Abstract:
Alcoholic off-flavor and accompanying volatile compounds produced by
bananas (Cavendishii spp) held at 20°C and subjected to aerobic (air control
treatment) or anaerobic conditions (nitrogen treatment) were compared by solid
phase micro extraction (SPME), a newly developed method for volatile
separation. In general, volatile production was suppressed under anaerobic
conditions but resumed, to some extent, after fruits were returned to air. The
effects of anaerobic conditions on individual compounds were separated into six
groups based on their production trends relative to those of air conditions. It was
clear that bananas subjected to anaerobic conditions produced ethanol that
could be detected easily by SPME. Anaerobic conditions almost completely
blocked the esterification step needed to produced normal volatile profiles of
ripening bananas.
The effects of anaerobic conditions on banana flavor and off-flavor
development were determined by a taste panel quality scaling method. In order
to determine the difference between bananas subjected to both conditions
(aerobic and anaerobic), the "difference from control" method was used in other
experiments. Generally, the bananas subjected to anaerobic conditions had
better physical appearance than bananas in the air control group but lacked fruit
flavor and firmness. Off-flavor developed to a greater extent in bananas under
anaerobic conditions than those under the air control which had almost no off-flavor.
The correlation between off-flavor and ethanol was very high (r = 0.87)
while for other volatiles was very low. This finding implies that ethanol is probably
the only volatile causing anaerobic off-flavor in ripening bananas. In order to
confirm this, headspace ethanol was detected by SPME, and tissue ethanol was
extracted and assayed enzymaticaily. The result showed that tissue ethanol was
correlated with headspace ethanol (r² = 0.66). The threshold for off-flavor
development in ripening bananas was 300 mg of tissue ethanol /100 g FW or
0.5 ppm for headspace ethanol.
Our results indicate that even three days in anaerobic conditions could
injure ripening bananas. Thus unlike other fresh fruits, O₂ levels at or below 1%
is not suitable for application as postharvest insect control treatment in ripening
bananas.
