Evaluation of physical properties of rice used in traditional Kyrgyz Cuisine

Abstract Eight staple rice cultivars consumed in Kyrgyzstan were evaluated for physical properties in this study. The dimensions of investigated grains correspond to 5.29–6.99 mm for length, 2.52–3.10 mm for width, and 1.88–2.13 for thickness. Equivalent diameter was in range of 3.14 – 3.47 mm, surface area took 25.35–31.90 mm². The sphericity analysis values varied from 0.480 to 0.559, aspect ratio from 0.39 to 0.55, volume of the grain was measured in range from 16.25 to 22.02 mm3, bulk density values were 0.77–0.87 g/cm3, and solid density from 1.17 to 1.41 g/cm3. The porosity of grain was equal to 28.27–39.83%, thousand kernel weight correspond to 19.67 to 27.15 g, rupture force of grain was measured in range of 63.47–155.50 N, color characteristic varied in parameters L*, a* and b*, 37.58–72.19, –0.22–10.17, and 9.65–21.12, respectively. Optimum cooking time ranged from 19.33 to 33.00 min. The water uptake ratios for 30 min of soaking were 1.21–1.28, 1.18–1.45, and 1.14–1.57 for 30, 45, and 60°C, respectively. While the water uptake ratios for 60 min of soaking were 1.22–1.42, 1.19–1.54, and 1.25–1.75 for 30, 45, and 60°C, respectively. Optimal cooking time showed that imported varieties needed lower interval for full grain cooking compared to the local Kyrgyz varieties. It was found that Kyrgyz rice varieties staying more firm after cooking as compared to imported varieties and therefore more suitable for the local traditional dish such as plov.

. Nevertheless, considerably less attention is given to rice grain quality research in other parts of the world, such as Central Asia, where rice has historically being recognized as the most popular staple food after wheat with important cultural role in local cuisine (Kochkunov, 2010;Zanca, 2003). Local rice varieties are still cultivated in this region. However, there is lack of scientific information about their qualitative and sensory attributes.
Typical country from Central Asia where rice plays important role in both food security as well as in local traditional cuisine is Kyrgyzstan. Based on Food and Agriculture Organization (FAO) statistics, the total cultivated area of rice is around 8,000 ha and annual production equal to 28,230 tonnes and per capita consumption equal to 7.3 kg (Food and Agriculture Organization (FAO), 2014; Food and Agriculture Organization (FAO), 2016). As mentioned earlier, rice plays a crucial role in the cuisine of central Asian countries including Kyrgyzstan and represents a main ingredient in traditional festive dish "plov" preparation (Kochkunov, 2010;Kokaisl, 2013;Vlkova et al., 2015;Zanca, 2003). The most popular Kyrgyz local variety of rice is called Ozgon rice, grown in the Osh province and being famous for its extraordinary taste. The grains differ from other rice varieties by red-brown color and longitudinal brown stripes on the grain body due to the unique climate, mineral composition of the soil as well farming conditions (Smanalieva, Salieva, Borkoev, Windhab, & Fischer, 2015). As there is according to our best knowledge, lack of scientific studies describing qualitative properties and attributes of local rice varieties in Central Asian countries particularly Kyrgyzstan, the main objective of the study was to examine and evaluate the physical properties of eight staple rice varieties consumed in that region. This study also determines the differences in physical, textural, and cooking properties between studied cultivars and implements them into the rice system scheme.

| Plant material
The dried rice kernels were purchased in February 2015 from the city market in Osh, South Kyrgyzstan. In total, eight different rice cultivars were bought, of which were five cultivars local varieties (Ozgon Champion, Batken, Ozgon Kakyr, Ozgon Uchuk and Ozgon Cerza), and three were imported varieties (Elita Krasnodar Russia from Russia, Pakistan from Pakistan, and Kapchygai Kazakhstan from Kazakhstan). The samples were collected from three different vendors, to sustain average sample quality of each variety (in average amount of 700 g). Cultivar samples were cleaned from small particles (as stones and dried weeds) and kept in closed plastic bags in room temperature till the laboratory tests. Only good quality rice grains were used during the analysis, and each measure-

| Length, width and thickness
The length L (mm), width W (mm), and thickness T (mm) of the rice kernels were determined by use of Vernier caliper with accuracy of 0.01 mm. Rice kernels were randomly selected, and each of their dimension was measured and recorded 20 times on each cultivar.

| Equivalent diameter
Equivalent diameter D e (mm) was determined using a following equation (Mohsenin, 1986):

| Surface area
For calculation of surface area S (mm 2 ) were used previously recorded variables length, width, and thickness. The formula for surface area was described by Mohsenin (1986) and Jain and Bal (1997) as the following: where B = (W × T) 1/2 (mm) is a function of width and thickness.

| Volume
Volume of grain V (mm 3 ) was calculated by the formula mentioned by Jain and Bal (1997) as following:

| Bulk density
The bulk density ρ b (kg/m 3 ) was calculated according to equation mentioned by Fraser, Verma, and Muir (1978) when the 200 ml beaker was filled with the rice up to 100 ml sign and then the mass of rice grains was weighed. The weight of the rice was divided with the volume of the beaker (100 ml). The procedure was repeated five times: where M g (g) is mass of the grain and V b (mm 3 ) is volume of the beaker.

| Solid density
The solid density ρ s (kg/m 3 ) was calculated by filling the 100-ml beaker with 50 ml of distilled water and then placing there 3 g sample of rice. The displaced water (volume of the grains) is recorded. The measurement is repeated three times (Shittu, Olaniyi, Oyekanmi, & Okeleye, 2012): where M gs (g) is mass of the grain and V dw (mm 3 ) is volume of displaced water.

| Porosity
Porosity ε (%) was calculated using results of analysis mentioned above-solid density and bulk density. The formula was described by Jain and Bal (1997):

| Thousand kernel weight
The 1000 kernel weight m1000 (g) was measured by random selection of one thousand grains of each cultivar and carefully weighed on digital scale Kern 572-30 with accuracy of 0.001 g following by estimation the final weight in grams. The procedure was repeated five times, and average values were taken (Varnamkhasti et al., 2008).

| Color characteristic
Color characteristics of the rice kernels L* (−), a* (−), b* (−) were determined using the spectrophotometer CM-600d (Konica Minolta Optics, Inc.) based on the CIE laboratory system. The colorimeter was adjusted on D 65-simulation of daylight and the angle of observation was 10°. The measurement was repeated five times with each cultivar, and the data were downloaded from the device to Excel file.

| Optimum cooking time
For the optimum cooking time determination Top (min), it was taken a sample of 5 g from each variety, which was placed in glass Petri dish. The water bath Memmert (Memmert GmbH + Co. KG., Schwabach, Germany) was filled with water till the marked line.
Inside of the water bath was placed 250 ml graduated beaker and filled with 100 ml of distilled water. The water bath was brought to the temperature of 100°C, when the water starts to boil. When water reaches the demanded temperature, rice sample was placed into the cylinder and the time started to be recorded. After 10 min of boiling, 3 grains of rice were removed and pressed between two glass plates, in order to examine the gelatinization of the core. Then every other minute, the procedure was repeated, until the rice grains have no more un-cooked centers. Until at least 9 of 10 grains were properly cooked and then were the rice cooked for another minute to ensure that all the grains are cooked. The optimal cooking time of each cultivar was recorded.

| Water uptake ratio
For water uptake ratio determination Wup (−), the water bath Memmert was used. From each rice variety, 18 samples (2 g each) were soaked on water with different temperatures and soaking times. The test temperatures were set on 30, 45, and 60°C and soaking time was set on 30 or 60 min. Each measurement was performed in triplicate. The 2 g sample was placed in 200 ml beaker which was filled with 100 ml of water and inserted into the water bath of certain temperature and soaked for certain time. After the rice was decanted through colander with dense mesh and dried with paper towel, the sample was reweighted and the new weight was recorded.
The water uptake ratio was calculated by dividing weight of rice after cooking to initial rice sample weight. It was preceded by recording the weight of the initial raw rice sample and the final rice sample on the electronic scale (Kern 572-30 with accuracy of 0.001 g) (Shittu et al., 2012).

| Rupture force
Rupture force Fr (N) was measured on Texture analyzer MPTest 5.050 (Labortech, Opava, Czech Republic). For each cultivar, it was used 20 grains to perform the measurement. Each grain was placed in the middle of the steel disk along its thickness, and the test was started. After breaking of the grain, the test was stopped and rupture force was recorded. TA B L E 3 Physical characteristic of imported rice varieties need to be involved (Bhattacharya, 2011 According to Mohsenin (1986) Bulk density describes grain behavior in the dry mass; meanwhile, the solid density is more focused on particular volume the grains take in space, when measured by water test. In this study were recorded values from 0.77 g/cm 3 to 0.87 g/cm 3 while the bottom was occupied by two Ozgon cultivars and top was owned by Therefore, in this study, the imported varieties would generally need smaller package for the same amount of rice compared to local varieties (Thakur & Gupta, 2006 (Tables 2 and 3). This pattern validate previous results about smaller grain dimensions and volume; therefore, apparently the weight of grain is lower as well. According to Smanalieva et al. (2015), the Ozgon varieties differed in their TKW from 23.63 to 24.94 g while this value was decreasing with increasing storage time. Those values are in agreement with our study and others authors, such as Mir et al. (2013) who measured TKW in range from 22.23 g to 28.63 g or Díaz et al. (2015) with quite similar results (15.3 -24.1 g). Also Ravi et al. (2014) measured comparable values in range from 20.6 g to 24.5 g of TKW. According to that article, the thousand kernel weight is also useful parameter to measure the "milling outturn" as a determination of the relative amount of foreign matter in a given volume of paddy rice.

| RE SULTS AND D ISCUSS I ON
Color characteristic of all rice varieties was examined with spectrophotometer CM-600d working in the CIE system. Therefore, the values for L* (lightness), a* and b* were examined, respectively. All the color values are noted in  Determination of cooking time of the rice varieties is one of two cooking characteristics examined during this study. Cooking time is very important information in relation to consumer preferences and also certain types of rice cultivars and their utilization. Figure 1 shows bellow summary of optimal cooking times of all cultivars. The outer borders of this measurement results belong to Ozgon Uchuk (with 33 min) and to Batken (with 19.33 min) which makes the difference between the extremes over 13 min. In the Kyrgyz, traditional varieties' group keeps the average cooking time around 30 min while the imported varieties are generally shorter in optimal cooking time.
According to Yadav and Jindal (2007), the cooking process is an important operation and the length of cooking and final texture of the rice kernels is crucial for customers to select the optimal variety for their consumption. As stated by Singh et al. (2005), main factors affecting variations in cooking quality of rice are genetic and environmental. As the differences between imported and local Kyrgyz varieties are significant, the results will be compared respectively to this frame. Similar results to optimal cooking time of Kyrgyz varieties (with exception of Batken) measured by Deepa, Singh, and Naidu (2008)  Kakyr were the only cultivars which reacted with steadily increasing amount of water uptake (Figure 2). On the contrary, the rest of cultivars behaved considerably different, when they all (with exception of Ozgon Kakyr) decreased in water uptake ratio at 45°C and again rise (with exception of Ozgon Champion) at 60°C but only to the level of 30°C values or slightly above that. Pakistan cultivar greatly stands out from the test sample with its absorption characteristics.
In the measurement with longer time period of soaking, 60 min, the results were actually similar, with slightly larger water uptake ratio values. Water uptake ratio was measured by several authors (Fofana et al., 2011;Meena et al., 2010;Mizuma, Kiyokawa, & Wakai, 2008;Mohapatra & Bal, 2006;Singh et al., 2005;Thakur & Gupta, 2006;Yadav & Jindal, 2007 have led to decrease in porosity of the material and consequently reduction in water absorption rate. The water uptake in this study did not showed large increase between 30 and 60 min; therefore, we can assume that the main factor influencing water uptake is temperature rather than time. Also the temperature levels used in this study (30, 45, and 60°C) were probably sufficient to model the precooking rice soaking. However, with an emphasis to the results of this measurement, those temperatures are too low to show significant increase in water uptake ratio. According to Mohapatra and Bal (2006), rice with higher water binding capacity normally yields soft textured cooked product, opposite to the lower binding where the grains remains more firms and structured. As the result we can claim, that the Kyrgyz rice is after cooking staying more firm and therefore probably more suitable for the local traditional dish "plov" compared to imported variety of Pakistan, which end up in soft textured product with different use in the national cuisine.
The rice grain characteristics obtained by this study are important for the producers and consumers in Kyrgyzstan and will provide guidance in terms of breeding, processing, and retail of those rice

| CON CLUS ION
This study represents extensive collection of information on physical properties of rice cultivars grown and consumed in Kyrgyzstan, Central Asia. The research had shown that the physical properties, F I G U R E 2 Water uptake ratio of selected rice varieties texture characteristics, and cooking characteristics among all cultivars differ significantly. The broad variation applied to grain length and shape (from medium to long and from bold to slender) which is particularly important information for designing milling machinery and all kinds of optimization in the postharvest operations (handling, processing, and packaging) while avoiding any loses and damage. According to grain dimensions and physical characteristics (equivalent diameter, surface area, and volume) had been proven that varieties with non-native origin differ greatly from the traditional Kyrgyz varieties, and in all those parameters, they showed significantly lower values. The sphericity, aspect ratio, solid density, and porosity showed results with wide range of values; however, in comparison between local and im-

AUTH O R CO NTR I B UTI O N S
Martina Nadvornikova provided most of the analysis and drafted the manuscript; Jan Banout designed the study, coordinated all analysis, finalized, and drafted the manuscript; David Herak suggested appropriate methods and contributed to results interpretation; Vladimir Verner collected the material, assisted in study design, and contributed to finalization of the manuscript. All authors read and approved the final manuscript.