Effects of Short-term Exposure to Low Oxygen Atmospheres on Phsyiological Responses of Sweetpotato Roots

Abstract

Sweetpotato roots were stored under a continuous flow of 0% or 1% O 2 (balance N 2 ) or air for 7 days at 20°C to study the effects of short-term exposure to low O 2 on their physiological responses and quality. During the course of the experiment, no visible signs of injury or decay were observed. However, low O 2 treatments increased the soluble solid content and weak off-odors were detected by olfactory evaluation in roots stored at 0% O 2 . The intensity of off-odors increased as the concentrations of acetaldehyde and ethanol increased in roots during storage. Ethanol concentrations were higher than those of acetaldehyde, which remained low during storage in 1% O 2 and air, but increased greatly in roots stored at 0% O 2 . Pyruvate decarboxylase (PDC) activities in roots exposed to 0% or 1% O 2 increased by 3.1-and 2-fold respectively over levels in roots stored in air by day 7. Alcohol dehydrogenase (ADH) activities in roots exposed to 0% or 1% O 2 increased by 1.6-and 1.7-fold respectively over levels in roots stored in air by day 7. ADH-specific activity was about 10-times that of PDC. The pH of root homogenate exposed to air remained constant, whereas the pH increased and decreased, respectively, in roots stored at 0% or 1% O 2 . PDC showed stability over the pH range 5.5-7.0, whereas ADH exhibited stability over the pH range 6.0-7.5. The Km of PDC in sweetpotato was 0.56 mM for pyruvate, whereas the Km of ADH was 0.19 mM for acetaldehyde. From these results, there may be some potential for the short-term exposure of sweetpotato roots to low O 2 in place of low temperature treatment to prolong shelf-life, although ethanol fermentation may be accelerated under low O 2 atmospheres.