Reconstitution behavior of cheese powders: Effects of cheese age and dairy ingredients on wettability, dispersibility and total rehydration

Journal of Food Engineering 270 (2020) 109763

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Journal of Food Engineering journal homepage: http://www.elsevier.com/locate/jfoodeng

Reconstitution behavior of cheese powders: Effects of cheese age and dairy ingredients on wettability, dispersibility and total rehydration Denise Felix da Silva a, *, Danai Tziouri c, Lilia Ahrn�e a, Nicolas Bovet b, Flemming Hofmann Larsen a, Richard Ipsen a, Anni Bygvrå Hougaard a a b c

Department of Food Science, Faculty of Science, University of Copenhagen, Rolighedsvej 26, DK-1958, Frederiksberg C, Denmark Department of Chemistry, Nano-Science Center, University of Copenhagen, Universitetsparken 5, DK-2100, København Ø, Denmark Lactosan A/S Nordbakken 2, DK-5750, Ringe, Denmark

A R T I C L E I N F O

A B S T R A C T

Keywords: Cheese powder Wettability Dispersibility Total rehydration Dairy ingredients

The addition of dairy ingredients (buttermilk powder and/or sodium caseinate) to the cheese feed before spray drying, as well as the age of the cheese used as raw material on reconstitution behavior of cheese powder without emulsifying salt were studied. Cheese powders made with addition of 2% sodium caseinate plus 2% buttermilk powder showed increased wettability and the lowest amount of fat on the surface, but a delayed dispersibility. Powders made using only buttermilk powder (4%) and powders produced with 45 weeks old cheese exhibited faster dispersibility, but reduced total rehydration. Reconstituted powders produced with 16 weeks old cheese showed the best total rehydration. The amount of surface fat, lactose, and protein interactions with water in the cheese casein network are pointed to be the main reasons for the differences observed, as they affect particle size distribution or ability of the powder components to interact with the water.

1. Introduction Cheese powder is a multifunctional ingredient used to provide taste and mouthfeel as well as to improve texture in various food formulations such as ready meals, sauces, dressings, biscuits, snacks, processed cheese, and creams. The convenience of use and long-term shelf life make cheese powders an advantageous ingredient compared to natural cheeses (Varming et al., 2013). Furthermore, the existence of a great variety of cheese powders, including PDO (Protected Designation of Origin) cheese powders such as Parmigiano Reggiano facilitates the accessibility to these cheeses all over the world. Cheese powders are produced by spray drying a uniform feed con­ sisting of melted cheeses, water, and other ingredients such as emulsi­ fying salt (ES). This mixture, denoted the cheese feed, is then heated, homogenized and pumped into the spray dryer. Cheese feed can be produced with a unique type of cheese or with a combination of many varieties of cheeses (Hougaard et al., 2015). However, the cheese type and characteristics such as the degree of maturation, fat and protein content along with the addition of ES can strongly affect the properties of the cheese feed and consequently, the final cheese powder (Erbay and Koca, 2015; Felix da Silva et al., 2018b, 2017b). Disodium hydrogen

phosphate is an ES commonly used in cheese powder manufacture to improve emulsification of cheese feed and enable a homogeneous dis­ tribution of fat within the powder particles after drying. Thereby, the use of ES reduces the risk of accumulation of excess free fat, which can be located at the powder particle surface, in pores and capillaries developed during the drying process (Kelly et al., 2014). However, the increasing demand for sodium reduction in foods has led to the devel­ opment of cheese powders with a reduced or zero amount of ES (Felix da Silva et al., 2018b, 2017b). Therefore, novel strategies for improving emulsification of cheese feeds made without ES are being developed (Kelimu et al., 2017; Ray et al., 2016; Varming et al., 2014). We previously showed that the addition of dairy ingredients (i.e. sodium caseinate and buttermilk powder) and the use of cheeses with different maturation time (age), significantly influenced the composi­ tion and rheological properties of the cheese feed and, thereby, the color, particle size distribution, flowability, and microstructure of the resultant cheese powders (Felix da Silva et al., 2018b). These differences were attributed to the changes in the composition and structure of the cheese feed (e.g., emulsification of the fat). The rheological properties of the feed can be controlled by the selection of cheese of a certain age or through addition of sodium caseinate and buttermilk powder. A

* Corresponding author. E-mail address: [email protected] (D. Felix da Silva). https://doi.org/10.1016/j.jfoodeng.2019.109763 Received 25 July 2019; Received in revised form 17 September 2019; Accepted 13 October 2019 Available online 15 October 2019 0260-8774/© 2019 Elsevier Ltd. All rights reserved.

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Journal of Food Engineering 270 (2020) 109763

Table 1 Cheese powders composition (w/w %) and mean particle size a. Cheese powder NO_16 B2S2_16 BMP_16 NO_30 B2S2_30 BMP_30 NO_45 B2S2_45 BMP_45 a

moisture (%) c

1.2 � 0.1 1.6 � 0.1b 1.4 � 0.1c 1.6 � 0.1bc 1.9 � 0.1ab 0.9 � 0.1d 1.4 � 0.1c 2.1 � 0.1a 1.2 � 0.1c

protein (%) a

43.2 � 0.7 44.6 � 0.5a 42.1 � 0.1a 42.6 � 1.0a 43.2 � 0.5a 41.9 � 0.1a 40.4 � 1.0a 43.5 � 0.5a 42.2 � 0.1a

fat (%)

free fat (%) a

43.0 � 1.0 41.6 � 0.5a 42.8 � 0.3a 43.9 � 0.3a 42.0 � 0.5a 43.3 � 0.4a 45.0 � 0.2a 43.0 � 0.5a 43.2 � 0.0a

a

87.2 � 1.0 77.4 � 0.8d 87.2 � 0.7a 83.6 � 0.5b 80.0 � 0.5c 81.4 � 0.8c 87.8 � 0.5a 85.0 � 0.5b 84.3 � 1.3b

pH 4.6 soluble nitrogen (%) b

10.0 � 0.4 9.9 � 0.5c 11.5 � 0.7b 11.2 � 0.4b 10.0 � 0.5c 12.0 � 0.0c 14.0 � 0.6a 10.3 � 0.5b 16.0 � 3.4a

lactose (%) c

0.1 � 0.0 1.2 � 0.0b 1.8 � 0.0a 0.1 � 0.0c 0.9 � 0.0b 1.8 � 0.1a 0.1 � 0.0c 0.7 � 0.1b 1.8 � 0.1a

ash (%)

D[3; 2] (μm) a

8.2 � 0.1 8.1 � 0.0a 7.4 � 0.3a 7.9 � 0.1a 8.2 � 0.6a 7.2 � 0.1a 7.8 � 0.6a 7.5 � 0.5a 7.2 � 0.1a

59.2 � 4.8b 42.0 � 1.7c 86.1 � 9.2a 46.8 � 1.1c 57.2 � 5.0b 59.1 � 2.0b 81.1 � 8.6a 46.6 � 1.34c 85.9 � 7.7a

Composition also presented on Felix da Silva et al. (2018b). The amount of free is presented as the percentage of total fat.

Fig. 1. SDS-PAGE of cheese powders with different formulations. 1: NO_16; 2: NO_30; 3: NO_45; 4: B2S2_16; 5: B2S2_30; 6: B2S2_45; 7: BMP_16; 8: BMP_30; 9: BMP_45; 10: SC; 11: BMP. Numbers 16, 30 and 45 refers to the cheese age of the cheeses used for cheese powder manufacture. Table 2 Ratio nitrogen and carbon (N/C) on cheese powder surface (10 nm depth) measured by X-ray photoelectron spectroscopy. Cheese powder

Ratio (nitrogen/carbon)

NO_16 B2S2_16 BMP_16 NO_30 B2S2_30 BMP_30 NO_45 B2S2_45 BMP_45

0.009 0.035 0.019 0.015 0.065 0.021 0.007 0.023 0.019

decreased amount of free fat and powder particle size as well as an improved flowability were observed upon the addition of ingredients and/or use of 30 weeks old cheeses in cheese powders. Powders con­ taining buttermilk powder showed reduced flowability and increased particle size due to spontaneous primary agglomeration (Felix da Silva et al., 2018b). The reconstitution behavior of cheese powders is important to ensure functionality and good end-product quality in a given food system. Hence, the addition of dairy ingredients with emulsifying properties is an alternative to addition of ES in the manufacture of cheese powders, decreasing the amount of free fat (Felix da Silva et al., 2018b) and aiding in assuring desirable reconstitution behavior. However, to the best of our knowledge, the reconstitution behavior of cheese powders produced without ES has not previously been investigated. Many factors can affect the reconstitution/rehydration behavior of a powder. For example, the bulk and surface composition, powder phys­ ical properties (particle size, densities, porosity and morphology) as well as the method used to reconstitute and evaluate the powder (Felix da Silva et al., 2017a; Fitzpatrick et al., 2016). The reconstitution process of powders is commonly described as consisting of five stages: wettability,

Fig. 2. Capillary rise wetting (g water/g powder) of cheese powders with different formulations. NO- without added ingredients (▪), B2S2- addition of 2% sodium caseinate plus 2% buttermilk powder ( ) and BMP- addition of 4% buttermilk powder ( ).Numbers 16, 30 and 45 refers to the cheese age of the cheeses used for cheese powder manufacture.

swelling, sinkability, dispersibility and dissolution/total rehydration (Crowley et al., 2016a,b; Felix da Silva et al., 2017a). During reconsti­ tution, two or more stages may occur simultaneously, for instance, wetting and swelling as well as dispersion and dissolution. Also, for specific powders, some stages may not occur or take longer time (rate-limiting stage) (Felix da Silva et al., 2017a). In the present study, we aimed at understanding the reconstitution behavior of cheese powders produced using dairy ingredients and cheeses of different ages as alternatives to addition of ES. All of these cheese powders were examined with respect to wettability, dis­ persibility, and total rehydration. Moreover the feasibility of the analytical methods selected were assessed and discussed. 2

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A

0.52

0.07 0.06 0.05

0.48

0.04

0.46

0.03

Ratio N/C

g water/g powder

0.50

0.02

0.44

0.01 0.42 NO_16 B2S2_16BMP_16 NO_30 B2S2_30BMP_30 NO_45 B2S2_45BMP_45

B

0.52

88

84

0.48

82

0.46

Free fat (%)

86

0.50

g water/g powder

0.00

80

0.44

78 0.42 NO_16 B2S2_16BMP_16 NO_30 B2S2_30BMP_30 NO_45 B2S2_45BMP_45

76

Fig. 3. Relationship between capillary rise wetting in g water/g powder (▪) and surface composition in N/C ratio (——) (Fig. 3A) and free fat (⋅⋅⋅⋅) (Fig. 3B). Numbers 16, 30 and 45 refers to the cheese age of the cheeses used for cheese powder manufacture.

2. Materials and methods

Denmark) and soft white cheese (25%, Nordex Food A/S, Dronninglund, Denmark). The cheese feeds were prepared to a final dry matter of 38 � 1% (w/w), and potassium hydroxide (KOH) was used to adjust the pH to 5.9 � 0.2. Cheese powders were produced with the addition of 2% (w/w) buttermilk powder plus 2% (w/w) sodium caseinate (B2S2) or with addition of 4% (w/w) buttermilk powder (BMP) on cheese feed wet basis using 16, 30 or 45 weeks old Danbo cheeses. Control formulations (NO - without any addition of ingredients) were also produced with varying Danbo cheese age. Those formulations were chosen based on previously performed research (Felix da Silva et al., 2018b; Kelimu et al., 2017). All cheese powders used in this study were dried using an inlet air temperature of 185 � C and an outlet air temperature of 80 � C (ΔT ¼ 105 � C). Samples were coded according to their ingredients addition (NO, B2S2 or BMP) followed by the Danbo cheese age used to produce the powder (16, 30 or 45 weeks), e.g., NO_16: no addition of ingredients produced with 16 weeks old Danbo cheese.

2.1. Cheese powders: manufacture, composition and physical properties The manufacture and composition of the cheese powders used in this study have been described in detail by Felix da Silva et al. (2018b). Sodium caseinate (88.0% protein, 1.5% fat, 0.3% lactose and 4.5% ash) and buttermilk powder (33.0% protein, 6.0% fat, 51.0% lactose and 8.0% ash) were purchased from Friesland Campina DMV (Amersfoort, €pings Mejeri (Falko €ping, Sweden), respec­ The Netherlands) and Falko tively. Selected compositional and physical characteristics (based on the importance to reconstitution properties) of each cheese powder formu­ lation were analyzed (Felix da Silva et al., 2018b) and are shown in Table 1. The amount of free is presented as the percentage of total fat. Briefly, cheese powders were produced by preparing a cheese feed containing smear-ripened Danbo cheese (75%, Them ost, Them, 3

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A

2.2. Gel electrophoresis

8

The protein profile of the cheese powders were evaluated using so­ dium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) analysis using NuPAGE Novex 10% Bis-tris gels (Invitrogen, Naerum, Denmark) under reducing and non-reducing conditions. This method was used aiming to characterize the difference in the proteins present in the cheese powders produced with cheeses of different age (16, 30 and 45 weeks old). Cheese powders samples were reconstituted for 20 h at 20 � 1.0 � C and mixed with NuPAGE™ LDS Sample Buffer 4X to a final protein concentration of 1 mg mL 1 and heated at 80 � C for 10 min. For reducing SDS-PAGE, NuPAGE® Sample Reducing Agent containing 500 mM dithiothreitol (DTT) was added to the mixture. Electrophoretic separation was performed by applying a maximum voltage of 200 V in cassettes containing cold MES SDS running buffer (Invitrogen). Coo­ massie Blue (Brilliant Blue G Acid Blue 90 SIGMA B0770) was diluted 0.2% (w/w) and used to stain the gels overnight. The gels were trans­ ferred to MilliQ water to de-stain and the protein bands were photo­ graphed using an Epson Perfection V750 pro Scanner (Epson, Nagano, Japan).

Volume (%)

6

4

2

0 0.1

1

10

100

Size distribution (µm)

1000

B

80 70

D(50) µm

60 50

2.3. Surface atomic composition of cheese powders

40

The surface composition of cheese powders was analyzed using X-ray photoelectron spectroscopy (XPS), a semi-quantitative surface sensitive technique, which provides chemical information of the top 10 nm at the surface. We used a Kratos Axis UltraDLD instrument (Kratos Analytical, Manchester, UK) equipped with a monochromated AlKα X-rays source (hν ¼ 1486.6 eV, power ¼ 150 W) and a charge neutralizer. The com­ mercial software CasaXPS (Kratos Analytical, Manchester, UK) was used for analysis of the data. The X-ray beam caused some beam damage on the cheese powder, noticeable by a decrease of the nitrogen content over time. To avoid this, the counting time was kept to a minimum (about 15 min) and the same acquisition time was used for all samples.

30 20 10 0

100

200

300

400

Reconstitution time (min)

80

20 hrs

C

70 60

2.4. Capillary rise wetting

40

The wettability of cheese powders was measured using a modified Washburn method based on capillary rise wetting (Felix da Silva et al., 2018a; Ji et al., 2017c, 2017a; 2016b, 2015; Washburn, 1921). In this study, 1 g of powder was added to a plastic tube without bottom (d ¼ 15 mm) using filter paper (d ¼ 125 mm) to hold the powder. The tube was fixed just above the surface of distilled water (20 � 2.0 � C) for 10 min, the additional adsorbed water mass was measured using an analytical balance. Each cheese powder was measured six times.

D(50) µm

50

30 20 10 0

100

200

300

400

Reconstitution time (min)

80

20 hrs

D

2.5. Dispersibility

60

The dispersibility of cheese powder was evaluated by monitoring the change in particle size during reconstitution at 20 � 2.0 � C using a Malvern Mastersizer 3000 (Malvern Instruments Ltd, Worcestershire, UK). Powders were dispersed in a 5% solution (w/w) and stirred at 700 rpm up to 20 h. An aliquot was placed into the dispersion unit to reach 6–8% obscuration, and the particle size distribution (PSD) was evaluated after 5, 15, 25, 45 and 60, 120, 240, 300 and 1200 min (20 h) of reconstitution. The refractive index used was 1.57 for the powders and 1.33 for water as previously described for casein powders (Felix da Silva et al., 2018a; Gaiani et al., 2009). The results were expressed as volume mean diameter (D50) over reconstitution time. Triplicate mea­ surements were carried out for each cheese powder.

D(50) µm

70

50 40 30 20 10 0

100

200

300

400

20 hrs

Reconstitution time (min) Fig. 4. Dispersibility of cheese powders with different formulations. A: particle size distribution after 5 (■), 25 (●), 45 (▴), 120 (▾), 180 (◆), 300 (◄) minutes and (▸) 20 h reconstitution. B, C, D changes in D(50) over time of powders produced with 16, 30 and 45 weeks old cheese, respectively, where NOwithout added ingredients (▪), B2S2- addition of 2% sodium caseinate plus 2% buttermilk powder (●) and BMP- addition of 4% buttermilk powder (▴).

2.6. Total rehydration 2.6.1. Solubility The total solubility of cheese powder was evaluated based on the total solids present after dissolution and centrifugation (Anema et al., 4

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in-house MATLAB (version R2012, The Math-Works, Natick, MA, USA) script designed for fitting the relaxation curves to a sum of exponential decays according to Equation (2).

Table 3 Dispersibility (D(50 μm)) after reconstitution. Data from Fig. 4. Cheese powder NO_16 B2S2_16 BMP_16 NO_30 B2S2_30 BMP_30 NO_45 B2S2_45 BMP_45

D(50) after 5 min reconstitution b

51.73 � 1.92 55.36 � 2.23b 40.20 � 2.78d 48.26 � 2.17c 62.20 � 2.87a 37.56 � 0.56d 31.73 � 0.37e 48.03 � 2.87c 23.30 � 0.62f

D(50) after 20 h reconstitution 10.33 � 0.10d 13.86 � 1.80c 9.15 � 0.18d 10.33 � 0.35d 24.46 � 0.20a 7.98 � 0.15e 10.66 � 0.66d 22.23 � 0.20b 7.40 � 0.11e

N X

ðweight of the dry supernatantÞ x 100 ðweight of the supernatant x 5%Þ

t=T2n

(2)

n¼1

In Equation (2), I(t) is the echo intensity as a function of time, N is the number of relaxation components, the transverse relaxation time for site n is T2n, and the corresponding abundance of site n is Mn. 2.7. Statistical analysis

2006; Havea, 2006; Schokker et al., 2011). A cheese powder in water solution (5% w/w) was stirred at 700 rpm for 30 min to allow dispersion at 20 � 1.0 � C. Dispersions were placed in a 50 mL conical tube and centrifuged using a Funke Gerber, Multi-purpose Centrifuge (Funke – Dr. N.Gerber Labortechnik GmbH) at 700�g for 10 min. The supernatant (5 g) was placed in a pre-weighed moisture dish dried overnight at 105 � C, cooled in a desiccator and then water holding reweighed. The solubility was calculated according to equation (1). solubilityð%Þ ¼

Mn*e

IðtÞ ¼

Analysis of variance (ANOVA unpaired t-test p � 0.05) was con­ ducted using Origin Pro 2016 (OriginLab Corporation, Northampton, MA, USA). Standard deviations are shown as error bars in the figures. 3. Results and discussion The composition and surface area mean particle diameter D[3; 2] of the cheese powders are shown in Table 1. Similar protein, fat and ash contents were observed for all the powders. Cheese powders containing 2% buttermilk powder plus 2% sodium caseinate produced with 16 weeks old cheeses (B2S2_16) showed the lowest amount of free fat, suggesting better fat emulsification in the feed and within the powder particle. However, no significant differences were found between for­ mulations NO and BMP produced with 16 weeks old cheese regarding the free fat content (Felix da Silva et al., 2018b). The presence of free fat in fat-rich powders can lead to issues such as poor flowability and low reconstitutability (Drapala et al., 2017; Kelly et al., 2014; Sadek et al., 2015). Values of “pH 4.6 soluble nitrogen” (Table 1) have been used as an indication of degree of cheese maturation; an increase in proteolysis with aging leads to increased “pH 4.6 soluble nitrogen” values (Felix da Silva et al., 2018b). The SDS–PAGE performed on the cheese powders is shown in Fig. 1. Likewise, visual inspection of the gels indicated that the protein bands became more diffuse and less defined upon cheese maturation; this is clearly visualized for the formulation not containing

(1)

2.6.2. Low-field nuclear magnetic resonance spectroscopy The total/final rehydration of cheese powders was monitored by 1H low field nuclear magnetic resonance (LF-NMR) spectroscopy using Maran Ultra spectrometer (Resonance Instruments Inc., Witney, UK) operating at 23.2 MHz for 1H. Prior to the measurements, cheese powder samples were reconstituted with distilled water and transferred into the NMR tube (18 mm o.d.). Reconstituted (1:1 w/w) cheese powders (RCP) were analyzed using the Carr-Purcell-Meiboon-Gill (CPMG) sequence at 20 � 1.0 � C. The parameters of CPMG for RCPs were set as follow: recycle delay of 16 s; τ-delay of 200 μs and 12 scans. Data from 8000 echoes were acquired with a receiver gain of 3.0 (Felix da Silva et al., 2018a, 2017c). Transverse relaxation times (T2n) and relative pop­ ulations (Mn) of different relaxation components were obtained using an

Fig. 5. Solubility (%) of cheese powders with different formulations. NO- without added ingredients (▪), B2S2- addition of 2% sodium caseinate plus 2% buttermilk powder ( ) and BMP- addition of 4% buttermilk powder ( ). Numbers 16, 30 and 45 refers to the cheese age of the cheeses used for cheese powder manufacture.

5

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n.p 12.09 � 0.79ab 14.91 � 0.22a n.p 11.64 � 0.46b 13.17 � 0.35a n.p 12.80 � 0.26a 14.85 � 0.47a n.p 68.22 � 1.29a 67.34 � 1.10a n.p 66.33 � 1.04a 66.53 � 0.39a n.p 67.50 � 0.28a 62.78 � 0.97b

Wettability is defined as the ability of particles to overcome the surface tension between the water and themselves (Felix da Silva et al., 2017a; Ji et al., 2017b). It is well-known that wetting can be a critical step in the rehydration process of dairy powders (Ji et al., 2016b). Wettability of dairy powders is a dynamic penetration process and it is believed that the wetting behavior of dairy powders can be specifically affected by the surface composition and particle size (Crowley et al., 2016a,b; Felix da Silva et al., 2018a). Particles with hydrophobic sur­ faces will not wet easily and powders containing a high amount of such particles exhibit a tendency to clump (Fitzpatrick et al., 2016). Agglomerated powders (with larger particle size) tend to present faster wetting since water can penetrate more easily into the larger void spaces between the particles (Ji et al., 2016a). In the present study, wettability of cheese powders is expressed as capillary rise wetting (g water/g powder) and is shown in Fig. 2. The water uptake per gram of powder differs significantly depending on the addition of ingredients. B2S2 powders absorbed a significantly higher amount of water per gram of powder (0.50–0.51 g water/g powder), except for powders produced with 45 weeks old cheeses. This behavior might be related to the lower amount of free fat (Table 1) and consequently the lower amount of surface fat on the particles as observed by the N/C ratio (Table 2), making it easier to wet. No significant differences were observed between NO and BMP samples. The cheese age (powders produced with 16, 30 or 45 weeks old cheese) did not affect the wettability significantly. Fitzpatrick et al. (2016) investigated the rehydration behavior (wettability and solubilization) of twelve different food powders and concluded that composition, in particular, had a major influence on wettability. More specifically, the high fat powders had the poorest wettability due to the hydrophobic nature of fat. In the present study, cheese powders present similar bulk fat (41.6–45.0%) and protein (40.4–44.6%) contents. However, a lower amount of free fat was observed for B2S2 powders produced with 16 or 30 weeks old cheeses (Table 1), and a significantly lower amount of fat on the surface (Table 2) was observed for B2S2 powders. In Fig. 3, a plot of wettability against the N/C ratio (Fig. 3A) as well as the wettability

T2n: Relaxation time of component n; Mn: Relative abundance of component n; n.p: not present.

M4 (%) M3 (%) M2 (%)

78.62 � 0.79a n.p n.p 80.76 � 0.31a n.p n.p 75.02 � 0.57b n.p n.p

M1 (%)

n.p 19.69 � 0.99b 17.75 � 1.01b n.p 22.03 � 0.81a 20.30 � 0.40b n.p 19.69 � 0.48b 22.37 � 0.65a

3.1. Wettability

n.p 140.03 � 5.03a 133.40 � 2.71b n.p 143.08 � 12.6a 143.21 � 6.24a n.p. 133.69 � 2.54b 133.33 � 2.07b

T25 (ms) T24 (ms)

n.p 33.29 � 1.27c 38.10 � 0.26b n.p 36.20 � 1.02b 39.80 � 1.78a n.p 33.50 � 0.44c 37.12 � 0.33a

106.44 � 6.6a n.p n.p 100.50 � 2.11a n.p n.p 101.66 � 3.49a n.p n.p

T23 (ms)

24.80 � 0.78a n.p n.p 24.33 � 1.19a n.p n.p 25.81 � 0.26a n.p n.p n.p 10.50 � 0.29a 10.86 � 0.46a n.p 10.00 � 0.57a 10.43 � 0.54a n.p 10.73 � 0.18a 11.94 � 0.25a NO_16 NO_30 NO_45 B2S2_16 B2S2_30 B2S2_45 BMP_16 BMP_30 BMP_45

T22 (ms) T21 (ms) Cheese powder

Table 4 Relaxation times and relative abundances obtained by 1H LF-NMR of reconstituted cheese powders (50%(w/w).

any added dairy ingredients (NO). As the ingredients have been added, the protein bands stemming from the ingredients also appear. As expected, the lactose content was higher with the addition of BMP, due to the high lactose content present in this dairy ingredient (51 w/w %). Cheese powders made using added BMP presented a signifi­ cantly larger particle size when produced with 16 or 30 weeks old cheeses (Table 1). This behavior might be due to the spontaneous agglomeration occurring in the powder mainly as a result of the pres­ ence of amorphous lactose (Felix da Silva et al., 2018b). On the other hand, powder NO_45 also presented a higher mean particle size. It should also be noted that B2S2 powders presented the smallest particles independent of cheese age. A higher nitrogen/carbon (N/C) ratio was observed on the surface of cheese powders containing both ingredients (B2S2) for all cheese ages when compared to NO and BMP (Table 2). This indicates a lower amount of fat present on the surface obtained by the addition of ingredients, a tendency most pronounced for the B2S2 samples having N/C ratios in the range 2.3–6.5%. The N/C ratio was similar for all BMP powders (1.9–2.1%) independent of cheese age, but for NO and B2S2 powders the lowest amount of surface fat was obtained using 30 weeks old cheeses, indicating better fat emulsification at this stage of maturation due to the protein emulsification capacity as previously suggested by Felix da Silva et al. (2018b). The content of free fat (Table 1) and the amount of surface fat seems to be correlated, since formulations containing B2S2 showed lower amount of free fat and surface fat. However, the amount of free fat in B2S2_30 powder was found not to be significantly different to BMP_30.

21.38 � 0.80c n.p n.p 19.24 � 0.35c n.p n.p 24.98 � 0.59c n.p n.p

M5 (%)

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and the percentage of free fat in the cheese powders (Fig. 3B) are pre­ sented. A positive correlation is expected between wettability and the ratio N/C, indicating a more hydrophilic cheese powder surface. As seen in Fig. 3A, the decrease in the N/C ratio is to an increase in wettability for most of cheese powders except for the B2S2_45. Therefore, it is also important to note that the method used to quantify the wettability presented a large variation (large standard deviation), and might not be able to detect small differences. Studies have shown that the high amount of lactose in dairy powders may contribute to increased hydrophilicity and thereby improved wettability (Crowley et al., 2015; Fitzpatrick et al., 2016; Gaiani et al., 2006). However, the wettability values (Fig. 2) did not differ between NO and powders with added dairy ingredients despite the higher amount of lactose and the fact that spontaneous agglomeration has been observed in BMP samples (Felix da Silva et al., 2018b). This indicates that even though the amount of lactose was significantly higher for BMP powders, it did not affect the wettability in cheese powders. This behavior might also be due to the high amount of fat present in cheese powder.

3.3. Total rehydration 3.3.1. Solubility The amount of total solids remaining in the supernatant after stirring and centrifugation has been widely used as a solubility method for dairy powders (Anema et al., 2006; Havea, 2006; Schokker et al., 2011). In the present study, the solubility of cheese powders is shown in Fig. 5. Fitz­ patrick et al. (2016) have suggested that the presence of lactose in milk powder contributes to improved solubility. Likewise, it has been shown that the dissolution is favored by the presence of small hydrophilic molecules (Lillford and Fellow, 1998). However, even though some powders had a higher amount of lactose or more degraded protein, no clear differences were observed using this method (except for B2S2_45, which presented significantly higher solubility). This might be due to the impaired reproducibility of the method, as this method seems to have limitations due to the low density or high-fat content character of cheese powders, which may not sediment after centrifugation (Felix da Silva et al., 2017a). The amount of water remaining bound to the powder after centri­ fugation, so called water-holding capacity, was also measured (data not shown). BMP powders presented the significantly lowest amount of g water per g of powder. No significant differences were observed with the cheese age.

3.2. Dispersibility Dispersibility is also an important step in the reconstitution/rehy­ dration process, and this subprocess is primarily related to the particle size (Goalard et al., 2006; Ji et al., 2016c). Changes in particle size can be used as a quantitative indicator to monitor the dispersion process (Forny et al., 2011). During the reconstitution process, the size of dispersing particles is decreasing, and thus the dispersibility can be quantified by the rate of decrease in particle size D(50). However, it is essential to evaluate the changes in the volume concentration due to the fact that powders consist of many single particles (Ji et al., 2016b). Thus, as an example, Fig. 4A shows how the particle size distribution of NO_16 cheese powder changes during the reconstitution as a function of time. The majority of particles had a size of 50 μm at 5 min (Table 3), whereas this value was 10–15 μm after 20 h of reconstitution. At the end of reconstitution, a bimodal distribution of particle size was still observed, implying that at least two populations exist. The D(50) was used as indicative of dispersibility of cheese powders (Fig. 4B, C and D). No complete dissolution (D(50) closer to 0) was observed for any of the cheese powders after 20 h, and in general cheese powders can be char­ acterized as slowly dispersible. The addition of 2% sodium caseinate plus 2% buttermilk powder (B2S2) resulted in larger particle size after 20 h reconstitution (Table 3). Samples containing only buttermilk powder (BMP) were characterized by a significantly decreased particle size during the beginning (5 min) and the end (20 h) of reconstitution, in high extent for powders pro­ duced with 45 weeks old cheeses. This implies a better dispersibility of powders upon addition of BMP during powder manufacture and might be due to a higher amount of lactose in the cheese powder bulk. The latter is in accordance with a previous study demonstrating a reduction in full reconstitution time for milk protein concentrate and milk protein isolate powders with a higher lactose concentration (Gaiani et al., 2007, 2006). Increased amount of lactose also decreased the dissolution time of native phosphocaseinate powders by causing water to enter the core of the powder particle (Richard et al., 2013). Baldwin (2010) concluded that lactose played an important role in the inhibition of protein-protein interactions by hydrogen bonding to the proteins in milk powders. Comparing cheese powders with the same formulation (NO, B2S2 or BMP) after 5 min reconstitution, powders produced with 45 weeks old cheese showed an improved dispersibility rate, reaching a constant value faster. This might be due to weaker interactions between proteins in the older (45 weeks old) cheese casein network as well the existence of smaller protein fractions as indicated in Fig. 1 due to proteolyses.

3.3.2. Low-field nuclear magnetic resonance Low-field nuclear magnetic resonance (LF-NMR) was also used to assess the final rehydration based on the strength of water binding in reconstituted cheese powders (RCP; 1:1 w/w). Transverse relaxation times (T21, T22, T23, T24, T25) and the corresponding relative abundance populations (M1,M2, M3, M4 M5) after tri-exponential fitting of the CPMG curves are shown in Table 4. This method can quantify the number of water fractions (components) present in RCP regarding the strength of water binding. Differences were observed in water binding in RCP, where five water fractions with different degree of mobility were identified for the powders. Five ranges of water mobility with respect to transverse relaxation were observed: 10–12 ms, 24–26 ms, 33–40 ms, 100–107 ms, and 133–144 ms. For the 16 week samples ranges 2 and 4 were observed, whereas ranges 1, 3 and 5 were observed for 30 and 45 weeks old cheese powder samples. The 16 week samples are charac­ terized by 75–80% of the water present as bound water (range 2), whereas the remaining 20–25% is more mobile (range 4). At 30 and 45 weeks 18–22% of the water is tightly bound (range 1), 63–68% is bound (range 3) and 11–15% is more mobile (range 5). Overall this demon­ strates that samples of cheeses aged 30 weeks or more results in a different distribution of water resulting in three rather than two pop­ ulations. The main part of the water is still bound, but both tightly bound water and more mobile water was observed as compared to the 16 week old samples. Those results are in accordance with previous studies where the rehydration of cheese powders produced with varying cheese type, the presence of emulsifying salts and spray dryer design (Felix da Silva et al., 2017c) or addition of sweet whey powder was evaluated (Felix da Silva et al., 2018a). No significant differences in the relaxation times were found regarding the addition of ingredients for powders produced with 16 weeks old cheeses, however, the relative abundance of component 2 (M2), which refers to the amount of tightly bound water, was signifi­ cantly lower for powder BMP_16 indicating that less water was inter­ acting with the proteins. Three water fractions and their respective relaxation times (T21. T23 and T25) were identified for powders produced with 30 and 45 weeks cheeses. These results indicate that maturation of the cheeses induce a more tightly bound water fraction as well as a more mobile fraction when compared to the samples produced from 16 week cheeses. This characteristic does not depend on added buttermilk or caseinate but only on the age of the cheese and therefore might be due to high amount of more degraded and loose protein structure. In addition, the amount of 7

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Journal of Food Engineering 270 (2020) 109763

tightly bound water (range 1) increase from 30 weeks to 45 weeks for BMP, whereas it decreases for NO and B2S2.

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4. Conclusions Addition of dairy ingredients, such as buttermilk powder and sodium caseinate, to the cheese feed, and the use of cheeses with different ages significantly influenced the wettability, dispersibility and final rehy­ dration of the powders. The amount of surface fat and, to some extent, the free fat have an impact on the wettability of the powders, consid­ ering that a reduction in surface and free fat led to an increase in the amount of absorbed water per gram of powders by capillary rise mea­ surement. On the other hand, the addition of ingredients and the cheese age determined how fast the powder dispersed. Powders produced with only buttermilk powder as well as powders produced with 45 weeks old cheeses presented faster dispersion when reconstituted in water. Contrarily, B2S2 presented a delayed dispersibility. The difference in cheese age was the main determinant of the total rehydration, i. e., powders made using young cheeses exhibited a stronger interaction with water and therefore better total rehydration. However, no correlations were observed with the total solubility or water holding capacity measurements, indicating that the methods used are not suitable for evaluating the reconstitution properties of cheeses powder. Acknowledgments We thank the Brazilian government’s Science without Borders Pro­ gram (National Council for Scientific Technological DevelopmentCNPq), the University of Copenhagen for financial support and Lactosan A/S. The valuable cooperation of Inger Hansen, Heidi Oest and Ann Rasmussen from Lactosan is gratefully acknowledged. References Anema, S.G., Pinder, D.N., Hunter, R.J., Hemar, Y., 2006. Effects of storage temperature on the solubility of milk protein concentrate (MPC85). Food Hydrocolloids 20, 386–393. https://doi.org/10.1016/j.foodhyd.2005.03.015. Baldwin, A.J., 2010. Insolubility of milk powder products – a minireview. Dairy Sci. Technol. 90, 169–179. https://doi.org/10.1051/dst/2009056. Crowley, S., Kelly, A., Schuck, P., Jeantet, R., O’Mahony, J., 2016. In: Advanced Dairy Chemistry: Volume 1B: Proteins: Applied Aspects, Fourth. Cork: Springer New York Heidelberg, Dordrecht London. Crowley, S.V., Desautel, B., Gazi, I., Kelly, A.L., Huppertz, T., O’Mahony, J.A., 2015. Rehydration characteristics of milk protein concentrate powders. J. Food Eng. 149, 105–113. https://doi.org/10.1016/j.jfoodeng.2014.09.033. Crowley, S.V., Kelly, A.L., Schuck, P., Jeantet, R., O’Mahony, J.A., 2016, fourth ed.. Rehydration and Solubility Characteristics of High-Protein Dairy Powders, Advanced Dairy Chemistry: Volume 1B: Proteins: Applied Aspects. https://doi.org/10.1007/ 978-1-4939-2800-2 Drapala, K.P., Auty, M.A.E., Mulvihill, D.M., O’Mahony, J.A., 2017. Influence of emulsifier type on the spray-drying properties of model infant formula emulsions. Food Hydrocolloids 69, 56–66. https://doi.org/10.1016/j.foodhyd.2016.12.024. Erbay, Z., Koca, N., 2015. Effects of whey or maltodextrin addition during production on physical quality of white cheese powder during storage. J. Dairy Sci. 98, 8391–8404. https://doi.org/10.3168/jds.2015-9765. Felix da Silva, D., Ahrn� e, L., Ipsen, R., Hougaard, A.B., 2017. Casein-based powders: characteristics and rehydration properties. Compr. Rev. Food Sci. Food Safe. 1–15. https://doi.org/10.1111/1541-4337.12319, 00. Felix da Silva, D., Ahrn� e, L., Larsen, F.H., Hougaard, A.B., Ipsen, R., 2018. Physical and functional properties of cheese powders affected by sweet whey powder addition before or after spray drying. Powder Technol. 323, 139–148. https://doi.org/ 10.1016/j.powtec.2017.10.014. Felix da Silva, D., Hirschberg, C., Ahrn� e, L., Hougaard, A., Ipsen, R., 2018. Cheese feed to powder: effects of cheese age, added dairy ingredients and spray drying temperature on properties of cheese powders. J. Food Eng. https://doi.org/10.1016/j. jfoodeng.2018.05.015. Felix da Silva, D., Larsen, F.H., Hougaard, A.B., Ipsen, R., 2017. The influence of raw material, added emulsifying salt and spray drying on cheese powder structure and hydration properties. Int. Dairy J. 74, 27–38. https://doi.org/10.1016/j. idairyj.2017.01.005. Felix da Silva, D., Larsen, F.H., Hougaard, A.B., Ipsen, R., 2017. The influence of raw material, added emulsifying salt and spray drying on cheese powder structure and hydration properties. Int. Dairy J. 74, 27–38. https://doi.org/10.1016/j. idairyj.2017.01.005.

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