This article was downloaded by: [Canadian Research Knowledge Network] On: 24 November 2010 Access details: Access Details: [subscription number 918588849] Publisher Taylor & Francis Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House, 3741 Mortimer Street, London W1T 3JH, UK Drying Technology Publication details, including instructions for authors and subscription information: http://www.informaworld.com/smpp/title~content=t713597247 Foam Mat Drying of Alphonso Mango Pulp P. Rajkumara; R. Kailappana; R. Viswanathana; G. S. V. Raghavanb; C. Rattic a Department of Food and Agricultural Process Engineering, Agricultural Engineering College and Research Institute, Tamil Nadu Agricultural University, Coimbatore, India b Bioresource Engineering, McGill University, Montreal, Canada c Department of Soil Science and Agri Food Engineering, Laval University, Quebec, Canada To cite this Article Rajkumar, P. , Kailappan, R. , Viswanathan, R. , Raghavan, G. S. V. and Ratti, C.(2007) 'Foam Mat Drying of Alphonso Mango Pulp', Drying Technology, 25: 2, 357 — 365 To link to this Article: DOI: 10.1080/07373930601120126 URL: http://dx.doi.org/10.1080/07373930601120126 PLEASE SCROLL DOWN FOR ARTICLE Full terms and conditions of use: http://www.informaworld.com/terms-and-conditions-of-access.pdf This article may be used for research, teaching and private study purposes. Any substantial or systematic reproduction, re-distribution, re-selling, loan or sub-licensing, systematic supply or distribution in any form to anyone is expressly forbidden. The publisher does not give any warranty express or implied or make any representation that the contents will be complete or accurate or up to date. The accuracy of any instructions, formulae and drug doses should be independently verified with primary sources. The publisher shall not be liable for any loss, actions, claims, proceedings, demand or costs or damages whatsoever or howsoever caused arising directly or indirectly in connection with or arising out of the use of this material. Drying Technology, 25: 357–365, 2007 Copyright # 2007 Taylor & Francis Group, LLC ISSN: 0737-3937 print/1532-2300 online DOI: 10.1080/07373930601120126 Foam Mat Drying of Alphonso Mango Pulp P. Rajkumar,1 R. Kailappan,1 R. Viswanathan,1 G. S. V. Raghavan,2 and C. Ratti3 1 Downloaded By: [Canadian Research Knowledge Network] At: 19:58 24 November 2010 Department of Food and Agricultural Process Engineering, Agricultural Engineering College and Research Institute, Tamil Nadu Agricultural University, Coimbatore, India 2 Bioresource Engineering, McGill University, Montreal, Canada 3 Department of Soil Science and Agri Food Engineering, Laval University, Quebec, Canada The foam mat drying of Alphonso mango pulp using various food foaming agents, namely soy protein (0.25, 0.5, 1.0, and 1.5%) with methyl cellulose (0.5%), glycerol mono stearate (0.5, 1.0, 2.0 and 3.0%), and egg albumen (2.5, 5.0, 10 and 15%) with methyl cellulose (0.5%), was studied. Drying was carried out in a batch type thin layer dryer at four drying temperatures (60, 65, 70, and 75
C) on 1-, 2-, or 3-mm thickness foamed samples. The optimum concentrations of each foaming agent were determined to be 1% soy protein, 2% glycerol mono stearate, and 10% egg albumen. All were obtained after 25 min whipping time. The drying time was lower for foamed mango pulps as compared to non-foamed pulp at all drying temperatures. Biochemical analysis showed that the foam mat dried powder at 60
C retained a significantly higher (P < 0.05) content of biochemical compounds than at higher temperatures. The treatment of mango pulp with 10% egg albumen and 0.5% methyl cellulose and drying at 60
C (1-mm foam thickness), retained the highest nutritional quality characteristics than the other treatments. Keywords Alphonso mango; Foaming agents; Foam mat drying; Foam thickness; Mango powder; Mango pulps; Whipping INTRODUCTION Mango (Mangifera indica L.) is by nature a highly perishable fruit with a limited shelf life and is susceptible to mechanical damage during post-harvest handling and transportation. Therefore, the conversion of the fruit into powder could be useful not only to reduce the post-harvest losses but also to retain nutritional quality in the processed products. New processed food products from mango are highly desirable, and dehydrated mango can be used in many food product formulations. Mango powder produced from the mango pulp can be used in puddings, bakery fillings, fruit dishes for children, and as a flavoring ingredient in ice cream, yogurt, mango fruit bar, mango cereal flakes, and mango toffee. Mango pulp occupies a Correspondence: G. S. V. Raghavan, Bioresource Engineering, McGill University, 21111 Lakeshore Road, Ste-Anne-de-Bellevue, H9X 3V9, Montreal, Quebec, Canada; E-mail: Vijaya.raghavan@ mcgill.ca major share with 19.7% of processed fruits and vegetable products exported from India.[1] Foam-mat drying is a process in which a liquid or semisolid material is converted into a stable foam by incorporating substantial volume of air or other inert gases in the presence of a foaming agent, which works as a foam inducer and=or stabilizer. The foam thus formed is spread as a thin mat or sheet and exposed to a stream of hot air until it is dried to the required moisture level. The dehydrated product is conditioned and converted into powder.[2–6] Few studies have reported on the drying of foamed and non-foamed fruit juices or purees. Jayaraman et al.[7] dried mango pulp foam by spreading it as a thin sheet on plain aluminum trays at a rate of 0.25 kg per tray (40  80 cm) in a cross flow drier, initially at 80
C for 30 min and subsequently at 65–70
C for 30–90 min to reduce the drying time. Baldry et al.[8] prepared Alphonso mango powder using 1.5% polyglyceryl stearate as a foaming agent by spreading in a 2-mm-thick layer and drying in the temperature range of 50 to 80
C for 20 min to the final moisture content of 3%. Although increasing the airflow rate (58–95 cm=s) at temperatures between 50 and 70
C increased the initial drying rates, a moisture content of less than 5% was not achieved at 50
C, a level normally required for safe storage. Furthermore, they noted that the drying rate increases as the foam dries in contrast to the usual drying behavior. Akintoye and Oguntunde[9] reported that a temperature of 65
C for 90 min was found to be more suitable for foam-mat drying of soymilk. They also concluded that the foam drying at 65
C occurred in the falling rate period and that the drying rate is dependent on the foam density. Beristain et al.[10] found that the best quality pineapple powder was obtained at 60
C with 5 mm foam thickness by using maltodextrin as the surfactant mixture. Foam-mat drying of star fruit by foaming with different concentrations of methyl cellulose and drying as a 5-mmthick layer in a mini kiln smoker at temperatures between 70 and 90
C and with an airflow rate of 0.12 m=s showed 357 Downloaded By: [Canadian Research Knowledge Network] At: 19:58 24 November 2010 358 RAJKUMAR ET AL. that obvious color and flavor changes were observed in the product dried at 90
C.[11] Similar foam-mat drying studies were reported for mango pulp,[12] apple pulp,[13] cowpea paste,[14] and lemon juice.[15] The transient drying behavior of banana pulp in terms of capillary model [ln (M=M0) ¼ Kt] showed that the drying time (t) was directly related to the thickness of the foam mat.[16] They also reported that the drying rate constant increased with an increase in drying temperature. Generally, pulp and sliced mangoes dry quite slowly in hot air–drying. This may be due to the dense physical structure of the fruit, as well as its sugar content and chemical composition. These factors do not allow rapid movement of internal moisture. But the drying rate can be increased by making the mango more porous, thus allowing rapid moisture movement within the fruit. The objectives of this work are therefore to optimize foaming agents and to study the foam mat drying characteristics of Alphonso mango pulp at different temperatures for producing mango flakes. MATERIALS AND METHODS Foaming Experiments Fresh, fully ripened, firm Alphonso mangoes having uniform color were selected. The percentage of peel, stone, and pulp present in the mangoes was calculated. The flesh portion of the mango was sliced and pulped using a pulper with a capacity of 0.6 kg per min (Kifco, Cochin, Kerala, India) for conducting experimental studies. Biochemical analyses of the fresh mango pulp were carried out to evaluate their relative losses during foam-mat drying. Biochemical analyses for measurement of acidity, pH, total soluble solids, total sugars, b-carotene, and ascorbic acid contents of mango pulps were done using standard methods.[17] Levels of Foaming Agents and Stabilizing Agent Used during the Experiment The foaming and stabilizing agents were added to the mango pulp for the production of the foam and to stabilize it during the drying operation. The foaming agents, namely soy protein (0.25, 0.5, 1.0, and 1.5%), glycerolmonostearate (0.5, 1, 2, and 3%), and egg albumen (2.5, 5, 10, and 15%) were selected for the experiment. To stabilize the foam, 0.5% methylcellulose was added to the foaming agents soy protein and egg albumen only, since glycerol-monostearate can be used for both foaming and stabilizing purposes. Considering the limits stipulated in the Prevention of Food Adulteration Act[18] and with the results of preliminary foaming trials, the minimum and maximum levels of foaming agents were selected. Dispersion of Foaming Agents The soy protein and methyl cellulose were incorporated sequentially into the mango pulp for foaming and stabilizing. For the dispersion of glycerol-monostearate, the mango pulp was first heated to 60
C for a short period of 5 min prior to the addition of the glycerol-monostearate. There was little loss of ascorbic acid due to the initial heating. The egg albumen was directly mixed with the fruit pulp for foaming and the methyl cellulose was added for stabilizing the foamed pulp.[19] Foaming Properties Foaming properties such as foam expansion, foam stability, and foam density were measured for each concentration of each foaming agent and their optimum levels were identified based on these results. During the entire study, all the experiments were conducted in triplicate and the mean values were recorded. The whipping speed that produced a maximum volume with a minimum density in the shortest time was identified and used in the foaming and drying studies. During the foaming experiments, mango pulp with foaming agents was whipped at 1400 rpm using whipping or foaming blades (Braun Multimix M880 handheld electric mixer) to get maximum foam expansion with minimum density:[20]   V1  V0  100 ð1Þ Foaming expansion (FE) ¼ V0 where V0 is the initial volume of pulp and V1 is the volume of foam, cm3. Foam stability was determined by leaving 100 mL of the foamed pulp in a transparent graduated beaker kept at room temperature for 3 h. The foam drainage in terms of volume reduction was measured as an index for the foam stability for every 30 min by using the following relationship:[21] Foam stability ¼ V0 Dt DV ð2Þ where DV is the change in foam volume during the time interval Dt, and V0 is the initial foam volume. The density of the foamed mango pulp was determined in terms of mass-to-volume ratio:[14] Foam density ðg=cm3 Þ ¼ m V1 ð3Þ Foam-Mat Drying The mango pulp foam was dried using a batch-type thinlayer cabinet dryer. The dryer consists of heating coils, a blower, a drying chamber, air outlet openings, and a thermostat as shown in Fig. 1. The main purpose of the heating coils is to heat the incoming air and lower the relative humidity, thereby facilitating the removal of moisture from the drying product. Eight coils, each with a capacity of 500 W, were vertically placed on two sides of the drying 359 FOAM MAT DRYING OF MANGO PULP Moisture Diffusivity Fick’s second law was used to describe the diffusion of moisture during drying of fresh and of foamed mango pulps spread in the form of a thin slab.[22] The equation is:   1 Dð2nþ1Þ2 p2 h X  Mt 8 2 4L ð4Þ ¼1 e 2 2 M1 n¼0 ð2n þ 1Þ p Equilibrium at the interphase as a boundary condition is a key factor for using Eq. (4). For long drying periods (t > 5 min), Eq. (4) can be simplified (Mt ¼ MI  Mh and M/ ¼ MI  Me) to the following form by taking n ¼ 0: Mh  M e MI  Me     2h D h  eff2 8 Dp 2 ¼ 2 e 4L ¼ Ae 4L p Downloaded By: [Canadian Research Knowledge Network] At: 19:58 24 November 2010 Moisture ratio (MR) ¼ where A ¼ (8=p2). Equation (5) can be linearized:     Mh  Me Deff h lnðMRÞ ¼ ln ¼ ln A  MI  Me 4L2 FIG. 1. Schematic view of tray dryer. chamber. The blower is used to supply fresh air to the main chamber, which drives out the hot moist air from the drying chamber. The blower was installed at the air delivery side and was run by a 0.5 H.P electric motor. The drying chamber measuring 100  100  100 cm was constructed of 3 mm thick mild steel sheets. The drying chamber can accommodate 24 (90  40  2.5 cm) stainless steel trays. The temperature inside the chamber was regulated using a digital k-type thermostat with an accuracy of 1
C. For the foam-mat drying of mango pulp, the homogeneous foamed mango pulps were evenly spread on the stainless steel trays at a thickness of 1, 2, and 3 mm. The foam thickness was determined by dividing the known volume (mass=bulk density) of foam by the drying area. During preliminary drying tests, it was found that the foamed and dried mango pulp firmly stuck to the stainless steel tray, and scraping off the foamed and dried mango pulp became a serious problem. To prevent sticking and to facilitate easy removal of the foamed fruit pulp after drying, the tray was lined with a non-stick food-grade Teflon sheet. In order to stabilize the temperature inside the drying chamber, the dryer was operated for a period of one hour at the required temperature before placing the trays in the dryer. The trays were taken out of the drying chamber at 10-min intervals for mass loss determination. The drying rate was computed for the different drying combinations of time and moisture contents. Drying curves were modeled using Fick’s law of diffusion. Drying was continued until the moisture content of the samples was constant. ð5Þ ð6Þ From Eq. (6), a plot of ln (MR) versus drying time should give a straight line with a slope P: Deff ð7Þ 4L2 The moisture diffusivity (Deff) can therefore be determined from the value of the slope. The acidity, pH, total soluble solids, total sugars, b-carotene, and ascorbic acid contents were determined for the foam mat dried mango pulp after reconstituting the powders to their original moisture content. The biochemical contents of the reconstituted foam mat dried powders were statistically analyzed as a factorial completely randomized block design (FCRD) using a statistical software package (AGRES) and compared with fresh mango pulps to optimize the drying and foaming parameters. The level of significance was defined at P  0.05. P¼ RESULTS AND DISCUSSION Physico-Chemical Properties of Mango Pulps The percentage of peel, kernel, and pulp recovery were found to be 16.8  0.3, 18.3  0.4, and 64.8  0.7%, respectively. The acidity, pH, total sugar, total soluble solids, b–carotene and ascorbic acid of the fresh mango pulp were determined to be 0.46  0.03%, 4.6  0.2, 13.2  0.5%, 19.1  0.4
Brix, 7960  3.9 mg=100 g, and 25.12  0.6 mg=100 g, respectively. These results of physical and biochemical properties are comparable to those reported by Chauhan et al.[23] and Kansci et al.[24] Foaming Characteristics of Mango Pulp The effect of whipping time on foam expansion for different concentrations of foaming agents is shown in 360 RAJKUMAR ET AL. TABLE 1 Effects of whipping duration on foam expansion (FE) Foaming agents Soy protein with methylcellulose Glycerol-monostearate Downloaded By: [Canadian Research Knowledge Network] At: 19:58 24 November 2010 Egg albumen with methylcellulose Foaming agents level (%) FE after 5 min. (%) FE after 10 min. (%) FE after 15 min. (%) FE after 20 min. (%) FE after 25 min. (%) FE after 30 min. (%) 0.25 þ 0.5 0.5 þ 0.5 1.0 þ 0.5 1.5 þ 0.5 0.5 1.0 2.0 3.0 2.5 þ 0.5 5.0 þ 0.5 10.0 þ 0.5 15.0 þ 0.5 1.1 4.7 6.8 7.1 1.0 3.1 5.2 5.4 1.1 4.7 3.0 7.0 2.6 12.6 19.2 20.9 2.4 10.6 14.2 16.9 3.5 10.8 21.2 25.0 4.3 23.5 41.8 43.3 4.3 20.9 38.2 38.9 8.1 33.8 47.2 46.3 6.4 44.0 68.4 76.1 4.9 35.2 66.5 68.7 12.3 56.4 65.7 74.7 6.4 58.6 88.5 94.6 4.9 56.1 85.3 91.2 12.7 65.6 89.3 94.2 6.4 58.8 88.8 94.8 4.9 56.5 85.6 92.0 12.7 65.9 89.6 94.8 Table 1. An increase in whipping time resulted in an increase in foam volume. It can also be seen that for the lowest concentration of foaming agent, increasing the whipping time up to 20 min increased foam expansion. At the highest concentration, a whipping time of up to 25 min can be used for all foaming agents. There was no significant increase in foam volume when the whipping time was increased from 25 to 30 min. For example, in the case of 1.5% soy protein with 0.5% methylcellulose, only 0.26% increase in foam volume occurred for an increase in the duration of the whipping operation from 25 to 30 min. In the case of glycerol-monostearate and egg albumen, the increases were only 0.84 and 0.68%, respectively, for the above increase in whipping time. Hence, it was decided to conduct all the foaming studies with a whipping time of 25 min for all types and concentrations of foaming agents. Among the different foaming agents studied, glycerolmonostearate at 0.5% level recorded the lowest volume expansion of 0.99%, whereas 15% egg albumen with 0.5% methyl cellulose and 1.5% soy protein with 0.5% methyl cellulose recorded the highest foam expansion of 94.8%. Kabirulla and Wills[25] reported 35% increase in foam volume for 1% soy protein while whipping at 10,000 rpm for one minute. In the present study, increasing the duration of whipping to 25 min increased the foam volume to 88.5% for the same level of soy protein addition. Table 2 describes the mango pulp foam characteristics using different foaming agents. The density of mango pulp varied between 1.02 and 1.05 g=cm3, whereas after TABLE 2 Foaming characteristics of mango pulp Foaming and stabilizing agents Soy protein with methylcellulose Glycerol-monostearate Egg albumen with methylcellulose Foaming agent level (%) Mass of fresh pulp (g) Vol. fresh pulp (cm3) Bulk density of pulp (g=cm3) Foam volume (cm3) Foam expansion (%) Foam density (g=cm3) 0.25 þ 0.5 0.5 þ 0.5 1.0 þ 0.5 1.5 þ 0.5 0.5 1.0 2.0 3.0 2.5 þ 0.5 5.0 þ 0.5 10.0 þ 0.5 15.0 þ 0.5 251.8 252.5 253.8 255.0 251.2 252.5 255.0 257.5 257.5 263.7 276.2 288.7 239.7 243.2 243.9 244.6 243.1 243.7 244.9 246.1 258.2 262.8 272.0 280.8 1.02 1.04 1.04 1.04 1.02 1.04 1.04 1.05 1.02 1.00 1.02 1.03 255.0 386.1 460.5 476.5 255.0 381.5 454.5 472.5 285.0 436.0 514.9 547.1 6.4 58.6 88.5 94.6 4.9 56.1 85.3 91.2 12.7 65.6 89.3 94.2 0.96 0.65 0.55 0.54 0.97 0.66 0.56 0.55 0.91 0.61 0.54 0.53 FOAM MAT DRYING OF MANGO PULP 361 Downloaded By: [Canadian Research Knowledge Network] At: 19:58 24 November 2010 whipping for 25 min, it decreased to between 0.97 and 0.53 g=cm3. Hart et al.[3] stated that for foam mat drying, the optimum range of bulk density of foamed material should be between 0.2 and 0.6 g=cm3. Foam densities of 0.53 to 0.56 g=cm3 were obtained with all three foaming agents tested, hence within the recommended limit as described by Hart et al.[3] for foam-mat drying. For both glycerol-monostearate and egg albumen, the foam volume increased and the foam density decreased with an increase in the concentration of foaming agents. Foam Stability of Mango Pulp Foam stability studies were conducted only for cases where foam densities were in 0.2 to 0.6 g=cm3 range, as indicated by Hart et al.[3] The results are presented in Figs. 2–4. Figure 2 shows that when soy protein concentration was 0.5%, the foam stability was 93.3% after 90 min and 90.0% after 180 min. Similarly, levels of 1.0 and 1.5% gave 98.0 and 97.2% stability after 90 min and 98.3 and 97.6% after 180 min, respectively. By increasing the soy protein from 1.0 to 1.5%, the stability of the foam increased by only 0.41% after 90 min and 0.36% after 180 minutes. From this, it is clear that the interaction effect of soy protein with methylcellulose for the stability of foamed mango pulps was higher at 1.0 and 1.5% of soy protein than at 0.5%. At 0.5% soy protein concentration, the foam drainage was higher and, in turn, the foam stability was lower. Similar results were reported by Kabirulla and Wills.[25] Table 2 and Fig. 2 show that foams made using 1.0% soy protein had a density of 0.55 g=cm3 and stability of 97.2% after 180 min. Since soy protein at 1.0 and 1.5% levels gave similar results, it was decided to continue further foaming studies with 1.0% soy protein with 0.5% methylcellulose. In the case of glycerol-monostearate, which acts both as a foaming and a stabilizing agent, it had foam stability values of 93.7, 97.8, and 98.4% after 90 min and 91.3, FIG. 2. Foam stability of mango pulp treated with soy protein (SP) and methylcellulose (MC). FIG. 3. Foam stability of mango pulp treated with glycerol-monostearate. 97.1, and 97.9% after 180 min for 1, 2, and 3% concentrations, respectively. That is, glycerol-monostearate at 1% recorded a relatively low stability value as compared to those for 2 and 3%. Between 2 and 3%, the foam stability values were similar with  1% variation. Table 2 and Fig. 3 show that 2% glycerol-monostearate gave a foam density of 0.56 g=cm3 and a foam stability of 97.8% after 90 min, whereas a concentration of 3% resulted in a density of 0.55 g=cm3 and a stability of 98.4% after 90 min. Both 2 and 3% concentrations of glycerolmonostearate gave similar results of 0.56  0.06 g=cm3 for foam density and 97.8  0.7% for foam stability. Hence, it was decided to select an addition of 2% glycerolmonostearate for further foam-mat drying studies. Foam stability studies were also conducted by adding egg albumen at 10 and 15% levels along with 0.5% methylcellulose. The results of the experiments are shown in Fig. 4, which shows that an increase in egg albumen level increased foam stability. The increase was 24% higher when the level of egg albumen was increased from 5 to 10%, while the increase in foam stability was less than 1% when the egg albumen level was increased from 10 to 15%. Likewise, FIG. 4. Foam stability of mango pulp treated with egg albumen (EA) and methylcellulose (MC). 362 RAJKUMAR ET AL. Downloaded By: [Canadian Research Knowledge Network] At: 19:58 24 November 2010 foam density was similar for 10 and 15% egg albumen (Table 2). It is also observed that the interaction effect of egg albumen with methylcellulose for the stability of foamed mango pulps was higher for 10 and 15% egg albumen. At 5% concentration, the interaction effect was lower, resulting in turn in a lower foam stability. Hence, to reduce the level of addition of foaming agent and subsequently the cost, it was decided to add 10% egg albumen with 0.5% methylcellulose to conduct the foam-mat drying studies. Effect of Foam Thickness on Drying of Foamed Mango Pulps Foam mat drying of Alphonso mango pulps was carried out using the various optimized levels of foaming agents namely 1% soy protein with 0.5% methylcellulose, 2% glycerol-monostearate, and 10% egg albumen with 0.5% methyl cellulose. Three foam thicknesses of 1, 2, and 3 mm and four drying temperatures of 60, 65, 70, and 75
C in a batch-type (cabinet) thin-layer dryer were studied. The drying study showed that the egg albumen foamed mango pulp dried at 60
C was found to be the best and hence these drying kinetics are discussed in comparison with fresh mango pulp dried at 60
C. The effect of foam thickness on the moisture content of egg albumen foamed mango pulp during drying at 60
C is shown in Fig. 5. From the figure, it was observed that the time taken for drying a 1-mm-thick foamed mango pulp from 393 to 5.8% (d.b.) moisture content was 40 min. The time taken for the same level of moisture reduction for a 2-mm-thick foam was 60 min and for a 3-mm-thick foam, it was 80 min. In the case of fresh pulp (Fig. 6), the time taken for drying a 1-mm-thick mango pulp from 391 to 6.6% (w.b.) moisture content was 100 min. For a 2-mm-thick pulp, it was 130 min and for a 3-mm-thick pulp, it was 190 min. Thus, the reduction in the moisture content of fresh mango pulp at any point of time during drying was lower when compared to the foamed mango pulps at all thicknesses studied. FIG. 5. Relationship between moisture content and drying time of egg albumen–foamed mango pulp at 60
C. FIG. 6. Relationship between moisture content and drying time of fresh mango pulp at 60
C. This is due to the high viscosity and bulk density of the mango pulp, which has less surface area exposed during drying, demonstrating that foaming was beneficial in reducing drying time. From Fig. 6, it is also noted that the reduction in the moisture content of mango pulp at any point of time during drying increased with a decrease in foam thickness. As expected, the drying data indicated clearly that the mango pulps with a smaller foam thickness dried at a faster rate than that of foamed mango pulps with a greater thickness. Similar types of drying results were reported by Eduardo et al.[26] for tamarind foam-mat treated with egg albumen and by Falade et al.[14] for cowpea treated with egg albumen. The calculated drying rates for egg albumen foamed mango pulp were 0.194, 0.324, and 0.403 g=min during the first 10 min, and 0.015, 0.023, and 0.037 g=min during the final stage of drying for 1-, 2-, and 3-mm-thick foams, respectively. For the fresh pulp, the drying rates were 0.176, 0.273, 0.349 g=min during the first 10 min and 0.013, 0.022, and 0.024 g=min in the final stage of drying for 1-, 2-, and 3-mm-thick pulps, respectively. This clearly indicates that foamed pulps dried faster than fresh pulps and that the drying rate of foamed mango pulp was higher during the initial stage as compared to the final stage of drying. Drying of egg albumen foamed mango pulps at all thicknesses occurred during the falling rate period with the rapid removal of moisture from the thin surfaces of foams. These drying results are in agreement with the results recorded in high moisture foods like tomato[7] and papaya.[27] Moisture Diffusion in Foamed and Fresh Mango Pulps The moisture diffusivity in foamed and fresh mango pulps was calculated using the relationship obtained by plotting ln(MR) vs. time, as shown in Figs. 7 and 8. At each foam and fresh mango pulp thickness, two trend lines were drawn by considering two falling rate periods during 363 Downloaded By: [Canadian Research Knowledge Network] At: 19:58 24 November 2010 FOAM MAT DRYING OF MANGO PULP FIG. 7. Relationship between ln (MR) and drying time for egg albumen–foamed mango pulp to determine the moisture diffusion based on Fick’s law. drying. The moisture diffusivity was calculated using Fick’s moisture diffusion equation and specifically from the value of the slope as shown in Table 3. The average moisture diffusivity values for foamed mango pulps ranged from 7.29  10 9 to 3.51  10 8 m2=s and for fresh mango pulps it ranged from 2.88  10 9 to 1.71  10 8m2=s at 60
C. The moisture diffusion studies clearly show that foaming gave higher moisture diffusivities when compared to nonfoamed mango pulp during drying due to larger exposed surface area in foamed pulps. Effect of Drying on Dried Mango Properties The biochemical contents of mango powder obtained at 60 and 75
C are shown in Tables 4 and 5 for comparison. It FIG. 8. Relationship between ln (MR) and drying time for fresh mango pulp to determine the moisture diffusion based on Fick’s law. was observed that there was a significant (P  0.05) reduction in ascorbic acid, total soluble solids (TSS), and b-carotene content in the mango powder dried at higher temperature of 75
C when compared to drying at lower temperature of 60
C. The loss might be due to the heat sensitive nature of ascorbic acid, TSS, and b-carotene when exposed to a higher temperature. Also, these biochemical changes were higher for 2- and 3-mm-thick foams than for 1-mm-thick foam due to a longer drying time at larger thicknesses. Similar reductions in biochemical contents due to drying were reported by Giovanelli et al.[28] But the other biochemical characteristics such as pH, acidity, and total sugar were less affected (P  0.05) by the increase in temperature and foam thicknesses. It is found that these biochemical contents could withstand TABLE 3 Moisture diffusion values based on Ficks’ formula Foamed pulp Foam thickness Regression equation y ¼ 0.0788x þ0.0351 1 mm y ¼ 0.1399x (II falling rate) þ1.2206 2 mm y ¼ 0.0567x þ0.0211 2 mm y ¼ 0.0777x (II falling rate) þ0.6168 3 mm y ¼ 0.0359x 0.0233 3 mm y ¼ 0.081x (II falling rate) þ2.2965 1 mm R2 value Moisture diffusion (m2=s) Average moisture diffusion (m2=s) Non-foamed (fresh) pulp Regression equation 0.9941 5.25  10 9 7.29  10 9 y ¼ 0.0381x þ0.0204 1 9.32  10 9 y ¼ 0.0485x þ0.3071 0.9981 1.51  10 8 1.79  10 8 y ¼ 0.0276x þ0.1371 0.9998 2.07  10 8 y ¼ 0.0599x þ2.6169 0.9984 2.15  10 8 3.51  10 8 y ¼ 0.018x þ0.0621 0.9688 4.86  10 8 y ¼ 0.039x þ2.3557 R2 value Moisture diffusion (m2=s) Average moisture diffusion (m2=s) 0.9981 2.54  10 9 2.88  10 9 0.9961 3.23  10 9 0.9753 7.36  10 9 1.67  10 8 0.9648 1.63  10 8 0.9912 1.08  10 8 1.71  10 8 0.9797 2.34  10 8 364 RAJKUMAR ET AL. TABLE 4 Biochemical composition of foam-mat-dried mango pulp at 60
C Downloaded By: [Canadian Research Knowledge Network] At: 19:58 24 November 2010 Bio-chemical compositions Acidity (%) pH TSS (
Brix) Total sugar (%) b-Carotene (mg=100 g) Ascorbic acid (mg=100 g) Soy protein with methylcellulose Glycerolmonostearate Egg albumen with methylcellulose Control Foam thickness (mm) Foam thickness (mm) Foam thickness (mm) Foam thickness (mm) 1 2 3 1 2 3 1 2 3 1 2 3 0.42 4.22 19.60 13.26 7905 0.41 4.22 19.60 13.26 7857 0.41 4.22 19.50 13.26 7733 0.41 4.27 18.90 13.25 7227 0.41 4.27 18.80 13.24 7219 0.40 4.28 18.90 13.24 7185 0.46 4.12 20.10 13.75 7945 0.45 4.12 20.00 13.75 7912 0.43 4.13 19.95 13.73 7897 0.45 4.15 19.00 13.30 7950 0.45 4.15 19.00 13.29 7945 0.44 4.15 19.00 13.22 7726 22.49 21.66 17.54 20.11 18.72 15.61 22.65 22.51 19.56 17.62 16.11 13.32 higher temperatures. Comparison of the results for foamed and non-foamed (control) dried mango pulp generally showed that the retention of biochemical contents in a foamed mango pulp was significantly higher than in nonfoamed mango pulp. This might be due to a higher drying rate with lower drying time in foamed pulp when compared to non-foamed pulp. A similar observation was made by Mishra et al.[13] for foam-mat drying of apple. Overall, it was observed that using 10% egg albumen with 0.5% methylcellulose, a drying temperature of 60
C, and a foam thickness of 1 mm retained significantly higher (P  0.05) amounts of biochemical and nutritional qualities when compared to other foaming agents. This was due to improved foaming quality with lower drying time. CONCLUSION The optimum level of foaming and stabilizing agents were found to be 1.0% soy protein with 0.5% methylcellulose, 2.0% glycerol-monostearate, and 10.0% egg albumen with 0.5% methylcellulose. The optimum whipping time was 25 min. The foam-mat drying study demonstrated that the time taken for drying egg albumen–treated mango pulp was 40, 60, and 80 min for 1-, 2-, and 3-mm-thick foams, respectively. But the time taken for drying the fresh (control) samples was 100, 130, and 190 min for 1-, 2-, and 3-mm pulp thicknesses, respectively. From the moisture diffusion study, it was observed that the moisture diffusion was higher in foamed mango pulp than with non-foamed pulp (control). Based on the overall foam-mat drying TABLE 5 Biochemical composition of foam-mat-dried mango pulp at 75
C Soy protein with methylcellulose Glycerolmonostearate Egg albumen with methylcellulose Control Foam thickness (mm) Foam thickness (mm) Foam thickness (mm) Foam thickness (mm) Bio-chemical compositions 1 2 3 1 2 3 1 2 3 1 2 3 Acidity (%) pH TSS (
Brix) 0.41 4.22 19.50 0.41 4.23 19.40 0.41 4.23 19.40 0.41 4.28 18.90 0.40 4.29 18.50 0.40 4.29 18.50 0.42 4.12 19.90 0.42 4.13 19.90 0.41 4.14 19.90 0.44 4.16 18.50 0.43 4.17 18.00 0.43 4.17 17.75 Total sugar (%) b-Carotene (mg=100 g) Ascorbic acid (mg=100 g) 13.26 7803 13.25 7698 13.24 7602 13.24 7200 13.23 6598 13.23 6914 13.74 7893 13.73 7598 13.71 7625 13.22 7837 13.21 7615 13.21 7127 17.92 13.78 10.75 14.91 11.79 9.26 18.01 13.88 11.27 13.78 9.17 6.95 FOAM MAT DRYING OF MANGO PULP study, it was concluded that the 10.0% egg albumen 0.5% with methylcellulose-treated powder dried at 60
C with 1mm foam thickness retained the highest biochemical content when compared to all other treatments. 10. Downloaded By: [Canadian Research Knowledge Network] At: 19:58 24 November 2010 11. NOMENCLATURE A Constant Deff Moisture diffusion (m2=s) Equilibrium moisture content (dry basis) Me Initial moisture content (dry basis) MI MR Moisture ratio Mh Moisture content (dry basis) at h time m Mass of the foamed liquid (g) P Slope of the trend line t Thickness of the foam mat (mm) V1 Volume of foam (cm3) Volume of solution (cm3) V0 Greek Letter h Time, min ACKNOWLEDGEMENTS The authors thank the All India Coordinated Research Programme on Post Harvest Technology Scheme, Tamil Nadu Agricultural University, and the Canadian International Development Agency for their financial and technical supports. REFERENCES 1. Srinivasan, N.; Elangovan, S.; Chinnaiyan, P. Consumer perception towards processed fruit and vegetables products. Indian Economic Panorama 2000, 10 (3), 11–12. 2. Morgan, A.I.; Graham, R.P.; Ginnette, L.F.; Williams,G.S. Recent developments in foam-mat drying. Food Technology 1961, 15, 37–39. 3. Hart, M.R.; Graham, R.P.; Ginnette, L.F.; Morgan, A.I. Foams for foam-mat drying. Food Technology 1963, 17, 1302–1304. 4. Berry, R.E.; Bissett, O.W.; Lastinger, J.C. Method for evaluating foams from citrus concentrates. Food Technology 1965, 19 (2), 144–147. 5. Chandak, A.J.; Chivate, M.R. Recent development in foam-mat drying. Indian Food Packer 1972, 26 (6), 26–32. 6. Labelle, R.L. Principles of foam mat drying. Journal of Food Technology 1984, 20, 89–91. 7. Jayaraman, K.S.; Goverdhanan, T.; Sankaran, R.; Bhatia, B.S.; Nath, H. Compressed ready to eat fruited cereals. Journal of Food Science and Technology 1974, 11 (3), 181–185. 8. Baldry, G.R; Breag, J.; Caygill, J.C.; Cooke, R.D.; Ferber, C.E.M.; Lalitha, K. Alternative methods of processing mangoes. Indian Food Packer 1976, 30 (5), 56–62. 9. Akintoye, O.A.; Oguntunde, A.O. Preliminary investigation on the effect of foam stabilizers on the physical characteristics and 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. 27. 28. 365 reconstitution properties of foam-mat dried soy milk. Drying Technology 1991, 9 (1), 245–262. Beristain, C.; Cortes, I.; Casilas, R.; Diaz, M.A. Obtainment of pineapple juice powder by foam-mat drying. Archives of Latino-American Nutrition 1990, 41 (2), 238–245. Karim, A.A.; Wai, C. Foam mat drying of star fruit puree, stability and air drying characteristics. Food Chemistry. 1999, 64 (3), 337–343. Srivastava, J.S. Mango processing industries—A scenario. Indian Food Packer 1998, 52 (6), 43–49. Mishra, H.N.; Jacob, J.K.; Srinivasan, N. Preparation of apple powder and evaluation of its shelf life. Beverage and Food World 2002, 29 (1), 49–52. Falade, K.O.; Adeyanju, K.I.; Uzo-Peters, P.I. Foam mat drying of cowpea (Vigna unguiculata) using glyceryl monostearate and egg albumen as foaming agents. European Food Research and Technology 2003, 217 (6), 486–491. Sharma, S.K.; Sharma, P.C.; Lalkanshal, B.B. Storage studies of foam mat dried hill lemon juice powder. Journal of Food Science and Technology 2004, 41 (1), 9–13. Sankat, C.K.; Castaigne, F. Foaming and drying behaviour of ripe bananas. Lebensmittel-Wissenschaft Technologie 2004, 37 (5), 517–525. Ranganna, S. Manual of Analysis of Fruit and Vegetable Products. II, (Reprint); Tata McGraw Hill Publishing Co. Ltd: New Delhi, 1979; 634. The Prevention of Food Adulteration Act, Act 37 of 1954, Government of India, 1955. Rao, T.S.S.; Murali, H.S.; Rao, K.R.G. Preparation of foam mat dried and freeze dried whole egg powder (hen’s). Journal of Food Science and Technology 1986, 24 (1), 23–26. Durian, D.J. Foam mechanics at the bubble scale. Physical Review Letters 1995, 75, 4780–4784. Akiokato, A.T; Matsudomi, N.; Kobayashi, K. Determination of foaming properties of egg white by conductivity measurements. Journal of Food Science and Technology 1983, 48 (1), 62–65. Crank, J. The Mathematics of Diffusion. Oxford University Press: London, 1975; 414. Chauhan, S.K.; Lal, B.B.; Joshi, V.K. Development of protein rich mango beverage. Journal of Food Science and Technology 1998, 35 (6), 521–523. Kansci, G.; Koubala, B.B.; Lape, I.M. Effect of ripening on the composition and the suitability for jam processing of different varieties of mango (Mangifera indica). African Journal of Biotechnology 2003, 2 (9), 301–306. Kabirullah, M.; Wills, R.B.H. Foaming properties of sunflower seed protein. Journal of Food Science and Technology 1988, 25 (1), 16–19. Eduardo J.V.; Pardes, G.E.; Beristain, C.I.; Tehuitzil, H.R. Effect of foaming agents on the stability, rheological properties, drying kinetics and flavour retention of tamarind foam mats. Food Research International 2001, 34 (4), 587–598. Levi, A.; Gagel, S.; Juven, B. Intermediate moisture tropical fruit products for developing countries. Technological data on papaya. Journal of Food Technology 1983, 18 (6), 667–685. Giovanelli, G.; Zanoni, B.; Lavelli, V.; Nani, R. Water sorption, drying and antioxidant properties of dried tomato products. Journal of Food Engineering 2002, 52, 135–141.