Influence of processing conditions on functional and reconstitution properties of milk powder made from Osmanabadi goat milk by spray drying

Small Ruminant Research 119 (2014) 130–137

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Influence of processing conditions on functional and reconstitution properties of milk powder made from Osmanabadi goat milk by spray drying Ravula Sudharshan Reddy a,∗ , C.T. Ramachandra a,∗∗ , Sharanagouda Hiregoudar a , Udaykumar Nidoni a , Jagjiwan Ram b , Mouneshwari Kammar c a Department of Processing and Food Engineering, College of Agricultural Engineering, University of Agricultural Sciences, Raichur 584 104, Karnataka, India b AICRP on Utilization of Animal Energy, College of Agricultural Engineering, University of Agricultural Sciences, Raichur, Karnataka, India c KVK, University of Agricultural Sciences, Raichur, Karnataka, India

a r t i c l e

i n f o

Article history: Received 20 November 2013 Received in revised form 28 January 2014 Accepted 31 January 2014 Available online 7 February 2014

Keywords: Goat milk Goat milk powder Spray drying Functional properties Reconstitution properties

a b s t r a c t The aim of this work was to study the influence of processing conditions on spray dried Osmanabadi goat milk powder. The milk solid loads of 35, 40 and 45% and inlet air temperature of 160, 170 and 180 ◦ C were chosen as independent variables to produce the spray dried Osmanabadi goat milk powder. A mixed fruit flavour was added to the concentrated milk to avoid the goaty flavour in the final powder. The mean values of proximate composition of spray dried Osmanabadi goat milk powder viz., moisture content, fat, protein, carbohydrates, ash and titrarable acidity were 4.08%, 26.85%, 25.48%, 36.99%, 6.60% and 0.14%, respectively. Colour L* , water activity, bulk densities including loose and tapped bulk densities were decreased with increase in inlet air temperature and bulk density increased with increase in concentration. The handling properties i.e., flowability was “possible” and “fair” according to Hausner ratio (1.24 ± 0.01) and Carr’s index (19.48 ± 0.88%) values. The solubility, wetting time and dispersibility of spray dried goat milk powder were significantly affected by the independent factors. © 2014 Elsevier B.V. All rights reserved.

1. Introduction Goat (Capra aegagrushircus) is one of the first domesticated animals for rural people. Goat milk is very useful for people who are suffering from different problems such as acidity, eczema, asthma, migraine, colitis, stomach ulcer, digestive disorder, liver and gallbladder diseases

∗ Corresponding author. Tel.: +91 9492883137. ∗∗ Corresponding author. Tel.: +91 9449627325. E-mail addresses: [email protected] (R.S. Reddy), [email protected] (C.T. Ramachandra). http://dx.doi.org/10.1016/j.smallrumres.2014.01.013 0921-4488/© 2014 Elsevier B.V. All rights reserved.

and stress-related symptoms such as insomnia, constipation and neurotic indigestion (Babayan, 1981; Silanikove et al., 2010). Today, milk powder industry has become a balance wheel of dairying all over the world (Sanghvan, 2012). Recently, a high volume of cosmetic products are produced from goat milk, including soaps, creams, body lotions, shampoos, hair conditioners and after shave lotions, which are marketed in countries such as USA and Switzerland (Ribeiro and Ribeiro, 2010). In India, goat milk is either consumed as such or mixed with cow or buffalo milk and then sold. As a result, surplus goat milk is rarely available for processing into different milk products (Sharma et al., 1995). Goat whole milk powders are manufactured in

R.S. Reddy et al. / Small Ruminant Research 119 (2014) 130–137

several European countries, USA, Australia and New Zealand and goat milk infant formula is in use in several countries, including Australia, New Zealand, Taiwan, Korea, Russia and China (Rutherfurd et al., 2008). Osmanabadi goats are mostly medium size animals usually black in colour, but in some areas of Maharashtra and Western Andhra Pradesh in India, it can also be seen in brown or spotted ones. In India, it covers the major part of Southern Maharashtra, especially Osmanabad, Sholapur, Beed, Parbani, Latur and Ahmed Nagar districts (Banerjee, 2006), Western Andhra Pradesh and North Eastern part of Karnataka i.e., Hyderabad–Karnataka region. The most important drying technique for drying of milk is the spray drying. Spray drying is the transformation of a feed from a fluid state into a dried form by spraying the feed into a hot drying medium (Gabites et al., 2010). Spray drying process mainly involves five steps: concentration, atomization, droplet-air contact, droplet drying and separation (Patel et al., 2009) each stage affect of which has associated process variables which affect the efficiency of the process or the quality of the product (Callaghan and Cunningham, 2005). Spray drying technology is suitable to dry many heat-sensitive products, e.g., dairy products, foods and pharmaceuticals, due to the short drying time and ability to obtain a product in the form of powder (Mujumdar et al., 2010). The advantages of spray drying of heat sensitive products include a combination of shorttime processing which leads to a better quality product. As observed for bovine milks, the spray drying process is an excellent option for extending the shelf-life of goat milk by converting milk into powder without changing its nutritional and sensory characteristics (Fonseca et al., 2011). The flow behaviour of powders under pressure, temperature and humidity are important in handling and processing operations, such as formulation and mixing, transportation, packaging and compression (Teunou et al., 1999). The properties of milk powder vary considerably depending on the type, composition of the powder and various treatments given to milk during concentration and drying process (Kelly et al., 2002). However, within the spray dried products, there are considerable variations in their properties. The reconstitution properties such as solubility, wettability and dispersibility will also be affected by the inlet air temperature and concentration, also play a major role in acceptability of powders for various food formulations. However, the functional and reconstitution properties of goat milk powder are very important criteria for its acceptability. Goat milk powder is not manufactured in India due to non availability of goat milk in large quantities in the market, lack of awareness of importance of goat milk and it cannot be stored for longer period. Under the conditions prevailing in India, it is essential to convert goat milk into powder in order to increase the shelf-life of the product without changing its nutritional qualities and sensory characteristics. Keeping in view, the importance of goat milk in health, food, pharmaceutical and cosmetic products, the aim of the present work was to study the influence the effects of processing conditions on the qualities of milk powder made from the milk of Osmanabadi goat by spray drying.

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2. Materials and method 2.1. Selection of fresh milk from Osmanabadi goat Fresh milk from Osmanabadi goat was procured (morning hours, December, 2012) from the surrounding region of Raichur, Karnataka, India. Prior to milking, the teats of all milking goats were washed with clean water and dried with single service paper towels. After discarding the first few strippings, milk sample was collected in a stainless steel container. The milk sample was brought to the Processing and Food Engineering laboratory, University of Agricultural Sciences, College of Agricultural Engineering, Raichur, India. Fresh goat milk was stored at 5 ± 1 ◦ C before the analysis. 2.2. Analysis of physico-chemical properties of raw goat milk and milk powder The physico-chemical properties of Osmanabadi goat milk (moisture content, fat, protein, ash, solids not fat and acidity) and spray dried Osmanabadi goat milk powder (protein and ash) were determined according to AOAC method (AOAC, 2005). Moisture content of spray dried goat milk powder was determined using hot air oven at a temperature of 102 ◦ C until constant weight was reached. Fat content in Osmanabadi goat milk was analyzed by Gerber method (AOAC, 2005; Method No. 2000.18). Milk sample (10.75 ml) was added with sulfuric acid (10 ml) in butyrometer followed by 1 ml of amyl alcohol and closed with rubber cork. The mixture was thoroughly mixed until curd was disappeared in butyrometer. Sample was centrifuged in Gerber centrifuge machine at 1100 rpm for 5 min and transferred to a water bath at 60 ◦ C for 4–5 min. The fat percentage was noted on the butyrometer scale. For determination of fat content in milk powder, the method described by Ramasamy et al. (1999) was used. Accurately weighed 1.69 g of powder in a beaker and dissolved it in 10 ml of water and added sulphuric acid (10 ml), 1 ml of amyl alcohol, then followed the same procedure as in milk test. The fat content (%) in milk and milk powder was computed using the following expressions: Fat (%) in milk = Reading at upper meniscus − reading at lower meniscus

(1)

Fat % butyrometer × 20 3

(2)

Fat(%) in milk powder =

The nitrogen content in milk sample was estimated by using Kjeltech instrument (Make: Foss; model: Kjeltec-2100) by Kjeldahl’s method (AOAC, 2005; Method No. 991.20). Fifteen grams of K2SO4, 1 g of CuSO4·5H2O and 5 g of warm milk (38 ± 1 ◦ C) were added to digestion tubes and then 25 ml of H2SO4 was added slowly. The digestion tubes were placed on fume ejection system until digest cleared in flask at the temperature of 410 ◦ C and was then cooled to room temperature. Digested sample was distilled with 50% NaOH using Kjeldhal distillation unit where steam was distilled over 4% boric acid (50 ml) containing an indicator for 5 min. The ammonia trapped in boric acid was determined by titrating with 0.1 N HCl until light pink colour was obtained. For estimation of protein in milk powder (AOAC, 2005; Method No. 930.29), accurately 1 g of milk powder sample was weighed and the process was repeated as described above. The percent protein was computed on total nitrogen basis using the following equation: Nitrogen (%) =

Volume (sample − blank) HCl (ml) × 0.1 × 14.007 weight of sample (g) × 1000 × 100

Percent protein on total nitrogen basis = N(%) × 6.38

(3)

(4)

The total ash content of fresh Osmanabadi goat milk (5 g) was determined by muffle furnace (Make: MAC; model: MSW-251) method (AOAC, 2005; Method No. 945.46) at a temperature of 550 ◦ C until carbon free ash was obtained. For determination of ash content in milk powder (AOAC, 2005; Method No. 930.30), accurately 1 g of milk powder sample was weighed into a crucible and the process was repeated as described for determination of ash in milk. Lactose content of milk and milk powder were estimated by difference method (Jinapong et al., 2008). Solids not fat were computed by difference method (AOAC, 2005; Method No. 990.21).

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The pH of Osmanabadi goat milk was measured using Systronic ␮ digital pH metre 361. Acidity in Osmanabadi goat milk samples was analyzed by the method (No. 947.05) given in AOAC (AOAC, 2005). Acidity in milk powder was determined according to procedure explained by Ramasamy et al. (1999); accurately 1 g of milk powder was dissolved in 10 ml of distilled water and titrated against 0.1 N NaOH. The volume of alkali used was noted. 2.3. Unit operations involved in production of spray dried goat milk powder The following unit operations were involved in the present study; preheating by water bath at temperature of 35 ◦ C, filtration by muslin cloth, standardization, homogenization by two stage homogenizer (GOMA; model: H-102) at 2500 psi in the I stage and 500 psi in the II stage, pasteurization by water bath (Make: Starter) at the temperature of 72 ◦ C for 15 s (HTST). Concentration (total solids) of goat milk was done using rotary vacuum flash evaporator (Superfit, Rotavap; PBU-6D) at a temperature of 60 ◦ C until achieved the desired concentration of milk i.e., 35, 40 and 45%. The desired feed total solids were calculated on the basis of mass balance. 2.4. Spray drying One drop of mixed fruit flavour (S1038, M/s. International Flavours and Fragrances Ltd., Chennai, India) was added to 100 g of concentrated milk to avoid the goaty smell in the final product before introducing into spray dryer (Make: SM Scientech, Kolkata, India). Spray drying involves atomizing the goat milk concentrate using two fluid nozzle at the inlet and outlet air temperatures, feed pump rate and blower rpm of 160/85 ◦ C, 170/85 ◦ C, 180/85 ◦ C, 18 rpm and 2100 rpm, respectively. The powder was collected from the powder boxes and immediately packed in a polyethylene terephthalate (PET) packaging material and stored at room temperature for analysis. Spray drying was carried out in triplicate for each treatment.

Sl. no.

Flowability

Carr’s index (%)

Hausner ratio

1 2 3 4 5 6 7

Excellent Good Fair Possible Poor Very poor Very, very poor

0–10 10–15 16–20 21–25 26–31 32–37 >38

1.00–1.11 1.12–1.18 1.19–1.25 1.26–1.34 1.35–1.45 1.46–1.59 >1.60

Source: Lebrun et al. (2012).

Tapped bulk density (g · cc−1 ) =

Functional properties such as colour, water activity, loose bulk density, tapped bulk density, Hausner ratio (HR) and Carr’s index (CI) of spray dried goat milk powder were determined using standard procedures as explained below. 2.5.1. Colour Hunterlab colourimeter (Model: Colour Flex EZ) was used for the measurement of colour of spray dried goat milk powder. The 3-dimensional scale L* , a* and b* was used. The L* is the lightness coefficient, ranging from 0 (black) to 100 (white), a* represents greenness and redness (+100 for red and −80 for green) while b* represents yellowness and blueness (+70 for yellow and −80 for blue), C represents chroma value and H represents hue angle. 2.5.2. Water activity The water activity ofspray dried goat milk powder was measured by Rotronic Hygrolab 3 water activity analyzer (Model: aw -HP23) at a room temperature. Before measuring the water activity, the instrument was calibrated for its accuracy by measuring the water activity of distilled water. 2.5.3. Bulk density The bulk density of the spray dried milk powder obtained from different treatments was measured according to the procedure described by Caparino et al. (2012) and Lebrun et al. (2012). Approximately, 1 g of goat milk powder was freely poured into a 5 ml glass graduated cylinder (readable at 1 ml) without tapping and disturbance and this was measured as loose bulk density of goat milk powder and the same samples were repeatedly tapped manually by lifting and dropping the cylinder under its own weight at a vertical distance of 14 mm ± 2 mm high until negligible difference in volume between succeeding measurements was observed, this was measured as tapped bulk density. The loose and tapped bulk density of milk powder was computed using the following expression: Weight of powder (g) Bulk powdered volume (cc)

(5)

Weight of powder (g) Tapped powdered volume (cc) (6)

2.5.4. Flowability and cohesiveness The spray-dried goat milk powder was evaluated for their flowability and cohesiveness in terms of Carr’s index (CI) and Hausner ratio (HR), respectively. Table 1 illustrates the specifications about the Carr’s index and the Hausner ratio. Both CI and HR were calculated from the loose and tapped bulk densities of the spray dried goat milk powder, according to the formula given by Olayemi et al. (2008). 2.5.5. Carr’s index (CI) It is a simple test to evaluate the Carr’s index from loose and tapped bulk density of goat milk powder. The formula for Carr’s index is as below: Carr s index (%) =

2.5. Functional properties

Loose bulk density (g · cc−1 ) =

Table 1 Specifications for Carr’s index and Hausner ratio.

Tapped bulk density (g · cc−1 ) − loose bulk density (g · cc−1 ) Tapped bulk density (g · cc−1 )

× 100

(7)

2.5.6. Hausner ratio (HR) The Hausner ratio is a number that is correlated to the flowability of a spray dried goat milk powder. It was calculated by using the following expression: Hausner ratio =

Tapped bulk density (g · cc−1 ) Loose bulk density (g · cc−1 )

(8)

2.6. Reconstitution properties 2.6.1. Solubility The solubility of the product was measured according to the method reported by Zhang et al. (2013) and Shittu and Lawal (2007). 2.6.2. Wettability Wettability of the powder sample was determined according to the method reported by Jinapong et al. (2008). 2.6.3. Dispersibility The dispersibility of Osmanabadi goat milk powder was measured according to the method reported by Fonseca et al. (2011). One gram of goat milk powder was stirred with 10 ml of water at 40 ± 1 ◦ C in a beaker. The reconstituted milk powder was then poured through the sieve of 150 ␮ size. The dry matter of the filtered reconstituted milk was estimated by measuring its moisture content using an oven at 105 ◦ C for 7 h. The dispersibility was calculated using the following expression: Dispersibility (%) =

(w + a)Sp aSj

(9)

where, a = amount of powder used, g; w = weight of water taken for reconstitution, g; Sp = total solid present in milk powder, %; Sj = percent dry matter present in reconstituted milk after it has been passed through the sieve.

T.A.b (%)

91.1

0.85 ± 0.03 6.6 ± 0.17* Mean ± standard deviation with 6 replications for raw goat milk and 3 replications for goat milk powder. * Significance level P < 0.05. ** Significance level P < 0.01. *** Significance level P < 0.001. a SNF = solids not fat. b T.A. = tiratable acidity expressed as lactic acid.

3.2.2. Water activity Water activity (aw ) is one of the most important factors that significantly influence the shelf-life of milk powder.

9.18 ± 0.30 –

3.2.1. Colour It is evident from Fig. 1 that the L* values of goat milk powder slightly decreased with increase in inlet air temperature due to the greater intensity of browning reactions (Bento et al., 2008), whereas there was not much variation in L* values of goat milk powder with concentration (Table 3). Fonseca et al. (2011) reported the mean L* values of goat milk powder as 83.07 ± 0.66 which was lower than spray dried Osmanabadi goat milk powder. Moreover, b* values of goat milk powder slightly decreased with increase in the inlet air temperature from 160 to 180 ◦ C at a concentration of 45%, whereas there was not much variation in b* values of goat milk powder with concentration.

87.2 ± 0.66 (wet basis) 4.08 ± 0.14*** (dry basis)

3.2. Functional properties

Fat (%)

Table 2 represents the proximate and physico-chemical composition of fresh Osmanabadi goat milk and spray dried Osmanabadi goat milk powder. The mean values of physico-chemical properties of Osmanabadi goat milk viz., moisture content, solids not fat, fat, protein, lactose, ash, pH, titrarable acidity, colour (L* , a* and b* ) and water activity were 87.20%, 9.18%, 4.12%, 3.98%, 4.35%, 0.85%, 6.75, 0.15%, 86.43 (L* ), −2.88 (a* ), 9.03 (b* ) and 0.95, respectively.

SNFa (%)

3.1. Proximate composition of Osmanabadi goat milk and goat milk powder

Table 2 Proximate and physico-chemical properties of raw Osmanabadigoat milk and Osmanabadigoat milk powder.

3. Results and discussion

Moisture (%)

The experimental design was done with the aid of the Design-Expert software version 7.7.0 (Stat-Ease Inc, 2005). Test of statistical significance was performed on the total error criteria, with a confidence level of 95%. The significant terms in the model were found by analysis of variance (ANOVA) for each response. Predictive models of each response are not presented in this paper. The effects of the independent variables on the functional and reconstitution properties of the spray dried powder were carried out in triplicate.

Protein (%)

Lactose (%)

2.7. Experimental design

Raw goat milk Goat milk powder

Fig. 1. Three dimensional plot on effect of treatments on L* values of spray dried Osmanabadi goat milk powder.

4.35 ± 0.22 36.99 ± 0.62***

Ash (%)

160.00 35.00 165.00 37.50 170.00 40.00 42.50 Temperature (°C) 175.00 Concentration (%) 180.00 45.00

3.98 ± 0.19 25.48 ± 0.23***

pH

84

4.12 ± 0.35 26.85 ± 0.61*

85.775

6.75 ± 0.07 –

87.55

**

Colour L*

89.325

133

0.15 ± 0.01 0.14 ± 0.01*

R.S. Reddy et al. / Small Ruminant Research 119 (2014) 130–137

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Table 3 Functional properties of spray dried Osmanabadi goat milk powder. Concentration (%)

Temperature (◦ C)

Colour * **

* ***

(aw *** )

(LBD)*** (g cc−1 )

(TBD)*** (g cc−1 )

(HR)***

(CI)*** (%)

* ***

(L )

(a )

(b )

35

160 170 180

89.24 88.16 87.77

−2.48 −2.21 −2.15

10.67 10.46 10.19

0.23 0.21 0.20

0.35 0.34 0.33

0.46 0.43 0.41

1.32 1.25 1.24

24.09 20.14 19.67

40

160 170 180

88.67 87.20 86.50

−2.51 −2.19 −2.10

10.57 10.45 10.20

0.22 0.20 0.19

0.38 0.37 0.35

0.49 0.46 0.43

1.27 1.24 1.23

21.23 19.43 18.75

45

160 170 180

89.72 87.53 86.15

−1.79 −1.44 −1.22

10.42 9.76 9.46

0.21 0.19 0.16

0.45 0.44 0.42

0.58 0.53 0.49

1.26 1.21 1.17

20.69 17.09 14.19

No of replications = 3. aw , water activity; LBD, loose bulk density; TBD, tapped bulk density; HR, Hausner ratio; CI, Carr’s index. ** Significance level P < 0.01 *** Significance level P < 0.001.

0.47

Loose bulk density (g/cc)

0.231

0.1895 0.16875 0.148

0.432 5 0.39 5 0.357 5 0.32

160.00

45.0 0

160.00

35.00 165.00

37.50

170.00 180.00 45.00

170.00

40.00

40.00

Temperature (°C) 175.00

165.0 0

42.50

Concentration (%)

42.50

Fig. 2. Three dimensional plot on effect of treatments on water activity of spray dried Osmanabadi goat milk powder.

As represented in Fig. 2 and Table 3, the water activity decreased with increase in inlet air temperature. Similar trend was observed by Schuck et al. (2005) who reported the water activity in whole milk powder as 0.32, 0.20 and 0.16 with different inlet air temperatures viz., 140, 190 and 210 ◦ C, respectively. Namhong (2009) also reported the water activity of goat milk powder as 0.27. 3.2.3. Bulk density It was revealed from the results that the variation in loose bulk density of goat milk powder was from 0.33 to 0.45 g cc−1 and also variation in tapped bulk density was from 0.41 to 0.58 g cc−1 (Table 3). Figs. 3 and 4 indicate that by increasing inlet air temperature, the bulk density is reduced. Increase in inlet air temperature often results in a rapid formation of dried layer at the droplet surface and particle size was due to skinning over or case-hardening of the droplets at the higher temperatures. This leads to the formation of vapour-impermeable films on the drop surface, followed by the formation of vapor bubbles and, consequently, droplet expansion. Bulk density increased with increase in feed concentration. The reason for this was

175.00

37.50

Temperature (°C)

35.00 180.00

Concentration (%)

Fig. 3. Three dimensional plot on effect of treatments on loose bulk density of spray dried Osmanabadi goat milk powder.

that as occluded air content decreased, it led to decrease in particle volume, thus increasing particle density and bulk density. These results were consistent with the findings of a number of studies (Chegini and Ghobadian, 2005; Kha

0.59

Tapped bulk density (g/cc )

Water acitivity

0.21025

0.5425 0.495 0.4475 0.4 160.00 45.00

165.00

42.50

170.00

40.00

Concentration (%)

37.50

175.00

Temperature (°C)

35.00 180.00

Fig. 4. Three dimensional plot on effect of treatments on tapped bulk density of spray dried Osmanabadi goat milk powder.

99.4

610

98.8

570

Wettability (s)

Solubility (%)

R.S. Reddy et al. / Small Ruminant Research 119 (2014) 130–137

98.2

97.6

135

530 490 450

97

35.00

160.00

180.00

37.50

165.00

42.50 Concentration

175.00 180.00

42.5 170.00

40.00

170.00

Temperature (°C)

45 175.00

(%)

Temperature (°C)

40 165.00

37.5 160.00

45.00

35

Concentration (%)

Fig. 5. Three dimensional plot on effect of treatments on solubility of spray dried Osmanabadi goat milk powder.

Fig. 6. Three dimensional plot on effect of treatments on wettability of spray dried Osmanabadi goat milk powder.

et al., 2010). Tonon et al. (2008) studied the effect of inlet air temperature (140, 170 and 200 ◦ C) on the bulk density of acai juice powder and they reported that increase in inlet drying air temperature resulted in decrease in bulk density.

3.3.2. Wettability As represented in Fig. 6, it is clear that the wetting time increased with increase in inlet air temperature as well as concentration, it might be due to decrease in the powder residual moisture content (Chegini and Taheri, 2013) and presence of free fat on the surface of the particles (Zbikowska and Zbikowski, 2006). Kim et al. (2002) reported the wetting time of >15 min for whole milk powder. The wetting time of goat milk powder was about 6 min as reported by Fonseca et al. (2011).

3.2.4. Flowability In terms of handling properties, the spray-dried goat milk powder had almost all similar flow characteristics for all treatments in the present study and were considered as “possible” and “fair” powders by their Hausner ratio (HR) given in Table 3 as classified in Table 1. This was in accordance with their medium Carr’s index (CI) (Table 1) which indicated that their flowability was “possible” and “fair” (Table 1). The reason behind this flowability at small particle sizes was due to the large surface area per unit mass of powder. There was more contact surface area between powder particles available for cohesive forces, in particular and frictional forces to resist flow (Fitzpatrick et al., 2004; Kim et al., 2002). The higher fat content of milk powder also caused the powder to have very poor flowability reported by Fitzpatrick et al. (2004).

3.3.3. Dispersibility It is evident from Fig. 7 that the dispersibility decreased with increase in inlet air temperature due to low wettability, whereas increased with increase in concentration, it might be due to low air content (Zbikowska and Zbikowski, 2006). The dispersibility of commercial goat milk powder was found to be 57.54% when compared to that of cow milk powder (Frederic et al., 1981). Fonseca et al. (2011) reported the dispersibility of goat milk powder was 87.20%.

3.3. Reconstitution properties 84.7

Reconstitution properties of spray dried Osmanabadi goat milk powder is presented in Table 4. Dispersibilty (%)

3.3.1. Solubility There was not much effect of inlet air temperature on solubility of goat milk powder with constant total solids whereas increase in total solids before introducing into spray dryer, resulted in decrease in solubility as shown in Fig. 5 and Table 4. It might have taken more residence time to reach the desired concentration, resulted in protein denaturation. The results were comparable with Baldwin et al. (1980) who reported that increasing the viscosity of the concentrate, resulted in a significant decrease in solubility. Singh and Creamer (1991) also concluded that as the evaporation increased the extent of denaturation of protein increased.

83 81.3 79.6 77.9

45

160.00

42.5

165.00 40

Concentration (%)

170.00 37.5

175.00 35 180.00

Temperature (°C)

Fig. 7. Three dimensional plot on effect of treatments on dispersibility of spray dried Osmanabadi goat milk powder.

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Table 4 Reconstitution properties of spray dried Osmanabadi goat milk powder. Concentration (%)

Temperature (◦ C)

Solubility*** (%)

Wettability*** (s)

Dispersibility*** (%)

35

160 170 180

99.19 99.07 98.95

418.80 501.60 563.40

81.35 79.81 78.38

40

160 170 180

98.81 98.72 98.19

491.40 541.80 570.00

82.23 81.86 80.63

45

160 170 180

98.35 98.02 97.11

500.40 556.20 594.00

84.11 83.51 81.40

No of replications = 3 *** Significance level P < 0.001.

4. Conclusions Mean values of functional properties of Osmanabadi goat milk powder viz., brightness (colour), water activity, loose bulk density and tapped bulk density were 87.88, 0.20, 0.38 g cc−1 and 0.47 g cc−1 , respectively. Moreover, flowability of powder such as Hausner ratio and Carr’s index obtained as 1.24 and 19.48%, respectively. According to these values, the flowability of powder was “possible” and “fair”. It was found that, inlet air temperature and feed total solids in the present investigation, influenced the flowability of spray dried Osmanabadi goat milk powder, the flowability might be directly related to moisture content, particle size and free fat of spray dried Osmanabadi goat milk powder. The reconstitution properties were significantly affected by independent variables. The mean values of solubility, wetting time and dispersibility of spray dried goat milk powder were 98.49%, 533.4 s and 81.48%, respectively. Suitable fruit flavours can also be added to goat milk to achieve the desired flavour in final product.

Conflict of interest None declared.

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