Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
~38~
DKt: 8469
RD 92001
YOGURT STARTER CULTUR~ AND P~O OE 5S
The present invention relates to a starter
culture for preparing yogurt products and more particularly
a milk based starter composition for yogurt cultures
particularly Streptococcus thermoPhilus used to prepare
frozen yogurt products.
Descri~tion of the Prior Art
Kirk & Othmer, Encyclopedia of Chemical Technolo-
gy, Third Edition, volume 1~, p. 564, John Wiley ~ Sons,Inc. (1981) describe ~ogurt as a fermented milk product
that is rapidly increasing in consumption in the United
- States. Milk is fermented with Lactobacillus bulqaricus
and Streptococcus thermophilus organisms producing lactic
~cid~ us~la ~y ~ fi;~ cream or nonfat dried milk is a~ae~ to
the milk in order to obtain a heavy-bodied product.
Yogurt is manufactured similarly to buttermilk.
Milk with a fat content of 1 to S% and a nonfat solids
content (SNF) of 11 to 14%, is heated to about 82C and
held for 30 minutes. After homogenization, the milk is
cooled to 43 to 46C and inoculated with 2% culture. The
product is incubated at 43C for three hours in a vat or in
the final container. The yogurt is cooled and held at less
than 4.4C. The cooled product should have a titratable
acidity of 1.0 to 1.2% and a pH of 4.3 to 4.4. The
titratable acidity is expressed in terms of percentage of
lactic acid which is determined by the amount of 0Ol N
NaOH/100 mL required to neutralize the substance. Thus, 10
mL of 0.1 N NaOH/100 mL required to neutralize the sub-
stance represents 0.10% acidity. Yogurts with less than 2%
Eat are popular. Fruit flavored yogurts are also common;
30 to 50 9 of fruit is placed in the carton before or with
the yogurt.
W.S. Arbuckle, Ice Cream, Fourth Edition, an Avi
Book, Van Nostrand Reinhold Company, l9a6, p. 3, indicates
frozen yogurt is a cultured frozen product containing the
n ~ n
% ~ 2
same ingredients as ice cream. It contains not less than
3.25% milk fat and not less than 8.25~ nonfat milk solids
and has a titratable acidity of not less than 0 .56 . The
finished frozen yogurt shall weight not less than 5 lb/gal.
SLow fat frozen yogurt contains not less than 0.5%
or more than 2.0% milk fat.
Nonfat yogurt contains less than 0.5% ~at. The
specifications for these products have not become sta~dard-
ized.
10On page 29, Arbuckle presents a table containing
in part the following information:
Approximate Comps~ition ~%) of Commercial
Ice Cream and Related Products
_
ProductHLLI~fat Non~t Sugar Stabilizers Approxin~te
l~lk andTS
S~ nulsiEier~
20 Econ~nq ice cream 10.010.0-11.0 15.0 0.10 35.0-37.0
12.0 ~.0-10.013.0-16.0 0.20 0.40
Trade brand i~e cream 12.0 11.0 15.0 ~.30 37.5-39.0
14.0 8.0-9.013.0-16.0 0.20-0.40
DellLxe ic~ cres~ 16.0 7.0-8.0 13.0-16.0 0.20-0.~0 40.U-41.0
(prem~ upar
pr~ni~)
18.0-20.0 6.0-7.516.0-17.0 0.0-0.20 ~12.0-45.0
20.0 5.0-6.014.0-17.0 0.25 ~6.0
Frozen logurt 3.25-6.08.25-13.0 15.0-17.0 0.50 30.0-33.(1
3 0 0.5-2.08.25-13.0 15.0-17.0 0.60 29.0-32.0
<0.5 8.25-14.015.0-17.0 0.60 28.(1-31.0
On page 434, Arbuckle presents standards for
35frozen yogurt. Froæen yogurt is the food prepared by
freezing while stirring a pasteurized mix consisting of the
same ingredients permitted for ice cream in the CFR, Title
21, Part 135 .110 . These in~redients are cultured after
pasteurization by one or more strains of Lactobacillus
40bulqaricus and Streptococcus _ thermophilus, provided,
however, fruit~, nuts, or other flavoring materials may be
added before or after the mix is pasteurized an~ cultured.
Bacteria and coliform requirements for frozen yogurt
applies to the mix before culturing. Frozen yogurt con-
njl/~pec/~69.djd
8 ~
tains not less than 3.25% milkfat and not less than 8.25%
nonfat milk solids and has a titratable acidity of not less
than 0.5~, expressed as lactic acid. This characteristic
acidity, developed as the result of bacterial activity, is
applied to the product after culturing. No heat or bacte-
riostatic trea~ment (other than refrigeration), which
results in the total destruction of the microorganisms, may
be applied to the product after culturing. The finished
yogurt weight is not less than 5 lb/gal.
Lowfat frozen yogurt is the food prepared from
the same ingredients and in the same manner prescribed in
the CFR for frozen yogurt. Lowfat frozen yogurt, exclusive
o any flavorings, shall not contain less than 0~5 or more
than 2% milkfat.
A typical formula and process is set forth by
Arbuckle on page 398.
Formula (10 gal)
(lb)
Yogurt base or whole milk 55.0
Sugar 17.0
Stabilizer 0.2
Fruit 17.8
Total 90.0
Place whole pasteurized, homogenized milk in vat
and inoculate with 1% yogurt culture; hold at 90F until
set; or place milk, sugar, and stabilizer in vat, pasteur-
ize and homogenize, and then inoculate and hold. Mix
stabilizer with 5 times its weight of sugar and disperse
carefully with good agitation. Add remainder of sweeteners
and fruit and allow to mix well. Pump to freezer flavor
tank. In continuous freezers use a temperature of 21F.
Freeze to 50~ overrun or 13 oz/pt. Harden at -20F in the
usual manner.
ni ~ /R/~ ~n ~
--4--
Summary of the Invention
The use of a reconstituted starter medium or
composition containing a major a~ount of milk product
solids and a milk protein nutrient having minimal flavor
- 5 impact on final yogurt flavor has been found to promote the
growth of Streptococcus thermophilus bacteria and to
produce a frozen yogurt product which has improved product
shelf life due to reduced gram negative spoilage and slow
acidity development during refrigerated storage, minimal
milk protein off flavor, a lack of undesirable acid flavor
resulting from the usual use of L. bul~aricus and improved
viscosity and water binding properties resulting from
polysaccharides developed by S. thermophilus during cultur-
ing.
The culture medium or composition contains a
major amount of whey and nonfat dry milk, minor amounts of
yeast extract and phosphate nutrients and a minor but
substantial amount of a milk nutrient, preferably prepared
from enzymatic treatment of lactalbumin.
The culture medium is hydrated in water, pasteur-
ized, cooled and inoculated with yogurt culture, preferably
containing a major amount of S. thermo~ilus and, prefera-
bly not containing L. bul~aricus. This composition is
cultured for up to 8 hours at pH 6Ø The cultured starter
medium is next added to pasteurized yogurt base to
innoculate the hase and cultured for about 6 hours in the
retail package or in a vat to develop the characteristic
yogurt acidity and viscosity or gel.
The enhancement of S. thermophilus growth insures
a mild flavored stable acid product which is stable for a
longer period of time than is obtained from normal yo~urt
cultures containing S. thermo~hilus and L. bul~aricus.
Detailed Description of the Invention
The culture composition of this invention com-
prises a dry mixture of a major amount of milk proteins,
minor amounts of yeast extract and phosphate nutrients and
~ P~/~4~q.~i~
~D8~2
--5--
a minor but substantial amount of a bland hydrolyzed milk
protein amino acid containing nutrient. An amount of the
culture composition is added to water, pasteurized and
cooled. Yogurt culture bacteria is then added to inoculate
the mixture which is cultured to develop the S.
thermophilus. The resulting starter culture is next
supplemented with sufficient freeze dried L. acidophilus
and L. bulqaricus to produce an initial starter culture
containing 10 to 20 million S. thermo~hilus and 1 million
each of L. acidophilus and L. bulqaric~s per milliliter of
starter culture added to a yogurt base containing milk,
sugar and optional flavorants. The starter culture is
designed to enhance the growth of S. thermophilus so that
resulting frozen yogurt products prepared from the starter
have a longer shelf life as a result of less development of
aciditv durina stor~ge, lower introduction of off flavor
which often results when using hydrolyæed casein protein
nutrients, and improve viscosity and mouthfeel due to
generation of polysaccharides by S. thermoPhilus and
greater stability against spoilage by gram negative bacte-
ria. The starter culture is then used to innoculate a
pasteurized yogurt base and fermented to produce the final
frozen yogurt product.
we prefer to use S. thermophilus per se or
optionally combined with L. acidophilus and to refrain from
use of L. bulgar cus although minor amounts may be used
particularly after preparing the starter culture if de-
sired. Frozen yogurt does not have a standard of identity
except in some states which requires the use of both S.
thermophilus and L. bulgaricus as is required for most
yogurt products. This invention would work equally well
making normal yogurt should the standard of identity be
changed or should L bulqaricus be used as set forth
previously.
In a preferred embodiment method we innoculate
the culture composition with 5. to obtain a
level of 10 to 20 million bacteria per milliliter after
n i ~ / Q ~ r~
culturing in the starter culture. We then add sufficient
freeze dried L. bul~ricus and Lo acidophilus to obtain an
initial level of about l million each per milliliter of
starter culture.
The dry culture medium or composition contains a
major amount of milk solids and a minor but substantial
amount of hydrolyzed milk protein nutrient. The composi-
tion additionally contains a yeast and phosphate nutrient.
The milk solids can include sweet whey, dry milk,
nonfat dry milk, cream and similar mil~ solids. We prefer
to employ from 50 to 75~ milk solids, more particularly 60
to 70~ primarily sweet whey and nonfat dry milk solids.
About 2 parts sweet whey is used for each part of dry
nonfat milk solids to develop the milk solids employed in
our composition.
We employ up to 5%, preferably 1 to 4% yeast
extract which can be obtail,ed ~rom any food approve~ edible
yeast.
We employ one or more phosphates to improve the
nutrient balance of our starter culture, preferably using
up to 5~, preferably 1 to 4~ of disodium phosphate
( Na2PO4 ) .
Finally, we employ up to 75%, preferably from 15
to 45% and more preferably from 20 to 40% of a hydrolyzed
milk protein of neutral flavor which can be prepared from
casein or lactalbumin. We pre~er to use an enzymatically
prepared lactalbumin, such as Dellac LE80GMX available from
Deltown Chemurgic Corporation, P.O. Box 712, Fraser, New
York, 13753.
Dellac LE80GMX is an enzymatic digest of lactal-
bumin specifically designed for nutritional applications.
The lactalbumin is an excellent source of nutritionally
balanced essential amino acids and has an exceptionally
good flavor. The lactalbumin has the following character-
istics:
nil /~/~4~9.~itl
2~3~
Amino Nitrogen (AN) 4.9%
Total Nitrogen (TN) 11.4%
AN/TN x 100 43.0%
Total Protein (TN x 6.38) 72.7%
Ash 4.3%
NaCl 1.3%
Moisture 5.5%
pH (6% solution) 6.8
Microblal Content
Standard Plate <30,000/gm
Coliform <10/gm
Thermophiles <1,000/gm
Yeast and Mold <100/gm
Salmonella Neg/25 gm
Solubility - 100 gm/liter at 25C.
The culture medium or composition is employed in
a concentration of 5 to 15%, preferably 10% in waterO We
use about 120 lbs. of dry culture composition for each 150
gallons of water or about 10% w/v. Obviously, more or less
of the culture medium may be added to the water but we have
found 10% of the formulation, which follows, gives good
results.
The preferred culture medium is prepared by dry
blending the following ingredients. ~lending and packaging
time should be minimized to prevent moisture absarptian
during blending.
DrY Culture In~redients Percenta~e in Dry Blend
Grade A Sweet Whey 45.0%
Grade A Nonfat Dry Milk 20.0%
YE 2200 yeast extract - Gist Biocades 2.5%
Disodium Phosphate 2.5%
Lactalbumin - LE80GMX, Deltown Chemurgics 30.0%
Total Ingredients: 100.0%
The medium should be checked for yuality prior to
use in preparing frozen yogurt. 100 grams of dry culture
ingredients are mixed into one liter of water ~or a fin
ished volume of 10~ (W/V). The mixture is pasteurized at
190F for 30 minutes. The pasteurized mixture is cooled to
108F and inoculated with S. thermoPhilus (DPL 610THj
freeze-dried culture. The inoculated culture is maintained
at a pH of 6.0 by the addition of a suitable base such as
ammonium hydroxide for about 8 hours to develop the bacte-
rial content of the cultuxe. 3000 gallons of pasteurizedyogurt base (18 to 19% nonfat solids) is innoculated with
7~ gallons of the starter culture ~about 2.5% W/V) and
incubated at 108 to 110F for 5 to 6 hours.
The yogurt i5 cooled to 40F when the titrata~le
acidity reaches 1.3 to 1.4%. The cooled yogurt is combined
with the remaining yogurt ingredie~ts to make the finished
product.
The nonfat solids content of the yogurt base is
adjusted to from 14 to 20%, preferably 16 to 20% and most
preferably 17 to 19%.
The starting pH of the starter mix will vary
dependent on the flavor, but generally it will be below pH
6Ø A relatively rapid drop in pH during storage of the
final product will generally prevent gram negative bacterl-
2~ al spoilage, but the high acid flavor is considered unde-
sirable in a frozen yogurt.
There follow several examples intended to illus-
trate but no~ limit the scope o~ our invention.
n i l / ~ r / ~ i A
- 9 -
~xampl~ 1
A plant trial was run using a culture medium
having the following formula:
Dry Culture IngredientsPercentage in Dry Blend
Grade A Sweet Whey 35.0~
Yeast Extract 2.5%
Disodium Phosphate 2.S~
Lactalbumin (enzymatically digested) 60.0
Total Ingredients 100.0~
The culture medium was added to water to give 10%
solids~ 250 gallons of the mixture was pasteurized and
cooled. 60 grams, freeze dried Streptococcus thermophilus
was added and the mixture cultured for eight hours at a
temperature of about 108Fo Liquid ammonia was added
during the fermentation to malntain a pH ~etween 5.8 and
6.3. The ripened starter mixture was added at 2.5% to a
pasteurized yogurt base and cultured. Freeze dried L.
acidolphilus and L. bulgaricus were each added to the
.
pasteurized yogurt base at a level of 0.01 grams per liter
of base. This resulted in an initial count of one million
of each microorganism per milliliter of base. The S.
thermoPhilus was present at a level of approximately 10 to
20 million organisms per milliliter of base. The activity
of the medium was good reaching 1.00% TA (total acidity) in
four hours. The acid development plateaued at 1.06% in
five hours and reached 1.17% after chilling. The fresh
frozen yogurt product had flavor as good or better than
yogurt made using standard cultures.
n~1 /cr~ q
--10--
Ex~mple 2
Another plant trial was made using a culture
medium having one half the lactalbumin replaced by skim
milk solids. The culture medium had the following formula-
Dry Culture_Ingredients Percenta~e in Dry Blend
Grade A Sweet Whey 45.0~
Grade A Nonfat dry milk 20.0%
Yeast Extract - YG 2200 from Gist Biocades 2.5%
Disodium Phosphate 2.5%
Lactalbumin - Dellac LE80GMX 30.0~
Total Ingredients 100.0%
The culture medium was added to water to give 10%
solids. 250 gallons of the mixture was pasteurized and
cooled. 60 grams freeze dried Streptococcus thermo,philus
added and the mixture cultured at 108F for 8 hours at pH
6 adjusting the pH using a suitable base. 2.5% of the
cultured starter was added to yogurt base as well as minor
amounts of L. acidolphilus and L. bulgaricus as in Example
1 to prepare two batches of yogurt having 18% and 14.5%
SNF. The activity of the culture medi~m was somewhat less
than Example 1 reaching 1.05% TA (total acidity) in 5 to 6
hours. The chilled TA of the la% SMF sample was 1.36%
versus 1.12 % in the 14.5% SNF sample. Both cultures gave
finished product with excellent flavor and mouthfeel and
the samples were sub]ected to shelf life studies at 40F
which are reported in Example 4.
The yogurt base is prepared from 15 to 20~ milk
solids made from condensed milk.
Frozen yogurt mix was prepared by blending the
ripened yogurt base with a second mixture containing
stabilizers, milk solids, sugar and water. ~he yogurt
portion of the base was used to 10 to 15% of the final mix
for low acid flavors or at 25 to 35% for high acid frozen
yogurt flavors.
n j 1/ spec / 84 69 . d i d
The higher solid level gave a higher plateau for
developed acidity. The plateau acidity can be adjusted as
high as 1.5 or 1.6 TA by using appropriate high solids
amounts. Levels of 16 to 20~ solids develop good TA.
t~
-12-
Example 3
A plant trial was made using the cul-ture medium
of Example 2 to prepare a starter culture as in Example 2.
The starter culture was added to yogurt base having a 19.2%
SNF level for maximum TA development. In addition, to an
initial count of 10 to 20 million per milliliter of S.
thermophilus, we added 0.01 gms per liter of L. acido~hilus
and L. bulqaricus~ to provide an initial count of about 1
million per milliliter of each microorganism. The activity
of the yogurt base improved to 1.20~ TA in 5.25 hours with
a final TA of 1.44% after chilling. This TA would be
equivalent to a TA of 1.35 to 1.4% for a nonfat solids
(SNF) content of 17.5 to 18~. The finished products from
this trial were indistinguishable from controls made with
a regular started system containin~ both S. thermoPhilus
and L. bulqaricus and the samples were subjected to shelf
life studies at ~0P whic' ale ie~OL~C.' ;,I Example 4.
~ Our cultures are typically 1 x 1011 organisms per gram
of freeze dried culture. We attempt to obtain an initial
count in which at least 80% and preferably 90% of the
microorganisms present are S. therm_~hilus.
nil /~ /R~q . li,l
-13-
Example 4
Products from both Example 2 and Example 3 were
stored at 40F and tasted periodically. Results are
summarized on the following Tables 1 and 2. Perhaps the
most significant observation from the shelf life studies
was a significant improvement both in resistance to gram
negative spoilage and in control of acid development in the
test samples. Between the two trials, 10 or 12 samples
showed no gram negative spoilage or high acid development
in six weeks at 40F. Of three control samples made with
the regular starter system, two displayed severe gram
negative spoilage and the third had dropped so low in pH to
4.37 that it could be considered acid spoiled. (Gram
negatives cannot grow below pH 4.6, but yogurt below this
pH is unpalatable.) More remarkably, four of the Example
2 samples were shelf stable for 75 days. These samples
were opened repeatedly for flavoring during tha~ time and
showed no significant acid development, and only two were
spoiled by gram negatives.
The Control Strawberry had a 6 week pH of 4.37
with a noticeable acid flavor whereas the two strawberry
mixes made with the starter culture of this invention had
considerably higher pH's of 5.24 and 4.86 with a good
flavor. A similar benefit can be seen in comparing the
Control Vanilla with the cultures of this invention. Even
though the Control Chocolate had a similar 6 week pH as did
the chocolate of this invention, there was a noticable
flavor difference with control resulting in bacterial
spoilaye.
A relatively rapid drop in pH during storage of
the final product will generally prevent gram negative
bacterial spoilage, but the high acid flavor is considered
undesirable in a frozen yogurt.
Samples were also tested for total lactic cell
counts and for L. acidophilus counts (Table 2). The
general trends observed are that th~re is no significant
difference between control and test samples in total lactic
ni l /~ r ~
~8~2
count and in survival of that count. The data suggests
that trial samples ma~ have superior survival of L. aci-
dophilus.
-15~
Table 1. S~elf-life o~ Fr~zen Yogurt Mi~ Sa~ples ~eld
at 40~:
FlavorExample 6 Week 6 11 11
Flavor Week Week Week
pH Flavor pH
Butter Pecan 2 Good 5.88Good 5.29
Strawberry 2 Good 5.24Good 4.72
Banana 2 Good 5.90 * 5.32
Vanilla 2 Good 5.98 * 5.51
Banana 3 Good 5.41
Pistachio 3 * 4.98
Vanilla 3 Good 5.25
Macadamia 3 * 5.24
Chocolate 3 Good 5.90
Strawberry 3 Good 4.86
White Russl_n 3 G~,od 5.42
Straw Cheesecake 3 Good5.59
~0
Control Chocolate 2 * 5~80
Control Strawberry 3 Fair4.37
Acidic
Control Vanilla 3 * 4.67
~ Off flavor resulting from gram negative bacteria caused
spoilage
n jl/spec/8469 . d jd
-16-
Table ~. Cell Count~ of Frozen Yogurt Samples
Total Count-Lactic Acid bacteria
3 Weeks 6 Weeks 6 Week~
FlavorExample at 40F at 40F at-40F
_ __ _ --
Strawberry 2 NA 2.8 x 10~ NA
(11 Week)
Vanilla 3 6.1 x 10~ 1.6 x 107 4.7 x 107
Chocolate 3 9.5 x 10' 5.4 x 107 NA
Strawberry 3 1.1 x 107 1.3 x 10~ 3.3 x 108
Control Vanilla 2 1.1 x 10~ NA 8.3 x 10'
Macadamia 3 4.7 x 107 NA 5.4 x 107
Pistaschio 3 4.9 x 10' NA 5.2 x 10'
Hard Pack 3 ~.4 x 10' NA 2.5 x 107
(3 Weeks
at 40F
and 3
Weeks at
-20F)
Control 2 NA ~ 1.0 x I0
Hard Pack
The preceding examples establish that the started
culture composition of this invention:
a) Improves product shelf life at 40F due to
reduced gram negative spoilage;
b) Improves or maintains high yogurt ide~tity
due to minimal flavor interference by the milk
protein nutrient and reduced after-acidification
by the conventional L._bulgaricus culture;
c) Improves L. acidoE~ilus levels and survival
due to reduced competition by L. bulgaricus;
3~
d) Improves control of acid development due to
self-limiting nature of the fermentation of S
thermop_ilus; and
e) Improves viscosity and water-bindlng proper-
tiss of the culture through use of various levels
n jl/spec/8469 . djd
-17-
of polysaccharride producing S. thermophilus
strains.
~ ogurt is normally not prepared using a starter
medium. It is prepared by simpl~ adding the mixture of S.
~ and L. bulg~ricus (equal portions ) to milk .
The prior art has heretofor believed that the L. bulgaricus
was necessary to promote the growth of S. thermo~hilus.
Starter systems were not used because they were too strong-
ly f lavored being normally used in chee~e manuf acture ~
We have f ound that by using a f lavor neutral
hydrolyzed milk protein, preferably enzymatically dige~ted
lactalbumin, we are able to culture yogurt using only S~
thermoPhilus or optionally combining with L. ac do~kilus.
~o L. bulq~ricuæ is used which prevents generation of acid
during refrigerated storage. In addition, the composition
and process of this invention are effective, for some
unknown reason, is reducing the amount of gram neg~ L.i~e
bacterial spoilage of finished product.
n~l/spe~/8469.djd
