Effect of calcium fortification and steaming on chemical, physical and cooking properties of milled rice

1 Division of Post Harvest Technology, Sher-e-kashmir University of Agricultural Sciences and Technology of Kashmir, Shalimar, Srinagar 191121, India. 2 Division of Pomology, Sher-e-kashmir University of Agricultural Sciences and Technology of Kashmir, Shalimar, Srinagar 191121, India. 3 Division of Plant Pathology, Sher-e-kashmir University of Agricultural Sciences and Technology of Kashmir, Shalimar, Srinagar 191121, India. 4 Division of Agronomy, Sher-e-kashmir University of Agricultural Sciences and Technology of Kashmir, Shalimar, Srinagar 191121, India.


INTRODUCTION
Rice (Oryza sativa L.) is the most popular cereal worldwide serving as a staple food for nearly half of the world's population and accounts for about 22% of the total energy intake (Chukwu and Osch, 2009).At least 90% of the world's rice farmers and consumers are in Asia, where rice provides up to 75% of the dietary energy and protein to 2.5 billion people (Gnanamanickam, 2009).Although milled rice is superior to brown rice in palatability and digestibility yet milling process results in loss of various nutrients in brown rice (Misaki and Yasumatsu, 1985).Depending upon the extent of milling process, two to five times of reduction have been *Corresponding author.E-mail: aditya.lone@gmail.com,rayees83@yahoo.in.(Harinarayan et al., 2007).

Group
India (mg/day) USA (mg/day) Adults 400 800-1000 Infants 500 500-750 Children 500 800-1300 Pregnant and lactating women 100 1200-1300 reportedly observed in nutrients such as thiamine, fat, fibre, niacin, phosphorus, potassium, iron, calcium, sodium and riboflavin at 10 to 12% degree of milling (Pillaiyar, 1988).Furthermore, mineral malnutrition is a serious threat to the health and productivity of more than two billion people worldwide particularly to women and children (Nagpal et al., 2005).Every night 800 million people go to bed hungry and about 842 million suffer from malnutrition for one or another reason (Toenniessen, 2002).Low energy and protein intakes as well as micronutrient deficiencies are common nutritional problems for people in rice consuming countries like India, Indonesia, Myanmar, Nepal, the Philippines, Bangladesh, Sri Lanka, and Vietnam (Dexter, 1998).It can be addressed by various programmes including supplementation and fortification of commonly eaten foods with required or missing micronutrients (Venkatesh and Sankar, 2004;Aquilanti et al., 2012).Furthermore, increasing intake of a variety of calcium-containing foods might be safer than calcium supplementation because the ingestion of large quantities of calcium concentrated in tablet form may suppress bone remodelling as well as bone resorption (Niewoehner, 1988).Calcium (Ca) is an essential nutrient required for critical biological functions and an adequate intake of calcium has been demonstrated to reduce the risk for chronic diseases such as osteoporosis, hypertension and possibly colon cancer, as well as a number of other disorders associated with aging.Table 1 shows the recommended dietary allowance (RDA) of calcium in India recommended by Indian Council of Medical Research (ICMR).It is 400 mg/day for adults, 500 mg/day for infants, 500 mg/day for children and 1000 mg/day for pregnant and lactating mothers, much lower than the RDAs in the United States of America, which are 800-1000, 500-750, 800-1300 and 1200-1300 mg/day, respectively (Harinarayan et al., 2007).The mean daily intake of calcium is very low in different parts of India (Joshi and Harinarayan, 2009).In Kashmir, the mean daily intake of calcium has been reported to be 230 ± 63 mg/day for men and 178 ± 45 mg/day for women (Zargar et al., 2007).Teotia and Teotia (2008) reported that in 22 States of India, 52% of the populations have nutritional bone diseases, 40.6% have dietary calcium deficiency in critical years of growth and 8% have calcium deficiency in adults and post menopause.Thus there is an urgent need to improve calcium intake through dietary and fortified sources.Therefore, enrichment and fortification of rice are of continued interests to consumers and food processors.Among various calcium sources, calcium lactate has been frequently selected for fortification because of its non-metallic and pleasant mouth feel (Lee et al., 1995).Keeping in view the above facts, the present study on the fortification of rice with calcium was undertaken on two local varieties with the objectives of assessing the impact of calcium fortification on physicchemical and cooking properties of milled rice.

MATERIALS AND METHODS
Two rice varieties, viz.Jehlum and Shalimar Rice-1 released by Sher-e-kashmir University of Agricultural Sciences and Technology of Kashmir (SKUAST-K) were used in the present study.Paddy was supplied by Seed Processing Centre, Division of Plant Breeding and Genetics, SKUAST-K, Shalimar.Paddy (14% MC) was cleaned and milled to rice, and samples were stored in plastic containers prior to analysis.

Method of fortification
The method employed was essentially based on the technique of fortification developed by Lee et al. (1995).The rice samples (1.5 kg of each variety) were separately soaked for three hours in calcium lactate solution or calcium gluconate solution using three concentrations (0.4, 0.6 and 0.8% a.i.Ca) for each treatment.Rice soaking solution ratio was kept constant at 1:0.75 for each treatment and soaking was done under ambient conditions (20 to 25°C).Soaking in distilled water (0% Ca) served as control.The solution/water was drained off by placing the soaked product on an 18-mesh sieve for 5 min.Each treatment sample was spread (<0.5 inch depth) onto cheese cloth in shallow stainless steel basket (9 × 11 inch in size, having 0.25 inch diameter holes at the bottom).The baskets with rice samples of each treatment were autoclaved in a retort at four different pressures and durations viz. 10 psi for 10 min (S 4 ), 10 psi for 5 min (S 3 ), 5 psi for 10 min (S 2 ) and 5 psi for 5 min (S 1 ).The samples of each fortified treatment concentrations were also maintained as un-steamed (S 0 ).The rice was removed from retort and all the samples including non-steamed samples were dried under ambient conditions (20 to 25°C) under shade to moisture content of 11 to 12%.Each treatment was replicated thrice in completely randomized design with 100 g of rice as a unit of replication.

Physical characteristics
Colour was determined by using colorimeter (Make: ColourTec PCM/PSM, New Jersey).The parameters L, a and b were determined for each sample.L (Luminosity or brilliance) varies from black (0) to white (100), a from green (-a*) to red (+a*) and b from blue (-b*) to yellow (+b*).

Chemical parameters
Samples were ground to flour prior to analyses.Crude protein was determined by the method described in official methods of analysis (AOAC, 1995).Starch and total sugars were determined according to the methods described by Nagi et al. (2007).Calcium content of both cooked and un-cooked rice was determined by official methods of analysis (AOAC, 1995).About 5 g flour samples were ashed at 550 to 600°C for 8 to10 h in a muffled furnace.The residue was treated with 5 ml concentrated HNO 3 and heated on a steam bath for 5 min and filtered.The filtrate was made up to 50 ml using one N HNO 3 and aspirated into the flame generated in an atomic absorption spectrophotometer (Make: Electronic Corporation of India Limited).To avoid interference, a few drops of 1% lanthanum chloride were added to each sample.

Cooking properties
To determine the elongation ratio, 5 g rice sample was taken in a 50 ml graduated centrifuge tube and 15 ml of water was added to each tube initially and cooked for 20 min on a water bath.The cooked rice was placed on a blotter paper and the length of 10 kernels was recorded randomly before and after cooking (DRR, 2000).The elongation ratio was calculated by using Equation ( 1): (1) To calculate volume expansion, five grams of head rice were weighed into a perforated basket (height = 7 cm and internal diameter = 4.2 cm).The basket was suspended in a long-type 150 ml beaker containing 100 ml of deionized water and allowed to stand for 10 min.The beaker was transferred into a rice cooker (RC-100H, Toshiba Corp., Tokyo) with the inner pan containing 200 ml of deionized water, and then steam-cooked for 30 min.The beaker with the cooked sample was taken out and excessive water was allowed to drain for five minutes.The height of the cooked rice in the perforated basket was taken at three points with a sliding steel tape.The average of the three measurements was used in calculating cooked rice volume.Volumetric expansion was expressed as the quotient of cooked rice volume over rice sample weight (Patindol et al., 2008).Samples were cooked by using the method described by Gujral and Kumar (2003).Two grams of rice was taken in a test tube from each sample and cooked in 20 ml distilled water at 90°C in a water bath.The weight of each sample was recorded using an analytical balance and water uptake was calculated by using Equation (2): (2) Where, WC and WUC represent the weight of cooked and uncooked rice samples respectively.The rice samples were cooked for minimum cooking time as described by Batcher et al. (1956).Two grams of rice was taken in a test tube from each sample and cooked in 20 ml distilled water at 90°C in a water bath.The minimum cooking time was determined by removing a few kernels at regular time intervals of one minute during cooking and pressing between two glass plates till no white core was left.The samples were considered to be cooked when no white core was left.

Statistical analysis
Analysis of variance (ANOVA) was carried out and critical difference (CD) test was used to describe means with 95% confidence.Analysis of variance was calculated by SPSS statistical software (SPSS Inc., Chicago, Illinois, USA) at a probability level of p < 0.05.Each test was performed in triplicates and the unit of replication was 100 g rice.The experimental design was completely randomized design (factorial).

Physical properties
It was observed that raw milled rice of Jehlum and SR-1 exhibited L (whiteness) values of 79.62 and 77.81, a (redness) value of 0.28 and 0.30, and b (yellowness) values of 16.96 and 16.90, respectively (Table 2).The differences in colour values between the test varieties could be governed by the genetic variability of the test varieties.However, soaking of milled rice in water or fortificant solution resulted in the reduction of L and a values, while as b values increased in response to soaking.Ca fortified rice of Jehlum variety exhibited significantly higher L, a and b values compared to that of SR-1 variety.Fortification treatments differed significantly from one another with regard to all the three colour values (Table 3).It was also observed that T 0 (control) samples exhibited the highest mean L (72.80) and a (-0.45) values, while the lowest (67.84 and -0.90) were recorded in T 3 (Ca lactate at 0.8% a.i.Ca) samples.In case of b values (yellowness), mean values were recorded highest (17.45 and 17.46) in statistically at par T 6 and T 3 treatments and minimum (17.23 and 17.25) in statistically at par T 5 and T 1 as against 17.14 value recorded in T 0 samples.The results are in agreement with the findings of Lee et al. (1995) and Chitpan et al. (2005).Steaming treatments differed significantly from one another with regard to their mean L, a and b values (Table 4).There was a gradual decrease in mean L and a values with increasing steaming intensity from S 0 (no steaming) to S 4 (10 psi pressure for 10 min), while as an increasing trend was noticed in mean b values from S 0 to S 4 steaming intensity.S 0 samples provided significantly higher L (74.71) and a (-0.33) values compared to the rest of the steaming treatments (S 1 to S 4 ), which showed 65.92 to 72.84 L values and -1.26 to -0.45 a values.In contrast, b values were recorded maximum (17.84) in S 4 and minimum in S 0 (17.09)samples.Similar effects on colour have been reported by Islam et al. (2002) and Lamberts et al. (2006) in response to steaming, and by Lee et al. (1995) and Chitpan et al. (2005)

Chemical properties
SR-1 variety possessed significantly higher crude protein content in raw milled as well as water soaked rice as compared to Jehlum variety which could be attributed to its inherently higher protein content (Table 2).Crude protein content was observed to decrease from 8.65% in raw milled rice to 8.60% in water soaked rice of SR-1 variety and from 8.42 to 8.37% in case of Jehlum variety.
Irrespective of variety, it was observed that chemical treatments (fortificant solutions) had no effect on crude protein content of Ca fortified rice Table 3).However, a significant decrease was observed in protein content with the increase in steaming intensity of fortified rice samples (Table 4).The decrease in protein content may be probably due to leaching of non-protein nitrogen, albumin and proteinaceous substances (Raghavendrarao and Julaino, 1970;Otegbayo et al., 2001).Jehlum variety possessed significantly (higher starch content in both raw milled as well as water soaked rice kernels in comparison to SR-1 variety.However, on soaking, starch content of milled rice decreased from 70.26 to 70.00% in Jehlum variety and 69.76 to 69.50% in SR-1 variety.Chemical treatments had non-significant effect on starch content of Ca fortified rice.The present study further indicated that steaming had a significant influence on mean starch content of Ca fortified rice, which decreased gradually with the increase in steaming intensity.Changes in starch content on steaming could be due to gelatinization of starch and some losses might have occurred during soaking and steaming process (Chukwu and Osch, 2009).Depending on the pressure, starch gets solubilized during parboiling process (Pillaiyar, 1988), which might have leached away with the soaking solution.Raghavendrarao and Juliano (1970) have attributed similar observations to appreciable decrease in molecular size of the starch in response to parboiling.Total sugar content of raw milled as well as calcium fortified rice varied significantly with respect to varieties.The mean value for total sugars in raw milled and calcium fortified rice was 0.74 and 1.00% in Jehlum and 0.71 and 0.94% in SR-1, respectively (Table 2).Chemical (fortification) treatments had nonsignificant impact on the level of total sugars in Ca fortified rice.Total sugars increased with soaking and the increasing intensity of steaming.Maximum mean total sugar (1.23%) was observed in S 4 (10 psi pressure for 10 min) and minimum (0.75%) was observed in S 0 (no steaming) which is shown in Table 4. Ali and Bhattacharya (1980) concluded that paddy grains are subjected to enzymatic action during the soaking stage, reducing sugars being produced from sucrose.The present findings are completely in consonance with the observations of Priestly (1976) and Lamberts et al. (2006).SR-1 proved significantly superior to Jelum variety with regard to Ca content of raw milled as well as fortified rice.SR-1 possessed significantly higher (12.46 mg/100 g) Ca content in raw milled rice as compared to Jehlum (5.36 mg/100 g) variety.On soaking in distilled water, Ca content of milled rice decreased to 11.25 and 4.65% in respective varieties, thus indicating a loss of 7.62 and 14.36% in Ca content, respectively.Irrespective of the source of Ca, fortified rice samples of both the test varieties showed a significant increase in Ca content with increasing Ca concentration in soaking solution.Irrespective of chemical and steaming treatments, Ca fortified samples of SR-1 variety exhibited significantly higher Ca content (124.10 mg/100 g) as compared to Jehlum (122.57mg/100 g), which could be attributed to its inherently higher Ca content.Irrespective of varieties, treatment T 3 (Ca lactate at 0.8% a.i.Ca) proved to be significantly superior by providing a maximum mean Ca content of 184.45 mg/100 g followed by 184.04 mg/100 g in T 6 (Ca gluconate at 0.8% a.i.Ca) as compared to 8.05 mg/100 g recorded in control (T 0 ).Soaking milled rice in the test solutions had increased the Ca content of fortified rice by 1211.05 to 2191.30% with a minimum increase recorded in samples subjected to Ca gluconate at 0.4% a.i.Ca (T 4 ) and a maximum increase in samples of T 3 (Ca lactate at 0.8% a.i.Ca).Varieties varied significantly in the retention of Ca in cooked raw milled rice, which was in accordance with the Ca content of raw milled rice in the respective variety.Before fortification, cooked rice of SR-1 had significantly higher Ca content (11.70 mg/100 g) than Jehlum (4.70 mg/100 g) variety.After soaking in distilled water, Ca content of cooked and 10% of Ca was lost during cooking and soaking in each variety.Almost similar findings have been reported by Cheigh et al. (1977) and Hayakawa and Igaue (1979) in response to combined washing and cooking of rice.However, test varieties showed a non-significant effect on Ca retention in fortified rice in the present study.Cooked samples showed a significant increase in retention of Ca in response to increasing Ca concentration in soaking solution as well as increasing steaming intensity.Irrespective of chemicals, treatment concentrations differed significantly from one another in Ca retention.The higher retention in T 3 and T 6 could be attributed to higher levels of Ca in these samples before cooking as a result of fortification.
Steaming had a significant effect on retention of Ca in cooked Ca fortified rice (Table 4).Maximum mean Ca content (111.24mg/100 g) was recorded in S 4 (10 psi pressure for 10 min) while minimum (73.34 mg/100 g) was recorded in S 0 (no steaming) cooked rice samples.Ca is a stable nutrient which reportedly gets lost by leaching (Chitpan et al., 2005).In the present study, about 10% of Ca was lost in S 4 samples, while as losses to the extent of 42% were recorded in S 0 samples.More or less similar losses have been reported by Hettiarachchy et al. (1996).The retention of Ca in fortified rice might be due to physical entrapment of Ca compound in the rice grain (Lee et al., 1995).Furthermore, Ca salt may possibly form complexes with amylose of rice starch during its contact period with the grain and subsequent heat treatment (Hettiarachchy et al., 1996).

Cooking properties
Steaming treatments had a significant influence on elongation ratio, volume expansion and water uptake of Ca fortified rice, which decreased significantly with the increase in steaming intensity.The present findings are in agreement with the observations of Raghavendrarao and Juliano (1970) and Sowbhagya and Ali (1991).Maximum and minimum mean elongation ratio of 1.63 and 1.34, volume expansion of 4.97 and 4.26 cm 3 /g, and water uptake of 2.55 and 2.30 ml/g were recorded in S 0 (no steaming) and S 4 (10 psi pressure for 10 min) samples, respectively (Table 4).The decrease in water uptake on parboiling is well supported by earlier findings of Mahedevappa and Desikachar (1968), Bhattacharya and Subbarao (1968), Ali and Bhattacharya (1972), Arai (1975), Anand (1983) and Patindol et al. (2008).The decrease in water uptake with increasing soaking and steaming time has been attributed to modification of starch granules by heating and parboiling process (Parnsakhorn and Noomhorm, 2008).While as Swasidisevi et al. (2010) concluded, the occurrence of partial pre-gelatinization in pre-steamed rice might have assisted in reduction of fissures within grain kernels and thus reduced water absorption.Chemical treatments Lone et al. 1075 exhibited non-significant impact on elongation ratio and volume expansion (Table 3).However, with the increase in Ca concentration of soaking solution, mean water uptake increased significantly from the minimum of 2.30 ml/g observed in T 0 (water dip-control) samples to maximum of 2.50 and 2.51 ml/g recorded in statistically at par T 3 and T 6 (Ca lactate or Ca gluconate at 0.8% a.i.Ca), respectively.Almost similar results have been observed by Lee et al. (1995) in Ca fortified rice and by Sudha and Leelavathi (2008) in Ca fortified wheat flour dough.Ca fortified rice developed from Jehlum variety exhibited significantly higher mean elongation ratio (1.51) as well as volume expansion (4.75 cm 3 /g) compared to 1.43 ratio and 4.57 cm 3 /g recorded in samples of SR-1 variety (Table 2).The differences in elongation ratio among rice varieties have also been reported by Adu-kwarteng et al. (2003), Singh et al. (2005) and Sidhu et al. (1975).However, the test varieties had a non-significant effect on water uptake of Ca fortified rice.Although chemical treatments showed varying influences on minimum time required for rice cooking yet significantly more cooking time (23.03 minutes) was required for T 0 (water dipcontrol) samples as against a minimum mean time of 21.40 min required for T 6 (Ca gluconate at 0.8% a.i.Ca) samples (Table 3).A minimum time required for cooking of fortified rice samples was observed to increase significantly with the increase of steaming intensity (Table 4).A minimum mean cooking time of 18.76 min required for S 0 (no steaming) samples was followed by 20.59 min for S 1 (5 psi pressure for 5 min) samples, which increased to a maximum of 25.29 min required for S 4 (10 psi pressure for 10 min).The increase in cooking time might have been due to increased kernel hardness during the steaming process (Islam et al., 2002).Ca fortified rice developed from SR-1 took significantly longer time (22.97 min) to cook as compared to 21.22 min recorded in samples of Jehlum variety (Table 2).The present findings are completely in accordance with the findings of Kaur et al. (1991), Islam et al. (2002) and Patindol et al. (2008).

Conclusion
From the present investigation, it can be concluded that, fortifying milled rice of Jehlum (V 1 ) or SR-1 (V 2 ) variety with 0.8% a.i.Ca through either Ca lactate (T 1 ) or Ca gluconate (T 4 ) resulted in enhanced levels of Ca in fortified rice as compared to raw milled rice.Steaming helped in retention of calcium in cooked rice.The fortified rice thus produced may be consumed as such and may also find applications in rice based food systems.

Table 1 .
Recommended dietary allowance (RDA) of calcium in India and in USA

Table 2 .
(Lamberts et al., 2006)ficants.The discolouration and intensity of colour has been reportedly attributed to Maillard type of nonenzymatic browning reaction and processing conditions during parboiling(Lamberts et al., 2006).Effect of variety on physical, cooking and chemical properties of milled rice.

Table 3 .
Effect of fortification treatments on physical, cooking and chemical properties of milled rice.

Table 4 .
Effect of steaming treatments on physical, cooking and chemical properties of milled rice.