EFFECT OF SEASONAL VARIATION IN MILK COMPOSITION ON DAIRY FOULING

B. Bansal

1, B. Habib

1, H. Rebmann

1 and X. D. Chen

2

1 Fonterra Research Centre, Private Bag 11029, Dairy Farm Road, Palmerston North 4442, New Zealand

E-mail: bipan.bansal@fonterra.com 2 Department of Chemical Engineering, Monash University, PO Box 36, Clayton Victoria 3800, Australia

E-mail: dong.chen@eng.monash.edu.au

ABSTRACT

The composition of raw milk is one of the most

important variables that influence dairy fouling. In New

Zealand, the milk composition changes during a typical

milking season and can be linked to the weather cycle.

Along with the changes in the amount of total solids present

in the milk, the protein and fat concentrations also change as

the season progresses. This paper discusses different issues

associated with the seasonal variation in the milk

composition and how they influence dairy fouling during

thermal processing.

INTRODUCTION

In New Zealand, every litre of milk has to be heat

treated at least once and therefore, thermal efficiency of the

heating processes is of great importance in dairy processing.

Fouling is considered to have a major impact on the

performance of thermal equipment as it not only reduces

heat transfer, it also increases pressure drop – both

phenomena leading to increased processing costs.

Furthermore, the formation of biofilms – leading to

increased numbers of bacteria – can lead to the early

shutdown of the plant for cleaning.

Fonterra Co-operative Group Limited (FCGL) is the

leading dairy exporter in the world. Within New Zealand, it

processes around 14 billion litres of milk per year. Like

other dairy processors, FCGL aims to mitigate fouling in its

processing plants. The literature is replete with work aimed

at understanding the fouling process and developing

appropriate methods of reducing it. The majority of this

work has been done using reconstituted dairy fluids and

caution needs to be taken when referring to this work. The

reasons for this are:

� The fouling behaviour of recombined and

reconstituted milks is found to be significantly

different from that of fresh milk (Changani et al.,

1997; Joshi and Patel, 1986; Newstead et al., 1998;

Srichantra et al., 2006; Visser and Jeurnink, 1997).

� Also, depending on the processing history of the

dairy powders used and how they get dissolved, the

behaviour of the reconstituted milks may vary

significantly.

Various studies have been conducted using raw milk

but there are issues around the variation in milk composition

across the season. In addition, ageing of the milk may be

another issue that needs to be taken into account.

SEASONAL VARIATION IN MILK COMPOSITION

The composition of different components in milk

depends on a number of variables like cow breed, cow age,

lactation stage, type of feed, and climatic conditions. The

seasonal variation in milk composition is due to changes in

the stage of lactation as well as in the feed. Towards the

beginning and the end of the lactation period, the protein

and fat concentrations tend to be higher compared with the

middle period. However, the trend is opposite for lactose.

Cows in New Zealand are grass fed and the seasonal growth

of the grass is somewhat linked to the milk composition.

During the drought period, as happened in New Zealand last

year, the yield of milk per cow decreases and the amount of

solids-not-fat (SNF) present in the milk also decreases.

Table 1 shows the variation in the composition of raw milk

that was delivered to Fonterra Research Centre, Palmerston

North during February and April 2008. The milk

composition was determined using certified analytical

methods.

Table 1. Composition of raw milk delivered to Fonterra

Research Centre, Palmerston North during February and

April in 2008.

Time Protein

%

Fat

%

Lactose

%

Early Feb < 3.50 ~ 4.50 4.60 – 4.75

Mid April 3.75 – 4.00 5.75 – 6.00 4.30 – 4.60

It is well documented that seasonal variation in milk

has an impact on fouling (Belmar-Beiny et al., 1993;

Burton, 1967; de Jong, 1997; Tewari and Juneja, 2007). An

increase in the protein concentration is generally considered

to be the reason for an increase in fouling. Whey proteins,

which constitute around 5% of the milk solids, account for

more than half of the fouling deposits in type A fouling

(Bansal and Chen 2006). Of the two major whey proteins

present in milk, β-lactoglobulin and α-lactalbumin, β-

Proceedings of International Conference on Heat Exchanger Fouling and Cleaning VIII - 2009 (Peer-reviewed) June 14-19, 2009, Schladming, Austria Editors: H. Müller-Steinhagen, M.R. Malayeri and A.P. Watkinson

165

lactoglobulin is considered to be the dominant protein in

heat induced fouling (Bansal and Chen 2006).

RESULTS

Figure 1 shows the fouling trends from the trials that

were recently performed at Fonterra Research Centre.

These trials were performed using a pilot plant based

experimental setup. Commercially available plate heat

exchangers were used to process raw whole milk that was

delivered daily. Hot water was used as the heating fluid to

heat the milk up to 84°C. The holding time of milk was less

than 1 s. All the trials were performed under turbulent flow

conditions and limiting heat transfer resistance was always

on the milk side.

2000

2500

3000

3500

4000

4500

5000

0 1 2 3 4

Time (h)

Hea

t tr

ansfe

r coeffic

ien

t (W

/m²K

)

Trial A

Trial B

Trial C

Trial D

Fig. 1 Effect of milk composition on fouling (reduction in

heat transfer coefficient) in a commercially available

plate heat exchanger.

All these trials were performed under similar operating

conditions and the only variation was in milk composition as

shown in Table 2.

Table 2. Milk composition for four trials shown in Fig. 1.

Trial Protein

%

Fat

%

Lactose

%

Total

solids

%

A 3.62 5.13 4.71 13.93

B 3.91 5.28 4.64 14.25

C 3.49 4.48 4.38 12.98

D 3.53 3.96 4.58 12.66

Observing the heat transfer trend for Trial B in Fig. 1,

one would tend to believe that the maximum deterioration in

heat transfer performance is due to the fact that the milk

processed during this trial had the highest protein

concentration and total solids. However, this correlation

does not hold true for Trial A which has the least reduction

in performance even though it has higher protein

concentration and total solids than in Trials C and D. Trial

D performs better than Trial C even though the protein

concentration is slightly higher in Trial D. The

concentration of β-lactoglobulin is observed to be the same

in Trials C and D (around 0.29%). Note that Trial C has a

higher concentration of fat.

The compositional analysis of the corresponding

fouling deposits, most of which were collected from the

hotter region of the heat exchanger, also fails to show any

specific trends related to protein and fat concentrations and

total solids. The fouling deposits for Trial D had the highest

protein concentration (well above 50%). Also, the amount

of fat present in the deposits in Trial D was in fact lower

than that in Trial C.

These results clearly show that further work is required

to understand the effect of seasonal changes in protein and

fat concentration on fouling in heat exchangers. An

uncertainty in understanding the effect of milk composition

on fouling means that it may be necessary at times to

conduct a complete set of trials using the same batch of

milk. However, this requirement can lead to further

complications considering that it is not recommended to

hold milk for long periods of time. Holding milk for up to

24 h at 4°C is observed to cause less fouling but any further

aging leads to more fouling (Burton, 1968; Changani et al.,

1997; Lewis and Heppell, 2000). This can be attributed to

the action of proteolytic enzymes (Burton, 1968; de Jong,

1997). This problem can be alleviated to some extent by

conducting parallel trials.

CONCLUSIONS

1. The composition of milk is observed to change during

the season. However, no clear fouling trends were

observed due to seasonal changes in protein and fat

concentrations and total solids.

2. Reconstituted milks behave differently from fresh milk

and the use of fresh milk leads to ageing related issues.

It is possible to overcome both these problems by

conducting parallel trials using fresh milk.

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milk fouling in heat exchangers, Comprehensive Reviews in

Food Science and Food Safety, Vol. 5, pp. 27-33.

Belmar-Beiny, M. T., Gotham, S. M., Paterson, W. R.,

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Reynolds number and fluid temperature in whey protein

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Heat Exchanger Fouling and Cleaning VIII – 2009

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