Accepted Manuscript Size-based fractionation of native milk fat globules by two-stage centrifugal separation Pramesh Dhungana, Tuyen Truong, Martin Palmer, Nidhi Bansal, Bhesh Bhandari, ARC Dairy Innovation Hub PII: S1466-8564(16)30229-6 DOI: doi: 10.1016/j.ifset.2017.03.011 Reference: INNFOO 1732 To appear in: Innovative Food Science and Emerging Technologies Received date: 30 August 2016 Revised date: 21 March 2017 Accepted date: 21 March 2017 Please cite this article as: Pramesh Dhungana, Tuyen Truong, Martin Palmer, Nidhi Bansal, Bhesh Bhandari, ARC Dairy Innovation Hub , Size-based fractionation of native milk fat globules by two-stage centrifugal separation. The address for the corresponding author was captured as affiliation for all authors. Please check if appropriate. Innfoo(2017), doi: 10.1016/j.ifset.2017.03.011 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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Accepted Manuscript
Size-based fractionation of native milk fat globules by two-stagecentrifugal separation
To appear in: Innovative Food Science and Emerging Technologies
Received date: 30 August 2016Revised date: 21 March 2017Accepted date: 21 March 2017
Please cite this article as: Pramesh Dhungana, Tuyen Truong, Martin Palmer, NidhiBansal, Bhesh Bhandari, ARC Dairy Innovation Hub , Size-based fractionation of nativemilk fat globules by two-stage centrifugal separation. The address for the correspondingauthor was captured as affiliation for all authors. Please check if appropriate.Innfoo(2017), doi: 10.1016/j.ifset.2017.03.011
This is a PDF file of an unedited manuscript that has been accepted for publication. Asa service to our customers we are providing this early version of the manuscript. Themanuscript will undergo copyediting, typesetting, and review of the resulting proof beforeit is published in its final form. Please note that during the production process errors maybe discovered which could affect the content, and all legal disclaimers that apply to thejournal pertain.
Mean values not sharing the same letter are significantly different from each other at p<0.05.
In both fractions, the range of zeta potential values varied considerably from the zeta
potential recorded for the original milk used in this study (-12.5 to -13.00 mV). According to
Michalski, Michel, Sainmont, & Briard (2002), the effect of fat content (relative to the
content of casein micelles) on zeta potential values of milk and cream would not be
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significant over a fat content range of 10-500 g.kg-1
; however we observed significant
variation in zeta potential values of various Fraction 1 samples within this range. In our case,
the zeta potentials of the original milk and Cream 1 (Table 2) were very close to each other
but an increase in zeta potential was observed for Fraction 1. Since Fraction 1 was the
intermediate fraction between milk and Cream 1, and with a lower fat content than milk, it is
suggested that the higher zeta potential of Fraction 1 could be an effect of casein micelles.
Michalski et al.,(2002) have reported the zeta potential of skimmed milk (fat content 5g.kg-1
)
to be between that of milk (-13.2 mV) and the casein micelle (-20.1mV). In the case of
Fraction 2, which contains a higher large proportion of larger, more shear-sensitive fat
globules, compared to the original milk, the higher observed zeta potentials might be
associated with shear damage of the original globules, followed by partial incorporation of
casein micelles into the globular membrane. Michalski et al.,(2002) reported that shear
damage to milk fat globules can cause an increase in zeta potential value, up to around -
20mV in the case of homogenization.
3.2 Effect of temperature and flow rate on the second separation stage (Cream 1 and
Cream 2)
3.2.1 Fat globule size of Creams 1 and 2
During the second stage, each of Fraction 1 and Fraction 2, obtained from the first stage
separation, were further processed under standard cream separation conditions to yield Cream
1 and Cream 2, respectively.
The volume mean diameter of fat globules in Cream 1 (light cream; 31.750-65.00 % fat),
ranged from 3.47 µm (7°C, high feed rate) to 1.35 µm (35°C, low feed rate) and was found to
be affected significantly (p<0.05) by both temperature and feed rate (Table 1). Volume mean
diameter of Cream 1 decreased with increasing temperature and decreasing feed rate (Fig.3c)
and showed a similar trend to Fraction 1, from which Cream 1 was concentrated. Cream 1
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samples showed no sign of coalescence, regardless of temperature or feed rate (Fig.5). At
7°C, for the lowest feed rate, there was a slight shift of the particle size distribution to a
smaller D [4, 3] value (Fig.5a). However, Cream 1 obtained at 15°C was noticeably affected
by change in feed rate. Slower feed rate led to a shift of distribution to the left, indicating a
decrease in D [4, 3] (Fig.5b). Cream 1 obtained from Fraction 1 at 25°C and 35°C showed
both a narrowing of size distribution and a decrease in D [4, 3] at the lowest feed rate. For
Cream 1, the general trend was for mean globule size to decrease with increasing feed
temperature and decreasing feed rate.
Fig-5: Effect of feed temperature [ a) 7°C b) 15°C c) 25°C d) 35°C] and feed rate[ 1800mL/min
1200mL/min 600mL/min] on milk fat globule size distribution of Cream 1
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Cream 2, “heavy cream”, concentrated from Fraction 2, contained the highest proportion of
LFG (Fig.2). Among the studied combinations for the first stage fractionation, 25°C and
medium feed rate yielded heavy cream with the largest volume mean diameter (29.16 µm)
whereas the lowest value (4.15 µm) was obtained for cream prepared at 35°C and high feed
rate (Fig-3d). Statistical analysis showed that both the process parameters and their
interaction had a significant (p<0.05) effect on the D [4, 3] value of Cream 2. The results
revealed that the creams obtained at 25 °C had larger degree of coalescence than at other
temperatures (Fig.3d). The higher the D [4, 3] value, the greater will be the extent of possible
coalescence into voluminous globules. The descending order in term of extent of possible
coalescence for other temperatures was 15, 7, and 35°C. Cream 2 prepared at 35°C (high feed
rate) and 35°C (medium feed rate) did not show any sign of coalescence (Fig.5d). It is
suggested that the apparently greater susceptibility to coalescence of cream from first stage
fractionation at 25°C could be attributed to physical state of fat inside the fat globule. At
35°C and above, fat is mostly in the liquid state. In contrast, fat at lower temperatures around
5°C is mostly in the solid state. The fat at 25oC is in semisolid state, where the solid fat
component can destabilise the fat globule membrane while the liquid component will assist
with the liquid-liquid coalescence. These results are in accordance with the statement of
Towler (1994), that free fat formation during cream separation is minimum when separation
temperature is either below 10°C or above 35°C, within the normal working range.
On the per unit mass basis, SFG containing cream consists higher amount of health
improving factors (phospholipids and sphingolipids) than LFG cream (Lopez et al., 2011).
Since our method is able to give the conditions to get various creams with distinct differences
in mean globule size with majority of small fat globules, these creams could be used in some
specialized foods like infant food, stable whipped cream etc.
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3.2.2 Fat contents of Creams 1 and 2
Fat content of Cream 1 ranged from 63.83% (7°C, high feed rate) to 29.50% (35°C, high feed
rate) (Table-1). For Cream 1, fat content increased significantly (p<0.05) with decreasing in
temperature but showed no significant change in relation to feed rate (Table-1). Fat content of
Cream 2 varied between 83% (25°C, high feed rate) to 61.50% (35°C, high feed rate) (Table-
1). Fat content of Cream 2 decreased significantly (p<0.05) with increasing feed temperature
(Table-1), with no observed significant effects of feed rate (although low feed rate data are
missing). Since the fat contents of Fraction 2 at low feed rate at all temperatures were fairly
high, these streams were not subjected to a second separation. The aim of the current work
was to explore the sets of process variables and steps to get cream with the least degree of
coalescence as possible.
3.2.3 Zeta potential of Creams 1 and 2
Zeta potential of Cream 1 samples varied between -12.20 mV (15°C, medium feed rate) to -
14.50 mV (7°C, low feed rate) (Table 2).The effect of temperature and feed rate on zeta
potential of Cream1 was not significant (p>0.05) Generally, zeta potential gives indication of
surface modification of fat globules (Lopez et al., 2011). The independency of zeta potential
across the range of Cream 1 processing conditions indicates that there was no consistent
change in surface composition during two-stage separation process.
In Cream 2, zeta potential ranged from -11.57 mV (25°C, medium feed rate) to -15.38 mV
(7°C, high feed rate) (Table 2). Of the process variables investigated, only temperature
affected zeta potential of Cream2 significantly (p<0.05). Effect of temperature on zeta
potential of Cream 2 could be attributed to loss of integrity of fat globules during separation
at lower temperatures especially at 15 and 25°C (Table 2).
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4 General discussion
The current proposed method for fractionation of cream based on MFG size has shown some
promising results. A varying degree of throughput of both Fraction 1and Fraction 2 could be
obtained depending upon mean fat globule size requirement. This method is able to yield
cream having different mean globule size depending upon the temperature and feed rate
(Fig.2b). Fig.2b depicts the extent of fractionation. The small fat globules of Cream 1 from
every combination of temperature and feed rate in the first stage, which are concentrated
from Fraction 1, had sustained double mechanical stress while going through two stage
separation stages. These creams did not show any sign of coalescence as it could be seen in
Fig.5 that there is no extension of distribution plot beyond 15.54 µm. Similarly, among the
heavy creams, those obtained from first stage separation at 35°C (high and medium feed
rates) also did not show any sign of coalescence. In our preliminary trials, we noticed that
aging of the milk for more than a day after bottling resulted in some coalescence even in the
first separation stage. As discussed earlier, there was deposition of cream while doing the first
stage separation at lower temperature especially at 15°C and 7°C. Deposition was more and
more as feed rate was decreased. The deposition could be related to design of cream
separator, with respect to size of annular space between milk feeding tube and separating disc
for drum, orifice of cream outlet and rotational speed of separating disc. Despite such
conditions, our preliminary work revealed no noticeable change in fat globule size
distribution of Fraction1 for at least one minute of first stage separation, which confirmed
that the characteristics of Fraction 1 were independent of deposition over this short period.
The effect of deposited cream as component of Fraction 2 could be the reason for high degree
of coalescence in all the high fat fractions from separation done at 7°C and 15°C. Since this
study covered only the effect of temperature and feed rate, a further study would be required
to investigate the effects of the rotational speed of the cream separator, further modification
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of the cream separator or use of a cream separator compatible with low processing
temperatures, which may help to prevent MFG damage and coalescence.
. In addition to the alternative methods discussed earlier, the recent work of Edén et
al.(2016), has also shown the potential application of a modified cream separator for MFG
fractionation; however, they were only able to separate a small MFG fraction with a D [4, 3]
value differing by only 0.5 µm from that of the original milk. By contrast, the method
developed in the present study was able to yield creams without coalescence with a maximum
of 2.93 µm difference (35-LF Cream1 and 35-MF Cream 2) in their D [4, 3] values. The
difference between D [4, 3] values of cream having smallest mean MFG size and the mean
MFG size of conventionally separated cream was 2.61 µm (1.35 µm for 35-LF Cream1 vs
3.96 µm for conventionally separated cream).
5 Conclusion
A novel two-stage separation method was developed to fractionate milk/cream based on
mean MFG size. The size range achieved without coalescence and maintaining the integrity
of MFG was 1.35 – 4.28 m. The milk temperature and feed rate during first stage of
fractionation affected the mean MFG size considerably. This method performed very well at
35°C for all feed rates. There was greater damage to larger fat globules at lower temperatures.
Overall, increase in temperature decreased volume mean diameter of MFG. In contrast,
increase in feed rate increased the volume mean diameter. There was no sign of MFG
damage in Cream 1 obtained from each level of temperature and feed rate. With some further
development, given its high throughput, good separation efficiency and use of conventional
processing equipment, this method could provide the basis for a new industrial process to
generate fractionated milks and creams with contrasting physical functionality and nutritional
value, based on MFG size.
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Acknowledgments
This research was supported under Australian Research Council's Industrial Transformation
Research Hub (ITRH) funding scheme (IH120100005). The ARC Dairy Innovation Hub is a
collaboration between the University of Melbourne, the University of Queensland and Dairy
Innovation Australia Ltd (currently disbanded).
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Industrial Relevance:
The developed method has potential for size based fractionation of native fat globules in
industrial scale.
Highlights
Native MFGs have different Physicochemical properties with respect to their sizes
Fractionation of native MFGs on size basis
Fractionation would help to provide product specific creams/milk fractions
Size based fractionation of native MFGs is possible in industrial scale