Nutrient Composition and Antioxidant Property ofPhilippine Indigenous Vegetables

Ilda G. Borlongan

ABSTRACT

This study determined the nutrient profile and the anti-oxidant property of edibleportions of 20 indigenous vegetables commonly consumed in the Philippines. The studyconcludes that most of the vegetables are important sources of carbohydrates, proteins,fiber, minerals and fats. The vegetables contain minerals (Ca, P and Fe) that can supply ourdaily micronutrient needs and possess an appreciable amount of anti-oxidant activity thatcan fight against many of the diseases as nutriceuticals.

On the dry weight basis, the protein contents of the vegetables range between 18.4to 35.4 % with okra having the lowest and jute (saluyot) having the highest. The crude fatcontents range from 0.11 to 8.5 % with okra having the lowest value and malunggay havingthe highest. For fiber contents, the values range from 6 to 11.5 % with taro (gabi) having thehighest value. The digestible carbohydrate (NFE) contents of the vegetables are relativelyhigher in comparison with other nutrients. They range from 38 to 64%. The highest value isfrom okra and the least in malunggay and gabi. The ash contents range from 5% to 18 %with kolitis having the highest ash content and cowpea (paayap) and pigeon pea (kadyos)have lowest ash contents. The moisture or water contents of the edible portion are high at(68 to 92.5%) leaving the dry matter contents at 7.5 to 32%. Alugbati has the highestmoisture content and therefore the lowest dry matter content. Cowpea and pigeon peahave the highest dry matter content. On a percent fresh weight basis, cowpea, pigeon peaand malunggay have the highest protein contents while okra and alugbati have the least.Results also reveal that malunggay has the highest crude fat content. Among the leafyvegetable samples, malunggay has the highest fiber content while among the fruit or podsamples, kadyos has the highest fiber. The digestible carbohydrates are highest in kamotetops, malunggay and apat-apat among the leafy vegetables while among vegetable podsamples, highest digestible carbohydrates contents are found in kadyos and cowpea.Percent ash or mineral contents are highest in malunggay, kolitis with spine, violet lupo andampalaya tops. As to the specific minerals, calcium (Ca) contents range from 103 to 2977mg/ 100g dry weight with malunggay having the highest and kadyos the least. Phosphorus(P) contents range from 320 to 610 mg/100g dry weight with apat-apat having the highestcontent. Iron (Fe) contents range from 7.15 to 101 mg/ 100g dry weight with jute (saluyot)having the highest value and okra the lowest.

The antioxidant properties of the different indigenous vegetables measured aspercent free radical scavenging activity and total polyphenolics are relatively high. Theantioxidant activities of all raw leafy vegetables and okra (75.7 to 92%) are higher thanthose of the blanched (64 to 83.4%) and boiled (59 to 80.1%) counterparts. This indicatesthat blanching and boiling greatly influence the loss of antioxidant components in leafyvegetables. Blanching decreases the activity from 5 to 15% while boiling decreases theactivity by 10 to 25%. For the vegetable pods, no significant differences in anti-oxidant

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activities are observed in the raw, blanched and boiled samples indicating that blanchingand boiling do not affect the anti-oxidant property of these vegetables.

Processing affects content, activity and bioavailability of bioactive compounds andtherefore health promoting capacity of vegetables depends on their processing history. Thisaspect should be strictly considered to obtain the optimum nutriceutical benefits fromthese vegetables.

The findings on the nutriceutical importance of these indigenous vegetables tohumans should provide a motivation for exploring their horticultural potential.

Key words: indigenous vegetables, nutrient composition, anti-oxidant property,nutriceuticals, free radical scavenging activity, polyphenolics

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INTRODUCTION

Background and Rationale

Vegetables are important items of diets in many Filipino homes and they arevaluable sources of nutrients specially in rural areas where they contribute substantially toprotein, minerals, fiber, vitamins and other nutrients (FAO, 1988; Flyman & Afolayan, 2006;Modi, et al., 2006). They add flavor, variety, taste, color and aesthetic appeal to diet.Scarcity of vegetables in the diet is a major cause of vitamin deficiency which causesmalnutrition to young children.

Indigenous vegetables can play a major role in the diversification of Filipino dietleading t a more balanced source of micronutrients. Studies have shown that thediversification of diets increases nutritional requirement intake (Hoe & Siong, 1999; Huang,et al, 2009). According to World Indigenous Vegetable (2006), although the production ofindigenous vegetables is challenged by the extensive cultivation of high-value commercialvegetables, the value and desirable traits of indigenous vegetables are comparable andsometimes better than the commercial varieties. These vegetables are well-adapted toharsh climatic conditions and disease infection and easier to grow in comparison to theirexotic counterparts. Indigenous vegetables generally have short growth period, with mostof them being ready for harvest within 1-4 weeks. They can also do well underintercropping and therefore are suitable as cash crops, source of daily sustenance, newcrops and variations to diversify production systems and diets. Furthermore, because mostof them have not been intensively selected, they have a wide genetic base.

Recent development in biomedicals point to the involvement of free radicals inmany diseases such as cancer, rheumatoid arthritis, and cardiovascular diseases (Hertog, etal., 1997; Gropper et al., 2005). Antioxidants can prevent undesirable oxidation process byreacting with free radicals, chelating free catalytic metals and also by acting as O2

scavengers (Whitney, et al., 2002). In addition, it has been suggested that there is aninverse relationship between dietary intake of antioxidant rich foods and the incidence ofhuman disease (Yen & Chen, 1995; Rice-Evans, et al., 1997; McCord, 2000; Jayaprakasha, etal., 2001).

The search for natural antioxidants, specially of plant origin, had increased greatly inrecent years. Natural antioxidants can be phenolic compounds (flavonoids, phenolic acidsand tannins); nitrogen containing compounds (alkaloids, chlorophyll, derivative amino acidsand peptides); carotenoids, tocopherols) or ascorbic acids and its derivatives (Yi-Fang, etal., 2002; Dell-Agli, et al., 2004; Soorbrattee, et al., 2005; Middleton, et al., 2000; Huang, etal., 2009 ). The awareness on the significance of nutrition in health has resulted to anincreasing quest for biochemical knowledge of the composition of foods. The present studywas conducted to evaluate the nutriceutical values of indigenous vegetables commonlyconsumed in the Philippines.

The study also looked into the effect of different food preparations on the anti-oxidant property of the vegetables. This is of great importance considering that only a small

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amount of vegetables are consumed in the raw state, most need to be processed for safety,quality and taste. Most indigenous vegetables are cooked before being consumed.

Objectives of the Study:

This study was conducted to determine the nutrient composition and antioxidantproperty of Philippine indigenous vegetables.

Specifically, this study was done to:1. determine the nutritional composition of selected Philippine indigenous

vegetables. The nutrients determined included protein, fat, ash or mineral, fiber, anddigestible carbohydrates.

2. determine important minerals which included calcium, iron and phosphorus of thevarious indigenous vegetables.

3. determine the gross antioxidant activities (expressed as free radical scavenging andtotal phenolics) of the various vegetables.

4. assess the effect of different preparations (raw, blanched, and boiled) on the grossantioxidant activities of the selected vegetables.

MATERIALS AND METHODS

Plant Materials

The indigenous vegetables examined are presented in Table 1. These vegetableswere purchased fresh from local markets (Leon, Sta. Barbara, and Dingle, Iloilo), the placeswhere most of the supply of indigenous vegetables in Iloilo come from. Three samplings perlocation (February, May, August, 2012) were done.

The authentication of the vegetables identity was done by the Life ScienceDepartment of Central Philippine University.

Sample Preparation

Samples of the fresh vegetables were quickly washed in potable water to removeunwanted matter, allowed to drip dry and edible portions used in traditional cooking wereseparated and analyzed. The samples were separated into two and were used in wet anddry forms. The portions used in the wet form were cut into small pieces, kept in coolcondition and used immediately for the antioxidant activity assays. The other portionswhich were used in the dry form were weighed and placed in an air-convection oven for 6hours at 105oC to determine the moisture and dry matter contents of the samples. Thedried samples were ground, sieved to uniform sizes by passing through Sieve #60 and wereused for proximate analysis in triplicate per location.

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Chemical Analyses

Proximate AnalysisProximate compositions of the various plant samples were determined following the

Official Methods of Analysis (AOAC, 2000). Crude protein was obtained by determining theorganic nitrogen content of the sample using micro-Kjeldahl method and multiplying thenitrogen by a protein conversion factor of 6.25. Ash or mineral content determinationinvolved the incineration of each sample in a muffle furnace at 550oC for 12 hours. Crudefat determination was done by directly extracting with petroleum ether in an intermittentSoxhlet extractor (Soxtec, Germany) for 4 hours. Crude fiber content was estimated fromthe loss in weight of the samples on ignition after ashing, following the sequential hydrolysisof the sample with sulfuric acid and sodium hydroxide. The nitrogen-free extractrepresenting the digestible carbohydrate fraction was obtained by subtracting from 100,the sum of ash, crude protein, crude fat and crude fiber values on dry matter basis.

Calcium and iron were measured using Flame Atomic AbsorptionSpectrophotometer after acid digestion of the ashed samples. Phosphorus contents wereobtained by the molybdate blue pigment spectrophotometric assay at 800nm wavelength.

Extraction procedure for the antioxidant assay

Fresh edible portions were cut into small pieces. Ten-gram samples were soaked inmethanol at a sample to solvent ratio of 1:3 (w/v). The samples were homogenized for 10minutes and allowed to stand overnight. After which, the homogenates were filteredthrough Whatman No. 40 filter paper. The filtrates were collected and the residues werewashed with methanol until the total volume of filtrates and washings were 40 ml, so thatthe concentration of the extracts were 0.25g/ml. The extracts were used immediately forthe antioxidant assays.

The same extraction procedure was followed for the blanched, and boiled samplesafter prior treatments. For the blanched samples, the cut fresh (10g) edible portions weredipped in boiling water (30 ml) for 1 minute, allowed to drip and used for extraction. Theboiled samples were prepared by boiling the cut fresh samples in water for 5 min, allowedto drain and used for extraction.Antioxidant Activity Assays

Free radical scavenging activity assay

The free radical scavenging activity was assayed by the decolorization of themethanolic solution of DPPH (2,2, diphenyl-1-picrylhydrazyl) (Cheel, et al., 2005). Twomilliters of the extract and 2 ml of the methanolic solution of DPPH (0.1mM) were mixedand allowed to stand for 20 minutes. The absorbance was read using UV-Visspectrophotometer set at 517 nm wavelength. The absorbance of the blank which consisted

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of 2 ml methanol and 2ml DPPH solution was also read. Free- radical scavenging activity wasexpressed as the inhibition percentage and calculated using the formula:

Absorbance control – Absorbance sample

% radical scavenging activity = ------------------------------------------------------- x 100%Absorbance control

Total Phenolics Assay

Total phenolic compounds were measured with Folin-Ciocalteu reagents usingtannic acid as a standard (Maillard, et al., 1996). A 5 ml of Folin-Ciocalteu reagent (dilutedtenfold in distilled water), 2 ml of 200 g/L Na2CO3 and 2ml of distilled water were added to 1ml of the methanolic extract of vegetable samples and mixed. After 1 hr at 30oC, theabsorbance at 755 nm wavelength was read.

Statistical Analysis

Data collected were subjected to Analysis of Variance (ANOVA) and differencesamong the nutritional components and antioxidant activities of the various vegetables weredetermined by Duncan’s Multiple Range Test (DMRT) using SAS Statistical Package. P values± 0.05 were considered statistically significant.

RESULTS AND DISCUSSION

The nutrient profile of 20 indigenous vegetables commonly consumed in thePhilippines is presented in Figures 1 to 3). On the dry weight basis (Figure 1), the proteincontents of the vegetables ranged between 18.4 to 35.4 % with okra having the lowest andjute (saluyot) having the highest. According to Hassan and Umar (2006), plant food thatprovides 12% (dry basis) of its caloric value from protein is considered a good source ofprotein.

The crude fat contents ranged from 0.11 to 8.5 % with okra having the lowest valueand malunggay having the highest. Samples containing high fats are said to be morepalatable because dietary fats function to increase food palatability by absorbing andretaining flavors (Lindsay, 1996). A diet providing 1-2 % of its caloric energy as fat is said tobe sufficient to human beings (Davidson, et al, 1975).

For fiber contents, the value ranged from 6 to 11.5 % with taro (gabi) having thehighest value. High fiber contents in vegetables help in the digestion and prevention ofcolon cancer (Saldanha, 1995). High fiber foods are also employed in the treatment ofdiseases such as obesity, diabetes and gastrointestinal disorders (Agostoni, et al, 1995).

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The digestible carbohydrate (NFE) contents of the vegetables were relatively higherin comparison with other nutrients. They ranged from 38 to 64%. The highest value wasobtained in okra and the least in malunggay and gabi.

The ash content ranged from 5% to 18 % with kolitis having the highest ash contentand cowpea (paayap) and pigeon pea (kadyos) having lowest ash contents. The high ashcontent is an indication of the high mineral contents of the sample.

The moisture or water contents of the edible portion were high at (68 to 92.5%)leaving the dry matter contents at 7.5 to 32% (Figure 2). Alugbati had the highest moisturecontent and therefore the lowest dry matter content. Cowpea and pigeon pea had thehighest dry matter content. The high moisture contents reveal that these vegetables needcare for appropriate preservation as they are prone to deterioration. Figure 3 presents thenutrient composition expressed in g per 100g edible portion or % fresh weight. On a percentedible portion basis, cowpea, pigeon pea and malunggay had the highest protein contentswhile okra and alugbati had the least protein contents. Results also revealed thatmalunggay had the highest crude fat content. Among the leafy vegetable samples,malunggay had the highest fiber content while among the fruit or pod samples, kadyos hadthe highest fiber. The digestible carbohydrates are highest in kamote tops, malunggay andapat-apat among the leafy vegetables. Among the vegetable pod or fruit samples, highestdigestible carbohydrates contents were found in kadyos and cowpea. Percent ash ormineral contents were highest in malunggay, kolitis with spine, violet lupo and ampalayatops. Minerals are important in the diet because they serve as cofactors for manyphysiologic and metabolic functions.

As to the specific minerals (Figures 4 and 5), calcium (Ca) contents ranged from 103to 2977 mg/100g dry weight or 33 to 599 mg/100g edible portion with malunggay havingthe highest and kadyos the least. Phosphorus (P) contents ranged from 320 to 610 mg/100gdry weight with apat-apat having the highest content. Calcium and phosphorus areassociated with each other for the development and proper functioning of bones, teeth andmuscles. Deficiency of Ca can lead to malformation of bones in young children (Dosunmu,1997; Turan et al, 2003). Phosphorus is important in the energy transfer of nucleic acids.

Iron (Fe) contents ranged from 7.15 to 101 mg/100g dry weight or 0.7 to 15 mg/100g edible portion with jute (saluyot) having the highest value and okra the lowest. Iron isimportant in the formation of hemoglobin of the blood and very beneficial for anemicpersons.

The recommended daily allowance (RDA) (WHO/ FAO, 2007) for Ca and P are both800mg for children and adult and 1200mg for pregnant and nursing mother. For Fe, theRDAs are 10 mg for children and adult male; 15mg for adult female and nursing mother. Therelatively high contents of these micronutrients in most vegetables studied make them themuch needed cheap sources of these micronutrients.

The antioxidant properties of the different indigenous vegetables measured aspercent free radical scavenging activity is presented in Figure 6 and the values wererelatively high. The antioxidant activities of all raw leafy vegetables and okra (75.7 to 92%)were higher than those of the blanched (64 to 83.4%) and boiled (59 to 80.1%)counterparts. This indicates that blanching and boiling greatly influence the loss ofantioxidant components in leafy vegetables. Blanching decreased the activity from 5 to 15%

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while cooking decreased the activity by 10 to 25%. Similar results were observed by Yadavand Senegal (1995) and Amin, et al. (2005), where blanching and cooking greatly influencethe loss of antioxidant components in African leafy vegetables.

For the vegetable pods, no significant differences in anti-oxidant activities wereobserved in the raw, blanched and cooked samples indicating that blanching and cookingdid not affect the anti-oxidant property of these vegetables.

Dietary antioxidants which include polyphenolic compounds, Vitamin E, vitamin Cand carotenoids are effective nutrients in the prevention of oxidative stress related diseasessuch as inflammation, cardiovascular disease, cancer and aging-related disorder.

Most of the indigenous vegetables studied are excellent sources of antioxidativepolyphenolics (Figure 7). The total phenolics of all vegetables in the raw state are higherthan the blanched and cooked samples. For the raw vegetables, highest value was obtainedin malunggay and kamote tops [9 mg TAE (tannic acid equivalent)/100g edible portion] andlowest in alugbati (2.10 mg TAE/100g edible portion.

Phenolics are strong anti-oxidants which prevent oxidative damage to biomoleculesin humans such as DNA, lipids and proteins which play a role in chronic diseases such ascancer and cardiovascular diseases (Hollman, 2001). Phenolics are able to scavenge reactiveoxygen species due to their electron-donating properties. Phenolics range from simple, lowmolecular weight, single aromatic-ringed compounds to large and complex tannins andderived polyphenols. Phenolics include: tannins and flavonoids which includesanthocyanins, flavonols, hydroxycinnamic acid (Crozier, et. al., 2009; Pereira, et al., 2009).

CONCLUSIONS AND RECOMMENDATIONS

The present study has provided some comparative biochemical information on theproximate composition and gross anti-oxidant property of 20 indigenous vegetables. Theresults obtained from proximate analyses establish that they can be ranked ascarbohydrate- rich vegetables due to their relatively high content (38 to 64%) whencompared with the other components. The study concludes that most of the vegetables areimportant sources of proteins, fiber, minerals and fats. The vegetables contain anappreciable amount of calcium, phosphorus and iron to supplement our daily micronutrientneeds.

The antioxidant property assay of the different indigenous vegetables at threepreparations (raw, blanched, boiled) revealed that % free radical scavenging activity andtotal phenolics of most vegetables are relatively high. The antioxidant activities of all rawleafy vegetables and okra (75.7 to 92%). are higher than those of the blanched (64 to 83.4%)and boiled (59 to 80.1%) counterparts. This indicates that blanching and boiling greatlyinfluence the loss of antioxidant components in leafy vegetables. Blanching decreased theactivity from 5 to 15% while boiling decreased the activity by 10 to 25%. Processing affectscontent, activity and bioavailability of bioactive compounds and therefore health promotingcapacity of vegetables depends on their processing history. This aspect should be strictlyconsidered to obtain the optimum nutriceutical benefits from vegetables.

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Over-all, there are indications that most of the indigenous vegetables studied aregood sources of nutrients and antioxidants at varying degree. Therefore, the choicedepends on the individual as they are potential sources of food that are suitable forfortification and their use as nutritional supplements is highly promising.The wide variation in color, tastes and textures of various vegetables can add an interestingtouch to Filipino meals. Indigenous vegetables can contribute significantly to the nutrientrequirements of humans and should be strongly recommended.

Further studies involving identification and quantification of specific antioxidants(carotenes, ascorbic acids, tocopherols, flavonoids and other phytochemicals) arerecommended.

Likewise, the findings on the nutritional importance of these indigenous vegetablesto humans should provide a motivation for exploring their horticultural potential.

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(FAO) Food and Agriculture Organization. (1988). Traditional Food Plants. Food andNutrition Paper 42/1 FAO, Rome, Italy.

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Table 1. Indigenous vegetables analyzed

English name Ilonggo name Tagalog name Scientific nameLeafy Vegetables1. Malabar night shade Alugbati Alugbati Basella rubra Linn2. Bitter melon (tops) Amargoso Ampalaya Momordica charantia3. Horse raddish Balunggay Malunggay Moringa oleifera4. Chinese spinach

(With spine variety)(Spineless variety)

Kolitis Kulitis Amaranthus spinosos

Amaranthus viridis5. Jute Tugabang Saluyot Corchurus olitorius6. Taro (leaves) Abalong Gabi Colocasia esculenta7. Hot Pepper (leaves) Katumbal Siling labuyo Capsicum frustescens8. Alligator weed

(green variety)(violet variety))

LupoAlternanthera sessilis

9. Sweet potato (tops)(green variety)(violet variety)

Camote Kamote Ipomea batatas

10. Four-leaf clover Apat-apat Oxalis repens11. swamp cabbage Tangkong Kangkong Ipomoea aquaticaPods/Fruit1. okra Okra Okra Abelmoschus esculentus2. String bean Balatong Sitao Phaseolus vulgaris3. Winged beans

(green variety)(violet variety)

Balagay Sigarilyas Psophocarpustetragonolobus

4. Cow pea Hantok Paayap Vigna sesquipedalis

5. Pigeon pea Kad-ios Kadyos Cajanus cajan

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Figure 1. Nutrient composition of indigenous vegetables (expressed as % dry weight)

Figure 2. Moisture and dry matter content of indigenous vegetables

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Figure 3. Nutrient composition of indigenous vegetables (expressed as g/100g edibleportion)

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Figure 4. Mineral content of indigenous vegetables (mg/100g dry weight)

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Figure 5. Mineral content of indigenous vegetables (mg/100g edible portion)

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Figure 6. Total anti-oxidant property of indigenous vegetables (Raw, Blanched, Boiled)expressed as % free radical scavenging activity

Figure 7. Total phenolic contents of indigenous vegetables (Raw, Blanched, Boiled)expressed as mg TAE (tannic acid equivalent)/100 g edible portion

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