Actinidina

Otros Nombres

Act c 1Act d 1actinidainActinidia anionic proteaseEC 3.4.22.14kiwifruit cysteine proteaseproteinase A2 of Actinidia chinensis

Sinopsis

Actinidin (Actinidain): A Comprehensive Reference

1. Identity

Names and Classification

Actinidain (EC 3.4.22.14), also spelled actinidin, and known by the synonyms Actinidia anionic protease and proteinase A2 of Actinidia chinensis, is a type of cysteine protease enzyme found in fruits, including kiwifruit (genus Actinidia), pineapple, mango, banana, figs, and papaya. In the context of kiwifruit allergenology, it is formally designated Act d 1. It is part of the peptidase C1 family of papain-like proteases.

The name actinidin is derived from Actinidia, the kiwifruit genus, and was first proposed by Arcus in 1959, who first described the enzyme after he observed that raw kiwifruit prevents the setting of jelly due to its digestion of gelatin. Actinidin can also be referred to as Actinidia anionic protease, actinidain, and Act d 1.

Botanical Source and Distribution

Actinidin is particularly abundant in green kiwifruit (Actinidia deliciosa), where it can constitute up to 40–50% of the fruit's soluble protein content at harvest. Actinidin constitutes up to 40% of the soluble protein in the green Hayward kiwifruit cultivar. Extremely high levels of an acidic actinidin protein were detected in A. deliciosa fruit and the EM4 cultivar, but this acidic protein appeared to be absent in 'Hort16A', the most important commercial cultivar of A. chinensis.

Both Hayward (green) and SunGold (gold) kiwifruit varieties contain a proteolytic enzyme, actinidin, that has been reported to enhance the upper tract digestion of animal proteins. Unlike the other gold varieties, which do not contain any actinidin, the SunGold variety contains significantly higher actinidin activity, but its activity is still much lower than that present in the green (Hayward) fruit.

The kiwifruit (Actinidia deliciosa), originally known as the Chinese gooseberry, is native to the Yangtze Valley of China. Seeds from China were taken to New Zealand and planted in 1906.

Molecular Characteristics

Ten different actinidin mRNAs have been identified encoding mature proteins of similar molecular weight (~24 kDa), but with predicted isoelectric points (pIs) ranging from acidic (pI 3.9) to basic (pI 9.3). In A. deliciosa 'Hayward' (green-fleshed kiwifruit) and A. chinensis 'Hort16A' and EM4 (gold-fleshed kiwifruit), actinidin mRNAs for acidic and basic proteins were expressed at comparable levels throughout ripening. Actinidin mRNA expression was highest in fruit at harvest, expression decreased as fruit ripened, and was much lower in the core compared with outer pericarp tissue.

Actinidin activity is highest in the pulp of ripe fruit at 27,600 U/kg fruit. The thiol protease actinidin from kiwifruit was purified 26-fold to a specific activity of 57 U/mg with K_m = 91 μM and k_cat = 101 s⁻¹ towards N-α-CBZ-lysine p-nitrophenyl ester at pH 6.0 and 25 °C.

The arrangement of active cysteine–thiol residues (Cys22–Cys65, Cys56–Cys98, and Cys156–Cys206) stabilizes the catalytic unit. A thiol group was identified to be essential for enzyme activity, which is why it was grouped with enzymes like papain and bromelain.

Common Forms and Preparations

Actinidin is delivered in several distinct forms depending on intended use:

Fresh whole kiwifruit — the primary natural vehicle for actinidin activity, used both for dietary consumption and, historically, as a meat-tenderizing marinade.
Freeze-dried kiwifruit powder — used in dietary supplement products such as Actazin® (a New Zealand green kiwifruit powder), which can assist with bowel regularity and issues with constipation and contains high levels of actinidin.
Aqueous kiwifruit extract — the form most commonly used in laboratory and commercial food-processing applications.
Purified enzyme preparations — isolated actinidin used in research, commercial meat tenderization, and milk coagulation applications. Actinidin has a high potential for commercial use in meat tenderization, milk coagulation, and health-promoting diet supplements.
Topical kiwifruit preparations — fresh fruit slices or pulp applied directly to wounds in exploratory clinical studies.

2. Traditional and Historical Use

Consumption of kiwifruit has long been claimed anecdotally to assist in gastric digestion. The earliest documented scientific observation of actinidin dates to 1959: actinidain was first identified in 1959 when A.C. Arcus examined why jellies made with kiwifruit did not solidify, an effect caused by a proteolytic enzyme acting on gelatin. This enzyme was named actinidin as it was identified in a fruit of the genus Actinidia (Actinidia chinensis).

Kiwifruit pulp or juice has been domestically used as an ingredient of a marinade to tenderize meat due to the actinidin activity. Actinidin has traditionally been used for meat tenderizing in home cooking for many years, and a process for tenderizing meat at commercial scale has recently been described.

Actinidin makes raw kiwifruit unsuitable for use in desserts containing milk or any other dairy products that will not be served within hours, because it rapidly digests milk proteins. This also applies to gelatin-based desserts, as the actinidin will dissolve the collagen proteins in gelatin very quickly, either liquefying the dessert or preventing it from solidifying. This property has been recognized in food culture for many decades.

The observation that topical kiwifruit might facilitate wound healing represents a more recent traditional usage documented in clinical settings in Iran and other countries. It is currently accepted that kiwifruit contains potent protein-dissolving enzymes (actinidin) and antibacterial agents that could play an important role in the wound healing process. Based on several in vitro and animal studies, kiwifruit has proven effects in ulcer debridement, angiogenesis, and disinfection.

3. Key Constituents and Mechanisms of Action

Catalytic Mechanism

Actinidin belongs to the papain-like family of cysteine proteases, sharing similarities with other plant-derived proteases such as papain from papaya and bromelain from pineapple. It belongs to the cysteine or thiol protease group due to its functional and structural resemblance to papain. The enzyme catalyzes hydrolysis of peptide bonds through a catalytic dyad involving a nucleophilic cysteine residue.

Actinidin has a very broad specificity compared to pepsin and can hydrolyze a wide range of peptide bonds that are unavailable to pepsin. This action may then open up more sites for pepsin activity. The increase in the rate of protein breakdown is probably due to the broader specificity of actinidin compared to pepsin.

The greater effect of actinidin in the gastric phase than in the small intestinal digestion phase has been linked with its near-optimal pH for actinidin activity, which has been reported to be 4 when using food proteins as substrates.

Thermal Stability

The denaturation temperature of actinidain is 60 °C (140 °F), lower than that of similar meat-tenderizing enzymes bromelain from pineapple and papain from papaya. The thermal inactivation kinetics of actinidin in both fresh and commercial green kiwifruit enzyme extracts were studied. Both extracts were inactivated at moderate sous vide temperatures (60 and 65 °C) in less than 5 minutes when alone. However, the inactivation times increased considerably (up to 24 hours at 60 and 65 °C) when these extracts were mixed with homogenised meat.

Gastrointestinal Stability

Active actinidin retained its primary structure and proteolytic activity after 2 hours of simulated gastric digestion, followed by 2 hours of intestinal digestion, as assessed by SDS-PAGE, zymography, and mass spectroscopy. Immunological reactivity of active actinidin was also preserved.

Substrate Specificity

For some proteins, the presence of kiwifruit extract resulted in a substantially greater loss of intact protein and different peptide patterns from those seen after digestion with pepsin and pancreatin alone. In particular, enhanced digestion of whey protein isolate, zein, gluten, and gliadin was observed.

Actinidin could efficiently cleave gluten proteins, the extremely resistant and immunogenic 33-mer gliadin peptide, and peptides comprising QQQ/PFP found in gluten epitopes. Actinidin showed better apparent degree of hydrolysis while digesting gliadin peptides as compared to papain, bromelain, and two other commercial glutenases sourced from Aspergillus species. LC-MS/MS data displayed that actinidin could cleave numerous peptide bonds at the N- and C-termini of proline residues under gastric conditions.

ACE-Inhibitory Peptide Generation

Angiotensin I-converting enzyme (ACE) inhibitory peptides were produced from five plant-derived proteins using actinidin. The yield of peptides varied from 7.2% to 14.2%, and the ACE inhibitory rates ranged from 71.1% to 88.3%. These findings are currently at the in vitro stage and do not constitute evidence of antihypertensive effects in humans.

α-Amylase Inhibition

The α-amylase inhibition potential of actinidin was determined. Treatment of α-amylase with actinidin at varied concentrations (0.5 mg/mL to 3 mg/mL) revealed 95% decreased amylolytic activity. The physiological and clinical significance of this observation remains to be established.

Antimicrobial Activity

Different studies showed the antimicrobial effect of the actinidin enzyme against foodborne pathogens, pathogenic gram-positive and gram-negative bacterial strains. These findings are based on in vitro experiments, and translational evidence is limited.

4. Scientific Evidence by Area of Use

4.1 Protein Digestion — Gastrointestinal Phase

In Vitro Evidence

The presence of the proteolytic enzyme actinidin was assumed to underlie anecdotal reports of improved gastric digestion. In vitro studies examined the effect of kiwifruit proteases (actinidin) on the digestion of a range of common food proteins under simulated gastric conditions. An extract from green kiwifruit containing actinidin was prepared. Several protein sources derived from soy, meat, milk, and cereals were incubated in the presence or absence of the kiwifruit extract using an in vitro digestion system consisting of incubation with pepsin at pH 1.9, simulating gastric digestion in humans.

A kiwifruit extract (actinidin) added to protein sources derived from soy, meat, milk, and cereals increased protein digestion by as much as 48%. A complementary in vitro study of the small intestinal phase likewise found that kiwifruit extract influenced the digestion patterns of all of the proteins to various extents. For some proteins, actinidin had little impact on digestion. However, for other proteins, the presence of kiwifruit extract resulted in a substantially greater loss of intact protein and different peptide patterns from those seen after digestion with pepsin and pancreatin alone.

Both Hayward (green) and SunGold (gold) kiwifruit varieties contain actinidin that has been reported to enhance the upper tract digestion of animal proteins. Unlike other gold varieties, the SunGold variety contains significantly higher actinidin activity, but its activity is still much lower than that in the green (Hayward) fruit. A study examined the effectiveness of actinidin in Hayward and SunGold kiwifruit in digesting alternative proteins including pea protein, almonds, tofu, and quinoa. The protein sources were digested using a three-stage in vitro oral-gastro-small intestinal digestion model. Both kiwifruit extracts enhanced the breakdown for all the studied protein sources, particularly during gastric digestion, possibly due to higher actinidin activity at gastric pH.

In Vivo Animal Evidence

A study aimed to determine the effect of dietary actinidin (provided as Hayward kiwifruit) on the gastric and small intestine digestion of six food protein sources in rats. For each protein source, two semi-synthetic test diets were formulated containing either freeze-dried Hayward kiwifruit (actinidin present) or freeze-dried Hort16A kiwifruit (actinidin absent). Actinidin activity is extremely low in Hort16A kiwifruit. Rats were fed freshly-prepared diets, euthanised, and the gastric and ileal contents collected. Dietary actinidin had no significant effect on the gastric degradability of zein and whey protein isolate, but increased gastric degradability of beef muscle protein, gelatin, soy protein isolate, and gluten by 40%, 60%, 27%, and 29% units, respectively.

A pig model study further examined actinidin's effects: actinidin was shown to increase the rate and extent of both gastric and intestinal digestion of different dietary proteins, including beef muscle, in both in vitro and in vivo studies with rats. Beef muscle protein was chosen to explore the effect of dietary actinidin on factors such as the rate of gastric emptying and the kinetics of gastric hydrolysis of proteins in the growing pig during a 7-hour postprandial period. Consumption of kiwifruit also improved the rate at which digested nitrogen entered the small intestine and the apparent amino acid digestibility at proximal and medial small intestine in pigs fed with a beef-based diet.

Human Clinical Evidence

A small-scale, randomized, cross-over human pilot trial was conducted using SmartPill™ wireless gastrointestinal motility technology. Ten healthy male subjects were recruited. The participants attended the clinic three times, having fasted overnight. They consumed a test meal consisting of 400 g lean steak and two 'Hort16A' or two 'Hayward' kiwifruit. Subjects completed visual analogue scales (VAS) rating feelings of hunger, satisfaction, fullness, and comfort, and swallowed a SmartPill™. After 5 hours, participants consumed an ad libitum lunch to assess satiety.

There were no significant differences in gastric emptying time, small bowel, or colonic transit time between the two kiwifruit arms of the study as measured by SmartPill™. Similarly, no significant differences were observed in VAS satiety measures or energy consumption at the ad libitum meal. However, the measurement of overall gastric comfort tended to be lower, and bloating was significantly reduced following the consumption of the steak meal with 'Hayward' kiwifruit (p < 0.028).

This small pilot study suggests that it is less likely to measure gastric emptying effectively following a high protein meal, as it may be delayed because of the meal's physical consistency. However, green kiwifruit, containing actinidin, may reduce bloating and other measures of gastric discomfort in healthy males. The study's very small sample size (n=10), exclusive use of healthy adult males, and exploratory design mean these findings must be interpreted cautiously.

A separate human study investigated protein anabolic response. The purpose of the study was to determine if actinidin protease aids gastric digestion and the protein anabolic response to dietary protein, using Hayward green kiwifruit because evidence of effects on in vitro and in vivo animal digestion is more developed than for other fruits. Detailed results from this study were not publicly accessible in full, and its outcomes remain provisional.

Overall evidence strength for protein digestion: The in vitro and animal (rat and pig model) evidence for actinidin's enhancement of gastric-phase protein digestion is moderately consistent and covers multiple protein types. Human clinical evidence is very limited — one small (n=10) pilot randomized cross-over trial — and did not confirm improvements in gastric emptying, though a reduction in bloating was reported.

4.2 Gluten Hydrolysis and Potential Relevance to Gluten-Related Disorders

Human gastrointestinal proteases cannot effectively hydrolyze proline- and glutamine-rich peptides in gluten proteins, leading to only partial hydrolysis of gluten in the upper gastrointestinal tract (GIT). This leads to the release of proline- and glutamine-rich peptides, some of which produce immune responses in genetically predisposed individuals with gluten-related health disorders (celiac disease, sensitivity, or gluten allergy).

Results of in vitro studies demonstrate that actinidin enhanced the rate of proteolysis of gluten and reduced the number of immunogenic gluten epitopes reaching the small intestine during simulated semi-dynamic GIT digestion. Actinidin, a cysteine protease in green kiwifruit (Actinidia deliciosa), has been identified as a potential enzyme to hydrolyse gluten within the lumen of the GIT. The study evaluated the effect of purified actinidin sourced from green kiwifruit on the digestion of gluten and the release of immunogenic peptides during GIT digestion. Purified gluten was digested for 180 minutes with or without actinidin.

In a pig model (used as a model for adult human digestion): Entire male pigs 9 weeks of age (n = 54) were fed whole wheat soda bread either with yellow kiwifruit (0 U protease actinidin activity/mL fresh juice) or green kiwifruit (27.0 U protease actinidin activity/mL fresh juice) for 8 days. Actinidin doubled the rate of digestion of wheat proteins in the stomach and subsequently reduced the rate of R5 epitopes entering the small intestine. Digestion of gluten immunogenic peptides is limited along the GIT, but it can be enhanced by a simultaneous intake of proteases.

Actinidin from kiwifruit has shown considerable promise in digesting immunogenic gliadin peptides compared to other plant-derived cysteine proteases.

Evidence strength: Preliminary. All gluten hydrolysis evidence is from in vitro models and a pig animal model. No human clinical trials in persons with celiac disease or non-celiac gluten sensitivity have been published. This remains an active area of research.

4.3 Meat Tenderization and Food Industry Applications

Actinidain is commercially used as a meat tenderizer and in coagulating milk for dairy products, like yogurt and cheese. When marinating with pork, actinidin was found to tenderize it by affecting the myofibrils and connective tissue, which are similar to the tissues that are broken down through mechanical tenderization.

Improved tenderness was observed with pork and rabbit muscle after actinidin treatment. The shear force was reduced by more than half with pork and rabbit muscle using the purified actinidin at a dosage of 0.5 mg/100 g muscle.

Actinidin from kiwifruit can tenderize meat and add value to low-value meat cuts. However, as with other proteases, over-tenderization of meat will occur if the reaction of actinidin is not controlled. A process to control the enzyme activity by heat denaturation after the desired degree of meat tenderization has been achieved has been described.

4.4 Milk Coagulation

Studies have shown that actinidin might be a good alternative milk coagulant, replacing chymosin, a common coagulant used in cheesemaking. Kiwifruit extract prepared at pH 5.0 had the best milk-clotting properties, with a nearly 30% better ratio of clotting activity to proteolytic activity than purified actinidin. This extract produced a casein coagulum clearly separated from the whey proteins, and was shown to be stable at room temperature for up to two months.

4.5 Wound Healing and Enzymatic Debridement

The most important constituent of kiwifruit used in wound applications is the actinidin enzyme, which is similar to the more common protease, papain (from papaya fruit). Actinidin is a cysteine protease responsible for the debridement properties of kiwifruit.

In a rat burn model study: thirty-five male rats were divided randomly into three groups. Under general anaesthesia, a limited standard full-thickness burn was produced on the back of each rat. For the intervention group (15 rats), the wounds were covered with fresh kiwifruit; for control groups (20 rats combined), the dressing was a neutral ointment. Debridement and scar contraction occurred faster in the kiwi-treated group than in the untreated group. Following rapid enzymatic debridement, healing appeared to progress normally, with no evidence of damage to adjacent healthy tissue.

Limited human observational data exist: based on several in vitro and animal studies, kiwifruit has proven effects in ulcer debridement, angiogenesis, and disinfection. A study investigated the effectiveness of fresh kiwifruit dressing on the treatment of pressure ulcers. Significantly higher levels of angiogenesis and vascularization were found in the kiwifruit-treated patients (p < 0.02). In addition, obvious antibacterial effect was observed in the kiwifruit group.

Evidence strength: Preliminary. Most wound-healing data derive from animal models and very small clinical case series. Actinidin's role has not been isolated from other kiwifruit bioactives (e.g., ascorbic acid, other phytochemicals) in wound studies. No large randomized controlled trials have been published.

5. Body Systems and Health Areas Associated with Actinidin

Gastrointestinal system: Augmentation of gastric-phase protein digestion; reduction of bloating after high-protein meals; potential motility effects from broader kiwifruit components.
Immune / allergenic response: Actinidain is an allergen in kiwifruit, acting as the major sensitizing protein in kiwifruit-allergic individuals.
Integumentary / wound repair: Enzymatic debridement of necrotic tissue in burn wounds, pressure ulcers, and diabetic foot ulcers (animal and limited clinical evidence).
Cardiovascular (exploratory): Generation of ACE-inhibitory peptides from food proteins in vitro, though no human cardiovascular data exist.
Metabolic / glycemic (exploratory): In vitro α-amylase inhibition; no human metabolic data available.

6. Dosage Forms and Dosages Reported in Studies

Actinidin is not approved as a pharmaceutical agent, and no official therapeutic dosages have been established. The following represent doses or exposures used in published research:

Human pilot trial (gastric comfort): Test meal consisting of 400 g lean steak and two 'Hayward' kiwifruit per session.
Pig (growing pig) gluten model: Green kiwifruit juice providing 27.0 U protease actinidin activity per mL of fresh juice, fed with whole wheat soda bread for 8 days.
Rat protein digestion model: Semi-synthetic test diets formulated with freeze-dried Hayward kiwifruit (actinidin present) or freeze-dried Hort16A kiwifruit (actinidin absent).
Meat tenderization: Purified actinidin at a dosage of 0.5 mg/100 g muscle reduced shear force by more than half in pork and rabbit muscle.
In vitro α-amylase inhibition: Actinidin at varied concentrations of 0.5 mg/mL to 3 mg/mL resulted in 95% decreased amylolytic activity.
In vitro gluten hydrolysis: Purified gluten was digested for 180 minutes with or without actinidin and subsequently analyzed for immunogenic epitopes.

7. Safety Considerations and Interactions

Allergenicity — the Primary Safety Concern

Act d 1 is a 30 kDa protein, also known as actinidin, and belongs to the cysteine protease protein family. It is the dominant allergen in kiwifruit. Act d 1, called actinidin, represents about 50% of the total soluble protein content and is considered a major allergen.

Kiwi allergy is a common food allergy that occurs when the immune system reacts to proteins found in kiwifruit. Initially considered rare, kiwi allergy is now recognized as a significant allergen worldwide, particularly among children. The primary allergen in kiwi is Act d 1 (actinidin), a protein that remains stable even after the fruit is processed.

A large European study reported that only Act d 1 was associated with disease severity, and individuals with severe symptoms (when compared with patients with mild symptoms) were often sensitized to actinidin. Actinidin (Act d 1) may serve as a marker for isolated kiwifruit allergy, while Act d 8 and Act d 9 might be indicative of typical cross-reactivity patterns.

Kiwifruit-allergic children develop systemic reactions most frequently following ingestion compared to adults. Act d 1 and Act d 2 are major allergens in the pediatric age group.

Latex–Fruit Syndrome and Cross-Reactivity

Kiwi allergy is highly associated with Latex–Fruit Syndrome. Many individuals who are allergic to natural rubber latex also react to kiwi because the proteins in both are structurally similar. Cross-reactivity with similar proteins from avocado, banana, and grape has been reported for Act d 2 (thaumatin-like protein).

Effect on Thermal Processing and Food Compatibility

Modification of secondary and tertiary structures of conformational epitopes of some kiwifruit allergens by heating (for example by steam cooking, boiling, etc.) or enzymatic hydrolysis results in the loss of potential IgE binding sites of these allergens. This prevents the triggering of allergic symptoms, thereby decreasing kiwi fruit sensitization in kiwifruit-allergic individuals.

Actinidin makes raw kiwifruit unsuitable for use in desserts containing milk or any other dairy products that will not be served within hours, because it rapidly digests milk proteins. This is a relevant practical food-handling consideration for persons consuming actinidin-rich kiwifruit extracts or powders in combination with protein-containing foods or supplements.

Intestinal Barrier Effects

Impairment of the intestinal barrier is one of the key events in the initiation of the sensitization process in food allergy. Research explored the effects of kiwifruit allergen Act d 1 on intestinal permeability and tight junction protein (TJP) gene expression in vivo and its potential to activate the NF-κB signaling pathway and regulate expression of epithelial pro-allergenic cytokines. Influences of Act d 1 on TJP gene expression and pro-allergenic cytokines in the mouse intestine were analyzed by qPCR upon allergen administration by oral gavage.

Administration of actinidin (Act d 1) increased intestinal permeability to β-lactoglobulin. This was accompanied by changes in gene expression of TJP mRNA and pro-allergenic cytokines IL-25, IL-33, and thymic stromal lymphopoietin (TSLP) compared to the control. These findings are based on mouse and cell-line (HEK293) experiments and have not been confirmed in human studies.

Inhibition by Metals and Other Agents

The minimum concentrations of Hg²⁺ and Cd²⁺ induced substantial inhibition of actinidin, whereas Na⁺, K⁺, Mg²⁺, Fe²⁺, Mn²⁺, and Ba²⁺ caused moderate inhibition of enzyme activity. These in vitro findings suggest that heavy metal ions can inhibit the enzyme's proteolytic function, though the dietary relevance of this observation is unknown.

Over-Tenderization Risk in Food Applications

Actinidin from kiwifruit can tenderize meat and add value to low-value meat cuts. However, as with other proteases, over-tenderization of meat will occur if the reaction of actinidin is not controlled. This is a practical food-safety consideration relevant to the use of actinidin in commercial meat processing.

References

Condiciones de Salud

Condiciones de salud que Actinidina puede ayudar a apoyar.

IndigestiónCientífico
Actinidin is a cysteine protease unique to kiwifruit with well-documented protein-digesting activity superior to pepsin for many food substrates. Multiple in vitro and animal studies confirm it enhances upper GI tract protein digestion across a range of meat, dairy, and plant proteins. It has been shown to enhance gastric protein digestion by up to 37–48% for casein fractions.

Sistemas Corporales

Sistemas corporales que Actinidina puede ayudar a apoyar.

No hay sistemas corporales disponibles.