Actinidin is a proteolytic enzyme primarily found in the fruits of kiwi (Actinidia chinensis and Actinidia deliciosa). This enzyme belongs to the cysteine protease family and has the ability to break down proteins, facilitating digestion and nutrient absorption. Due to its enzymatic properties, actinidin is used in various cosmetic and industrial applications for its exfoliating and regenerative effects. In the cosmetic field, actinidin is valued for its ability to promote gentle skin exfoliation, enhancing cell renewal.

Chemical Composition and Structure

Actinidin is a protease that belongs to the cysteine protease group, similar to other enzymes like papain (from papaya) and bromelain (from pineapple). Its chemical structure allows it to break peptide bonds in proteins, facilitating their breakdown. It consists of a single polypeptide chain that contains a cysteine residue crucial for its catalytic activity.

Physical Properties

It is water-soluble and stable over a wide pH range, making it suitable for use in various cosmetic products. In isolated form, it appears as a fine powder or a clear liquid when included in aqueous solutions. It is mainly used in skincare products for its exfoliating and moisturizing benefits.

Production Process
Actinidin is extracted primarily from kiwi fruits through a purification process that involves crushing the fruit and isolating the enzyme. After extraction, the actinidin is purified to produce a highly active enzyme, ready for use in various cosmetic and industrial applications.

• Harvesting the Fruits: Kiwi fruits are harvested when ripe. It is essential to follow sustainable harvesting practices to ensure the quality of the plant material.

• Cleaning: After harvesting, the fruits are cleaned to remove dirt, residues, and impurities. This step is crucial to ensure that the final extract is of high quality.

• Extraction: The extraction of actinidin typically occurs through a process of grinding and pressing the fruits. The fruits are crushed and then pressed to release the juice, which contains the actinidin enzyme.

• Filtration: After extraction, the juice is filtered to remove undissolved solids and impurities, resulting in a liquid extract containing actinidin.

• Purification: The actinidin extract may be further purified using techniques such as chromatography to isolate the pure enzyme and remove other proteins and impurities.

• Quality Control and Packaging: Finally, actinidin undergoes quality control checks to verify its purity, efficacy, and compliance with standards. After analysis, it is packaged in appropriate containers for distribution and use in food and cosmetic products.

Applications

• Skin Exfoliants: Actinidin is used in gentle exfoliating products, where it helps remove dead skin cells without damaging the skin barrier. This leaves the skin brighter and smoother.

• Regenerative Skincare: The enzyme helps stimulate cell renewal, improving skin texture and contributing to a younger, fresher appearance.

• Anti-aging Treatments: Due to its ability to gently exfoliate and promote cell renewal, actinidin is used in anti-aging products to reduce the appearance of wrinkles and fine lines.

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Health and Safety Considerations

Safety in Use
Actinidin is generally considered safe for use in cosmetics. However, as with all enzymes, the use of this ingredient may cause sensitivity in individuals with sensitive skin or allergies to kiwi fruits. Regulatory authorities, such as the European Union and the FDA, permit its use in cosmetic products.

Allergic Reactions
Allergic reactions to actinidin may occur, especially in individuals allergic to kiwi fruits, as the enzyme can cause skin irritation or allergic reactions. A patch test is always recommended before use on sensitive skin.

Toxicity and Carcinogenicity
Topical use is considered safe and poses no known health risks.

Environmental Considerations
The extraction of actinidin from kiwi fruits is a sustainable process, as it utilizes a natural, renewable resource. Enzyme extraction has a limited environmental impact, and the enzyme is biodegradable, causing no pollution.

Regulatory Status
The use of actinidin in cosmetics is regulated and approved by major authorities, including the European Union and the FDA in the United States. It is an accepted ingredient in many skincare formulations.

References__________________________________________________________________________

Kaur L, Mao B, Bailly J, Oladeji O, Blatchford P, McNabb WC. Actinidin in Green and SunGold Kiwifruit Improves Digestion of Alternative Proteins-An In Vitro Investigation. Foods. 2022 Sep 6;11(18):2739. doi: 10.3390/foods11182739. 

Abstract. 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 objective of this study was to determine 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. The findings showed that both kiwifruit extracts enhanced the breakdown (observed through SDS-PAGE) for all the studied protein sources, particularly during gastric digestion, possibly due to higher actinidin activity at gastric pH. The increase in the rate of protein breakdown was probably due to the broader specificity of actinidin compared to pepsin. For many protein sources, most of the intact proteins disappeared within the first few minutes of gastric digestion with added kiwifruit extract. Green kiwifruit extract, due to its higher actinidin activity, had a higher effect on protein breakdown than the SunGold extract. However, for some proteins and under certain digestion conditions, SunGold extract resulted in higher protein breakdown. The latter, in the absence of any digestive enzymes, also led to some protein breakdown during the small intestinal digestion phase, which was not the case for the green kiwifruit extract. The green kiwifruit extract led to the greater breakdown of polypeptide chains of Pru-du 6, a major allergen in almonds. The results, for the first time, suggest that both Hayward and SunGold kiwifruit can lead to improved breakdown and digestion of alternative proteins when consumed as part of a meal; and therefore, have the potential to be used as a digestive aid in population groups looking to achieve faster and greater protein digestion such as athletes, elderly and people with the impaired digestive system.

Martin H, Cordiner SB, McGhie TK. Kiwifruit actinidin digests salivary amylase but not gastric lipase. Food Funct. 2017 Sep 20;8(9):3339-3345. doi: 10.1039/c7fo00914c. 

Abstract. Kiwifruit contains the cysteine proteinase actinidin whose strong activity allows kiwifruit to be used as a meat tenderiser. This raises the possibility digestive enzymes, also proteins, are themselves susceptible to degradation by actinidin. Salivary amylase and gastric lipase are exposed to the highest concentrations of actinidin whereas duodenal enzymes are less likely to be inactivated by actinidin due to dilution and inactivation of actinidin by gastric juice. The saliva of six volunteers was exposed to Actinidia deliciosa homogenate and then examined for loss of the starch digesting enzyme, alpha-amylase. In agreement with the known distribution of salivary amylase concentration in saliva, the range of amylase activity within the group of volunteers varied by around 100 fold. Within 5 minutes of incubation of 3 parts saliva to one part green kiwifruit at 37 °C, approximately 85% of the amylase activity was lost. The use of E-64, a selective inhibitor of cysteine proteinases, confirmed that the loss of amylase function was due to actinidin. Amylase protein degradation was followed by SDS-PAGE and western blotting. Recombinant human gastric lipase resisted digestion with kiwifruit even after 30 minutes incubation and remained functionally active after this time period. However, both mountain papaya and pineapple extracts degraded gastric lipase fully during a 30 minutes digestion period. Under conditions where cooked starch is consumed along with kiwifruit it is possible that starch digestion may be retarded whereas lipid digestion in the stomach is unlikely to be affected by kiwifruit consumption.

Maddumage R, Nieuwenhuizen NJ, Bulley SM, Cooney JM, Green SA, Atkinson RG. Diversity and relative levels of actinidin, kiwellin, and thaumatin-like allergens in 15 varieties of kiwifruit (Actinidia). J Agric Food Chem. 2013 Jan 23;61(3):728-39. doi: 10.1021/jf304289f. 

Abstract. In the last 30 years the incidence of kiwifruit allergy has increased with the three major allergenic proteins being identified as actinidin, kiwellin, and thaumatin-like protein (TLP). We report wide variation in the levels of actinidin and TLP in 15 kiwifruit varieties from the four most widely cultivated Actinidia species. Acidic and basic isoforms of actinidin were identified in Actinidia deliciosa 'Hayward' and Actinidia arguta 'Hortgem Tahi', while only a basic isoform of actinidin was identified in Actinidia chinensis 'Hort16A'. One isoform each of kiwellin and TLP were identified in ripe fruit. The cysteine protease activity of actinidin correlated with protein levels in all species except A. arguta. Protein modeling suggested that modifications to the S2 binding pocket influenced substrate specificity of the A. arguta enzyme. Our results indicate that care is necessary when extrapolating allergenicity results from single varieties to others within the same and between different Actinidia species.

Weir I, Shu Q, Wei N, Wei C, Zhu Y. Efficacy of actinidin-containing kiwifruit extract Zyactinase on constipation: a randomised double-blinded placebo-controlled clinical trial. Asia Pac J Clin Nutr. 2018;27(3):564-571. doi: 10.6133/apjcn.122017.03.

Abstract. Background and objectives: Zyactinase® is an extract of green kiwifruit, formulated into the consumer healthcare products marketed as Phloe® and Kivia, used to assist in the relief of the symptoms associated with a range of digestive system dysfunction, including constipation and Irritable Bowel Syndrome (IBS).....Conclusions: The green kiwifruit extract significantly in-duced normal bowel movements with no adverse effects. The kiwifruit extract relieved constipation and the symptoms of IBS such as bloating, flatulence and abdominal pain.