Khanin Pathak1, Bhabesh Gogoi2and Syed Wasifur Rahman3
1Department of Biochemistry and Agricultural Chemistry, Assam Agricultural University, Jorhat, Assam, India
2Scientist (Soil Science), Assam Agricultural University, Jorhat, Assam, India
3Department of Agricultural Biotechnology, Assam Agricultural University, Jorhat, Assam, India

Different macro and micro minerals present in rice play an important role in body regulatory functions and metabolism. In the present investigation, the mineral content of different rice cultivars of the hilly region of Assam was analysed. The ash content of hill rice cultivars was ranged from 1.0 - 2.2%. In the hill rice cultivars, the range of macro elements such as P, K, Na, Mg and Ca were found to be 0.314 - 0.556%, 0.207 - 0.453%, 0.052 - 0.075%, 0.042 - 0.057% and 0.023 - 0.047%, respectively; whereas the micro elements like Zn, Fe, Mn and Cu were found to be 2.55 - 4.28 mg/100g, 2.67 - 4.18 mg/100g, 1.87 - 3.87 mg/100g and 0.97 - 1.91 mg/100g, respectively. The mineral contents in rice genotypes were followed an order as P > K > Na > Mg > Ca > Zn > Fe > Mn > Cu and there a significant correlation was observed among different minerals.
Key words: Hill rice cultivars, Ash content, Macro and micro minerals, Assam

1. Introduction
Rice (Oryza spp. L.) is the staple food of about half the world’s human population. It provides the majority of dietary nutrients to billions of people and serves as the major source of energy, protein and some of the water soluble vitamins. Rice also supplies minerals like calcium, magnesium and phosphorus along with some traces of iron, copper, zinc and manganese in the diet of majority of Asiatic people (Juliano, 1997; Oko et al.,2012).  Unfortunately, rice does not furnish minerals adequately and moreover the loss of minerals, particularly of Fe, during rice milling is high (Doesthale et al., 1979). Iron and zinc are very important limiting trace minerals in rice grains. Nutritional quality of rice has received more attention in the developing countries, where monotonous consumption of rice may lead to deficiencies of essential minerals, vitamins, and other nutritional compositions. An investigation conducted by Food and Agricultural Organization (FAO) showed that the element contents such as Fe, Zn, Mn etc. in the foods of most developing countries decreased during 1979 – 1995 (Zeng et al., 2004). It is well established that malnutrition is a health concern, but its solution lies more on food based actions rather than on other preventive or curative approaches (Tamanna et al., 2013). For this reason, seeking the crop germplasm resources and breeding new crop varieties with high mineral elements content has become the key aim to resolve this risk of nutrition. To achieve food-based actions to prevent malnutrition and also for grain mineral elements content improvement programme, information on nutrient contents in foods must be known.

Rice can be grown practically anywhere, even on a steep hill or mountain. North-east India, including Assam, is endowed with exceptionally rich rice diversity and has already been recognized as one of the centers of origin of rice. In Assam, rice is grown in all the six agro climatic zones and rice occupies about two third of the total cropped area in the state. The hill zone of Assam constitutes 1.24 lakh ha rice area (i.e. only 5% of the total rice area of the state) contributing 1.74 lakh tonnes production for rice. One common traditional method of cultivation practised by farmers of hill region of North-east India is called “Jhum” cultivation. In Jhum cultivation, a large number of traditional cultivars of rice are grown in hill region of Assam. These cultivars are neither described nor evaluated for their mineral composition. These under exploited traditional cultivars differ in various characters from those which are grown commonly in the plains. 

It is worth mentioning that there is a rapid expansion of rice cultivation in hilly areas of Assam. But, for boosting research and development efforts on hill rice research system, the agricultural research in hilly areas requires particular emphasis. No systematic efforts have so far been made for the mineral characterization of hill rice germplasms. A nutritionally superior rice germplasm, if found in hilly region of Assam, will help in the rice breeding programme. Rice improvement in grain mineral elements content is always one of the major targets for researchers. A systematic evaluation of essential mineral composition of hill rice genotypes with good agronomic traits will be useful for scientists to select genotypes to be used in rice improvement programme. Considering the importance, a comparative assessment was carried out on mineral profile of rice cultivars grown in the hilly terrain of Assam of NE region of India.

2. Objective
Through this paper, an attempt is made to analyze the mineral content of different rice cultivars of the hilly region of Assam.

3. Materials and Methods
The present investigation was designed to evaluate mineral profiles of grains of some conventional rice cultivars commonly grown in hill zones of Assam. Grains of seventeen rice cultivars viz. Bairing Gurmu, Vandana, Joradhan, Miren, Laldhan, Maibee, Maichukik, Dimrou, IRAT-141, Bairing, Sakbothung, Buarcha, Sakcharap, Vijoy, Bijor, Pakai and Konchom were procured from the Regional Agricultural Research Station (RARS), Assam Agricultural University (AAU), Diphu, Assam. The grains were oven dried at 100°C (± 2°C) and converted into fine powder with the help of an electric grinder and kept in a Desiccator for analytical works.

The ash content was determined and the mineral solution was prepared according to the method described by AOAC (1970). The different standards were prepared for different minerals like 1.0 – 2.0 ppm (P), 0.1 – 0.6 ppm (Na), 0.5 – 2.0 ppm (K), 2.0 – 10.0 ppm (Fe), 2.0 – 8.0 ppm (Cu), 0.2 – 1.0 ppm (Zn), 1.0 – 4.0 ppm (Mn), 1.0 – 4.0 ppm (Ca) and 0.1 – 0.5 ppm (Mg). The minerals (P, K, Na, Mg, Ca, Zn, Fe, Mn and Cu) were estimated using Double-Beamed Atomic Absorption Spectrophotometer as described by Baruah and Borthakur (1997) where the narrow emission lines, which are to be absorbed by the sample, are, generally provided by a ‘hollow cathode lamp’ which has a cathode made of the element being sought.

4. Results and Discussion              
In the present study, the range of ash content of rice cultivars was 1.0 – 2.2 % and it was similar with the findings of Oko et al. (2012). A higher range of 3.16 – 3.79% of ash in rice had been reported by Anjum et al. (2007). The variation in the ash content of different rice grains may primarily be due to cultivar differences, climatic condition as well as nutrient status of soil.

The data on the minerals content namely phosphorus, potassium, sodium, magnesium, calcium, zinc, iron, manganese and copper estimated in the rice samples are presented in the Table 1. Analysis of variance indicated that the varietal effect on each of the minerals is highly significant. Correlation among the minerals themselves and with other parameters studied is shown in the Table 2.

4.1 Phosphorous
The phosphorus content in 17 hill rice cultivars varied widely from 0.314 to 0.556%, with a mean value of 0.407 % (Table 1). The highest value was observed in Sakcharap and the lowest on Sakbothung. It was almost similar with the findings of Singh et al. (1998). However, phosphorous content was found lower than the findings of Oko et al. (2012). Phosphorus was found to be the highest among all the minerals estimated for the rice samples. 

4.2 Potassium
The potassium content was found to be highest (0.453%) in the cultivar Maichukik and the lowest (0.207%) in the Pakai with an average content of 0.292% in the rice cultivars under study (Table 1). The result is in good agreement with the result of Oko et al. (2012) who reported the potassium content of Nigerian rice cultivars within the range of 0.15-0.23%. Zeng et al. (2004) reported a wider range of K content (0.172-0.452%) in core collection of Yunnan rice.

4.3 Sodium
In the present study, the range of Na content in 17 hill rice cultivars was 0.052-0.075% with an average of 0.065% (Table 1). The highest value was observed in Dimrou and the lowest on Bijor. The values for Na content was found higher than the reported values by  Sotelo et al. (1989) and Tinalin and Hashmi (2008). Oko et al. (2012) reported higher sodium content with a wider range of 0.09 – 0.17% for few Nigerian rice varieties.

4.4 Magnesium
Magnesium content of 17 hill rice cultivars used in the present study was found to vary between 0.042 - 0.057% with the average of 0.049% (Table 1). The highest value was observed in Bijor and the lowest on Dimrou. The Mg content in rice cultivars was found to be higher than those reported by Sharma et al. (2012). Oko and Ugwu (2011) reported a higher range of magnesium content (0.19-0.26%) in some rice varieties from South East Nigeria. Zeng et al. (2004) reported average magnesium content for 653 accessions from core rice collection of Yunan to be 0.159 per cent. 

4.5 Calcium
The range of Ca (0.023% -0.045%) was found among the 17 hill rice cultivars used in the study with an average value of 0.034% (Table 1).The cultivar “IRAT was recorded highest and Sakbothung was recorded lowest Ca content. The result is in good agreement with the results of Bhagabati (2000) who worked with glutinous rice varieties of Assam. However, there are several reports with much higher calcium content with a greater range (Oko and Ugwu, 2011; Oko et al., 2012). Average calcium content for 465 glutinous rice landraces was reported to be 0.015 per cent against 0.013% for non glutinous rice (Zeng et al., 2004).The variation might be mainly because of the differences in the genetic makeup of the rice cultivars and to certain extent geographical location, cultural practices adopted and the environmental factors. 

4.6 Zinc     
In the present study, the range of Zn content in the rice cultivars was 2.55 (Laldhan ) to 4.28 mg/100 g (Pakai) with an average of 3.70 mg/100 g (Table 1) was almost similar with the findings of Jiang et al. (2007).  Tinalin and Hashmi (2008) reported that Zn content of husked rice was 2.52 to 3.42 mg/100 g in some Malaysian rice varieties. Thongbam et al. (2012) found the Zinc content to range from 1.33 to 3.42 mg/100 g in some indigenous rice cultivars from Tripura. Ascheri et al. (2012) observed Zn content in semi polished red rice grains to be 2- 2.5 mg per 100 g. However, Anuradaha et al. (2012) reported a higher level of Zn content (2.62 mg/100g-6.73 mg/100g) among the 126 rice genotypes. 

4.7 Iron              
The range of iron content in 17 hill rice cultivars (2.67- 4.18 mg/100 g) (Table 1) was almost similar with the findings of Borua et al. (2004). The highest value was observed in IRAT-141 and the lowest on Vandana. Anjum et al. (2007) reported lower range of iron content (1.37 - 1.94 mg/100 g ) of  some Pakistani coarse rice varieties. The average iron content of 3.24 mg/ 100 g observed in the present study was much lower than the average value of 5.58 mg/ 100 g for the glutinous rice landraces of Yunnan province (Zeng et al., 2004). Anuradaha et al (2012) reported a higher level of Fe content (0.62 mg/100g-7.16 mg/100g) among the 126 rice genotypes. 

4.8 Manganese
Manganese content of 17 hill rice cultivars was found in the range between 1.87 (Sakbothung)  and 3.87 mg/100 g (Maibee) with an average of 2.81mg/100 g (Table 1). The average manganese contents of core collection, glutinous and non glutinous rice landraces of Yunnan province were reported as 1.52, 1.47 and 1.52 mg/100 g respectively (Zeng et al., 2004). Anjum et al. (2007) reported a range of 1.57 - 2.33 mg/100 g of manganese for Pakistani coarse rice varieties.

4.9 Copper                                      
The average copper content in 17 hill rice cultivars was 0.97 mg/100 g with highest in cultivar Vijoy (1.91mg/100 g) and the lowest in Bairing (0.66 mg/100 g) (Table1).  Jiang et al. (2007) observed copper content in milled rice to vary between 0.3-2.5 mg/ 100 g. The glutinous and non glutinous rice landraces from Yunnan province had the average copper content as 1.58 and 1.7 mg/100 g, respectively (Zeng et al., 2004). This difference might be because of the differences in the rice cultivars used for the studies.

4.10 Genotypic correlation among different minerals
It has been found that there is a significant positive correlation in between ash content and Ca and Fe (Table 2).  The P content was found to be positively correlated with Na. This is also good agreement with Oko et al, (2012). There was also a positive correlation observed between Fe with Zn .Significantly positive correlations were also recognized between Fe and Zn by many workers (Cheng et al., 2006; Jiang et al., 2007) which holds good for the present investigation also. These results suggested that high Fe content might be accompanied with high Zn contents of rice. Most of the minerals studied here were pigmented in nature.

This result shows that there is a significant variation in the composition of all the minerals among the rice genotypes used in the study. The mean mineral content values in brown rice of the cultivars were as follows: P > K > Na > Mg > Ca > Zn > Fe > Mn > Cu. However, Jiang et al. (2008) reported an order of mean mineral content values for eight minerals in brown rice as K > Mg > Ca > Na > Zn > Fe > Mn > Cu. 

Milling of rice generally decreases the mineral contents in rice. The complete milling and polishing that converts brown rice into white rice destroys half of the manganese, half of the phosphorus and 60 per cent of the iron (Oko et al., 2012).The nutritional composition of rice also differs with nature of the soil, environmental conditions and fertilizers applied (Amissah et al., 2003). It has been reported that the genotypic variations provided opportunities to select materials with dense contents of mineral elements (Gregorio et al., 2000).

5.   Policy Implication
Hill rice cultivars are excellent source of the trace minerals some of which have the excellent potentiality of preventing chronic disease.Therefore, research into identifying the nutritionally superior rice cultivars would have significant and long-term impact on global nutritional challenges with their greatest effect in developing countries. The outcomes from such research programs should be integrated with other efforts aiming to deliver climate-ready varieties that resist the challenges of the climate change in way, keeping the acceptability of such varieties by the consumers to meet the physical and sensory properties in other. Techniques for testing nutritional claims from such rice research may also provide the conduit for collaboration between the medical community and agricultural scientists to enable rice varieties to be developed to provide solutions to chronic diseases. However, in addition to the nutrients highlighted here in this article, further an in-depth nutritional profile study of the rice cultivars of hilly region of north-east India is of utmost importance. 

6. Conclusion
Significant genetic variations for grain concentration of all nine elements were observed, but not a single germplasm was found superior over the others for the all nine mineral content studied.In this case, breeder can go for independent selection of genotype for parental line for a particular mineral for rice breeding programme. It is also necessitate collecting more numbers of hill rice cultivars from different hill region of Assam and evaluating their mineral profile. A systematic evaluation of essential mineral composition of hill rice genotypes with good agronomic traits will be useful for rice breeder to select genotypes to be used in rice breeding programme.

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