Ripening physiology and anticancer effects of baby kiwifruit Actinidia arguta

Actinidia arguta, known as 'hardy kiwifruit' or 'baby kiwifruit' in English or 'Darae' in Korean, has recently become popular in the market because consumers want fruits with new tastes and healthy food. The hardy kiwifruits are smaller than fuzzy kiwifruits (Actinidia deliciosa) and can be eaten whole, without peeling. Hardy kiwifruit commonly exists in mountainous areas and is commercially cultivated in countries with colder climates, such as Japan, China and New Zealand along with some European countries, including Poland

Hardy kiwifruits are harvested when sugar levels reach 10–14°Brix. If the fruits are left on the vine, the fruit will reach 18–25°Brix. Although the quality is best when the fruits are ripened on the vine to maximize the development of aroma and flavor, their shelf life is then shortened. However, they are commonly picked before they are vine ripened; otherwise, they would be too soft for package and shipping to commercial markets.

The storage life of hardy kiwifruits, picked at the firm and mature stage, is only 1–2 months at 0°C. In commercial markets in Korea, the recommended storage period of hardy kiwifruits is one to 2 weeks and an additional 2 or 3 days for shelf life. The main reasons for the short storage life are fruit softening, skin wrinkling due to water loss (dryness) and fruit decay.

Fruit softening rapidly increases at the room-temperature ripening period, after harvest or cold storage. Compared to A. deliciosa, the hardy kiwifruits are very sensitive to dryness because of their smooth peels that lack hair. This characteristic is the main reason for the short-storage time and fast loss of postharvest quality.

Korean scientists have investigated the effects of 1-methylcyclopropene (1-MCP) on the postharvest quality changes of hardy kiwifruits to extend the storage life of the fruits and the therapeutic effects of the extract against various human cancer cell lines. Moreover, they studied how the ripening-related gene expressions of hardy kiwifruits were affected by 1-MCP during cold storage.

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Scientists have conducted a postharvest investigation on the hardy kiwifruit 'Cheongsan' to understand the ripening physiology at the molecular level and have suggested anticancer effects of the fruit extracts besides a well-known clinical effect in atopic dermatitis.

For the study, hardy kiwifruits were treated with 20 µL/L 1-MCP for 16 h at 10°C and subsequently stored at 1 ± 0.5°C. Anticancer properties of the fruit extracts were tested against five different human cancer cells. The hardy kiwifruits, without 1-MCP treatment, showed increases in both respiration and ethylene production rates during fruit storage. The 1-MCP treatment remarkably inhibited fruit ripening by reducing respiration and ethylene production. Fruits with the 1-MCP treatment could be stored for up to 5 weeks by maintaining higher fruit firmness, ascorbic acid and total phenolic contents compared to the control. The hardy kiwifruit extracts showed anti-proliferative effects to Hep3B and HeLa cells but not to HT29, HepG2 and LoVo cells.

They concluded that the fruit showed climacteric-like characteristics after harvest, and 1-MCP treatment clearly delayed fruit ripening by down-regulating the expressions of AcACO, AcACS, and AcLOX, which are commonly known as ripening or senescence genes in fruits. They confirmed their putative ripening functions in hardy kiwifruits. 1-MCP extended the cold storage lives of the fruits for up to 5 weeks at 1 ± 0.5°C by minimizing fruit softening and nutritional losses. The suggested health benefits produced by the hardy kiwifruits might be helpful for selecting genetic resources for breeding programs as well as for the food processing industry to develop functional foods.

Sooyeon Lim, Seung Hyun Han, Jeongyun Kim, Han Jun Lee, Jeong Gu Lee, Eun Jin Lee, 'Inhibition of hardy kiwifruit (Actinidia arguta) ripening by 1-methylcyclopropene during cold storage and anticancer properties of the fruit extract', January 2016, Food Chemistry, Vol. 190, pages 150–157.

Eun Jin Lee
Department of Plant Science, Research Institute for Agriculture and Life Sciences, Seoul National University
Seoul 151-921, Republic of Korea

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