Available online at www.sciencedirect.com Journal of Food Engineering 87 (2008) 422–427 www.elsevie r.com/locate /jfoodeng Effects of coconu t sugar and stabilizi ng agents on stabilit y and appare nt viscosit y of high- fat coconu t milk Karun thapa t Jirape angto ng, Suwit Siriw atana yothi n, Naph aporn Chie wcha n * D e p a r t m e n t o f F o o d E n g i n e e ring, Faculty of Engineering, King Mongkut’s University of Technology Thonburi, 1 2 6 P r a c h a u - t i d R o a d , B a n g k o k 1 0 1 4 0 , T h a i l a n d Received 27 September 2007; received in revised form 7 December 2007; accepted 1 January 2008 A v a i l a b l e o n l i n e 8 J a n u a r y 2008 Abstract This study was aimed at determining the physical properties of sterilized high-fat coconut milk (30%) as affected by coconut sugar (10– 30%) and stabilizing agents, namely carboxymethyl cellulose (CMC, 0.6–1.0%) and Montanox 60 (0.6–1.0%). The emulsion stability (ES) and rheological properties were determined after thermal processing at 121 C for 60 min. At similar sugar content, increasing concen- tration of CMC or Montanox 60 resulted in an increase in ES. The concentrations of CMC and Montanox 60 in the range of 0.8–1.0% were found to give the ES in the range of 81.16–91.15%. These conditions were selected to conduct the rheological measurements. It was found that all samples exhibited pseudoplastic behavior with the flow behavior index (n) between 0.63 and 0.84. The results suggested that suitable ratio between coconut sugar and stabilizing agent contents should be specified in order to obtain a high quality of processed sweetened coconut milk. 2008 Elsevier Ltd. All rights reserved. Keywords: Coconut milk; Emulsion stability; Rheological propertie s; Stabilizing agent; Sugar; Viscosity 1. Intr oductio n In Thailand, many traditiona l foods contain c oconut milk as a main ingredient. The sweetened coconut milk for desserts is typically prepared by adding granulated cane sugar, coconut or palm sugars to fresh or heated coconu t milk and mixed thoroughly . The fruits or gelatinized formed flour may also be added during heati ng. Coconut milk naturally contained about 54% mois ture, 35% fat and 11% solid non-fat (Simuang et al., 2004) and is categorized as oil in water emulsion. The separation of an emulsion into creamy and water phases usually occu r after standing for a while. This leads to the physical defect of coconut milk . * Corresponding author. Tel.: +66 2470 9243; fax: +66 2470 9240. E-mail address: naphaporn.rat@kmutt.ac.th (N. Chiewchan) . Many factors have been reported to affect the stability of oil in water emulsion including processed coconut milk, e.g. fat content, type and amount of stabilizing age nts, homogenizing pressure and thermal process cond itions (Sringam, 1986; Seow and Gwee, 1997; Phunga mngoen et al., 2004 ). Sringam (1986) reported that type and quality of emul- sifier and homogenization affected the stability of coconut milk. Klinkesorn et al. (2004) reported that addition of maltodextrin to corn oil in water emuls ion had a pro- nounced effect on the emulsion stability and flow behavior of the emulsion. Thungkao (1988) reported that the most stable cann ed coconut milk (14.5% fat) was found for the coconut milk with the addition of 0.5% emulsifier (Tween 60 and Span 80 (sorbitan monooleate) mixed to obtain a hydroph ilic/ lipophilic balance, HLB , of 14.5). Srithunma (2002) found that 0.4% carboxymethyl cellulose (CMC) in combinat ion with 0.6% Montanox 60 (polyoxyethylene sorbit an 0260-8774/$ - see front matter 2008 Elsevier Ltd. All rights reserved. doi:10.1016 /j.jf oodeng.2 008.0 1.001 K. Jirapeangtong et al. / Journal of Food Engineering 87 (2008) 422–427 423 monostearate or Tween 60) provided good emulsion for coconut milk containing 15–30% fat. Phungamngoen et al. (2004) studied the effects of CMC (0.2–1.0% w/v) and Montanox 60 (0.2–1.0% w/v) on the quality of canned high-fat coconut milk (30%) after com- mercially sterilizing process (121.1 C for 60 min to achieve F 0 = 5 min). Their results showed that using CMC or Montanox 60 alone could not improve the quality of coconut milk in terms of emulsion stability, curding and color. The combination of the stabilizing agents used, i.e. CMC:Montanox 60 (0.6:0.6% w/v) could provide high sta- bility products (ES > 80%), no curding and no significantly difference in colors comparing to fresh coconut milk after heat treatment . In addition, the ingredients added to the emulsion also affected the stability. For example, sucrose had an effec t on the thermal stability of protein-stabilized emulsions and consequently led to an increase in droplet aggrega tion (Kulmyrzaev et al., 2000; Kim et al., 2003). Onsaard et al. (2005) reported an increase in droplet aggregation and creaming of corn oil in water emulsion when higher salt concentration was added to the system. In terms of rheological properties, coconut milk has been found to exhibit pseudoplastic behavior ( Vital i et al., 1985; Simuang et al., 2004; Chiewchan et al., 2006). The composition of the coconut milk, such as stabi - lizing agent and fat content, has been reported to have sig- nificant effect on the flow behavior of coconut milk (Simuang et al., 2004; Tangsuphoom and Coupl and , 2005; Chiewchan et al., 2006; Peamprasart an d Chiewchan, 2006 ). Although the stable formulation for production of canned high-fat coconut milk (30%) has been reco m- mended (Phungamngoen et al., 2004), the preli minary study showed that the suggested condition could not pro- vide a good emulsion for the coconut milk containing sugar. The suitable formulation of emulsifiers is requ ired to obtain the sweetened coconut milk with high stabili ty. Therefore, this research was aimed at determining the effects of coconut sugar (10–30% w/v) and stabi lizing agents, i.e. CMC and Montanox 60, in the range of 0.6– 1.0% w/v, on the physical properties of sweetened high- fat coconut milk. The physical characteristics wer e studied in terms of emulsion stability and apparent viscosity. The information obtained would provide the understanding of the function of sugar on the stability of coconut milk and could be used as guidelines for production of ster ilized sweetened coconut milk. 2. Materials and methods 2.1. Sample prepar atio n Coconut milk without added water from a local market was used in the experiments. The initial fat content of coco- nut milk (35–39%) was determined using Rose– Gott lieb method ( AOAC, 1990). The fresh coconut milk ( 1.5 l per batch) was diluted by distilled water to obtain the coco- nut milk with 30% w/v fat. Coconut sugar (Baan Tal Purk, Nonthaburi, Thailand) was then added to adjust the con- centrations to 10–30% w/v, respectively. Montanox 60 (Adinop, Thailand ) and CMC (Thai Food and Chemical, Thailand) at the concentrations of 0.6– 0.8% w/v were added while the samples were heated and stirred continu- ously. The sample was held on a hot plate for 1 min once its temperature reached 70 C to inhibit lipase. The pre- pared sample was passed through a two-stage homogenizer (GEA NS200 6L, Italy) at 11/4 MPa . The homogenized sample was then filled into glass bottles and sterilized at 121 C for 1 h ( Phunga mngoen et al., 2004) using an auto- clave (Hirayama HA-300D , Jap an). 2.2. Determination of emulsion stabi lity To evaluate the stability, the sterilized samples were kept at room temperature ( 30 C) for 3 days and determ ined the stability of emulsion following the method descri bed by Phungamngoen et al. (2004). The emulsion stabi lity can be calculated by following formula: % Emulsion stability ð ES Þ Height of emulsion phase 100 % ¼ Height of whole coconut milk 2.3. Rheological meas urement The measurements were carried out using a rotation al, concentric cylinder viscometer (HAAKE VT500, Ger- many) with NV type measuring system. The sampl e (9 ml) was filled into the cup and shear rate was increa sed from 0 to 300 s 1 in 2 min. The temperature of the sampl e was maintained at 30 C during the measurements by means of thermostat bath for controlling the stability of the sampl e. 2.4. Microscopic study A few drops of paprika oleoresin with 100,000 Color Unit (Chr Hansen, Murcia, Spain) were added to 10 ml of coconut milk sample and subsequently stirred for at least 1 min to disperse the dye. A few drops of the sample were transferred to the slide and a cover slip was placed over the sample. A standard light microscope (Olympus CH30, Japan) was used to determine the fat structure at a magnification of 100 and photographs were taken from typical fields. 2.5. Experimental design and data analys is A 3 3 factorial design was used in scheduling of the experiments. The experiments were performed at three lev- els of CMC (0.6%, 0.8%, 1.0% w/v), three levels of Mon ta- nox 60 (0.6%, 0.8%, 1.0% w/v) and three levels of coconut 424 K. Jirapeangtong et al. / Journal of Food Engineering 87 (2008) 422–427 sugar. The data were reported as an average of two repli- cates. Analysis of variance (ANOVA ) of the three factors and interactions were applied to the different sets of data with a significance level of 95% ( a = 0.05) . 3. Results and discussion 3.1. Emulsion stabili ty The influence of coconut sugar and stabilizing agents on the ES of coconut milk samples are given in Table 1. A t each level of coconut sugar concentration, the ES of coco - nox 60 up to 1.0% and fixing either CMC or Montanox 60 to 0.6% could not provide good emulsion stability. The results suggested that at least 0.8% of CMC and 0.8% M ontanox 60 were required to produce the high sta- bility of sweetened high-fat coconut milk. 3.2. Rheological proper ties The plots of apparent viscosity against shear rate of coconut milk are shown in Fig. 1. The rheograms obtaine d 0.4 nut milks increased as the total amount of stabi lizing agents increased. Montanox 60, acted as an emuls ifier, was adsorbed to the surface of fat droplets preventing the aggregation of the fat droplets while CMC caused an increase in viscosity of continuous phase therefore retarded the gravitational separation of the droplets ( McCl ement s, 1999; Klinkesorn et al., 2004; Phungamngoen et al., 2004 ). The better stability of coconut milk was obtained in the systems containing higher coconut sugar con tents. The results implied that sugar plays a significant role on the sta- bility of coconut milk. Sugar may increase the viscosity of the continuous phase ( Kim et al., 2003; McCl ements, 2004 ) and this resulted in the retardation of the fat droplet aggre- gation. The results also showed that the ES of coconut milk samples increased as the coconut sugar content increased . An increase in stability of oil in water emulsion as affected by sugar was also reported by Maskan and G o ¨ g ˘ u } s (2000) . The effect of stabilizing agents on the ES was also observed. The results showed that both CMC and M onta- nox 60 concentrations had marked effect on the ES of sweetened coconut milk. A significant increase ( P < 0.05) in the emulsion stability was observed for the samples con - tai ni ng hi gh er co nc en tr ati on of eit he r C M C or M o nt a n ox 60 . Ph un ga m ng oe n et al. (2 00 4) re po rte d that the ad dition of 0.6% CMC and 0.6% M ontanox 60 was applicable for the production of canned high-fat coconut milk (30% fat) and could provide the ES of higher than 80%. How ever, it was found in this present investigation that the previ- ously suggested concentrations of stabilizing agents could not be applied to the coconut milk sampl es containing sugar. Furthermore, increasing levels of CMC or Mo nta- Table 1 The emulsion stability of coconut milk at each condition Ap par ent vis co sit y (P a.s ) Ap par ent vis co sit y (P a.s ) 0.35 0.3 0.25 0.2 0.15 0.1 0.05 0 0.4 0.35 0.3 0.25 0.2 0.15 0.1 0.05 0 0.4 0.35 0.3 0.25 0.2 0.15 0.1 0.05 0 0.4 0.35 0.3 0.25 a 0 50 100 150 200 250 300 350 Shear rate (1/s) b 0 50 100 150 200 250 300 350 Shear rate (1/s) c 0 50 100 150 200 250 300 350 Shear rate (1/s) d Suga r (%) CMC (%) Montanox 60 (%) 0.6 0.8 1.0 0.2 0.15 10 0.6 52.02 ± 0.57 a 52.77 ± 0.13 a 53.00 ± 0.21 a 0.8 54.77 ± 1.91 ab 56.33 ± 1.56 ab 65.07 ± 1.60 de 1.0 60.40 ± 0.08 bcd 81.16 ± 0.28 hi 85.14 ± 4.02 i 20 0.6 53.10 ± 0.54 a 55.39 ± 1.86 ab 62.49 ± 0.84 cd 0.8 57.79 ± 3.77 abc 64.52 ± 0.36 d 72.50 ± 0.86 fg 1.0 69.97 ± 1.31 ef 82.54 ± 1.65 hi 86.09 ± 0.59 ij 0.1 0.05 0 0 50 100 150 200 250 300 350 Shear rate (1/s) 30 0.6 53.92 ± 2.50 ab 72.53 ± 1.54 fg 73.55 ± 0.01 fg 0.8 65.14 ± 0.64 f 73.00 ± 1.61 fg 85.09 ± 4.21 i 1.0 77.44 ± 0.71 gh 84.08 ± 0.92 i 91.15 ± 0.59 j Fig. 1. The change in apparent viscosity of coconut milk samples containing 10% ( e ), 20% ( j ) and 30% ( M ) coconut sugar with varying stabilizing agents: (a) CMC 0.8% and Montanox 60 0.8% (b) CMC 0.8% and Montanox 60 1.0% (c) CMC 1.0% and Montanox 60 0.8% and (d) Values followed by the same letter are not significantly different ( P < 0.05). CMC 1.0% and Montanox 60 1.0%. Ap pa re nt vis co sit y (P Ap par ent vis co sit y (P a.s ) K. Jirapeangtong et al. / Journal of Food Engineering 87 (2008) 422–427 425 were similar for all conditions. Power law model was applied to describe the rheological behavior of the cocon ut Table 4 The apparent viscosity, Pa s (shear rate at 300 s 1 ) of coconut milk at milk. different levels of coconut sugar and stabilizing agents s ¼ K c n ð 1 Þ where s is the shear stress, c is the shear rate, K is the co n- sistency index (Pa s n ) and n is the flow behavior index. It was found that high-fat coconut milk with coconu t CMC (%) Montanox 60 (%) Coconut sugar (%) 10 20 30 2 d 6.78 10 2 c 11.24 10 2 a sugar possessed pseudoplastic or shear-thinning b e havior. 1 4.18 10 Similar trends were observed for different sets of data. Power law model could be used to fit the data with high correlation ( R 2 = 0.996–0.998). A s the shear rate increased, the particle–particle interaction was deform ed and finally disrupted which resulted in the size reduction of the flocs and led to a decrease in viscos ity (McClements, 1999). The values of the consistency index (K) and flow behavior index (n) obtained from the curve fitting are given in Tabl es 2 and 3 . It was considered that an increase in CMC content had more effect, comparing with Montanox 60, on an increase in K value and a decrease in n value. CMC performed as a thickening agent that functioned to increase the viscosity of continuous phase (McClements, 1999) which prevent ed the droplet aggregation, while Montanox 60 perfor med as a binding agent which could precipitate with the ex cess amount (McClements, 1999; Phungamngoen et al., 2004 ). In addition, at each level of CMC and Montanox 60, it was suggested that K value increased with an increase in sugar content . It seems that samples with lower % of CMC and Monta- nox 60 contents tended to be closer to Newtonian flow. At a fixed concentration of stabilizing agents, the magnitude of n values of coconut milk samples decreased with an increase in sugar content. However, n value did not change significantly ( P < 0.05) for coconut milk sampl es with different sugar content s. Table 2 The K (Pa s n ) of coconut milk samples CMC (%) Montanox 60 (%) Coconut sugar (%) 10 20 30 1.0 0.23 d 0.53 c 0.89 a Values followed by the same letter are not significantly different ( P < 0.05). Table 3 T he n value of coconut milk samples CMC (%) Montanox 60 (%) C oconut sugar (%) 0.8 0.8 2.90 10 2 k 4.79 10 2 i 5.72 10 1 2.99 10 2 e 5.01 10 2 c 6.64 10 2 b 1 0.8 3.86 10 2 j 5.96 10 2 g 8.36 10 2 f 0.8 0.8 0.08 k 0.13 i 0.19 h 1.0 0.10 e 0.18 c 0.28 b 1.0 0.8 0.17 j 0.44 h 0.55 f Values followed by the same letter are not significantly different ( P < 0.05). Table 4 shows the values of apparent viscosity at a max- imum shear rate (300 s 1 ). There was a statistically signifi- cant difference ( P < 0.05) in the apparent viscosity of the coconut milk samples containing different concentrations of CMC , Montanox 60 and coconut sugar. It was found that the emulsions wer e more viscous when higher sugar contents were added to the coconut milk samples. The effects of added ingredients on the rheological properties have been reported previously. Maskan and G o ¨ g ˘ u } s (2000) found that an increase in sugar concentration increased the viscosity of sunflower oil in water emulsion s. Tantayotai and Pongsawatmanit (2004) reported that the apparent viscosity of the coconut oil in water emuls ions increased with increasing concentration of NaCl. When sucrose was added to the coconut milk and subse- quently heated, higher sucrose concentration caused more aggregation of fat globules of coconut milk. The reason was that sucrose may alter the droplet– droplet inter action. Although the viscosity of the aqueous phase increased, this could not prevent the extensive droplet flocculation. Simi- lar results were observed by Kim et al. (2003). They reported that an increase in droplet particle size, whi ch indicated an increase of the droplet flocculation, was observed in the oil in water emulsion containing NaCl. 3.3. Microstructure of coconut milk Fig. 2 exemplifies the fat structure of fresh coconut milk and homogenized coconut milk before and after steriliza- tion. In fresh coconut milk, the fat globule s were of variable size and non-uniformly dispersed with some aggre- gates. The presence of finer and more uniform fat globule size were exhibited after homogenization comparing with the fresh sample. A goo d dispersion of fat globules in an aqueous phase was clearly seen for the sample with 10% sugar after homogenization. However, it was observed that adding more concentration of coconut sugar resulted in the aggregation of fat globules. Furthermore, the effe ct of sugar concentration was more pronounced after steriliza- tion. The fat globules tended to move closer and form ed 1.0 0.73 0.67 c 0.63 a resulted in an increase in aggregation of fat globules. Sim- Values followed by the same letter are not significantly different ( P < 0.05). ilar results were also observed in the oil in water emulsion 10 20 30 stronger structure of aggregates. At 30% sugar 0.8 0.8 0.84 k 0.81 i 0.79 h the larger size of aggregates was exhibited with the 1.0 0.82 a 0.78 c 0.76 b unoccupied aqueous phase. Moreover, increasing 1.0 0.8 0.74 j 0.67 h 0.67 f nox 60 to 1.0% by fixing the concentration of d 426 K. Jirapeangtong et al. / Journal of Food Engineering 87 (2008) 422–427 Fig. 2. Micrographs (100 magnification) of fresh coconut milk (a) and coconut milk containing 10% (b, c), 20% (d, e) and 30% (f, g) coconut sugar and 1.0% CMC and 0.8% Montanox 60 before (b, d, f) and after (c, e, g) sterilization. system containing NaCl (Onsaard et al., 2005 ). Onsaa rd et al. (2005) found that the extent of droplet aggregation and creaming increased with an increase in NaCl concen- tration. Moreover, heating may denature the adsorbed proteins to undergo conformational changes. These con- formational changes could increa se the attractive forces between fat droplets which led to the aggregation ( Kim et al., 2003 ). Although the area of unoccupied aqueous phase and more aggregation of fat globules were clearly seen, the vis- cosity of the emulsion system containing sugar was increased significantly. The results implied that sugar may increase the viscosity of an aqueous phase, which hence resulted in an increase of the viscosity of emulsion and higher stability. 4. Conclusions Thi s study has revealed that stabilizing agents, i.e. CMC and M ontanox 60, and coconut sugar had significant effect [...]... Jirapeangtong et al / Journal of Food Engineering 87 (2008) 422–427 on both emulsion stability and rheological properties of high-fat coconut milk Higher sustain the colloidal concentrations of stabilizing agents were required 0.8–1.0% of CMC and system con-60 were sugar The to for the production taining recommended Montanoxstability sweetened coconut milk The quality of high of sweetened coconut milk, ... A., 2004 Effects of fat and temperature on the apparent viscosity of coconut milk Journal of Food Engineering 64, 193–197 Sringam, S., 1986 Preparation and stabilization of coconut milk Food Science and Technology Research Project Agro-Industry Faculty, Kasetsart University, Bangkok p 25 Srithunma, S., 2002 Effects of fat content and homogenization pressure on apparent viscosity of coconut milk Thesis for... Degree of Food Engineering Faculty of Engineering, King Mongkut’s University of Technology Thonburi, Thailand, p 42 Tangsuphoom, N., Coupland, J.N., 2005 Effect of heating and homogenization on the stability of coconut milk emulsions Journal of Food Science 70, 466–470 Tantayotai, T., Pongsawatmanit, R., 2004 Effect of homogenizer types and sodium chloride concentration on the physical properties of coconut. .. emulsions Current Opinion in Colloid and Interface Science 9, 305–313 Onsaard, E., Vittayanont, M., Sringam, S., McClements, D.J., 2005 Properties and stability of oil-in-water emulsions stabilized by coconut skim milk proteins Journal of Agricultural and Food Chemistry 53, 5747–5753 Peamprasart, T., Chiewchan, N., 2006 Effect of fat content and preheat treatment on the apparent viscosity of coconut milk. .. emulsion changes viscosity, curding and color, during storage stability, determined to assure good quality of the should be study of the combination effect of sugar product and stabilizing agents with different fat A content on emulsion stability and rheological propercontents ties is also interesting and is recommended for future work Acknowledgements The authors wish providing Montanox 60 Thailand,... sucrose on the thermal denaturation, gelation, and emulsion stabilization of whey proteins Journal of Agricultural and Food Chemistry 48, 1593– 1597 427 Maskan, M., Go¨sunflower oil-water emulsions Journal rheological g˘u} s, F., 2000 Effect of sugar on the of Food properties of 43, Engineering 173–177 McClements, D.J., 1999 Food Emulsions: Principles, Practice and Techniques CRC Press, Boca Raton, p 378... emulsions Kasetsart Journal (Natural Science) 38, 1–7 Thungkao, P., 1988 Application of emulsifiers and gums for the stabilization of canned coconut milk Thesis for the Master’s Degree of Science Department of Food Science and Technology, Kasetsart University, Thailand Vitali, A.A., Soler, M.P., Rao, M.A., 1985 Rheological behavior of coconut milk In: Maguer, M.L., Jelen, P (Eds.), Food Engineering and. .. coconut milk after homogenization Journal of Food Engineering 77, 653–658 Phungamngoen, C., Chiewchan, N., Siriwatanayothin, S., 2004 Effect of some stabilizers on the quality of canned high fat coconut milk Journal of KMUTT’s Research and Development 27, 376–390 Seow, C.C., Gwee, C.N., 1997 Coconut milk: chemistry and technology International Journal of Food Science and Technology 32, 189–201 Simuang,... Association of Official Analyticaled The Association1990 Official Method of Chemists, Virginia Chemist (AOAC), of Official Agricultural Analysis, 15th Chiewchan, N., Phungamngoen, C., and sterilizing condition on Siriwattanayothin, S., 2006 Effect of of canned high pressure quality homogenizing fat coconut milk Journal of Food Engineering 73, 38–44 Kim, H.J., Decker, E.A., McClements, D.J., 2003 Influence of sucrose... sucrose on droplet flocculation in hexadecane oil-in-water emulsions stabilized by b-lactoglobulin Journal of Agricultural and Food Chemistry 51, 766– 772 Klinkesorn, U., Sophanodora, P., Chinachoti, P., McClements, D.J., 2004 Stability and rheology of corn oil-in-water emulsions containing maltodextrin Food Research International 37, 851– 859 Kulmyrzaev, A., Bryant, C., McClements, D.J., 2000 Influence of . studied in terms of emulsion stability and apparent viscosity. The information obtained would provide the understanding of the function of sugar on the stability of coconut milk and could. Emulsion stabili ty The influence of coconut sugar and stabilizing agents on the ES of coconut milk samples are given in Table 1. A t each level of coconut sugar concentration, the. emulsion containing NaCl. 3.3. Microstructure of coconut milk Fig. 2 exemplifies the fat structure of fresh coconut milk and homogenized coconut milk before and after steriliza- tion. In