ABSTRACT

1
Effect of High Pressure Processing of Swiss
Cheese Starter Organisms on Growth, Free Amino
Acid Production and Aroma Formation in a Sterile
Slurry System N. Akin1, G. Y. Kim2 and W. James
Harper3 Selcuk University, Turkey1 Kangwon
National University, Korea2 The Ohio State
Unversity3
ABSTRACT
Figure 1. Effect of high pressure on the viable
numbers of Propionibacterium freundreichii and
Lactobacillus helveticus
The outgrowth of the Propionibacterium was
markedly affected by the HPP treatment. The
untreated organisms reached their highest numbers
after 14 days. Those treated at 200 MPa only
achieved a maximum of 2.1 x 10 5 after 14 days.
The growth of the Propionibacterium in the
culture treated at 500 and 800 MPa was
accelerated and reached maximum numbers in 8
days, showing a decline at 14 days. The
stimulation of growth was greater for those
treated at 800 MPa. At 5 days the numbers of
Propionibacterium was 1.5 x 108 and 2.5 x 108 for
samples treated at 500 and 800 MPa respectively.
There is no information at this time as to
whether the surviving organisms were a mutant
form, or whether the surviving organisms had
altered their growth characteristics. There is
need to know if all strains of the Lactobacillus
helveticus would show the same growth
characteristics
The slurries separated into three clusters.
Cluster 1 contained the control slurries at 6 and
14 days Cluster 2 contained all samples at 0
days and samples treated at 200 MPa for 6 and 14
days. The third cluster had the samples treated
at 500 and 800 MPa at both 6 and 14 days.
Lactobillus helveticus and
Propionibacterium freudenreichii in combination
were treated at 0, 200, 400 and 800 MPa in an
aqueous solution and then added to a sterile
slurry system pre-acidified to pH 5.6 with lactic
acid. The slurries were evaluated at 0, 2, 4, 6.
8, 10 and 14 days for growth in selective media,
free amino acid content and aroma differences
with an electronic nose using a Mass Spectrometer
as the sensor system.  Numbers of
Lactobacillus decreased by 3 and gt 4 log cycles
after treatment at 200, 500 and 800 MPa
respectively. Upon addition to the slurry, the
L. helveticus showed recovery after 2 and 4 days
for the organisms treated at 200, 500 and 800 MPa
respectively. A 4 log cycle increased was noted
after high pressure treatment in all cases. 
Numbers of Propionibacterium were not affected
by the high pressure treatment. The increase in
numbers after addition to the slurry system was
greater for those organisms treated at 500 and
800 MPa than the control or the sample treated at
200 Mpa.  Free amino acids values increased
during ripening at different rates depending upon
treatment of the starter organisms. The initial
rate of increase was greater during the first 6
days for the sample treated at 200 and 500 MPa,
whereas the high free amino acid content was in
the control after 14 days of incubation.
Treatment at 800 MPa resulted in a marked
reduction in free amino acid values.  Aroma,
as detected by the electronic nose, was different
among the slurries and each treatment showed a
different aroma pattern during the incubation
period. Treatment at 800 Mpa resulted in an
increase in the aroma components that
differentiated the treated sample from the
control.
Figure 6. Electronic nose mass abundance of
selected masses significant in differentiation of
aromas (in thousands)
Figure 4. Effect of HPP on free amino acids
during incubation (mMe1/kg of cheese)
Lactobacillus helveticus was reduced to lt10
organisms per gram after treatment at 500 and 800
MPa, whereas the Propionibacterium freundreichii
was not affected by treatment of 5 minutes at any
pressure.
INTRODUCTION
Figure 2. Effect of HPP on numbers of
Lactobacillus in slurries during incubation at 20
deg C (number in tens of thousands)
For the selected masses, the abundance of the
volatile compounds contributing to the masses
were greater for the organisms treated at 800 MPa
than for the control of other treated samples.
The reason for this apparent increase in the
selected aroma compounds remains to be determined.

CONCLUSIONS
OBJECTIVE
1. To determine the effect of high pressure
processing (HPP) on the growth and metabolism of
a Swiss Cheese starter culture combination when
added to a sterile slurry after treatment.
Free amino acids increased in all slurring during
the 14 day incubation period. For the first 8
days the increase was more rapid for the
organisms treated at 200 and 500 MPa, as compared
to the control. During this time period the rate
of free amino acid production was retarded for
the sample treated at 800 MPa. After 14 days,
the free amino acid concentration was highest in
the control and about the sample for the samples
treated at all pressures.
High pressure treatment of an aqueous solution of
a combination of Lactobacillus helveticus and
Propionibacterium freundenreichii resulted in
loss of viability of the lactobacillus, but no
change in the number of viable Propionibacterium.
Both organisms increased in nubers during
incubation at 30oC regardless of treatment.
Higher pressures appeared to alter the rate
outgrowth in a sterile slurry system, alter the
rate of production of free amino acids and
volatile compounds related to aroma.
PROCEDURES
The lactobacillus showed growth in the slurries
for all treatments.For all treatments, the the
lactobacillus showed increased growth in four
days and then a decline. For the samples treated
at 800 MPa, the growth at 4 days exceed the
untreated control, the 500 MPa treated samples
was about the same and growth was slowest for the
sample treated at 200 Mpa. At four days the
numbers of lactobacillus were 20 x 106, 23 x 106,
50 x 106 and 3 and 105 for the control and
samples treated at 200, 500 and 800 MPa
respectively
Lactobillus helveticus and Propionibacterium
freudenreichii were combined in an aqueous
suspension and given a high pressure processing
treatment of 0, 200, 500 and 800 Mpa for 10
minutes. These suspensions were added to a
sterile slurry (4), made from UHT milk and
adjusted to pH 5.5 with lactic acid, to provide
105 and 102 cells respectively. The slurries
were then incubated at 25 deg C. for 0, 2, 4, 6,
8, 10 and 14 days. Analyses were made for growth
after addition to the slurries (1,3) , free amino
acid production and aroma changes measured by an
electronic nose using head space sampling and a
mass spectrometer as the sensor system (2).
Figure 5. Cluster analysis for the aroma
profiles of all slurries as determined by the
electronic nose.
REFERENCES

• Baer, A, Ryba, I, Meyer J. and Butikofer, U
  1996. Lebbemsmitel Wissenschaft und Technol.
  2958-62
• Dave, R. I. And Shah, N. P. 1996 Evaluation of
  media for selective enumeration of Streptococcus
  thermomphilus and I Lactobacillus delbruekii spp.
  bulgaricus, Lactobacillus acidophilus, and
  Bifidobacteria. J. Dairy Sci. 791529-1536.
• 3. Drake, M.A., Gerard P. D., Kleinhenze, J. P
  and Harper, W. J. (2002) Application of an
  electronic nose to correlate with descriptive
  senssory analysis of Cheddar cheese.
  Lebbemsmitel Wissenschaft und Technol. 35
  Accepted for publication
• 4. Hettinga, D. H., Vedamuthu, E. R. and
  Reinbold, W. G. 1968. Pouch method for isolating
  and enumerating Propionibacteria. J. Dairy Sci.
  511707-1709.
• 5.  Roberts, M, Wijesundra, C., Bruinberg, D and
  Limsowtin, G. K. Y. 1995 Development of an
  aseptic cheese curd slurry system for cheese
  ripening studies. Australian J. Dairy Technol.
  50.66-69.
•  

Figure 3. Effect of HPP on numbers of
Propionibacterium in slurries during incubation
(numbers in thousands).

RESULTS
The effect of high pressure treatment for 5
minutes on the viable cell count for the
lactobacillus and Propionibacterium are shown in
Figure 1.
Department of Food Science and Technology, The
Ohio State University, Columbus, OH 43210