
In accelerated softening of kiwifruit induced by dehydration, elevated ETH production is observed due to the upregulation of ETH synthesis genes (e.g., AcACS1 and AcACO1) [40]. In contrast, the inhibition of DNA methylation delays kiwifruit softening, accompanied by a retardation in the degradation of starch and cell wall polysaccharides, which is attributed to suppressed ETH biosynthesis [41]. The ETH signaling pathway involves ETH binding to receptors, which leads to CTR1 repression and subsequent activation of transcription factors such as EIN3/EIL [42,43], AdNAC2, and AdNAC72 [44]. EIN3/EIL upregulate genes encoding cell wall-degrading enzymes (e.g., pectinases and cellulases), AdEIL2 and AdEIL3 in kiwifruit activate the promoter of AdACO1 (a key ETH synthesis gene), accelerating ETH production and subsequent softening [42,43], and AdNAC2 and AdNAC72 increase the expression of AdMsrB1, an enzyme that promotes methionine recycling and 1-aminocyclopropane-1-carboxylic acid (ETH precursor) accumulation, further increasing ETH synthesis and fruit softening [44]. These processes degrade cell wall integrity, reducing skin-flesh adhesion, which may improve peelability.
ABA is usually linked to stress responses, which orchestrate the majority of fruit ripening processes [45]. Under postharvest dehydration, the ABA content, which is predominantly controlled by the key biosynthesis gene AcNCED4, is strongly correlated with the progression of fruit softening [40]. Exogenous ABA treatment significantly increased the expression levels of cell wall degradation-related genes, such as AcPL1, AcXTH5, and AcMAN1, and ultimately promoted kiwifruit fruit ripening [40,46]. However, there is controversy regarding whether ABA interacts with ETH during fruit ripening. Most studies have indicated that ABA mediates fruit softening via the ETH signaling pathway [45]. In contrast, recent research has indicated that during postharvest dehydration, ABA may promote fruit softening through an ETH-independent pathway [40]. The regulatory role of ABA in fruit ripening may depend on factors such as fruit species, maturity, dose, and other variables.
The cell wall structure built during the early expansion phase (10~40 days postanthesis) lays the structural groundwork for postharvest fruit softening, thereby governing kiwifruit peelability. Indole-acetic acid (IAA) plays a key role in the development of young kiwifruit berries, driving early fruit growth by promoting cell division, enlargement, and xylem differentiation [47]. IAA delays the postharvest ripening process of kiwifruit. ETH response factors (e.g., AcERF1B and AcERF073) positively regulate IAA degradation by activating the transcription of the AcGH3.1 promoter, thereby accelerating postharvest kiwifruit ripening [48,49]. Exogenous IAA treatment promotes the accumulation of endogenous IAA, inhibits the peak of endogenous ABA and lipoxygenase activity, and delays the postharvest ripening and softening of kiwifruit [46]. However, exogenous IAA application has been shown to accelerate postharvest kiwifruit softening by modulating starch and cell wall metabolism [50]. Similarly, treatment with 1-naphthylacetic acid enhances fruit softening in kiwifruit through upregulation of the auxin-responsive gene AcGH3.1 [49]. The regulatory role of IAA in fruit ripening is speculated to depend on the fruit development period.
In summary, kiwifruit softening is regulated by a hormonal network dominated by ETH, with ABA and IAA either interacting with ETH or functioning independently, depending on developmental and environmental contexts. These phytohormones collectively orchestrate cell wall metabolism, gene expression, and enzyme activity to regulate postharvest softening. Additionally, early cell wall development establishes a critical structural framework that may indirectly influence peelability; however, direct mechanistic evidence for phytohormonal regulation of peeling traits remains limited. Understanding these integrated regulatory mechanisms (Figure 2) can inform strategies to optimize kiwifruit ripening and peelability for commercial applications. Similarly in citrus fruits, peel firmness and adhesion strength exhibit significant associations with multiple growth and developmental traits, including peel cellular architecture, cell wall polysaccharide content, activities of associated degradative enzymes, and endogenous phytohormone profiles [51]. Nevertheless, targeted research is required to validate the putative role of phytohormones in peelability and elucidate their underlying mechanistic framework.

7. Artificial Manipulation of Kiwifruit Peelability

Given the scarcity of easy-peeling kiwifruit cultivars, artificial manipulation techniques have emerged as indispensable strategies to increase peelability. Currently, approaches such as manual peeling benchmarking, lye peeling optimization, and thermal peeling have been employed in the artificial manipulation of kiwifruit peelability. These approaches, encompassing physical, chemical, and thermal interventions, aim to weaken skin-flesh adhesion or alter the peel structure, thereby facilitating mechanized or manual peeling processes.

7.1. Manual Peeling Benchmarking

Manual peeling of kiwifruit, typically performed with a sharp knife, is a traditional and widely used method in small-scale or artisanal processing. Key technical points include careful manipulation to separate thin, tightly adherent skin from the underlying pulp, which requires manual dexterity to minimize flesh loss [52]. Although manual peeling is a straightforward and tool-free method, its practical application is constrained by high weight loss, low efficiency, and compromised nutrient retention, highlighting the need for alternative methods (e.g., lye peeling or thermal) in industrial contexts. Additionally, manually scooping kiwifruit flesh from halved fruit using a spoon is also feasible; however, this approach is not prioritized because of the inconvenience of requiring a specialized tool and the associated issue of substantial pulp loss.

7.2. Lye Peeling Optimization

Lye peeling (NaOH-based) for kiwifruit involves immersing fruits in heated sodium hydroxide solutions, with optimized parameters typically reported as a 15% NaOH concentration at 95 °C for 4 min [52,53,54]. Key technical aspects include precise control of the solution concentration, temperature, and immersion duration: higher concentrations or temperatures reduce the required time but risk excessive tissue softening, whereas lower intensities may fail to fully detach the peel. Lye peeling results in less weight loss and greater retention of nutrients (vitamin C) than hand peeling does [53]. NaOH dissolves epicuticular waxes on the kiwifruit surface, allowing the solution to penetrate the epidermis. The alkali then reacts with pectic substances (e.g., protopectin and oxalate-soluble pectin) in the middle lamella, breaking cross-linkages between cells and weakening the peel-flesh interface [55].

7.3. Thermal Peeling

The thermal peeling of kiwifruit primarily involves immersing fruits in 100 °C hot water for 30 s, followed by rapid cooling with cold tap water (20 °C) to halt heat transfer and prevent overcooking. The mechanism underlying this process operates through the thermal disruption of cell structures at the skin-flesh interface, specifically via depolymerization of pectic polysaccharides and diminished intercellular adhesion [52]. The advantages of thermal peeling over alkali or manual methods include minimal weight loss, superior color retention, and the absence of chemical residues. Notably, infrared heating technology effectively softens the tissues at the skin-flesh interface, thereby reducing interfacial adhesion. This method achieves a high peelability of 90% while minimizing mass loss (4.5% weight loss), demonstrating its potential as a promising alternative to conventional thermal peeling methods [56]. Additionally, as a novel and alternating thermal processing technology, ohmic heating has been employed for tomato peeling [57] and holds potential for application in kiwifruit peeling.

8. Conclusions and Perspectives

The quantification of fruit peelability, an essential quality trait, has been systematically established in citrus through standardized metrics (“penetration resistance” and “skin-flesh adhesion”). In contrast, kiwifruit peelability research remains nascent, constrained by critical limitations, e.g., the absence of universally accepted mechanical evaluation protocols, overreliance on subjective parameters vulnerable to operator variability, and insufficient characterization of genotype-specific peelability determinants. In the present study, we proposed “skin-flesh adhesion” and “peel toughness” as robust, instrument-quantifiable indicators that overcome current methodological shortcomings.
Globally, the dearth of well-characterized easy-peeling kiwifruit germplasms, particularly the non-eriantha genus, impedes mechanistic studies. Current research disproportionately focuses on Actinidia chinensis cultivars with limited peelability variation, limiting analyses of cell wall polysaccharide-protein interactions. The recent identification of elite genotypes such as ‘Guifei’ (Actinidia longicarpa) provides unprecedented opportunities to resolve peelability determinants through comparative multiomics. According to emerging evidence, it is speculated that (i) polysaccharide metabolism during the fruit development period regulates fruit peelability and that (ii) phytohormones may regulate kiwifruit peelability by modulating cell wall metabolism, fruit softening, and structural development. Currently, methodologies for artificial manipulation of kiwifruit peelability primarily involve physical methods, temperature treatment, and ripening manipulation to facilitate easier separation of the peel from the pulp, including manual peeling, lye peeling optimization, and thermal peeling.
To deepen our understanding of kiwifruit peelability, we propose the following further validation strategies. The first is methodological innovation. ISO-certified protocols for peel toughness measurement should be developed, hyperspectral imaging for nondestructive peel integrity assessment should be implemented, and genotype-specific peelability classification thresholds should be established. The second is germplasm development. Wild Actinidia germplasm resources (e.g., Actinidia latifolia) should be screened to identify novel alleles associated with superior peelability traits, and pectin gradient mutants should be generated via gene-editing [58], which specifically targets pectin methylesterase isoforms to modulate cell wall adhesion. The third is mechanistic elucidation. The three-dimensional pectin architecture should be solved via µ-CT and atomic force microscopy, ETH-pectin crosstalk should be mapped through time-resolved transcriptomics, and mechanical signal transduction pathways linking cell wall remodeling to peel detachment should be identified. These advancements will enable predictive models of peelability and accelerate the breeding of next-generation cultivars with multiple optimizations of nutritional and sensory attributes and ease of peeling. Concomitantly, cultivars amenable to direct skin-on consumption, as exemplified by Actinidia arguta, are advocated as prospective candidates for commercialization.

Author Contributions

Conceptualization, B.Q.; methodology, B.Q. and P.L.; validation, B.Q., P.L., F.W. and M.Z.; formal analysis, B.Q. and P.L.; investigation, B.Q. and P.L.; resources, J.L. and F.W.; writing—original draft preparation, B.Q. and M.Z.; writing—review and editing, B.Q., F.W. and M.Z.; visualization, B.Q.; supervision, J.L. and F.W.; project administration, B.Q., J.L. and F.W.; funding acquisition, B.Q., J.L. and F.W. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the National Natural Science Foundation of China (grant no. 32260733), the Science and Technology Major Project of Guangxi, China (grant no. Guike AA2323008), the Guangxi Natural Science Foundation (grant no. 2025GXNSFAA069537), the Earmarked Fund for China Agriculture Research System-Deciduous Fruit Tree (nycytxgxcxtd-2023–13-01) and the Fund of Guangxi Key Laboratory of Plant Functional Phytochemicals and Sustainable Utilization (ZRJJ2024-18).

Data Availability Statement

All data are available in the manuscript.

Acknowledgments

The authors thank the anonymous reviewers for their work.

Conflicts of Interest

The authors declare no conflicts of interest.

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Horticulturae 11 00927 g001
Figure 1. Genotypic variation in kiwifruit peelability. * and ** indicate significance at the p < 0.05 and p < 0.01 levels, respectively. GH, guihong cultivar (Actinidia chinensis var. chinensis); CY, cuiyu cultivar (Actinidia chinensis var. chinensis); HY, hongyang cultivar (Actinidia chinensis var. chinensis); 16A, hort 16A cultivar (Actinidia chinensis var. chinensis); GH4, guihai No. 4 cultivar (Actinidia chinensis var. chinensis); GF, guifei cultivar (Actinidia longicarpa).
Figure 1. Genotypic variation in kiwifruit peelability. * and ** indicate significance at the p < 0.05 and p < 0.01 levels, respectively. GH, guihong cultivar (Actinidia chinensis var. chinensis); CY, cuiyu cultivar (Actinidia chinensis var. chinensis); HY, hongyang cultivar (Actinidia chinensis var. chinensis); 16A, hort 16A cultivar (Actinidia chinensis var. chinensis); GH4, guihai No. 4 cultivar (Actinidia chinensis var. chinensis); GF, guifei cultivar (Actinidia longicarpa).
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Figure 2. Putative mechanisms of kiwifruit peelability. GF, guifei cultivar (Actinidia longicarpa).
Figure 2. Putative mechanisms of kiwifruit peelability. GF, guifei cultivar (Actinidia longicarpa).
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Table 1. Genotypic divergence in kiwifruit peelability.
Table 1. Genotypic divergence in kiwifruit peelability.
PeelabilityGenotypesGenusReference
Highly peelable‘Guifei’Actinidia longicarpa[13]
Easily peelable‘Ganlv 1’, ‘White’, ‘Sweet white’, ‘Ganlv 6’, ‘Ganmi 6’, ‘Ganlv2’, ‘G2’, ‘YH-3’Actinidia eriantha[11,14,17,18]
‘G3’, ‘G5’F1 hybrids of Actinidia deliciosa (♀) and Actinidia eriantha (♂)[10]
Moderately peelable‘Jinfeng’(金丰)
‘Jinfeng’(金奉)		Actinidia chinensis var. chinensis[11]
Poor peelability‘G1’Actinidia eriantha[10]
‘Skelton’, ‘Hayward’, ‘Tomua’Actinidia deliciosa var. deliciosa[8,10]
‘Guichang’, ‘Jinkui’, ‘Miliang 1’, ‘Hayward’Actinidia chinensis var. deliciosa[8,9,11]
‘Hongyang’, ‘Donghong’, ‘Hongshi 2’, ‘Jinyuan’, ‘Lushanxiang’, ‘Jinyan’, ‘Jinguo’, ‘Wanding 1’, ‘Yunhai 1’, ‘Zaoxian’, ‘Jingkui’, ‘Kuimi’, ‘Cuiyu’, ‘Puyu’, ‘Hort16A’Actinidia chinensis var. chinensis[10,11]
Note: ♀, female parent; ♂, male parent.
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Qi, B.; Li, P.; Li, J.; Zha, M.; Wang, F. Kiwifruit Peelability (Actinidia spp.): A Review. Horticulturae 2025, 11, 927. https://doi.org/10.3390/horticulturae11080927

AMA Style

Qi B, Li P, Li J, Zha M, Wang F. Kiwifruit Peelability (Actinidia spp.): A Review. Horticulturae. 2025; 11(8):927. https://doi.org/10.3390/horticulturae11080927

Chicago/Turabian Style

Qi, Beibei, Peng Li, Jiewei Li, Manrong Zha, and Faming Wang. 2025. "Kiwifruit Peelability (Actinidia spp.): A Review" Horticulturae 11, no. 8: 927. https://doi.org/10.3390/horticulturae11080927

APA Style

Qi, B., Li, P., Li, J., Zha, M., & Wang, F. (2025). Kiwifruit Peelability (Actinidia spp.): A Review. Horticulturae, 11(8), 927. https://doi.org/10.3390/horticulturae11080927

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