Local Root Crops as Antioxidants

Assessment of antioxidant activities of some local root crops in the Philippines by researchers from the University of the Philippines Diliman reveals that the phenolic content of sweet potato has the highest antioxidant property among the local root crops studied.

Phytochemicals are non-nutritive plant chemicals that have protective properties against diseases. Some phytochemicals have antioxidant properties which protect cells from free radicals—harmful unstable molecules that damage cells and contribute to aging and diseases including cancer. Common antioxidants like ascorbic acid, carotenoids, and phenolic compounds are substances in fruits and vegetables which can help reduce the incidence of age-related degenerative diseases such as cancer, cardiovascular disease, cataracts, and brain and immune dysfunction (Ames, Shigenaga and Hagen, 1993; Liu, 2004; Scalbert and Williamson, 2000; Eastwood, 1999; Zino et al., 1997; Ness and Powles, 1997). However, results of clinical trials done to assess the efficacy of antioxidants including vitamin C, vitamin E, and β-carotene against free radicals are rather inconclusive (Wu et al., 2004; Halvorsen et al., 2002). Prof. Rowena Grace O. Rumbaoa and Ms. Djanna F. Cornago of the College of Home Economics conducted a study entitled Evaluation of Antioxidant Activities of Some Local Rootcrops (2006) to determine if phenolic compounds in these agricultural products have antioxidant activity. They used root crops that are commonly consumed as food in the Philippines.

In the study, the researchers screened the phenolic content of different varieties of root crops cultivated in the Philippines: purple yam or ubi (Dioscorea alata), lesser yam or tugui (Dioscorea esculenta), potato (Solanum tuberosum), sweet potato or kamote (Ipomoea batatas), cassava (Manihot esculenta), taro or gabi (Colocasia esculenta), carrot (Daucus carota) and yacon (Smallanthus sonchifolius). Through in vitro [1] evaluation of the root crop extracts, it was found out that root crops are rich sources of phenolic compounds. Analyzing the antioxidant properties of the root crop extracts also revealed significant antioxidant activity compared to α-tocopherol, or commonly known as vitamin E. The root crop with the highest antioxidant activity was sweet potato, followed by taro, potato and purple yam while the lowest antioxidant activity was obtained from carrot. Although carrot contains carotenoids, a known antioxidant, its mechanism of action is different from the assay used in their study.

This study provides baseline data for future clinical trials, commercial applications, and studies on production processes and food processing. For future applications of the results of this study, researchers Rumbaoa and Cornago recommend that genotype, growth conditions, sample preparation and extraction of root crops must be considered in determining the desirable amount of phenolic content and antioxidant property. Also, for applications to future clinical studies, results of the study must be supported with bioavailability [2] data and antioxidant activity in vivo [3].

Rowena Grace O. Rumbaoa is an assistant professor at the Department of Food Science and Nutrition, College of Home Economics in the University of the Philippines Diliman. She teaches Food Chemistry and Analysis, Food Packaging, Food Processing, and Principles of Food Preparation. She is currently involved in a research on the nutrient fortification of aseptically processed fruit and vegetable juice blends.

Djanna F. Cornago is also a faculty member at the Department of Food and Science and Nutrition in U.P. Diliman. She is currently handling courses on General Microbiology, Food Microbiology, and Food Hygiene and Sanitation. Her research interests include microbial and chemical food safety and postharvest handling of food.

[1] In vitro is an experimental situation outside the organism. It is a biological or chemical work done in the test tube (in vitro is Latin for "in glass") rather than in living systems.
[2] Bioavailability is the degree and rate at which a substance (as a drug) is absorbed into a living system or is made available at the site of physiological activity.
[3] In vivo means in the living body of a plant or animal.

Published: 23 Jul 2008

Contact details:

University of the Philippines-Office of the Vice Chancellor for Research and Development LGF Phivolcs Bldg., C.P. Garcia Ave., University of the Philippines, Diliman, Quezon City

(632) 927-2567; (632) 927-2309
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Research Folio, The Electronic Newsletter of UP-OVCRD