VietNamNet Bridge - Dr. Pham Thi Thu Ha from the Institute of Chemistry under the Vietnam Academy of Science and Technology (VAST) and her colleagues have successfully developed a process of preserving litchis for over one month with MAP (modified atmosphere packaging) technology.

The MAP technology was developed by the Institute of Chemistry beginning in 2008. The membrane is made of thermoplastic in primary form and therefore ensures food hygiene.

The research team has added additives which allow the MAP bag to absorb air selectively, thus restricting the respiration of fruits, so that fruits can stay fresh. 

There is no stagnant water inside the MAP bag like other kinds of bags and membranes.

Ha and her co-workers at VAST began working on the project in 2015, when they were assigned to use MAP technology for preserving litchis for at least four weeks in order to stabilize the quality and color of litchis, a specialty fruit in Vietnam, grown mostly in the provinces of Hung Yen and Bac Giang.

Tests showed that after four weeks at the temperature of 4oC, the percentage of rotten fruit preserved in MAP bags manufactured by VAST was equal to that of the fruit preserved MAP bags sourced from South Korea – about 4 percent. 100 percent of fruit kept in normal PE bags rotted.

Tests showed that after four weeks at the temperature of 4oC, the percentage of rotten fruit preserved in MAP bags manufactured by VAST was equal to that of the fruit preserved MAP bags sourced from South Korea – about 4 percent. 100 percent of fruit kept in normal PE bags rotted.

However, Ha and her co-workers were not satisfied with the result as they realized that the stability of the litchi color was not high.

Therefore, they proposed a method for stabilizing fruit color by lowering pH through pre-treatment with oxalic acid. According to Ha, this acid is a family of Vitamin C, so it is not toxic and doesn’t affect the quality of litchi.

As such, the scientists have found a process of preserving litchis with MAP technology in association with pre-treatment with organic acid, which prolongs the preservation time to five weeks (35 days) with post-preserving loss a proportion of less than 10 percent.

Litchis, after harvested, need to be soaked for seven minutes in the water at the temperature of 47oC to reduce microorganism. 

After that, they will be soaked in oxalic acid solution with the pH=3 for six minutes to stabilize the color. Later, they will be put into MAP bags and preserved at the temperature of 4-5oC and the humidity of 85-90 percent. Litchis after being taken away from thevstore will need to be kept at the temperature of 16-18oC.

It now takes 15-17 days to transport export litchis abroad, while normal PE bags can preserve litchis for 15-17 days only. This means that the traditional preservation method does not preserve litchis for a long time. MAP bags can help settle the problem.

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