INTRODUCTION

Since time immemorial, additional sources of valuable nutrients and minerals are provided by many herbs that are not provided by the conventional vegetables and fruits. These herbs supplied interesting flavors and negligible amount of calories to human diet (Pachkore et al., 2010). Also, various minerals present in plants play important role in human nutrition (Prasad and Bist, 2011). Lamiaceae includes several aromatic herbs represented by 236 genera and 7172 species (Harley et al., 2004) which play significant roles to humans. They contain valuable pool of multifarious chemical compounds having different biological activity depending on the structural composition (Harley and Reynolds, 1992). Due to presence of these chemicals, plant derived medicines are also used for treatment of many diseases for their lesser side effects and better compatibility (Karim et al., 2011). Members of this family comprise a rich storehouse of photochemicals including flavonoids, phenolic acid and terpenoids which can be exploited for its antimicrobial activities, food preservatives, insect repellants and therapeutic purposes (Palsson and Jaenson, 1999; Karanika et al., 2001; Sokovic et al., 2009; Matkowski and Piotrowska, 2006; Mishra and Mishra, 2011).

The state of Manipur is one of the North-Eastern states of India which is a part of Indo-Myanmar hotspot regions of the world (Myers et al., 2000). It harbours around 40 genera and 104 species of Lamiaceae with some of them commonly used by the people of Manipur for various utilities especially as culinary herbs due to its aromatic nature. These herbs have been grown since the dawn of civilization and popularity increases for their ability to act as flavouring agents in various food items (Zheng and Wang, 2001). All plants have its own nutritional composition besides having pharmacologically important phytochemicals. Among these, macronutrients like carbohydrate and proteins play an important role as a source of energy and also in satisfying human needs for different life processes. Although, nutritional contributions of many herbs are thought to be negligible, they complement human diet in addition with many other important pharmaceutical and healthcare products. For nutritional and toxicological analyses in foodstuffs, the macro and micro elements are usually determined (Cabrera et al., 2003). The consumption of these plants provides several minerals required by human body. In this line, the present experiment was taken up with an idea to find out the carbohydrates, amino acids, protein and elemental constituents of eight taxa of edible Lamiaceae plants.

MATERIALS AND METHODS

The study was carried out during the period of 2006-2009. The seeds of eight taxa of Lamiaceae shown in Table 1 and Fig. 1 under the subfamily Nepetoideae were collected locally and planted in experimental fields. Among them, H. suaveolens is widespread as a noxious weed and reported to have medicinal values (Devi et al., 2008) while the seven other plants are widely cultivated and used as culinary herbs in Manipur. Specimens were identified and the vouchers were deposited at Manipur University Museum of Plants (MUMPS), Department of Life Sciences, Manipur University. The aerial parts of these plants were collected just before the flowering time. The collected samples were shade dried and ground into powder form by a grinder.

Estimation of carbohydrates, amino acids and proteins: Different methods were followed for estimation of total soluble sugar, reducing sugars and non-reducing sugars. Total soluble sugar was estimated following the method of Dubois et al. (1951). Reducing sugars were estimated following the method of Nelson (1944) as modified by Smogyi (1952). Estimation of non reducing sugar was done following Malhotra and Sarkar (1979). The total free amino acid was estimated by the method of Yemm and Cocking (1955). The crude protein content in plant sample was estimated by Kjeldahl Method (Gupta, 2006) and the total soluble protein content was estimated by the method of Lowry et al. (1951).

Table 1:	Eight selected edible taxa of Lamiaceae with their local names and voucher numbers

Fig. 1 (a-h):	Habit photographs, (a) Elsholtzia blanda Benth, (b) E. communis (Coll. and Hemsl.) Diels var. purple flower, (c) E. communis (Coll.and Hemsl.) Diels var. white flower, (d) E. stachyodes (Link) Raizada and Saxena, (e) Hyptis suaveolens Poit., (f) Ocimum americanum L., (g). O. basilicum L. and (h) Perilla frutescens L.

Estimation of minerals: Wet diacid digestion method of Capar et al. (1978) was followed for the analysis of different minerals. K was estimated in a systronics-105 flame photometer. Sulphur and Phosphorus were estimated in a UV-VIS double beam Spectrophotometer following the procedures described by Murthy (2006) and Gupta (2006). Ca, Mg, Mn, Zn, Fe, Cu and Co was analyzed in a Parkin Elmer atomic absorption spectrophotometer, Analyst AA-200.

Statistical analysis: Each parameter was replicated three times. The mean values and their respective Standard Error Means (SEM) with significance differences were calculated by performing ANOVA test with the help of SPSS (9).

RESULTS AND DISCUSSION

It was found that out of the eight edible plants taken up for nutrient and mineral element contents, all of them showed different quantities in all the parameters studied. The carbohydrate contents (total soluble sugar, reducing sugar and non reducing sugars), total soluble amino acid and protein (crude protein and total soluble protein) contents in the selected taxa are given in Table 2. It was observed that the total sugar ranged from 2.01±0.122 in Elsholtzia stachyodes (Fig. 1d) to 10.90 mg g^-1 in Perilla frutescens (Fig. 1h). The maximum and minimum reducing sugar content ranged from 1.68 mg g^-1 in E. stachyodes to 0.40 mg g^-1 in H. suaveolens (Fig. 1e). The values of non reducing sugar varied from 0.33 mg g^-1 in E. stachyodes to 9.38 mg g^-1 in P. frutescens. Kavitha et al. (2009) evaluated the total sugar in 37 genotypes of Coleus forskohlii grown in Tamil Nadu and Karnataka and reported total sugar content in the range of 59.0-100.3 mg g^-1. The values of total amino acid varied from 1.90 mg g^-1 in H. suaveolens to 8.63 mg g^-1 in E. communis var. purple flower (Fig. 1b). Higher values of crude protein (157.50 mg g^-1) and the total soluble protein content (31.60 mg g^-1) were found in O. americanum (Fig. 1f) while minimum values of crude protein (43.74 mg g^-1) and soluble protein (17.60 mg g^-1) were recorded in P. frutescens respectively (Table 2). Variable amounts of protein content in Teucrium (64.7 to 438 mg g^-1) were reported by Juan et al. (2004). Kavitha et al. (2009) reported crude protein content in the range of 61.4-90.5 mg g^-1 in 37 genotypes of Coleus forskohlii. However, crude protein in the hybrids of O. gratissimum ranged from 91.90 to 179.40 mg g^-1 (Edeoga et al., 2006) which agrees with the present results.

Table 2:	Available carbohydrates, proteins and amino acid contents (Mean±SEM; n = 3) in mature aerial parts of some Lamiaceae (mg g-1)
Different letters between taxa denote significant differences (LSD, p<0.05)

Table 3:	Elemental constituents (Mean±SEM; n = 3) in mature aerial parts of some Lamiaceae plants (mg g-1)
Different letters between taxa denote significant differences (LSD, p<0.05)

Trace elements are essential for enzymatic processes of biological systems and these elemental requirements are obtained by human body from different sources, the major source being the plants. The elemental constituents in the eight plants within the studied taxa are given in Table 3. Potassium (K) and nitrogen (N) were found to be the most abundant elements in these plants. The primary role of potassium (K) is its capacity to maintain water balance in plant cells and its content in plants varied from 1.58-3.75%. In the present study, E. blanda (Fig. 1a) (27.25 mg g^-1) represented maximum K content and minimum by E. stachyodes (6.83 mg g^-1). Nitrogen (N) content in plant ranges from 1.5-4% and is one of the most important macro-elements in plants for being an important constituent of amino acids, proteins, nucleic acids, co-enzymes, pigments, alkaloids and vitamins (Popovic et al., 1998). The contents of N varied from 9.80 mg g^-1 in E. stachyodes to 25.20 mg g^-1 in O. americanum whereas Phosphorus (P) content ranged from 1.99 mg g^-1 in Elsholtzia blanda to 5.25 mg g^-1 in E. stachyodes. Sulphur (S) content was found maximum in O. basilicum (Fig. 1g) (1.27 mg g^-1) and minimum in P. frutescens (0.83 mg g^-1) however, Calcium (Ca) and Magnesium (Mg) ranged from 3.41 mg g^-1 in E. blanda to 7.64 mg g^-1 in O. basilicum and 7.33 mg g^-1 in O. basilicum to 1.99 mg g^-1 in E. blanda (Table 3).

The micronutrients were found in trace quantities and the amounts of differences among the selected plants were less. The main features of Iron (Fe) are its polyvalence and chelating capability. Its content was found maximum in E. communis var. white flower (Fig. 1c) and minimum in E. blanda (0.82 mg g^-1). Zinc (Zn) activates to more than 300 enzymes and influences many metabolic processes in the living cell. Zinc which is the only element present in all the six classes of enzymes is found to be the second most abundant transition metal in organisms after iron (Fe) (Broadley et al., 2007). E. stachyodes showed maximum Zn content (0.28 mg g^-1) while E. blanda recorded minimum content (0.09 mg g^-1). These findings were in agreement with the earlier reports that plants contain Zn in the range of 0.25-1.20 mg g^-1. Cobalt (Co) is known to be responsible for a number of vital metabolic processes and its distribution in plants reported to be in the range of 0.0001-0.0010 mg g^-1 (Jaleel et al., 2009). Co content ranged from 0.02 mg g^-1 in H. suaveolens to 0.05 mg g^-1 in E. communis var. purple flower, E. communis var. white flower, E. stachyodes and O. basilicum while Copper (Cu) content ranged from 0.03 mg g^-1 in E. blanda and E. communis var. purple flower to 0.05 mg g^-1 in E. stachyodes and O. basilicum. Manganese is one of the microelements which are actively absorbed by the plants and have a significant effect on the formation of plant mass.

Table 4:	Dietary reference standards for macronutrients and elements in human adult*
*NRC (1989); ‡Zello (2006)

Mn content ranged from 0.03 to 0.15 mg g^-1 while the minimum is recorded in E. blanda, E. stachyodes and H. suaveolens and the maximum value being found in E. communis var. white flower. Beck et al. (2006) reported Mn content in Satureja hortensis to be 0.097 mg g^-1. As Mn being one of the elements having multi-functional activities especially for its anti-oxidant capacity, the present finding of 0.15 mg g^-1 Mn content in E. communis var. white flower seems to be promising for commercial exploitation. In the case of other elements, the present findings are in agreement with the reports of Kadifkova-Panovska et al. (1997) wherein the amount of K was found to be the highest (18.24 mg g^-1) followed by Ca (4.71 mg g^-1) and Mg (3.41 mg g^-1) with significant quantities of Fe (0.72 mg g^-1), Mn (0.203 mg g^-1) and Cu (13.19 mg g^-1). Mineral contents of these plants are comparable with the data provided by several workers in various vegetables (Al-Naqeep et al., 2009; Saupi et al., 2009; Ihedioha and Okoye, 2011; Seal, 2011). Ultimately, the significant amount of nutritional and elemental values in the selected plants under study will help in meeting the dietary requirements of human health with the recommended daily intake for human adult given in Table 4.

CONCLUSION

In the present study, the eight selected plants of Lamiaceae commonly taken by the people of Manipur as culinary herbs are found to have significant amount of carbohydrates, amino acids, proteins and minerals. These nutrients and elemental constituents have significant and specific roles inside our body and recommended for daily consumption. The selected taxa were found to have more amounts of proteins than carbohydrates. So, these plants will provide an important additional food item to those ailing people who abstained from taking higher amounts of carbohydrates. The nutritional contributions of these selected herbs will complement human diet in addition to many other important pharmaceutical and healthcare products. As an overall, regular intake of these plants will help in supplementation of nutritional values and minerals required inside our body and to protect from various ailments.

ACKNOWLEDGMENTS

Authors are thankful to UGC, New Delhi, India (No. F.17-31/98(SA-1) for providing financial assistance to Sandhyarani Devi Khomdram for her research programme as SRF/NET and Head of Department, Life Sciences Department, Manipur University for all facilities and encouragements given for the study.