Identification of Important Physical Properties and Amylose Content in Commercially Available Improved and Traditional Rice Varieties in Sri Lanka

Commercially available, fourteen different rice varieties (improved and traditional) in Sri Lanka were subjected to determine amylose content and important physical properties. Under physical properties, milling parameters (such as brown rice content, husk content and total milling recovery), hardness and dimensions (length, width & thickness) including water absorption capacity (by dipping at 70°C for four hours) were measured. Amylose content of each rice variety was determined by measuring the optical density of amylose-iodine complex using spectrophotometer, while amylopectin content was obtained using the relationship equation. Results revealed, brown rice content, husk content, total milling recovery, hardness and water absorption capacities of these rice varieties were within the range of 76-78%, 20-23%, 69-72% & 28-30% respectively. Statistical analysis also indicated, those physical properties of fourteen rice varieties were significantly different to each other (p0.05).


INTRODUCTION
Utilization of rice grains have been increasing considerably, as an major ingredient in other food applications , other than the major staple in domestic usage. The reasons for increasing usage of rice could be depending upon the cost effectiveness, functional properties, and unique medicinal values, appealing organoleptic properties and being a cereal of free from gluten. Consumer acceptability and market value of rice is defined from various quality traits such as milling quality, physical quality, cooking and eating quality or nutritional quality (Bao, 2012;Rebeiraet al.,2014;Fernando et al.,2015 ).Some of these quality parameters are intrinsically governed by physicochemical properties such as amylose and amylopectin (Rohillaet al., 2000;Rebeiraet al.,2014). Amylose and amylopectin are the building material of starch in rice endosperm (Martin and Smith, 1997;Duanet al., 2012). Amylose are linear molecules made by linking Dglucose units with α-1.4 glucosidic bonds, while amylopectin are highly branched molecules, consist with both α-1.6 and α-1.4 glucosidic bonds. (Denardinet al., 2012;Kaufmanaet al., 2015). The ratio of these two types of polymeric substances is contributing the functional properties of rice (Kaufmanaet al.,2015). Amylose content is often contributed, to the differences in cooking and eating qualities of rice about 65 % (Juliano, 1971). Cheng et al. (2012) reveal, higher amylose tends to absorb more water during the cooking process and resulting higher volume expansion of rice. After cooking, it receives dry and fluffy texture and grains can be separated easily. While rice varieties with lower amylose content are moist, chewy, clingy and less separable after cooking (Juliano,1985;Mir et al.,2013;Srikaeo and Arranz-Martínez,2015).Amylose content of a rice variety is  Kong et al., 2015). Amylose is also responsible for the retrograding of starch by forming hydrogen bonds between molecules by creating a firm gel matrix (Ganiet al.,2013;Kong et al.,2015) and is a vital quality parameter of staling of starch base foods. (Mariottiet al., 2009;Shifenget al., 2009 ;Hug-Itenet al., 2003). As in many other Asian counters, Sri Lanka cultivates plenty of rice varieties (improved & traditional) commercially, with largely diversify physical properties, including amylose & amylopectin content too. Hence, the aim of this study is to determine the imported physical properties (milling properties, dimensions, hardness, water absorption capacity) and amylose/amylopectin content of selected improved & traditional rice varieties in Sri Lanka.

Collection and Preparation of Test Samples
Commercially available seven improved and seven traditional rice varieties were purchased from recognized paddy suppliers in Sri Lanka. Each rice/paddy sample was stored six months, under ambient condition (28-30°C/R.H.70-75%) in plastic containers. Subsequently, two kilos of samples from each rice variety were drawn and divided using a sample divider to obtain the test portions. There after the test portion was divided into four sub portions and each portion was used to determine milling properties, dimensions, water absorption capacity (WAC), hardness and amylose content.

Milling Properties & Dimensions
At the beginning, moisture contents of the rough rice (paddy) samples were measured using digital grain moisture meter (G-Won -GMK303A) and found it was within the range of 12-14%. 150g of rough rice samples from each rice variety were de-husked using SATAKE-THU de-husker. The barn of brown rice (unpolished) were removed up to 8±1.1% using SATAKE TMO-5 Polisher. At each point, brown rice yield, husk percentage & total milling recovery were calculated according to the equations given below, Brown Rice %=( Weight of de-husked rice) ×100 /Weight of rough rice Husk %=( Weight of husk) ×100 /Weight of rough rice Total Milling Recovery %=( Weight of milled rice) ×100 /Weight of rough rice Dimensions such as length, width & thickness of fifty rice kernels from each variety were measured using laboratory thickness indicator at 0.01mm resolution.

Hardness
Hardness of rice kernels were determined by placing randomly selected fifty brown rice grains on the platform of rigidity tester (KIYA) & applied the force by rotating the screw head down words. Readings were taken at the point of rupturing the grains individually and means of hardness were calculated.

Water Absorption Capacity (WAC)
The Water Absorption Capacity of rice varieties was investigated as stated in Thilakarathna et al.(2015). About 10g of rough rice samples in each variety were soaked in hot water at 70 0 C for 4 hours. The temperature of the soaking water was maintained throughout the soaking period with the aid of thermostatic water bath (Gallenkamp-BKS350).Soaked rice samples were removed from the water bath and the remained water was drained off. Subsequently, wet rice grains were blotted quickly with filter papers to remove superficial water. Weights of the damp rice grains were measured with digital weighing scale (OHAUS-Discovery) and moisture increments of each rice variety was estimated using a hot air oven (Leader), maintain at 105±2°C for 24hours.

Amylose & Amylopectin Content
Amylose content was determined based on simplified colorimetric method outlined by Juliano (1971) & ISO 6647-2: (2015) with slight modifications. Initially, milled rice samples were ground to fine powder using a disk mill (FFC-23) and sieved (180µm pore size) using a sieve shaker (IMPACAT).Sieved rice samples were packed in a metalized pouches and stored at 4°C. Prior to the analysis, samples were kept at room temperature for three hours and moisture content was measured using digital moisture analyzer (SHIMADZU-MOC63u). Then, accurately, 100 ± 0.5mg of prepared rice flour sample was weighed into a 100 ml conical flask. To the same flask, 1.0 ml of 95% ethanol was pipetted out and wetted by shaking slightly. Then, 9.0ml of 1N sodium hydroxide solution was pipetted into the same conical flask, mixed well and allowed to stand in overnight. The completely disperse rice flour in the conical flask was transferred to a 100ml volumetric flask and empty volume was made up with distilled water to prepare initial stock solution. Finally, 5.0ml of stock solution, 1.0 ml of 1N acetic acid and 2.0 ml of 2% iodine solution were added into another 100 ml volumetric flask and the volume was made up with distilled water to get a coloured solution. The colored solution was mixed by inverting and let stand for 20 minutes in a dark place avoiding direct light. The absorbance was measured at 620 nm using UV-Vis spectrophotometer (HACH-DR6000). Amylose content of rice varieties were calculated from the calibration curve, constructed using purified amylose standard-from potatoes (Sigma Aldrich). Final results were given as percentage by mass on dry basis. Amylopectin contents (%) of rice varieties were calculated by subtracting the obtained amylose content (%) from hundred (%) as describe by Juan et al. (2006).

Statistical Analysis
The experiment was complete randomized design. Descriptive analysis, analysis of variance (ANOVA) and Pearson correlation analysis were performed using minitab statistical software, at 95% confidence level.

Physical properties
Physical properties such as milling properties, hardness, dimensions, size & shape of rice grains obtained from fourteen different rice varieties including improved & traditional, were given in Table 01. Physical properties of rice grains are important quality components, since it Impacts on the market demand and production cost. Kernel size, shape, milling recovery, degree of milling and grain appearance are frequently assessing as physical properties (Cruz &Khush, 2000).Referring to the data given in  Figure 01. A cold or hot soaking process facilitates the water absorption of rice grains & is an essential practice in parboiling, wet milling or cooking operations (Kashaninejad et al., 2007). As in Figure 01: rice varieties were showed different water absorption capacities after four hours of hot soaking at 70 0 C. Generally, the final moisture contents of all rice varieties were reached to 28-30% (w.b.). Among the all rice varieties, highest WAC was shown by Unakola samba (30.65%, w.b.) and lowest was displayed by Rathna samba (28.32%, w.b.). Under the improved rice varieties, highest water absorption was reported by BG300 (30.34%, w.b.) and lowest was given by BG358 (28.82%, w.b.).BG300, Suduru samba, Kahamaala and Suwandall showed comparatively higher WACs (>30%) than the other varieties. During soaking, water enters into the starch granules and void spaces in the rice endosperm, as a result of molecular absorption, capillary absorption and hydration . However, the water absorption rate of the grains is also impacted varietal difference, consisting differences in   IM2 IM3 IM4 IM5 IM6 IM7 TR1 TR2 TR3 TR4 TR5 TR6 TR7 WAC,% (w.b.) ://dx.doi.org/10.22161/ijaers.4.12.27  ISSN: 2349-6495(P) | 2456-1908(O) www.ijaers.com Page | 190

Amylose and Amylopectin Content
Total endospermic starch content in rice, is generally consisted with 0-30% fraction of amylose content and 70-100% fraction of amylopectin content (Martin & Smith, 1997).Nevertheless, rice varieties can be grouped based on its amylose content into higher (25-33%), intermediate (20-25%), low (12-20%), very low (2-12%) and waxy (0-5%) (Juliano, 1971). Amylose and amylopectin contents of improved and traditional rice varieties are graphically illustrated in Figure 02. As presented in Figure 02, amylose contents of improved rice varieties were found in between 25.02 -27.62%. Thus, all of these varieties belongs to the higher amylose class (>25%   (Kim &Wiesenborn, 1995) can cause for the variations. The amylopectin content of rice varieties were varied from 71.7 to 79.6%. Under traditional varieties, highest amylopectin content was reported by Suduru samba and the lowest amylopectin content was found in Kahawanu. BG360 reported the highest amylopectin content from improved varieties and BG352 reported the lowest. Further, statistical analysis of data to amylopectin contents of rice varieties were also significantly different (p<0.05) to each other. Sclafani et al. (1987) and Ramirez, (1991) reveals, rice with higher amylopectin content or highly branched chain structures are more palatable than higher amylose or less branched structure. In contrast with amylose, branched and expanded nature of amylopectin, permits for greater access for digestive enzymes. Therefore, amylopectin provides a higher glucose compared to that of amylose and influenced the body weight gain and increasing serum triglycerides and cholesterol (Denardinet al., 2012).  IM1 IM2 IM3 IM4 IM5 IM6 IM7 TR1 TR2 TR3 TR4 TR5 TR6  An important observation in this study was, relatively higher amylopectin contents were in Suduru samba, Suwandall and BG360. The rice flour obtained from these three varieties are ideal for producing bakery and extruded products. As revealed by , stickiness or pasting property of amylopectin can be utilized to trap the gases evolve during the bakery fermentation. While heat moisture treatment and fine particle size (<200micron) of starch will further improve this phenomena by providing more surfaces for creating hydrogen bonds amongst amylopectin and water molecules. Flour or starch obtained from these rice varieties can also be used as binders in food industry such as process meat, confectioneries etc. An inherited taste & aromatic properties of rice (e.g. Suwandall) can be used to deliver appetizing sensation to regular bakery and other food products too.

Effect of Amylose and Amylopectin Content on Hardness and WAC
In order to investigate the relationship between amylose & amylopectin content, against the test parameters, "amylose vs. hardness", "amylopectin vs. hardness", amylose vs. WAC", "amylopectin vs. WAC" and "hardness vs. WAC" are given in scatter diagrams of Figure 03.

Fig.3: Relationship between amylose content, amylopectin content, hardness and WAC
According to the Figure 03, there was no strong linear correlation ship between the test parameters and the obtained coefficient of correlation indicate the weak or moderate correlation ship. A weak positive correlation ship was observed between amylose content and grain hardness, while weak negative correlation ship (r=-0.215) was reported in between amylopectin content and hardness. Both these correlations were statistically insignificant (p>0.05). However, amylose content and WAC had moderately negative correlation ship (r= -0.427,p<0.05).Amylopectin contents and WACs of tested rice varieties were given moderately positive correlation ship (r=0.427, p<0.05), by signifying the contribution of amylopectin for absorbing and holding the water in rice. Correlation pattern of amylose and amylopectin content with WAC were compatible with the swelling power as well. More compact and linear nature of the amylose molecules less tend to absorb and hold water than highly branched & expanded structures of the amylopectin. Instead of that, hydrophilic parts of proteins and carbohydrates structures are responsible for enhancing

IV. CONCLUSION
Pertaining to the milling properties of the selected Improved and traditional rice varieties, 76-78% of brown rice content, 20 -23 % of husk contents and 69-72% of total milled recovery (TMR) were recorded. These rice varieties consisted with different grain dimensions as well (highest length-BG300; highest width & thickness-Kahawanu ; lowest dimensions -Suduru samba).Sizes and shapes of most rice varieties were short round or short bold (Samba), except, BG300, BG352, BG366, AT307 and Kahamaala, those of which were coming under the intermediate bold(Nadu). Hardness of both rice categories were varied between 21.31N to 34.18N. BG352 had the highest grain hardness and BG358 was the lowest. After four hours of soaking process at 70 0 C, final moisture contents of rice varieties were reached to 28-30% (wet basis). Unakola samba showed the highest water absorption capacity (WAC) ( 30.65%, w.b.) and Rathna samba takes the lowest (28.32%, w.b.). BG300, Suduru samba, Kahamaala and Suwandall were recognized as the varieties with comparatively higher water absorption capacities (>30%).
Measured dimensions (length,width,thickness), hardness and WACs were significantly different (p<0.05) among the selected rice varieties Amylose contents of selected rice varieties were varied from 20-28% (d.b.). BG352 reported the highest amylose content (27.62%) and BG360 reported the lowest (25.02%) among the improved rice varieties. All improved rice varieties can be grouped under higher amylose class(>25%).Traditional rice varieties such as Suwandall and Suduru samba were grouped under intermediate amylose class (20-25%) and other traditional rice varieties were coming under higher amylose class. Kahawanu reported the highest Amylose content (28.6%) and lowest was given by Suduru samba (20.4%).The amylopectin contents of all of these varieties were varied from 71-79 %. Highest and lowest amylopectin contents were reported by Suduru samba and Kahawanu respectively. There was no strong linear correlation ship between those test parameters like amylose content, amylopectin content, hardness and WACs, therefore, none of these parameters are affected along, on the behavior of the other parameter. However, the combine effect of several different factors (chemical & physical) associated with the raw rice grains itself should be the circumstance for variability of each and every parameter.