Durian Tested for Degree of Ripeness

28 Aug 2014

A Farmer in Thailand was jailed for selling unripe Durian. But why? And why should we care?

In the last few months, a farmer in Thailand was jailed for selling unripened Durian. But why? And why should we care?

Durian is native to Southeast Asia and commonly referred to as the "King of Tropical Fruits." It ripens naturally on the tree and drops when it is at its peak and is then collected.  Highly regarded as a delicacy, its unique taste and nutritional value, which provides high levels of carbohydrate, calcium, phosphorus and ascorbic acid, means that the fruit is used in a multitude of desserts and preserves.

In 2013, Thailand alone exported 367,056 tonnes, worth a staggering 7.34 billion baht. Whilst the market appears lucrative, it is only through the protection of the ripeness of the fruit that it has been an export success.

The ripeness of the fruit is a highly sensitive matter and the Thai Office of Agricultural Economic claim that is it for the benefit of the industry that unripened Durian are kept off the shelves. This protects the reputation of the fruit and the experience of the consumer.  In the past, Durian fruit sent for export to international markets were rejected, causing damage to the image of the Thai Durian and impacting the trade price.

Guidelines have now been developed recommending specific standards, for example for varieties such as the Montong, it is recommended that the inside of the fruit should not dry more than 32%. If the fruit are found to be too dry, an official should mark the fruit as "prohibited to sell".  Consumers are also encouraged to report incidents and these may lead to prosecution.  

Unfortunately, this evaluation of ripeness can be impractical, as it involves invading the fruit in various ways and may ruin the appearance of the fruit, making it impossible to sell on.

A more practical method was therefore required to check the 'ripeness of Durian' and protect the integrity of the fruit.  Experts have found that during the ripeness stage, quantities of ethylene gas; also referred to as the ripening hormone, are secreted. This has led to the development of a colour indicator test, which reacts to naturally occurring chemicals.

This method, predominately used during the "post harvesting" period, has many advantages where the ripeness of the fruit may not be visible from its external appearance.  This sticker test does not impact the quality of the fruit for the consumer and provides a clear indication of the level of ripeness.  The chemical emission of the fruit can be clearly distinguished in three distinct degrees of maturation; white /rare (0 – 1.5 ppm), sky blue /crisp (1.5 – 3.0 ppm) and dark blue /soft (3.0 – 8.0 ppm). Normally high degree of ripeness means ethylene gas is more than 8 ppm ethylene per kilogram per hour which can also be noticed by cracks in the Durian's shell.

Given the potential high economic yield of the Durian, at the 18th meeting of the Codex Committee on Fresh Fruits and Vegetables (CCFFV) Thailand proposed that the CCFFV consider a Thai Durian Standard as an International Standard. Intertek Testing Services (Thailand) Limited's Food laboratory has helped develop ripeness tests using Gas Chromatography methods, Maximum Residue Limit of Pesticides methods, and inspection services to provide quality assurance for a wide variety of produce including the Durian.

For more information, visit https://www.intertek.com/food/testing/