Food Sci. Tecnol. Res., 14 (1), 49 54, 2008 Pysicocemical Properties of Starces from Sri Lankan Rice Varieties Hetti Araccige Mangalika WICKRAMASINGHE 1 and Takairo NODA 2* 1 Department of Agricultural Biology, Faculty of Agriculture, University of Peradeniya, Peradeniya 20400, Sri Lanka 2 National Agricultural Researc Center for Hokkaido Region, Sinsei, Memuro, Hokkaido 082-0081, Japan Received October 23, 2006; Accepted October 4, 2007 Pysico-cemical properties; amylose content, swelling power, pasting properties by Rapid Visco Analyzer (RVA), termal properties by Differential Scanning Calorimeter (DSC), and enzymatic digestibility of starces isolated from 19 different Sri Lankan rice varieties were analyzed. Significant variation was sown in all te tested properties among tested varieties in wic te amylose content varied from 16.0% to 34.7%. Amylose content appears to be te major factor controlling almost all pysico-cemical properties of rice starc, as it sowed significant correlations to all oter properties tested. It correlated negatively to te peak and breakdown viscosities by RVA and enzyme digestibility but positively to all oter tested properties. Te peak and onset gelatinization s and enzyme digestibility correlated to all properties except entalpy for starc gelatinization. Te peak and onset gelatinization s, as well as te blue value, sowed negative correlations to te peak and breakdown viscosities, indicating te importance of low amylose for easy starc pasting. According to our results, low amylose starces started to gelatinize at lower s. During eating and cooling, suc starc slurry sowed iger peak and breakdown viscosities, but resulted in a softer gel. Low amylose starc was also easily digestible by enzymes. Tese properties are probably associated wit te reduced compactness in te amorpous area of starc granules. Due to lower amylose in te amorpous area, loosely packed starc granules result in iger swelling power and disorganization wit eating. Keywords: rice starc, RVA pasting properties, DSC termal properties, digestibility Introduction Rice is te staple food for million of people in Souteast Asia, and it is te single most important crop in Sri Lanka in terms of area cultivated, production, number of farming families engaged in its production, and political sensitivity (IRRI, Rice Knowledge Bank, 2006). Breeding efforts at te national level ave resulted in ig-yielding varieties wit resistance to different biotic and abiotic stresses. More tan 50 rice cultivars ave been recommended for Sri Lanka, and te present rice productivity as reaced about 3.8 t/a (IRRI, Rice Knowledge Bank, 2006). Te recent increase in per capita income wit oter development as created a growing consumer demand for pysical purity as well as for better intrinsic quality in rice (Kotagama and Kumara, 1996). Amylose content is te key determinant of te cooking and eating qualities of rice. Furtermore, recent studies ave *To wom correspondence sould be addressed. E-mail: noda@affrc.go.jp sown tat te amylopectin fine structure is also one of te most important factors determining te pasting and gelatinization properties. Generally, ig-quality rice is considered to be soft and sligtly moist wen cooked, and suc qualities are provided by starces wit intermediate amylose and moderate gelatinization s. Terefore, breeders sould give attention to developing varieties wit suc grain qualities. However, few studies ave been conducted to evaluate te cooking and eating qualities of Sri Lankan rice germplasm. Rice starc as commercial interest as an important ingredient in different industries. Rice starc as te smallest particle size among commercial starces, te witest powder color, and a neutral state. Terefore, gelatinized rice starc is very smoot and creamy, and does not ave any flavor. Furtermore, it provides a texture perception similar to tat of fat (Campagne, 1996) and sows potential for replacing fat in some dairy products. Rice is preferably used in producing cosmetic products, suc as baby powder, as its native
50 granules are very small. Tese granules form aggregates tus, pure rice starc is used in parmaceutical industries as a filling agent (Pucongkavarin et al., 2005). Sri Lanka as now become self-sufficient in rice production. Terefore, producing quality rice for te international market and increasing rice-based industries are major callenges to breeders and rice researces in te country. Altoug in a few applications, suc as cosmetics and tableting, te type of starc used is not important, te properties of te starc are important for most oter applications. Te main objective of te present study was to analyze te pysico-cemical properties of starces from Sri Lankan rice varieties, wic could ten be used in different ways in applied studies. Furtermore, tis study examines te different pysico-cemical properties and teir relationsips in indica rice varieties wit ig amylose. Materials and Metods Materials Nineteen different Sri Lankan rice varieties, bot traditional and popular inbred cultivars, were used in te study. Seed samples of all varieties were collected from te Rice Researc and Development Institute (RRDI), Batalagoda, Sri Lanka. All of tem were grown in te Yala season (May to August) of 2005 in RDDI fields. Seed samples were deulled (Satake Deusking Macine, THU 354), polised (Satake Witening Macine MC 250), and ten ground for starc isolation. Starc isolation was carried out as described by Noda et al. (2003). After drying te isolated starc at room for two days, its moisture content was estimated by drying samples in an oven at 115ºC for 3. Te analysis of starc properties was carried out at Memuro Upland Farming Researc Station, National Agricultural Researc Center for te Hokkaido Region, Memuro, Hokkaido, Japan. Amylose content Te amylose content was estimated by te blue value metod as described by Noda et al. (1992) witout defatting te starc. A 2% starc suspension was prepared by dissolving starc in dimetyl sulfoxide (DMSO) at 70ºC for 3 and diluting te mix into a 0.1% starc suspension using distilled water. Te absorbance at 680 nm was recorded using a Beckman DU-640 Spectropotometer (Beckman Coulter, Inc., Fullerton, CA, USA) for a mixture (5 ml) containing 0.2 mg of starc, 0.4 mg of iodine (I2), and 4 mg of potassium iodide (KI) after 30 min after color development. Te amylose content was ten calculated using an equation developed by Asaoka et al. (1994): Amylose content = 99.1 (blue value) 5.0. Pasting properties Te pasting properties were analyzed using a Rapid Visco Analyzer (RVA-4, Newport Scientific Pty., Ltd., Australia) as described earlier (Wickramasinge H. A. M. WICKRAMASINGHE et al. et al., 2003). Te peak, breakdown, final, setback, pasting, and peak time were recorded for samples, wit two replications. Te pasting properties, except te pasting and peak time, were expressed in Rapid Visco Units (RVU). Termal properties A 30% starc suspension was eated from 25ºC to 130ºC at te rate of 2ºC/min in a sealed sample cell for te analysis of termal properties by Differential Scanning Calorimeter (DSC 6100, Seiko Instruments, Inc., Tokyo, Japan), as described by Noda et al. (2004). A pan wit distilled water was used as te reference, and peak gelatinization, onset gelatinization and entalpy for te starc gelatinization were measured for eac sample, wit two replicates. Swelling power A starc slurry, 200 mg of starc (dry weigt basis) in 5 ml of distilled water, was gelatinized at 80ºC for 20 min wit frequent mixing to avoid te formation of starc clots. Gels were cooled at 20ºC for 5 min and ten centrifuged at 1700 g for 5 min. Te swelling power was calculated according to Yasui et al. (1999) and was expressed as te weigt of swelled starc residue per 1 g of starc (dry weigt). Te analysis was repeated tree times. Enzyme digestibility One milliliter of 2% raw starc suspension was digested wit 3.71 units of crystalline glucoamylase from Rizopus sp. (Oriental Yeast Co., Ltd., Tokyo, Japan) for 4 at 40ºC according to te modified metod of Noda et al. (1992). Te amount of glucose released during enzyme digestion was estimated by te penol-sulfuric metod (Dubois et al., 1956), and enzyme digestibility was calculated as te percentage of glucose released during incubation wit te enzyme to te total amount of sugar in te starc on a weigt basis. Data analysis Data were subjected to statistical analysis using Microsoft Excel 2003 software. Te means were compared by te least significant difference (LSD) for eac property. Results and Discussion Blue value and amylose content Te blue value and apparent amylose content of rice starces of tested varieties ranged from 0.212 to 0.400 and 16.0% to 34.7%, respectively, and statistical analysis sowed a significant variation in te caracter among tested varieties (Table 1). Te apparent amylose contents were relatively ig for most samples and iger tan te amylose content previously measured by te iodine affinity test (Juliano, 1971) (data not sown). Asaoka et al. (1994) proposed te following equation using 33 rice varieties: amylose content = 99.1 (blue value) 5.0. All except one were Japonica rice wit low amylose. Teir amylose content varied from 8% to 31%. Te structures of amy-
Propearties of Sri Lankan Rice Starces Table 1. Blue values, apparent amylose content and termal properties of starces from different Sri Lankan rice varieties. Variety Blue value Apparent amylose content (%) DSC Termal properties gelatinization (ºC) Onset gelatinization (ºC) Entalpy (J/g) Traditional varieties Batapola wee 0.400a 34.6* 78.8c 73.7d 14.9def Uvar Rellai 0.393abc 33.9 77.5g 72.6ef 15.8bcd Kalu Heenati 0.389bc 33.5 76.2k 70.5i 14.2fg Dik wee 246 0.379d 32.6 79.1bc 75.4ab 16.9a Dewareddari 0.388c 33.4 78.6d 74.8bc 15.2cde Herat Banda 280 0.398ab 34.4 77.1ij 72.9ef 15.5cd Bandara Hettanawa 0.304j 25.1 76.7j 70.8i 14.9def Bata Mawee 0.348g 29.5 78.0efg 71.5g 14.5efg Heenati 662 0.399a 34.5 77.3i 72.5f 17.0a Martin Samba 0.359f 30.6 77.3i 70.3i 13.7g Suduru Samba 0.262k 21.0 76.8ij 70.9 14.0g Improved varieties BG 357 0.359f 30.6 78.8c 74.8c 16.0bc BG 358 0.326 27.3 78.2def 72.8ef 12.0 BG 450 0.368e 31.5 77.8fg 73.5e 16.5ab BG 352 0.379d 32.6 79.4b 75.1bc 15.2cde BG 379-2 0.376d 32.3 80.0a 75.9a 15.7bcd BG 300 0.391bc 33.7 79.0bc 74.6c 17.3a AT 306 0.312i 25.9 78. 5de 73.9d 15.5cd AT 405 0.212l 16.0 69.4l 64.1j 14.2fg Values followed by te same letter in te same column are not significantly different at P<0.05 level. *Mean comparison was not done for tis caracteristic, as it is derived from blue values. Table 2. RVA pasting properties of starces from different Sri Lankan rice varieties. Rice variety (RVU) Pasting properties by RVA Breakdown Final Set back Pasting (RVU) (RVU) (RVU) (ºC) time (min) Traditional varieties Batapola wee 218k 146k 305f 232de 84.0a 4.47c Uvar Rellai 292g 189g 371bc 269b 79.8f 4.33e Kalu Heenati 284 183g 332e 230de 81.5d 4.47c Dik wee 246 348b 223c 351d 226de 82.3c 4.40d Dewareddari 262j 155j 331e 224ef 82.3c 4.53a Herat Banda 280 270i 171i 318ef 219ef 80.6e 4.50b Bandara Hettanawa 332d 238b 233g 149i 80.6e 4.47c Bata Mawee 333d 209de 362bcd 235cde 80.6e 4.44d Heenati 662 272i 153jk 321e 203g 80.0f 4.40d Martin Samba 423cd 190g 433a 285a 80.6e 4.33d Improved varieties BG 357 322e 207ef 323e 209fg 82.3c 4.40d BG 358 311f 217cd 367bcd 272ab 82.7c 4.47c BG 450 325e 217cd 358cd 251c 80.7e 4.33e BG 352 340c 213de 375b 248c 82.3c 4.33e BG 379-2 281 175i 333e 228de 83.1b 4.40d BG 300 321e 199f 363bcd 242cd 81.5d 4.33e AT 306 321e 243b 243g 166 82.3c 4.40d AT 405 458a 380a 177 99j 73.5g 4.00f Values followed by te same letter in te same column are not significantly different at P<0.05 level. 51 lose (Takeda and Hizukuri, 1986) and amylopectin (Takeda and Hizukuri, 1987) of indica and japonica rice varieties were analyzed, and only a sligt variation in te structures of amylose was identified. However, a significantly iger iodine affinity and blue value were observed in amylopectin of indica rice tan in tat of japonica. Terefore, tese iger blue values could cause iger apparent amylose in indica rice. Pasting properties by RVA All pasting properties were significantly different among te varieties tested (Table 2). Te igest peak, igest breakdown, lowest setback, lowest final, lowest pasting, and lowest peak time were recorded for variety AT405, wic as te lowest amylose content. Te opposite caracteristics were sown wit some traditional varieties tat ad a iger amylose content, suc as Batapola wee, Martin Samba, and Dewaradderi (Table 2). Han and Hamaker (2000) observed tat almost all amylose in te granule is leaced out at te level of peak. Tus, te influence of amylose on te breakdown would be very low, even toug te peak could be affected by bot amylose and amylopectin (Han and Hamaker, 2001). Our present data indicated a negative correlation between te blue value and breakdown. Tus, furter studies on te amylopectin structures of our samples would be useful to analyze te effect of te molecular structure of amylopectin on different pasting properties. Vandeputte et al. (2003b), owever, concluded tat te amylopectin structure ad no correlation to te peak, breakdown, final viscosities, and setback. However, tey did sow tat te starting gel point as an influence on te structure of amylopectin. Swelling power Te swelling power at 80ºC also sowed a significant variation among te varieties used (Figure 1) and ranged from 7.33 g for AT 405 and 16.12 g per 1 g of dry starc for a traditional variety, Dik wee. AT 405 was te variety wit te lowest amylose content, and Dik wee was among te varieties wit iger amylose contents of te samples tested. Previously, Lii et al. (1995) explained tat amylopectin and te crystal region of te starc granule are responsible for swelling and observed ig swelling wit low amylose in rice. Tester and Morrison (1990) also demonstrated tat amylose and lipids actively inibited swelling in cereal starces. Raw starc digestibility As wit oter properties, te raw starc digestibility by fungal crystalline glucoamylase varied significantly among tested samples (Figure 1). AT 405 gave te igest values for enzyme digestibility, and very ig resistance to enzymes was sown by some traditional rice varieties, suc as Batapola wee and Dik wee. Our results demonstrated tat starc ydrolysis tends to be very quick for low amylose starces in comparison to ig amylose starces, wic was comparable wit previous reports
52 H. A. M. WICKRAMASINGHE et al. Enzyme digestibility (%) Swelling power (g/g) 60 50 40 30 20 10 0 Batapola wee Uvar Rellai 18 16 14 12 10 8 6 4 2 0 Kalu Heenati Dik wee Dewareddari Herat Banda Bandara Hettanawa Bata Mawee (Hu et al., 2004; Noda et al., 2003). Termal properties by DSC All termal properties measured by DSC on starc gelatinization ad significant variations among te varieties under investigation (Table 1). Starces wit low amylose, suc as AT 405, gelatinized easily and required low energy for te gelatinization. Some traditional varieties, suc as Dik wee, Heenati, and a new improved variety, BG 300, required very ig energy for gelatinization. Generally, tese varieties ad iger amylose in starc. Te peak gelatinization and onset gelatinization of our samples ranged from 69.4 to 80.0ºC and 64.1 to 75.9ºC, respectively. Te entalpy for starc gelatinization varied from 12.0 to 17.3 J/g. Correlation analysis among tested caracteristics of rice Te blue value of tested varieties sowed significant correlations wit all oter properties, tus again proving k efg k ef d Batapola wee Uvar Rellai Kalu Heenati k i fg ef e fg a bc de c bc d ef i g i Heenati BG 357 BG 358 BG 450 BG 352 BG 379-2 BG 300 bc def Dik wee Dewareddari Herat Banda Bandara Hettanawa Bata Mawee Heenati BG 357 BG 358 BG 450 BG 352 BG 379-2 BG 300 AT 306 b j b bcd c AT 306 AT 405 Martin Samba Suduru Samba g te importance of amylose content as a major factor determining starc properties (Table 3). Te igest correlation (0.92) was sown wit te breakdown at RVA, and te least was sown wit te blue value (0.46). Te relationsips of te blue value wit te peak, breakdown, and enzyme digestibility were negative, wile all oters were positive. Similar relationsips were also found in previous studies, suc as negative relationsips wit peak and breakdown (Collardo and Corke, 1997; Hu et al., 2004; Vandeputte et al., 2003b; Zeng et al., 1997) and enzyme digestibility (Noda et al., 2003), and positive correlations wit termal properties suc as peak gelatinization and entalpy for starc gelatinization by DSC (Pratepa et al., 2005; Saif et al., 2003). As for te RVA parameters, very ig correlations between te blue value and all RVA parameters ave been al- a i b fg AT 405 Martin Samba Suduru Samba Fig. 1. Swelling power and enzyme digestibility of starces from different Sri Lankan rice varieties. Bars labeled wit te same letters are not significantly different at te P < 0.05 level. d
Propearties of Sri Lankan Rice Starces 53 Property Table 3. Correlation coefficients among tested starc properties in Sri Lankan rice varieties Breakdown Final Set back Pasting temp. time Swelling power Enzyme digestibility Blue value -0.72** -0.92** 0.68** 0.71** 0.66** 0.63** 0.46* -0.87** 0.69** 0.70** 0.47* 0.80** -0.14-0.30-0.66** -0.76** -0.25 0.69** -0.58** -0.62** -0.23 Breakdown -0.61** -0.67** -0.74** 0.79** -0.34 0.80** -0.75** -0.67** -0.21 Final 0.96** 0.48* 0.32 0.41-0.63** 0.61** 0.48* 0.01 Set back 0.57* 0.41 0.39-0.72** 0.64** 0.51* -0.08 Pasting 0.79** 0.66** -0.77** 0.93** 0.87** 0.08 time 0.55* -0.66** 0.70** 0.62** -0.03 Swelling power -0.61** 0.67** 0.67** 0.14 Enzyme digestibility -0.80** -0.77** -0.40 gel. temp Onset gel. temp. Entalpy gelatinization Onset gelatinization 0.95** 0.30 0.45 ** and * indicate significance at P < 0.01 and P < 0.05 levels, respectively. ready described. Apart from significant correlations among some RVA parameters, tey all were igly correlated to enzyme digestibility, peak gelatinization, and onset gelatinization at DSC. Furtermore, te pasting and peak time sowed significant correlations wit te swelling power. No relationsips were found between te peak and te final and setback viscosities or between te setback and te peak time. According to te correlation coefficients given in Table 3, te swelling power sowed significant correlation wit te blue value (0.46), peak (0.67) and onset (0.67) gelatinization s by DSC, and pasting (0.66) and peak time (0.55) by RVA, proving te importance of amylopectin, its structure, and relative crystallinity for tis property. In te present study, te relationsip between te blue value and swelling power was positive. Even toug tis correlation is statistically significant, it was te least significant correlation sown by te blue value among oter tested caracteristics. Te enzyme digestibility sowed negative correlations to all caracteristics, except te peak and breakdown at RVA and te gelatinization entalpy at DSC. Te enzyme digestibility sowed te igest correlation to te blue value (0.87), indicating tat te amylose content of rice starc is of great importance in predicting te enzyme digestibility of starc. Our results sowed tat starc containing low amylose started gelatinization at lower s. Wile eating and cooling, suc starc slurry sowed iger peak and breakdown viscosities but resulted in a softer gel. Suc starc is also easily digestible by enzymes. Tese properties are probably associated wit te reduced compactness in te amorpous area of starc granules and tat may facilitate te easy absorption of water to te granule and speed up te disorganization of starc wit eating. Excepting te blue value, no oter properties ave a significant impact on entalpy for starc gelatinization. Interestingly, none of te pasting properties measured by RVA correlated to te entalpy for starc gelatinization as estimated by DSC. Lai et al. (2001) proved tat te gelatinization properties varied due to te molecular structure of amylopectin and amylose by using two rice cultivars wit apparently similar amylose content. From te amylose in te granule, absolute amylose and free amylose could facilitate gelatinization, wereas lipid complex amylose delayed it (Vandeputte et al., 2003a). Furtermore, te same autors expressed tat sort amylopectin cains wit DP 6 9 and long amylopectin cains wit DP 12 22 decreased and increased te gelatinization s of rice starc, respectively. Since te amylose content in our samples correlated significantly (0.69) to te peak gelatinization, te amylopectin structure and relative crystallinity of te granule would be te oter factors governing gelatinization. Conclusion According to te correlation analysis, te amylose content proved to be te most important factor in determining te pysico-cemical properties of rice starc. As all properties varied significantly among te varieties tested, te
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