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Yogurt: The Product and its Manufacture


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Even if yogurt is one of the oldest fermented dairy products, it remains very popular today because of its image as ‘modern’ fermented food, resulting from its attractive nutritional properties and its increasing diversification, associated with the industrialization of its manufacture. After a short definition of yogurt and fermented milks, the microbiological characteristics and the main biochemical mechanisms involved in their manufacture are presented. The three main steps of the manufacturing process, that is, the mix preparation, fermentation, and harvesting/packaging, are then developed. Finally, the main microbiological, physicochemical, and sensory analyses and controls of the yogurts' quality are summarized.
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Corrieu G., and Béal C. (2016) Yogurt: The Product and its Manufacture. In: Caballero, B., Finglas, P., and
Toldrá, F. (eds.) The Encyclopedia of Food and Health vol. 5, pp. 617-624. Oxford: Academic Press.
© 2016 Elsevier Ltd. All rights reserved.
Yogurt: The Product and its Manufacture
G Corrieu, Bioval Process Co., Canet en Roussillon, France
´al, AgroParisTech INRA, Thiverval-Grignon, France
ã2016 Elsevier Ltd. All rights reserved.
An ancestral version of yogurt probably appeared 9000 or 8000
years BC in Mesopotamia and Egypt and subsequently spread
in the northeast of Africa, in the Middle East, in Central Asia,
and later in Balkan countries, offering a large variety of
‘fermented milks.’ Originally, yogurt resulted from a spontane-
ous, accidental lactic acid fermentation leading to the acidifi-
cation and coagulation of milk, thus resulting in an efficient
way to preserve this raw material otherwise vulnerable to spoil-
age. Along the following centuries, the knowledge for making
homemade yogurts and fermented milks spread all over the
world. The first attempts to produce yogurt industrially were
performed in Barcelona in 1919 by Isaac Carasso. Since the
1950s, the production of yogurt has grown significantly thanks
to the intervention of several powerful agrofood groups setting
up international activities. If ‘set-type’ and ‘stirred’ yogurts are
the basic products, a large number of new recipes and processes
have been created to diversify the products and address market
demands. These alternations include the modification of the
texture, resulting in drinking, frozen, and concentrated yogurts;
modification of aroma and taste by addition of fruit, jam, and
aroma compounds; modification of nutritional properties by
changing the fat and sugar contents; and development of
health-related elements with the use of probiotic strains or
the inclusion of vitamins or phytostanols. The coverage of
these issues has been contributing to a significant expansion
of the overall consumption of yogurt and fermented milks
As a result, the industrial production of yogurt and fermen-
ted milks in the world reached about 32–35 million tons in
2012, for an expected global market in 2015 of about $67
billion. In Europe (27 countries), the annual production was
around 9.3 million tons, with Germany, France, and Spain
being the three main producers covering 20%, 18%, and 9%
of the European production, respectively. For the last 5 years in
Europe, the total production increased by 10%, whereas for the
last 30 years in France, the increase was of 38%. Besides
Europe, the main producers of yogurt are China, Russia, Iran,
and the United States, with 4.0, 2.5, 2.2, and 2.0 million tons
per year, respectively. Production in South America and Cen-
tral America and in Africa remains low with 1.5 and 0.4 million
tons per year, respectively.
Definition and Main Types of Yogurts
Definition of Yogurt and Probiotic Fermented Milks
In essence, yogurts are fermented dairy products obtained from
lactic acid fermentation by two species of lactic acid bacteria,
that is, Streptococcus thermophilus and Lactobacillus delbrueckii
subsp. bulgaricus. This fermentation leads to acidification and
milk coagulation, without addition of rennet (as in cheese),
and allows an increase of the shelf life as a result of the low pH.
The sensory properties of yogurts rely on three main characters:
(1) the composition of milk as raw material, which differs
according to the milk source (e.g., cow, goat, or sheep; con-
ventional or organic) and the fat content that can be adjusted
to obtain full-fat, low-fat, or nonfat products; (2) the addition
of ingredients that allow modifying the sensory properties
(flavor, color, and texture) of the products, such as sweetening
agents (sugar or other sweeteners for low-calorie products),
flavoring agents (fruit aromas or vanilla) or fruits (small pieces
enriched with sugar or jam), stabilizers (pectin, starch, or
gelatin), or emulsifiers; and (3) the technology employed for
the manufacture, which may vary depending on the operations
during milk pretreatment (fat and nonfat solid standardiza-
tion, homogenization, or heat treatment) or yogurt post-
treatment (stirring, concentration, mixing, cooling, drying, or
Even if yogurt is the most consumed within the wider
family of fermented milks, many probiotic fermented milks
are traded around the world. They involve probiotic bacteria,
which are defined according to the FAO/WHO in 2011 as ‘live
microorganisms that, when administered in adequate
amounts, confer a health benefit on the host.’ As European
regulation has stated that these health benefits have to be
demonstrated before using the probiotics in foods and supple-
ments, the health claims are not anymore maintained. In other
countries, and depending on the country regulation, the fol-
lowing health benefits are recognized: reduction of lactose
intolerance, prevention of microbial infections, stimulation
of the immune system, and regulation of immune responses.
Main Types of Yogurts and Fermented Milks
Yogurt diversification is reflected by various textures (set-type
or firm, stirred, drinking, frozen, concentrated, or powder
yogurts), numerous flavors (natural, sweetened, flavored, or
with added pieces of fruits or honey), and diverse shelf life and
nutritional (fat content and residual lactose content) proper-
ties. Figure 1 proposes a synthetic scheme of the several char-
acters that lead to yogurt diversity.
Classification of fermented milks is also based on their
potential health properties. They are mainly related to the
decrease in lactose content in the product, as a result of lactic
acid production. Some strains of S. thermophilus and
L. delbrueckii subsp. bulgaricus are able to survive in the gastro-
intestinal tract, thus being able to play a role in the gut health.
Finally, the development of US versions of Greek yogurt is
associated to high protein but low carbohydrate contents,
thus contributing to the weight management of consumers.
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Microbiological and Biochemical Mechanisms
Involved in Yogurt Manufacture
Microbiological Characteristics of Yogurts
The two thermophilic lactic acid bacteria, S. thermophilus and
L. delbrueckii subsp. bulgaricus, which trigger yogurt fermenta-
tion, are considered as ‘Generally Recognized as Safe’ in the
United States and possess the ‘Qualified Presumption of Safety’
status in Europe, as a consequence of a long history of safe use
in food and an absence of pathogenicity. They are Gram-
positive, anaerobic, aerotolerant, and catalase-negative, do
not form spores, and have less than 55% GþC content in
their DNA. They are able to grow between 42 and 50 C, but
not at 10 C. S. thermophilus forms linear chains of rods,
whereas L. delbrueckii subsp. bulgaricus grows as ovoid cells.
They convert lactose into galactose that is not metabolized and
glucose that is fermented predominantly to lactic acid, thus
corresponding to homofermentative metabolism.
In milk, these two species demonstrate a positive interac-
tion called protocooperation, which is mutually favorable.
This phenomenon induces a more rapid growth and acidifica-
tion, higher production of aroma compounds and exopolysac-
charides, and more pronounced proteolysis. An upregulation
of biosynthesis pathways for nucleotides and sulfur-containing
amino acids is also observed. Growth of S. thermophilus is
promoted by free amino acids and small peptides that arise
from milk proteins by the action of the cell wall protease PrtB
of L. delbrueckii subsp. bulgaricus. In return, L. delbrueckii subsp.
bulgaricus is stimulated by formic acid, folic acid, and CO
are synthesized by S. thermophilus in milk. As a consequence of
this interaction, growth of S. thermophilus starts first by using
the nitrogen compounds and stops early as this species is very
sensitive to lactic acid inhibition. Growth of L. delbrueckii
subsp. bulgaricus begins later but is prolonged even at low
pH, due to the better resistance of this species to acidity.
Probiotic bacteria involved in fermented milk production
other than yogurt include different lactobacilli and bifidobac-
teria. The main bacterial species found in commercial products
are Lactobacillus acidophilus,L. casei,L. paracasei,L. rhamnosus,
Bifidobacterium animalis subsp. lactis, and B. breve. These bacte-
ria demonstrate numerous interactions with the classical yog-
urt cultures, which depend on specific strain associations.
Biochemical and Physicochemical Changes During Lactic
Acid Fermentation
Growth of lactic acid bacteria in milk induces many changes
that are desirable in yogurt. These changes include the synthe-
sis of different metabolites (lactic acid, exopolysaccharides,
and aroma compounds) and the modification of the texture
and the nutritional value of the product.
Lactic acid production
As a result of glycolysis, one mole of lactose is theoretically
transformed into one mole of galactose and two moles of lactic
acid, together with the production of intracellular energy in the
form of two moles of ATP. S. thermophilus,L. delbrueckii subsp.
bulgaricus, and L. acidophilus operate these reactions according
to a homofermentative metabolic pathway that is summarized
in Figure 2.
Lactose is first internalized into the cell with the help of a
lactose permease energized by a proton gradient. Intracellular
lactose is then hydrolyzed into glucose and galactose by the
enzyme a-galactosidase. Glucose is catabolized to pyruvate via
the glycolytic pathway (Embden–Meyerhof–Parnas), whereas
galactose is excreted out of the cell. Pyruvate is then reduced
into lactic acid through a lactate dehydrogenase, together with
the reoxidation of NADH formed earlier. Two different isomers
are synthesized: L(þ) lactic acid by S. thermophilus and D()
lactic acid by L. delbrueckii subsp. bulgaricus. Finally, the intra-
cellular lactate is excreted out of the cell via a symport with
protons, thus inducing acidification of extracellular medium
and progressive inhibition of bacterial growth.
Other lactobacilli and bifidobacteria may use hetero-
fermentative pathways to produce their intracellular energy
together with lactic acid. L. rhamnosus, L. casei, and
L. paracasei produce one mole of each lactic acid, ethanol,
, and ATP from one mole of glucose. Bifidobacteria syn-
thesize three moles of acetic acid and two moles of (Lþ) lactic
acid and ATP, without generation of CO
from two moles of
glucose. These different pathways induce different acidification
Added with fruits
Storage :
Chilled (4 °C)
Dehydrated (Ambient)
Frozen (–20 °C)
Fat content:
Type of milk:
Figure 1 Classification scheme for yogurts and fermented milks.
Glucose + Galactose
Lactic acid
1 NAD+
Lactic acid
Extracellular mediumIntracellular medium
Figure 2 Simplified scheme of metabolic reactions involved in
homofermentative metabolism in yogurt bacteria.
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rates and, consequently, different sensory properties of the
final product.
During milk fermentation, the proteolytic system of lactic acid
bacteria degrades caseins into peptides and free amino acids
that are essential to bacterial growth and participate in the
generation of flavor. L. delbrueckii subsp. bulgaricus possess
the cell surface proteinase PrtB that is highly active and pro-
motes fast growth and rapid acidification of milk. In contrast,
even if a few strains of S. thermophilus possess the cell wall
proteinase PrtS, most strains are protease-negative. Growth of
S. thermophilus is nevertheless effective in mixed cultures, since
available nitrogen compounds are supplied from the protein-
ase of L. delbrueckii subsp. bulgaricus.
Flavor compound production
Yogurt taste is mainly characterized by an acid character due to
the presence of lactic acid in the product. Yogurt aroma is
characterized by about hundred volatile compounds that con-
sist of carbonyl compounds (mainly acids and esters), alco-
hols, and heterocyclic and sulfur-containing compounds.
Among them, acetaldehyde is the major flavor compound of
yogurt, where it confers a pleasant fresh and fruity aroma. It is
produced by the lactic acid bacteria at a final concentration
comprised between 5 and 40 mg kg
. Most of the acetalde-
hyde is directly synthesized from pyruvate with the aid of
pyruvate decarboxylase or indirectly from acetyl coenzyme A,
through the action of pyruvate dehydrogenase and aldehyde
dehydrogenase. L. delbrueckii subsp. bulgaricus is also able to
convert threonine into acetaldehyde and glycine, through the
action of serine hydroxyl-methyl transferase. In addition,
S. thermophilus produces a-acetolactate that is partially metab-
olized into diacetyl or acetoin through the action of a-
acetolactate decarboxylase that allows regulating leucine and
valine biosynthesis.
Acidification of milk leads to coagulation as a result of desta-
bilization of the casein micelles. The mechanism relies on two
concomitant phenomena. During acidification, the net nega-
tive charge on casein micelles decreases, thus reducing electro-
static repulsion between charged groups. In the same time, the
colloidal calcium–phosphate complex is solubilized, which
results in the depletion of calcium in the micelles. Then, elec-
trostatic and casein–casein attractions increase due to
enhanced hydrophobic interactions. When the isoelectric
point of caseins (pH 4.6) is achieved, coagulation occurs as a
result of the formation of a three-dimensional network con-
sisting of clusters and chains of caseins, which leads to the
formation of the yogurt gel.
Exopolysaccharide production
Some strains of lactic acid bacteria contribute to the physical
properties of stirred fermented milks through biosynthesis of
extracellular polysaccharides (EPS), which are either homo- or
heteropolysaccharides. These polymers are composed of
several hundreds to thousands of repeating units of monosac-
charides such as D-glucopyranose, D-fructofuranose, D-glucose,
D-galactose, L-rhamnose, N-acetyl-D-galactosamine, and
N-acetyl-D-glucosamine, withmolecular masses ranging between
and 6 10
Da. S. thermophilus and L. delbrueckii subsp.
bulgaricus produce EPS during growth, to final concentrations
comprised between 30 and 600 mg l
in milk.
Biosynthesis of exopolysaccharides is governed by well-
characterized gene clusters. It involves the production of
precursors that are formed in the cytoplasm, related to the
sequential addition of activated carbohydrates (UDP-glucose,
UDP-galactose, and dTDP-rhamnose) by specific glycosyl-
transferases. These repeating units are coupled to lipid carriers
and translocated across the membrane before polymerization.
Changes in nutritional value
Nutritional characteristics of yogurts differ from those of milk
by the three main following aspects: (1) as a consequence of
lactic acid production, the lactose content is lower in yogurt
) than in milk (50 g l
), which is important for
lactose-intolerant people, by limiting the formation of organic
acids, hydrogen, methane, and carbon dioxide in the human
gut; (2) the levels of calcium and potassium are higher in
yogurt than in milk (200 and 255 mg 100 g
, respectively),
as a consequence of nonfat solid adjustment; and (3) the
concentration of folic acid is higher in yogurt than in milk.
The latter essential vitamin is biosynthesized by S. thermophilus
in the range of 20–150 mgl
, during which it is consumed by
L. delbrueckii subsp. bulgaricus, thus leading to an average net
level in yogurt of 80 mgl
, which exceeds the one in milk
(40 mgl
Yogurt Manufacture
General Diagrams of Yogurt Manufacture
The industrial manufacture of yogurts is organized along three
main steps: (1) the preparation of the mix and all correspond-
ing physical treatments such as homogenization, heat treat-
ment, cooling, and deaeration; (2) the fermentation process
starting after inoculation of the mix; and (3) the yogurt harvest-
ing, post-treatment, and packaging. Depending on the steps
performed, at least four types of yogurt can be considered,
whose manufacture is presented in Figure 3. One has to notice
that each step of the manufacture affects the final quality of the
yogurts and that, except for set-type yogurts, the product fla-
voring and the cup filling are performed after fermentation.
Preparation of the Mix
Milk standardization
In order to obtain the mix to be fermented, milk preparation
involves mainly fat and protein content standardization and
optional addition of sweeteners and stabilizers. Fat standardi-
zation consists of fat removal by centrifugation (at about
55 C), followed by cream reincorporation to reach the tar-
geted fat content, ranging from nonfat (0.01%), to low- or
light-fat (1–2%), to whole-fat yogurts (>3.2%). Protein stan-
dardization aims at increasing the protein content of the mix
(from 3% to 5–15%) in order to improve the yogurt firmness
(texture) and reduce its syneresis. It is mostly done by addition
of milk powder, which is the easier and traditional way. The
use of milk proteins or milk replacers as caseinates or whey
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powders is also common. A complete mixing of the dry ingre-
dients without air incorporation is recommended. Concentra-
tion of milk by membrane processes (ultrafiltration and
reverse osmosis) is an alternative method to increase the pro-
tein content of the mix.
For some yogurt recipes, sugars or other sweetening agents
are added to the mix, generally after the physical treatments
described in the succeeding text. In some countries, the use of
thickeners and stabilizers (gelatin, pectin, xanthan gum, carra-
geenan, starch, etc.) at concentrations varying from 5% to 10%
is allowed by FAO/WHO to improve the yogurt texture.
Physical treatments of the mix
Heat treatment is an essential step of the mix preparation. It
allows removing spoilage microorganisms, inactivating lacto-
peroxidases and producing stimulatory compounds in milk. In
parallel, heat treatment contributes to improved yogurt texture
by allowing whey protein denaturation and interaction with
casein, resulting in a decrease of gel syneresis and an increase of
gel firmness. During industrial yogurt manufacture, the mixes
are generally heated at 90 or 95 C for 3–7 min before cooling
down to fermentation temperature. Plate heat exchangers, with
a tubular holding zone, are generally used and are designed in
order to cool the mix accurately at the fermentation tempera-
ture (between 37 and 43 C).
Two other physical treatments of the mix, deaeration and
homogenization, are closely associated with the heat
treatment, and the design of the heat exchangers takes into
account the temperature favoring their effect. Homogenization
is compulsory for yogurt quality, as it increases the gel texture
and reduces syneresis. It provokes a reduction of the size of the
fat globules (near 2 mm) and a better link between fat and
hydrophilic proteins. Homogenization of the mix is done at
high pressure (20 or 25 MPa) and at a temperature close to
70 C. Associated with the heat treatment of the mix, it takes
place just after the holding section of the heat exchanger.
Double-stage high-pressure homogenizers are recommended
for high-fat yogurts. Vacuum deaeration of the mix is per-
formed at large industrial scale to reduce its oxygen content
and consequently shorten the fermentation time, as to improve
the yogurt texture and to remove off-flavors. This step is gen-
erally performed at 70 C, before homogenization.
The Fermentation Process
Inoculation of the mix
At industrial scale, yogurts are prepared through inoculation of
the mix with concentrated starter cultures of the two yogurt
bacteria (S. thermophilus and L. delbrueckii subsp. bulgaricus).
The commercial starter cultures are composed of specific
pe Stirred
Fermentation in cup (42 C)
Fermentation in tank (42 C)
Filling (10 C, aseptic conditions)
Cooling (18–25 C)
Mixing of the coagulum
Filling (10 C)
Reception and storage of milk (4 C)
Fat standardization (not-fat, low-fat, full-fat)
Protein standardization (5–15%)
Homogenization (20–25 Mpa at 70 C)
Deaeration (70 C)
Inoculation (106–107 CFU ml–1)
Cooling to incubation temperature (42 C)
Cooling at 10–12 C
Heat treatment (90–95 C, 3–7 min)
Cooling (5 C), cold storage, transportation, delivery
Figure 3 Schematic diagram of the production processes of set-type, stirred, drinking, and concentrated yogurts.
620 Yogurt: The Product and its Manufacture
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blends of selected and well-defined strains, at a concentration
higher than 10
colony-forming units (CFU)g
, and are
preserved as frozen or freeze-dried formulations. The inocu-
lated mix contains generally 10
CFU ml
of bacteria.
After mixing, it is transferred to the fermentation tanks (for
stirred, drinking, or concentrated yogurt manufacture) or
directly to the packaging machine for fermentation in cups
(for set-type yogurt manufacture).
Fermentation step
During the lactic acid fermentation of milk, numerous param-
eters vary as a function of time, as shown in Figure 4. The
growth of S. thermophilus occurs first, followed by that of
L. delbrueckii subsp. bulgaricus, reaching final concentrations
close to 10
(Figure 4(a)). The consumption of lac-
tose and nitrogenous compounds permits the growth of both
strains and leads to the accumulation of many relevant metab-
olites. Lactic acid, galactose, acetaldehyde, and exopolysacchar-
ides are the most important ones, contributing to flavor and
texture of the yogurt (Figure 4(b)). The synthesis of extracel-
lular lactic acid provokes an acidification of the mix character-
ized by a decrease of the pH (Figure 4(a)), the coagulation of
proteins, and the subsequent gel formation. Acetaldehyde con-
fers to yogurt its particular aroma, and exopolysaccharides
contribute to its texture.
The acidification process is controlled by the final pH of
the yogurt and the acidification rate, which are key factors to
master quality. The fermentation is stopped (by a fast cooling
of the product) when the final pH of the yogurt is reached.
The targeted final pH varies from 4.8 to 4.5, as a function of
the type of yogurt. A significant postacidification during the
yogurt’s cooling, harvesting, and storage has to be considered
in defining this target. Generally, online measurement of pH
of the mix is avoided, because the glass pH probes may break
inside the mix and need to be submitted to cumbersome
protocols of cleaning and calibration. Consequently, only
manual sampling is done during the acidification process to
allow offline pH measurements, and the decision to stop the
fermentation by cooling requires a good expertise of the
process. The acidification rate acts directly on the fermenta-
tion time, so that its knowledge and control are very impor-
tant to properly schedule industrial production. It is
influenced by various factors, such as starter composition
and activity, mix composition and physical treatments, and
fermentation temperature. However, accurate temperature
control is quite impossible during yogurt fermentation
because of the coagulation phenomenon that occurs at
about pH 5.2. As a consequence, the fermentation time can
vary in important ranges. For probiotic yogurt, fermentation
time can reach 6–8 h, whereas for stirred yogurt, a 3–4 h
Galactose and lactic acid concentrations
Lactose and acetaldehyde concentrations
(g l–1)
Fermentation time (h)
Lactic acid
Bacterial concentrations (CFU ml–1)
Fermentation time (h)
S. thermophilus
L. bulgaricus
Figure 4 Growth of S. thermophilus and L. delbrueckii subsp. bulgaricus and milk acidification (a) and evolution of lactose, galactose, lactic acid, and
acetaldehyde concentrations (b) as a function of fermentation time.
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process is the common target. However, industrial manufac-
turers have difficulties to master perfectly all the parameters of
the process, and longer fermentation times (5 or 8 h) are
frequently attained.
The fermentation of set-type yogurts is generally performed
in cabinets, incubation rooms, or large tunnels in which the
pallets move forward gradually with forced ventilation of
warm air. The fermentation of stirred yogurts is performed in
large tanks (15–20 m
for the largest ones) equipped with
mixing devices for mix homogenization, starter mixing, and
gel breaking after fermentation.
Yogurt Harvesting and Packaging
Cooling and harvesting of yogurt
The first step in yogurt harvesting corresponds to a fast cooling
of the product in order to stop its acidification. It takes place
when the required final pH of yogurt is obtained. Set yogurts
are cooled within 1 or 2 h to 4 or 5 C using cold air in
ventilated cabinets, cooling rooms, or tunnels, as a function
of the size of the manufacturing unit. For stirred yogurt, the
cooling is performed in an external heat exchanger reaching an
intermediate temperature (between 18 and 25 C) in less than
1 h (20–60 min for industrial tanks). At this temperature,
some additives as aroma compounds, sweeteners, and fruits
(jam, pulp, and pieces) can be added to stirred yogurts. In
modern large plants, these additions are generally performed
online at the level of the packaging machine, using metering
pumps and mixers.
The final texture of yogurts, especially stirred ones, is a
critical factor for consumer acceptance. As the texture is influ-
enced by many factors (mix composition, strains used, and
processing conditions), it is a real challenge to obtain the
targeted texture. The mechanical constraints exerted on stirred
yogurt by all the harvesting devices (pumps, heat exchangers,
pipes, mixers, filling machine, etc.) tend to reduce its texture
but can give them some smoothness.
Packaging of yogurt
Yogurt packaging ensures its hygiene and protection during
distribution. If plastic and glass cups are always used for set-
type yogurts, large up-to-date packaging units use the
‘form–fill–seal’ technology. The same packaging machine real-
izes the three main following operations: (1) the thermo-
formation of the containers at 150–200 C, using multilayer
thermoplastic materials, (2) the filling of the preformed con-
tainers under a closed environment and sterile air overpressure,
and (3) the thermosealing of the filled containers with an
aluminum lid labeled to deliver product information. These
high-tech packaging machines allow reaching high security
and high capacity (up to 70 000 cups per hour) standards.
Consequently, they correspond to the most expensive invest-
ment in an industrial manufacturing unit of yogurt.
Overpackaging is then carried out, in the form of multipacks
of 2, 4, 8, or 16 cups, with the help of an automatic tray packer.
After packaging and overpackaging, the yogurts are stored at
low temperature (4 or 5 C), which is maintained during
transportation and commercialization. This low temperature
maintenance permits limiting the postacidification in the prod-
ucts and preserving their safety.
Industrial Design of Yogurt Manufacturing Units
All equipments used for milk storage, mix preparation, fermen-
tation and yogurt cooling, and harvesting and packaging are
especially designed to allow for the cleaning in place (CIP)
procedures commonly used in dairy industry. These proce-
dures assume the existence of a CIP kitchen in the factory to
automatically provide the cleaning mixtures at the right tem-
perature and for the right duration.
Yogurt fermentation is a batch process, but some opera-
tions such as mix preparation and treatment and yogurt cool-
ing and packaging are designed and managed as continuous or
semicontinuous processes. In industrial manufacturing units,
automation and process control systems are more and more
popular. They encompass (1) sensors that essentially measure
physical parameters such as temperature, pressure, level, and
weight; (2) programmable logic controllers controlling valves,
pumps, and motors that permit the regulation of the main
process parameters; and (3) computer supervision that allows
traceability. Nevertheless, as an accurate control of the yogurt
acidification rate remains limited, optimization of yogurt man-
ufacture is not possible.
Finally, even if the acidity of yogurt contributes to its safety,
industrial manufacturers observe good manufacturing prac-
tices to control the microbial risk. They act mainly on food
contact surfaces that have to be cleaned and sanitized before
use and impose clothing and hair covering for the staff.
Control of Yogurt Quality
Yogurt quality requires controls of the raw materials, during
the course of the manufacturing process and on the final
Quality Controls of Raw Materials
Microbiological controls are carried out on raw materials, in
particular fresh milk, powder milk, fruits, sweeteners, and
starters. Somatic cell counts are also verified on fresh milk. In
addition, many physicochemical properties are checked: (1)
temperature, titratable acidity, and fat and protein contents of
the fresh milk; (2) the absence of antibiotics, solubility,
moisture, and fat content of the milk powder; and (3) pH,
viscosity, and Brix of the added fruits. Acidification activity of
starter cultures is also assessed, mostly by using the Cinac
system that allows determining various quantitative kinetic
descriptors such as the absolute value of the maximum acidi-
fication rate (Vm, in min
) and the time (tm, in min) neces-
sary to reach Vm. The lower the value of tm and the higher
the value of Vm, the higher the acidification activity will be.
Figure 5 shows typical acidification curves and corresponding
first derivatives (kinetics) of two yogurt starter cultures growing
in milk and displaying low (Vm ¼1.33 pH unit h
tm¼2.55 h) or high acidification activity (Vm ¼1.44 pH
unit h
;tm¼2.05 h).
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Author's personal copy
Controls During the Process
During yogurt manufacture, controls are accomplished to
ensure repeatability of the productions and maximal levels of
quality and food safety of the products. They refer mainly to
the control of temperature (in fermentation tanks, heat
exchangers, incubation rooms, and cooling systems), pH (by
sampling either in the fermentation tanks or directly in cups),
and duration of the different steps of manufacture.
In addition to these controls, the use of food safety man-
agement systems such as ISO 22000 or International Food
Standards is requested to control foodborne safety hazards
and guarantee the products’ safety. By implementing Hazard
Analysis and Critical Control Point systems according to the
Codex, three steps are identified as critical control points for
microbiological hazards during yogurt manufacture: pasteuri-
zation of milk, refrigerated packaging, and cold storage. In
addition, packaging is also related to physical hazards.
Quality Controls of the Final Product
Various controls are performed on the final products at the end
of their manufacture and during their shelf life. The frequency
of sampling is defined by each dairy factory, as stated by its
own good hygiene practices.
Counts of S. thermophilus and L. delbrueckii subsp. bulgaricus
are controlled to verify that the targeted value of 10
at shelf life is achieved. The presence of spoilage and patho-
genic microorganisms, including Listeria monocytogenes,Salmo-
nella spp., coliforms, yeasts, or molds, is also checked.
Physicochemical analyses consist of the verification of the
fat and total solid contents, the titratable acidity or the pH of
the products, and the assessment of some texture parameters
including firmness, consistency, or viscosity, depending on the
type of yogurt (set-type, stirred, or drinking yogurt). Sensory
evaluations are completed with experienced panelists. The fol-
lowing main sensory attributes are generally employed:
appearance (syneresis and color), texture (palatability, firm-
ness, and consistency), aroma and odor, and taste and after-
taste (freshness, acidity, and persistency).
Yogurt is an ancient traditional fermented food that has
known, since half a century, a tremendous industrialization
of its manufacturing conditions. In more recent years, an
intense innovative diversification of recipes and products
occurred, which partly explain the increase of their consump-
tion. Although artisan production schemes persist, including
homemade yogurt manufacture, the industrial manufacture of
yogurt is now well established. Breakthrough innovations are
limited and the improvements in process productivity relate
mainly to the design and the management of the manufactur-
ing units. Nevertheless, the interesting nutritional properties of
yogurts and more generally of fermented milks, their diversity,
and the opening and increasing of new markets offer impor-
tant perspectives for their development at world scale.
See also: Bifidobacteria in Foods: Health Effects;Fermented Foods:
Use of Starter Cultures;Lactic Acid Bacteria;Packaging: Aseptic Filling;
Probiotics;Rheological Properties of Food Materials;Yogurt: Dietary
Importance;Yogurt: Yogurt Based Products.
Further Reading
Aureli P, Capurso L, Castellazzi AM, et al. (2011) Probiotics and health: an evidence-
based review. Pharmacological Research 63: 366–376.
´al C and Helinck S (2014) Yogurt and other fermented milks. In: Ray RC and
Montet D (eds.) Microorganisms and fermentation of traditional foods,
pp. 139–185. Boca Raton, FL: CRC Press.
Benezech T and Maingonnat JF (1993) Flow properties of stirred yogurt: structural
parameter approach in describing time-dependency. Journal of Texture Studies
24: 455–473.
Cheng H (2010) Volatile flavor compounds in yoghurt: a review. Critical Reviews in
Food Science and Nutrition 50: 938–950.
Corrieu, G., Spinnler, H. E., Jomier, Y. and Picque, D. (1988). Automated system to
follow up and control the acidification activity of lactic acid starters. Fr. Pat.
2 629 612.
Courtin P, Monnet V, and Rul F (2002) Cell-wall proteinases PrtS and PrtB have a
different role in Streptococcus thermophilus/Lactobacillus bulgaricus mixed
cultures in milk. Microbiology 148: 3413–3421.
Time (h)
dpH/dt (h
Time (h)
Figure 5 Acidification activity of two yogurt starter cultures, displaying high acidification activity (—) and low acidification activity (—) determined
using the Cinac system.
Yogurt: The Product and its Manufacture 623
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Author's personal copy
FAO/WHO (2001) Health and nutritional properties of probiotics in food including
powder milk with live lactic acid bacteria: report of a joint FAO/WHO expert
consultation. Cordoba, Argentina: FAO/WHO.
FAO/WHO (2011) Codex Alimentarius: codex standards for fermented milks 243-2003.
In: FAO/WHO (ed.) Milk and milk products, 2nd ed., pp. 6–16. Rome: FAO/WHO.
Lee WJ and Lucey JA (2010) Formation and physical properties of yogurt. Asian-
Australasian Journal of Animal Sciences 23: 1127–1136.
Ruas-Madiedo P and de los Reyes-Gavila
´n CG (2005) Methods for the screening,
isolation, and characterization of exopolysaccharides produced by lactic acid
bacteria. Journal of Dairy Science 88: 843–856.
Saint-Eve A, Levy C, Le Moigne L, Ducruet V, and Souchon I (2008) Quality changes in
yogurt during storage in different packaging materials. Food Chemistry
110: 285–293.
Shiby VK and Mishra HN (2013) Fermented milks and milk products as functional foods
– a review. Critical Reviews in Food Science and Nutrition 53: 482–496.
Sodini I, Remeuf F, Haddad S, and Corrieu G (2004) The relative effect of milk base,
starter, and process on yogurt texture: a review. Critical Reviews in Food Science
and Nutrition 44: 113–137.
Tamime AY and Robinson RK (2007) Yoghurt: science and technology. Boca Raton, FL:
CRC Press.
Vinderola CG, Mocchiutti P, and Reinheimer JA (2002) Interactions among lactic acid
starter and probiotic bacteria used for fermented milk products. Journal of Dairy
Science 85: 721–729.
Relevant Websites
624 Yogurt: The Product and its Manufacture
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... lactis etc. are also not uncommon in some countries (Mckinley, 2005). The use of these traditional cultures has some advantages that it can grow even at low pH and their growth is not affected by acidity (Aswal et al., 2012;Corrieu and Beal, 2016;Mbaeyi-Nwaoha et al., 2017). Our literature search showed that pH, titratable acidity, syneresis and sensory profiles of yoghurt samples from the Kingdom of Lesotho have not been reported previously. ...
... However, among these volatile compounds, acetaldehyde is the major flavour compound of yoghurt which gives pleasant, fresh and fruity aroma. The low flavour values could be due to the high content of carbohydrate which increases the sweetness of yoghurt (Ndife et al., 2014;Corrieu and Beal, 2016). ...
... Y 1 received the lowest score of 2.2 and this may be attributed mainly due to its high viscosity. The panellists appreciated the increased viscosity as it makes yoghurt chewable before swallowing (Corrieu and Beal, 2016). Even though appearance, texture and thickness are very important characteristics to contribute the quality of yoghurt, the flavour is generally considered as the most important of all and critical indicator of consumer acceptability (Olugbuyiro and Oseh, 2011). ...
A total of nine yoghurt samples purchased from the Kingdom of Lesotho were evaluated for their pH, titratable acidity, syneresis and sensory profiles following standard procedures. The pH, titratable acidity and syneresis of these nine samples were found to be in the range of 3.94-4.22, 0.69-1.81 and 1.76-35.15%, respectively. The sensory profiles such as appearance, texture, aroma, flavour, taste and overall acceptability of these nine samples were found to be in the range of 2.5-4.5, 2.2-3.3, 2.5-4.1, 1.7-4.0, 2.1-4.3 and 2.3- 3.9, respectively. The pH of all nine yoghurt samples was complying in accordance with FDA specifications. The percentages of titratable acidity of some yoghurt samples were complying in accordance with FDA specifications and some samples were not. On the other hand, some samples have remarkably high syneresis. Our study showed that the pH, titratable acidity, syneresis and sensory profiles of these yoghurt samples were significantly different (p<0.05). Sensory properties, particularly, flavour, taste and aroma of yoghurt samples are needed to be improved for a better consumer overall acceptability. To the best of our knowledge, this is the first report of this kind on yoghurt samples from the Kingdom of Lesotho.
... bulgaricus grows as ovoid cells. They convert lactose into galactose that is not metabolized and glucose that is fermented predominantly to lactic acid, thus corresponding to homofermentative metabolism (Corrieu & Béal, 2015). ...
... pH, viscosity, and Brix of the added fruits. Acidification Acidification activity of starter cultures is also assessed, mostly by using the Cinac system that allows determining various quantitative kinetic descriptors (Corrieu & Béal, 2015). ...
... They refer mainly to the control of temperature (in fermentation tanks, heat exchangers, incubation rooms, and cooling systems), pH (by sampling either in the fermentation tanks or directly in cups), and duration of the different steps of manufacture. In addition to these controls, the use of food safety management systems such as ISO 22000 or International Food Standards is requested to control foodborne safety hazards and guarantee the products" safety (Corrieu & Béal, 2015). ...
Full-text available
Yogurt is a semisolid fermented product made from a standardized milk mix by the activity of a symbiotic blend of Streptococcus salavarius subsp. thermophilus and Lactobacillus delbruechii subsp. bulgaricus cultures. For the sake of brevity we shall term the yogurt culture organisms as ST and LB. Milk of various mammals is used for making yogurt in various parts of the world. However, most of the industrialized production of yogurt uses cow's milk. It is common to boost the solids-not-fat fraction of the milk to about 12% with added nonfat dry milk or condensed skim milk. The increased protein content in the mix results in a custard like consistency following the fermentation period (Hui, 1992). The typical composition and nutrient profile of yogurt are shown in Table below. In general, yogurt contains more protein, calcium, and other nutrients than milk, reflecting extra solids-not-fat content. Today, yoghurt remains a milk-based fermented milk that is presented to the consumer in either a gel form (set yoghurt) or as a viscous fluid (stirred yoghurt) but, as figures for consumption have risen, so manufacturers have expanded the market by introducing an ever wider range of fruit flavours and/or changing the image of the product, e.g. by raising the total solids and fat contents of a standard stirred yoghurt to give a product with a luxury image. Nevertheless, despite these and other innovations, the method of manufacture is still based on the system employed by nomadic herdsmen many centuries ago. For example, the majority of yoghurts consumed worldwide are manufactured with cultures of bacteria with growth optima of 37–45ºC, and this characteristic derives from the fact that the species in question, namely Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus thermophilus, evolved in the Middle East where the ambient temperature in the summer months is often well in excess of 35ºC. Similarly, the universal method of manufacturing a satisfactory yoghurt is based on the traditional process expanded (Tamime, 2006).
... bulgaricus grows as ovoid cells. They convert lactose into galactose that is not metabolized and glucose that is fermented predominantly to lactic acid, thus corresponding to homofermentative metabolism (Corrieu & Béal, 2015). ...
... pH, viscosity, and Brix of the added fruits. Acidification Acidification activity of starter cultures is also assessed, mostly by using the Cinac system that allows determining various quantitative kinetic descriptors (Corrieu & Béal, 2015). ...
... They refer mainly to the control of temperature (in fermentation tanks, heat exchangers, incubation rooms, and cooling systems), pH (by sampling either in the fermentation tanks or directly in cups), and duration of the different steps of manufacture. In addition to these controls, the use of food safety management systems such as ISO 22000 or International Food Standards is requested to control foodborne safety hazards and guarantee the products" safety (Corrieu & Béal, 2015). ...
Yogurt is a semisolid fermented product made from a standardized milk mix by the activity of a symbiotic blend of Streptococcus salavarius subsp. thermophilus and Lactobacillus delbruechii subsp. bulgaricus cultures. For the sake of brevity we shall term the yogurt culture organisms as ST and LB. Milk of various mammals is used for making yogurt in various parts of the world. However, most of the industrialized production of yogurt uses cow's milk. It is common to boost the solids-not-fat fraction of the milk to about 12% with added nonfat dry milk or condensed skim milk. The increased protein content in the mix results in a custard like consistency following the fermentation period (Hui, 1992). The typical composition and nutrient profile of yogurt are shown in Table below. In general, yogurt contains more protein, calcium, and other nutrients than milk, reflecting extra solids-not-fat content.
... bulgaricus grows as ovoid cells. They convert lactose into galactose that is not metabolized and glucose that is fermented predominantly to lactic acid, thus corresponding to homofermentative metabolism (Corrieu & Béal, 2015). ...
... pH, viscosity, and Brix of the added fruits. Acidification Acidification activity of starter cultures is also assessed, mostly by using the Cinac system that allows determining various quantitative kinetic descriptors (Corrieu & Béal, 2015). ...
... They refer mainly to the control of temperature (in fermentation tanks, heat exchangers, incubation rooms, and cooling systems), pH (by sampling either in the fermentation tanks or directly in cups), and duration of the different steps of manufacture. In addition to these controls, the use of food safety management systems such as ISO 22000 or International Food Standards is requested to control foodborne safety hazards and guarantee the products" safety (Corrieu & Béal, 2015). ...
... Yoghurt is a dairy product produced through the action of lactic acid bacteria (LAB) on milk. The action of these bacteria leads to the acidification and coagulation of milk [1]. Yoghurt is one of the most commonly consumed products among different populations owing to its intrinsic benefits [2]. ...
... 5 g of each sample was placed in an oven dryer at 105°C for 3h, the initial mass before drying and the final mass after drying was measured and used in the determination of the total solids. (1) Where; M 3 -the mass/weight of the sample and Petridish after drying, M 2 -the mass/weight of sample and Petri dish before drying and M 1 -the mass/weight of the empty Petridish. ...
Conference Paper
Full-text available
Yoghurt is a probiotic food readily consumed among different populations owing to its nutritional and intrinsic benefits. This product serves as an excellent source for fortification with other bioactive compounds making it a suitable vehicle for fortification with Moringa oleifera which contains a substantial quantity of bioactive compounds. This study evaluates the physicochemical parameters of low-fat yoghurt enriched with Moringa oleifera leaf powder during 14 days of storage at 4±1⁰C. Five samples of low-fat yoghurt were produced and coded samples 1, 2, 3, 4, and 5. Sample 1 served as the control sample, while samples 2, 3, 4, 5 were low-fat yoghurt enriched with moringa leaf powder at 0.3%, 0.5%, 0.7%, 1.0%, respectively. The pH of the samples at different concentrations was significantly different (p<0.05) ranging from 4.517 to 4.260 and decreased in all samples during storage while there was a significant increase in titratable acidity of the samples (0.780% to 1.410%) during storage. Water holding capacity (WHC) was found to be higher in samples fortified with moringa as compared to the control and syneresis significantly reduced in samples fortified with moringa. There was a significant difference (p<0.05) between the viscosity of samples with different moringa concentrations besides, samples fortified with moringa leaf powder were higher in viscosity than the control sample. Sample 5 which had the highest concentration of moringa was low in viscosity, WHC and higher in total solids in comparison to the control. Based on the data obtained from this present study, samples with a lesser concentration of moringa are recommended for further studies as they enhance the physicochemical properties of yoghurt.
... Total lactic acid bacteria ranged from 3.7 x 107 to 2.6 x 108 CFU mL-1 in accordance with SNI standards (2009). Corrieu and Beal (2016) stated that two thermophilic lactic acid bacteria, namely S. thermophilus and L. delbrueckii subsp. bulgaricus, which triggers yoghurt in fermentation, is considered safe. ...
Full-text available
Ciomas Rahayu Village, Bogor Regency is an area with populated densely. Knowledge of the benefits and making of Yoghurt for moms of family welfare coaching is very important. Because Yoghurt has been shown to improve the body's immune system and overcome lactose intolerance. The purpose of this program was provide counseling and accompanying about the making of yoghurt for the family as well as explanation of the benefits of yoghurt if consumed. Activity method was practice in making yoghurt from basic ingredients of milk and were given starter to be fermented by moms of family welfare coaching Ciomas Rahayu Village Bogor Regency on 30 people cadres. Milk was fermented in a bottle is done for 2 x 24 hours at a temperature of 37oC-42oC. Fermentation results were added sugar expected can make the family business knowledge. Evaluation of Yoghurt production results done that moms can make yoghurt well so that result satisfactory. To do business need existence of cooperation with other party funding. Outcome of this activity was the increasing understanding and skill of partner of Ciomas Rahayu Village, Bogor Regency in making Yoghurt and increasing family business skill.
... According to the increase in yogurt consumption [15], it is important to seek new opportunities to expand their offers to consumers and to develop products enriched with health substances at various stages of production, as well as in gastronomy or home conditions. The use of fiber as a food additive modifies its physical properties [11] and therefore it is valid to investigation the rheological properties and stability of the obtained systems using modern techniques. ...
Full-text available
The influence of the amount of inulin addition (3%, 6%, 9%, 12% or 15% w/w) on the physicochemical properties of natural yogurt was analyzed. The acidity (titration; pH), texture parameters (penetration test), viscosity curves (rotational rheometer), microrheology (macroscopic viscosity index, MVI; elasticity index, EI; solid-liquid balance—SLB; multi-speckle diffusing-wave spectroscopy, MS-DWS) and physical stability (syneresis; LUMiSizer test) of yogurts were investigated. All samples were non-Newtonian pseudoplastic liquids. The sample with 15% inulin content presented an approx. 4% higher pH value (4.34), 3-fold greater MVI and almost 5-fold higher penetration force, compared to the control sample (0% of inulin). In turn, the use of inulin addition in the range of 3–15% w/w resulted in a reduction of syneresis (p < 0.05). A linear decrease in the values of instability indexes and sedimentation velocities was noted in the function of inulin content increase (LUMiSizer test). The application of inulin (in the range of 3–15% w/w) as a functional additive to yogurts significantly contributed to enhancement of their physical stability. Summing up, the possibility of obtaining natural yogurts with a high content of this prebiotic has been demonstrated, thus such products can be classified as functional foods and a health claim can be put on the label.
... The discovery and emergence of the milk fat globule membrane in the last two decades, has increasingly drawn the attention of many researchers around the world, due to its wide range of applications, not only that, including extraction, isolation, and purification techniques. The need for functional foods is increasing daily, of which set yoghurt is regarded as one, considering its wide range of therapeutic properties and functions towards human health (Lee and Lucey, 2004;Aziznia et al., 2008;Hassan et al., 2015;Corrieu and Béal, 2016). In addition, a combination of milk fat globule membrane (MFGM), an important novel food ingredient, with milk to produce yoghurt, not only supply nutritional and health benefits, but also provide technological functionality in order to eliminate some obvious problems in yoghurt production, which include syneresis, low gel strength, poor appearances, and taste changes, etc. ...
Lacprodan®PL20, a material rich in protein and polar lipids, was incorporated into set yoghurts produced from non-homogenized raw milk. The set yoghurts were prepared using 2, 4 and 6% Lacprodan®PL20 concentrations, but the control sample was only supplemented with skim milk powder. The effect of Lacprodan®PL20 on the physical, chemical properties, rheology and microstructure of set yoghurts was thoroughly investigated to examine some likely improvement and changes. It was observed that Lacprodan®PL20 gradually improved the set in nutritive values, water holding capacity, and apparent viscosity. Also, it altered the firmness and steadily improved the gel strength, especially at 4 and 6% levels with a noticeable comparison with the control sample. The pH values showed a slight delay in the fermentation process at 4 and 6% concentrations and slightly increased the pH, as the concentration increased. The microstructure of the set yoghurts produced with Lacprodan®PL20, as examined by scanning electron microscopy showed a much thicker structure with less and smaller holes in the gel matrix. Also, the appearance had a slight similarity between the samples especially the color b*(-blue to +yellow) but decreased as the concentration increased. Moreover, no significant differences were observed in the L* (lightness) and a* (-green to red) colors of the samples. These results vividly showed that Lacprodan®PL20, an enriched milk fat globule membrane fragment, has the potential to improve significantly the quality of set yoghurt, therefore, reducing some defects associated with set-yohurt such as syneresis, low gel strength, low dry solids, and the likes, by providing the required functions.
... bulgaricus. This fermentation leads to acidification and milk coagulation [13]. ...
Aims: The present work investigates the effect of tartary buckwheat flavonoid (TBF) capsules on the physical and chemical properties of yoghurt using polymeric whey protein (PWP) as a wall material. Methods: PWP was prepared by thermal polymerisation. TBF was encapsulated using PWP as the wall material via the pore-coagulation bath method. The physicochemical properties of the TBF capsules, such as the entrapment yield, moisture, average particle size, particle size distribution, surface morphology, molecular interactions, and thermal stability were investigated, in addition to the release of TBF in simulated gastric and intestinal juices. Yoghurt formulation was carried out using encapsulated TBF (3%, w/w), blank PWP beads (2.7%, w/w), and unencapsulated TBF (0.3%, w/w). A control yoghurt sample was prepared without these ingredients. The effects of encapsulated TBF on the chemical composition, acidity, texture, synaeresis, sensory properties, number of Streptococcus thermophilus and Lactobacillus, and other physical and chemical properties of the yoghurt were investigated. Results: TBF capsules were found to be sphere-shaped with porous surfaces, an average particle size of 1728.67 μm, an encapsulation yield of 92.85 ± 1.98% (w/w), and a glass transition temperature of 152.06 °C. When the TBF capsules were exposed to simulated gastric fluid for 4 h, the TBF release rate was 15.75% (w/w), while in simulated intestinal fluid, the TBF release rate reached 65.99% (w/w) after 1 h. After 5–6 h in simulated intestinal fluid, the TBF release rate reached 100% (w/w). The protein content of the yoghurt with encapsulated TBF was 3.57 ± 0.26% (w/w, p < 0.01), and the numbers of Lactobacillus and Streptococcus thermophilus were 2.45 ± 0.98 × 10⁸ (p < 0.01) and 5.43 ± 2.24 × 10⁷ CFU/mL (p < 0.05), respectively, with strong water retention being detected (p < 0.01). Samples containing the encapsulated TBF exhibited a significantly higher acceptability than the unencapsulated TBF (p < 0.01). Conclusions: Encapsulation using PWP effectively delivers TBF to the small intestine through the stomach. It also masks the bitter taste, enhances the colour of TBF-containing yoghurt, and improves the physical and chemical properties of the yoghurt.
Full-text available
Yogurt gels are a type of soft solid, and these networks are relatively dynamic systems that are prone to structural rearrangements. The physical properties of yogurt gels can be qualitatively explained using a model for casein interactions that emphasizes a balance between attractive (e.g., hydrophobic attractions, casein cross-links contributed by calcium phosphate nanoclusters and covalent disulfide cross-links between caseins and denatured whey proteins) and repulsive (e.g., electrostatic or charge repulsions, mostly negative at the start of fermentation) forces. Various methods are discussed to investigate the physical and structural attributes of yogurts. Various processing variables are discussed which influence the textural properties of yogurts, such as total solids content, heat treatment, and incubation temperatures. A better understanding of factors contributing to the physical and structural attributes may allow manufacturers to improve the quality of yogurt.
Full-text available
Considerable knowledge has been accumulated on the volatile compounds contributing to the aroma and flavor of yogurt. This review outlines the production of the major flavor compounds in yogurt fermentation and the analysis techniques, both instrumental and sensory, for quantifying the volatile compounds in yogurt. The volatile compounds that have been identified in plain yogurt are summarized, with the few key aroma compounds described in detail. Most flavor compounds in yogurt are produced from lipolysis of milkfat and microbiological transformations of lactose and citrate. More than 100 volatiles, including carbonyl compounds, alcohols, acids, esters, hydrocarbons, aromatic compounds, sulfur-containing compounds, and heterocyclic compounds, are found in yogurt at low to trace concentrations. Besides lactic acid, acetaldehyde, diacetyl, acetoin, acetone, and 2-butanone contribute most to the typical aroma and flavor of yogurt. Extended storage of yogurt causes off-flavor development, which is mainly attributed to the production of undesired aldehydes and fatty acids during lipid oxidation. Further work on studying the volatile flavor compounds-matrix interactions, flavor release mechanisms, and the synergistic effect of flavor compounds, and on correlating the sensory properties of yogurt with the compositions of volatile flavor compounds are needed to fully elucidate yogurt aroma and flavor.
Full-text available
Interactions among lactic acid starter and probiotic bacteria were investigated to establish adequate combinations of strains to manufacture probiotic dairy products. For this aim, a total of 48 strains of Streptococcus thermophilus, Lactobacillus delbrueckii subsp. bulgaricus, Lactococcus lactis, Lactobacillus acidophilus, Lactobacillus casei, and Bifidobacterium spp. (eight of each) were used. The detection of bacterial interactions was carried out using the well-diffusion agar assay, and the interactions found were further characterized by growth kinetics. A variety of interactions was demonstrated. Lb. delbrueckii subsp. bulgaricus was found to be able to inhibit S. thermophilus strains. Among probiotic cultures, Lb. acidophilus was the sole species that was inhibited by the others (Lb. casei and Bifidobacterium). In general, probiotic bacteria proved to be more inhibitory towards lactic acid bacteria than vice versa since the latter did not exert any effect on the growth of the former, with some exceptions. The study of interactions by growth kinetics allowed the setting of four different kinds of behaviors between species of lactic acid starter and probiotic bacteria (stimulation, delay, complete inhibition of growth, and no effects among them). The possible interactions among the strains selected to manufacture a probiotic fermented dairy product should be taken into account when choosing the best combination/s to optimize their performance in the process and their survival in the products during cold storage.
Most of the comments marked have a question mark at the end. As such the changes carried out by us need to be checked very carefully.
Fermented foods and beverages possess various nutritional and therapeutic properties. Lactic acid bacteria (LAB) play a major role in determining the positive health effects of fermented milks and related products. The L. acidophilus and Bifidobacteria spp are known for their use in probiotic dairy foods. Cultured products sold with any claim of health benefits should meet the criteria of suggested minimum number of more than 10(6) cfu/g at the time of consumption. Yoghurt is redefined as a probiotic carrier food. Several food powders like yoghurt powder and curd (dahi) powder are manufactured taking into consideration the number of organisms surviving in the product after drying. Such foods, beverages and powders are highly acceptable to consumers because of their flavor and aroma and high nutritive value. Antitumor activity is associated with the cell wall of starter bacteria and so the activity remains even after drying. Other health benefits of fermented milks include prevention of gastrointestinal infections, reduction of serum cholesterol levels and antimutagenic activity. The fermented products are recommended for consumption by lactose intolerant individuals and patients suffering from atherosclerosis. The formulation of fermented dietetic preparations and special products is an expanding research area. The health benefits, the technology of production of fermented milks and the kinetics of lactic acid fermentation in dairy products are reviewed here.
The time dependent rheological behaviour of 4 commercial stirred yoghurts was evaluated at constant shear rate within the range 18 to 280 s-1.The viscosity decreased greatly to an equilibrium value after 600 s of shearing. A simple model based on a structural approach was used. A rheological test was designed and carried out at a constant shear rate of 111 s-1 and a temperature of 10C. Three types of stirred yoghurt processed in the laboratory under standard conditions were compared with the 4 commercial brands. Two parameters of the model were highly significant for comparing the different stirred yoghurts. These were the rate constant of the structural decay and the consistency index at equilibrium.
The influence of packaging polymers (polypropylene or polystyrene) on the sensory and physicochemical characteristics of flavoured stirred yogurts with either 0% or 4%-fat content was investigated during the 28 days of storage at 4°C. Regardless of the packaging type, complex viscosity and thickness perception increased during storage due to exopolysaccharide production, whereas the pH of yogurts decreased. Packaging type had a greater impact on 0%-fat yogurts than on 4%-fat yogurts for both sensory and physicochemical characteristics. During storage, 0%-fat yogurt conditioned in glass displayed the lowest aroma quantity decrease of the three types of packaging, in accordance with the olfactory properties. However, between the two polymer types, polystyrene packaging seemed to be preferable for limiting aroma compound losses and subsequent fruity note intensities, and for avoiding the development of odour and aroma defects. Less significant packaging effect was observed for 4%-fat yogurts. Copyright © 2008 Elsevier Ltd. All rights reserved.
Yoghurt: Science and Technology is a standard work in its field for both industry professionals and those involved in applied research. Because manufacture is still, essentially, a natural biological process, it remains difficult to control the quality of the final product. Such control depends on a thorough understanding of the nature of yoghurt and both the biochemical changes and process technologies involved in production. Yoghurt: Science and Technology provides just such an understanding. Since the last edition, the industry has been transformed by the introduction of mild-tasting "bio-yoghurts", changing both consumer markets and manufacturing practices. This new edition has been comprehensively revised to take on board this and another major developments in the industry. Thus, today, millions of gallons of yoghurt are produced each year, yet manufacture is still, in essence, a natural biological process in which success can never be taken for granted. It is this capricious nature of the fermentation that leaves the system prone to variation. So, though some aspects of production of yoghurt have become fairly standard, there are so many areas of potential difficulty. This book offers preliminary guidance on the intricacies of production and distribution of yoghurt so as to minimize product failure.