Effect of fat globule size and addition of surfactants on whippability of native and homogenised dairy creams

Journal Pre-proof Effect of fat globule size and addition of surfactants on whippability of native and homogenised dairy creams Pramesh Dhungana, Tuyen Truong, Nidhi Bansal, Bhesh Bhandari PII:

S0958-6946(20)30041-8

DOI:

https://doi.org/10.1016/j.idairyj.2020.104671

Reference:

INDA 104671

To appear in:

International Dairy Journal

Received Date: 19 October 2019 Revised Date:

21 January 2020

Accepted Date: 29 January 2020

Please cite this article as: Dhungana, P., Truong, T., Bansal, N., Bhandari, B., Effect of fat globule size and addition of surfactants on whippability of native and homogenised dairy creams, International Dairy Journal, https://doi.org/10.1016/j.idairyj.2020.104671. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. 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. © 2020 Published by Elsevier Ltd.

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Effect of fat globule size and addition of surfactants on whippability of native and

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homogenised dairy creams

3 4 5 6 7 8

Pramesh Dhunganaa, Tuyen Truonga,b, Nidhi Bansala, Bhesh Bhandaria*

9 10 11 12 13 14 15 16

a

ARC Dairy Innovation Hub, School of Agriculture and Food Sciences, The University of

Queensland, St Lucia QLD-4072, Australia b

School of Science, RMIT University, Victoria-3001, Australia

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* Corresponding author. Tel.: +61 7 33469192

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E-mail address: [email protected] (B. Bhandari)

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__________________________________________________________________________

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ABSTRACT

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Fuctional properties of creams with mean fat globule sizes (D[4,3]) of 2.5, 4.3 and 4.8 µm for

29

freshly prepared native creams prepared by two-stage cream separation of whole milk and

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approximately 1.5, 2.5, 3.5 and 4.2 µm for homogenised creams prepared from market cream

31

were studied. Increase in fat globule size of freshly prepared native cream decreased the

32

whipping time (265 to 153 s) and overrun (118.8 to 102.2%). In contrast, in homogenised

33

cream, increase in average fat globule size increased the whipping time but decreased

34

overrun. In both native and homogenised creams, increase in fat globule size increased the

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storage and loss modulus. An increase in total protein (2.2 to 2.5%) in homogenised cream

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increased whipping time and overrun and decreased moduli. The addition of Tween 80 (0 to

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0.25%) decreased whipping time and overrun and increased the moduli in homogenised

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cream.

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___________________________________________________________________________

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1.

Introduction

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Whipping cream is a special variant of cream having an excellent capacity to form

43

foam. Whipped cream begins to form when the incorporated air bubbles become surrounded

44

by proteins at the initial stage of the whipping process. The average size of the incorporated

45

air bubbles decreases and bubble size distribution narrows as whipping progresses. This is

46

followed by a partial breakdown of the milk fat globule membrane and adsorption of fat

47

globules and spreading of liquid fat at the air-water interface, strengthening the three-

48

dimensional structure of air bubbles embedded predominantly in the network of partially

49

coalesced fat globules (Han et al., 2018; Hotrum, Stuart, van Vliet, Avino, & van Aken,

50

2005; Jakubczyk & Niranjan, 2006; Van Aken, 2001). Whippability of dairy creams is

51

typically assessed by measuring the whipping time, overrun, serum drainage and rheological

52

parameters. In general, whipped cream with shorter whipping time, relatively higher overrun,

53

and minimum serum drainage is thought to be ideal whipped cream.

54

Numerous studies have shown that there are various influential factors on the

55

whippability of dairy creams, such as composition, tempering of cream, and fat globule size,

56

etc. (Börjesson, Dejmek, Löfgren, Paulsson, & Glantz, 2015; Edén, Dejmek, Löfgren,

57

Paulsson, & Glantz, 2016; Moens, Masum, & Dewettinck, 2016; Phan, Moens, Le, Van der

58

Meeren, & Dewettinck, 2014). According to Van Aken (2001), the nature of the serum

59

affects the final properties of whipped cream. An increase in protein content in the serum

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phase of whipping cream resulted in an increase in whipping time, whereas an increase in

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ionic strength of the serum decreased whipping time (Börjesson et al., 2015). Loss of air

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bubbles followed by phase inversion of the whipped mass into butter grains happens if the

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whipping process is prolonged, resulting in lower overrun (Schmidt & Hooydonk, 1980).

64

Tempering of oil-in-water emulsion alters the crystal size and position within fat

65

droplets without affecting emulsion properties (Boode, Bisperink, & Walstra, 1991). It also

66

affects whipping properties depending upon the tempering temperature. Nguyen, Duong, and

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Vu (2015) reported that creams tempered at 20 and 30 °C before cooling to 4 °C had shorter

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whipping time than those tempered at 40 °C. Shorter whipping time is the indication of

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surface-mediated partial coalescence and tempering of cream at a temperature near to

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crystallisation temperature favour such event (Boode et al., 1991; Hotrum et al., 2005). A

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mid-level solid fat content, i.e., a minimum of 40% in whipping cream, is required to promote

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enough partial coalescence (Darling, 1982). High sterilisation intensity process (115 °C for

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20 min >139 °C for 7 s) decreased overrun and resulted in whipped cream with a denser

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network structure (Long, Zhao, Sun-Waterhouse, Lin, & Zhao, 2016), which could be due to

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the formation of the larger aggregate of denatured protein.

76

Incorporation of small molecule surfactants on protein stabilised emulsions and foams

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results in adverse effects on their physical stability; however, the extent of their influence on

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emulsion stability depends on their nature (Dickinson, Owusu, & Williams, 1993; Walstra,

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Wouters, & Geurts, 2005). Such surfactants displace the protein from the protein-stabilised

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fat globule interface. Most of the low molecular weight surfactants used in food preparation

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are non-ionic, and weaken the strong protein-protein interactions in protein-stabilised

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emulsions making them shear sensitive (Courthaudon, Dickinson, & Dalgleish, 1991a; Wilde,

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Mackie, Husband, Gunning, & Morris, 2004). Tween 60, a water-soluble small molecule

84

surfactant, was found to be more effective in displacing protein from the interface than oil-

85

soluble surfactants or monoglycerides (Pelan, Watts, Campbell, & Lips, 1997). Similarly,

86

Goff, Liboff, Jordan, and Kinsella (1987) reported a reduction in the number of casein

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micelles from fat globule membranes due to the addition of Tween 80 (polyoxyethylene

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sorbitan mono-oleate). Addition of small molecular weight emulsifiers such as a lactic acid

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ester of mono-glycerides and saturated mono-glycerides before emulsification displaced

90

sodium caseinate in 25% hydrogenated palm oil emulsion (Munk, Larsen, van den Berg,

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Knudsen, & Andersen, 2014). A recent study on the churnability of butter prepared from

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microfluidised native cream (D[3,2] of 0.6 µm) containing 2.5% protein (2% initial protein +

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0.5% added sodium caseinate), showed that the addition of Tween 80 caused a dramatic

94

reduction in butter-churning time from 32 min (no added Tween 80) to 4 min (with added

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Tween 80) (Panchal, Truong, Prakash, Bansal, & Bhandari, 2017). Therefore, a careful

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selection of low molecular weight surfactants may be used for controlled destabilisation (to

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promote partial coalescence) of the emulsion to control the formation and stability of

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whipped or aerated products (Munk et al., 2014). The size of native fat globules in bovine milk ranges from 0.5 to 20 µm. On the other

99 100

hand, churning time of cream dramatically increased from 3 to 32 min when average fat

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globule size of microfluidised cream decreased from 3.5 to 0.6 µm (Panchal et al., 2017).

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The fat globule size of dairy-based emulsions ranging from 0.2 µm to 1.2 µm was also shown

103

to influence whipping properties of the resultant emulsions (Truong, Bansal, & Bhandari,

104

2014).

105

There is scant published information on the effect of globule size on whipping

106

properties of native and homogenised cream. Edén et al. (2016) reported that a decrease in

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average milk fat globule size of native cream caused longer whipping times and less overrun.

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However, that study included globule sizes ranging from 4.0 to 4.9 µm only. Therefore, the

109

results may not be conclusive as this study did not include smaller fat globules (< 4 µm) that

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constitute a considerable proportion of total fat globules present in milk. A major challenge in

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such kind of research is the lack of effective methodology to fractionate native milk fat

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globules to obtain the desired size. One such method, among several other published

113

approaches (Edén et al., 2016; Goudédranche, Fauquant, & Maubois, 2000; Ma & Barbano,

114

2000; Olsson & Mamic, 2015), called two-stage centrifugal separation and developed in our

115

laboratory by Dhungana, Truong, Palmer, Bansal, and Bhandari (2017), is able to produce

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native cream with mean fat globule size ranging from 1.35 to 4.28 µm, without affecting the

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integrity of the fat globules. In our earlier study, it was found that smaller fat globules are

118

more heat stable than larger fat globules. It is thus crucial to understand the influence of a

119

wide range of fat globule sizes in native milk on the whipping properties of dairy creams.

120

This may present baseline information for the industrial manufacture of whipping cream with

121

better creaming stability and whipping properties. Microfluidisation, a variant of high-pressure homogenisation, has been used as an

122 123

alternative to the conventional homogenisation process (Hardham, Imison, & French, 2000;

124

Jafari, He, & Bhandari, 2006; McCarthy et al., 2016). High shear, cavitation, and impact

125

force of two streams during microfluidisation results in greater particle size reduction with

126

narrower size distribution (Jafari et al., 2006; McCarthy et al., 2016). Therefore, providing a

127

narrower size distribution, use of microfluidiser for emulsification can be considered as an

128

appropriate method for studying the effect of droplet sizes on properties of emulsion based

129

dairy products. This study aimed to elucidate the effect of fat globule size of native and homogenised

130 131

cream with or without variation in protein levels in serum and the addition of low molecular

132

weight surfactants on their whipping properties. The study employed two-stage centrifugal

133

separation to produce the globule size-differentiated native creams.

134 135

2.

Materials and methods

2.1.

Materials

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Fresh milk (4.2%, w/w, fat content) was purchased from the university dairy farm

139 140

(Gatton Campus, University of Queensland, Australia) and transported to the laboratory and

141

kept overnight at 4 °C in the cold room before separation. Market native cream (MNC) (40%,

142

w/w, fat content; 2.1%, w/w, protein; Parmalat Australia Pty Ltd., Brisbane, Queensland,

143

Australia) was purchased from a local market to produce homogenised cream (HC) with

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various average fat globule sizes. Sodium caseinate used in this study was purchased from

145

Murray Goulburn Co-op (Melbourne, Victoria, Australia).

146 147

2.2.

Sample preparation

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Each of the creams used in this study had 36 ± 0.3% (w/w) fat content. Fat and

150

protein contents of the homogenised creams were adjusted by mixing market native cream

151

(40%, w/w, fat content, 2.1%, w/w, protein content), sodium caseinate solution and water. In

152

case of fresh native cream (FNC), concentrated creams (~5%, w/w, fat) obtained after cream

153

separation were diluted with fresh skim milk.

154 155 156

2.2.1. Fresh native creams. A small scale commercial cream separator (11,500 rpm) modified according to

157

Dhungana et al. (2017) was used to undertake size-based fractionation of native milk fat

158

globules. The two-stage centrifugal process developed in our laboratory (Dhungana et al.,

159

2017) was used to prepare fresh native creams (FNC) with volume mean diameter D[4,3] of

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2.5 and 4.8 µm (termed FNC-2.5 and FNC-4.8, respectively) while that with D[4,3] of 4.3

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µm (FNC-4.3) was prepared from normal separation process.

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2.2.2. Homogenised cream.

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Microfluidisation of the MNC was done to prepare homogenised creams (HC) with

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four mean fat globule sizes. Total protein was varied in two levels (2.2 and 2.5%, w/w) for

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each fat globule size cream. Sodium caseinate solution of 15% (w/w) was used as the stock

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solution for adjusting protein content in the cream before microfluidisation. As shown in

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Table 1, creams with mean globule size ranging from 1.5 to 4.2 µm were prepared with

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protein contents ranging from 2.2 to 2.5% (w/w). At 2.2% total protein level, it was

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impossible to obtain homogenised cream with D[4,3] ~1.5 µm; therefore 0.1% protein

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(sodium caseinate) was added to the cream before microfluidisation which enabled us to

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produce homogenised cream having D[4,3] of 1.6 µm. On the other hand, 3.7 µm was the

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largest size cream that could be produced at 2.5% total protein level using the lowest possible

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operating pressure (9.6 MPa) of the microfluidiser (Model M-10 L, Microfluidics,

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Westwood, MA, USA). In addition to 2.2% and 2.5% protein containing MNC, an MNC with

176

1.9% protein content (MNC-1.9) was also included in experimental design. The MNC-1.9

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cream contains no added protein. It was prepared by diluting 40% (w/w) fat containing

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commercial market cream with water to make 36% (w/w) fat content. Since homogenised

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creams were prepared from MNC, whipping characteristics of homogenised and MNC will

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be discussed together. Details of mean globule size and protein content of the homogenised

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and MNCs are presented in Table 1.

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2.2.3. Tween 80 added homogenised cream.

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Homogenised cream with mean fat globule size of 1.1, 1.5, 2.5 µm and commercial

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native cream with 2.5% total protein were taken to study the effect of the addition of Tween

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80 on the whipping properties of the creams. Tween 80 concentration in the four treatments

187

was: 0.00%, 0.06%, 0.13% and 0.25%. The required amount of Tween 80 was added to the

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respective cream emulsion and was stirred at low speed for 30 min at 50 °C.

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2.3.

Experimental design

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Three sets of experiments are reported in this publication: Set 1, effect of native fat

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globule size on whipping properties of FNC; Set 2, effect of fat globule size and protein

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content on whipping properties of HC and MNC; Set 3, effect of fat globule size and added

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low molecular weight surfactant (Tween 80) on whipping properties of HC.

196 197

2.4.

Whipping properties

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2.4.1. Whipping time Each sample of cream was whipped at 5 °C in a cold room using an electrical kitchen

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whisker (Chef Titanium, Kenwood, China) set at 650 rpm. Whipping time was determined by

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monitoring the surge in the current while whipping. As whipping progresses, the electrical

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current drawn by the whipping device surges following an increase in foam stiffness and

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starts to decline on further whipping leading to the formation of butter grains (Börjesson et

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al., 2015). Therefore, the time taken to reach the maximum current was taken as whipping

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time and was expressed in seconds (s). To measure current flow, the whisker was connected

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to power through a digital power meter with a current measurement range from 0.01 to 10 A

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(Model No. PC222, Energy Cost Meter, Arelec, China).

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2.4.2. Serum drainage Whipped cream (50 ± 5 g), sampled when maximum foam stiffness reached, was

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placed on a sieve with a mess of 1 mm as described by van Lent, Le, Vanlerberghe, and Van

213

der Meeren (2008). Serum drainage was defined as a percentage (w/w) of serum loss from the

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whipped cream over 2 h at 25 °C. Serum drainage of each experimental replicate was

215

calculated as a mean of two measurements.

216 217 218

2.4.3. Overrun Each sample of cream was weighed in a 12.5 mL circular cup (12 mm height) before

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and after whipping. Overrun was expressed as a percentage change in the density of cream

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before and after whipping. The formula used is as follows:

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Overrun % =

× 100

(1)

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where ρ0 and ρw are the densities of cream before and after whipping respectively. Four

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measurements were done on each replicate.

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2.4.4. Rheological measurements The freshly prepared whipped cream was used to determine the linear viscoelastic

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region using a TA Rheometer ARG2 (TA Instruments UH Ltd., UK). A strain sweep test was

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carried out at 5 °C with strain from zero to 5% at 1 Hz frequency using 60 mm parallel

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stainless steel plate. The moduli were found to be independent of strain at 0.01% strain. A

230

time sweep test was carried out using the same steel plate at 5 °C, 0.01% strain and 1 Hz

231

frequency for 600 s. Comparison of Gʹ and Gʺ and loss tangent (Tanδ) among the cream

232

samples was done using respective values at 300 s. Each replicate was taken as an average of

233

two readings.

234 235 236

2.4.5. Microstructure of whipped cream The microstructure of some of the representative creams was analysed by confocal

237

laser scanning microscopy (CLSM) using a Zeiss LSM 700 confocal microscope (Carl Zeiss

238

Ltd. New South Wales 2113, Australia). Before whipping, a mixture of 0.02% (w/v) Nile Red

239

and fluorescein isothiocyanate (FITC) was added to whipping cream at 1 mL 100 g-1 cream to

240

stain fat and protein, respectively. Whipped creams were examined using a 63× magnification

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objective lens. FITC and Nile Red were excited at 555 nm and 488 nm with argon laser,

242

respectively.

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2.4.6. Measurement of cream fat globule size Average fat globule size of creams was examined using a particle size analyser

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(Malvern Mastersizer 2000, Malvern Instruments Ltd, Worcestershire, UK). Cream samples

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without dilution were added dropwise to the water (dispersant) to achieve laser obscuration

248

between 10 and 10.5%. The pump speed was kept constant at 2000 rpm. Refractive index

249

used for dispersant and dispersing material were 1.330 and 1.462, respectively. In this article,

250

mean size of fat droplets corresponds to volume mean diameter (D[4,3]).

251 252

2.5.

Statistical analysis

253

One- and two-way ANOVA and Tukey HSD tests were performed depending upon an

254 255

experimental design using Minitab 17 (Minitab Ltd., Coventry, UK) at 5% level of

256

significance. All graphs were prepared using SigmaPlot 13.0 software (Systat Software Inc.,

257

Chicago, Illinois). In this study, all mean values presented are the mean of triplicate

258

measures.

259 260

3.

Results and discussion

261 262 263

In this section, the results are presented in three sub-sections. In sub-section 3.1, the effect of native fat globule sizes on whipping properties of freshly prepared native cream are

264

presented. In the sub-section 3.2, the effect of fat globule size and protein content on

265

whipping properties of homogenised and market native creams are presented. Homogenised

266

creams were prepared from market native creams. Similarly, the effect of fat globule size and

267

addition of Tween 80 (low molecular weight surfactant) on the whipping properties of

268

homogenised and market native creams are presented in sub-section 3.3.

269 270

3.1.

Effect of native fat globule size on whipping properties of freshly prepared native

271

cream (FNC)

272 273 274

3.1.1. Whipping time Whipping time of the fresh native cream decreased significantly (p < 0.05) with an

275

increase in mean fat globule size (Fig. 1a). Average-whipping time of FNC-2.5, FNC-4.3 and

276

FNC-4.8 were 265.00 ± 5.00, 201.67 ± 7.64 and 153.00 ± 10.82 s, respectively. This trend is

277

in agreement with previous work of Edén et al. (2016). These authors reported a 47 ± 7%

278

reduction in whipping time when average fat globule size of native cream increased from 4.0

279

to 4.9 µm. Small fat globules are relatively more shear resistant than larger fat globules,

280

which is reflected in the longer whipping time for the smaller globules in our study.

281 282 283

3.1.2. Overrun Overrun of the fresh native cream (FNC) significantly (p < 0.05) increased with a

284

decrease in average milk fat globule size (Fig. 1b). Overrun was 118.81 ± 1.34, 108.87 ± 0.91

285

and 102.28 ± 2.74% for FNC-2.5, FNC-4.3 and FNC-4.8, respectively. This result is similar

286

to the results of overrun of homogenised creams at fixed protein content (described in section

287

3.2.2 of this paper). However, it is opposite to the results of Edén et al. (2016) where the size

288

range used was minimal, (only 4.1 to 4.9 µm). This range does not include the smaller fat

289

globules, which make up a considerable fraction of fat globules in bovine milk. The present

290

results reflect that the small fat globules help to entrap more air during whipping process.

291 292

3.1.3. Serum drainage

293

Serum drainage decreased slightly with an increase in average fat globule size (Fig.

294

1c), but there was no significant (p > 0.05) difference between the three creams tested. This

295

result is consistent with the study by Edén et al. (2016) and our result in protein added

296

homogenised creams with variable mean fat globule sizes (discussed later). In fact, the

297

differences in the absolute value of the serum drainage among all the creams studied were

298

relatively low (about 2%).

299 300 301

3.1.4. Rheological properties Storage modulus (Gʹ) values of each cream over the measurement period were always

302

higher (p < 0.05) than their loss modulus (Gʺ) values (Fig. 2a,b), which suggests an elastic

303

solid-like nature of the all the whipped creams tested. It was observed that fat globule size

304

significantly affected Gʹ, Gʺ but not Tanδ. Gʹ values increased significantly (p < 0.05) with an

305

increase in mean fat globule size from 2.5 to 4.3 µm. However, there was no significant

306

difference (p > 0.05) between the mean values of Gʹ of FNC-4.3 and FNC-4.8 (Fig. 2a). Since

307

FNC-4.3 and FNC-4.8 contained larger proportion of bigger fat globules than in the cream

308

FNC-2.5, breakdown of bigger fat globules resulted in the dense mass of whipped cream in

309

FNC-4.3 and FNC-4.8 leading to higher Gʹ and Gʺ than in FNC-2.5. Bigger fat globules are

310

more prone to shear-induced coalescence than the smaller one (Truong et al., 2015). In the

311

case of FNC-2.5, small fat globule cream, the intact small fat globules might have imparted

312

the whipped cream a more fluid-like consistency. This might be the reason for the higher

313

storage and loss modulus values for the larger fat globule creams.

Variation of Gʺ followed a similar trend to Gʹ (Fig. 2b). Despite being statistically not

314 315

different, average Tanδ values of the native creams increased slightly with an increase in

316

mean fat globule size (Fig. 2c). It is worthwhile to mention that the Tanδ value of whipped

317

creams from both fresh and aged native creams (MNC) were almost the same and were

318

significantly higher (p < 0.05) than the values for homogenised creams (described in section

319

3.2.4 of this paper). Therefore, it could be said that the native milk fat globule membrane can

320

significantly alter the rheological properties by tending to increase the plasticity of whipped

321

cream.

322 323

3.2.

Effect of fat globule size and protein content on whipping properties of homogenised

324

(HC) and market native cream (MNC)

325 326

3.2.1. Whipping time

327

Whipping time was the longest (715.66 ± 3.78 s) for HC-2.5-3.5 whereas the shortest

328

whipping time (60 ± 0.00 s) was found for MNC-1.9 (cream with no added protein) (Fig. 3a).

329

There were significant (p < 0.05) effects of average fat globule size, protein content and their

330

interaction term (fat globule size*protein content) on whipping time of homogenised creams.

331

Whipping time depends on the extent of partial coalescence of fat globules in whipping

332

cream (Hotrum et al., 2005). On the other hand, the development of partial coalescence is

333

influenced by the strength of the adsorbed emulsifier layer around the fat droplets. Strong

334

adsorbed layer, which forms under sufficient emulsifier concentration, does not favour

335

partial coalescence (Goff, 1997).

336

In this study, whipping time increased significantly (p < 0.05) with an increase in

337

average fat globule size from 2.5 to 4.2 µm and from 1.5 to 3.5 µm for creams with 2.2% and

338

2.5% total protein content, respectively (Fig. 3a). However, HC-2.3-1.6 and HC-2.5-3.7 did

339

not follow the same trend. HC-2.3-1.6, despite being the smallest among the 2.2-2.3% total

340

protein-containing creams, had longest whipping time. Similarly, HC-2.5-3.7 had the shortest

341

whipping time although it is the biggest sized cream among the homogenised creams with

342

2.5% total protein. As mentioned earlier, the production of HC-2.3-1.6 was not possible at

343

2.2% total protein. Therefore, the addition of an extra 0.1% sodium caseinate was required to

344

create a stable cream with 1.6 µm average fat globule size. The addition of extra protein might have improved the integrity of the interface;

345 346

therefore, HC-2.3-1.6 size cream became more resistant to whipping, reflected as the longest

347

whipping time among the 2.2-2.3% total protein-containing creams (Fig. 3a). Whipping time

348

was much shorter in the HC-2.5-3.7 than in the HC-2.5-3.5. A possible explanation for this

349

could be the use of lower pressure (9.7 MPa) to produce the HC-2.5-3.7 cream than for the

350

HC-2.5-3.5 cream (13.8 MPa). The homogenisation process involves the breakdown of

351

existing droplets followed by the creation of new droplets in the presence of an emulsifier. At

352

lower pressure, the shearing process in the microfluidiser might not disintegrate all the native

353

fat globules to create new protein-coated fat droplets thereby leaving some fractions as intact

354

native fat globules. In such circumstances, the resulting cream could have a higher proportion

355

of fat globules in the native state making homogenised cream very similar to native cream. In

356

support of this, the HC-2.5-3.7 cream had the shortest whipping time (232.33 ± 5.55 s)

357

among the homogenised creams and whipping time was near to MNC-2.5 (134 ± 11.5 s) (Fig.

358

3a).

359

Protein content of cream also affected whipping time significantly (p <0.05). Higher

360

protein content resulted in longer whipping time in HC-2.5-1.5, HC-2.5-2.5 and HC-2.5-3.5

361

creams (Fig. 3a). This result is also in agreement with results of Börjesson et al. (2015) where

362

an increase in protein content of cream increased whipping time significantly. Goff (1997)

363

suggested that the longer whipping time in UHT cream than in raw and pasteurised creams in

364

the study of Bruhn and Bruhn (1988), and the increased emulsion stability in denatured whey

365

protein added emulsion in the study of Britten, Giroux, Jean, and Rodrigue (1994), were due

366

to higher adsorption of protein in the droplet interface. Therefore, fat droplets with an

367

adequate amount of emulsifier on the interface would acquire maximum resistance to shear-

368

induced (Orthokinetic stability) coalescence. In this study, protein in the 2.5% protein

369

containing creams might have covered the droplet interfaces with more protein during

370

homogenisation, making them stronger than fat droplets in creams containing only 2.2%

371

protein. In addition, the added sodium cseiante, being flexible in nature, can cover the newly

372

formed globule surface effectively even at lower concentration than whey protein (Hunt &

373

Dalgleish, 1994). A weaker adsorbed layer in the fat droplet interface promotes partial

374

coalescence and decreases whipping time (Goff, 1997; Williams & Dickinson, 1995).

375

HC-2.2-4.2 cream had longer (p <0.05) whipping time (438 ± 18.68 s) than H-2.5-3.7

376

cream (232.3 ± 5.5 s) (Fig. 3a). The microfluidiser was operated at a higher pressure for HC-

377

2.2-4.2 than HC-2.5-3.7 cream; 22.1 MPa vs 9.7 MPa. Therefore, replacement of native

378

interfacial material might have happened in a larger extent in HC-2.2-4.2 than HC-2.5-3.7

379

cream. The former became a protein-stabilised emulsion whereas the later became partially

380

protein-stabilised with properties closer to that of native cream. A protein stabilised emulsion

381

has better orthokinetic stability than native cream emulsions, as shown by the differences in

382

their whipping time.

383

Although all market native creams (MNCs) demonstrated shorter whipping time than

384

homogenised creams, there were also differences in whipping time between protein-added

385

and not added MNCs. Protein-added market native creams had significantly (p < 0.05) longer

386

whipping time than protein not added cream (MNC-1.9) (Fig. 3a). The reasons might be the

387

effect of added protein as a barrier to partial coalescence development and/or partial

388

replacement of native interfacial material by added protein, making droplets more

389

orthokinetically stable. The overall result of whipping time agreed with the results of Panchal

390

et al. (2017), where there was a significant increase in butter-churning time in homogenised

391

creams than in un-homogenised cream, indicating a strengthened interface because of higher

392

protein adsorption in the homogenised cream.

393 394

3.2.2. Overrun

395

In the current study, HC-2.5-1.5 cream had the highest overrun (208.40 ± 3.98%)

396

whereas the lowest overrun (114.53 ± 5.05%) was found in MNC-1.9 (Fig. 3b). ANOVA

397

results indicated that fat globule size, protein content and their interaction term affected the

398

overrun significantly (p < 0.05). At each protein level, increase in average fat globule size of

399

homogenised creams decreased overrun of the whipped creams except for HC-2.5-3.7 cream

400

with 2.5% protein. This cream had similar overrun to that of protein-added native creams

401

(Fig. 3b). The reason could be that homogenisation did not modify the interface of the fat

402

globules extensively while preparing HC-2.5-3.7 cream making its nature similar to protein-

403

added native creams. An exceptionally high overrun (208.40 ± 3.98 %) of HC-2.5-1.5 cream

404

as compared with the remaining homogenised creams (109.27–140.57%) might indicate the

405

possibility of the cumulative influence of both fat globule size and protein content on

406

overrun. During the structural development of whipped cream, protein stabilises the initial

407

foam followed by the adsorption of fat globules on the foam interface (Brooker, Anderson, &

408

Andrews, 1986). Similarly, the presence of a sufficient number of smaller size droplets might

409

facilitate the formation of a smooth curvature and compact interface around the air cell in

410

whipped cream making the air cells relatively more stable than the air cells with protein only.

411

Therefore, within our design space, it could be said that the optimum condition for the

412

maximum overrun is a volume mean size of the fat globule of 1.5 µm; fat content of 36%;

413

and protein content of 2.5%. In addition, the poorer overrun of protein-not-added cream than

414

protein-added creams could be the influence of serum protein content of the emulsion on

415

overrun. Since no homogenisation was carried out after the addition of protein in MNC, the

416

added fraction remained in the serum phase. Therefore, the foam formed from added protein

417

might have increased the overall overrun of the protein added market cream.

418 419 420

3.2.3. Serum drainage Serum drainage corresponds to foam stability. Liquid drainage and gas

421

disproportionation happens when bubble coalescence and drainage of liquid from the lamella

422

film starts (Damodaran, 2005). In a whipped cream, minimum serum drainage implies that

423

the whipped structure is able to hold the incorporated air bubbles with minimum loss of its

424

mass. In the present study, serum drainage of homogenised creams ranged from 21.48 ±

425

4.42% for HC-2.5-1.5 cream to 0.69 ± 0.66% for MNC-1.9, respectively. Among the

426

homogenised and protein-added MNCs, a significant difference in serum drainage value was

427

observed between HC-2.5-1.5 and HC-2.5-3.5 creams. As shown in Fig. 3c, serum drainage

428

values of MNCs and MNC-1.9 were dramatically lower than all other creams tested. This

429

might be due to the effect of protein foam formed during whipping, which was later broken

430

down resulting in an increase in serum loss. In our study with freshly prepared native cream

431

described earlier, no trend of serum loss was found with mean fat globules of the creams.

432

Edén et al. (2016) also observed no statistical differences in serum drainage in whipped

433

cream prepared from native creams with different average fat globule size.

434 435 436 437

3.2.4. Rheological parameters Measurement of rheological properties in dynamic mode by the time sweep test revealed higher storage modulus (Gʹ) values than loss modulus values (Gʺ) in all types of

438

creams subjected to whipping process in this study (Fig. 4a–d). This rheological behaviour

439

(Gʹ > Gʺ) indicates a solid-like mass of whipped cream.

440

Tanδ value of all the whipped creams decreased, in addition, Gʹ value increased with

441

time indicating the whipped creams as elastic solids (Fig. 4e,f). Further, Gʺ increased only

442

slightly, which suggests no breakage of the structure of the whipped cream over the

443

measurement period. Such behaviour of the whipped creams had also been reported by Long

444

et al. (2016) in their study of whipped cream prepared from cream subjected to varying

445

sterilisation conditions and protein contents. Results showed a significant (p < 0.05%) effect

446

of average fat globule size, protein content and their interaction term (size*protein content)

447

on Gʹ, and Gʺ whipped cream.

448

The average Gʹ values obtained at 5 min ranged from 3.6 kPa (MNC-2.5) to 37.6 kPa

449

(H-2.2-4.2). As can be seen in Fig. 3d, Gʹ of the whipped cream increased with an increase in

450

the average size of fat globules between size range of 1.6 to 4.2 µm and 1.5 to 3.5 µm for

451

2.2% and 2.5% protein containing creams, respectively. In contrast to the increasing trend in

452

Gʹ values with an increase in fat globule size in the 2.5% protein containing creams, the Gʹ

453

value for the HC-2.5-3.7 cream was dramatically lower than the H-2.5-3.5 cream. Gʹ values

454

of protein added MNCs, HC-2.5-1.5, HC-2.5-2.5, and HC-2.5-3.7creams and HC-2.3-1.6

455

cream were not significantly (p < 0.05%) different from each other (Fig. 3d). The reason for

456

the similarity in the Gʹ values of the HC-2.5-3.7 cream and the protein added MNCs could be

457

that they had similar interfacial chemical makeup in their fat globules. However, the

458

relatively low Gʹ values of HC-2.5-1.5, HC-2.5-2.5 and HC-2.3-1.6 creams than that of the

459

protein-added MNCs, might be due to the higher proportion of smaller fat globules with a

460

robust globular interface. The fat globules of whipping creams with enhanced physical

461

stability favour the formation of whipped network with intact fat globules around the air cell.

462

This makes the movement of fat globules much easier than in whipped cream with air cell

463

surrounded by partially coalesced fat globules.

464

Variation in loss modulus (Gʺ) followed a similar trend as for Gʹ (Fig. 4d,e).

465

However, Gʹ and Gʺ decreased with an increase in protein content in each type of cream.

466

Similarly, the MNC with no added protein (MNC-1.9) had significantly high Gʹ and Gʺ

467

values than the protein added MNCs (Fig. 3d,e). These outcomes suggest that an excess of

468

protein in the serum phase may decrease the elasticity of whipped cream. Therefore, there is a

469

critical protein level to obtain a maximum elastic gel-like strength in the cream with same

470

average fat globule size.

471

Fat globule size, protein content and their interaction term (fat globule size* protein

472

content) significantly (p < 0.05) affected Tanδ, the ratio of Gʺ to Gʹ. Average Tanδ value

473

ranged from 0.16 to 2.6 for 2.2% total protein containing 1.6 µm cream and native cream,

474

respectively (Fig. 3f). A smaller Tanδ value signifies the elastic nature of viscoelastic

475

material (Long et al., 2016). In Fig. 3f, all the creams used in this study can be divided into

476

two clusters based on their Tanδ values. All the homogenised creams, except for the HC-2.5-

477

3.7 had significantly lower Tanδ values than MNC. This trend might be the result of surface

478

modification of fat globules during homogenisation.

479

As discussed earlier, the 3.7 µm cream was obtained at the lowest microfluidisation

480

pressure among all microfluidised creams. The processing conditions may have resulted in

481

only a small fraction of fat globules with protein-coated interfaces, leaving a larger fraction in

482

the native state. Therefore, 3.7 µm cream had a Tanδ value similar to that of native creams.

483

The predominantly protein interface on homogenised fat globules helps to form a network

484

with adjacent fat globules and serum protein, thereby making whipped cream relatively more

485

elastic than whipped cream made from native un-homogenised cream. In native cream, milk

486

fat globule membrane is predominantly phospholipids that may lack this network-forming

487

ability.

488 489

3.3.

Effect of fat globule size and added low molecular weight surfactant (Tween 80)

490

onwhipping properties of market native cream (MNC) and homogenised creams (HC)

491 492 493

3.3.1. Whipping time Whipping time ranged from 96 ± 5 (MNC-2.5 with 0.25% Tween 80) to 705.33 ±

494

15.50 s (H-2.5-1.5 cream). There was a significant (p < 0.05) effect of cream type, Tween 80

495

concentration and their interaction term on whipping time. Addition of a small molecule

496

surfactant such as Tween 80 in protein-stabilised emulsions replaces the protein from the

497

droplet interface, the rate and degree depending upon the concentrations of the surfactant and

498

protein (Courthaudon et al., 1991a).

499

Weak interaction favours partial coalescence and makes droplets more shear sensitive.

500

Complete replacement of interfacial protein occurs at high surfactant to protein ratio

501

(Courthaudon, Dickinson, Matsumura, & Williams, 1991b; Damodaran, 2005). Among the

502

creams without Tween 80, only native creams had significantly shorter whipping time than

503

all homogenised creams (Fig. 5a). Addition of Tween 80 to the homogenised creams

504

dramatically reduced whipping time, and there was further reduction in whipping time with

505

increase in Tween 80 concentration, in most cases. Hotrum et al. (2005) also reported a

506

decrease in whipping time of whey protein isolate and sodium caseinate stabilised emulsions

507

due to the addition of Tween 20 and Span 80.

508

The reduction in whipping time due to the addition of Tween 80, was cream type/size-

509

dependent. The whipping time of HC-2.5-1.1, HC-2.5-1.5, HC-2.5-2.5 and MNC-2.5 creams

510

were shortened by 64.1%, 46.1%, 49.1% and 20%, respectively when 0.06% (w/w) Tween 80

511

was added to each cream. Cream with 1.1 µm fat globule size was the smallest possible mean

512

size of fat globules among homogenised creams that can be obtained under our experimental

513

conditions using the cream with 2.5% total protein. For such cream, it could be assumed that

514

the maximum possible amount of protein from the serum had been utilised to create fat

515

globule membrane surfaces, leaving a large proportion of the fat globules with incomplete

516

coverage of protein. Therefore, the greater reduction in whipping time of HC-2.5-1.1 cream

517

at 0.06% (w/w) Tween 80 concentration than in the HC-2.5-1.5 and HC-2.5-2.5 creams,

518

could be a cumulative effect of weak membrane plus weakened membrane as a result of

519

protein replacement by Tween 80.

520

When 0.25% (w/w) Tween 80 was added to each cream, whipping time shortened by

521

71.2%, 70.2%, 58.2 and 28.4% for HC-2.5-1.1, HC-2.5-1.5, HC-2.5-2.5 and MNC-2.5

522

creams, respectively. In contrast to the whipping time of homogenised creams at 0.06%

523

(w/w) Tween 80, percentage reductions in whipping time of HC-2.5-1.1 and HC-2.5-1.5

524

creams were similar to each other at 0.25% (w/w) Tween 80 and were much higher than HC-

525

2.5-2.5 and MNC-2.5 creams. Since HC-2.5-2.5 cream being produced at a lower pressure

526

than that of HC-2.5-1.1 and HC-2.5-1.5 creams, there might be the chance that some of the

527

native fat globules especially smaller were still in native form even after homogenisation.

528

Otherwise, if the interfacial membrane was made up of protein only, there should be bigger

529

reduction in whipping time in HC-2.5-2.5 cream than HC-2.5-1.1 and HC-2.5-1.5 creams

530

since the ratio between Tween 80 and interfacial surface area is lower in HC-2.5-2.5 cream

531

than HC-2.5-1.1 and HC-2.5-1.5 creams.

532

Native fat globules contain a minimal quantity of proteins (mostly composed of

533

phospholipids) on their globular membrane. Therefore, destabilisation of the emulsion by

534

Tween 80 by replacing protein happens to a much smaller extent in native than homogenised

535

fat globules. As a result there was a much lesser and non-significant reduction in whipping

536

time of native creams with addition of Tween 80 at all concentrations. Overall, reduction in

537

whipping time from added Tween 80 was dependent on fat globule surface area and

538

membrane chemistry. Reduction in whipping time as a result of Tween 80 addition in our

539

study is in agreement with the report of Panchal et al. (2017) where there was a dramatic

540

decrease in churning time of sodium caseinate-added homogenised cream when Tween 80

541

was added to the emulsion. Whipping and churning processes imply the same method of

542

mechanical energy input.

543 544

3.3.2. Overrun Overrun of the whipped creams ranged from 91.98 ± 10.08% (HC-2.5-1.1 cream with

545 546

0.25% Tween 80) to 210.14 ± 1.65% (HC-2.5-1.5cream). There was a significant effect (p <

547

0.05) of fat globule size, Tween 80 concentration and their interaction on overrun. Overrun

548

decreased in each cream with an increase in Tween 80 concentration (Fig. 5b). This result is

549

in line with the findings of Hotrum et al. (2005). Small molecule surfactants like Tween 80

550

favours partial coalescence when added after emulsification (Munk et al., 2014). Therefore,

551

in contrast to creams with no added Tween 80, the whipped cream structure might have

552

developed via partial coalescence mediated phenomenon resulting in lesser overrun than with

553

Tween 80 cream. Increase in Tween 80 concentration proportionally replaces protein from

554

the interface resulting in a weaker interface. On whipping, the weaker interface is likely to

555

have facilitated the exposure of the dense crystallised fat to the serum, which might have

556

hindered air entrapment and resulted in poor overrun at the higher concentrations of Tween

557

80.

558 559

3.3.3. Serum drainage

560

In the present study, serum drainage of the whipped cream containing 0.06%, 0.13%,

561

and 0.25% Tween 80, ranged from 0% to 9.9% for HC-2.5-1.1 cream, 1.88 ± 1.03% to 15.45

562

± 0.75% for HC-2.5-1.5 cream, 0% to 12.53 ± 0.79% for HC-2.5-2.5 cream and 4.65 ± 0.34%

563

to 9.22 ± 2.16% for MNC-2.5 cream. Average serum drainage values for HC-2.5-1.1cream,

564

HC-2.5-1.5cream, HC-2.5-2.5 cream, and MNC-2.5 without Tween 80 were 14.47 ± 0.80%,

565

19.62 ± 1.70%, 19.66 ± 1.77% and 19.08 ± 2.31% respectively. Serum drainage of whipped

566

creams was significantly (p < 0.05) influenced by fat globule size, Tween 80 concentration

567

and their interaction term. An increase in average fat globule size of homogenised cream

568

from 1.1 to 1.5 µm increased serum drainage, with no further increase in cream with 2.5 µm

569

average fat globule size. In addition, there was an inverse relationship between Tween 80

570

concentration and serum drainage (Fig. 5c). The lower the serum drainage at a constant

571

temperature, the higher is the stability of whipped cream. Therefore, relatively stable

572

whipped cream with low overrun could be obtained by the addition of a suitable amount of

573

Tween 80 to the cream after homogenisation.

574 575 576

3.3.4. Rheological parameters The time sweep test of whipped cream always showed higher Gʹ than Gʺ at each

577

Tween 80 concentration in all types of creams studied (data not shown), indicating a solid

578

mass like nature of whipped cream. There was a significant effect of cream type, Tween 80

579

concentration and their interaction term on storage modulus (Gʹ), loss modulus (Gʺ) and

580

Tanδ. The Gʹ value ranged from 4290 to 72288 Pa for no Tween 80 and 0.25% Tween 80-

581

containing HC-2.5-1.1 cream, respectively.

582

The storage modulus of each cream increased steadily with an increase in Tween 80

583

concentration (Fig. 5d). This result is in agreement with the report of Munk et al. (2014)

584

where authors reported an increase in Gʹ when small molecular weight surfactants was added

585

to a sodium caseinate stabilised the emulsion. However, unlike homogenised creams, the

586

effect of the addition of Tween 80 was very nominal in MNC. This might be due to lower

587

interfacial protein to be replaced by Tween 80. A good negative correlation (r > –0.9) between serum drainage and Gʹ values of each

588 589

cream at different Tween 80 concentration indicated that the increase in Gʹ as a result of an

590

increase in the concentration of Tween 80 ensures more stable whipped cream. Variation in

591

loss modulus of as an effect of average fat globules sizes and Tween 80 concentration also

592

followed the trend of storage modulus variation (Fig. 5e). Different to the moduli, Tanδ was

593

significantly higher in MNC than in homogenised creams with Tween 80 (Fig. 5f). In

594

addition, an increase in Tween 80 concentration in MNC did not change Tanδ significantly (p

595

> 0.05). A higher value of Tanδ signifies plastic nature of whipped cream. Interestingly, the

596

Tanδ values of freshly prepared native creams, MNC-1.9, MNC-2.2, NMC-2.5 and NMC-2.5

597

with Tween 80 are similar to each other (Figs. 1f, 3f, 5f). This highlights the critical role of

598

interfacial chemistry on structural development in Tween 80 added whipped cream. In the

599

case of homogenised creams, Tanδ value decreased slightly with an increase in Tween 80

600

concentration (Fig. 5f).

601 602

3.4.

Microstructure of selected whipped creams

603 604

Fig 6 represents the confocal images of selected whipped creams from homogenised

605

and unhomogenised creams. Fig. 6a shows fat particles fully covering the numerous small air

606

cells. Complete coverage of the air cell by fat particles would prevent the air cell from

607

collapsing, thus this could be the reason that HC-2.5-1.5 had the highest overrun (208%).

608

Addition of Tween 80 caused significant change to the microstructure of whipped

609

cream. Although the air cells were perfectly covered by fat droplets in whipped cream

610

prepared from Tween 80 added (0.125%) HC-2.5-1.5, the presence of fat aggregates around

611

the air cells was significant than that of without Tween 80. Addition of Tween 80 not only

612

destabilises the emulsion but also replaces protein from the interface (Munk et al., 2014). The

613

dual action of Tween 80 could be the reason for whipped cream with well-covered air cell as

614

well as many fat aggregates. However, the air cells of the whipped cream prepared from HC-

615

2.5-3.5, did not have such fully covered boundary (Fig. 6c). The air cells were bigger as well.

616

The reason could be the presence of larger fat globules, which were not packed densely on

617

the air cell boundary. Besides, because of the presence of larger fat globules, coverage of the

618

air cell might not happen as swiftly as in whipped cream prepared from HC-2.5-1.5 leading to

619

larger cells.

620

Similarly, whipped cream from MNC-2.5 also had bigger air cells but was partially

621

covered by fat (Fig. 6d). In contrast to the images of whipped creams from homogenised

622

creams without Tween 80, significant amounts of fat aggregates were also visible in Fig 6d.

623

Similar images have been reported by Han et al. (2018) for market UHT cream with 35% fat

624

content. Much larger fat aggregates around the air cells were found in the whipped cream

625

prepared from MNC-1.9 (Fig. 6e). This could be due to the relatively limited amount of

626

protein available to assist in the segregation of fat aggregates as did occur in whipped creams

627

prepared from MNC-2.5.

628

Interestingly, green signal, which represents protein in Fig. 6, is weaker in images of

629

2.5% protein containing whipped creams ( Fig. 6a,b) than in images of 2.2% protein

630

containing whipped creams (Fig. 6c–e). The reason is: Presence of higher protein content was

631

sufficient to form numerous small fat globules. And, these fat globules did not break during

632

whipping. Therefore, in Fig. 6a,b more free fat globules were in the field (can be seen as red

633

dots) masking the green background. However, in case of Fig. 6c–e, an extensive breakdown

634

of the fat globules caused the formation of big fat clusters leaving much of field space

635

without fat globules. Therefore, green signal representing protein is much stronger in Fig. 6c–

636

e than in Fig. 6a,b.

637 638

4.

Conclusion

639

Analysis of whipping and rheological properties of the native and homogenised

640 641

creams with different fat globule size were performed. Increase in fat globule size of freshly

642

prepared native cream decreased overrun, whipping time, and serum drainage while increased

643

storage and loss modulus; however, an increase in size did not affect Tanδ. In the case of

644

homogenised cream, an increase in the size of fat globules increased whipping time, storage

645

modulus, and loss modulus and decreased overrun. Among the homogenised creams, the

646

highest overrun (~208%) was obtained from the cream with (D[4,3]) =1.5 µm.

647

An increase in protein content on homogenised and MNCs increased whipping time,

648

overrun, serum drainage and Tanδ, while decreased storage and loss modulus. Interestingly,

649

the Tanδ values of whipped cream from native creams were always higher than homogenised

650

cream and were almost independent of fat globule size and protein content indicating the

651

importance of the nature of fat globule’s interfacial material on the rheology of whipped

652

cream.

653

Addition of small molecule surfactant (Tween 80) on homogenised cream after

654

homogenisation reduced whipping time, overrun, serum drainage and Tanδ values and

655

increased storage modulus and loss modulus of whipped creams of all fat globule sizes In all

656

cases, except for Tween80-added creams, serum drainage values were high. Therefore, a

657

strategy to make whipped cream more stable might be the use of hydrocolloids. Since

658

whipping and rheological properties of whipped cream also depend on the properties of

659

interfacial materials, evaluation of the effects of other kinds of proteins, such as whey

660

protein, on the properties of whipped cream, might be a fruitful area for future study.

661 662

Acknowledgements

663 664

This research was supported under Australian Research Council's Industrial

665

Transformation Research Hub (ITRH) funding scheme (IH120100005). The ARC Dairy

666

Innovation Hub is a collaboration between the University of Melbourne, the University of

667

Queensland and Dairy Innovation Australia Ltd (currently disbanded).

668 669

References

670 671 672 673

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Edén, J., Dejmek, P., Löfgren, R., Paulsson, M., & Glantz, M. (2016). Native milk fat globule

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Figure legends

Fig. 1. Whipping and rheological parameters of fresh native cream with variable fat globule sizes: a, whipping time (s); b, overrun (%); c, serum drainage (%); d storage modulus (Gʹ); e, loss modulus (Gʺ); f, Tanδ. Error bars represent standard deviation.

Fig. 2. Rheological parameters (measured at 5 °C, 0.01% strain and 1 Hz frequency) of fresh native cream with 4.8 µm ( ), 4.3 µm (), and 2.5 µm ( ) mean fat globule sizes: a, storage modulus (Gʹ); b, loss modulus (Gʺ); c, Tanδ. Error bars represent standard deviation.

Fig. 3. Whipping and rheological parameters market native cream and homogenised cream with 2.2% (w/w) protein content ( ) and 2.5 % (w/w) protein content ( ): a, whipping time; b, overrun; c, serum drainage; d, storage modulus (Gʹ); e, loss modulus (Gʺ); f, Tanδ. Error bars represent standard deviation.

Fig. 4. Storage moduli (Gʹ; a and b), loss moduli (Gʺ; c and d) and Tanδ (e and f) (measured at 5 °C, 0.01% strain and 1 Hz frequency) of homogenised cream and market native cream (MNC) with 2.2% (w/w) protein content (a, c, e) and 2.5% (w/w) protein content (b, d, f): MNC-1.9; cream;

, ~1.5 µm cream; , protein added MNC;

, ~2.5 µm cream;

,

, ~3.5 µm

, ~4.2/3.7 µm cream. Error bars represent standard deviation.

Fig. 5. Whipping and rheological parameters of homogenised cream and market native cream with 0% ( ), 0.06% ( ), 0.125% ( ) and 0.25% ( ) Tween 80: a, whipping time (s); b,

overrun (%); c, serum drainage (%); d, storage modulus (Gʹ); e, loss modulus (Gʺ); and f, Tanδ. Error bars represent standard deviation.

Fig. 6. CLSM images of selected whipped creams: a, D[4,3] = 1.5 µm with 2.5% total protein; b, 0.125% Tween 80 added and D[4,3] = 1.5 µm with 2.5% total protein; c, D[4,3] = 3.5 µm with 2.5% total protein; d, unhomogenised market cream with 2.5% total protein; e, MNC-1.9. Red colour represents fat; green colour represents protein.

Table 1 Mean fat globule size and protein content of homogenised (HC) and market native creams (MNCs). a Cream

Average fat globule size (D[4,3]; µm) 1.6 2.5 3.5 4.2

Pressure (MPa)

Temperature (°C)

Total protein

Abbreviated name

62.1 62.1 34.5 22.1

43 43 43 30

2.3 2.2 2.2 2.2

HC-2.3-1.6 HC-2.2-2.5 HC-2.2-3.5 HC-2.2-4.5

2.5% total protein creams

1.1 1.5 2.5 3.5 3.7

62.1 41.36 20.7 13.8 9.7

43 43 43 43 30

2.5 2.5 2.5 2.5 2.5

HC-2.5-1.1 HC-2.5-1.5 HC-2.5-2.5 HC-2.5-3.5 HC-3.7-2.5

Market native cream Market native cream Market native cream

-

-

-

2.5 2.2 1.9

MNC-2.5 MNC-2.2 MNC-1.9

2.2% total protein creams

a

The 1.9% protein MNC contains no added protein; MNC with 40% (w/w) fat and 2.1%

protein content was used to prepare all the creams.

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6