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This is to certify that the

thesis entitled

Germicidal PrOperty of Milk as
Influenced by the Temperature

of Storage.

presented by

I". Mr. Harichand Dalaya

has been accepted towards fulfillment

of the requirements for

‘, I‘Ioso degree in Dairy

Date 1,831 26*,

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THE GERMICIDAL PROPERTY OF MILK AS
INFLUENCED BY THE TEMPERATURE OF STORAGE

HARICHAND MEGEA EMA

A THESIS
Submitted to the School of Graduate Studies of Michigan
state College of Agriculture and Applied Science
in partial fulfilment of the requirements
for the degree 0!
MASTER OF SCIENCE

Department of Dairy

1948

THESIS

 

ACUOVIEWMENTS

The author wishes to express his
gratitide to Dr.G.M. Trout,Department of Dairy and
Dr.A.L.Bortree Department of Bacteriology and
Public Health for their valuable guidance.

TABLE OF CONTENTS

 

 

 

 

Page No.
Introduction — _ ~¢ ~‘ A# _ 1
Review of literature -~----—~-----4---- 3
Experimental procedure —— — — 10
Results — — ———— —= ——— ——= 14
Discussion.— ——7— — —— ———=———— ——-- 24
Summary} — =— -—-==—— — — — — 25

 

Literature cited ---------------------- 26

INTRODUCTION

Many workers have regarded the germicidal
property of milk as being too feeble to be of much
importanceJ'his was the view-point when the search
was in progress for a substitution for
pasteurization of milk.Although the germicidal
property of milk cannot be relied upon for main-
taining thd safety of milk recent developments
in the milk industry and further work in the field
indicate that it may be of significance in
maintaining milk quality.Before the milk reaches
the milk plant in the present day milk industry it
has to stand sometimes for hours at farms or in
transport.During this time the germicidal pr0perty
of milk may best serve its purppse.Hence conditions
are ideal to make use of the germicidal property,
of milk to keep down the growth of microrganisms
during the period between milking and processing.
The final quality of milk often depends greatly
upon its initial handling.Milk with small
populations of microrganisms from the start is
generally superior in quality to the milk with
large numbers of microrganisms at the start even
though the number of microrganisms is much reduced

after processing.Also milk with a low number of
bacteria when delivered to the plant may mean an
additional income to the farmer by way of premiums.

Methods of preserving the germicidal
property of milk in all its effectiveness over
longer periods of time would fit in with this need
of the farmer and the milk industry in general.
Various studies on the germicidal property of
milk have shown that the temperature factor is the
most important one.‘1'he other factors are the pH of
the milk, the type or microrganisms,time of holding
and breed of cattle.The control of time and
temperature is well within the“ means of the farmer
and is of use in general.To this and studies

reported herein were made.

REVIEW OF LITERATURE

The germicidal property of raw milk
was first found by Fokker (1890) during his studies
on goats milk.Hunziker (1901)observed that the
number of bacteria might be reduced to one-tenth
by its action.Jones (1930)showed a way of extracting
the germicidal property which he called lactenin.

l-Tegperature and time relationship.
Most of the investigators found that at

lower temperatures the germicidal property of milk
lasted for a longer period of time but was of a
lesser intensity than at moderate temperatures and
also that it could be heat-destroyed.H1mziker(1901)
Heineman (1921) and Jones (1928) confirmed the
findings that the germicidal property was most
effective at 37°C.At this temperature it may last
from one to ten hours ,but on an average it lasted

for four to six hours.

Hunziker (1901) presented the following data:

 

1
1

 

 

: : Cooled : 70°F. , 50°F. 70°F. : 70°F.:
: :naturally : (No.0f :(No.of :for 5 hr: 4% hr.:
: Hours : No.0f : bact.) bact.) :then at :the8.at:
: : bact.) : : :50°F. : 50 . :
: : : : :(No.of :(No.0f :
: : : ;1_ abact.).i;Q§2£;L;
: cow- : : : : : :
: warm. : 5,055 : 5,055: 5,055 : 5,055 : 5,055 :
: after : : : : : :
: 3 hrs.: 8,545 : 4,280: 4,080 : : :
: after : : : : : :
: 4% hrs: 48,000 : 8,550: 5,760 : 5,100 : :
: after : : : : :- :
: gfhrs.:182,000 : 15,250: 5,982 : 4,570 : 6,580 :
: er : : : : : 3
: 9 hrs.: inn. : 180,000: 4,960 : 7,480 :19,500 :
: after : : : : : :

e
(D
O
O
O

:30 hrs, gogg, , cogg, 3&1,000 ,5 , I99,000
He noted that with.natural cooling there

was not only no decrease in the bacteria count but
as early as three hours the number of.microrganisms
increased very markedly.Vhen the milk was kept at
70°F. there was a slight decrease,while at 50°F.

the bactericidal action was decidedly more distinct.

Hunziker (1901) also showed the effect of heat on.the
germicidal property of milk.as noted by the data which
follow:

 

 

Number of Bacteria
: heated to :Eeaged to

 

 

    

     

1'. O. O. O. .0 O. O. O.

 

     

Hours nit heated : 212°F. :176 F. :
W:

:ke t atskegt at: egt at: at :ke t at: .a :

o o .OOF o O o

: cowawarm. : , 8 : : : : : :
:inoculated : : : 220: 220: 615: 615:
: after 5 hr : 7,494:10,526 : 514: 247: 5 ,715:1,760:
: after 6 hrs: 9,914:10,546 : 27,120: 510: 125, 000: 760:
: after 9 hrs: 56,000: 9,654 :100,000: 547: 960,000: 840:
: after 12 " :116,000:10,740 : inn. : 840: inn. :1,547:
5 after 15 u ; inn. :10,67441 : : 17.540:

 

These data show that germicidal action.in
milk exposed to 212°F. and to 176°F. for 20 and 40
minutes respectively had ceased completely.The inoculated
bacteria increased immediately after inoculation while
the inocula introduced into parallel samples which were
not subjected to heat and kept at exactly the same
temperatures suffered a decided dimunition in their
bacterial count.

Jones (1928) working on the germicidal
property of’mdlk reported that 60°C for 80 minutes of
boiling destroys this property.Milk.heated at 65°C. for
20 minutes and at 70°C for 15 minutes still retained its
inhibitory activities.

Hansen(1924) proposed that in view of this fact the
germicidal property is different from alexines as
they are much less heat resistant and are destroyed
at 75°C for 15 minutes.He thought it was in close
relation to oxidizing enzymes of milk.Rogers (1955)
found that fresh milk with an average count of
approximately 4,000 when held at 4.5°C showed
approximately the same count after 24 hours.At 10°C
the count was about 15,000 after 24 hours while at
15.5°c the average was about 1,500,000.3eineman(1921)
found that freezing seemed to have no destructive
influence upon the germicidal property of milk unless
the time factor entered.Hillard and Davis (1917)
showed that intermittent freezing of bacteria
exerted a more effective germicidal action than
continuous freezing due to the mechanical effect.The
reduction of counts was much less in milk and cream
than in pure water due to physical protection offered
to bacteria by. colloidal and solid matter in suspension.
The degree of cold below freezing was not a very
important factor in destruction of bacteria.There was
no critical temperature below freezing where the
germicidal effect was greatly accelerated.
Crystallization probably resulted in mechanical

crushing. .

Prayer (1952) proposed that cooling milk
immediately to 50°F. was fairly satisfactory even
when it was to be held overnight.Cooling morning
milk to 60°F.was never quite satisfactory even
tholgh it was cooled immediatelyJIost consistently
beneficial results were obtained by cooling milk
immediately to and holding at 40°F. or below.

2-The name of the. gemicidal property of milk.
Chambers (1920) was of the opinion that no

comon relationship between agglutination and
bacterial inhibition was noted ,except that both were
destroyed by heating the milk and its specificity

and reaction to heat suggest a serelogic origin.

Jones and Little (1927) in their experiment ruled

out agglutination by using the streptococcus for which
'milk is a poor agglutin.They further slid that if the
substance was of blood origin the inhibitory substance
should be greatly increased in the whey since with
rennet coagulation there was a considerable
concentration of blood proteins ,as seen by the blood
precipitin test of the whey.The view that the
substance may have been "alexinflfrom the blood was
not supported by their observations.The mixing of

fresh blood serum with a special medium containing
casein and lactose did not inhibit the growth of

the strdptococcus .They also disproved Hansen's(l924)
theory that bactericidal property of milk was closely
related to the oxidizing enzymes of milk and that it
depended upon the variation in the ration of the cow,
by conducting their experiment with the same feed all
through the year.

.5-The prgperties of the bactericigg substance in
milk. Jones (1928)noted the following characteristics:

a. Tmerature. Germicidal property was
destroyed at 60°C for 30 minutes or when boiled or
at 80°C or 90°C for two minutes.Milk heated at 65°C
for 20 minutes and at 70°C for 15 minutes still
retained its inhibitory activities.

b. Influence of age fl eggs of lactatigg.
The time and maximlm concentration of the substance
in the milk of young cows might be as great as in
older cows .The inhibitory substance was present in
colostrum of the first day was not quite as effective
as it'w‘as in the milk obtained a few days later.

c. Quarters In their experiment the milk
from the right half of the udder contained more
principle than that from the left half but the
difference was very little.

6.. Reactivation Addition of active milk
to inactivated milk showed only a slight degree of
inhibitory effect.

e. Filterabilitx Whey obtained by
coagulation with rennet contained the the inhibitory
substancethen this whey was filtered through a
Berhefeld Candle almost all the inhibitory substance
was removed.

1'. Adsorbentg A considerable portion of
the inhibitory substance of raw milk was taken out
by animal charcoal.

g. Degsication When dried in vacuo over
sulfuric acid in a refrigerator,the milk or whey
showed that the inhibitory substance would with-
stand druing.Some of the commercially dried milk
powders showed inhibitory properties to a greater
extent but the concentration of this substance
was not the same as the original milk.Alcohol
extraction destroyed the substance.

-10..

EXPERIMENTAL PROCEDURE

The reduction in bacterial population in
milk was used as a criterion of the existence of
the germicidal property.The bacterial population
was determined by the standard plate count method.
This consisted in plating milk or its dilutions
in sterile water,into standard plates.The standard
tryptone-glucose-extract—milk agar with the
following composition was used:

Composition
Agar,best quality,not oven dried.....l.5 percent
Beef extract.........................0.5 N_
Tryptone.............................0.5 "
Glucose..............................0.l "
Distilled water

Reaction pH 6.6 to 7.0

Preferred reaction pH 7.0

One percent sterile skim milk was added
Just before plating.This is a modification over
the standard method wherein skim milk was added
just before final sterilization.No sterile skim
milk was added for dilution 1:10 or lower.

The plates after the solidification were
inverted and incubated at 57°C for 48 hours.

Colony counts were made with 3. Quebec colomr counter.
Plates having celery counts between 50 and 500 were
considered for compilation of the data.

The samples were collected from cows in
the Michigan State College Dairy herd.The milk
samples were collected in sterile Erlenmeyer flasks
from the milking machines.The flasks were carried
in a vacuum Jug to prevent change of temperature.
The lapse of time between milking and first plating
(called the zero hour reading)varied from 15 to 20
minutes.

Two organisms were used for simulating
conditions of heavy contamination by coliforms and
pathogens.The organisms used were Escherichia £91.;
and Staphylococcus m.Twenty—four hour culture (in
F.D.A.broth(Food and Drug Administration) incubation
temperature being 57°C ,was used for inoculation.The
inoculum used was at the rate of 0.1 m1.per 100 ml.
of milk.

Detailed procedure was different in parts
of the study as shown in the following:

-12..

W: In this experiment the effect of

the temperature upon the growth curve of the
inoculated milk was determined.The sample was
collected as above and then one portion was
inoculated and plated ,while the other portion

was plated as such.The inoculated,as well as the
uninoculated milk was divided into three parts

and kept at three different temperatures ,that is,
40°F.,60°F.,and 80°F.D11utions of the milk held

at each temperature were plated again after one
hour,two hours,four hours ,eight hours ,eighteen
hours , twenty-four hours and every twenty-four
hours until one hundred and twenty hours were
completed or until the milk curdled.

Table No.2: In this experiment, instead of

keeping milk immediately at storage temperature

of 40°F.,60°F. and 80°F. coolim was delayed for
two hours at room temperature.The rest of the
procedure was the same as the above.

Table No, : The milk sample was collected as before
and one portion was inoculated and plated while the
other was plated as such.After this each of these
portions were divided into three parts and kept at
the temperatures of 40°F. ,60°F. and 80°F". for a

-15..

period of ten hours.After ten hours plates were
made for the six samples and then all samples
were held at 70°F. After this they were plated
at intervals of 2,4,8,l2,25 hours and after this
every 24 hours for 1.20 hours or until the milk
coagulated.

Table No.4: In this experiment the same procedure
as in Experiment three was followed except that
the cooling was delayed at room temperature for
two hours before it was kept at storage temperatures
of 40°F.,60° F. and 80°F. for eight hours.

_ 14 ..
RESULTS

The influence of coolgg upon the germicidal
properly 0 milk.

Four to five trials were run on the
milk of two cows to ascertain the effect of
cooling the milk to various temperatures on the
inhibition of growth of the bacteria present.The
data are included in Tables 1 and 2,Part l.Here
it will be noted that the germicidal property of
milk is effective for less than four hours,when
the milk is cooled to 80°F.Ilhen the milk is
cooled immediately to and held at 60°F.the
germicidal effect is extended to 18 hours or
longer.0n the other hand when the milk was cooled
imediately to 40°F.,it.appeared that the germicidal
property maintained its action for at least 48
hours.Some variations in the data occurred :however ,
the data would seem to indicate clearly that an
inhibitive effect on bacterial growth exists and
its influence extended over a longer period when
the milk is cooled immediately to 40°F.

-15...

The influence or the gelmicidalfieffect on bactgpigl
growth when the milk is contaminated.

The samples of milk,data of which were
reported on Part l,Table l and 2,were inoculated
with E, coli and Staph, aureus to ascertain the
effect of the natural germicidal property of milk
upon the growth of contaminating bacteria.The data
are presented in Tables I and II,part 2,and 5.
Again the data seem to indicate that the germicidal
property of milk was prolonged when the milk was
cooled immediately and held to a low temperature.
In fact,the germicidal effect was more marked in
the inoculated milk than in that milk containing
the organisms present when the milk was first drawn
from-the udder.The effect seemed to be greater of
W than on 3.2.9921 at low temperatures.
This may be due to the fact that the optimum
temperature for the favorable growth of W
is 57°C (98.BBOF.)while M grows well beWeen
10°C (50°F.)and 45°C (115°F.)

-16...

Destruction of organisms in.uninoculated and
inoculated milk.

 

Bacterial
destruction
Num er :Percent

Baoteria count at

Ten mpgrature :0 hours* :2“hours*

: O
.3_

UNINOCULATED
80 :180,000 57,000 :145,000:

L. t. .. .. ..

 

 

 

 

 

 

: : 80 :
: 60 :180,000 : 56,000 :144,000: 80 :
; 40 :620,000 5170.000 13450.000' 62 1
gINOCULATED VITH E,co i 0
: 80 :l,400,000:425,050 :420, 000 75 :
: 60 :1,400,000:770,000 :650, 000: 45 :
° 40 :1 400 000:580,000 :820:000: 58 :
:INogngTED: WITH STAPH. aureus '
: 0 ,00: 550, 000 :750, 555: 68 :
: 60 :1,100,000: 570,000 ”750 000: 66 :

 

. 4O '1 100 000: 250 000 '870,000: 79
m only.

From comparisons of the non-inoculated
and inoculated milk it appeared that although the
number of organisms destroyed was greater in the
case of inoculated milk the percentage of destruction
was more in the case of uninoculated milk.

When samples inoculated "1th.§§229a aureus
were held at 40°F. the percentage of destruction
as well as the total number of organisms destroyed
was greater than.in the case of the uninoculated
milk.This may be due to the fact that the milk
‘was being held at a temperature which was almost
60°F. below the optimum.temperature for the
organisms

-17..

The luence of the tem erature of cool u on

its germicidal ppopgrpz when the cooled milk wag
warmed to a favorable growth temperature after
10 hourg gtorgge.

Several trials were run on milk cooled

 

to 80°,60°,and 40°F. and after 10 hours storage

at those temperatures was held at 70°F.to determine
if the germicidal property persisted and was
sufficiently strong to inlmbit subsequent bacterial
growth.The data are presented in Table 5.Here it
will be noted that when the milk was cooled to
40°F. immediately after being drawn from the udder
that the germicidal property was maintained and

was effective in inhibiting bacterial growth for

at least 4 hours after having been warmed to favorable
growth temperature.Although the germicidal property
of milk was still present when the milk was cooled
and held at 60°F.,its inhibitive action was not so
prolonged when the milk was warmed after 10 hours
storage at favorable growth temperature.Also,when
milk was cooled and held to 80°F.then tempered to
70°F.after 10 hours storage,no germicidal activity
whatsoever wax evident.Likewise when the milk was
contaminated with E,coli and gag, aureg 10 hours
after cooling and the milk allowed to warm to

-18....

favorable growth temperature ,some germicidal
property existed in that milk cooled and stored

at 40°and 60°F. From the data obtained it appears
therefore that adequate and prompt cooling of milk
stored 10 hours might warm up in transit without
an appreciable increase in bacteria population,if
the milk is delivered with two to four hours after

warming up.
The effect of a delay in cooling milk upon its
germicidal promrpy.

Two trials were run on fresh milk to
ascertain the effect of a two-hour delay in
cooling the milk upon its germicidal preperty.

The data are included in Table 4.Here it will be
‘hoted again that the germicidal property of milk

is present when the milk is cooled finally to 40°
and 60°F. respectively after a two-hour delay
following production.Bowever , the germicidal

property did not seem to be present when the milk
was cooled only to 80°F.The effect of the germicidal
property was noticed particularly when the milk was
warmed to a favorable growth temperature after

lO-hour storage.The germicidal property still

-19...

persisted at 40°F.,was less at 60°F. and did
not exist at 80°F.Even when the milk was
contaminated with W and Staph, aurep§,the
germicidal effect was apparent at 40°F.

- 20 -

Table I. The influence of the
germicidal action of

m.erature of coplipg upon the

(Guernsey cow No.57.)

 

 

 

 

 

 

 

 

 

    
   

 

 

 
 

{Bacteria per m1.hy standard plate count when.milk was :

:cooled immediately to and held at temperatures :

,indicated, p: g__:
:(hours :No.cf : : : o :No.o?;? :
: ~trials- 80°F °trialg: 60 F. :trials: 40°F. :
- Part 1 NONINOCULATED MILK _J; :
: O : 4 180,000: 4 : 180,000: 4 : 620,000:
: 2 : 4 : 57,000: 4 : 56,000: 4 : 170,000:
: 4 : 4 : 64,000: 4 : 71,000: 4 : 240,000:
: 8 : 4 : 550,000: 4 : 55,000: 4 : 500,000:
: 18 : 2 : 85,000,000: 5 : 270,000: 4 : 470,000.
: 24 : 2 : ,400,000,000: 5 : 140,000: 4 : 670,000:
: 48 : : oagulated : 2 : 160,000: 4 : 520,000:
: 72 ': : : 2 : 520,000: 4 : 760,000:
: 93 : : : 2 : 25,000,000: 4 :l,2gg,000:
; 12 : E : l :250,009,000: 4 :1,4 QQOOQ
-Part INO TED WITH E co 1 AT HOUR ‘pr ,__:
'é' "'0" :""4"' : 1,4001%, :"4 : 1,400,001)? 4 :1,400,000:
: 2 : 4 : 420,000: 4 : 770,000: 4 : 580,000:
: 4 : 4 : 400,000: 4 : 1,100,000: 4 : 510,000:
: 8 : 4 : 5,500,000: 4 : 670,000: 4 : 550,000:
: 18 : l : 200,000,000: 5 : 10,000,000: 4 :5,800,000:
: 24 : l : 200,009,000: 5 : 900,000: 4 :1,200,000:
: 48 : : oagulated : 2 : 55,000,000: 4 :5,000,000:
: 72 : : : 2 :980,000,000: 4 :5,900,000:
: 96 : : : l :540,000,000: 4 :17000,000:
; 120 g : : l 1:750,000,000: 4 :9s5005000:
- art 5. INOCULATED WITH ta 8 T O OURi :
: : 4 : , , : : , , : 4 :1,100,000:
: 2 : 4 : 550,000: 4 : 570,000: 4 : 250,000:
: 4 : 4 : 620,000: 4 : 770,000: 4 : 690,000:
: 8 : 4 : 12,000,000: 4 : 440,000: 4 : 510,000:
: 18 : 1 : 270,000,000: 5 : 1,100,000: 4 : 250,000:
: 24 : 1 :7,400,000,000: 5 : 1,500,000: 4 : 410,000:
: 48 : : coagulated : 2 : 1,100,000: 4 : 1,200000:
: 72 : : : 2 : 55,000,000: 4 : 560,000:
: 96 : : : 2 :100,000,000: 4 : 740,000:
g 120 pig 3 : 1 :750,000,000: 5 :2,900,000:

Table II

   

   

action of milk.

_ - 21 -
The effect of del

in cool
ersey cow No.145)

upon the germicidal

 

§eo§

m

 

otrials:

teria perfiml.hy igandard plate count when there
1

 

 
   

 

   
  
 

 

 

 

  

 

 

,ggpt , INCCULATED Mlpg
: 5 : , : 5 : 2,000: 5 : ‘2,000:
: 2 : 5 : 1,700: 5 : 1,900: 5 : 1,800:
: 4 : 5 : 15,600: 5 : 5,700: 5 : 1,500:
: 8 : 5 : 150,000: 5 : 47,000: 5 : 1,800:
: 18 : 5 : 59,000,000: 5 : 58,000: 5 : 29,000:
: 24 : 4 : 260,000,000: 5 : 280,000: 5 : 220,000:
: 48 : 5 : 1,800,000,000: 5 : 51, 000,000: 5 : 22,000:
: 72 : 2 :18,000,000,000: 5 : 180,000,000: 5 : 25,000:
: 96 : : coagulated : 5 : 270, 000, 000: 5 : 48,000:
' .’0 ' ' 5 :1 1001000: 000: 4 ; §5,000§
: 0 : 4 : 9 4 : ,00 ° 4 : 250_000:
: 2 : 4 : 770,000: 4 : 720,000: 4 : 480,000:
: 4 : 4 : 2,100, 000: 4 : 2, 200, 000: 4 : 660, 000:
: 8 : 4 : 12,000,000: 4 : 1,000, 000: 4 : 520,000:
: 18 : 4 : 510,000,000: 4 : 4,700,000: 4 :1400,000:
: 24 : 4 :29,000,000,000: 4 : 220,000,000: 4 : 870, 000:
: 48 : 2 : 2,800,000,000: 4 : 110,000,000: 4 :1500, 000:
: 72 : 2 : 5,400,000,000: 4 : 670,000,000: 4 :2800,000:
: 9g : : coagulated : 4 : 520,000,000: 4 :2580,000:
’ ° : : 2 :1 700 000 000: 5 : 6 0,000:
- 'armW ' av. aur :AT 0 .Ofifi :
: ' : 5 : 5 0,000: : 570,000: : 5 0,000:
:- 2 : 5 : 270,000: 5 : 270,000: 5 : 260,000:
: 4 : 5 : 540,000: 5 : 520,000: 5 : 500,000:
: 8 : 5 : 1,400,000: 5 : 500,000: 5 : 410,000:
: 18 : 5 : 110,000,000: 5 : 470,000: 5 : 290,000:
: 24 : : coagulated : 5 : 1,700,000: 5 : 510,000:
: 48 : : : 5 : 61,000,000: 5 : 570,000:
: 72 : : : 5 : 470,000,000: 5 : 550,000:
: 96 : : : 5 : 100,000, 000: 5 : 570,000:
' : a : 2 :

#129

 

1,
2 §O0,000,000: 2 ; 260,000:

- 22 -

Tabla 1;; The effect of the temperature of cooling milk
upon bacterial growth when the cooled milk was
warmed after ten hours storage to a favorable
growth temperature(70°F.)(Guernsey cow No.57)

 

TIE; :Eacteria per ml.by standard’plate count when the miIE

L. ..

 

 

In
I.

after °was warmed to 70°F.a§ter ten hours atorage at:
il‘ ::‘0.o : :No.o : :No.o

 

 

 

 

 

 

 

 

 

: he s - rialo- 80°_ - i=1 ~ 60°F otrial-- 40°_ :
:2333lfllflflhfiflfllg ’! 'iik :
: 0 : 4 : 51,000: 4 : 51,000: 4 : 51,000:
: 10 : 4 : 180,900,000: 4 : 150,000: 4 : ,_50,000:
:T e : :
:after : :
:warming: 3
: hour _: :
: : 4 :5", 600' W“, 000, : 4 : “0,00 , 4 : W:
: 4 : 3 : 560,000,000: 4 : 2,500,000: 4 : 77,000:
: 8 : :coagulated : 5 : 45,000,000: 4 : 600,000:
: 12 : : : 5 :510,000,000: 5 :120009000:
: 24 O O O :

- r

, coagulated: :_coag.
,Ea E 2;:EOCULATED WITH E coli
T :Bacteria per m1.§y standard plate count when.the milkfi
after :was warmed to 70 F.after ten hours storage at:
:No 0? ° :No.o : - :No.cf :

80o °trials: 60°F.

 

 

    
    

40°F.

   
  

  
   

   
   

 

 

 

 

 

0 : 4 : 40,000: : , . : 7 ,000:

%O 3 4 _:5 55,000,000;_ 4 ,3 2,100,000; 4 1;, 780,000:

: e : ' :
:after : :
:wa : :
: hours : :
: : 4 :2—1807000:000?’ 4 : 650:000? 4 : 780,000:
: 4 : 4 : 440,000,000: 4 : 5,000,000: 4 :11000,000:
: 8 : : coagulated : 4 : 59,000,000: 4 :56000,000:
: 12 : : : 4 : 89,000,000: 5 :46000,000:
: 24 : : : l :150,000,000: : coag. :
: 48 i, : : _:Coagulated : i :

 

- 23 -

Table IV The effect of a 2-hour delay in cooling of milk
(at room temperature)upon bacterial growth.when
cooled milk was warmed after 10 h8urs storage to
a favorable growth.temperature(70 .)

(Guernsey cow No.57)

 

 

  
       

 

 

 

 

 

 

 

 

 

?_Time :BaEteria pef'ml.hy standard plate count with :
:after :delazed coolapg and_a§oraga at: :
:milk :No.cf : 0 :No.cf : o :No.cf : 0 :
: °trials: 80 F °trials: 60 F._ atrials: 40 F. :
:Eart ED MILKL. _;__:
: 0 : : 44,000: 2 : 44,000: 2 : 44,000:
: 10 : 2 :a 41,800,000: 2 : 25,000: 2 : 50,000:
:TIEe : - :
:after : 3
:Va : :
:hmms: , :
: 2 : 2 : 8,300,000: 2 : 250,000: 2 : 24,000:
: 4 : 2 : 17,000,000: 2 : 220,000: 2 : 42, 000:
: 8 : 2 : 71,000,000: 2 : 7,900,000: 2 : 4500,000:
: 12 : 1 : 178,000,000: 2 :28,000,000: 2 :71000, 000:
: 24 ° - coa ated :coagulated: : coag.___

__a___.______£.u_li
,gart2 INOCULATED VITH .coli
T e :BacterIa per ml.5§ standard—plate count with delayed
after :cool%pg and storage at: _:t
0.0 : :No.cf o :No.cf

 

  
 
   

 

O. O. O. O. .0 0.

 

 

 

0 2
10 2 : 72:0001000: 2 : 1 400,000: 2 g_,» 860 000:
‘Time
:after
:wa

 

        

: ; : 100,: : ,.000 - 2 :

: 4 2 : 250, 000, 000: 2 :25, 000, 000: 2 : 560,000
: 8 2 : 690,000,000: 2 :40, 000, 000. 2 : 660, 000
: 12 1 :1, 500,000,000: 1 :70, 000,000: 2 :50000,000
: 24 :coagulated :. :coagulated: : coag,

 

 

 

DISCUSSION

The influence of temperature upon the
germicidal property of milk was the same as that
usually seen in the common germicides.The germicidal
property of milk became more effective at higher
temperatures.Also at higher temperatures ,this
property was exhausted in a short period of time,
while it was retained over a longer period when the
temperature was low.This finding is in full
agreement of reports of the previous workers(7,9,10).

Most of the workers (7,9,10)have
reported that the germicidal effect is more
proncunced in inoculated milk than in uninoculated
milk.From the findings herein reported it seemed
that the above observation was true only when the
number of organisms destroyed was taken into
consideration.If,however,the percentage of destruction
was taken into consideration the effectiveness of
the germicidal property seemed to be greater in
uninoculated milk than in inoculated milk.

-25 ..
SUMMARY

The criteria of the reduction of the
bacteria count in the milk was used to demonstrate
the germicidal property.The influence of the
germicidal property can be used to reduce the
bacterial count if the milk is stored at 40°F.
and delivered with 72 hours,if kept at 60°F.it
should be delivered within eight hours,and if
kept at 80°F.it should be delivered within four
hours.

This may be one of the reasons why
morning milk which is delivered within eight
hours without being cooled,does not have a very
high bacteria count.

As the percentage of destruction of
organisms was greater in uninoculated milk it may
be suggested that in order to make the most
effective use of this property the contamination
of milk should be kept down to a minimum.

(1)

(2)

(3)

(4)

(5)

(6)

('7)

(8)

(9)

- 26 -
LITERATURE CITED

American Public Health Association
1941. Standard Mbthod for the Examination

1

of Del ProduCts.8th éd.288 pp. ‘—
AmerIcan Pufilic Health Association;
New York.

Chambers, U.H.
1920. Bacterial inhibition.I.Germicidal
action in milk.Jour.Bact.5:527h559.

Fokker, A.P.

1890. Ztschr.f.Hyg.,9:4l.189O (cited by
Heineman,P.H. and Glen,T.H. J0ur.
Infect.Dis.5:554-54l.1908. Original
not seen.)

Frayer, J.M.

1952. Influence of delayed cooling upon
bacterial counts in raw milk.
Proc.25th Ann.Conv.Internat.Assoc.
iMilk Dealers,Plant Sec.pp.5-l6.

Hanssen, F.S.
1924. The bactdriological property of milk.
British J0ur.Expt.Path.5:271—280.

Heineman, P.G. and Glen, T.H.
1908. Experiments on the germicidal action
of cows'milk.Jour.Infect.Dis.
5 3 534-541 0

Heineman, P.G.
1921. ¥§1§.645 pp.V}B.Sanders Co.Philadelphia.
e germicidal action of fresh.cows'
milk.pp.249~257.

Hilliard, C.M. and Davis, M.A.
1917. The germicidal action.of freezing
temperature upon bacteria.Jour.Bact.
5:425-450.

Hunzikar, O.F.
1901. Investiggtion concerning the germ.cida1
action cows' milk.N.Y. Cornell
Agr.Expt.Sta.Bull.197

(10)

(11)

(12)

(l3)

(14)

(15)

(16)

- 27 -

Jones, F. S.
1928. The properties of the bactericidal
substance in.milk. Jbur.Expt. Med.
47:877-888.

Jones, F.S. and Little, R.B.
‘F 1927. The bactericidal property of cows'
milk.JCur.Expt.Med.45:5l9.

Jones,F.S. and Simms,H.S.

1950. The bacterial growth inhibitor.
Jour.Expt.Med.51:527-559.

McCulloch, E.C.

1945. Disinfection and §terilization.
2nd ed. pp.Lea and Fe iger:

Philadelphia.

Merris, 0.8.
1945. Presence in raw milk of a bactericidal
substance specific for certain strains
of coliform organisms.Nature.155:22.

Rogers, L. A. and Associates.
1955. The germicidal property of milk.
Fundamentals of Da 3cience.2nd ed.
pp.Re o Pu_1 8 ing 00.:New
York. pp.281.

Ross, H.E.
1959. The care and handl of milk.Rev.
e .4 .pp.0range Jud Pu is ing 00.:
New'Tork.pp.5l.

 

 

 

 

 

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