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Thermal Stability of Ascorbic Acid and Ascorbic Acid Oxidase in African Cowpea Leaves ( Vigna unguiculata ) of Different Maturities.
MedLine Citation:
PMID:  21309563     Owner:  NLM     Status:  Publisher    
Abstract/OtherAbstract:
Cowpea, an African leafy vegetable ( Vigna unguiculata ), contains a high level of vitamin C. The leaves harvested at 4-9 weeks are highly prone to vitamin C losses during handling and processing. Therefore, the purpose of this research was to study the effect of thermal treatment on the stability of ascorbic acid oxidase (AAO), total vitamin C content (l-ascorbic acid, l-AA), and dehydroascorbic acid (DHAA) and l-AA/DHAA ratio in cowpea leaves harvested at different maturities (4, 6, and 8 weeks old). The results showed that AAO activity, total vitamin C content, and l-AA/DHAA ratio in cowpea leaves increased with increasing maturity (up to 8 weeks). Eight-week-old leaves were the best source of total vitamin C and showed a high ratio of l-AA/DHAA (4:1). Thermal inactivation of AAO followed first-order reaction kinetics. Heating at temperatures above 90 °C for short times resulted in a complete AAO inactivation, resulting in a protective effect of l-AA toward enzyme-catalyzed oxidation. Total vitamin C in young leaves (harvested at 4 and 6 weeks) was predominantly in the form of DHAA, and therefore temperature treatment at 30-90 °C for 10 min decreased the total vitamin C content, whereas total vitamin C in 8-week-old cowpea leaves was more than 80% in the form of l-AA, so that a high retention of the total vitamin C can be obtained even after heating and/or reheating (30-90 °C for 10 min) before consumption. The results indicated that the stability of total vitamin C in situ was strongly dependent on the plant maturity stage and the processing conditions applied.
Authors:
Michael Wawire; Indrawati Oey; Francis Mathooko; Charles Njoroge; Douglas Shitanda; Marc Hendrickx
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Publication Detail:
Type:  JOURNAL ARTICLE     Date:  2011-2-10
Journal Detail:
Title:  Journal of agricultural and food chemistry     Volume:  -     ISSN:  1520-5118     ISO Abbreviation:  -     Publication Date:  2011 Feb 
Date Detail:
Created Date:  2011-2-11     Completed Date:  -     Revised Date:  -    
Medline Journal Info:
Nlm Unique ID:  0374755     Medline TA:  J Agric Food Chem     Country:  -    
Other Details:
Languages:  ENG     Pagination:  -     Citation Subset:  -    
Affiliation:
Department of Food Science and Technology, South Eastern University College , P.O. Box 170, Kitui 90200, Kenya.
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