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Edible coating materials—their properties and use in the fortification of rice with folic acid
Food Research International 36 (2003) 921–928 www.elsevier.com/locate/foodres
Edible coating materials—their properties and use in the fortification of rice with folic acid§ Ashok K. Shrestha, Jayashree Arcot, Janet L. Paterson* Food Science and Technology, School of Chemical Sciences, The University of New South Wales, Sydney 2052, Australia Received 10 November 2002; accepted 11 June 2003
Abstract This study investigated the technical feasibility of adding folic acid on to rice and coating with edible polymers. The coating solutions were cast into film and their properties were investigated. A concentrated premix of rice was prepared in a rotating coating pan by spraying first with folic acid solution, and then with polymer solutions and drying. The fortified rice premixes were evaluated for washing and cooking losses. The loss of folic acid in washing was lowest in rice premixes coated with ethyl cellulose followed by pectin, composite mixtures of locust bean and other coating materials with highest loss in gum arabic coated rice. No edible polymer could satisfactorily retain folic acid during boiling in excess water. Edible polymers failed to mask the yellow color of folic acid and additional masking agent was needed. The premixes had a higher water uptake ratio than raw milled rice had. Triangle tests did not show any significant difference (=0.05) between the sensory qualities of cooked fortified rice and raw milled rice. # 2003 Elsevier Ltd. All rights reserved. Keywords: Folic acid; Rice fortification; Processing loss; Sensory test
1. Introduction Folate or folic acid is the term most commonly used to refer to a family of vitamers with related biological activities. In recent years, interest in the fortification of foods with folic acid has increased, largely in response to the findings of epidemiological studies that link folate with neural tube defects (NTDs), coronary heart disease and megaloblastic anemia (MRC Vitamin Group, 1991; Selhub et al., 1995). Fortification of folic acid in one or more of the commonly consumed dietary items is now regarded as the best method to ensure that women increase their folate intakes to reduce the risk of having a pregnancy affected by neural tube defects. The United States Food and Drug Administration (USFDA) have already made it mandatory for all manufacturers of grain products to add folic acid for enrichment of products, effective from 1 January 1998. The general range of enrichment as given by FDA is 100–300 mg per 100 g for all types of grain products (Hoffpauer & Bonnette, § A less detailed version of this paper as a one-page abstract was published in the Proceedings of the 17th International Congress of Nutrition, Vienna, Austria, August 27–31, 2001. * Corresponding author. Fax: +61-2-9385-5931. E-mail address: [email protected] (J.L. Paterson).
0963-9969/$ - see front matter # 2003 Elsevier Ltd. All rights reserved. doi:10.1016/S0963-9969(03)00101-7
1998). Most of the developed countries, including Australia, practice voluntary fortification with folic acid. Rice is an ideal food for micronutrient fortification because it is a staple diet for more than half of the world’s population (Juliano, 1990). Milled rice is one of the poorest sources of folate (3–14 mg/100 g) and other water-soluble vitamins (Marshall & Wadsworth, 1994). The nutritional value of milled rice may be further reduced as a result of the method used to prepare rice for eating such as washing and cooking in excess water and draining (Malakar & Banerjee, 1959). Most of the enrichment methods for rice fortification use acids (Hoffman La Roche method, USA, as described by Mickus, 1955; Rice Growers’ Co-operative Limited method, Australia, as described by Bramall, 1986; Shingen method, Japan as described by Misaki & Yasumatsu, 1985; Cross-linking method, as described by Joseph, Liuzzo, & Rao, 1990) which make them unsuitable for folic acid fortification because folic acid is unstable under acidic conditions. There are two additional criteria for a good folic acid fortification method: it should prevent the leaching of vitamins during washing and cooking and it should mask the yellow color of folic acid in fortified rice. Previous studies have shown that edible polymer coating(s) help retain added micronutrients in fortified rice during washing and cooking
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tests (Peil, Barrett, Rha, & Langer, 1981; Cort, Borenstein, Harley, Osadca, & Scheiner, 1976). Studies so far have evaluated only a limited range of polymers for their suitability to prevent the loss of micronutrients in fortified rice during processing. Therefore the objectives of this study were to examine the ability of various edible polymers to prevent the loss of added folic acid in rice during rinsing and cooking; and to investigate the physiochemical and sensory properties of the folic acid fortified rice. All the tests except sensory properties were carried out on the premix, designed to be diluted 1:100 with raw milled rice.
polymer films, about 40 ml of polymer solution was poured and sprayed onto a level, rectangular (1612 cm2) glass plate by means of a standard applicator for thin-layer chromatography. The film forming solution was dried in a ventilated oven set at 50 C for about 2 h to evaporate water and a homogenous film was then formed. The dried films were cut into small rectangular pieces of about 32 cm and dropped into water (20 C) in a 500 ml beaker. The behavior of the edible film in water was then observed. The color, transparency and strength of the film were also evaluated subjectively. 2.3. Preparation of a concentrated rice premix
2. Materials and methods 2.1. Materials Australian long grain rice, Sunrice, was provided by the Rice Grower’s Cooperative Limited, NSW, Australia. Various polymer coatings were obtained from respective suppliers such as methylcellulose (MC) and hydroxypropyl methylcellulose (HPMC), ethylcellulose (EC), locust bean gum (LBG), gum tragacanth, carrageenan, gum guar and low methoxyl pectin (from citrus peel, methoxyl content 9.7%) from Sigma Chemicals Co. St Louis, MO, USA; Modified corn starches e.g. Pure Cote 790, and some maltodextrins from Grain Processing Corporation, Muscatine, IA, USA; tri-calcium phosphate, carboxymethyl cellulose (CMC), sodium alginate, rice starch from Swift and Company Ltd., Victoria, Australia; starch powder from National Starch and Chemical Pty Ltd., Bridgewater, NJ, USA; and gum arabic from TIC GUMS, MD, USA. Rice protein concentrate (65% protein) was provided by Quest International, Australia. Shellac solution (dewaxed superblonde) was provided by Shine Pty. Ltd., Sydney, Australia. Media for folic acid analysis were purchased from Difco Laboratories (Detroit, MI, USA). Folic acid (pteroylglutamic acid) was obtained from Sigma Chemical, St. Louis, MO, USA. 2.2. Preparation of coating solution and polymer films Most of the coating solutions were prepared by slowly dissolving a known amount of coating material into 75– 100 ml distilled water, heated to about 80 C in a 250 ml beaker with continuous stirring until the coating materials dissolved or at least were suspended in the solution. The consistency of solution was such that it could be sprayed by a hand held nozzle spray. Solutions for MC, HPMC or their composite mixtures were prepared according to Nelson and Fennema (1991). Ethylcellulose solution was prepared in ethanol (100%). The amount of coating materials needed to form a sprayable solution in 100 ml solvent was noted. To prepare the
A stainless steel, spherical (diameter 20 cm at mouth), tablet coating pan with adjustable motor speed (Erweka AR 401, Serial No. 71378:ab53, D63150 Heusenstamm, Germany) was used for the fortification process. The coating pan was also fitted with an Infra-Red Lamp (Elstein lot 150 230 V, 150 W, 450 C) for heating. Rice (250 g) was fortified by first spraying folic acid solution (100 mg in about 20 ml water) followed by a coating solution and with constant mixing and drying to initial weight as shown in Fig. 1. Various materials were applied on one set of the rice premix (LBG+Xanthan gum coated premix), separately, to study their ability to mask the yellow color of folic acid: rice gruel, rice gruel with shellac solution and starch solution were sprayed to the dry premix; calcium phosphate and starch powder were puffed on to the surface towards the rolling premix at the end of the spraying and drying cycle. 2.4. Determination of washing and cooking losses The washing and cooking losses of raw milled rice and rice premixes were determined in a room with subdued light as folic acid is sensitive to light. All the glassware was covered with aluminum foil. For washing or rinsing test, 20 g rice premix in a 250 ml conical flask was rinsed with 60 ml distilled water by gently swirling for exactly 60 s. For the cooking test, 5 g sample in a 125 ml conical flask was mixed with 100 ml water, boiled for 30 min in a water bath (97 3 C), and cooled immediately. The cook-water and wash-water were decanted and centrifuged (Sorvall, Dupont, CT, USA) at 3000 rpm for 15 min. The supernatant (5 ml) was pipetted to 50 ml volumetric flask, brought to volume with phosphate-ascorbate buffer (0.1 M potassium phosphate, 1% ascorbic acid and pH 6.1) and mixed well. The extract was transferred into small-labeled brown bottles and stored at 20 C. 2.5. Folic acid analysis The raw milled rice (control) was extracted for folic acid (or undeconjugated folate) according to Shrestha,
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Arcot, and Paterson (2000). The wash-water and cookwater were further diluted with phosphate ascorbate buffer and analyzed for folic acid by microbiological assay using Lactobacillus casei according to Shrestha, Arcot, and Paterson (2000). The loss of folic acid during washing and cooking tests were therefore estimated from the initial added amount for fortification [100 mg folic acid was added to 250 g rice (40,000 mg/100 g)].
with some modification. Three grams of sample in a spherical tea infuser (internal diameter 35 mm, CPS, China) was lowered into a 250 ml beaker containing 175 ml boiling water, and covered with a watch glass. The rice was cooked for 20 min in a boiling water bath (97 3 C) and drained for 2 min. The water uptake ratio was calculated by dividing the increase in weight on cooking by the weight of the original rice.
2.6. Measurement of color of the fortified rice
2.8. Sensory evaluation of fortified rice
The color characteristics (‘L’, ‘a’ and ‘b’) of raw milled rice and the rice premixes were measured quantitatively using a color difference meter (Minolta Chroma meter, CR-300 Series, Osaka, Japan) calibrated with a white standard plate (‘L’=98.12, ‘a’= 0.03 and ‘b’=1.22). ‘L’ value indicates white (100) to black (0); ‘a’ value indicates red (100) to green ( 80); ‘b’ value indicates yellow (70) to blue ( 80).
Eating quality of rice largely depends on the textural properties of cooked rice, which is determined by the degree of cooking and the rice–water ratio (Juliano, 1985). Before actual cooking of rice, optimum water to rice ratio for the best eating quality of milled rice was determined subjectively on the basis of taste and tenderness of the cooked rice. Rice was cooked in four different rice to water ratios (1:1.7; 1:1.8; 1:1.9; and 1:2) for 20 min using automatic rice cookers (2.5 l capacity, Model DF020, Sunbeam, Thailand). The optimum ricewater ratio was 1:1.9. A simple (classical) triangle test was chosen for sensory evaluation (Jellinek, 1985) of cooked milled rice and fortified rice (rice premix coated with LBG+xanthan gum+rice protein concentrate diluted to 1:100 with raw milled rice). Sensory evaluation of the warm cooked rice(s) was carried out by an untrained panel of 36 students and staff from Food Science and Technology, The University of New South Wales, Sydney, Australia. The test was carried out in a sensory evaluation laboratory using white light. The staple diet of most of the panelists was not rice. Each panelist was served three small plates of cooked rice, two alike and one different. Samples were coded with three digit randomly generated numbers to avoid bias (Cochran & Cox, 1957). They were asked to judge each cooked rice sample for its appearance, color, aroma, flavor, tenderness or hardness and to select the odd sample. The data obtained were tabulated and the statistical analysis to test the significance of the result was carried out according to Roessler, Pangborn, Sidel, and Stone (1978).
2.7. Water uptake ratio Water uptake capacity of fortified rice was measured according to Batcher, Hemintoller, and Dawson (1956)
3. Results and discussion 3.1. Properties of edible films
Fig. 1. Outline of folic acid fortification procedure.
The composition and properties of edible films is presented in Table 1. MC, HPMC, CMC and their composite mixture gave excellent transparent, flexible and fairly strong films. However, these films dissolved readily in cold water. EC film was strong, less flexible, and insoluble in water. EC has been cleared by Food and Drug Administration (Federal Register, 1962) for use as
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Table 1 Composition and properties of edible polymers and their composite mixtures Composition of coating solutiona
Film propertiesc
1.15 g MC in 50 ml water 0.6 g sodium alginate in 50 ml water 15 g gum arabic in 50 ml water 7.5 g PC 790 in 75 ml water
Transparent, thin, flexible, readily soluble Transparent, thin, flexible, readily soluble Pale yellow film, firmly stuck to the glass, soluble Transparent, rough surface, slight rigid, slowly dissolve in water Transparent, soft, easy to tear, readily soluble Slight translucent, soft but good tensile strength, insoluble in water Translucent, soft, readily collapse in water forming mucilaginous mass Thick gel, could not be dried completely Transparent, thick, fairly strong, slowly dissolve in water Translucent, soft but good tensile strength, insoluble in water Translucent, thin, firmly attached to glass, swell and dissolve in water Transparent, thin, flexible, readily soluble in water Translucent, hard and good tensile strength, shrink but did not dissolve in water Translucent, soft, insoluble in water
1 g tragacanth in 120 ml water 1 g carrageenan in 50 ml water 0.3 g xanthan gum in 50 ml water 1 g agar in 75 ml water 2.5 g CMC in 50 ml water 3.0 g EC in 50 ml ethanol 0.25 g LBG in 50 ml water (1.5 g MC+0.5 g HPMC) in 50 ml water 0.5 g carrageenan in 50 ml water+1 g agar in 50 mlb 1 g carrageenan in 50 ml water+0.7 ml sodium alginate in 50 ml waterb 0.5 g carrageenan in 50 ml water+0.2 g xanthan gum in 50 ml waterb 1 g agar in 75 ml water+0.375 g LBG in 75 mlb (1.5 g MC+5 g PC 790) in 50 ml water (2 g MC in 50 ml+1 g agar) in 75 ml waterb (0.25 g LBG+0.2 g xanthan gum) in 80 ml water 0.375 g LBG in 75 ml+1 g agar in 75 ml waterb 0.375 g LBG in 75 ml+7.5 g PC 790 in 75 mlb
Translucent, soft, insoluble in water Slight translucent, rough surface, hard, insoluble in water Transparent, rigid, slowly dissolve in water Translucent, thick, strong but flexible, slowly dissolve in water Translucent (milky), soft, insoluble in water Translucent, rough surface, brittle, insoluble in water Transparent, rough surface, brittle, swell and slowly dissolve in water
Solutions were prepared in hot water (805 C), except EC. Individually prepared and mixed together in equal portions. c Solubility in water. MC=methylcellulose; HPMC=hydroxypropyl methylcellulose; EC=ethylcellulose; CMC=carboxymethylcellulose; PC 790=pure cote 790 (modified corn starch); LBG=locust bean gum. a
b
a binder and filler in dry vitamin preparations and as a component of protective coatings for vitamin and mineral tablets (Glicksman, 1969) but it is not a permitted additive in Australia and New Zealand. Agar solution produced a thick homogenous-gelled structure that was difficult to dry, did not produce any film even after drying for 5–6 h. However, when mixed with xanthan gum, or with LBG, agar formed a translucent, flexible film that remained insoluble in water for a long time (> 15 min). Armisen (1999) reported that agar has a synergistic effect with LBG, producing more elastic and less brittle structures. The pectin film stuck to the glass plate and was hard to peel off. The film was pale yellow, flexible, and dissolved slowly in water (> 30 min). LBG formed a soft, translucent film, firmly attached to glass, which swelled in water and dissolved after a long time (> 30 min). The presence of a small number of d-galactose in the insoluble fibrous structure of d-mannan in LBG accounts for its limited solubility (Fox, 1999). LBG has the unusual synergistic effect of imparting desirable elastic properties to xanthan gum, carrageenan and agar gels
(Glicksman, 1969; Fox, 1999). When mixed with xanthan gum, LBG produced a flexible, translucent and water-insoluble film. Xanthan gum itself, however, produced a soft, translucent film that readily collapsed in water forming a mucilaginous mass. PC 790, a modified corn-starch, produced a transparent, brittle film that slowly dissolved in water. Carrageenan solution produced a smooth, translucent, strong but flexible film that did not dissolve in water. In combination with most of the polymers such as agar, sodium alginate and xanthan gum, carrageenan produced a fairly insoluble film. Gum arabic, tragacanth and sodium alginate solutions gave thin transparent films that were highly soluble in water (see Table 1 for concentration of the gums). 3.2. Loss of folic acid during washing The amount (and percentage) of folic acid in washwater and percentage loss from rice and premixes is given in Table 2. The folic acid content of raw milled rice used for fortification was 41 mg/100 g. There was a loss of 30 mg folic acid (73%) in unfortified or raw
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A.K. Shrestha et al. / Food Research International 36 (2003) 921–928 Table 2 Loss of folic acid in wash- and cook-water in rice and rice premixes using various coating materials Rice premixes
Wash-water (mg/100 g)a,b
Cook-water (mg/100 g)a,b
Raw milled rice MC MC+HPMC MC+LBGc MC+dextrinc MC+PC 790 MC+LBG MC+carrageenan CMC CMCc CMC+sodium alginate CMC+carrageenan CMC+LBG Ethylcellulose Guar gum LBG LBG+carrageenan LBG+xanthan gumc LBG+xanthan gum LBG+agar LBG+PC 790 LBG+sodium alginate Carrageenan Carrageenan+sodium alginate Carrageenan+PC 790 PC 790 PC790+maltodextrin PC790+sodium alginate Gum acacia Gum arabic Gum arabic+agarc Agar+xanthan gumc Folic acid solution Pectin
303 (73) 5322710 (49) 4211869 (49) 392198 (46) 7531549 (44) 207779 (53) 922732 (42) 336853 (41) 562667 (56) 757351 (52) 1562641 (60) 825835 (52) 8312581 (52) 949143 (2) 13 5982421 (34) 9483559 (24) 14 16983 (35) 80281286 (19) 8553363 (21) 4595622 (11) 19 39159 (42) 22 0321612 (55) 20 4032119 (51) 18 1091442 (45) 14 575184 (36) 22 3153176 (56) 20 903964 (52) 21 6141289 (54) 21 201390 (53) 24 2371053 (61) 21 075178 (53) 10 301482 (26) 19 465750 (49) 368616 (9)
394.6 (96) ND 28 4673451 (71) ND ND ND ND ND ND ND ND ND ND 24 3032193 (61) ND 37 0141419 (93) ND 29 6403756 (74) 35 5981337 (89) 36 0831409 (90) ND ND ND ND ND ND ND ND ND ND ND 34 5932823 (86) 34 5212837 (86) 27 5392212 (69)
19 19 18 17 21 16 16 22 20 24 20 20
ND=not determined. a Mean valuestandard deviation (three replicates). b Values in parenthesis in indicate the % loss during washing or cooking, based on a 40 000 mg folic acid/100 g in rice premixes. c Folic acid was dissolved in 30 ml rice protein concentrate solution and sprayed prior to coating solution.
milled rice during the washing test. Diminishing nutritional value of rice during washing and cooking has been well documented. Washing of milled rice has been reported to remove 22–59% of the thiamin, 11–26% of the riboflavin and 20–60% of the niacin (as reviewed by Juliano, 1985). EC was the best coating material followed by pectin, each with washing loss of 2 and 9% respectively. EC has been used as a coating material in rice fortification by Wright Enrichment Inc., USA (Cort et al., 1976). The relatively hydrophobic nature of EC is responsible for lower washing loss of folic acid. The pH of pectin solution was 3.5, the acidic solution might have reacted with surface starch forming a thin, sugar layer (Bramall, 1986). As the liquid mixture on the rice surface was absorbed and subsequently dried, the folic acid was bound to the rice in the sugar coating. Lower solubility of low methoxyl pectin (Glicksman, 1969) and hydrophobic interaction between pectin and rice components
such as starch and protein could have further reduced the loss of folic acid during washing. MC, HPMC CMC, modified corn starch, dextrin, sodium alginate, gum arabic, gum acacia, carrageenan and their composite mixtures lost more than half of the added folic acid during rinsing (Table 2). The use of 10% rice protein concentrate as a carrier of folic acid did not improve the retention of folic acid in fortified premixes, as seen in CMC and LBG+xanthan gum coated rice (Table 2). The smaller droplets of agar solution on spraying and drying formed fine gels that subsequently turned into finer particles causing a dust problem. This was overcome by using composite mixture of agar with other polymers such as xanthan and LBG. The rice premix coated with agar and LBG lost 11.5% folic acid in wash-water, whereas the loss was almost doubled when xanthan gum was used with agar. LBG and its composite mixture with xanthan gum also showed improved folic acid retention during rinsing.
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LBG forms a strong, thermo-reversible, cohesive, elastic gel with xanthan gum, a functionality of which neither of the hydrocolloids exhibits alone (Fox 1999; Sworn, 2000). Coating rice with folic acid solution alone retained almost half of the added folic acid during rinsing, better than many coated rice premixes. This may be because the outer starch layer was gelatinized during spraying and drying and because one wetting and drying resulted in a lesser degree of cracking. 3.3. Loss of folic acid during cooking The loss of folic acid from the premix cooked in excess water is given in Table 2. Milled raw rice lost almost all of its folic acid whereas other coated rice lost 61–93% of the added folic acid in cook-water during cooking test. Table 2 shows that no coating material was strong enough to prevent leaching of folic acid from fortified premixes when boiled in excess water. It was unlikely that any edible polymer could preserve the physical integrity of rice kernel when it is boiled for 20 min in excess water. In the fortification process rice went through frequent soaking (spray) and drying that gelatinized the outer starch layer and also caused cracking. During boiling, water gets easy access to the interior of the cracked grain, increasing hydration and subsequent leaching of the vitamin into the cooking water. The loss of folic acid in cook-water was lowest in EC coated rice at 61%. It could be due to impermeability of ethylcellulose film in water. Although MC derivatives are reported to be insoluble in hot water Table 3 Color characteristics of rice premix coated with various polymer coatings Coating ingredients
Color characteristics ‘L’
Milled rice FA only Pectin EC MC+ HPMC MC+ HPMCa LBG LBG+agar LBG+agara LBG+xanthan gum LBG+xanthan guma Rice gruelb Starch solutionb Ca3PO4 powderb Rice starchb Shellac: rice gruel (1:1)b a
69.61 76.55 74.52 73.36 75.76 75.99 78.46 78.54 77.10 79.44 75.6 76.81 79.51 84.23 75.93 74.60
‘a’ 1.27 5.30 3.9 4.54 4.44 3.39 4.79 4.66 3.47 4.82 2.76 3.94 3.31 1.57 2.1 1.14
‘b’ 10.71 29.73 29.41 24.83 25.84 20.65 28.46 27.34 20.97 28.03 19.37 24.19 18.93 11.62 18.67 22.98
Folic acid was dissolved in 30 ml rice protein concentrate solution and sprayed prior to coating solution. b Color masking agents applied to rice premix coated with LBG+xanthan gum.
(Nisperos-Carriedo, 1994; Zecher & Gerrish, 1999) there was cooking loss of more than 70% folic acid in rice coated with MC+HPMC. In similar studies, Peil et al. (1981) reported a loss of 82, 82 and 79% thiamin, niacin and riboflavin respectively when rice coated with MC+HPMC (1:3 ratio) was cooked in the same way. 3.4. Color of the fortified rice Table 3 shows a significant difference in the color characteristics of the raw milled rice and the rice premixes indicating that coating materials failed to mask the yellow color of folic acid. There was a marked increase in lightness (‘L’), redness (‘a’) and yellowness (‘b’) values when folic acid and edible polymers were applied to milled rice. It is necessary that the fortified rice grains blend well with raw rice so that consumers will not reject them. To restore the color of the fortified rice, various color-masking agents were applied. Calcium phosphate restored the redness and yellowness values closest to the milled rice but the premix appeared chalky with a slight metallic tinge. When the premix was mixed with milled rice in 1:100 ratios, difference in color appeared minimal. Consumers are unlikely to pick the fortified grains as defective. 3.5. Water uptake by fortified rice Table 4 shows the water uptake ratio of milled rice and some rice premixes. The water uptake ratio for milled (long-grain type) rice was 3.03. Except EC coated rice, all the premixes registered water uptake ratio more than 4. The cooked EC coated rice kernels were well separated and tender: the texture was close to cooked milled rice. Other fortified rice kernels were split and had starch leaching out from the cracks. These kernels remained clumped together in the tea infuser. The fortified premix rice kernels were cracked during fortification which might have caused the greater water uptake Table 4 Water uptake ratios of raw milled rice and some rice premixes Rice premixes
Water uptake ratio (g/g)a
Raw milled rice MC+HPMC Ethylcellulose LBG LBG+xanthan gum LBG+agar Agar+xanthan gumb Folic acid solution Pectin
3.03 0.03 4.02 0.05 3.29 0.01 4.6 0.08 4.84 0.14 4.8 0.05 4.31 0.12 3.75 0.07 4.11 0.01
a
Mean valuestandard deviation (three replicates). Folic acid was dissolved in 30 ml rice protein concentrate solution and sprayed prior to coating solution. b
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Table 5 Performance rankinga of best rice premixes Rankinga 1 2 3 4 5 6 7 8 9 10
Washing loss EC Pectin LBG+agar Rice gruel LBG+xanthan gumb LBG+xanthan gum LBG Agar+xanthan gumb MC+HPMC Folic acid only
Cooking loss
Color
EC Pectin MC+HPMC LBG+xanthan gumb Folic acid only Agar+xanthan gumb LBG+xanthan gum LBG+agar LBG ND
Water absorption ratio b
LBG+xanthan gum MC+HPMC Agar+xanthan gumb Rice gruel EC LBG+agar LBG+xanthan gum Pectin LBG Folic acid only
EC Folic acid only MC+HPMC Pectin Agar+xanthan gumb LBG LBG+agar LBG+xanthan gum ND ND
a Ranking is based on the best performances of premixes e.g., less folic acid in wash- or cook-water, less yellow color, and less water absorption ratio. b Folic acid was dissolved in 30 ml rice protein concentrate solution and sprayed prior to coating solution.
and therefore, shorter cooking time (Juliano, Onate, & Mundo, 1965). Besides, there were greater number of broken kernels in fortified premixes which absorb more water due to their greater surface area. Lee, Hettiarachchy, McNew, and Gnanasambandam (1995) also reported a significant increase in water uptake value and disintegration of cooked calcium fortified rice when compared to the control sample. 3.6. Sensory evaluation of cooked rice Initially rice premixes with better folic acid retention during washing (rice coated with LBG+xanthan gum, LBG+agar, MC+HPMC, pectin, and ethylcellulose) were blended with raw milled rice (1:100 ratio) and cooked under predetermined optimum conditions (rice to water ratio, 1:19 and 20 min cooking time). There was no difference in sensory properties, e.g., appearance, flavor, and texture, in all cooked fortified rice. The coating materials appeared to dissolve (melt) during cooking of rice, causing leaching and dissipation of folic acid from the surface of the coated rice into the cooking medium. The yellow color of folic acid was too diluted in the cooked rice to be noticed by general inspection. Therefore, it was ineffective to compare the sensory properties of various samples of cooked fortified rice. Instead, the sensory properties of one of the representative samples of cooked fortified rice were evaluated against unfortified rice by triangle test. The fortified rice coated with LBG+xanthan gum+ rice protein concentrate solution was chosen to be tested for evaluation considering its lower washing loss and lesser ‘a’ and ‘b’ values. Among 36 panelists, only 16 correctly identified the odd samples while the majority of the panelists (20) failed to do so. Most of the panelists commented that there was hardly any difference between cooked milled rice and cooked fortified rice. Statistical analysis for significant of triangle test
(P=1/3) showed no significant difference between the samples (level of error of =0.05). This meant that the difference between the samples was too small to be recognized sensorially. 3.7. Comparison of best performing coating materials Table 5 shows the performance ranking of nine best rice premixes against the quality criteria such as washing and cooking loss, color, and water absorption ratio. Ethylcellulose was ranked best in all quality criteria except color. But its use as an edible polymer is controversial as it is insoluble in water, and is not a permitted additive in Australia. Thus it serves only as a reference coating material in this study. Low methoxyl pectin was the next best performer. It retained more folic acid during washing and cooking than did the other edible coating polymers. Although it failed to mask the yellow color of folic acid, the color problem could be overcome by using masking agent(s).
4. Conclusion and recommendations The properties of films cast from the coating solutions exhibited varying solubility, color and texture qualities. Rice premixes coated with locust bean gum, agar, and xanthan gum, pectin, and some of their composite mixtures retain more folic acid during washing test than other edible polymers used in this study. No coating material could prevent the significant loss of folic acid during cooking in excess water. Similarly none of the coating solutions was successful in reducing or masking the yellow color of the folic acid in the coated rice. Sensory evaluation of fortified rice showed that the majority of the panelists failed to identify the fortified rice from normal cooked rice. It is technically feasible to produce folic acid fortified rice using edible polymers,
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which will meet the needs of the target consumer in terms of quality and expectations and RDI levels. However, this warrants additional studies in pilot plant size operations. Use of emulsifying agents and cross linking agents such as glycerol, lecithin, polyethylene glycol, propyleneglycol alginate etc. reduce the brittleness of the film, thus may improve the performance of the coating material. The effect of storage conditions and sensitivity to insect infestation and microbial attack to the fortified rice should be investigated. The mechanism by which added nutrients are released from the polymer coatings should be studied. Finally the bioavailability of folic acid from the coated rice should be elucidated by human trials. Acknowledgement Ms E. Djapardi identified and ranked films used in this paper.
References Armisen, R. (1999). Agar. In A. Imeson (Ed.), Thickening and gelling agents in foods (pp. 1–21). MD: Chapman and Hall. Batcher, O. M., Hemintoller, K. F., & Dawson, E. H. (1956). Development and application of methods for evaluating cooking and eating quality of rice. Rice Journal, 59, 4–32. Bramall, L. D. (1986). A novel process for fortification of rice. Food Technology in Australia, 38, 281–284. Cochran, W. G., & Cox, G. M. (1957). Experimental design. New York: John Wiley & Sons. Cort, W. M., Borenstein, B., Harley, J. H., Osadca, M., & Scheiner, J. (1976). Nutrient stability of fortified cereal products. Food Technology, 30, 52–62. Fox, J. E. (1999). Seed gums. In A. Imeson (Ed.), Thickening and gelling agents in foods (pp. 262–283). MD: Chapman and Hall. Glicksman, M. (1969). Gum technology in the food industries. New York: Academic Press. Hoffpauer, D. W., & Bonnette, R. E. (1998). Enrichment update on folic acid. Cereal Food Worlds, 4, 365–367. Jellinek, G. (1985). Sensory evaluation of food—theory and practice. England and Germany: Ellis Harwood and VCH. Joseph, E. W., Liuzzo, J. A., & Rao, R. M. (1990). Development of wash and cook-proof methods for vitamin enrichment of rice grains. Journal of Food Science, 55, 1102–1107. Juliano, B. O. (1990). Rice grain quality: problems and challenges. Cereal Foods World, 35, 245–253.
Juliano, B. O. (1985). Polysaccharides, proteins and lipids. In B. O. Juliano (Ed.), Rice: chemistry and technology (pp. 59–160). MN: Association of American Cereal Chemists Inc. Juliano, B. O., Onate, L. U., & Mundo, A. M. (1965). Relation of starch composition, protein content, and gelatinization temperature to cooking and eating qualities of milled rice. Food Technology, 1006–1011. Lee, M. H., Hettiarachchy McNew, R. W., & Gnanasambandam, R. (1995). Physiochemical properties of calcium-fortified rice. Cereal Chemistry, 72, 352–355. Malakar, M. C., & Banerjee, S. N. (1959). Effects of cooking rice with different volumes of water on the loss of nutrients and on digestibility of rice in vitro. Food Research, 24, 751–756. Marshall, W. E., & Wadsworth, J. I. (1994). Rice science and technology. New York: Marcel Dekker. Mickus, R. R. (1955). Seal enriching additives on white rice. Food Engineering, 27, 91–160. Misaki, M., & Yasumatsu, K. (1985). Rice fortification and enrichment. In B. O. Juliano (Ed.), Rice: chemistry and technology (pp. 289–402). MN: The American Association of Cereal Chemists. MRC. (1991). Vitamin Study Research Group. Prevention of neural tube defects: results of the Medical Research Council Vitamin Study. Lancet, 338, 131–137. Nelson, K. L., & Fennema, O. R. (1991). Methylcellulose films to prevent lipid migration in confectionery products. Journal of Food Science, 56, 504–509. Nisperos-Carriedo, M. O. (1994). Edible coatings and films based on polysaccharides. In J. M. Krochter, E. A. Baldwin, & M. O. Nisperos-Carriedo (Eds.), Edible films to improve food quality (pp. 305–335). Lancaster, PA: Technolic Publishing. Peil, A., Barrett, F., Rha, C., & Langer, R. (1981). Retention of micronutrients by polymer coatings used to fortify rice. Journal of Food Science, 47, 260–262. Roessler, E. B., Pangborn, R. M., Sidel, J. L., & Stone, H. (1978). Expanded statistical tables for estimating significance in pairedpreference, duo-trio and triangle tests. Journal of Food Science, 43, 940–944. Selhub, J., Jacqes, P. F., Bostom, A. G., D’Agostino, R. B., Wilson, P. W. F., Belenger, A. J., O’Leary, D. H., Wolf, P. A., Schaeffer, E. J., & Rosenberg, I. H. (1995). Association between plasma homocysteine concentrations and extracranial carotid-artery stenosis. New England Journal of Medicine, 332, 286–291. Shrestha, A. K., Arcot, J., & Paterson, J. (2000). Folate assay of foods by traditional and tri-enzyme treatments using cryoprotected Lactobacillus casei. Food Chemistry, 71, 545–552. Sworn, G. (2000). Xantham gum. In G. O Philips, & P. A. Williams (Eds.), Handbook of hydrocolloids (pp. 103–115). Cambridge, UK: Woodhead Publishing Ltd. Zecher, D., & Gerrish, T. (1999). Cellulose derivatives. In A. Imeson (Ed.), Thickening and gelling agents in foods (pp. 60–83). MD: Chapman and Hall.
Edible coating materials—their properties and use in the fortification of rice with folic acid§ Ashok K. Shrestha, Jayashree Arcot, Janet L. Paterson* Food Science and Technology, School of Chemical Sciences, The University of New South Wales, Sydney 2052, Australia Received 10 November 2002; accepted 11 June 2003
Abstract This study investigated the technical feasibility of adding folic acid on to rice and coating with edible polymers. The coating solutions were cast into film and their properties were investigated. A concentrated premix of rice was prepared in a rotating coating pan by spraying first with folic acid solution, and then with polymer solutions and drying. The fortified rice premixes were evaluated for washing and cooking losses. The loss of folic acid in washing was lowest in rice premixes coated with ethyl cellulose followed by pectin, composite mixtures of locust bean and other coating materials with highest loss in gum arabic coated rice. No edible polymer could satisfactorily retain folic acid during boiling in excess water. Edible polymers failed to mask the yellow color of folic acid and additional masking agent was needed. The premixes had a higher water uptake ratio than raw milled rice had. Triangle tests did not show any significant difference (=0.05) between the sensory qualities of cooked fortified rice and raw milled rice. # 2003 Elsevier Ltd. All rights reserved. Keywords: Folic acid; Rice fortification; Processing loss; Sensory test
1. Introduction Folate or folic acid is the term most commonly used to refer to a family of vitamers with related biological activities. In recent years, interest in the fortification of foods with folic acid has increased, largely in response to the findings of epidemiological studies that link folate with neural tube defects (NTDs), coronary heart disease and megaloblastic anemia (MRC Vitamin Group, 1991; Selhub et al., 1995). Fortification of folic acid in one or more of the commonly consumed dietary items is now regarded as the best method to ensure that women increase their folate intakes to reduce the risk of having a pregnancy affected by neural tube defects. The United States Food and Drug Administration (USFDA) have already made it mandatory for all manufacturers of grain products to add folic acid for enrichment of products, effective from 1 January 1998. The general range of enrichment as given by FDA is 100–300 mg per 100 g for all types of grain products (Hoffpauer & Bonnette, § A less detailed version of this paper as a one-page abstract was published in the Proceedings of the 17th International Congress of Nutrition, Vienna, Austria, August 27–31, 2001. * Corresponding author. Fax: +61-2-9385-5931. E-mail address: [email protected] (J.L. Paterson).
0963-9969/$ - see front matter # 2003 Elsevier Ltd. All rights reserved. doi:10.1016/S0963-9969(03)00101-7
1998). Most of the developed countries, including Australia, practice voluntary fortification with folic acid. Rice is an ideal food for micronutrient fortification because it is a staple diet for more than half of the world’s population (Juliano, 1990). Milled rice is one of the poorest sources of folate (3–14 mg/100 g) and other water-soluble vitamins (Marshall & Wadsworth, 1994). The nutritional value of milled rice may be further reduced as a result of the method used to prepare rice for eating such as washing and cooking in excess water and draining (Malakar & Banerjee, 1959). Most of the enrichment methods for rice fortification use acids (Hoffman La Roche method, USA, as described by Mickus, 1955; Rice Growers’ Co-operative Limited method, Australia, as described by Bramall, 1986; Shingen method, Japan as described by Misaki & Yasumatsu, 1985; Cross-linking method, as described by Joseph, Liuzzo, & Rao, 1990) which make them unsuitable for folic acid fortification because folic acid is unstable under acidic conditions. There are two additional criteria for a good folic acid fortification method: it should prevent the leaching of vitamins during washing and cooking and it should mask the yellow color of folic acid in fortified rice. Previous studies have shown that edible polymer coating(s) help retain added micronutrients in fortified rice during washing and cooking
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tests (Peil, Barrett, Rha, & Langer, 1981; Cort, Borenstein, Harley, Osadca, & Scheiner, 1976). Studies so far have evaluated only a limited range of polymers for their suitability to prevent the loss of micronutrients in fortified rice during processing. Therefore the objectives of this study were to examine the ability of various edible polymers to prevent the loss of added folic acid in rice during rinsing and cooking; and to investigate the physiochemical and sensory properties of the folic acid fortified rice. All the tests except sensory properties were carried out on the premix, designed to be diluted 1:100 with raw milled rice.
polymer films, about 40 ml of polymer solution was poured and sprayed onto a level, rectangular (1612 cm2) glass plate by means of a standard applicator for thin-layer chromatography. The film forming solution was dried in a ventilated oven set at 50 C for about 2 h to evaporate water and a homogenous film was then formed. The dried films were cut into small rectangular pieces of about 32 cm and dropped into water (20 C) in a 500 ml beaker. The behavior of the edible film in water was then observed. The color, transparency and strength of the film were also evaluated subjectively. 2.3. Preparation of a concentrated rice premix
2. Materials and methods 2.1. Materials Australian long grain rice, Sunrice, was provided by the Rice Grower’s Cooperative Limited, NSW, Australia. Various polymer coatings were obtained from respective suppliers such as methylcellulose (MC) and hydroxypropyl methylcellulose (HPMC), ethylcellulose (EC), locust bean gum (LBG), gum tragacanth, carrageenan, gum guar and low methoxyl pectin (from citrus peel, methoxyl content 9.7%) from Sigma Chemicals Co. St Louis, MO, USA; Modified corn starches e.g. Pure Cote 790, and some maltodextrins from Grain Processing Corporation, Muscatine, IA, USA; tri-calcium phosphate, carboxymethyl cellulose (CMC), sodium alginate, rice starch from Swift and Company Ltd., Victoria, Australia; starch powder from National Starch and Chemical Pty Ltd., Bridgewater, NJ, USA; and gum arabic from TIC GUMS, MD, USA. Rice protein concentrate (65% protein) was provided by Quest International, Australia. Shellac solution (dewaxed superblonde) was provided by Shine Pty. Ltd., Sydney, Australia. Media for folic acid analysis were purchased from Difco Laboratories (Detroit, MI, USA). Folic acid (pteroylglutamic acid) was obtained from Sigma Chemical, St. Louis, MO, USA. 2.2. Preparation of coating solution and polymer films Most of the coating solutions were prepared by slowly dissolving a known amount of coating material into 75– 100 ml distilled water, heated to about 80 C in a 250 ml beaker with continuous stirring until the coating materials dissolved or at least were suspended in the solution. The consistency of solution was such that it could be sprayed by a hand held nozzle spray. Solutions for MC, HPMC or their composite mixtures were prepared according to Nelson and Fennema (1991). Ethylcellulose solution was prepared in ethanol (100%). The amount of coating materials needed to form a sprayable solution in 100 ml solvent was noted. To prepare the
A stainless steel, spherical (diameter 20 cm at mouth), tablet coating pan with adjustable motor speed (Erweka AR 401, Serial No. 71378:ab53, D63150 Heusenstamm, Germany) was used for the fortification process. The coating pan was also fitted with an Infra-Red Lamp (Elstein lot 150 230 V, 150 W, 450 C) for heating. Rice (250 g) was fortified by first spraying folic acid solution (100 mg in about 20 ml water) followed by a coating solution and with constant mixing and drying to initial weight as shown in Fig. 1. Various materials were applied on one set of the rice premix (LBG+Xanthan gum coated premix), separately, to study their ability to mask the yellow color of folic acid: rice gruel, rice gruel with shellac solution and starch solution were sprayed to the dry premix; calcium phosphate and starch powder were puffed on to the surface towards the rolling premix at the end of the spraying and drying cycle. 2.4. Determination of washing and cooking losses The washing and cooking losses of raw milled rice and rice premixes were determined in a room with subdued light as folic acid is sensitive to light. All the glassware was covered with aluminum foil. For washing or rinsing test, 20 g rice premix in a 250 ml conical flask was rinsed with 60 ml distilled water by gently swirling for exactly 60 s. For the cooking test, 5 g sample in a 125 ml conical flask was mixed with 100 ml water, boiled for 30 min in a water bath (97 3 C), and cooled immediately. The cook-water and wash-water were decanted and centrifuged (Sorvall, Dupont, CT, USA) at 3000 rpm for 15 min. The supernatant (5 ml) was pipetted to 50 ml volumetric flask, brought to volume with phosphate-ascorbate buffer (0.1 M potassium phosphate, 1% ascorbic acid and pH 6.1) and mixed well. The extract was transferred into small-labeled brown bottles and stored at 20 C. 2.5. Folic acid analysis The raw milled rice (control) was extracted for folic acid (or undeconjugated folate) according to Shrestha,
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Arcot, and Paterson (2000). The wash-water and cookwater were further diluted with phosphate ascorbate buffer and analyzed for folic acid by microbiological assay using Lactobacillus casei according to Shrestha, Arcot, and Paterson (2000). The loss of folic acid during washing and cooking tests were therefore estimated from the initial added amount for fortification [100 mg folic acid was added to 250 g rice (40,000 mg/100 g)].
with some modification. Three grams of sample in a spherical tea infuser (internal diameter 35 mm, CPS, China) was lowered into a 250 ml beaker containing 175 ml boiling water, and covered with a watch glass. The rice was cooked for 20 min in a boiling water bath (97 3 C) and drained for 2 min. The water uptake ratio was calculated by dividing the increase in weight on cooking by the weight of the original rice.
2.6. Measurement of color of the fortified rice
2.8. Sensory evaluation of fortified rice
The color characteristics (‘L’, ‘a’ and ‘b’) of raw milled rice and the rice premixes were measured quantitatively using a color difference meter (Minolta Chroma meter, CR-300 Series, Osaka, Japan) calibrated with a white standard plate (‘L’=98.12, ‘a’= 0.03 and ‘b’=1.22). ‘L’ value indicates white (100) to black (0); ‘a’ value indicates red (100) to green ( 80); ‘b’ value indicates yellow (70) to blue ( 80).
Eating quality of rice largely depends on the textural properties of cooked rice, which is determined by the degree of cooking and the rice–water ratio (Juliano, 1985). Before actual cooking of rice, optimum water to rice ratio for the best eating quality of milled rice was determined subjectively on the basis of taste and tenderness of the cooked rice. Rice was cooked in four different rice to water ratios (1:1.7; 1:1.8; 1:1.9; and 1:2) for 20 min using automatic rice cookers (2.5 l capacity, Model DF020, Sunbeam, Thailand). The optimum ricewater ratio was 1:1.9. A simple (classical) triangle test was chosen for sensory evaluation (Jellinek, 1985) of cooked milled rice and fortified rice (rice premix coated with LBG+xanthan gum+rice protein concentrate diluted to 1:100 with raw milled rice). Sensory evaluation of the warm cooked rice(s) was carried out by an untrained panel of 36 students and staff from Food Science and Technology, The University of New South Wales, Sydney, Australia. The test was carried out in a sensory evaluation laboratory using white light. The staple diet of most of the panelists was not rice. Each panelist was served three small plates of cooked rice, two alike and one different. Samples were coded with three digit randomly generated numbers to avoid bias (Cochran & Cox, 1957). They were asked to judge each cooked rice sample for its appearance, color, aroma, flavor, tenderness or hardness and to select the odd sample. The data obtained were tabulated and the statistical analysis to test the significance of the result was carried out according to Roessler, Pangborn, Sidel, and Stone (1978).
2.7. Water uptake ratio Water uptake capacity of fortified rice was measured according to Batcher, Hemintoller, and Dawson (1956)
3. Results and discussion 3.1. Properties of edible films
Fig. 1. Outline of folic acid fortification procedure.
The composition and properties of edible films is presented in Table 1. MC, HPMC, CMC and their composite mixture gave excellent transparent, flexible and fairly strong films. However, these films dissolved readily in cold water. EC film was strong, less flexible, and insoluble in water. EC has been cleared by Food and Drug Administration (Federal Register, 1962) for use as
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Table 1 Composition and properties of edible polymers and their composite mixtures Composition of coating solutiona
Film propertiesc
1.15 g MC in 50 ml water 0.6 g sodium alginate in 50 ml water 15 g gum arabic in 50 ml water 7.5 g PC 790 in 75 ml water
Transparent, thin, flexible, readily soluble Transparent, thin, flexible, readily soluble Pale yellow film, firmly stuck to the glass, soluble Transparent, rough surface, slight rigid, slowly dissolve in water Transparent, soft, easy to tear, readily soluble Slight translucent, soft but good tensile strength, insoluble in water Translucent, soft, readily collapse in water forming mucilaginous mass Thick gel, could not be dried completely Transparent, thick, fairly strong, slowly dissolve in water Translucent, soft but good tensile strength, insoluble in water Translucent, thin, firmly attached to glass, swell and dissolve in water Transparent, thin, flexible, readily soluble in water Translucent, hard and good tensile strength, shrink but did not dissolve in water Translucent, soft, insoluble in water
1 g tragacanth in 120 ml water 1 g carrageenan in 50 ml water 0.3 g xanthan gum in 50 ml water 1 g agar in 75 ml water 2.5 g CMC in 50 ml water 3.0 g EC in 50 ml ethanol 0.25 g LBG in 50 ml water (1.5 g MC+0.5 g HPMC) in 50 ml water 0.5 g carrageenan in 50 ml water+1 g agar in 50 mlb 1 g carrageenan in 50 ml water+0.7 ml sodium alginate in 50 ml waterb 0.5 g carrageenan in 50 ml water+0.2 g xanthan gum in 50 ml waterb 1 g agar in 75 ml water+0.375 g LBG in 75 mlb (1.5 g MC+5 g PC 790) in 50 ml water (2 g MC in 50 ml+1 g agar) in 75 ml waterb (0.25 g LBG+0.2 g xanthan gum) in 80 ml water 0.375 g LBG in 75 ml+1 g agar in 75 ml waterb 0.375 g LBG in 75 ml+7.5 g PC 790 in 75 mlb
Translucent, soft, insoluble in water Slight translucent, rough surface, hard, insoluble in water Transparent, rigid, slowly dissolve in water Translucent, thick, strong but flexible, slowly dissolve in water Translucent (milky), soft, insoluble in water Translucent, rough surface, brittle, insoluble in water Transparent, rough surface, brittle, swell and slowly dissolve in water
Solutions were prepared in hot water (805 C), except EC. Individually prepared and mixed together in equal portions. c Solubility in water. MC=methylcellulose; HPMC=hydroxypropyl methylcellulose; EC=ethylcellulose; CMC=carboxymethylcellulose; PC 790=pure cote 790 (modified corn starch); LBG=locust bean gum. a
b
a binder and filler in dry vitamin preparations and as a component of protective coatings for vitamin and mineral tablets (Glicksman, 1969) but it is not a permitted additive in Australia and New Zealand. Agar solution produced a thick homogenous-gelled structure that was difficult to dry, did not produce any film even after drying for 5–6 h. However, when mixed with xanthan gum, or with LBG, agar formed a translucent, flexible film that remained insoluble in water for a long time (> 15 min). Armisen (1999) reported that agar has a synergistic effect with LBG, producing more elastic and less brittle structures. The pectin film stuck to the glass plate and was hard to peel off. The film was pale yellow, flexible, and dissolved slowly in water (> 30 min). LBG formed a soft, translucent film, firmly attached to glass, which swelled in water and dissolved after a long time (> 30 min). The presence of a small number of d-galactose in the insoluble fibrous structure of d-mannan in LBG accounts for its limited solubility (Fox, 1999). LBG has the unusual synergistic effect of imparting desirable elastic properties to xanthan gum, carrageenan and agar gels
(Glicksman, 1969; Fox, 1999). When mixed with xanthan gum, LBG produced a flexible, translucent and water-insoluble film. Xanthan gum itself, however, produced a soft, translucent film that readily collapsed in water forming a mucilaginous mass. PC 790, a modified corn-starch, produced a transparent, brittle film that slowly dissolved in water. Carrageenan solution produced a smooth, translucent, strong but flexible film that did not dissolve in water. In combination with most of the polymers such as agar, sodium alginate and xanthan gum, carrageenan produced a fairly insoluble film. Gum arabic, tragacanth and sodium alginate solutions gave thin transparent films that were highly soluble in water (see Table 1 for concentration of the gums). 3.2. Loss of folic acid during washing The amount (and percentage) of folic acid in washwater and percentage loss from rice and premixes is given in Table 2. The folic acid content of raw milled rice used for fortification was 41 mg/100 g. There was a loss of 30 mg folic acid (73%) in unfortified or raw
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Wash-water (mg/100 g)a,b
Cook-water (mg/100 g)a,b
Raw milled rice MC MC+HPMC MC+LBGc MC+dextrinc MC+PC 790 MC+LBG MC+carrageenan CMC CMCc CMC+sodium alginate CMC+carrageenan CMC+LBG Ethylcellulose Guar gum LBG LBG+carrageenan LBG+xanthan gumc LBG+xanthan gum LBG+agar LBG+PC 790 LBG+sodium alginate Carrageenan Carrageenan+sodium alginate Carrageenan+PC 790 PC 790 PC790+maltodextrin PC790+sodium alginate Gum acacia Gum arabic Gum arabic+agarc Agar+xanthan gumc Folic acid solution Pectin
303 (73) 5322710 (49) 4211869 (49) 392198 (46) 7531549 (44) 207779 (53) 922732 (42) 336853 (41) 562667 (56) 757351 (52) 1562641 (60) 825835 (52) 8312581 (52) 949143 (2) 13 5982421 (34) 9483559 (24) 14 16983 (35) 80281286 (19) 8553363 (21) 4595622 (11) 19 39159 (42) 22 0321612 (55) 20 4032119 (51) 18 1091442 (45) 14 575184 (36) 22 3153176 (56) 20 903964 (52) 21 6141289 (54) 21 201390 (53) 24 2371053 (61) 21 075178 (53) 10 301482 (26) 19 465750 (49) 368616 (9)
394.6 (96) ND 28 4673451 (71) ND ND ND ND ND ND ND ND ND ND 24 3032193 (61) ND 37 0141419 (93) ND 29 6403756 (74) 35 5981337 (89) 36 0831409 (90) ND ND ND ND ND ND ND ND ND ND ND 34 5932823 (86) 34 5212837 (86) 27 5392212 (69)
19 19 18 17 21 16 16 22 20 24 20 20
ND=not determined. a Mean valuestandard deviation (three replicates). b Values in parenthesis in indicate the % loss during washing or cooking, based on a 40 000 mg folic acid/100 g in rice premixes. c Folic acid was dissolved in 30 ml rice protein concentrate solution and sprayed prior to coating solution.
milled rice during the washing test. Diminishing nutritional value of rice during washing and cooking has been well documented. Washing of milled rice has been reported to remove 22–59% of the thiamin, 11–26% of the riboflavin and 20–60% of the niacin (as reviewed by Juliano, 1985). EC was the best coating material followed by pectin, each with washing loss of 2 and 9% respectively. EC has been used as a coating material in rice fortification by Wright Enrichment Inc., USA (Cort et al., 1976). The relatively hydrophobic nature of EC is responsible for lower washing loss of folic acid. The pH of pectin solution was 3.5, the acidic solution might have reacted with surface starch forming a thin, sugar layer (Bramall, 1986). As the liquid mixture on the rice surface was absorbed and subsequently dried, the folic acid was bound to the rice in the sugar coating. Lower solubility of low methoxyl pectin (Glicksman, 1969) and hydrophobic interaction between pectin and rice components
such as starch and protein could have further reduced the loss of folic acid during washing. MC, HPMC CMC, modified corn starch, dextrin, sodium alginate, gum arabic, gum acacia, carrageenan and their composite mixtures lost more than half of the added folic acid during rinsing (Table 2). The use of 10% rice protein concentrate as a carrier of folic acid did not improve the retention of folic acid in fortified premixes, as seen in CMC and LBG+xanthan gum coated rice (Table 2). The smaller droplets of agar solution on spraying and drying formed fine gels that subsequently turned into finer particles causing a dust problem. This was overcome by using composite mixture of agar with other polymers such as xanthan and LBG. The rice premix coated with agar and LBG lost 11.5% folic acid in wash-water, whereas the loss was almost doubled when xanthan gum was used with agar. LBG and its composite mixture with xanthan gum also showed improved folic acid retention during rinsing.
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LBG forms a strong, thermo-reversible, cohesive, elastic gel with xanthan gum, a functionality of which neither of the hydrocolloids exhibits alone (Fox 1999; Sworn, 2000). Coating rice with folic acid solution alone retained almost half of the added folic acid during rinsing, better than many coated rice premixes. This may be because the outer starch layer was gelatinized during spraying and drying and because one wetting and drying resulted in a lesser degree of cracking. 3.3. Loss of folic acid during cooking The loss of folic acid from the premix cooked in excess water is given in Table 2. Milled raw rice lost almost all of its folic acid whereas other coated rice lost 61–93% of the added folic acid in cook-water during cooking test. Table 2 shows that no coating material was strong enough to prevent leaching of folic acid from fortified premixes when boiled in excess water. It was unlikely that any edible polymer could preserve the physical integrity of rice kernel when it is boiled for 20 min in excess water. In the fortification process rice went through frequent soaking (spray) and drying that gelatinized the outer starch layer and also caused cracking. During boiling, water gets easy access to the interior of the cracked grain, increasing hydration and subsequent leaching of the vitamin into the cooking water. The loss of folic acid in cook-water was lowest in EC coated rice at 61%. It could be due to impermeability of ethylcellulose film in water. Although MC derivatives are reported to be insoluble in hot water Table 3 Color characteristics of rice premix coated with various polymer coatings Coating ingredients
Color characteristics ‘L’
Milled rice FA only Pectin EC MC+ HPMC MC+ HPMCa LBG LBG+agar LBG+agara LBG+xanthan gum LBG+xanthan guma Rice gruelb Starch solutionb Ca3PO4 powderb Rice starchb Shellac: rice gruel (1:1)b a
69.61 76.55 74.52 73.36 75.76 75.99 78.46 78.54 77.10 79.44 75.6 76.81 79.51 84.23 75.93 74.60
‘a’ 1.27 5.30 3.9 4.54 4.44 3.39 4.79 4.66 3.47 4.82 2.76 3.94 3.31 1.57 2.1 1.14
‘b’ 10.71 29.73 29.41 24.83 25.84 20.65 28.46 27.34 20.97 28.03 19.37 24.19 18.93 11.62 18.67 22.98
Folic acid was dissolved in 30 ml rice protein concentrate solution and sprayed prior to coating solution. b Color masking agents applied to rice premix coated with LBG+xanthan gum.
(Nisperos-Carriedo, 1994; Zecher & Gerrish, 1999) there was cooking loss of more than 70% folic acid in rice coated with MC+HPMC. In similar studies, Peil et al. (1981) reported a loss of 82, 82 and 79% thiamin, niacin and riboflavin respectively when rice coated with MC+HPMC (1:3 ratio) was cooked in the same way. 3.4. Color of the fortified rice Table 3 shows a significant difference in the color characteristics of the raw milled rice and the rice premixes indicating that coating materials failed to mask the yellow color of folic acid. There was a marked increase in lightness (‘L’), redness (‘a’) and yellowness (‘b’) values when folic acid and edible polymers were applied to milled rice. It is necessary that the fortified rice grains blend well with raw rice so that consumers will not reject them. To restore the color of the fortified rice, various color-masking agents were applied. Calcium phosphate restored the redness and yellowness values closest to the milled rice but the premix appeared chalky with a slight metallic tinge. When the premix was mixed with milled rice in 1:100 ratios, difference in color appeared minimal. Consumers are unlikely to pick the fortified grains as defective. 3.5. Water uptake by fortified rice Table 4 shows the water uptake ratio of milled rice and some rice premixes. The water uptake ratio for milled (long-grain type) rice was 3.03. Except EC coated rice, all the premixes registered water uptake ratio more than 4. The cooked EC coated rice kernels were well separated and tender: the texture was close to cooked milled rice. Other fortified rice kernels were split and had starch leaching out from the cracks. These kernels remained clumped together in the tea infuser. The fortified premix rice kernels were cracked during fortification which might have caused the greater water uptake Table 4 Water uptake ratios of raw milled rice and some rice premixes Rice premixes
Water uptake ratio (g/g)a
Raw milled rice MC+HPMC Ethylcellulose LBG LBG+xanthan gum LBG+agar Agar+xanthan gumb Folic acid solution Pectin
3.03 0.03 4.02 0.05 3.29 0.01 4.6 0.08 4.84 0.14 4.8 0.05 4.31 0.12 3.75 0.07 4.11 0.01
a
Mean valuestandard deviation (three replicates). Folic acid was dissolved in 30 ml rice protein concentrate solution and sprayed prior to coating solution. b
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Table 5 Performance rankinga of best rice premixes Rankinga 1 2 3 4 5 6 7 8 9 10
Washing loss EC Pectin LBG+agar Rice gruel LBG+xanthan gumb LBG+xanthan gum LBG Agar+xanthan gumb MC+HPMC Folic acid only
Cooking loss
Color
EC Pectin MC+HPMC LBG+xanthan gumb Folic acid only Agar+xanthan gumb LBG+xanthan gum LBG+agar LBG ND
Water absorption ratio b
LBG+xanthan gum MC+HPMC Agar+xanthan gumb Rice gruel EC LBG+agar LBG+xanthan gum Pectin LBG Folic acid only
EC Folic acid only MC+HPMC Pectin Agar+xanthan gumb LBG LBG+agar LBG+xanthan gum ND ND
a Ranking is based on the best performances of premixes e.g., less folic acid in wash- or cook-water, less yellow color, and less water absorption ratio. b Folic acid was dissolved in 30 ml rice protein concentrate solution and sprayed prior to coating solution.
and therefore, shorter cooking time (Juliano, Onate, & Mundo, 1965). Besides, there were greater number of broken kernels in fortified premixes which absorb more water due to their greater surface area. Lee, Hettiarachchy, McNew, and Gnanasambandam (1995) also reported a significant increase in water uptake value and disintegration of cooked calcium fortified rice when compared to the control sample. 3.6. Sensory evaluation of cooked rice Initially rice premixes with better folic acid retention during washing (rice coated with LBG+xanthan gum, LBG+agar, MC+HPMC, pectin, and ethylcellulose) were blended with raw milled rice (1:100 ratio) and cooked under predetermined optimum conditions (rice to water ratio, 1:19 and 20 min cooking time). There was no difference in sensory properties, e.g., appearance, flavor, and texture, in all cooked fortified rice. The coating materials appeared to dissolve (melt) during cooking of rice, causing leaching and dissipation of folic acid from the surface of the coated rice into the cooking medium. The yellow color of folic acid was too diluted in the cooked rice to be noticed by general inspection. Therefore, it was ineffective to compare the sensory properties of various samples of cooked fortified rice. Instead, the sensory properties of one of the representative samples of cooked fortified rice were evaluated against unfortified rice by triangle test. The fortified rice coated with LBG+xanthan gum+ rice protein concentrate solution was chosen to be tested for evaluation considering its lower washing loss and lesser ‘a’ and ‘b’ values. Among 36 panelists, only 16 correctly identified the odd samples while the majority of the panelists (20) failed to do so. Most of the panelists commented that there was hardly any difference between cooked milled rice and cooked fortified rice. Statistical analysis for significant of triangle test
(P=1/3) showed no significant difference between the samples (level of error of =0.05). This meant that the difference between the samples was too small to be recognized sensorially. 3.7. Comparison of best performing coating materials Table 5 shows the performance ranking of nine best rice premixes against the quality criteria such as washing and cooking loss, color, and water absorption ratio. Ethylcellulose was ranked best in all quality criteria except color. But its use as an edible polymer is controversial as it is insoluble in water, and is not a permitted additive in Australia. Thus it serves only as a reference coating material in this study. Low methoxyl pectin was the next best performer. It retained more folic acid during washing and cooking than did the other edible coating polymers. Although it failed to mask the yellow color of folic acid, the color problem could be overcome by using masking agent(s).
4. Conclusion and recommendations The properties of films cast from the coating solutions exhibited varying solubility, color and texture qualities. Rice premixes coated with locust bean gum, agar, and xanthan gum, pectin, and some of their composite mixtures retain more folic acid during washing test than other edible polymers used in this study. No coating material could prevent the significant loss of folic acid during cooking in excess water. Similarly none of the coating solutions was successful in reducing or masking the yellow color of the folic acid in the coated rice. Sensory evaluation of fortified rice showed that the majority of the panelists failed to identify the fortified rice from normal cooked rice. It is technically feasible to produce folic acid fortified rice using edible polymers,
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which will meet the needs of the target consumer in terms of quality and expectations and RDI levels. However, this warrants additional studies in pilot plant size operations. Use of emulsifying agents and cross linking agents such as glycerol, lecithin, polyethylene glycol, propyleneglycol alginate etc. reduce the brittleness of the film, thus may improve the performance of the coating material. The effect of storage conditions and sensitivity to insect infestation and microbial attack to the fortified rice should be investigated. The mechanism by which added nutrients are released from the polymer coatings should be studied. Finally the bioavailability of folic acid from the coated rice should be elucidated by human trials. Acknowledgement Ms E. Djapardi identified and ranked films used in this paper.
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