Thermal Stability of Ascorbic Acid and Ascorbic Acid Oxidase in African Cowpea Leaves ( Vigna unguiculata ) of Different Maturities.
Summary of "Thermal Stability of Ascorbic Acid and Ascorbic Acid Oxidase in African Cowpea Leaves ( Vigna unguiculata ) of Different Maturities."
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.
Affiliation
Department of Food Science and Technology, Faculty of Agriculture, Jomo-Kenyatta University of Agriculture and Technology, P.O. Box 62000, Nairobi 00200, Kenya.
Journal Details
This article was published in the following journal.
Name: Journal of agricultural and food chemistry
ISSN: 1520-5118
Pages: 1774-83
Links
- PubMed Source: http://www.ncbi.nlm.nih.gov/pubmed/21309563
- DOI: http://dx.doi.org/10.1021/jf103469n
Medical and Biotech [MESH] Definitions
Ascorbic Acid Deficiency
A condition due to a dietary deficiency of ascorbic acid (vitamin C), characterized by malaise, lethargy, and weakness. As the disease progresses, joints, muscles, and subcutaneous tissues may become the sites of hemorrhage. Ascorbic acid deficiency frequently develops into SCURVY in young children fed unsupplemented cow's milk exclusively during their first year. It develops also commonly in chronic alcoholism. (Cecil Textbook of Medicine, 19th ed, p1177)
Ascorbate Oxidase
An enzyme that converts ascorbic acid to dehydroascorbic acid. EC 1.10.3.3.
Ascorbic Acid
A six carbon compound related to glucose. It is found naturally in citrus fruits and many vegetables. Ascorbic acid is an essential nutrient in human diets, and necessary to maintain connective tissue and bone. Its biologically active form, vitamin C, functions as a reducing agent and coenzyme in several metabolic pathways. Vitamin C is considered an antioxidant.
L-gulonolactone Oxidase
An enzyme involved in the metabolism of ASCORBIC ACID and aldarate. It catalyzes the oxidation of L-gulono-1,4-lactone to L-xylo-hex-3-ulonolactone.
2,3-diketogulonic Acid
Metabolite of ASCORBIC ACID and the oxidized form of the lactone DEHYDROASCORBIC ACID.
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