A system for ripening fruits and vegetables with gaseous ethylene and its experimental application in stimulating banana ripening

Astract:【Objective】Fruits and vegetables, such as banana, avocado, kiwifruit and tomato are harvested at green mature status. They are subsequently allowed to ripen at ambient conditions for uniform color Currently in China, dipping or spraying with ethephon is the most common method to induce ripening of fruits and vegetable. Because the use of ethephon is banned in many countries due to health and environmental reasons, there is great need to develop ripening device and techniques using ethylene gas. The gaseous ethylene is a plant hormone promoting physiological senescence. For successful induction of ripening, accurate control of relative humidity (RH) , temperature, and ethylene and CO2 concentrations in the airtight ripening room is very important. Otherwise, there will be negative effects on ripening, pigmentation and quality. Because of their delicious, nice yellow-colored and nutritious pulp, bananas are the most popular fruit in China, especially in the north part. Ethephon is still commercially used in wholesale markets to ripen banana. Little information on ripening banana using gaseous ethylene has been reported, and there is need to standardize the method of ripening banana with this gas so that the uniformly ripened banana can fetch a remunerative price in domestic and international markets.【Methods】A system for inducing fruit and vegetable ripening with gaseous ethylene was designed and built in a storage room with automatic temperature and RH controlling. The system consisted of three main parts: 1) ethylene gas input, sensing and regulation settings; 2) a device for sensing CO2 concentration and removing excessive CO2 released by fruit respiration; 3) a micro-computer controlling terminal, software and other attached accessories. The system was a dry-fog humidity control system, inwhich mists generated through the fogger can rapidly spread providing steady RH as high as 90%-98%.Sensors for ethylene, CO2, temperature and RH in the ripening room can continually sense their changes and transmit the signal to the corresponding micro-computer controlling terminal, then the controlling unit can automatically turn on or off each part, so that ethylene, CO2, temperature and RH in the ripening room could constantly be maintained at the optimized points, which are most important for successful ripening characterized by uniform color and minimum weight loss and rotting.【Results】Application test and evaluation of the ripening system used for banana ripening was conducted. Results showed that the ripening system can accurately control ethylene, CO2 and RH in the airtight ripening room at the set points. Banana fruit harvested at 75%-80% full maturity were exposed to 0.01% (φ) ethylene gas for three days at 18-20 ℃ and RH 95%. Commercial properties of the ripe banana fruit treated with gaseous ethylene were excellent with better bright yellow color, higher hardness in pulp, later development of pericarp brown flecks and longer shelf-life as compared to the control bananas ripened with ethephon dipping. In addition, there was no significant difference in quality parameters between ethylene gas treated banana and ethephon dipped banana. However, the content of vitamin C in ethylene gas treated banana was slightly higher. Moreover, there was less weight loss and less mechanical damage in ethylene gas treated bananas.【Conclusion】In conclusion, one of the advantages of the ripening system using ethylene gas for fruits and vegetables is its accurate and automatic control of all the parameters needed for artificial ripening. The operation of the ripening system needs just water, electricity, air and ethylene gas with no production of wastes, such as plastic packaging film and ethephon derives. Therefore, this ripening system is energy saving, environmental friendly and labor saving. In a ripening room as big as500 cubic meters, up to fifty tons of bananas can be ripened. This ripening system using gaseous ethylene is a good alternative to the traditional method with ethephon and meets the international food safety standards. The ripening system can also be used in ripening fruits such as tomato, mango and kiwifruit and in citrus de-greening. With the development of domestic fruit and vegetable industries, the ripening system has a wide range of potential applications. However, further experiments and commercial tests should be conducted to find the optimal conditions for different fruits and vegetables at different maturity stages.