Proximate composition, nutritional attributes and mineral composition of Peperomia pellucida L. (Ketumpangan Air) grown in Malaysia.

This study presents the proximate and mineral composition of Peperomia pellucida L., an underexploited weed plant in Malaysia. Proximate analysis was performed using standard AOAC methods and mineral contents were determined using atomic absorption spectrometry. The results indicated Peperomia pellucida to be rich in crude protein, carbohydrate and total ash contents. The high amount of total ash (31.22%)suggests a high-value mineral composition comprising potassium, calcium and iron as the main elements. The present study inferred that Peperomia pellucida would serve as a good source of protein and energy as well as micronutrients in the form of a leafy vegetable for human consumption.

The plant has been widely used for different medicinal purposes and has been used culturally for a variety of ailments including conjunctivitis, convulsions, fatigue, fever, headache, gout, rheumatic pains, skin diseases, to lower blood cholesterol level and breast cancer [1]. Its properties have been further affirmed by a number of research reports. Aerial parts of P. pellucida demonstrated dose-dependent analgesic and anti-inflammatory actions by interfering with prostaglandin synthesis [2][3][4]. Khan et al. [5,6] reported a dose-dependent depressant effect and antipyretic effect of P. pellucida leaf comparable to standard aspirin, while Mutee et al. [4] presented the potential use of the plant as an antioxidative agent. Nwokocha et al. [7] suggested a dose-dependent hypotensive effect of P. pellucida via enhancement of endothelial nitric oxide (NO)-dependent vasorelaxation. P. pellucida leaf also exhibited broad spectrum bactericidal [8] and fungicidal activity against Helminthosporium oryzae [9] and Trichophyton mentagrophytes [10].
It is an edible plant and is frequently used as a leafy vegetable or condiment in many parts of the tropics. Egwuche et al. [13] reported the proximate and mineral composition of P. pellucida leaf. Although some preliminary information has been presented in an earlier report, but detailed investigations are still required as P. pellucida is being consumed on a major scale and is traditionally prescribed as folk medicine in the whole plant form. No report on the nutritional and mineral profile of P. pellucida, indigenous to Malaysia, has been presented so far. Nutritional composition and phytochemical properties are reported to vary with agroclimatic conditions, humidity and species of the plant [14]. This study was, therefore, carried out to determine the proximate composition and mineral contents in P. pellucida whole plant collected from Malaysia.

Results and Discussion
The findings for proximate composition of P. pellucida whole plant are presented in Table 1. The moisture content of fresh whole plant P. pellucida was found to be 93.14%, contributed by the bulk tissue weight of fleshy and succulent stem. After oven drying, the P. pellucida whole plant still contained a moisture level with a mean value of 8.33%. The high water content in P. pellucida makes it ideal for vegetable juicing as a supplement to whole vegetables. Nevertheless, in terms of natural product stability, high moisture content tends to promote microbial contamination and chemical degradation [15], as it provides a medium for many reactions to occur. The protein and lipid contents of the whole plant were 10.63 and 3.24%, respectively. Protein content of P. pellucida is comparable to that of other leafy vegetables, where the protein content ranged from 1 to 7% of fresh weight or 8 to 30% of dry weight basis [16]. The major components of P. pellucida oil had been reported to be dillapiole and trans-caryophyllene [17,18] where trans-caryophyllene had previously exhibited anti-inflammatory action in mice [19]. The caloric value of P. pellucida was found to be 258 kcal/100 g DW; indicating it could be an important source of energy. The carbohydrate level (46.58%) was the highest calorie contributor, as the total lipid and protein contents did not considerably affect the determination of energy produced.
The ash content is generally recognized as a measure of quality for the assessment of the functional properties of foods [20]. P. pellucida contained high levels of total ash, up to 31.22%, in the dried plant. This, in turn, indicated a high content of minerals such as potassium (6,977 mg/100 g DW), followed by calcium (483 mg/100 g DW) and iron (119.3 mg/100 g DW). The mineral profile of P. pellucida whole plant is shown in Table 2. The high content of potassium compared to sodium led to a very low Na/K ratio, which is favorable from nutritional point of view, as diets with low Na/K ratio are associated with lower incidence of hypertension [21]. This may explain the nitric oxide (NO)-dependent hypotensive effect reported by Nwokocha et al. [7] and the rationale behind the traditional use of the plant in managing hypertension [22]. Calcium was found to be the second most abundant mineral element present in this plant. Therefore P. pellucida can be considered an appropriate dietary source of calcium to maintain the biological role of nerve transmission, muscle contraction, glandular secretion as well as mediating vascular contraction and vasodilation [23].
Iron deficiency is a common nutritional problem affecting many people worldwide. Primarily, it occurs as a result of chronic bleeding, infections, inadequate intake of bioavailable iron, deficiencies of folic acid, vitamin A or vitamin B 12 , pregnancy, increased requirements throughout growing periods and menstrual losses in women during reproductive age. The high amount of iron found in P. pellucida indicated that the plant could be a good source of dietary iron to overcome nutritional deficiency of iron, if supplemented in the diet. Copper and zinc are the essential trace elements that are needed only in minute amounts by the human body for important biochemical functions. The levels of copper and zinc are closely interrelated. Zinc stimulates the synthesis of metallothionein. Metallothionein has a high affinity for copper and it hinders copper systemic absorption within the intestinal cells [24]. Excessive ratio of zinc to copper (>16) from dietary sources causes imbalance in their bioavailability and has been linked to increased risk of cardiovascular system disorders [25]. The recommended zinc/copper ratio in human tissues is four to six [26,27]. P. pellucida, with its zinc/copper ratio of four, represents a potential food source to counter copper-zinc imbalances.

Procurement and Preparation of Plant Materials
Peperomia pellucida (L.) plant was harvested as one batch from Guar Chempedak, Kedah, Malaysia. The collected plant sample was washed under running tap water, rinsed with distilled water and oven-dried at 40 °C for 48 h using a material test chamber M720 (Binder GmbH, Tuttlingen, Germany). Obtained dry matter was ground to a fine powder, sifted in a sieve (35 mm) and stored at −20 °C in air-tight containers till further analyses.

Moisture
Moisture content was measured using air-oven following official methods of Association of Official Analytical Chemists [28]. A material test chamber M720 (Binder GmbH, Tuttlingen, Germany) was used to dry the samples till constant weight. The percentage of moisture content was calculated as: % 1 100

Lipid
Determination of lipid content was performed following Soxtec method previously described by Noureddini and Byun [29], using a Soxtec TM 2050 automated analyzer (FOSS Analytical, Hillerød, Denmark). Petroleum ether was used for the extraction, whereas percentage of lipid was obtained following equation below: % 100

Protein
The total nitrogen amount in the sample was determined according to method described by Ng et al. [30] using Kjeltec TM 2200 Auto Distillation Unit (FOSS Tecator, Höganäs, Sweden). A nitrogen-to-protein conversion factor of 4.4 was used for the determination of protein present in the samples.

Ash Content and Ash Solution
A dry ashing method was used to determine the ash content [28]. The samples were incinerated in a furnace (Furnace 62700, Barnstead/Thermolyne, Dubuque, IA, USA) at 550 °C. The remaining inorganic material was cooled, weighed and further used for the determination of mineral contents. An ash solution was prepared by dissolving the ash in 100 mL of 1 M HCl.

Carbohydrate and Caloric Value
The total carbohydrate content (%) in the samples was calculated by difference method. The caloric value was calculated by sum of the percentages of proteins and carbohydrates multiplied by a factor of 4 (kcal/g) and total lipids multiplied by a factor of 9 (kcal/g).

Statistical Analysis
Statistical analyses were conducted using GraphPad Prism (San Diego, CA, USA) version 5.02 for Windows. All the determinations were carried out in triplicate and data were expressed as mean ± standard deviation.

Conclusions
In conclusion, the potential of P. pellucida as an important source of nutritional and mineral compounds in the tropics is highlighted in the present study. In line with increasing global demand for food, P. pellucida finds use as potential source of functional foods.