Hubbry Logo
RipeningRipeningMain
Open search
Ripening
Community hub
Ripening
logo
8 pages, 0 posts
0 subscribers
Be the first to start a discussion here.
Be the first to start a discussion here.
Ripening
Ripening
Ripening
View on Wikipedia
from Wikipedia
A bunch of Cabernet Sauvignon wine grapes at varying levels of ripeness

Ripening is a process in fruits that causes them to become more palatable. In general, fruit becomes sweeter, less green, and softer as it ripens. Even though the acidity of fruit increases as it ripens, the higher acidity level does not make the fruit seem tarter. This effect is attributed to the Brix-Acid Ratio.[1] Climacteric fruits ripen after harvesting and so some fruits for market are picked green (e.g. bananas and tomatoes).

Underripe fruits are also fibrous, not as juicy, and have tougher outer flesh than ripe fruits (see Mouth feel). Eating unripe fruit can sometimes lead to stomachache or stomach cramps, and ripeness affects the palatability of fruit.

Science

[edit]
1‑Methylcyclopropene is used as a synthetic plant growth regulator.[2]

Developing fruits produce compounds like alkaloids and tannins. These compounds are antifeedants, meaning that they discourage animals who would eat them while they are still ripening. This mechanism is used to make sure that fruit is not eaten before the seeds are fully developed.[3]

At the molecular level, a variety of different plant hormones and proteins are used to create a negative feedback cycle which keeps the production of ethylene in balance as the fruit develops.[4][5]

Agents

[edit]
Lemons turn yellow as they ripen.

Ripening agents accelerate ripening. An important ripening agent is ethylene, a gaseous hormone produced by many plants. Many synthetic analogues of ethylene are available. They allow many fruits to be picked prior to full ripening, which is useful since ripened fruits do not ship well. For example, bananas are picked when green and artificially ripened after shipment by being exposed to ethylene. Catalytic generators are used to produce ethylene gas simply and safely. Ethylene sensors can be used to precisely control the amount of gas. Covered fruit ripening bowls or bags are commercially available. These containers increase the amount of ethylene and carbon dioxide gases around the fruit, which promotes ripening.[6]

Calcium carbide is also used in some countries for artificially ripening fruit. When calcium carbide comes in contact with moisture, it produces acetylene gas, which is similar in its effects to the natural ripening agent, ethylene. Acetylene accelerates the ripening process. Use of Calcium carbide is illegal[7] in most developed countries, due to contamination leading to production of the highly toxic compounds phosphine and arsine.

Climacteric fruits continue ripening after being picked, a process accelerated by ethylene gas. Non-climacteric fruits can ripen only on the plant and thus have a short shelf life if harvested when they are ripe.

Indicators

[edit]

Iodine (I) can be used to determine whether fruits are ripening or rotting by showing whether the starch in the fruit has turned into sugar. For example, a drop of iodine on a slightly rotten part (not the skin) of an apple will stay yellow or orange, since starch is no longer present. If the iodine is applied and takes 2–3 seconds to turn dark blue or black, then the process of ripening has begun but is not yet complete. If the iodine becomes black immediately, then most of the starch is still present at high concentrations in the sample, and hence the fruit has not fully started to ripen.

Stages

[edit]

Climacteric fruits undergo a number of changes during fruit ripening. The major changes include fruit softening, sweetening, decreased bitterness, and colour change. These changes begin in an inner part of the fruit, the locule, which is the gel-like tissue surrounding the seeds. Ripening-related changes initiate in this region once seeds are viable enough for the process to continue, at which point ripening-related changes occur in the next successive tissue of the fruit called the pericarp.[8] As this ripening process occurs, working its way from the inside towards outer most tissue of the fruit, the observable changes of softening tissue, and changes in color and carotenoid content occur. Specifically, this process activates ethylene production and the expression of ethylene-response genes affiliated with the phenotypic changes seen during ripening.[9] Colour change is the result of pigments, which were always present in the fruit, becoming visible when chlorophyll is degraded.[10] However, additional pigments are also produced by the fruit as it ripens.[11]

In fruit, the cell walls are mainly composed of polysaccharides including pectin. During ripening, a lot of the pectin is converted from a water-insoluble form to a soluble one by certain degrading enzymes.[12] These enzymes include polygalacturonase.[10] This means that the fruit will become less firm as the structure of the fruit is degraded.

Ripening grape tomatoes in multiple stages

Enzymatic breakdown and hydrolysis of storage polysaccharides occurs during ripening.[10] The main storage polysaccharides include starch.[10] These are broken down into shorter, water-soluble molecules such as fructose, glucose and sucrose.[13] During fruit ripening, gluconeogenesis also increases.[10]

Acids are broken down in ripening fruits[13] and this contributes to the sweeter rather than sharp tastes associated with unripe fruits. In some fruits such as guava, there is a steady decrease in vitamin C as the fruit ripens.[14] This is mainly as a result of the general decrease in acid content that occurs when a fruit ripens.[10]

Tomatoes

[edit]

Different fruits have different ripening stages. In tomatoes the ripening stages are:

  • Green: When the surface of the tomato is completely green
  • Breaker: When less than 11% of the surface is red
  • Turning: When less than 31% of the surface is red (but not less than 11%)
  • Pink: When less than 61% of the surface is red (but not less than 31%)
  • Light Red: When less than 91% of the surface is red (but not less than 61%)
  • Red: When the surface is nearly completely red.[15]

Lists of climacteric and non-climacteric fruits

[edit]

This is an incomplete list of fruits that ripen after picking (climacteric) and those that do not (non-climacteric).

Honeycrisp apples

Climacteric

[edit]
Cultivated blackberries at various stages of ripeness: unripe (pale), ripening (red), and ripe (black)

Non-climacteric

[edit]

Regulation

[edit]

There are two patterns of fruit ripening: climacteric that is induced by ethylene and non-climacteric that occurs independently of ethylene.[18] This distinction can be useful in determining the ripening processes of various fruits, since climacteric fruits continue ripening after they are removed due to the presence of ethylene, while nonclimacteric fruits only ripen while still attached to the plant. In non-climacteric fruits, auxins act to inhibit ripening. They do this by repressing genes involved in cell modification and anthocyanin synthesis.[19] Ripening can be induced by abscisic acid, specifically the process of sucrose accumulation as well as color acquisition and firmness.[20] While ethylene plays a major role in the ripening of climacteric plants, it still has effects in non-climacteric species as well. In strawberries, it was shown to stimulate color and softening processes. Studies found that the addition of exogenous ethylene induces secondary ripening processes in strawberries, stimulating respiration.[21] They suggested that this process involves ethylene receptors, a type of gasoreceptor, that may vary between climacteric and non-climacteric fruits.[22]

Methyl jasmonate

[edit]

Jasmonate is involved in multiple aspects of the ripening process in non-climacteric fruits. This class of hormones includes jasmonic acid and methyl jasmonate. Studies showed that the expression of genes involved in various pathways in ripening was increased with the addition of methyl jasmonate.[18] This study found that methyl jasmonate led to an increase in red coloration and the accumulation of lignin and anthocyanins, which can be used as ripening indicators. The genes they analyzed include those involved in anthocyanin accumulation, cell wall modification, and ethylene synthesis; all of which promote fruit ripening.[18]

Abscisic acid

[edit]

ABA also plays an important role in the ripening of non-climacteric plants. It has been shown to increase the rate of ethylene production and anthocyanin concentrations.[20] Ripening was enhanced, as seen with the accelerated fruit coloration and softening. This occurs because ABA acts as a regulator of ethylene production, increasing synthesis similarly to climacteric fruits.[20]

See also

[edit]
  • Bletting, a post-ripening reaction that some fruits undergo before they are edible
  • Cervical ripening, when the pregnant human cervix degrades collagen and proteins and then changes shape prior to delivery

References

[edit]
[edit]
Revisions and contributorsEdit on WikipediaRead on Wikipedia

Ripening

View on Grokipedia
from Grokipedia
Ripening is a complex physiological and biochemical process in fruits that marks the transition from maturity to edibility, involving coordinated changes in color, texture, flavor, aroma, and nutritional content to attract seed dispersers and ensure reproductive success. This process encompasses the degradation of chlorophyll leading to vibrant pigmentation, cell wall breakdown causing softening, accumulation of sugars and organic acids for enhanced sweetness and taste, and the production of volatile compounds that develop characteristic aromas. Fruits are broadly classified into climacteric and non-climacteric types based on their ripening behavior and respiratory patterns. Climacteric fruits, such as apples, bananas, and tomatoes, exhibit a burst in production and respiration after , allowing them to ripen fully off the plant. In contrast, non-climacteric fruits like strawberries, grapes, and must remain attached to the plant to complete ripening, as they lack this -driven climacteric rise and show a gradual decline in metabolic activity. , a key , acts as the primary regulator in climacteric ripening by triggering autocatalytic production and activating downstream for metabolic shifts. The regulation of ripening involves intricate genetic, hormonal, and epigenetic mechanisms, with thousands of genes influencing processes like starch-to-sugar conversion, solubilization, and pigment synthesis. Environmental factors, including temperature, light, and mechanical stress, can modulate sensitivity and ripening kinetics, while post-harvest technologies like storage exploit these dynamics to extend . Understanding ripening has significant implications for , enabling optimized harvesting, reduced waste, and improved quality through breeding and .

Fundamentals

Definition and Process

Ripening refers to the coordinated series of biochemical and physiological changes that occur in fleshy fruits during the later stages of development, leading to maturation characterized by softening of tissues, changes in pigmentation, development of aroma and flavor compounds, and alterations in texture and nutritional content. These transformations collectively enhance the fruit's and appeal to seed-dispersing animals, thereby promoting in angiosperm . The process is genetically programmed and irreversible, resembling in its degenerative yet purposeful nature, and is unique to fleshy fruits as an adaptation for animal-mediated dispersal. Ripening typically follows the precursor phases of fruit growth and maturation, during which the fruit expands, accumulates , and achieves physiological maturity, thereby gaining the capacity to undergo ripening. It can proceed either on the or post-harvest, depending on the fruit's inherent , allowing for practical management in to optimize timing and storage. Scientific interest in ripening emerged in the , with early observations noting the effects of illuminating gases on accelerating fruit softening and color changes, laying the groundwork for understanding gaseous influences on tissues. Fruits are broadly classified as climacteric or non-climacteric based on distinct patterns of respiration during ripening, with climacteric types capable of continuing the process after detachment from the plant. This foundational process sets the stage for exploring variations in ripening behavior across species.

Climacteric vs. Non-Climacteric Classification

Fruits are classified into climacteric and non-climacteric categories based on their respiratory and ethylene production patterns during ripening. Climacteric fruits exhibit a characteristic burst in respiration and autocatalytic ethylene synthesis at the onset of ripening, enabling them to continue the process post-harvest even if picked at the mature green stage. In contrast, non-climacteric fruits display a steady decline in respiration rates with minimal or no autocatalytic ethylene production, necessitating that they ripen fully on the plant to achieve optimal quality, as they do not respond significantly to exogenous ethylene after harvest. The primary physiological distinction lies in the respiration dynamics: climacteric fruits undergo a "climacteric rise," marked by an exponential increase in CO₂ production and levels that coordinates ripening events, whereas non-climacteric fruits show a linear or gradual decline in respiration without such a surge. This difference influences post-harvest handling, with climacteric fruits like apples benefiting from storage to manage ethylene, while non-climacteric fruits such as grapes require immediate consumption or cooling to preserve quality. From an evolutionary perspective, the climacteric trait is thought to enhance in wild by allowing fruits to ripen and soften rapidly after detachment from the parent plant, attracting dispersers through heightened aroma and color changes at opportune times. Non-climacteric ripening, conversely, may align with strategies where fruits must remain attached longer for synchronized maturation with environmental cues. Recent research in the 2020s has highlighted hybrid or atypical varieties that blur these classifications, such as certain cultivars exhibiting intermediate responses and respiration patterns, challenging the traditional binary model and prompting reevaluation through genetic and physiological studies. These findings suggest potential for engineered fruits with tunable ripening behaviors via targeted modifications in signaling pathways.

Biochemical Mechanisms

Core Scientific Processes

Ripening in fruits is driven by a series of coordinated biochemical and physiological processes that transform the mature but unripe into a fully ripened state, involving enzymatic degradation, metabolic shifts, and gene regulation. These changes are essential for softening, color development, flavor enhancement, and preparation for , primarily occurring in the fruit's cells. Cell wall degradation is a central process leading to fruit softening, mediated by hydrolytic enzymes that disassemble the pectin-rich and primary . Polygalacturonase (PG) hydrolyzes the α-1,4-galacturonic acid linkages in de-esterified , solubilizing and depolymerizing the matrix, while pectin methylesterase (PME) demethylates , creating sites for PG action and releasing . These enzymes increase in activity during ripening, resulting in loss of integrity and tissue softening, as observed in various fruits where suppression of PG or PME extends firmness but alters texture post-ripening. Pigment changes contribute to the visual maturation of fruits, involving the breakdown of and the accumulation of chromoplast pigments. Chlorophyll degradation in chloroplasts uncovers underlying , such as β-carotene and , which provide yellow, orange, or red hues, while anthocyanins are synthesized in vacuoles for purple or blue coloration in certain species. This transition is regulated by enzymatic pathways, including chlorophyllase for chlorophyll and genes upregulated during ripening, leading to a net increase in carotenoid content from less than 1 mg/kg in green stages to over 100 mg/kg in ripe fruits. Flavor and aroma development arise from metabolic conversions that balance sweetness, acidity, and scent profiles. Soluble sugars like glucose, , and accumulate through and activity, often increasing from 5-10% in unripe fruits to 15-20% in ripe ones, while organic acids such as malic and citric decrease via respiratory , shifting the sugar-acid ratio for optimal . Aroma volatiles, including esters, aldehydes, and derived from fatty acids, , and , are biosynthesized via pathways like and branched-chain amino acid degradation, with over 300 compounds contributing to the characteristic scent, peaking in concentration during late ripening. Respiratory metabolism provides the energy and substrates for these ripening events through enhanced and the tricarboxylic acid (TCA) cycle. converts glucose to pyruvate, feeding the TCA cycle to generate ATP, NADH, and intermediates like α-ketoglutarate, which support anabolic processes; in climacteric fruits, respiration rates can surge 10-100 fold during the climacteric rise. Hormones like trigger this upregulation, but the core pathways remain central to carbon flux. In climacteric fruits, respiration rate often follows a model dependent on concentration, approximated by Michaelis-Menten kinetics: v=Vmax⁡⋅[E]Km+[E]v = \frac{V_{\max} \cdot [E]}{K_m + [E]} where vv is the CO₂ production rate, Vmax⁡V_{\max} is the maximum rate, [E][E] is concentration, and KmK_m is the half-saturation constant (typically 0.1-1.0 µL/L). This derives from receptor binding kinetics, similar to enzyme-substrate interactions, with experimental fits showing R2>0.95R^2 > 0.95 for and . activities in ripening, such as PG, also obey Michaelis-Menten for substrate affinities, e.g., PG's KmK_m for polygalacturonic acid around 0.5-2 mg/mL. Recent post-2020 research highlights epigenetic regulation in ripening , particularly modifications in genomes. deacetylases like SlHDA7 repress ripening genes by reducing H3K9ac and H3K27ac marks, while demethylases such as SlJMJ6 remove to activate transcription factors like RIN, enabling for coordinated expression; mutations in these modifiers delay ripening by 20-50%. also modulates pathway genes, with inhibitors accelerating color development.

Indicators of Ripening

Ripening in fruits is assessed through a variety of physical, chemical, and sensory indicators that provide measurable signs of maturity progression. These indicators allow for practical evaluation in agricultural and post-harvest settings, enabling decisions on harvest timing and quality control. Physical indicators include changes in texture and appearance, such as fruit softening, which is quantified using a penetrometer to measure the force required for probe penetration, typically expressed in Newtons (N). For instance, firmness values often decrease from over 50 N in unripe stages to below 20 N in ripe fruits, depending on species. Color transformation is another key physical sign, evaluated via the Hunter Lab color scale, where parameters like L* (lightness), a* (green-to-red), and b* (blue-to-yellow) track shifts from green chlorophyll dominance to carotenoid-based hues. Visual indices, such as the proportion of surface area showing color break, complement these measurements for on-field assessments. Chemical indicators focus on internal composition changes that influence taste and shelf life. Total soluble solids (TSS), primarily sugars, are measured in degrees Brix (°Brix) using refractometry, with ripe fruits typically reaching 10-15 °Brix or higher to indicate optimal sweetness. Titratable acidity (TA), determined by titration to a pH endpoint like 8.2, quantifies organic acids and decreases during ripening, often from 1-2% in unripe fruit to 0.5-1% in mature stages, balancing sourness with emerging sweetness. Sensory indicators involve perceptible qualities like aroma and taste. Aroma volatiles, such as esters and , intensify and diversify, detected through gas chromatography-mass spectrometry (GC-MS) to profile over 100 compounds that evolve during maturation. profiles, assessed via trained panels, reflect the interplay of , acidity, and astringency, though these are subjective and often corroborated by chemical metrics. Technological methods enable non-destructive evaluation for efficiency in processing. Near-infrared (NIR) scans fruit surfaces or transmits light through them to predict internal quality attributes like TSS and firmness without damage, achieving correlations above 0.85 with reference methods. Industry standards provide benchmarks for these indicators. The (USDA) defines color break stages, such as "" where less than 10% of the surface shows non-green coloration, to standardize maturity grading across commodities like tomatoes. Recent advancements from 2023 to 2025 incorporate AI-based imaging for real-time ripening detection in supply chains. models integrated with hyperspectral or smartphone cameras classify ripeness stages with over 90% accuracy, reducing waste by enabling automated sorting and predicting during transport.

Developmental Stages

General Stages

The ripening process in fruits generally unfolds through a series of sequential stages, transitioning from physiological maturity to full and eventual decay, driven by coordinated hormonal and metabolic shifts applicable across most . These stages provide a framework for understanding the developmental timeline, with variations influenced by genetic, environmental, and post-harvest factors. Recent multi-omics models, integrating transcriptomics and data, have refined our grasp of these transitions by revealing dynamic networks that mark shifts between phases, such as ethylene-responsive pathways activating at initiation. In the pre-ripening , also known as the mature green phase, fruit growth ceases as and expansion halt, while initial hormone signals, including low-level production via System 1 pathways in climacteric fruits, prepare the tissue for subsequent changes. levels remain high, supporting residual , and the achieves physiological maturity but remains firm and unpalatable. This sets the foundation for ripening without initiating visible alterations. The initiation stage marks the onset of ripening, characterized by the color break where degradation begins and pigmentation shifts occur, often signaled by an burst in climacteric fruits through the transition to autocatalytic System 2 production. In non-climacteric fruits, this phase relies on external cues without a respiratory climax. Transitions into this stage are typically defined by thresholds like 10-20% surface color change or initial firmness reductions, detectable via profiling of upregulated biosynthesis genes. During the progression stage, the fruit undergoes rapid transformations, including tissue softening from cell wall breakdown, flavor compound accumulation through sugar and volatile synthesis, and peak respiration rates that enhance aroma and nutritional quality. Pigment accumulation intensifies, leading to vibrant hues, while metabolic —evident in post-2020 transcriptomic studies—coordinates these traits for optimal edibility. This phase represents the core of ripening, balancing development and consumption readiness. The stage, or over-ripening, follows as the becomes excessively soft, with increased susceptibility to microbial decay due to membrane deterioration and initiation. Indicators include accelerated weight loss and pathogen invasion, marking the end of viable post- life. Overall, the entire ripening timeline spans days to weeks, varying by —such as faster progression in bananas under warm conditions versus slower in apples—and modulated by , , and maturity at .

Example: Tomatoes

Tomatoes (Solanum lycopersicum) serve as a classic model for climacteric fruit ripening, where production surges to drive coordinated changes in , texture, and flavor. As a climacteric fruit, tomatoes exhibit a respiratory climacteric peak during maturation, enabling post-harvest ripening if harvested at appropriate stages. This process transforms the firm, green fruit into a soft, red, aromatic one, primarily through the breakdown of and synthesis of carotenoids. The ripening of tomatoes progresses through distinct color-based stages defined by the (USDA) standards. The breaker stage occurs when up to 10% of the fruit surface shows color change, typically a pale or yellow at the blossom end, marking the onset of visible maturation. This is followed by the turning stage (more than 10-30% color), where the fruit shifts to a mix of and hues; the stage (more than 30-60% color), with predominant pinkish- coverage; the light stage (more than 60-90% color); and the stage, where more than 90% of the surface is or deep , indicating complete ripeness. These stages reflect underlying biochemical shifts, such as degradation and accumulation, allowing for standardized assessment in commercial settings. A hallmark of tomato ripening is the dramatic accumulation of , the red pigment responsible for the fruit's color and a potent , which increases 10- to 14-fold from green to red stages. This buildup occurs via upregulation of biosynthesis genes, peaking in the later stages and contributing to . Variety differences influence this process; for instance, cherry tomatoes (e.g., S. lycopersicum var. cerasiforme) typically ripen faster—often within 50-60 days from transplant—due to their smaller size and higher sensitivity, resulting in quicker synthesis and sweeter profiles, whereas beefsteak varieties (e.g., 'Big Beef') take longer (70-80 days) and accumulate more gradually, yielding larger fruits with meatier texture but potentially uneven ripening if environmental stresses occur. Genetic studies using mutants like rin (ripening inhibitor) illustrate key regulatory blocks in development. The rin , a gain-of-function in the MADS-RIN , arrests fruits at the mature stage by repressing ethylene-responsive genes and downstream ripening pathways, preventing color change, softening, and flavor development even under ethylene exposure. This results in yellow, firm fruits with blocked accumulation, demonstrating RIN's central role as a master regulator that coordinates over 1,200 ripening-associated transcripts. Such mutants have been instrumental in dissecting the genetic architecture of ripening, revealing additive effects with other loci like nor. In practice, harvest timing optimizes and quality for transport. Mature green es, harvested just before the breaker stage, can be ripened off-vine with treatment and stored for up to 14 days at 12.5°C without significant quality loss, minimizing damage during shipping while allowing color development to the breaker stage in 1-5 days. This approach extends marketability, as fully ripe fruits have shorter (3-7 days) due to rapid softening. Recent advances in gene editing have targeted ripening for . In 2024, overexpression of the SlHDA7 gene in tomatoes delayed ripening by modulating deacetylation, reducing softening and extending by weeks, which could cut post-harvest food waste—estimated at 20-50% for tomatoes—by preserving firmness and nutritional content during distribution. This builds on rin-inspired insights, offering non-transgenic varieties with tunable maturation for reduced losses.

Regulatory Factors

Hormonal Agents

serves as the primary hormonal agent regulating ripening, particularly in climacteric fruits where it acts as a master coordinator of the process. Its biosynthesis begins with the , which is converted to (ACC) by the rate-limiting ACC synthase (ACS), followed by the oxidation of ACC to by ACC oxidase (ACO). In climacteric fruits such as tomatoes and bananas, production exhibits an autocatalytic nature, where initial low levels of induce the expression of ACS and ACO genes, leading to a rapid burst in synthesis that triggers and sustains ripening. The autocatalytic feedback amplifies levels dramatically during the climacteric phase, with internal concentrations typically reaching 1-10 ppm to drive metabolic shifts like increased respiration and cell wall degradation. This production can be modeled simplistically as the rate of ethylene formation depending on ACC availability, given by : Ethylene production rate=k[ACC]\text{Ethylene production rate} = k [\text{ACC}] where kk represents the rate constant influenced by ACO activity. In practice, this rate escalates from basal levels of less than 0.1 ppm to the climacteric peak due to on ACS transcription. Other plant hormones modulate ethylene's effects on ripening. Auxins, such as (IAA), generally inhibit ripening by suppressing biosynthesis and signaling, maintaining fruit in a pre-ripening state during development. For instance, high auxin levels in unripe fruit antagonize action, delaying the onset of color changes and softening. (GAs), on the other hand, promote cell expansion and growth during early fruit development but delay ripening when applied exogenously, as seen in tomatoes where GA treatment reduces sensitivity and slows metabolic transitions. Ethylene exerts its influence through a signaling pathway involving membrane-bound receptors like ETR1 in and homologs in fruits such as tomatoes. Upon binding , these receptors are inactivated, relieving inhibition on downstream components like CTR1 , which allows activation of transcription factors including EIN3/EIL and, in tomatoes, the MADS-box factor RIN that upregulates ripening-related genes. This cascade integrates with other hormones; for example, can crosstalk by modulating receptor sensitivity. Recent studies have highlighted brassinosteroids (BRs) as co-regulators, particularly in non-climacteric fruits like strawberries and grapes. In a 2023 review, BRs were shown to promote pigment accumulation and other ripening processes in non-climacteric fruits, such as enhancing levels in grapes and accelerating coloration in strawberries, without relying on a climacteric burst. A study further demonstrated BRs' role in modulating hormone crosstalk during non-climacteric maturation, where BR signaling via BZR1 transcription factors coordinates with low-level to regulate for flavor and texture development.

Molecular and Environmental Regulators

Molecular regulators of fruit ripening primarily involve transcription factors and epigenetic modifications that orchestrate networks controlling metabolic shifts. Transcription factors from the NAC family, such as NAC4 and NAC9 in , promote ripening by upregulating ethylene biosynthesis genes like ACS2, ACS4, and ACO1, while their silencing reduces production and accumulation. Similarly, transcription factors, including RIN, FUL1, and TAGL1, regulate ethylene-dependent and independent pathways, influencing biosynthesis, cell wall metabolism, and synthesis in fleshy fruits like and . Epigenetic mechanisms, such as and modifications, further fine-tune ripening by modulating accessibility; for instance, DNA demethylases like SlDML2 in facilitate ripening gene activation, and their dysfunction delays maturation. Recent 2025 studies have identified modifications, such as (m6A), as key regulators of during development and ripening. Additionally, has been shown to restrict ripening by generally repressing and signaling. (), a volatile derivative of the pathway, plays a key role in stress-induced ripening by altering . In , exogenous application accelerates softening, accumulation, and soluble solids increase by upregulating phenylpropanoid pathway genes and cell wall-modifying enzymes like EG1 and XTH1, while also enhancing and genes such as , AOS, and ACS. Abscisic acid (ABA) accumulates prominently during ripening in non-climacteric fruits, where it promotes color development and softening. In , ABA levels rise from the white to full-red stage via upregulation of biosynthesis genes like FaNCED1, with overexpression accelerating accumulation through MYB10 activation and remodeling via expansins (e.g., FaEXP2) and xyloglucanases (e.g., FaXyl1), leading to softer texture. Exogenous ABA similarly enhances and synthesis in fruits like and , while promoting texture changes by inducing polygalacturonase genes such as PavPL18 in sweet cherry. Environmental factors significantly influence ripening rates, with , , and CO2 levels modulating metabolic processes. Optimal s of 20–25°C accelerate ripening in many fruits like and by enhancing sensitivity and volatile emissions, though exceeding 30°C can cause uneven maturation; lower s (e.g., 12–15°C) delay it but risk chilling in tropical . exposure inhibits production in by affecting ACC oxidase activity, indirectly slowing ripening, while elevated CO2 (5–20%) suppresses genes, extending storability in apples and grapes at levels like 10 kPa CO2 with 6 kPa O2. ABA and exhibit crosstalk during ripening, particularly under drought stress, where ABA accumulation negatively regulates ethylene biosynthesis via transcription factors like ABI4, which repress ACS4 and ACS8, thereby balancing stress tolerance and maturation in fruits. Recent research highlights the fruit microbiome's influence on ripening through volatile emissions. In diseased ripening berries affected by sour rot, microbial communities in the carposphere produce or induce volatile organic compounds that modulate aroma profiles and accelerate softening, with bacterial and fungal taxa correlating to increased and emissions during maturation. Surface microbes in fruits like apple also contribute to volatile blends, enhancing ecological interactions that indirectly affect ripening dynamics via plant-microbe signaling.

Fruit Classifications

Climacteric Fruits

Climacteric fruits are characterized by their dependence on for ripening, which enables a surge in respiration and metabolic activity, allowing these fruits to continue maturing after . This post-harvest ripening potential provides flexibility in harvesting and transportation, as fruits can be picked at physiological maturity and ripened later under controlled conditions. Prominent examples of climacteric fruits include apples, avocados, bananas, , mangoes, papayas, peaches, pears, tomatoes, and muskmelons, along with apricots, guavas, passion fruits, plums, and persimmons. These fruits share the trait of ethylene-mediated softening, color changes, and flavor development that can occur off the , distinguishing them from other categories. Climacteric fruits hold significant economic value in global due to their storage and shipping advantages, which reduce spoilage during long-distance trade. For instance, bananas, a major climacteric export, account for approximately 20 million tonnes in annual world trade, supporting economies in tropical regions. Within climacteric fruits, variations exist based on botanical subgroups, such as stone fruits (drupes) like peaches, plums, and apricots, which feature a single pit and rapid softening, versus berries like bananas and tomatoes, which often show more gradual responses.

Non-Climacteric Fruits

Non-climacteric fruits are characterized by the absence of a respiratory climacteric, meaning they do not experience a sharp increase in respiration and production during ripening. Instead, their maturation occurs gradually and independently of , requiring at or near full since post-harvest ripening does not continue. This independence distinguishes them from climacteric fruits, limiting their and necessitating on-plant maturation for optimal quality. Common examples of non-climacteric fruits include strawberries, raspberries, blueberries, blackberries, grapes, cherries, fruits (such as oranges, lemons, grapefruits, and limes), pineapples, bell peppers, gooseberries, and currants. Recent genomic studies, including whole-genome resequencing of diverse genotypes, have updated classifications to position figs as transitional non-climacteric, exhibiting bursts in tissues but primarily ABA-regulated, non-climacteric ripening in the receptacle based on identified genetic variants like endo-β-1,4-glucanases. These fruits share key traits, including low sensitivity and production, which prevent autocatalytic ripening off the , thus emphasizing the need for vine- or tree-ripening to achieve desirable texture, flavor, and color. Economically, their high perishability poses transport challenges; for instance, strawberries suffer up to 50% post-harvest losses from fungal decay, mechanical , and loss, often confining distribution to local markets rather than global supply chains. Non-climacteric fruits exhibit structural variations, including simple fruits derived from a single —such as grapes (berries) and cherries (drupes)—and aggregate fruits formed from multiple ovaries in one flower, like strawberries (achenes on a receptacle) and raspberries (drupes). Pineapples, as multiple fruits aggregating from numerous flowers, further diversify this category while maintaining non-climacteric ripening patterns.

References

  1. https://pmc.ncbi.nlm.nih.gov/articles/PMC6504782/
  2. https://portal.nifa.usda.gov/web/crisprojectpages/0212590-identifying-genetic-mechanisms-determining-ripening-and-quality-in-fruits.html
  3. https://pmc.ncbi.nlm.nih.gov/articles/PMC6270112/
  4. https://extension.umd.edu/resource/ethylene-and-regulation-fruit-ripening
  5. https://pmc.ncbi.nlm.nih.gov/articles/PMC3550874/
  6. https://www.salk.edu/news-release/why-fruits-ripen-and-flowers-die-salk-scientists-discover-how-key-plant-hormone-is-triggered/
  7. https://pmc.ncbi.nlm.nih.gov/articles/PMC3682129/
  8. https://pmc.ncbi.nlm.nih.gov/articles/PMC10315308/
  9. https://www.sciencedirect.com/topics/medicine-and-dentistry/fruit-ripening
  10. https://pubmed.ncbi.nlm.nih.gov/17364693/
  11. https://treefruit.wsu.edu/wp-content/uploads/2016/01/15-Mattheis_Fruit-Maturity-Quality.pdf
  12. https://www.scielo.br/j/gmb/a/HTgBD9By9tMcLmHRZk4SsLn/
  13. https://pmc.ncbi.nlm.nih.gov/articles/PMC10627154/
  14. https://crisosto.ucdavis.edu/sites/g/files/dgvnsk6166/files/inline-files/158-15-Non-climacteric-ripening-and-sorbitol-homeostasis-in-plum-fruits.pdf
  15. https://ucanr.edu/sites/default/files/2023-09/388262.pdf
  16. https://royalsocietypublishing.org/doi/10.1098/rsbl.2021.0352
  17. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9343914/
  18. https://pmc.ncbi.nlm.nih.gov/articles/PMC3550369/
  19. https://www.scionresearch.com/__data/assets/pdf_file/0003/59097/10Brummell.pdf
  20. https://pmc.ncbi.nlm.nih.gov/articles/PMC8750800/
  21. https://www.sciencedirect.com/science/article/pii/S246801412400075X
  22. https://www.sciencedirect.com/science/article/abs/pii/S006522960800801X
  23. https://agriculture.institute/food-chemistry-and-physiology/compositional-changes-fruits-vegetables-ripening/
  24. https://pmc.ncbi.nlm.nih.gov/articles/PMC6831743/
  25. https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2020.00080/full
  26. https://www.tandfonline.com/doi/full/10.1080/10942912.2016.1160921
  27. https://academic.oup.com/ijfst/article/51/3/777/7739629
  28. https://pmc.ncbi.nlm.nih.gov/articles/PMC10539587/
  29. https://www.newswise.com/pdf_docs/175488197959648_uhae234.pdf
  30. https://www.sciencedirect.com/science/article/abs/pii/S0956713524003438
  31. https://www.sciencedirect.com/science/article/abs/pii/S0925521418302965
  32. https://www.researchgate.net/publication/235707636_Hunter_Colour_Determination_of_Blueberry_Cultivars
  33. https://ucanr.edu/sites/default/files/2016-03/237098.pdf
  34. https://felixinstruments.com/blog/brix-as-a-metric-of-fruit-maturity/
  35. https://www.sciencedirect.com/science/article/pii/S2405844021024269
  36. https://www.sciencedirect.com/science/article/abs/pii/S0925521402001175
  37. https://blog-fruit-vegetable-ipm.extension.umn.edu/2024/08/fruit-update-determining-fruit-ripeness.html
  38. https://www.sciencedirect.com/science/article/pii/S2772502225005074
  39. https://www.sciencedirect.com/science/article/pii/S2949736125001368
  40. https://pmc.ncbi.nlm.nih.gov/articles/PMC12476098/
  41. https://hal.science/hal-04346856v1/document
  42. https://doi.org/10.1093/jxb/erad324
  43. https://bmcplantbiol.biomedcentral.com/articles/10.1186/s12870-021-03411-w
  44. https://felixinstruments.com/blog/how-the-fruit-ripening-process-affects-freshness-and-quality/
  45. https://edis.ifas.ufl.edu/publication/VH079
  46. https://academic.oup.com/jxb/article/53/377/2107/497219
  47. https://nph.onlinelibrary.wiley.com/doi/10.1111/nph.16362
  48. https://postharvest.ucdavis.edu/produce-facts-sheets/tomato
  49. https://doi.org/10.1093/hr/uhae234
  50. https://pmc.ncbi.nlm.nih.gov/articles/PMC4677914/
  51. https://www.nature.com/articles/s41598-023-51075-3
  52. https://www.isaaa.org/resources/publications/pocketk/12/default.asp
  53. https://pmc.ncbi.nlm.nih.gov/articles/PMC10231374/
  54. https://www.annualreviews.org/doi/pdf/10.1146/annurev.pp.30.060179.002533
  55. https://pubmed.ncbi.nlm.nih.gov/17816629/
  56. https://pmc.ncbi.nlm.nih.gov/articles/PMC157269/
  57. https://pmc.ncbi.nlm.nih.gov/articles/PMC12197253/
  58. https://www.sciencedirect.com/science/article/pii/S2468014124000827
  59. https://www.sciencedirect.com/science/article/abs/pii/S0304423823001243
  60. https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2023.1269090/full
  61. https://link.springer.com/article/10.1007/s42994-025-00240-5
  62. https://nph.onlinelibrary.wiley.com/doi/10.1111/nph.70127
  63. https://pubmed.ncbi.nlm.nih.gov/23835361/
  64. https://pmc.ncbi.nlm.nih.gov/articles/PMC9252103/
  65. https://pmc.ncbi.nlm.nih.gov/articles/PMC10731311/
  66. https://pmc.ncbi.nlm.nih.gov/articles/PMC4062679/
  67. https://pmc.ncbi.nlm.nih.gov/articles/PMC7997433/
  68. https://pmc.ncbi.nlm.nih.gov/articles/PMC11578972/
  69. https://www.frontiersin.org/journals/agronomy/articles/10.3389/fagro.2023.1216520/full
  70. https://pmc.ncbi.nlm.nih.gov/articles/PMC8440034/
  71. https://agriculture.institute/food-chemistry-and-physiology/climacteric-vs-non-climacteric-fruits/
  72. https://www.fao.org/4/ae075e/ae075e21.htm
  73. https://www.fao.org/markets-and-trade/commodities-overview/bananas-tropical-fruits/bananas/9/en
  74. https://www.ipipotash.org/udocs/296-IPI-Bulletin-19.pdf
  75. https://onlinelibrary.wiley.com/doi/full/10.1111/ppl.14482
  76. https://academic.oup.com/jxb/article/70/1/115/5099540
  77. https://www.intechopen.com/chapters/81319
  78. https://journalwjarr.com/sites/default/files/fulltext_pdf/WJARR-2025-3487.pdf
  79. https://agrotonomy.com/climacteric-fruits-versus-non-climacteric-fruits/
Add your contribution
Related Hubs
User Avatar
No comments yet.