Moisture sorption isotherms and storage study of spray dried tamarind pulp powder

Moisture sorption isotherms and storage study of spray dried tamarind pulp powder

Powder Technology 291 (2016) 322–327 Contents lists available at ScienceDirect Powder Technology journal homepage: www.elsevier.com/locate/powtec M...

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Powder Technology 291 (2016) 322–327

Contents lists available at ScienceDirect

Powder Technology journal homepage: www.elsevier.com/locate/powtec

Moisture sorption isotherms and storage study of spray dried tamarind pulp powder Khalid Muzaffar ⁎, Pradyuman Kumar Department of Food Engineering and Technology, Sant Longowal Institute of Engineering and Technology, Longowal 148106, Punjab, India

a r t i c l e

i n f o

Article history: Received 16 September 2015 Received in revised form 4 December 2015 Accepted 29 December 2015 Available online 30 December 2015 Keywords: Tamarind pulp powder Sorption isotherm Storage LDPE ALP Glass

a b s t r a c t Moisture adsorption isotherms and storage study of spray dried tamarind pulp powder were evaluated in this work. Adsorption isotherms of tamarind pulp powder were determined at four different temperatures (20, 30, 40 and 50 °C) using a gravimetric technique. The sorption isotherms were found to be typical type II sigmoid. The experimental data obtained was fitted to several mathematical models viz. two-parameter (BET, Oswin, Smith, Caurie, and Iglesias and Chirife), and three-parameter (GAB) relationships. A non-linear least square regression analysis was used to evaluate the model constants. The GAB followed by Oswin model best fitted the experimental data. Changes in physicochemical properties of tamarind pulp powder were evaluated during storage (at 0, 1, 2, 3, 4, 5 and 6 months), using three different packaging materials (low density polyethylene, LDPE; aluminum laminated polyethylene, ALP and glass). Color parameters, moisture content, titratable acidity, bulk density and flowability of the powder varied to different extent during storage, depending on the type of packaging material used. Compared to other packaging materials, powder packed in LDPE showed considerable changes in physicochemical properties during storage. The magnitude of the change in physicochemical properties of the powder measured during storage suggests that glass is best for long term storage of tamarind pulp powder. © 2015 Elsevier B.V. All rights reserved.

1. Introduction Water sorption isotherms are considered important thermodynamic tools to determine the interaction between water and food components. They represent the relationship of the equilibrium moisture content of a food product with the relative humidity of its surrounding environment at a particular temperature and provide useful information for food processing operations such as drying, packaging and storage [1,2]. A moisture sorption isotherm can be used to predict the amount of water that a material will hold if it is exposed to air at a certain relative humidity. This moisture content is dependent on the temperature and the environmental relative humidity, as well as on the composition of the material [3]. The sorption isotherms are commonly presented by mathematical models based on empirical and/or theoretical criteria. In the literature, a large number of isotherm models are available which can be categorized into various groups; kinetic models based on an absorbed monolayer of water (BET model), kinetic models based on a multi-layer and condensed film (GAB model), semi-empirical (Halsey model) ⁎ Corresponding author. E-mail addresses: [email protected] (K. Muzaffar), [email protected] (P. Kumar).

http://dx.doi.org/10.1016/j.powtec.2015.12.046 0032-5910/© 2015 Elsevier B.V. All rights reserved.

and purely empirical models (e.g. Oswin and Smith models). The moisture sorption isotherms are unique for every material and must be evaluated experimentally. Fruit juice and pulp powders are valuable materials in terms of transportation, packaging, storage and shelf life, compared with their liquid counter parts. Spray drying is one of the common technique used for production of powders from liquid solutions and suspensions. Tamarind pulp in powder form is one of the important tamarind product. However due to high amount of sugars and acids in tamarind pulp, higher significant product loss occurs during spray drying because of the stickiness of the powder. Hence to overcome the stickiness problem, drying aids are added during spray drying of tamarind pulp [4,5]. Besides this, physicochemical properties of spray dried powder are affected by the conditions used during powder production and storage. In our previous study, effect of processing conditions on physicochemical properties of spray dried tamarind pulp powder was studied [5], however there is no investigation about the quality changes of tamarind pulp powder during storage. Thus, the objective of the present study was to provide experimental data for sorption characteristics of spray dried tamarind pulp powder in order to model the sorption isotherms using selected models and to evaluate the changes in physicochemical properties of spay dried tamarind pulp powder during storage.

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2. Materials and methods 2.1. Sample preparation Tamarind fruit pods were deshelled and soaked in water in the ratio 1:2.5 under optimum conditions of 33 min soaking time and 39 °C soaking temperature [6]. The mixture was then homogenized and sieved to separate fiber, rags and seeds from the pulp. The pulp was passed through three layers of muslin cloth to obtain fine pulp. 2.2. Spray drying of tamarind pulp A tall type laboratory scale spray dryer (S.M. Scientech, Calcutta, India) with cocurrent regime (flow of feed spray and drying air in same direction) and a two-fluid nozzle (inside diameter of 0.5 mm) atomizer was employed for spray drying process. Feed was metered into the dryer by means of a peristaltic pump. Based on our previous study, the derived optimum conditions for spray drying of tamarind pulp were 25% carrier (soya protein isolate) concentration, 170 °C inlet air temperature and 400 ml/h feed flow rate [5] Feed temperature, compressor air pressure and blower speed were kept at 25.0 ± 0.5 °C, 0.06 MPa and 2300 rpm, respectively. After the completion of the experiment, the powder was collected from the cyclone and cylindrical parts of dryer chamber by lightly sweeping the chamber wall as proposed by Bhandari et al. [7]. 2.3. Determination of sorption isotherms Sorption isotherms were determined by the gravimetric method. Eight saturated salt solutions were prepared in order to provide different relative humidity values. The salt solutions used and the corresponding relative humidities at different temperatures are given in Table 1 [8]. Triplicate samples (1 g) of freshly prepared spray dried tamarind pulp powder were placed in previously weighed alumunium dishes. The samples were then kept in desiccators over the saturated salt solution of known relative humidity. The desiccators were placed in temperature-controlled cabinets maintained at 20, 30, 40 and 50 °C (±1 °C) and the samples were allowed to equilibrate until there was no distinct weight change (±0.0001 g). A test tube containing thymol was placed inside the desiccators with high relative humidity to prevent mold growth during storage. The required time period for equilibration was about 3–4 weeks. The total time for removal, weighing, and putting back the sample in the desiccator was about 30 s. This minimized the degree of atmospheric moisture sorption during weighing. The equilibrium moisture content was determined in a vacuum oven, at 70 °C until constant weight was obtained [9]. The measurements were recorded as the mean of triplicates samples. 2.4. Storage study Freshly prepared tamarind pulp powder samples (15 g) were packed in three different packaging materials (low density polyethylene, LDPE; aluminum laminated polyethylene, ALP and glass) and

Lithium chloride Potassium acetate Magnesium chloride Potassium carbonate Magnesium nitrate Potassium iodide Sodium chloride Potassium chloride

placed in desiccators filled with saturated solution of Magnesium nitrate in order to provide a constant relative humidity of 53% during the storage period. The desiccators were then stored at 25 ± 1 °C, representing room temperature. The powder samples were periodically analyzed (at 0, 1, 2, 3, 4, 5 and 6 months) for different physicochemical properties (color, moisture content, acidity, bulk density and flowability). 2.4.1. Color measurement The color of the powder samples was determined by using a color spectrophotometer (CM-3600d, Konica Minolta). The results were expressed in terms of Hunter color values of L*, a*, and b*, where L* denotes lightness/darkness, a* redness/greenness, and b* yellowness/ blueness. 2.4.2. Moisture content The moisture content (%) of the powder samples was determined according to AOAC method [9]. About 2 g of the powder sample was taken in a petriplates and dried in a vacuum oven at a temperature of 70 °C until a constant weight was obtained. The samples were analyzed in triplicates and the mean was recorded. 2.4.3. Titratable acidity The titratable acidity (%) of the powder sample was determined by titration with standardized 0.1 N NaOH to the phenolphthalein end point, according to the method described by Rangana [10]. Titratable acidity was measured in terms of tartaric acid. The samples were analyzed in triplicates and the mean value was calculated. 2.4.4. Bulk density For the determination of loose bulk density a known quantity of powder sample was freely poured into a 10 ml graduated cylinder (readable at 0.1 ml) and the volume occupied was noted and then used to calculate bulk density (weight/volume). 2.4.5. Powder flowability Powder flowability was measured in terms of cohesive index by using a Powder flow analyzer attached to a texture analyzer (Stable Micro Systems, UK). A fixed powder volume of 25 ml was poured into the cylindrical vessel of the analyzer prior to testing. During the test, the blade of the analyzer took a downward and then upward movement for three cycles inside the cylinder, corresponding to three compaction and decompaction phases. The force–displacement curve was thus generated by the system, exhibiting the force exerted on the cylinder bottom due to blade movement and powder displacement. A cohesion coefficient (g.mm) was derived by Texture Exponent software (Stable Micro System, UK) through integrating the negative area underneath the curve during the decompaction cycle. The cohesion index (mm) was defined as the ratio of the negative area under force displacement curve to the sample weight. 2.5. Sensory evaluation A panel comprising of seven trained judges did sensory evaluation of tamarind pulp powder after a regular interval of one month storage period by using 9-points hedonic scale scorecard.

Table 1 Relative humidities of selected saturated salt solutions at different temperatures. Salt

323

Relative humidity (%) 20 °C

30 °C

40 °C

50 °C

11.3 23.1 33.1 43.2 54.4 69.9 75.5 85.1

11.3 21.6 32.4 43.2 51.4 67.9 75.1 83.6

11.2 20.8 31.6 40.0 48.4 66.1 74.7 82.3

11.1 20.4 30.5 38.5 45.4 64.5 74.4 81.2

2.6. Analysis of sorption data The equilibrium moisture content of the powders for each temperature was plotted against the corresponding water activity (relative humidity/100) to produce the sorption isotherms. Six different mathematical models presented in Table 2 were used to fit to the experimental data using regression analysis. The curve fitting and regression analysis were performed using Statistica. V.8. (Statsoft, India Pvt. Ltd. New Delhi). The goodness of the fit of each model was evaluated in terms

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2.7. Statistical analysis

Table 2 Moisture sorption isotherm models used for experimental data fitting. Name of the model

Mathematical expression

GAB [26]

0 :C:K:aw M ¼ ð1−K:awM Þð1−K:aw þC:K:aw Þ M0 :C:aw M ¼ ½ð1−aw ÞþðC−1Þ: ð1−aw Þ: aw  M = A . (aw/1 − aw)B

BET [27] Oswin [28] Caurie [30] Smith [29] Iglesias and Chirife [31]

M = exp (A +B .aw) M = A +Blog(1 − aw) M = A + B . (aw/1 −aw)

The experimental data for physico-chemical properties of the powder was expressed as the mean value ± standard deviation. The experimental data was further analyzed using two way ANOVA. The factors (and levels) were packaging material (LDPE, ALP and glass) and storage time (0, 1, 2, 3, 4, 5 and 6 months). The ANOVA included the main effects of packaging material, storage time and their interaction. 3. Results and discussion 3.1. Sorption isotherm

of minimum standard error of estimate (SE), minimum percent root mean square error (%RMSE), minimum mean absolute percentage error (P), and the maximum adjusted R-square, (R2Adjusted) and were calculated as follows: vffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi u N uX SE ¼ t ðY i −Y i 0Þ2 = F

ð1Þ

i¼1

vffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi u N u1 X ðY −Y i 0=Y i Þ2  100 %RMSE ¼ t N i¼1 i P¼

N 100 X ðY −Y i 0=Y i Þ N i¼1 i

ð2Þ

ð3Þ

XN W i Y i −Y i 0Þ2 ðN−1Þ R2Adjusted ¼ 1− XNi¼1 W i Y i −Y″Þ2 ðN−MÞ i¼1

ð4Þ

Where Y Y′ Y″ N F W M

experimental value of equilibrium moisture content; predicted value of equilibrium moisture content; mean of experimental data of equilibrium moisture content number of observations; degree of freedom of the regression model; weighting applied to each data point, which was set to unity in these analyses; and number of coefficients in each equation.

Moisture sorption behavior of spray dried tamarind pulp powder at four different temperatures (20, 30, 40, and 50 °C) is described by Fig. 1. The sorption isotherms revealed an increase in equilibrium moisture content with increase in water activity at a constant temperature, a characteristic feature of amorphous materials rich in hydrophilic components. This behavior can be attributed to the hydrophilic nature of carbohydrates and protein present in spray dried tamarind pulp powder. At low and intermediate water activities, the so-called multilayer sorption region, equilibrium moisture content increases linearly with water activity, whereas at high water activities, the so-called capillary condensation region, a sharp increase in equilibrium moisture content was observed [11,12]. This trend has been reported in the literature for many food materials including raisins, figs, apricots, prunes [13], grapes, apples [14], tomato pulp powder [11] and orange juice powder [15]. Experimental data indicated that the equilibrium moisture content decreased with increasing temperature, at a constant water activity. This behavior may be due to the decrease in the total number of active sites for water binding as a result of physical and/or chemical changes induced by temperature. At increased temperatures water molecules get activated to higher energy levels and break away from the waterbinding sites of the food, thus decreasing the equilibrium moisture content [16]. The results of regression analysis for fitting the experimental data to six different models along with standard error of estimate (SE) on EMC, percent root mean square error (%RMSE), mean absolute percentage error (P), and adjusted R-square (R2Adjusted) are presented in Table 3. In terms of the mean absolute percentage error (P) of the fits, those with less than 10% error can be considered acceptable [17] and an R2Adjusted of N 0.98 may also indicate a good fit. Regarding the BET model only

Fig. 1. Adsorption isotherms of spray dried tamarind pulp powder at various temperatures.

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Table 3 Estimated parameters of isotherm models for spray dried tamarind pulp powder at different temperatures. Goodness of fit parameters

Model coefficients/constants

Model

Temperature (°C)

SE⁎

%RMSE⁎⁎

P (%)

Adjusted-R-Square

A

B

C

GAB

20 30 40 50 20 30 40 50 20 30 40 50 20 30 40 50 20 30 40 50 20 30 40 50

0.624 0.682 0.639 0.435 0.245 0.234 0.269 0.136 0.714 0.741 0.777 0.699 1.171 0.931 0.952 1.685 1.375 1.128 1.207 1.191 1.704 1.485 1.072 0.656

3.577 4.476 4.527 1.642 3.824 3.695 5.251 2.111 6.093 6.761 9.350 11.307 9.733 8.207 9.541 13.016 12.163 11.310 12.700 15.075 22.736 19.450 13.345 5.456

3.338 4.221 3.939 3.451 3.620 3.477 4.514 1.854 5.406 6.110 7.742 8.298 7.508 6.002 6.851 10.265 10.273 9.807 10.959 11.951 12.995 11.766 8.380 9.525

0.9956 0.9931 0.9932 0.9962 0.9999 0.9983 0.9982 0.9995 0.9952 0.9932 0.9913 0.9928 0.987 0.9892 0.9870 0.9889 0.9826 0.9842 0.9791 0.9792 0.9726 0.9726 0.9835 0.9889

7.7031, Mo 7.2252, Mo 6.3523, Mo 5.6038, Mo 6.7714, Mo 6.1819, Mo 5.6897, Mo 5.1050, Mo 12.4952 11.6746 11.0874 10.2142 0.9779 0.946 0.914 0.7786 0.8582 1.028 0.9959 0.6030 5.5210 4.9196 4.3505 3.5888

6.5691, C 6.4869, C 8.1833, C 8.3491, C 9.0380, C 9.9163, C 12.3717, C 12.2353, C 0.6147 0.6120 0.6277 0.6622 3.0348 2.9429 2.9519 3.0669 −17.75 −16.1837 −15.4952 −14.9805 5.7694 5.5737 5.6264 5.6588

0.9375, K 0.9357, K 0.9619, K 0.9875, K – – – – – – – – – – – – – – – – – – – –

BET

Oswin

Caurie

Smith

Iglesias and Chirife

⁎ Standard error of estimate. ⁎⁎ %RMSE = percent root mean squared error, p; mean absolute percentage error.

experimental data with aw b 0.50 was fitted to the BET equation, because above that value the model hypothesis fails and the equation is not able to predict sorption behavior accurately. Table 3 shows that GAB model gives the minimum values for SSE, RMSE and P and the maximum R2Adjusted when used to predict the moisture sorption isotherm of tamarind pulp powder at different temperatures. So the GAB best describes the experimental adsorption data through the entire range of water activity. This observation is similar to that obtained by Goula et al. [11] and Sormoli and Langrish [15] who studied sorption isotherms of tomato pulp powder and orange juice powder respectively. After GAB model, smith model also adequately fitted the experimental data of sorption showing minimum values of SE, RMSE and P. This suggests that GAB and Oswin sorption equations could best describe the adsorption behavior of tamarind pulp powder. The shape of moisture sorption isotherms (Fig. 1) and the value for model parameter, C N 1 of the BET equation (Table 3) imply that the moisture sorption isotherms for tamarind pulp powder are sigmoid and based on the classification of isotherms given by Brunauer et al. [18] belong to type II class of isotherms. 3.2. Parameters of GAB equation The GAB equation and the definition of its three parameters are given in Eqs. (5)–(8) M¼

M0 :C:K:aw ð1−K:aw Þð1−K:aw þ C:K:aw Þ

ð5Þ

C ¼ C 0 expðΔH c =RT Þ

ð6Þ

K ¼ K 0 expðΔHk =RT Þ

ð7Þ

M0 ¼ M0 expðΔH x =RT Þ:

ð8Þ

Where ‘M0,’ known as monolayer moisture content is the amount of water that is adsorbed in a monolayer on the surface of the adsorbent and is a measure of the availability of active sorption sites. The parameter ‘C’ determines the strength of binding for water molecules to the

primary binding sites on the product surface. The larger the value of C, the stronger the bonds between water molecules in the monolayer and the binding sites on the surface of the sorbent. The parameter ‘K’ is a correction factor for multilayer molecules relative to the bulk liquid; when K = 1 the molecules beyond the monolayer have the same characteristics as pure water. ΔHc = the difference between the heat of sorption for monolayer of water and the heat of sorption for multilayer water, and ΔHk = the difference between the latent heat of condensation of pure water and the heat of sorption for multilayer water. ΔHx is a constant parameter to express the temperature dependence of the monolayer moisture [19]. GAB model is based on the monolayer moisture concept and provides the value of monolayer moisture content of the material, considered as the safe moisture for dried foods during preservation, while most other models lack this parameter. The monolayer moisture content (Mo) indicates the amount of water that is strongly adsorbed to specific sites at the food surface and is considered as the moisture content affording the longest time period with minimum quality loss at a given temperature [11]. The fit of GAB equation to the water vapor sorption data of dried tamarind pulp powder was performed by non-linear regression analysis of the standard three parameter GAB equation (Eq. (5)) and the three parameters of the GAB equation (Mo, C and K) were determined at each temperature (Table 3). Then the constants Co, Ko, M′, ΔHc, ΔHk and ΔHx were calculated by using a successive regression of Eqs. (6) to (8) (Table 4). The values of the monolayer moisture contents (Mo) decreased slightly as the temperature increased, whereas the parameter K and C first slightly decreased at 30 °C and then increased. A Table 4 GAB constants calculated by linear regression of GAB parameters and reciprocals of absolute temperature. C0 ΔHc (J/mol) K0 ΔHk (J/mol) Mʹ (% dry basis) ΔHx (J/mol)

8.44 3241.63 1.25 −620.31 0.54 or 5.4 × 10−1 3697.57

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similar trend for GAB parameters was also observed by Sormoli and Langrish [15] for orange juice powder. According to Lewicki [20] in order to represent a sigmoid type of sorption isotherm, the parameters of the GAB equations should be in the following ranges: C N 5.67 and 0 b K b 1 and the same is depicted by GAB parameters for tamarind pulp powder. A positive value for ΔHc was expected as a result of the exothermic interaction of the water molecules with the sorption sites on the surfaces of the powders. A negative value is usually expected for ΔHk due to the weaker bonding of the multilayer molecules [21] which has been the case here. However, a positive value of the ΔH2 has been also reported for fruits at high water activities and has been related to the endothermic dissolution of fruit sugars in the absorbed water [19]. 3.3. Storage study Changes in physicochemical properties of the food materials occur during storage. The packaging material is one of the important factor that influences the physical, chemical and sensory properties of dried food powders. The effect of packaging material on physicochemical properties of tamarind pulp powder during storage is discussed below. 3.3.1. Color Color is a very important quality characteristic of fruit and vegetable products which influences the consumer acceptability. Color changes of tamarind pulp powder samples during storage using different packaging material are presented in Table 5. During storage there was a decrease in L⁎ and b⁎ value and an increase in a⁎ value for color. The ANOVA results showed that both packaging material and storage period significantly (P b 0.05) affected the color values of tamarind pulp powder (Table 6). With respect to the package used it was observed that change in color values was minimum for the powder samples stored in glass while there was a considerable change in color values for the powder packed in LDPE. The minimum color change for the powder in glass bottle may be due to impermeability of glass to air and moisture which favor the reactions responsible for color change. The change in color values can be attributed to Maillard reaction. 3.3.2. Moisture content, acidity and bulk density Moisture content, acidity and bulk density values of tamarind pulp powder packed in different packaging materials are summarized in

Table 5. The data shows that except for the powder samples filled in glass there was a gradual increase in moisture content of the samples during storage. As per ANOVA results, the effect of packaging material and storage time on moisture content was significant (Table 6). The possible reason for increase in moisture content of the powder during storage is due to the ingress of moisture through the packages which have different degree of permeability to water vapor. Titratable acidity of the powder samples showed an increase during storage, suggesting the interaction between various constituents and resulting chemical changes (Table 5). ANOVA results indicated that the type of packaging material and storage time significantly affected the titratable acidity of tamarind pulp powder (Table 6). The increase in titratable acidity may be due to the reaction of basic amines to form compounds of lower basicity and to the degradation of sugars into acids during the Maillard reaction [22]. These results are in agreement with the findings of Chauhan and Patil [23] and Liu et al. [24], found during storage of mango milk powder and tomato pulp powder respectively. Bulk density of tamarind pulp powder samples increased with storage period depending on the extent of moisture gain of the powder samples packed in different packaging materials (Table 5). Type of Packaging material and storage time had a significant effect (P b 0.05) on bulk density values (Table 6). Increase in bulk density with increasing moisture content during storage was also observed by Chauhan and Patil [23] in mango milk powder. An increase in bulk density may also be attributed to increased cohesiveness between powder particles caused by absorption of moisture during storage. 3.3.3. Flowability Flowability of tamarind pulp powder samples was measured in terms of cohesion index. Higher the cohesion index, higher is the cohesiveness of the powder, thus poorer flowability. On the basis of cohesive index, the powders are categorized as follows: 19+, extremely cohesive; 16–19, very cohesive; 14–16, cohesive; 11–14, easy flowing and 11, free flowing (Stable Micro Systems Ltd., UK). Table 5 shows the changes in cohesive index of the powder samples packed in various packaging materials during storage. The effect storage of period and packaging material on the cohesion index of the powder samples is related to their effect on moisture content of the powder. Increase in moisture content increases the cohesiveness of the powder and thus leads to reduction in flowability [25]. Both packaging material and

Table 5 Changes in physicochemical properties of spray dried tamarind pulp powder at ambient conditions (25 °C temperature and 45% relative humidity) during storage using three different packaging materials. Packaging material

LDPE

ALP

Glass

Storage period (months)

0 1 2 3 4 5 6 0 1 2 3 4 5 6 0 1 2 3 4 5 6

Color L⁎

a⁎

b⁎

66.56 ± 0.61 65.32 ± 0.49 62.19 ± 0.82 59.12 ± 0.40 56.62 ± 0.33 53.67 ± 0.57 46.34 ± 1.58 66.56 ± 0.61 66.01 ± 0.31 65.93 ± 1.05 65.86 ± 0.32 62.59 ± 0.41 61.39 ± 0.44 58.78 ± 2.41 66.56 ± 0.61 66.43 ± 0.27 66.39 ± 0.44 66.12 ± 0.18 66.02 ± 0.46 65.81 ± 0.67 65.27 ± 0.66

10.87 ± 0.47 10.94 ± 0.98 11.36 ± 0.49 11.42 ± 0.97 12.57 ± 1.37 12.99 ± 0.46 13.52 ± 0.61 10.87 ± 0.47 10.99 ± 0.91 10.96 ± 0.75 11.13 ± 0.86 11.42 ± 0.61 11.72 ± 0.66 12.06 ± 0.65 10.87 ± 0.47 10.87 ± 0.88 10.93 ± 0.68 10.95 ± 0.39 10.95 ± 0.42 10.97 ± 0.85 11.03 ± 0.12

27.21 ± 0.52 27.09 ± 0.61 26.93 ± 0.45 26.66 ± 0.40 25.97 ± 0.79 25.83 ± 0.74 24.75 ± 0.77 27.21 ± 0.52 27.16 ± 0.73 27.15 ± 0.51 27.14 ± 0.67 27.09 ± 0.67 27.05 ± 0.93 26.94 ± 1.01 27.21 ± 0.52 27.20 ± 0.37 27.20 ± 0.70 27.18 ± 0.63 27.17 ± 0.54 27.15 ± 0.35 27.18 ± 0.22

Moisture (%)

Acidity (%)

Bulk density (g/ml)

Cohesion index (mm)

2.62 ± 0.02 3.16 ± 0.06 4.19 ± 0.24 5.11 ± 0.15 6.93 ± 0.06 7.39 ± 0.50 7.87 ± 0.67 2.62 ± 0.02 2.70 ± 0.02 2.83 ± 0.03 3.06 ± 0.14 3.59 ± 0.26 4.36 ± 0.51 4.95 ± 0.08 2.62 ± 0.02 2.62 ± 0.03 2.62 ± 0.05 2.65 ± 0.02 2.64 ± 0.03 2.65 ± 0.03 2.62 ± 0.07

9.33 ± 0.06 9.41 ± 0.04 9.55 ± 0.03 9.71 ± 0.07 9.92 ± 0.08 10.15 ± 0.06 10.26 ± 0.10 9.33 ± 0.06 9.35 ± 0.06 9.40 ± 0.02 9.43 ± 0.04 9.65 ± 0.11 9.72 ± 0.09 9.97 ± 0.23 9.33 ± 0.06 9.33 ± 0.13 9.36 ± 0.08 9.38 ± 0.08 9.40 ± 0.05 9.66 ± 0.05 9.89 ± 0.10

0.43 ± 0.01 0.46 ± 0.01 0.49 ± 0.03 0.52 ± 0.03 0.58 ± 0.03 0.64 ± 0.02 0.66 ± 0.03 0.43 ± 0.01 0.44 ± 0.01 0.46 ± 0.02 0.48 ± 0.01 0.49 ± 0.02 0.51 ± 0.02 0.52 ± 0.03 0.43 ± 0.01 0.43 ± 0.02 0.43 ± 0.02 0.43 ± 0.02 0.44 ± 0.03 0.44 ± 0.04 0.46 ± 0.02

10.19 ± 0.32 10.64 ± 0.06 11.56 ± 0.13 14.52 ± 0.12 15.36 ± 0.13 16.77 ± 0.29 17.88 ± 0.63 10.19 ± 0.32 10.34 ± 0.04 10.87 ± 0.09 11.40 ± 0.13 11.97 ± 0.39 12.49 ± 0.48 13.18 ± 0.35 10.19 ± 0.32 10.19 ± 0.24 10.20 ± 0.10 10.22 ± 0.08 10.22 ± 0.14 10.24 ± 0.03 10.31 ± 0.18

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Table 6 ANOVA for physicochemical properties of spray dried tamarind pulp powder during storage. Source of variation

Packaging material (PM) Storage period (SP) PM × SP Error

df

2 6 12 42

MSS L⁎

a⁎

b⁎

Moisture content

Acidity

Bulk density

Cohesive index

315.49⁎⁎ 108.44⁎⁎ 34.56⁎⁎ 0.66

5.54⁎⁎ 2.41⁎⁎ 0.79⁎ 0.52

4.46⁎⁎ 0.97⁎⁎ 0.70⁎ 0.40

40.04⁎⁎ 8.81⁎⁎ 3.46⁎⁎ 0.06

0.455⁎⁎ 0.630⁎⁎ 0.034⁎⁎ 0.007

0.056⁎⁎ 0.019⁎⁎ 0.005⁎⁎ 0.0005

70.86⁎⁎ 17.72⁎⁎ 7.12⁎⁎ 0.07

⁎⁎ Mean significant at P b 0.05. ⁎ Mean non-significant at P b 0.05.

storage time significantly affected the cohesion index value (Table 6). Tamarind pulp powder packed in LDPE showed higher decrease in powder flowability due to considerable increase in moisture content and the powder became cohesive after a period of two months, with cohesive index greater than 14. Flowability of the powder packed in ALP also decreased but showed easily flowing behavior after six months of storage period. However powder packed in glass showed almost no decrease in powder flowability and remained in a free flowing state throughout the storage period, with cohesive index less than 11. 3.4. Sensory quality Packaging material and storage time had marked influence on the sensory quality of tamarind pulp powder. Tamarind pulp powder packed in LDPE was acceptable up to 2 months of storage period. Powder samples packed in ALP and glass showed acceptable sensory quality throughout 6 months of storage period. However glass offered the highest protection against loss in sensory scores of tamarind pulp powder. 4. Conclusion The moisture sorption isotherms of spray dried tamarind pulp powder followed a sigmoid isotherm curve, typical of the type II BET classification shape. Temperature affected the sorption behavior, with equilibrium moisture content decreased with increasing temperature at constant water activity. Within the temperature range investigated, the kinetic three-parameter GAB model and the empirical two parameter Oswin model were found best to represent the experimental data throughout the entire range of water activity. Therefore the GAB model and Oswin model were chosen as the preferred models for predicting the moisture sorption isotherms of tamarind pulp powder. In general, it can be concluded that among the three packages used, the glass is recommended for long term storage of tamarind pulp powder. Acknowledgments The first author is thankful to University Grant Commission, New Delhi for financial support. References [1] P. Kumar, H.N. Mishra, Moisture sorption characteristics of mango-soy fortified yogurt powder, Int. J. Dairy Technol. 59 (2006) 22–28. [2] R.V. Tonon, A.F. Baroni, C. Brabet, O. Gibert, D. Pallet, M.D. Hubinger, Water sorption and glass transition temperature of spray dried acai (Euterpe oleracea Mart.) juice, J. Food Eng. 94 (2009) 215–221. [3] J.V. García-Perez, J.A. Carcel, G. Clemente, A. Mulet, Water sorption isotherms for lemon peel at different temperatures and isosteric heats, LWT Food Sci. Technol. 41 (2008) 18–25. [4] S.N. Bhusari, K. Muzaffar, P. Kumar, Effect of carrier agents on physical and microstructural properties of spray dried tamarind pulp powder, Powder Technol. 266 (2014) 354–364.

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