Correlation between Some Nutritional Components and the Total Antioxidant Capacity Measured with Six Different Assays in Eight Horticultural Crops RENE D. CORRAL-AGUAYO, †,‡ ELHADI M. YAHIA,* ,† ARMANDO CARRILLO-LOPEZ, ‡ AND GUSTAVO GONZ ´ ALEZ-AGUILAR § Facultad de Ciencias Naturales, Universidad Auto ´noma de Quere ´taro, Juriquilla, Quere ´taro 76230, Mexico, Maestrı ´a en Ciencia y Tecnologı ´a de Alimentos, Facultad de Ciencias Quı ´mico-Biolo ´gicas, Universidad Auto ´noma de Sinaloa, Culiaca ´n, Sinaloa, Mexico, and Centro de Investigacio ´n en Alimentacio ´n y Desarrollo, Hermosillo, Sonora, Mexico The contents of antioxidant nutritional compounds, total soluble phenolics (TSP), vitamin C, vitamin E, -carotene, and total carotenoids (TC), were correlated with the total antioxidant capacity (AOC) of hydrophilic (HPE) and lipophilic extracts (LPE) from eight horticultural crops, namely, guava, avocado, black sapote, mango, papaya, prickly pear fruit, cladodes, and strawberry. AOC was measured using six different assays: 2,2′-diphenyl-1-picrylhydrazyl (DPPH), N,N-dimethyl-p-phe- nylendiamine (DMPD), ferric-ion-reducing antioxidant power (FRAP), oxygen radical absorbance capacity (ORAC), Trolox equivalent antioxidant capacity (TEAC), and total oxidant scavenging capacity (TOSC). AOC values from HPE were about 95 times higher than LPE values. HPE of guava had the highest AOC value when evaluated with DMPD, DPPH, FRAP, TEAC, and TOSC assays, whereas with ORAC assay, black sapote had the highest value. HPE of papaya and prickly pear fruit presented the lowest AOC values with all assays. From HPE, vitamin C and TSP contents were highly correlated with AOC for all assays, while from LPE, TC and -carotene contents possessed a high correlation with AOC only in the DMPD assay. KEYWORDS: Antioxidant capacity; fruits; vegetables; carotenoids; vitamin C; vitamin E; total soluble phenolics; tocopherol; ascorbic acid INTRODUCTION Several clinical and epidemiological studies have shown that the consumption of natural antioxidant-rich foods, such as fruits and vegetables, are beneficial to health because of their capacity to prevent some health problems, such as heart diseases and cancer, cataracts, macular degeneration, and neurological diseases (1, 2). The beneficial effects of plant foods are attributed to their high content of antioxidant compounds that diminish the free-radical oxidative stress, which is responsible for cellular damage (3). However, there is a lack of information regarding the bioactive compounds content and antioxidant capacity (AOC) of fruits cultivated in the tropics. Different studies have demonstrated that the individual contribution of the bioactive compounds to AOC varies with the type and concentration present in the tissue (4). Various methods have been developed to measure the AOC of fruits and vegetables, but results usually vary depending upon the type of product and method used (5). There is still a lack of information on the appropriate method(s) that need to be used for different products. For this reason, it is recommended that at least two different methods be used to measure AOC in any given sample. In this study, the content of antioxidants, such as total soluble phenolics (TSP), vitamin C, vitamin E, -carotene, and total carotenoids (TC), in eight horticultural crops (avocado, black sapote, guava, mango, papaya, prickly pear fruit, cladodes, and strawberries) were correlated with the AOC of hydrophilic (HPE) and lipophilic extracts (LPE) being measured using six different antioxidant assays. MATERIALS AND METHODS Chemicals and Solvents. Reagents were obtained from Sigma- Aldrich (St. Louis, MO), unless stated otherwise, and standard purity was 97% for -carotene and 95 and 90% for R- and δ-tocopherol, respectively. High-performance liquid chromatography (HPLC)-grade methanol, acetone, n-hexane, and ethanol were purchased from J.T. Baker (Baker Mallinckrodt, Mexico). HPLC-grade water was prepared by a Milli-Qplus purification system (Millipore Corp., Bedford, MA). Materials. About 3-5 kg (depending upon the fruit size) each of eight horticultural crops were selected on the basis of ripeness, freedom of damage, and uniformity of size and color. These were strawberries (Fragaria ananassa L. cv Sweet Charlie), guava (Psidium guajaVa L. cv Media China), mango (Mangifera indica L. cv Ataulfo), papaya (Carica papaya cv Maradol), prickly pear fruit (Opuntia ficus-indica M. cv Reina), prickly pear cladodes, known in Mexico as “nopal” (Opuntia ficus-indica M. cv Milpa Alta), avocado (Persea americana * To whom correspondence should be addressed. Telephone: +52- 442-1921200, ext. 5354. Fax: +52-442-2342951. E-mail: yahia@uaq.mx. † Universidad Auto ´noma de Quere ´taro. ‡ Universidad Auto ´noma de Sinaloa. § Centro de Investigacio ´n en Alimentacio ´n y Desarrollo. 10498 J. Agric. Food Chem. 2008, 56, 10498–10504 10.1021/jf801983r CCC: $40.75  2008 American Chemical Society Published on Web 10/29/2008