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ARS Home » Research » Publications at this Location » Publication #92233
Title: THE NATURE OF THE TARO ACRIDITY FACTOR

Author
item PAULL, ROBERT - UNIVERSITY OF HAWAII
item TANG, CHUNG-SHIH - UNIVERSITY OF HAWAII
item Gross, Kenneth
item URUU, GAIL - UNIVERSITY OF HAWAII

Submitted to: Postharvest Biology and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/3/1998
Publication Date: N/A
Citation: N/A

Interpretive Summary: Edible aroids, such as taro and related Araceae species, contain an active principle confers acridity on all parts of the plant. This acridity limits the use of fresh taro corms and leaves by humans and animals. Estimates of losses because of acridity have ranged up to one half of the biomass and represents a considerable loss in the use of this major tropical crop. The cause of this acridity is unknown, but two major explanations have been proposed; needle-like calcium oxalate raphides and one or more "chemical" irritants possibly on the surface of the raphides. The preponderance of evidence now supports the "chemical" irritant hypothesis. The need to rely on a bioassay to determine acridity using animals and human volunteers is unreliable and does not allow ready isolation and purification to determine the chemical nature of the acridity factor. These bioassays show considerable variability between subjects associated with differences in sensitivity. Thus, the objectives of this project were to determine the nature of the chemical irritants causing acridity. Users of these results will be other scientists involved in attempting to reduce the level of acridity and therefore loss in use of taro and other tropical crops.

Technical Abstract: The acridity in Araceae species was not apparently due to the calcium oxalate raphides. Some irritant on the raphide surface caused the acridity, with the raphides apparently functioning to carry the acridity factor. Methanol and methylene chloride extracts from purified raphides did not show any compounds in gas chromatography/mass spectrometry analysis that could be regarded as acrid. The data suggested that a 26 kD protein, possibly a cysteine proteinase, was the active factor. There were a few other uncharacterized protein bands associated w3ith the raphides that could also be involved. Some amino acid sequence data for the 26kD protein was obtained.