Antioxidant activity and polyphenol content in cultivated and wild edible fruits grown in Panama.

OBJECTIVES: The present research was undertaken to determine the antioxidant activity and total polyphenol content of cultivated and wild edible fruits consumed in Panama.
MATERIALS AND METHODS: 39 cultivated and wild edible fruits antioxidant activity and total polyphenol content was assessed by using the DPPH and the Folin-Ciocalteu assays, respectively. RESULTS AND DISCUSSION: The antioxidant composition of the fruits varied between 1083.33 and 16.22 mg TEAC/100 g fresh weight. On the other hand, the total phenolic content of the 39 fruits tested ranged from 604.80 to 35.10 mg GAE/100 g FW. Ziziphus mauritania presented the highest antioxidant activity and the largest phenolic content, whereas most fruits had a moderate TEAC value.
CONCLUSION: Fruits polyphenol content was strongly correlated with antioxidant properties, which pointed out the important role of these compounds in the prevention of many types of cancer, neurological ailments, and cardiovascular diseases through diverse antioxidant mechanisms.

Free radicals are very reactive chemical species that are produced as part of the normal cell metabolism, yet environmental factors such as pollutants, tobacco smoke, and UV radiation can yield these substances as well. Overproduction of these and others pro-oxidants can cause, under certain conditions, damage to biomolecules such as DNA, lipids, proteins, and carbohydrates, leading to health impairments.[1-3] Epidemiological studies suggest that a high intake of fruits reduces the risk of some types of cancer and prevents heart pathologies and Alzheimer's disease, owing to their high content in bioactive antioxidants such as polyphenols, vitamin C, and carotenoids, which limit the available oxidation potential.[3-5] Antioxidant protection in the cell includes scavenging reactive oxygen species, chelation of trace elements involved in free radical production, inhibition of enzymes that form reactive substances, and regulation of antioxidant defense.[6] Polyphenols such as flavonoids, phenolic acids, coumarines, stilbenes, tannins, and anthocyanins are ubiquitous secondary metabolites present in plants that serve as protection against biotic and abiotic stresses such as UV radiation, fungal infection, extreme temperatures, parasites, and other pathogens.[78] Research on these compounds in the last years has awakened a substantial interest in their anti-mutagenic, anti-carcinogenic, neuro-protective, and cardioprotective characteristics. Benefits were associated not only with antioxidant capacity per se, but to their ability to regulate gene transcription of antioxidant enzymes linked to mediation of oxidative stress, inhibition of signaling molecules and genes that modulate inflammatory pathways, and regulation of angiogenesis and cell proliferation.[9-14]

Phenolic distribution in fruits is large and varies depending on growing conditions, cultivars, climate, geography, and ripening. The distribution of poliphenolic compounds is different in the seed, peel, and edible part of the fruit.[15-17] Panama is a country that is under the influence of a tropical climate that favors the presence of an important variety of fruits. There are no reports regarding the antioxidant potential and polyphenol content of fruits consumed in Panama. In the present study, the antioxidant activity and total polyphenol content of cultivated and wild edible fruits were assessed by using the 2,2-diphenyl-1-picylhydrazyl (DPPH·) assay and the Folin-Ciocalteu method, respectively. An assessment of the correlation between the antioxidant activity of the fruits and total polyphenol and vitamin C content was performed.

Materials and Methods

Chemicals

Folin-Ciocalteu's reagent, trolox (6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxilic acid), DPPH (2,2-diphenyl-1-picylhydrazyl), trolox (6-hydroxy-2,5,7,8-tetramethylchroman-2 carboxylic acid), gallic acid, and ascorbic acid were purchased from Sigma Chemical Co. (St. Louis, MO). All other reagents used were of analytical grade.

Fruit samples

39 completely ripened fruits were collected during the fruit-bearing season. Surface color and firmness of the fruits were used as criteria for selecting the samples. Fruits were classified in 2 categories depending on plant domestication: Cultivated and wild edible fruits. Cultivated fruits were obtained from the central market of Panama City, Panama, and wild edible fruits were harvested from their fruit tree. After the fruits were cleaned with tap water, edible portions were cut and analyzed.

Extraction

The edible part of the each fruit (10 g) was homogenized using a blender for approximately 2 min. Homogenized samples were then placed in an Erlenmeyer flask and extracted at room temperature with 40 ml of methanol for 1 h by using an orbital shaker. The extracts were filtered through a filter paper under suction. The residue was re-extracted and filtered. The fruit extract was then used for the different assays. All samples were assayed immediately in triplicate.

Measurement of antioxidant activity

Antioxidant activity of the fruit extracts was measured according to the method described by Lamaison et al.,[18] namely by measuring the reduction of the colored free radical DPPH· in the presence of the fruit extract at 517 nm. A calibration curve was computed by using trolox, and the total antioxidant activity was expressed as mg trolox per 100 g of fresh fruit weight (mg TEAC/100 g FW).

Analysis of total phenolic content

Total phenolics were estimated from the fruits extracts spectrophotometrically as described by Singleton and Rossi.[19] Developed blue color was read at 750 nm with gallic acid serving as standard. Phenolic content was expressed as gallic acid equivalent per 100 g of fresh weight (mg GAE/100 g FW).

Vitamin C analysis

A tritrimetric method was used for determination of vitamin C content in certain fruit extracts by using the 2,6-dichloroindophenol as indicator.[20] Results were expressed as mg ascorbic acid, equivalents per 100 g of fresh weight (mg AA/ 100 g FW).

Results and Discussion

There have been reports in the scientific literature of a strong relation between a regular intake of fruits and a reduced risk of various pathologies such as cardiovascular diseases, cancer, and neurological impairment.[21-23] Oxidative stress, i.e. disequilibrium between the body antioxidant defense system and the generation of radical species, has been linked largely to these ailments. Fruits contain phytochemicals that possess known antioxidant activity such as polyphenols and vitamin C, which can reinforce the body antioxidant defense response by using different mechanisms such as scavenging deleterious free radicals from susceptible cells and tissues. Consequently, the antioxidant activity of a fruit is a significant parameter to take into account for establishing its nutritional value.[24] The present study provided novel data on fruits grown in Central America.

DPPH radical-scavenging assay measures the ability of an antioxidant to react with DPPH· radicals generated in the experimental milieu. This assay was used to assess and compare the scavenging activity of extracts of 39 tropical fresh fruits harvested in Panama, 7 of which are not domesticated fruits, i.e. caimito (Chrysophyllum cainito), guava (Inga edulis), algarrobo (Hymenaea coubaril), nance (Byrsonima crassifolia), jobo (Spondias mombin), jagua (Genipa americana), and toreta (Anona purpurea). Table 1 summarizes the fruits surveyed, their antioxidant activity reported as trolox antioxidant capacity (TEAC), and the total phenolic content. Of the 39 fruits studied, guinda (Ziziphus mauritania), soursop (Annona muricata), and coffe plum (Flacourtia jangomas) exhibited the highest antioxidant capacity (1083.33, 975.00, 928.57, and 928.27 mg TEAC/100 g FW, respectively). On the other hand, avocado (Persea americana) and toreta (Anona purpurea) presented very low antioxidant activity (17.00 and 16.00 mg TEAC/100 g FW). In this research, tree tomato showed a very similar TEAC as guava, which may be due to the possibility that at their physiological maturity (determined by subjective criteria such as their characteristic aroma, taste, and color), both fruits held compounds that altogether make up similar antioxidant activity. In the present study, undomesticated fruits showed a moderate radical scavenging capacity, yet Chrysophyllum cainito showed a remarkable high antioxidant capacity (886.36 mgTE C/100 g FW).

Table 1

The total phenolic content and TEAC of Panamanian tropical fruits (based on fresh weight)

Ikram et al.[25] studied the antioxidant activity of underutilized Malaysian fruits, and found that Ziziphus mauritania had a moderate antioxidant activity compared to our results. Our results regarding the high antioxidant properties of Psidium guajava (780.00 mgTEAC/100 g FW) edible pulp is consistent with surveys conducted in fruits harvested in Mauritius,[26] the United States,[27] and India,[28] all of which confirm this fruit's substantial nutritional value.

Polyphenols determine central fruits quality properties such as color, taste, and nutritional value.[29] Epidemiological research has established an association between the high consumption of fruit polyphenols and a reduced risk of certain kinds of cancer and cardiovascular ailments.[930] These compounds exert their protective bioactivity due to their antioxidant capacity. Polyphenols can end hazardous free radicals propagation, which causes cell lipid peroxidation by transferring an electron equivalent to radicals. In spite of the role these substances play in health maintenance, they are neglected in most food composition surveys. Extensive reports can be found in the literature regarding polyphenols in fruits from non-tropical regions; nevertheless, there is a lack of a comprehensive investigation on polyphenols contained in fruits from tropical areas of the world, mainly Central America, despite the wide variety of exotic fruits that are consumed by their populations. Bearing this in mind, we evaluated the total polyphenols contained in fruits harvested and most commonly consumed in Panama, by using the Folin-Ciocalteu's reagent, and correlated this information with the antioxidant activities of the extracts obtained from each assayed fruit.

The total phenolic content of the 39 fruits tested are presented in Table 1, ranging from 604.80 to 35.10 mg GAE/100 g FW. The largest concentration of polyphenols were found in Ziziphus mauritiana, followed in order by Hibiscus sabdariffa, Annona cherimola, Chrysophyllum cainito, Flacourtia jangomas, and Annona muricata (more than 400 mg GAE/100 g FW). On the other hand, Genipa americana, Musa balbisiana, Anona purpurea, Persea Americana, and Bactris gasipaes showed the lowest polyphenol content. Most of the fruits analyzed possess a moderate phenolic concentration (between 90 and 400 mg GAE/100 g FW). Comprehensive studies have been carried out to study the antioxidant capacity and polyphenol content of common and underutilized tropical fruits harvested in Asia,[2531] showing substantial differences when the same fruits are compared with the Panamanian species. This variability may be due to different growing conditions, cultivars, climate, geography, and maturation stage.

Mahattanatawee et al.[27] reported decreasing total phenolic content values for Psidium guajava > Averrhoa carambola > Pouteria sapota > Manguifera indica > and Carica papaya, in fruits grown in the United States. On the other hand, 7 fresh fruits commonly consumed in Brazil were assessed for their polyphenolic content, 3 of which, i.e. Psidium guajava > Averrhoa carambola > Ananas comosus, were included in the present study as well.[32] When considering the total polyphenol content of fruits grown in Panama, a similar trend emerges, excepting for Manguifera indica.

In order to determine the influence of polyphenols contained in fruits grown in Panama on the overall antioxidant activity, the correlation between these 2 factors was evaluated [Figure 1]. A strong relationship was found [r(37) = 0.89, P < 0.001] between polyphenol compounds and fruits’ antioxidant properties, a finding that is in agreement with previous studies on tropical and non-tropical fruits.[2633] As far as we know, this is the first report of the total phenolic content and antioxidant activity that includes such ample variety of tropical fruits (common and uncommon edible fruits) cultivated in the American Continent. The DPPH radical scavenging method employed in the present study is one way to measure the antioxidant capacity of polyphenol extracts. The following step is to test other mechanisms by which the fruits′ polyphenol extracts exert their antioxidant activity by using different in vitro methods such as superoxide anion scavenging assay, singlet oxygen assay, and the potassium ferricyanide reducing method. We are currently developing these methods in our laboratory.

Figure 1

Correlation between TEAC and total phenolic compounds of 39 fruits of Panama

Vitamin C (ascorbic acid) is an important biochemical compound contained in many fruits and mainly in citrus that has a remarkable nutritional value and known antioxidant properties. Vitamin C content was quantified in 20 fruits [Table 2]. The amount of vitamin C present in the samples varied between 1.45 and 213 mg ascorbic acid/100 g FW. Observing the vitamin C contents, Psidium guajava and Morinda citrifolia had the highest amounts (>100 mg ascorbic acid/100 g FW), while the lowest quantity was found in Solanum quitoense, Manguifera indica, Hibiscus sabdariffa, Passiflora edulis, Ananas comosus, Musa sapientum, Manilkara zapota, and Annona muricata (<10 mg ascorbic acid/100 g FW). Most of the fruits had a moderate concentration of this nutrient (between 100 and 10 mg ascorbic acid/100 g FW). When considering the influence of vitamin C on the antioxidant activity of the fruits, vitamin C has a negligible influence [r(18) = 0.32, n.s.] upon the overall antioxidant properties of the fruits [Figure 2], which is consistent with previous observations.[262731]

Table 2

Vitamin C content of fruits surveyed (based on fresh weight)

Figure 2

Assessment of the effect of vitamin C content on the antioxidant activity of 20 Panamanian tropical fruits

Conclusions

The present research provides, for the first time, a comprehensive report on the antioxidant activity and total polyphenol content of 39 fruits that are part of the Panamanian diet. Most of the fruits contained between a moderate and large antioxidant activity and polyphenol content, with a strong correlation between these 2 parameters, indicating that polyphenols presented in the fruits, are strongly associated with their antioxidant activity. When considering the contribution of fruits in the prevention of cardiovascular diseases, many types of cancer, and neurological disorders, such as Alzheimer's and Parkinson disease, the important role that polyphenols play in the antioxidant mechanism of prevention of these ailments should be stressed.Our results can be used in epidemiologic surveys regarding the intake of polyphenolic antioxidants that foster healthy living conditions in the Panamanian population.