Bananaroma

Cold temperatures lower the expression of aroma-causing genes in ripening bananas.

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According to the U. S. Department of Agriculture, Americans eat, on average, eleven pounds of bananas per year. Nearly all these bananas come from Central and South America or from Asia. To prevent them from ripening, or rotting, before reaching consumers, bananas are refrigerated during shipping. However, bananas lose some of their aroma along the way. In a new study, researchers have found that cold temperatures inhibit the activity of genes that would ordinarily contribute to aroma production during the ripening process.

Scientists had previously identified more than 250 aroma compounds in ripe bananas that attract pollinators and seed-dispersers. To find out how and which of these compounds might be affected by cold, researchers led by Jian-fei Kuang, of the South China Agricultural University in Guangzhou, gathered unripe, green bananas from a local orchard. A chilled group of fruit was kept for three days at 7°C (45°F), and a non-chilled group at 22°C (72°F). The team then sampled genetic material from each banana batch and ran genetic expression tests.

As expected, the chilled group did not ripen as fast as the room-temperature group. The chilled bananas also displayed so-called chilling injuries, such as browning and pitting. Compared to the room-temperature group, the levels of gene expression for producing multiple aroma-related proteins were significantly reduced in the chilled bananas. Kuang’s team identified specific proteins, called transcription factors, that play a key role in activating the aroma genes in question. Levels for these transcription factors were lower in the chilled bananas.

This better understanding of the genetic regulatory process tied to ripening banana aroma may help address the drawbacks of cold storage for other fruits that have their essential smell diminished in this manner; tomatoes, peaches, mangoes, and papayas also pay a price for chill-delayed ripening. The breeding of banana stocks for genetic traits, or engineering modifications genetically, could enable bananas to still smell sweet, despite the distance from their native tropical climes. (Journal of Agricultural and Food Chemistry)