Effects of Shear and Cooling Rate on the Crystallization Behavior and

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Effects of Shear and Cooling Rate on the Crystallization Behavior and Structure of Cocoa Butter: Shear Applied During the Early Stages of Nucleation Pere R. Ramel, Rodrigo Campos, and Alejandro G. Marangoni Cryst. Growth Des., Just Accepted Manuscript • DOI: 10.1021/acs.cgd.7b01472 • Publication Date (Web): 07 Dec 2017 Downloaded from http://pubs.acs.org on December 10, 2017

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Crystal Growth & Design

Effects of Shear and Cooling Rate on the Crystallization Behavior and Structure of Cocoa Butter: Shear Applied During the Early Stages of Nucleation

Pere R. Ramel, Rodrigo Campos, and Alejandro G. Marangoni* Department of Food Science, University of Guelph, 50 Stone Road East, Guelph, Ontario, N1G 2W1, Canada

*Corresponding author: [email protected]

1

ABSTRACT

2

Here we investigated the effects of applied shear and temperature during the early stages of

3

nucleation on the isothermal crystallization behavior and microstructure of cocoa butter (CB).

4

Results showed that the composition of nucleating triacylglycerols (TAGs) as well as crystalline

5

microstructure and polymorphism of CB were affected by mixing and temperature gradients

6

while still in the molten state. The initial crystalline material isolated from CB after it had been

7

subjected to shear had a similar TAG composition as native CB. On the other hand, in the

8

absence of shear, high melting TAGs such as trisaturates (SSS) along with lower amounts of

9

mono-unsaturated TAGs (SUS) were present, possibly due to fractionation. After subjecting CB

10

to shear in its molten state, crystallization rates were faster due to the co-crystallization of

11

different TAGs into a mixed crystal, however, the polymorphic transition into the more stable β-

12

V form, were found to be slower due to inherent complexity in TAG composition. Under static

13

conditions, the presence of high amounts of homogenous TAGs (SSS), were correlated to faster

14

polymorphic transformations possibly due to a templating effect.

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15

INTRODUCTION

16

The crystallization behavior and crystal structure of cocoa butter (CB) greatly affects the overall

17

properties of chocolate. CB is rich in triacylglycerols (TAGs) composed of stearic acid (S),

18

palmitic acid (P), and oleic acid (O); with POP, POS, and SOS as the TAGs with the highest

19

concentrations

20

often matched. However, besides chemical composition, processing conditions (e.g.,

21

crystallization temperature, cooling rate, shear rate) applied to CB also affect its physicochemical

22

properties

23

tempering procedure for chocolate mass consists of cooling the molten mixture to 26–28 °C with

24

agitation to induce the crystallization of cocoa butter, after which it is heated to 30–32 °C to melt

25

the unstable crystal forms present 8,9.The tempered chocolate mass is then poured into molds and

26

cooled at approximately 16 °C. This process allows for the crystallization of CB in small stable

27

β-V crystals, which are desirable for chocolate to have adequate gloss, snap, mouth feel and

28

melting properties 3,9–11.

29

Numerous studies have been conducted to understand the effect of composition and various

30

external factors on the crystallization behavior and structure of CB, and the effect of the resulting

31

crystal network on the properties and stability of chocolate products 4,5,7,12–15. These studies were

32

also carried out to understand the mechanisms behind the tempering process developed by

33

chocolatiers. During crystallization of CB, or fats in general, a phase transition occurs from the

34

liquid state to the solid state which is brought about by the supersaturation and arrangement of

35

TAGs in a crystal lattice to form stable nuclei. These nuclei will then serve as a starting point for

36

the growth and aggregation of crystal clusters, eventually forming a three-dimensional fat crystal

37

network. The crystal structure of CB has been extensively studied at different length scales,

4–7

1–4

. In the search for CB alternatives or substitutes, the levels of these TAGs are

. A very important process in the manufacture of chocolate is tempering. A typical


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namely, molecular level (polymorphism), nanoscale (properties of crystalline nanoplatelets,

39

CNPs), meso – or microstructure (poly-crystal aggregate size, shape, and mass distribution), and

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macro-scale 6,7,9,13,14,16.

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In a previous work by Campos and Marangoni 9, the importance of shear during the processing

42

of cocoa butter was shown by describing the effect of shear on the crystallization kinetics,

43

microstructure, and rheological properties of cocoa butter. Previous work on CB focused on the

44

crystal structure of CB after crystallization. However, in order to gain insights into how the

45

structures are formed during crystallization with the application of shear, it is necessary to study

46

the events that occur during the early stages of nucleation 2,17,18.

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In this study, the crystallization behavior of CB during shearing and cooling of the melt between

48

60 and 28 °C, prior to any “observable” crystal formation, was investigated. This will allow the

49

examination of the influence of heat and momentum transfer history of the melt on the early

50

stages of nucleation and crystal growth of CB under static and dynamic (shear) conditions.

51 52

MATERIALS AND METHODS

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Samples and processing conditions performed in the current study are based on the previous

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work by Campos and Marangoni (2014)9.

55 56

Cocoa Butter

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Refined Callebaut CB was used for all experiments performed (Qzina Specialty Foods Inc,

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Toronto, ON, Canada).

59 60



61

Processing of Cocoa Butter

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CB samples were placed in stainless steel beakers and melted in an oven at 60 °C for 30 min to

63

ensure that all crystal memory was erased. Samples were then transferred to a temperature

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controlled Neslab water bath RTE-11 (Neslab, Portsmouth, NH, USA) for cooling from 60 °C to

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28°C at 0.1, 1, and 5 °C/min. Shear was applied while cooling by using a Lightning Lab Master

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Mixer (Lightning, Rochester, NY, USA) equipped with a radial flow impeller (2” R100 5/16”)

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and operated at a speed of 400RPM. The radial flow impeller was chosen because it provides a

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high shear field, with a maximum shear rate of 120s-1. Samples were processed under the

69

described shear conditions (labeled as dynamic in this work) and compared to samples processed

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in the absence of shear (labeled as static) until a temperature of 28 °C was reached. Samples

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were obtained and transferred for isothermal crystallization at 15, 20, 24, and 26 °C. A sampling

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temperature of 28 °C was chosen as it corresponds to the temperature to which a chocolate mass

73

is cooled during a typical chocolate tempering procedure.

74 75

Solid fat content

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At the sampling temperature (28 °C), approximately 3 grams of CB were placed in glass pNMR

77

tubes (10 mm diameter, 1mm thickness, and 180 mm height) and immediately transferred to a

78

water bath set at the different crystallization temperatures. It is of utmost importance to transfer

79

the samples as fast as possible to ensure that samples have reached the crystallization

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temperature prior to taking any measurements, thereby ensuring that the kinetic analysis is done

81

under isothermal conditions. SFC readings were obtained at appropriate time intervals using a

82

Bruker PC/20 series pNMR analyzer (Bruker, Milton, ON, Canada). The sampling points and

83

duration of the experiment depended on the crystallization temperature and were as follows:


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every minute for 15 °C, 2 min for 20 °C, 30 min for 24 °C, and 60 min for 26 °C. Measurements

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were taken until the SFC readings reached a plateau and the system had stabilized, reaching an

86

equilibrium SFC reading. The isothermal crystallization curves were then fitted into the Avrami

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equation to obtain the kinetics of crystallization (Avrami crystallization constant and index)9.

88 89

Thermal Properties

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The thermal behavior of cocoa butter samples was studied using a DSC 2910 differential

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scanning calorimeter (DSC) (DuPont Instruments, Willington DE, USA). At the sampling time,

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5-10 mg aliquots of cocoa butter were placed into pre-tempered DSC pans and hermetically

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sealed. The weight was recorded. They were immediately transferred to temperature-controlled

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incubators set at the crystallization temperatures (15, 20, 24, and 26 °C). Samples were melted in

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the DSC after 1, 3, 6, and 12 h, 1, 3, 5, 10 and 24 days. The DSC cell was pre-tempered at the

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crystallization temperature prior to loading the sample. After the sample was loaded, the DSC

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cell was allowed to equilibrate for 1 min. The sample was then melted at a rate of 5 °C/min from

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the temperature of crystallization to 60°C. The peak melting temperatures were obtained from

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the thermograms using TA Instruments Universal Analysis 2000 V.4.2E software (TA

100

Instruments, Mississauga ON, Canada).

101 102

Powder X-ray diffraction

103 104

A high resolution XRD transmission instrument coupled with a DSC, called Microcalix was used

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to study the polymorphism of the sample blends, while measuring the heat flux that resulted from

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the crystallization process. The Microcalix was developed in the Laboratory for Physical –

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Chemical Studies of Poly-phase Systems, at the University of Paris-South (92296 Châtenay –



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Malabry, France). The coupled XRD recorded simultaneously at both small (q=0-0.45Å-1) and

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wide (q=1.1-2.1Å-1) angles through two position sensitive gas linear detectors placed at 177 and

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30 cm respectively from the sample. The detector channels were calibrated to express the

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collected XRD data in the scattering vector q (Å-1), were q =

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angle of incidence of X-rays relative to the crystalline plane, λ is the X-ray wavelength, d(Å) is

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the repetition distance between two planes. The detectors were calibrated at wide angles with

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high-purity glyceryl tristearin complemented at small angels with silver behenate standards. The

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DSC was calibrated with lauric acid. Glass capillaries (1.4±1 mm diameter and 80 mm long)

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were used as sample holders. The molten fat was filled into the capillary tubes with the aid of a

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specially developed syringe as to fill the lower 15 mm of the capillary. At this level of filling, an

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average sample size of 20 mg is expected. Samples were melted in an oven at 80°C for 30

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minutes, after which they were placed in the sample holder. The sample holder was pre-set to

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60°C. After sample insertion, it was cooled to 24°C at a rate of 5°C/min, after which they were

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kept isothermally at the crystallization temperature. An XRD diffraction pattern was obtained

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after acquiring diffraction data for a period of 1200 seconds when samples were crystallized at

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24°C. A total of 32 patterns were obtained for each temperature. During the duration of the

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experiment the DSC acquired data every 3 seconds.

4π sin θ

λ

=

2π , and θ(°) is the d

125 126

Microstructure

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The microstructure of the processed CB samples was imaged by polarized light microscopy

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(PLM). When viewed by PLM, the birefringent solid microstructural elements of the network

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can be directly observed as white features in a black background. At the sampling temperature,

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one droplet of the cocoa butter was rapidly placed on a pre-tempered glass slide, using a pre-


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tempered capillary tube. A pre-tempered glass cover slip was carefully placed over the sample.

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The cover slip was placed parallel to the plane of the microscope slide and centered on the drop

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of sample to ensure a uniform thickness and prevent the presence of air bubbles. The prepared

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slides were then transferred to temperature - controlled incubators for storage at the different

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crystallization temperatures. The microstructure was imaged after 1, 3, 6, and 12 h, 1, 3, 5, 10,

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and 28 days of storage at each crystallization temperature. At the time of imaging, the prepared

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slides were placed on a temperature – controlled microscope stage (Linkam Scientific

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Instruments, Surrey, UK) set at each crystallization temperature. The microstructure was viewed

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using an Olympus BH light microscope (Olympus America Ltd., Melville NY, USA) using a 20x

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objective lens. Images were acquired using a Sony XC-75 CCD video camera (Sony

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Corporation, Japan) with the gain switch in the auto position. The images were digitalized using

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Scion Image software (Scion Corporation, Fredrick, MD, USA). Two slides were prepared for

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each time point, and at least 5 micrographs were obtained from each slide.

144 145

Seed Crystal Isolation

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The crystalline material present at different time points was isolated from the melt for further

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thermal and chemical analysis. The times of isolation varied with the temperature of

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crystallization, ranging from 30 seconds to 24 h of storage. The separation was done by

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centrifugation operated at 10,000 rpm at 22 °C of the cocoa butter aliquots in Eppendorf snap-

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cap microcentrifuge 2 ml tubes (Fisher Scientific, Ottawa ON, Canada) using an Eppendorf

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microcentrifuge 5410 (Brinkman Instruments Inc, Missassauga, ON, Canada). The liquid

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fraction was decanted. The crystalline mass was washed with cold isobutanol (5°C) (Sigma-

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Aldrich Canada Ltd, Oakville, ON, Canada). The precipitate was further washed with cold



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isobutanol, for a total of 3 washings. After each washing, the solvent was separated by

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decantation. After the last washing, the remaining solvent was allowed to evaporate in a fume

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hood. The crystalline material was then melted and its chemical properties were characterized

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for fatty acid composition using gas chromatography (GC) and TAG analysis using high

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performance liquid chromatography (HPLC).

159 160

RESULTS AND DISCUSSIONS

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Effect of shear and cooling rate (applied during the early stages of nucleation) on the

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isothermal crystallization behavior of CB

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In order to gain insights into the effect of shear and cooling rate applied during the early stages

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of nucleation on the crystallization behavior of CB, it was subjected to shear and different

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cooling rates during cooling from 60 to 28 °C. After that, SFC was monitored as a function of

167

time using pNMR during isothermal crystallization at 15, 20, 24, and 26 °C. By doing so, any

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differences observed in the crystallization behavior of CB during isothermal crystallization

169

would be a consequence of the heat, mass, and momentum transfer history of the melt or during

170

the early stages of nucleation (i.e., during the initial cooling from 60 to 28 °C).

171 172

The crystallization behavior of CB cooled statically or dynamically at different cooling rates,

173

from 60 °C to 28 °C, and then crystallizing isothermally at 24 °C, is shown in figure 1. It can be

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observed that regardless of shear or cooling rate applied, the crystallization behavior of CB is

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similar during isothermal crystallization at 24 °C, although slight differences (especially at 0.1

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°C/min cooling rate) can be noted in the crystallization constant, k and Avrami index, n. In terms


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of crystallization temperature, however, large differences can be observed (figure 2 and table 1).

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Crystallization at 15 °C results in relatively higher SFC during the early times of isothermal

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crystallization than other temperatures studied. Furthermore, the maximum SFC (SFCmax)

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reached at about 60–72 h is highest at 15 °C, followed by 20, 24 and then 26 °C (table 2).

181 182

These results show the importance of the degree of undercooling (∆T), defined as the

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temperature difference between the melt (i.e., 28 °C) and crystallization temperature, which

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provides the energy required to overcome the barrier for the induction of crystallization and

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eventually increase in SFC

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supersaturated in the melt and self-assemble to form ordered domains. As fat is further cooled,

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lower melting TAGs also crystallize onto the pre-existing nuclei allowing for crystal growth. At

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high ∆T, induction times are shorter as supersaturation of more TAGs is achieved faster than at

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low ∆T. Furthermore, at low crystallization temperatures, more TAGs (high and low melting

190

ones) can crystallize resulting in higher SFCmax, while at higher crystallization temperatures,

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only those TAGs with melting points higher than the crystallization temperature can crystallize,

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resulting in lower SFCmax.

8,19

. During crystallization, higher melting TAGs become

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Results of the crystallization of CB in time indicate that regardless of the processes applied

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during the early stages of nucleation, the induction time for CB crystallization and SFCmax

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remain unaffected at similar crystallization temperatures.

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Polymorphism

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CB polymorphs, or fat polymorphs in general, can be distinguished by their thermal properties as

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different polymorphs have been characterized by different melting points using DSC

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work, the peak melting temperatures of cocoa butter samples cooled under different conditions

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and stored at different temperatures were determined and are shown in figure 3.

20

. In this

205 206

Peak melting temperatures shown in figure 3 and figure 4 indicate the presence of different

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polymorphs of CB in time during isothermal crystallization at 15, 20, 24, and 26 °C, after

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cooling the CB melt at different cooling rates and in the presence and absence of shear. During

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isothermal crystallization at 15°C, it can be observed that regardless of shear and cooling rate -

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0.1 °C/min (figure 3) or 5 °C/min (figure 4) applied during the early stages of nucleation, the

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initial polymorph observed (at time = 1 h) was the β′-IV form, indicated by melting points

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between 20-27°C21. According to van Malsen et. al. (1999)21 and Marangoni and McGauley

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(2003)15, when CB is cooled to 15 °C, it initially crystallizes in the unstable α form that readily

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transforms (after about 20 min) into the β′-IV form. However, as we were only able to sample

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after 1 h, it is assumed that the CB samples initially crystallized in the α form and then

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transformed into the β′-IV form within 1 h of crystallization at 15 °C. This β′-IV polymorph of

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CB was found to be stable for up to 72 h (3 days) at 15 °C. After 3 days of storage, a dramatic

218

increase in the melting point from 27.5 to 31.7 °C was observed in samples previously statically

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cooled at 5 °C/min (figure 4), which indicates the polymorphic transformation of the β′-IV

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polymorph to the more stable β-V form. On the other hand, the rest of the samples (other

221

cooling rates with or without shear) transformed to the β-V form within 5 days, except those


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cooled dynamically at 5 °C/min, which transformed at a later time, and were in the β-V form

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after 10 days.

224 225

At 20 °C, initial crystallization of CB in the α form (with melting points between 23–24 °C)

226

followed by a solid-solid transformation to the β′-IV form was observed

227

crystallization, CB samples previously cooled either statically at 0.1 °C/min (figure 3) or under

228

shear at 5 °C/min (figure 4) were found to have an average peak melting temperature of 27.8 °C

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(β′-IV form) while the rest of the samples were found in the stable β-V form (with an average

230

peak melting point of 30.6 °C). After 3 h of isothermal crystallization at 20 °C, all samples were

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found in the more stable β-V form. Further increase in the melting points were observed over

232

time.

15,21,22

. After 1 h of

233 234

Crystallization of CB directly into the β′-IV polymorph from the melt at 24 °C has been reported

235

by various authors 15,21, with subsequent transformation into the β-V form within 12 h of storage.

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In Figure 3, it can be inferred that all samples crystallized into the β-V polymorph due to the

237

high melting points (29.6 to 32.2 °C) obtained after only 1 h of isothermal crystallization at 24

238

°C. However, upon further examination of the crystallization of CB at 24 °C under static

239

conditions using X-ray diffraction (Figure S1), it can be observed that cocoa butter crystallizes

240

initially in the α form when cooled at 5 °C/min, which transforms into the β′-IV polymorph in

241

time. A possible explanation for the presence of high melting peaks after only 1 h of isothermal

242

crystallization at 24 °C could be that at this high temperature, only high melting TAGs of CB

243

crystallize initially in their metastable β′-IV form.

244



245

Similar to crystallization at 24 °C, CB samples crystallized at 26 °C had melting points of

246

roughly 29-30 °C (initially around 1 h), indicative either of the presence of the more stable β-V

247

form21, or an increase in the crystallinity of such Form V. A significant increase in melting point

248

was observed between 6 h and 3 days. It is believed that such an increase in melting point

249

corresponds to a transformation from the form V to form VI, which has a melting temperature in

250

the range of 33.8 and 36.3 °C 20.

251 252

These results suggest that although very small differences in polymorphic transitions can be

253

observed (CB samples cooled at different temperatures), the processes applied during the early

254

stages of nucleation can affect the dynamics of polymorphic transformations of CB during

255

isothermal crystallization. There is an indication that static cooling of CB results in a faster

256

transition of the β′-IV form to a more stable β-V form than those previously cooled under shear,

257

particularly under cooling rates of 5 °C/min at 15 °C (figure 4).

258 259

Microstructure

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Among the different structural levels of a fat crystal network, microstructure has been reported to

261

greatly affect the macroscopic properties of fats and fat products such as spreadability, hardness,

262

mouthfeel

263

rates and shear during cooling from 60 to 28 °C, and then crystallizing isothermally at 15, 20, 24,

264

and 26 °C was monitored in time (from 1 h to 28 days).

14,19,23,24

. The resulting microstructure of CB after subjecting it to different cooling

265 266

Micrographs in figure 5 show the effect of conditions applied during pre-crystallization (0.1

267

°C/min statically - figures 5A-F vs 5 °C/min dynamically, i.e., with shear - figures 5H-N), on the


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changes that occur in time during isothermal crystallization at 15 °C. Granular (needle-like)

269

crystals were observed after 1 h of crystallization (figure 5A and 5H), regardless of the cooling

270

rate or shear applied to the melt (0.1 °C/min statically vs 5 °C/min dynamically). At this time

271

point (1 h), the SFCmax had been reached, resulting in a very high-density crystalline network.

272

However, in time, large crystals (round, spherulitic crystals) emerged on top of the initially

273

observed granular crystals which further grew throughout 28 days of storage. After 28 days,

274

these large crystals reached sizes of about 500-600 µm (figure 5F-G, 5M-N). The observed large

275

spherulites are consistent with the morphologies previously reported elsewhere15. It should be

276

noted that the time point at which these large crystals start to appear was affected by the cooling

277

rate and shear applied during the early stages of nucleation. Individual large crystals start to

278

appear at 3 h when samples were subjected to high cooling rates and/or shear during the pre-

279

crystallization cooling of the melt (figure 5J), whereas for samples cooled statically at 0.1 °C/min

280

these round spherulitic structures were not observed until after 3 days of storage (figure 5D).

281

Relating these results to polymorphism, the β′-IV polymorph was present in all treatments after 1

282

h at 15 °C, which corresponds to the dense granular microstructure observed. With time,

283

transformation to the stable β-V form was observed (between 3-5 days). It is believed that the

284

development of the large round spherulitic microstructures is related to the polymorphic

285

transformation from the β′-IV to the β-V form.

286 287

Micrographs in figure 6 show the effect of various conditions applied during pre-crystallization

288

on the microstructure of CB, especially after 28 days of isothermal crystallization at 20 °C. In a

289

previous work by Marangoni and McGauley (2003)15, it was found that after 1 h of isothermal

290

crystallization at 20 °C, β′-IV granular crystals formed clusters that increased in size and evolved



291

into bigger microstructures. These microstructural changes were also observed in the current

292

study, i.e., relatively smaller crystals after 1 h of isothermal crystallization, (figure 6A and 6B)

293

that grow into larger structures in time, regardless of the pre-crystallization conditions applied

294

(0.1 and 1 °C/min under shear). After 6h of isothermal crystallization (5 °C/min with shear),

295

areas of significantly higher crystalline mass or clusters were formed over the existing

296

continuous granular crystals (figure 6C-D). At 5 °C/min, 0.1 °C/min, and 1 °C/min, all with

297

shear, and then isothermal at 20 °C for 3 days, 5 days, and 10 days, respectively (figure 6E-G),

298

distinct crystals emerge and grow, having a small granular center with layers of featherlike

299

structures. At 28 days, even though similar large microstructures were observed in all treatments

300

(i.e., static or dynamic, slow or fast cooling), more rounded clusters with small granular centers

301

and a large portion of featherlike structure layers were observed when cooling under static

302

conditions (figure 6H-J). On the other hand, under shear, more clusters of granular morphology

303

with a layer of small featherlike structures were observed (figure 6I).

304 305

At higher crystallization temperatures, 24 and 26 °C, similar microstructures can be observed

306

with or without shear and different cooling rates. During isothermal crystallization at 24 °C,

307

large differences in the microstructure relative to lower temperatures were observed (figure 7).

308

At 24 °C (5 °C/min statically), very small spherical crystals can be initially observed (figure 7A-

309

B). After 6 h of isothermal crystallization, small clusters of needle-like crystals continue growing

310

(figure 7C-F). Furthermore, areas of high crystalline concentration seem to result from the

311

continuous growth of the clusters of needle crystals to the point where they impinge into one

312

another (figure 7G). The appearance of large crystals with featherlike structures is also noted

313

(figure 7I-J). At 26 °C (figure 8), similar initial crystal structures (needle-like clusters) to that of


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24 °C can be observed (figure 8A-E). Between 1 and 3 days, with or without shear, respectively,

315

larger crystals were formed, with granular centers and featherlike structures emerging from their

316

centers (figure 8F-G). As time elapsed, these crystals continued to grow and reached sizes large

317

enough to be observed by the naked eye (figure 8H-L). For this reason, micrographs obtained at

318

a lower magnification were included (figure 8M-R).

319 320

Upon crystallization at 24 and 26 °C the β′-IV polymorph forms directly from the melt, rather

321

than via the α form, as for the case of 15 and 20 °C 15,21. At 24 and 26 °C, the initially observed

322

morphology is that of clustered, needle-like structures, whereas at 15 and 20 °C, a granular

323

morphology was observed. With time, the melting points of all samples increased as they

324

transformed to the stable β-V form. The β form has varied morphologies that range from granular

325

to needles, to crystal aggregates and then to very large microstructures with featherlike crystals

326

15

327

observed. However, it must be noted that regardless of the fact that the samples ended in the β

328

polymorphic forms, the microstructures created were highly dependent on the path followed to

329

get there (especially at lower temperatures). These microstructures will most probably have an

330

effect of eventual final product quality when incorporated into chocolate. Interestingly, these

331

changes were induced by affecting the mass and temperature transport properties of the CB melt

332

prior to actual crystallization.

. Changes in the microstructure can then be correlated with the polymorphic transformations

333 334

Microstructural characterization of the CB crystals during isothermal crystallization at different

335

temperatures shows that the processes applied during the early stages of nucleation affect initial



336

crystalline mass and transformation of small granular crystals to larger ones (higher and faster

337

transition with the application of shear especially at higher temperatures).

338 339 340

Chemical Composition of the Isolated Crystals

341

To determine whether differences exist in the composition of the crystals formed initially, the

342

fatty acid (FA) profile of native CB, along with those crystals isolated from the samples of CB

343

isothermally cooled at different crystallization temperatures, after treating CB to different shear

344

and cooling rate conditions.

345 346

The FA profile of native CB statically cooled from 60 to 28 °C at 0.1, 1 and 5 °C/min and then

347

isothermal at 20 °C for 5 min, are shown in table 2. Native CB used in this study, consists of

348

mainly palmitic (C16:0), stearic (C18:0), and oleic acid (C18:1), and smaller concentrations of

349

linoleic (C18:2) and arachidonic (C20:0), which corresponds well with levels found in the

350

literature. Comparing this FA profile with that of isolated crystalline materials obtained from

351

previously statically cooled CB, at different cooling rates, and then isothermally crystallized at

352

20 °C, no significant differences were observed (P

Effects of Shear and Cooling Rate on the Crystallization Behavior and

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