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Accepted Manuscript Agglomeration during spray drying: Physical and rehydration properties of whole milk/ sugar mixture powders S. Chever, S. Méjean, ...

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Accepted Manuscript Agglomeration during spray drying: Physical and rehydration properties of whole milk/ sugar mixture powders S. Chever, S. Méjean, A. Dolivet, F. Mei, C.M. Den Boer, G. Le Barzic, R. Jeantet, P. Schuck PII:

S0023-6438(17)30307-9

DOI:

10.1016/j.lwt.2017.05.002

Reference:

YFSTL 6218

To appear in:

LWT - Food Science and Technology

Received Date: 29 October 2016 Revised Date:

2 May 2017

Accepted Date: 3 May 2017

Please cite this article as: Chever, S., Méjean, S., Dolivet, A., Mei, F., Den Boer, C.M., Le Barzic, G., Jeantet, R., Schuck, P., Agglomeration during spray drying: Physical and rehydration properties of whole milk/sugar mixture powders, LWT - Food Science and Technology (2017), doi: 10.1016/ j.lwt.2017.05.002. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

ACCEPTED MANUSCRIPT Agglomeration during spray drying: physical and rehydration properties of whole milk/sugar mixture

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powders

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S. Chevera, S. Méjeana,b, A. Doliveta, F. Meic, C.M. Den Boerd, G. Le Barzicd, R. Jeanteta and P.

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Schucka,*

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a

STLO, UMR1253, INRA, Agrocampus Ouest, 35000 Rennes, France

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b

BIONOV, 85 rue de Saint Brieuc, 35042 Rennes, France

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Mondelez International, 200 Deforest Avenue, East Hanover, New Jersey 07936, United States of

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America

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Mondelez UK R&D Ltd, Banbury, Oxon, OX16 2QU, United Kingdom

*Corresponding author. Address: INRA UMR 1253, 35000 Rennes, France. Fax: +33 (0)2 23 48 53

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50.

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E-mail address: [email protected]

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Abstract

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In general, milk powders are submitted to agglomeration in order to enhance their rehydration

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properties. This study evaluated the impact of six different methods of agglomeration of the same

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sweet whole milk powder on the physical and rehydration properties of the final product: non-

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agglomerated powder (control); agglomerated powder with fines returned to the top of the dryer,

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above the internal fluid bed (IFB) or above the cone; and agglomerated powder with fines returned

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above the IFB with a nozzle that injects steam or sprays water in the middle of the IFB, respectively.

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As expected, the biochemistry results showed no difference since the same concentrate was used in the

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whole set of experiments. The physical properties led to higher bulk densities, tapped densities and

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interstitial air for the control, and higher occluded air and particle size for agglomerated powders,

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regardless of the agglomeration process.

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rehydratability. In fact, the wetting time and the dispersibility of sweet whole milk powder were

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All of these physical properties influenced the

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significantly improved by the agglomeration method, with the return of fines and steam injection in

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the IFB. An experimental design of the agglomeration process was devised for this agglomeration

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approach.

29 Keywords: Rehydratability, Dairy powder, Granulation, Fine recirculation

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1. Introduction

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The rehydratability of a powder in water is an essential property of food powders for the consumer

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(King, 1966). Three main stages are usually distinguished in the rehydration process: wetting,

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dispersion and solubilization (Freudig, Hogekamp, & Schubert, 1999; Písecký, 1997). These stages are

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characterized by three indices: the wettability index (WI), the dispersibility index (DI) and the

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solubility index (SI), respectively. The WI measures the ability of the powder to adsorb water on its

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surface, to be wetted, and to penetrate the free surface of still water (Sharma, Jana, & Chavan, 2012).

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The DI represents the ability of a powder to separate into individual particles when dispersed in water

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with gentle mixing (Sharma, Jana, & Chavan, 2012), and the SI provides an overall measurement of

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the ability of a powder to dissolve in water (Schuck et al., 2012). In order to realistically consider the

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rehydratability of a powder, Schuck, Dolivet, & Jeantet (2012) proposed considering the ‘instant’

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criterion (IC), which applies to powders that are wettable (WI < 20 s), dispersible (DI > 95%) and

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soluble (SI > 99%) at the same time.

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Rehydratability depends on the composition and structure of a powder, especially the affinity

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between its components and water (Dupas-Langlet, Benali, Pezron, Saleh, & Metlas-Komunjer, 2012;

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Crowley, Kelly, Schuck, Jeantet, & O’Mahony, 2016) and the accessibility of the water to its

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components, and on the rehydration conditions (Jeantet, Schuck, Six, Andre, & Delaplace, 2010).

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Whole milk powder cannot be wetted within a reasonable time (Kim, Chen, & Pearce, 2002) and the

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dispersibility is not satisfactory compared to skim milk powder (Vignolles et al., 2009; Tamime, 2009)

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due to the hydrophobic nature of the surface of the particle incorporating free fat (Petit et al., 2017). 2

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To improve these rehydration properties, manufacturers are required to add natural surfactants such as

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oil lecithin or a hygroscopic ingredient such as an amorphous carbohydrate. Apart from this approach based on modifying the composition, powder agglomeration is

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recognized to be one way to control and improve certain properties of a disperse system, especially

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with regard to rehydratability (Buffo, Probst, Zehentbauer, Luo, & Reineccius, 2002; Gaiani, Banon,

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Scher, Schuck, & Hardy, 2005). Indeed, agglomeration is known to have an impact on certain physical

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properties of powders such as density, granulometry, stickiness and cakiness, as well as on instant

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properties. The latter are mainly determined by the agglomeration process and then by the

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time/temperature to which the product is subjected in the system, including the processing steps prior

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to spray drying. The agglomeration mechanism consists of joining fines or small primary particles in

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order to form larger particles. Different agglomeration techniques, either in the dry or the wet state, are

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currently proposed, but the wet granulation process in a fluid bed is by far the most commonly used in

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the food industry (Gaiani, Schuck, Scher, Hardy, Desobry, & Banon, 2007; Turchiuli, Barkouti,

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Dumoulin, & Carcel, 2011; Turchiuli, Smail, & Dumoulin, 2012; Cuq, Mandato, Jeantet, Saleh, &

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Ruiz, 2013).

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The aim of this study was to determine the impact of six configurations of a semi-industrial drying

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pilot on the physical and rehydration properties of a given dairy formulation consisting of a sweet

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whole milk powder whose biochemical composition was kept constant. The efficacy of five different

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agglomeration processes was compared to a control non-agglomeration process.

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2. Material and methods

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2.1. Preparation of the concentrate

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Concentrates with 40 g.100 g-1 total solids (TS) were recombined at Bionov (Rennes, France) from

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a non-agglomerated medium-heat Whole Milk Powder (WMP, Lactalis Ingredients, Bourgbarré,

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France) and a mix of carbohydrates composed of sucrose (Begin-say, Tereos, Lille, France) and

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lactose (Lactalis Ingredients, Bourgbarré, France) at a 40/60 g/g sucrose/lactose ratio. The final target 3

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of the carbohydrate content was 55 g/100 g TS. The carbohydrate solution was dissolved at 70 °C to

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obtain a carbohydrate in amorphous form, and the temperature was then decreased to 51 °C before

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incorporation in the whole milk solution. The temperature of the final concentrate before drying was

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maintained at 51 ± 2 °C.

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The TS in the concentrates were checked by calculation of the weight loss after drying 5 g of the concentrate mixed with sand in an oven at 105 °C for 7 h.

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The fat globule size distribution was measured in the concentrate by Static Laser Light Scattering

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(SLS) using the Mastersizer 2000 device (Malvern Instruments, Orsay, France) with 1 mL of

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ethylenediaminetetraacetic acid (EDTA, 35 mM, pH 7.0), which is a chelating agent of calcium ions

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used to dissociate casein micelles. Measurements were performed in duplicate at room temperature to

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reach obscuration of between 4 and 12% with the water circulating in the sampling unit at a stirring

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speed of 1500 rpm, using refractive indices of water and milk fat of 1.33 and 1.458, respectively. The

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results (fat globule size distribution) were based on volume and expressed as sphere-equivalent

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diameters. The diameter D[4.3], i.e., the mean volume diameter, was calculated.

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2.2. Spray drying

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Spray drying of the concentrates were performed at Bionov in a 3-stage pilot plant spray dryer

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(GEA, Niro Atomizer, Saint Quentin en Yvelines, France) (Fig. 1). Six trials were performed,

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corresponding to six different spray-drying configurations (Fig. 2): (i) non-agglomerated powder (NA

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- control); (ii) agglomerated powder with fines returned to the top of the dryer (AT) (Fig. 3); (iii)

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agglomerated powder with fines returned above the internal fluid bed (IFB) (AIFB); (iv) agglomerated

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powder with fines returned above the cone, without IFB (AC); (v) agglomerated powder with returned

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fines and steam injection in the middle of the IFB at 8 kg/h maximum as the fluidized powder layer

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rose in order to boost agglomeration (outlet steam temperature = 99 °C) (AS); and (vi) agglomerated

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powder with returned fines and spraying of water (water temperature: 20 °C) in the middle of the IFB

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at 6 kg/h as the fluidized powder layer rose in order to boost agglomeration (AW). All agglomerated

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powders were obtained by reintroduction of the fine particles from the cyclones. A 2-mm diameter

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sieve was previously installed to collect powders. Each spray-drying parameter for each trial was maintained at the same confidence interval, i.e., as

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close as possible to a mean constant value, regardless of the spray-drying configuration being tested.

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The atomizer was equipped with a 72/21 pressure nozzle throughout the trial (Spraying System Emani,

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Nantes, France). The flow rate of the concentrate was 101 ± 2 L/h, the inlet air temperature was set at

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208 ± 7 °C, and the outlet air temperature at 90 ± 2 °C (Table 1). The air temperature of the first and

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second section of the external fluid bed was at 50 ± 2 °C and 22 ± 2 °C, respectively. All inlet airs

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were monitored and adjusted by a dehumidifier (Munters, Sollentuna, Sweden) to obtain an absolute

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humidity close to 1 g water per kg of dry air. The duration of each trial was at least 1 h to obtain stable

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spray-drying parameters. The air velocity in Table 1 was measured before the heat exchanger on a

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straight pipe by using a pitot tube (Kimo, Rennes, France).

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A range of biochemical analyses was performed on the resulting powders, including protein,

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carbohydrate, ash and total fat content, to validate the identical biochemistry of the powders and

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moisture and free fat content, which can have an impact on the rehydration properties. All these

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analyses were performed according to the protocols described in Schuck, Dolivet, & Jeantet (2012).

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Each powder was analyzed in duplicate.

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2.3.1. Protein content

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The nitrogen content (TN) and non-protein nitrogen (NPN) of the powders were determined

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by the Kjeldahl method according to the IDF Standards (2001a,b), respectively. The protein content

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was calculated according to TN-NPN.

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2.3.2. Ash content Ash content was measured after incineration at 550 °C for 5 h. Each powder was analyzed twice, according to the protocols described in Schuck, Dolivet, & Jeantet (2012)

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The total fat was measured by Gerber’s acid-butyrometric method after dissolution of proteins

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by the addition of sulfuric acid and of amyl alcohol to facilitate the separation of milk fat by

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centrifugation. Each powder was analyzed twice.

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2.3.4. Sugar content

The carbohydrate content was calculated according to the following formula: Carbohydrate content = 100 - (humidity + protein content + ash content + total fat content)

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2.3.5. Free fat content

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The amount of free fat was evaluated by solvent extraction. Two extractions were performed

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by stirring a mixture of 10 ± 0.05 g powder with 50 mL petroleum ether and filtration on a 110-mm

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diameter filter paper (Whatman paper, n° 40, Cat n°1440 125, Whatman International Ltd Maidstone,

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England). The solvent was evaporated at 55 °C under vacuum with a rotary evaporator (Heidolph,

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Serlabo Technologies, Entraigues sur la Sorgue, France) and then kept in an oven at 105 °C overnight.

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The free fat content was determined by weight after evaporation of the solvent. Each powder was

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analyzed twice.

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2.4. Physical analysis

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ACCEPTED MANUSCRIPT Various physical analyses were performed on the resulting powders: water activity (aw),

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density, particle size and friability. These physical properties can differ according to the agglomeration

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method implemented and can have an impact on the rehydration properties. All these determinations

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were performed according to the protocols described in Schuck, Dolivet, & Jeantet (2012). Each

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powder was analyzed in duplicate.

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157 2.4.1. Humidity or moisture content

The moisture content of the powder was calculated by weight loss after drying 2 g of the

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powder mixed with sand in an oven at 105 °C for 7 h. Each powder was analyzed twice.

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2.4.2. Water activity (aw)

The aw was measured in a water activity meter (aw-meter; Novasina RTD 200/0 and RTD 33,

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Lachen, Switzerland). Each powder was analyzed three times.

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2.4.3. Bulk and tapped density and air content

Bulk density (ρB) (kg m-3) was obtained by weighing a cylinder, and tapped density (ρT) (kg.m-

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tapped density provides the interstitial air (IA) according to the following equation:

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=

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) by tapping the cylinder used for measuring bulk density 180 times. The difference between bulk and



× 100000

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where ρT is the tapped density (kg m-3) and ρB the bulk density (kg m-3).

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Occluded air (OA) (cm3.100 g-1) is the difference between the tapped density (ρT) and the true

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density measured using a gas pycnometer with both helium and nitrogen on an ATC pycnometer

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(Thermo Fisher Scientific, Courtaboeuf, France). It takes account of the air included in the powder

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particle. OA was calculated as follows: 7

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× 100000

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where ρT is the tapped density (kg m-3) and ρTR the true density (kg.m-3). The total air content (kg.m-3)

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is the sum of IA and OA.

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Particle size distributions and friability were measured by SLS using a Malvern Mastersizer

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2000 device. The powder was placed on the optical bench and illuminated by laser light. The

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compressed air pressure was fixed at 50 kPa or 400 kPa for friability for particle size analysis and the

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vibration at 30%. Each powder was analyzed twice. The results (particle size distribution) are based on

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volume and expressed as sphere-equivalent diameters. The diameter D[4.3], i.e., the mean volume

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diameter, was calculated. Different diameters were also calculated: i.e., D[0.1], D[0.5] and D[0.9],

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which means that 10, 50 and 90% of the sample were below this diameter, respectively. Using these

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diameters, the dispersion of the sample or the span (s) can be determined as follows:

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× 100

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The compressed air pressure was fixed at 4 bars for the friability analysis and the vibration at

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30%. The friability (F) can be deduced from the result obtained by laser particle size analysis. F (%) is

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equal to:

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=

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[ .



[ .



[ .

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2.5. Rehydration analysis

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Each powder was analyzed in quadruplicate.

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The wettability index (WI) was determined by adding 13 g of powder to 100 g of water at 40 °C

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without stirring. The wettability index is the time (s) required for a powder to become completely wet.

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For wettability > 120 s, the results should be considered as purely informative (Schuck, Dolivet, &

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Jeantet, 2012). The dispersibility index (DI) was determined by adding 13 g of powder to 100 g of water at 40

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°C with stirring with a spatula for 15 s. The dispersibility index is the amount of dry matter dispersed

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in water, expressed as a percentage (w/w), which can pass through a 200-µm sieve.

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Solubility (SI) was determined by adding 13 g of powder to 100 g of water at 40 °C and

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mixing in a blender for 90 s after adding two droplets of defoaming agent (octan-1-ol). SI is the

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percentage (v/v) of soluble particles (or supernatant).

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In order to consider the rehydratability of the powder at an overall level, the ‘instant’ criterion

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(IC), which applies to powders that are wettable (WI < 20 s), dispersible (DI > 95%) and soluble (SI >

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99%) at the same time was considered for each powder produced, as proposed by Schuck, Dolivet, &

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Jeantet (2012).

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2.6. Statistical analysis

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Principal Component Analysis (PCA) was carried out with R software (R Development Core

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Team) to summarize the main information from the collected data. The first two principal components

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(PC) were used to show the correlations between variables and the main differences between products.

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The experimental set was projected onto the map determined by PC1 and PC2 with samples. A map

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was also defined by the first and the third principal component of the PCA . One-way analysis of

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variance, followed by Tukey’s HSD test, were used on each variable to determine whether there were

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any statistical differences between any pairs of products at a 95% confidence level (test conducted

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with JMP software).

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3. Results and Discussion

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3.1. Concentrate 9

ACCEPTED MANUSCRIPT As explained above, the dry matter of the concentrate was good at 40.00 ± 0.01 g/100 g . The

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D[4.3] of the fat droplet size in the presence of EDTA was 0.76 ± 0.01 µm. The correlation between

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the free fat content and greater fat droplet diameters has already been established: to achieve low free

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fat content in powders, the fat droplet size in the concentrate has to be less than 1 µm before spray

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drying (Vignolles et al., 2009).

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3.2. Biochemical composition of powders

The average biochemical composition of all the powders was 17.5 ± 3.0 g/100 g DM, 56.5 ± 0.5

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g/100 g DM, 4.6 ± 0.1 g/100 g DM and 18.6 ± 0.1 g/100 g DM for protein content, carbohydrate

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content, ash content and total fat content, respectively. The results show that the biochemical

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composition (protein, ash, fat and carbohydrate content) was the same for all powders. Since each of

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the powders showed the predictable composition, it confirmed that the dilution and recombining step

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had been correctly validated. Moreover, the differences in powder properties were assumed to

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originate from the process and, in particular, from the agglomeration method implemented.

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The free fat, hydrophobic component present at the surface of the powder particles can have a

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negative impact on rehydration properties, on flowability and on oxidation during storage. Statistical

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analysis showed significant differences between the free fat content of powders, with a lower free fat

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content for AT (Table 2). However, free fat content varied only from 1.5 ± 0.0 to 3.3 ± 0.2 g/100 g fat

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. These values were low considering that the free fat content of standard spray-dried whole milk

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powders is around 2 g/100 g fat (Písecký, 1990). It can thus be concluded that these differences in free

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fat content were not great enough to affect rehydration properties.

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3.3. Physical properties of powders

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The humidity (Table 3) was in the range of 1.3 to 2.9 g/100 g, which is common for milk

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powders (Schuck, Dolivet, & Jeantet, 2012). Powder humidity may be affected by the biochemical

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ACCEPTED MANUSCRIPT composition, the outlet temperature and the drying time. Písecký (1997) showed that the moisture

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content decreased when the outlet air temperature increased, and even a small variation in the outlet

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temperature (e.g., a 1 °C increase) can have substantial consequences on the humidity of the powder (a

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0.2 g/100 g decrease) (Písecký, 1997; Schuck, Dolivet, & Jeantet, 2012). In this study, the outlet

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temperature (Table 1) and biochemical composition (Table 2) were the same, and it could be

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considered that differences in humidity were the consequences of residence time in the dryer. In fact,

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the longer the powder residence time is, the lower the humidity will be (Das & Langrish, 2012). The

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residence time of the product was affected by the dryer configuration, with a shorter residence time

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when fines were returned to the top of the dryer because of better agglomeration (Jeantet, Ducept,

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Dolivet, Méjean, & Schuck, 2008).

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aw is one of the most important factors that significantly influence the shelf-life of milk

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powder (Roos, 2002). Efstathiou, Feuardent, Méjean, & Schuck (2002) showed that, in general,

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product preservation is optimal when aw is 0.2 at 25 °C. The aw of powders is correlated with moisture

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content: the higher the humidity value is, the higher the aw value will be (Schuck, Dolivet, Méjean, &

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Jeantet, 2008). aw in this study ranged from 0.103 to 0.173, i.e., ≤ 0.2. This aw range corresponds to a

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strongly bound monolayer of water, which is fairly difficult to eliminate (Brunauer, Emmett, & Teller,

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1938).

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Particle size is an important physical property of powder, which can be linked to its

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appearance, reconstitution and flow characteristics. Significant differences (P ≤ 0.1) were obtained for

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D[4.3] diameter with the different configurations (Table 3). D[4.3] values were the highest with

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agglomeration by a nozzle in the IFB, which spayed steam (AS: D[4.3] = 308 ± 1 µm), and the lowest

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without agglomeration (NA: D[4.3] = 54 ± 0 µm). Between these extreme values, powders were

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ranked by descending order, i.e., AW, AT, AIFB and AC (D[4.3] = 287 ± 1, 255 ± 9, 140 ± 10 and

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133 ± 2 µm, respectively). All agglomerated powders presented higher mean particle sizes compared

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to the non-agglomerated control powder. Indeed, the aim of powder agglomeration is to join fine

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particles to make larger particles. The largest particle size was obtained with agglomeration in the IFB

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with the injection of steam or water spraying. Agglomeration was favored in this case, as in the wet

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return the fines above the IFB, recirculation of fines to the top of the dryer increased agglomeration

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efficacy: a cloud of fine particles clustered around the nozzle and stuck together with sprayed droplets

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of the concentrate before final drying (Jeantet, Ducept, Dolivet, Méjean, & Schuck, 2008).

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Agglomeration above the IFB provided smaller particle size since agglomeration was even more

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limited with IFB recirculation, in which case the fine particles were mixed with almost dried particles

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(Jeantet, Ducept, Dolivet, Méjean, & Schuck, 2008).

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Principal component analysis (PCA) was carried out to obtain an overall representation of the

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experimental dataset (Fig. 4a). The results are represented by a map defined by the first and the second

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principal components (PC1 and PC2) of the PCA, which explained 81% of the overall inertia of the

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data, and the projection of the individual sets on this map. The biochemistry results are not represented

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on this map because of the lack of difference between powders. aw and powder humidity are not

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included since they depend on the outlet temperature rather than on the agglomeration approach.

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Particle size, i.e., D[4,3], was better represented on the PC1 and PC3 maps (Fig. 4a, not shown), and

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was highly correlated with wettability and dispersibility. This confirms that rehydration properties are

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improved with higher D[4.3]. Very dispersible powders were agglomerated and DI increased with

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particle size to an optimum of approximately 150 to 200 µm (Schuchmann, Hogekamp, & Schubert,

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1993; Sharma, Jana, & Chavan, 2012), whereas the D[4,3] value of NA was 54.4 ± 0.0 µm and the

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D[4,3] for agglomerated powders ranged from 133 ± 2 to 308 ± 0 µm, closer to this optimum range.

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The span (uniformity index) also showed differences between configurations (Table 3). The

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agglomeration of powders at the top of the dryer or above the IFB (without a nozzle) resulted in

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powders with spans of 1.3 and 1.4, respectively, corresponding to very uniform particle size. One aim

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of agglomeration is in fact to achieve uniform particle size (Greensmith, 1998). Without

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agglomeration, particle size was not as uniform. For agglomeration above the IFB with injection of

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steam or water spraying, it was very difficult to control the particle size, and a class of particles as

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large as 1000 µm was observed for powders AS and AW (Fig. 5). Lastly, all the powders could be 12

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considered to be friable according to their friability values, ranging from 30 to 41.2% (Table 3)

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(Schuck, Dolivet, & Jeantet, 2012). Tapped densities and, to a lesser extent, bulk densities were higher for NA than for

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agglomerated powders, in agreement with the literature (Banjac., Stamenić, Lečić, & Stakić, 2009;

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Sharma, Jana, & Chavan, 2012).The density of a non-agglomerated powder is generally higher than

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that of the corresponding agglomerated powder because of the formation of a porous structure during

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the agglomeration process, which involves occluded air or a vacuole (Barkouti, Turchiuli, Carcel, &

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Dumoulin, 2013). The OA for agglomerated powders was at least twice that of NA (from 123 to 135

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cm3/100 g of powder compared to 61 cm3/100 g of powder) (Table 3). The IA was greater for the non-

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agglomerated powder NA. IA content decreased due to agglomeration, whereas OA content increased,

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resulting in a higher total air content in all of the agglomerated powders (AT to AW, between 186 to

314

228 cm3/100 g) compared to the non-agglomerated powder NA (168 cm3/100 g). This can be

315

explained by the part of the IA that would be trapped by the particle during agglomeration, thus

316

leading to an increase in the OA content and the total air content.

317 318

3.4. Rehydration properties

TE D

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SC

RI PT

305

Dispersibility and wettability were well represented on the PC1 (Fig. 4a). Solubility was not

320

included in the PCA because of the lack of variation between the powders. Greater dispersibility

321

corresponded to positive scores on the PC1, in contrast to better wettability, diametrically represented

322

by negative scores. Wettability and dispersibility appeared to be negatively correlated. On the other

323

hand, dispersibility was significantly positively correlated with partial or total occluded air (p = 0.023)

324

and negatively correlated with tapped density (p = 0.017). Indeed, dispersible powders are obtained by

325

production of agglomerated powders that contain a large quantity of occluded air and that can rapidly

326

fill with water on contact (Písecký, 1997). Moreover, bulk and tapped density are also influenced by

327

agglomeration: in general, the larger the particle size is, the lower the density will be (Börjesson,

328

Innings, Trägårdh, Bergenståhl, & Paulsson, 2014). Tapped density and occluded air were also

AC C

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319

13

ACCEPTED MANUSCRIPT 329

significantly correlated (p = 0.002). Occluded air is in fact a key factor for density control: as occluded

330

air increases, particle volume increases and, thus, particle density decreases. All the agglomerated powders produced in this study were considered to be wettable since

332

their WI was lower than 120 s (Haugaard Sorensen, Ktag, Pisecky, & Westergaard, 1978). In contrast,

333

the non-agglomerated NA powder was not wettable (Table 4). The presence of large agglomerated

334

particles (Table 3 and Fig. 4) promoted wetting. In fact, the larger the diameter is, the lower the

335

particle surface-to-volume ratio is and the easier the wetting step will be. Several authors have

336

reported that particle sizes greater than 200 µm provided better wettability (Szulc and Lenart, 2012;

337

Písecký, 1997). In agreement with this, the best wettability was obtained for AS and AW, the powders

338

with the largest particles, and the worst wettability for ACNA powder with the smallest particles.

339

These results are confirmed by negative correlation between particle size distribution and wettability

340

time with an R2 close to 0.85. The agglomeration approach that returns the fines to the top of the

341

drying chamber seemed to enhance wettability more effectively than the agglomeration approach

342

above the IFB.

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331

Similarly, since their DI was over 95%, all agglomerated powders were dispersible (Haugaard

344

Sorensen, Ktag, Pisecky, & Westergaard, 1978), regardless of the technological approach, whereas the

345

non-agglomerated NA powders were not dispersible. However, and using this index, AW did not show

346

the best behavior. Rapid dispersion required particle sizes in the range of 150 to 200 µm, but

347

dispersibility was probably increased even more because a hygroscopic agent (carbohydrates) had

348

been added.

EP

AC C

349

TE D

343

Milk powders are considered soluble if the SI is more than 99% (Haugaard Sorensen, Ktag,

350

Pisecky, & Westergaard, 1978). Thus, all powders considered in this study were soluble. Their

351

insoluble particles probably originated from the raw WMP material used, which presented an initial

352

0.4% content of insoluble particles. It can thus be concluded that there was no effect of the

353

agglomeration approach on the solubility of these powders.

14

ACCEPTED MANUSCRIPT 354

In view of the simultaneous WI of less than 20 s, a DI of more than 99% and an SI of more

355

than 99%, our results showed overall that AS was an instant powder (Schuck, Dolivet, & Jeantet,

356

2012). In general, this study emphasized the fact that agglomeration enhanced rehydration properties,

357

in agreement with previous results (Buffo, Probst, Zehentbauer, Luo, & Reineccius, 2012).

RI PT

358 Regarding the influence of agglomeration methods on rehydration properties, the experimental

360

set of individual powders was projected onto the map determined by PC1 and PC2 (Fig. 4b). This map

361

made it possible to define just three groups: non-agglomerated powder (NA), powders agglomerated at

362

the top of the dryer and above the IFB (ATAT, AIFB and AC), and agglomerated powders above the

363

IFB with steam injection or water spraying in the IFB (AS and AW). Better wettability and

364

dispersibility were found for samples on the right of this map, i.e., AS and AW. In contrast, NA, i.e.,

365

the non-agglomerated powder, had the poorest rehydration properties. The rehydration behaviors of

366

ATAT, AIFB and AC were intermediate, with medium DI and low WI.

M AN U

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359

Since AS had the best rehydration properties among the different powders considered in this

368

study, it was concluded that the best agglomeration approach to enhance rehydration properties was

369

the one with fine recirculation and steam injection. In this configuration, droplets were formed by

370

steam condensation in the IFB on the cold particle surface of primary or agglomerated particles. Steam

371

injection thus increased both the water content and the temperature T of the powder. Since increasing

372

the water content leads to a decrease in the glass transition temperature Tg of the powder, the injection

373

of steam in the IFB resulted in an increase in the (T-Tg) difference, which is suitable for the

374

agglomeration process (Roos, 1997). The resulting liquid layer on the surface of the particles may

375

dissolve the hydrophilic substances in the particle core to constitute a sticky surface (Roos, 1997).

376

Agglomerates were formed by collision of sticky particles joined by viscous liquid bridges, which

377

were further solidified by the drying process (Schuchmann, Hogekamp, & Schubert, 1993).

AC C

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367

378

15

ACCEPTED MANUSCRIPT Thus, wet agglomeration seems to be a better approach to obtaining instant powders than dry

380

agglomeration, in agreement with previous studies (Barkouti, Turchiuli, Carcel, & Dumoulin, 2013;

381

Schuchmann, Hogekamp, & Schubert, 1993; Turchiuli, Barkouti, Dumoulin, & Carcel, 2011).

382

However, in contrast to the latter, wet agglomeration was directly conducted in our study in the drying

383

chamber, and not post-drying using other granulation equipment.

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379

384 385

5. Conclusion

This study showed that different dryer configurations may have an impact on the physical

387

properties of powders, influencing rehydration properties. In general, powder agglomeration enhanced

388

rehydration properties. For instance, the best technological approach from a rehydratability point of

389

view appeared to be a combination of the reintroduction of fine particles with simultaneous steam

390

injection in the internal fluid bed, but this approach is highly dependent on the specific drying tower

391

considered and the drying conditions applied in the tower. Further work on this new agglomeration

392

configuration will focus on optimizing the steam or water flow rate in relation to the mass of powder

393

being used in order to more effectively control particle size.

394

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386

References

396

Banjac, M., Stamenić, M., Lečić, M., Stakić, M. (2009). Size distribution of agglomerates of milk

AC C

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powder in wet granulation process in a vibro-fluidized bed.

398

Engineering, 26, 515–525.

399 400

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Barkouti, A., Turchiuli, C., Carcel, J.A., Dumoulin, E. (2013). Milk powder agglomerate growth and properties in fluidized bed agglomeration. Dairy Sciences and Technology, 93, 523–535.

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Börjesson, E., Innings, F., Trägårdh, C., Bergenståhl, B., Paulsson, M., 2014. Evaluation of particle

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measures relevant for powder bed porosity - A study of spray dried dairy powders. Powder

403

Technology, 253, 453–463.

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Brunauer, S., Emmett, P.H., Teller, E. (1938). Adsorption of Gases in Multimolecular Layers. Journal of the American Chemical Society, 60, 309–319. Buffo, R.A., Probst, K., Zehentbauer, G., Luo, Z., Reineccius, G.A. (2002). Effects of agglomeration

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on the properties of spray-dried encapsulated flavours. Flavour and Fragrance Journal, 17, 292–

408

299.

RI PT

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Crowley S.V., Kelly A.L., Schuck P., Jeantet R. & O’Mahony J.A. (2016). Rehydration and solubility

410

characteristics of high-protein dairy powders. In P.L.H. McSweeney & J.A. O’Mahony (Eds.),

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Advanced Dairy Chemistry-1B Proteins: Applied Aspects, (pp.99-131). Springer Publishers, New

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Cuq, B., Mandato, S., Jeantet, R., Saleh, K., Ruiz, T. (2013). Food powder agglomeration. In:

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Bhandari, B., Bansal, N., Zhang, M., Schuck, P. (Eds.), Handbook of Food Powders (pp.200-

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229).Cambridge: Woodhead Publishing Series in Food Science, Technology and Nutrition.

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Das, D., Langrish, T.A.G. (2012). Combined Crystallization and Drying in a Pilot-Scale Spray Dryer. Drying Technology, 30, 998-1007.

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Dupas-Langlet, M., Benali, M., Pezron, I., Saleh, K., Metlas-Komunjer L. (2012). Deliquescence

419

lowering in mixtures of NaCl and sucrose powders elucidated by modeling the water activity of

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corresponding solutions. Journal of Food Engineering, 115, 391-397.

EP

418

Efstathiou, T., Feuardent, C., Méjean, S., Schuck, P. (2002). The use of carbonyl analysis to follow the

422

main reactions involved in the process of deterioration of deshydrated dairy products: predeiction

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of most favorable degree of dehydration. Le Lait 82, 423-439.

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Freudig, B., Hogekamp, S., Schubert, H. (1999). Dispersion of powders in liquids in a stirred vessel. Chemical Engineering Processing, 38,525-532.

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Gaiani C., Banon S., Scher J., Schuck P. Hardy J. (2005). Use of a turbidity sensor to characterize

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micellar casein powder rehydration: influence of some technological effects. Journal of Dairy

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Science, 88, 2700-2706.

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Gaiani C., Schuck P., Scher J., Hardy J., Desobry S., Banon S. (2007). Dairy powder rehydration:

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Influence of protein state, incorporation mode, and agglomeration. Journal of Dairy Science, 90,

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570-581.Greensmith, M. (1998). Practical Dehydration. (2nd ed). Cambridge: Woodhead

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produits laitiers déshydratés. Niro Atomizer, Copenhague, Danemark.

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Haugaard Sorensen, I., Ktag, J., Pisecky, J., Westergaard, V. (1978). Méthodes d’analyses des

IDF, 2001b. International standard 20-4: Milk - Determination of nitrogen-content - Part 4: Determination of non-protein-nitrogen content.

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Jeantet, R., Ducept, F., Dolivet, A., Méjean, S., Schuck, P. (2008). Residence time distribution: a tool to improve spray-drying control. Dairy Science and Technology, 88, 31-43. Jeantet, R., Schuck, P., Six, T., Andre, C., Delaplace, G. (2010). The influence of stirring speed,

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temperature and solid concentration on the rehydration time of micellar casein powder. Dairy

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Kim, E.H.-J., Chen, X.D., Pearce, D. (2002). Surface characterization of four industrial spray-dried

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dairy powders in relation to chemical composition, structure and wetting property. Colloids and

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Surfaces B: Biointerfaces, 26, 197–212.

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King, N. (1966). Dispersibility and reconstitutability of dried milk. Dairy Science Abstracts, 28, 105– 118.

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Petit, J., Michaux, F., Jacquot, C., Chavez Montes, E., Dupas, J., Girard, V., Gianfrancesco, A., Scher,

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J. & Gaiani, C. (2017). Storage-induced caking of cocoa powder. Journal of Food Engineering,

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Písecký, J. (1990). 20 years of instant whole milk powder. Scandinavian Dairy Information. 2, 1–5.

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Písecký, J. (1997). Handbook of Milk Powder Manufacture. Copenhagen: Niro A/S. ,. 18

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346). London: Chapman et Hall Roos, Y.H. (2002). Importance of glass transition and water activity to spray drying and stability of dairy powders. Le Lait, 82, 475–484. Schuchmann, H., Hogekamp, S., Schubert, H. (1993). Jet agglomeration processes for instant food.

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Roos, Y. H. (1997). Water in milk products. In P.F. Fox (Ed), Advanced dairy chemistry (pAIFB03-

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Schuck, P., Dolivet, A., Jeantet, R. (2012). Analytical Methods for Food and Dairy Powders. (First ed) Chichester:John Willey & Sons, Ltd, 228p.

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Schuck, P., Dolivet, A., Méjean, S., Jeantet, R. (2008). Relative humidity of outlet air: the key

463

parameter to optimize moisture content and water activity of dairy powders. Dairy Science and

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Technology, 88, 45–52.

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Sharma, A., Jana, A.H., Chavan, R.S. (2012). Functionality of Milk Powders and Milk-Based Powders

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for End Use Applications - A Review. Comprehensive Reviews in Food Science and Food Safety,

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11, 518–528.

470 471 472 473 474 475

powders. Journal of Food Engineering, 109, 135-141

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Szulc, K., Lenart A. (2012). Water vapour adsorption properties of agglomerated baby food

Tamime, A.Y. (2009). Dairy Powders and Concentrated Products. (First ed) Chichester:John Willey & Sons, Ltd,.380p.

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Turchiuli, C., Barkouti, A., Dumoulin, E., Carcel, J.A. (2011). Skim milk agglomerates growth furing fluidized bed wet agglomeration and drying. Eur. Dry. Conf. Turchiuli, C., Smail, R., Dumoulin, E. (2012). Fluidized bed agglomeration of skim milk powder: analysis of sampling for the follow-up of agglomerate growth. Powder Technology, 238, 161–168.

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Vignolles M.L., Lopez C., Madec M.N., Ehrhardt J.J., Méjean S., Schuck P, Jeantet R. (2009). Fat

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properties during homogenization, spray-drying and storage affect the physical properties of dairy

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powders. Journal of Dairy Science, 92, 58–70. 19

ACCEPTED MANUSCRIPT 479

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20

ACCEPTED MANUSCRIPT Table 1. Spray-drying parameters for the six powders. AT

AIFB AC

AS

AW

Flow rate

L/h

100

102

101

104

100

100

Inlet air

°C

206

206

197

208

215

215

IFB air

°C

55

55

55

55

70

70

IFB plate

°C

53

63

57

-

76

IFB powder

°C

58

68

63

-

78

Outlet air

°C

93

89

88

92

89

IFB air

m/s

11

10

11

12

12

Major air

m/s

15

15

15

16

14

73

75

90

15

SC

NB: “-“ is indicated when there is no value.

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NA

M AN U

velocity

Air

Temperature

Feed

Unit

14

AC C

EP

TE D

Legend: IFB: Integrated Fluid Bed; NA = Non-Agglomerated powder; AT = Agglomerated powder at the Top of the dryer; AIFB = Agglomerated powder above the Internal Fluid Bed; AC = Agglomerated powder above the Cone, without integrated fluid bed; AS = Agglomerated powder above the integrated fluid bed with a nozzle in the middle of the integrated fluid bed that sprayed Steam in the fluidized powder layer; AW = Agglomerated powder above the integrated fluid bed with a nozzle in the middle of the integrated fluid bed that sprayed Water in the fluidized powder layer.

ACCEPTED MANUSCRIPT Table 2. Free fat content expressed per g for 100 g of fat. Samples with the same letter (a,b,c) in a group of the same composition were not statistically different (P < 0.05) (n=2).

Total free fat

Unit

NA

AT

g/100 g fat

2.4 ± 0.5b

1.5 ± 0.0c

AIFB

AC

AS

AW

RI PT

Sample

2.8 ± 0.1a,b 2.8 ± 0.0a,b

3.3 ± 0.2a

2.9 ± 0.1a,b

AC C

EP

TE D

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Legend : NA = Non-Agglomerated powder; AT = Agglomerated powder at the Top of the dryer; AIFB = Agglomerated powder above the Internal Fluid Bed; AC = Agglomerated powder above the Cone, without integrated fluid bed; AS = Agglomerated powder above the integrated fluid bed with a nozzle in the middle of the integrated fluid bed that sprayed Steam in the fluidized powder layer; AW = Agglomerated powder above the integrated fluid bed with a nozzle in the middle of the integrated fluid bed that sprayed Water in the fluidized powder layer.

ACCEPTED MANUSCRIPT

Table 3. Properties of powders: moisture content, water activity (aw), density and particle size. Samples with the same letter (a,b,c) in a group of the same

Unit

NA

AT

AIFB

AC

AS

AW

Moisture

%

2.5 ± 0.0

2.9 ± 0.0

1.5 ±0.0

1.5 ± 0.0

2.0 ± 0.1

1.3 ± 0.0

aw

-

0.14 ± 0.00

0.17 ± 0.01

0.11 ± 0.01

0.12 ± 0.00

0.11 ± 0.00

0.10 ± 0.02

Bulk density

kg/m3

407 ± 4

370 ± 2

332 ± 3

330 ± 2

339 ± 3

373 ± 2

Tapped density

kg/m3

720 ± 2

500 ± 4

495 ± 1

484 ± 3

454 ± 1

494 ± 2

Partial true density

kg/m3

1288 ± 2

1294 ± 1

1259 ± 3

1273 ± 2

1177 ± 5

1214 ± 3

Total true density

kg/m3

1309 ± 1

1319 ± 2

1291 ± 4

1302 ± 2

1244 ± 3

1269 ± 4

Interstitial air

cm3/100 g

107 ± 3

70 ± 1

99 ± 2

96 ± 1

75 ± 2

66 ± 1

Occluded air

cm3/100 g

61 ± 1

123 ± 3

123 ± 0

128 ± 2

135 ± 0

120 ± 1

Total air

cm3/100 g

168 ± 4

193 ± 4

222 ± 2

224 ± 3

210 ± 2

186 ± 2

D [4,3]

µm

54 ± 0a

255 ± 9b

133 ± 2c

140 ± 10c

308 ± 0d

287 ± 10e

Span

-

2.0 ± 0.0b

1.3 ± 0.0c

1.4 ± 0.0c

1.4 ± 0.0c

3.3 ± 0.1a

2.0 ± 0.0b

Friability

%

30 ± 0

38 ± 1

41 ± 4

38 ± 2

35 ± 1

SC

M AN U

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EP 30 ± 2

RI PT

Sample

AC C

composition are not statistically different (P < 0.05) (n=2).

Legend: NA = Non-Agglomerated powder; AT = Agglomerated powder at the Top of the dryer; AIFB = Agglomerated powder above the Internal Fluid Bed; AC = Agglomerated powder above the Cone, without integrated fluid bed; AS = Agglomerated powder above the integrated fluid bed with a nozzle in the middle of the integrated fluid bed that sprayed Steam in the fluidized powder layer; AW = Agglomerated powder above the integrated fluid bed with a nozzle in the middle of the integrated fluid bed that sprayed Water in the fluidized powder layer.

ACCEPTED MANUSCRIPT Table 4: Rehydration ability of powders: wettability, dispersibility and solubility. Samples with the same letter (a,b,c) in a group of the analysis were not statistically different (P < 0.05) (n=4).

Wettability

Unit

NA

AT

AIFB

AC

s

> 120 ± 1e

47 ± 2b

66 ± 2c

112 ± 1d

%

62.0 ± 0.1a 99.7 ± 0.1c 97.8 ± 3.4b,c 94.9 ± 0.2b

%

14 ± 1a

99.7 ± 2.2c

97.5 ± 0.3b,c

99.6 ± 0.0a 99.6 ± 0.0 a 99.6 ± 0.0 a 99.6 ± 0.0 a 99.6 ± 0.0 a

99.6 ± 0.0 a

SC

index Solubility

AW

16 ± 1a

index Dispersibility

AS

RI PT

Sample

index

AC C

EP

TE D

M AN U

Legend: NA = Non-Agglomerated powder; AT = Agglomerated powder at the Top of the dryer; AIFB = Agglomerated powder above the Internal Fluid Bed; AC = Agglomerated powder above the Cone, without integrated fluid bed; AS = Agglomerated powder above the integrated fluid bed with a nozzle in the middle of the integrated fluid bed that sprayed Steam in the fluidized powder layer; AW = Agglomerated powder above the integrated fluid bed with a nozzle in the middle of the integrated fluid bed that sprayed Water in the fluidized powder layer.

ACCEPTED MANUSCRIPT

2.00 m

RI PT

0.37 m

Area of each section: : 3.18 m2 : 9.42 m2 : 8.83 m2 : 0.52 m2

M AN U

1.50 m

SC

0.25 m

Total area: 21.95 m2

EP

TE D

2.12 m

0.33 m

AC C

0.50 m

Fig.1. Dimensions of the spray dryer (not to scale).

TE D

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SC

RI PT

ACCEPTED MANUSCRIPT

EP

Fig. 2. Simplified diagram explaining the different approaches to agglomeration (NA = NonAgglomerated powder; AT = Agglomerated powder at the Top of the dryer; AIFB = Agglomerated

AC C

powder above the Internal Fluid Bed; AC = Agglomerated powder above the Cone, without integrated fluid bed; AS = Agglomerated powder above the integrated fluid bed with a nozzle in the middle of the integrated fluid bed that sprayed Steam in the fluidized powder layer; AW = Agglomerated powder above the integrated fluid bed with a nozzle in the middle of the integrated fluid bed that sprayed Water in the fluidized powder layer).

SC

RI PT

ACCEPTED MANUSCRIPT

AC C

EP

TE D

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Fig. 3. Diagram showing the recirculation of fine particles on the spray nozzle.

ACCEPTED MANUSCRIPT

1.0

Partial true density

0.5 Wettability

Partial occluded air

Interstitial air

Dispersibility

SC

Total occluded air

0.0

-0.5

M AN U

Dim 2 (22.31%)

Total air

RI PT

Total true density

Tapped density

Bulk density

Free fat

Span

TE D

-1.0

-0.5

0.0 Dim 1 (59.06%)

0.5

1.0

EP

-1.0

d(4.3)

Fig. 4a. Map defined by the first two principal components of the principal component analysis

AC C

(PCA), which was carried out to obtain an overall representation of the experimental dataset. Legend: IFB: Integrated Fluid Bed; NA = Non-Agglomerated powder; AT = Agglomerated powder at the Top of the dryer; AIFB = Agglomerated powder above the Internal Fluid Bed; AC = Agglomerated powder above the Cone, without integrated fluid bed; AS = Agglomerated powder above the integrated fluid bed with a nozzle in the middle of the integrated fluid bed that sprayed Steam in the fluidized powder layer; AW = Agglomerated powder above the integrated fluid bed with a nozzle in the middle of the integrated fluid bed that sprayed Water in the fluidized powder layer.

ACCEPTED MANUSCRIPT 3 AC 2

1

RI PT

Dim 2 (22.31%)

AIFB AT

0

-1

NA

-6

-4

-2

SC

AW

-2

0

2

AS

4

M AN U

Dim 1 (59.06%)

Fig. 4b. Projection of the experimental set on the map defined by the first two principal components of the principal component analysis (PCA). Sample classification was obtained by hierarchical cluster analysis

AC C

EP

TE D

Legend: IFB: Integrated Fluid Bed; NA = Non-Agglomerated powder; AT = Agglomerated powder at the Top of the dryer; AIFB = Agglomerated powder above the Internal Fluid Bed; AC = Agglomerated powder above the Cone, without integrated fluid bed; AS = Agglomerated powder above the integrated fluid bed with a nozzle in the middle of the integrated fluid bed that sprayed Steam in the fluidized powder layer; AW = Agglomerated powder above the integrated fluid bed with a nozzle in the middle of the integrated fluid bed that sprayed Water in the fluidized powder layer.

ACCEPTED MANUSCRIPT 10 9 8

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Volume (%)

7 6 5 4

SC

3

1 0 1

10

NA

AT

M AN U

2

Size (µm)

AIFB

100

AC

1000

AS

AW

TE D

Fig. 5. Particle size distribution of powders resulting from different agglomeration approaches.

AC C

EP

Legend : NA = Non-Agglomerated powder; AT = Agglomerated powder at the Top of the dryer; AIFB = Agglomerated powder above the Internal Fluid Bed; AC = Agglomerated powder above the Cone, without integrated fluid bed; AS = Agglomerated powder above the integrated fluid bed with a nozzle in the middle of the integrated fluid bed that sprayed Steam in the fluidized powder layer; AW = Agglomerated powder above the integrated fluid bed with a nozzle in the middle of the integrated fluid bed that sprayed Water in the fluidized powder layer.

ACCEPTED MANUSCRIPT 1

Figure captions

2 Figure 1

4

Dimensions of the spray dryer (not to scale)

RI PT

3

5 Figure 2

7

Simplified diagram explaining the different approaches to agglomeration (NA = Non-Agglomerated

8

powder; AT = Agglomerated powder at the Top of the dryer; AIFB = Agglomerated powder above

9

the Internal Fluid Bed; AC = Agglomerated powder above the Cone, without integrated fluid bed; AS

M AN U

SC

6

= Agglomerated powder above the integrated fluid bed with a nozzle in the middle of the integrated

11

fluid bed that sprayed Steam in the fluidized powder layer; AW = Agglomerated powder above the

12

integrated fluid bed with a nozzle in the middle of the integrated fluid bed that sprayed Water in the

13

fluidized powder layer).

14

TE D

10

Figure 3

16

Diagram showing the recirculation of fine particles on the spray nozzle.

EP

15

18

AC C

17 Figure 4

19

(a): Map defined by the first two principal components of the principal component analysis (PCA),

20

which was carried out to obtain an overall representation of the experimental dataset.

21

(b): Projection of the experimental set on the map defined by the first two principal components of

22

the principal component analysis (PCA). Sample classification was obtained by hierarchical

23

cluster analysis.

24 1

ACCEPTED MANUSCRIPT 25

Figure 5

26

Particle size distribution of powders resulting from different agglomeration approaches.

AC C

EP

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SC

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27

2

ACCEPTED MANUSCRIPT Highlights

Various agglomeration steps to rehydrate sweet milk powders were studied.



The rehydration properties depended on the configuration of the dryer.



The optimal scheme consisted of steam injection in the internal fluidized bed.

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ACCEPTED MANUSCRIPT Gail WAGMAN French-English Translator and Interpreter 13 rue du Terrail 30610 SAUVE France

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Tel.: 04 66 77 55 00 Email: [email protected]

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CERTIFICATE OF PROOFREADING

This is to certify that I, the undersigned, Gail WAGMAN, a native English speaker and professional translator and interpreter, have read and corrected the following paper, “Agglomeration during spray drying: physical and rehydration properties of whole milk/sugar mixture powders”, written by S. Chever, S. Méjean, A. Dolivet, F. Mei, C.M. Den Boer, G. Le

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Barzic, R. Jeantet and P. Schuck, and that it has met with my entire satisfaction.

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Gail Wagman Sauve, May 2, 2017