Starter Cultures and Fermented Milks


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Lecture Module 1. Introduction Lesson 1. Introduction to Starter Cultures and Fermented Milks, History of Starter Culture. Module 2. Role Function and Classification of starters Lesson 2. Starters cultures and their classification Module 3. Propagation of Starter cultures Lesson 3. Purpose of propagation, Traditional MethodsAdvantages And Limitations. Module 4. Mechanically and Chemically Protected Systems for Starter Propagation. Module 5. Metabolism of starters and biochemistry of fermentation Metabolism in Starter Cultures. Vitamin Metabolism in Starter Cultures Module 6. Quality and activity of starters
Module-7 Antimicrobial Compounds Produced By Starters and
Interactions among Starters Cultures
Module 8. Defects in Starter Culture
Problems associated with starter itself with control of starters with
milk and with production methods.
Bacteriophage action ultra structures, classification,, detection and
control

Page No. 2-4 5-11
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24-30 31-33 34-37 38-44
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Module 10. Starter distillates

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Lesson-1
Introduction to Starter Cultures and Fermented Milks
1.1 INTRODUCTION
Starter cultures are those microorganisms that are used in the production of cultured dairy products such as dahi, yogurt and cheese. The organisms selected for this purpose of need to produce the desired effect in the finished product.
Starters are a group of active and desirable microorganims capable of bringing about desirable changes in the milk product through the process of fermentation. These are carefully selected microorganisms that are deliberately added to milk to initiate ("Start') and carry out the desired fermentation in the production of fermented milk products. In other words starters bring about the specific changes in the appearance, body, texture and flavor characteristics of the final products.
The natural micro flora of the milk is inefficient, uncontrollable and unpredictable or is destroyed altogether by the heat treatments given to the milk. A starter culture can produce particular characteristics in a more controlled and predictable fermentation when added to milk.
The most common use of starter cultures is for the production of lactic acid from latose (milk sugar). Which in most cases causes or assists in the coagulation of milk protein by lowering pH of milk. Cultures that produce lactic acid are generally referred to as "lactic acid lacteria" (LAB). Certain starter organisms are added specificaly for their ability to produce flavor compounds such as diacetyl. Starter organisms can also influence texture of cultures and/or aged products though the breakdown of proteins, fats and other milk constituents in addition to the pH effect. The lower pH of cultured products can be inhibitory to certain spoilage organisms, although inhibition is associated with other by – products of growth with some starters.
More recently, probiotic cultures are finding their way into cultures milk products. These organisms posses some claimed health benefit for the consumer. e.g., better digestion, anti cancer compounds and presentation of heart disease etc. Probiotic cultures may be added as adjuncts or they may be directly involved in the fermentation process.
1.2. HISTORY OF STARTER CULTURES AND FERMENTED MILKS

Fermented foods and beverages have long been manufactured without the use of commercial starter cultures. Traditional methods of production include back slopping, or using a small amount of the finished specifically preserved product to inoculate a new batch, the use of microorganisms found naturally on the product, and the use of special containers that allow for the survival of the starter culture microorganisms within cracks and pores. These traditional methods allow for the development of individual varieties of fermented foods and beverages, and they are still practiced today for small- to mid-scale production facilities, as well as in less developed countries and in homemade-type products. Traditional methods, however, are prone to slow or failed fermentations, contamination, and inconsistent quality. In contrast, modern large-scale industrial production of fermented foods and beverages demands consistent product quality and predictable production schedules, as well as stringent quality control to insure food safety. (Durso, and Hutkins, 2003)
The pure culture techniques in microbiology were not developed until Pasteur in the 1860s Similarly Lactic acid bacteria (LAB), were identified by Lister in the 1870s, it is important to note that an industry developed technique to produce pure cultures only a short time later. Storch ( Denmark) Weigman (Germany), and Conn (USA) in late 1880s showed that pure cultures could be used to ripen cream, and soon the role of flavor-producing bacteria (i.e., citrate-fermenting diacetyl-producers) was established. By 1878 Christian Hansen began a culture business that continues even today to be a major supplier of starter cultures for the dairy, meat, brewing, baking, and wine industries. Initially, starter strains were prepared by the manufacturer by growing pure strains in heatsterilized milk. Calcium carbonate was often added as a buffer in order to maintain a neutral pH. These liquid cultures remained popular until relatively recently, even though they had a relatively short shelf-life due to the loss of cell viability and fermentative activity. Eventually, rather crude dry culture preparations were produced which required several transfers in milk to revive the culture to an active state. Freeze-dried cultures also became available, but the early product also required growth in intermediate or mother cultures. Frozen cultures, now the most common form for dairy cultures, were not introduced until the 1960s. Significant improvements in freezing and freeze-drying technologies have led these types of cultures to dominate the starter culture market. The modern starter culture industry provides cultures for nearly every type of fermented food and beverage. Most culture houses also produce and sell the media used to propagate

starter cultures, the enzymes used to coagulate milk for cheese production, and other ancillary products. In addition, the starter culture companies maintain a staff of highly trained microbiologists who provide expert technical service and support when issues or problems related to culture performance arise. And although there are many small culture manufacturers throughout the world, specializing in cultures for specific products or applications, the industry is dominated by a small number of large companies. View chapter 1.3.ADVANTAGES OF MILK FERMENTATION/ROLE OF FERMENTATION IN FOOD
The Feremented food have following advantages as listed below:
1. Enrichment of human diet through a wide variety of flavours, aroma and texture of foods.
2. Preservation of foods via lactic acid, alcoholic, acetic acid and alkaline fermentations 3. Bio-enrichment of food with proteins, essential amino acids, Essential fatty acids and
vitamins. 4. Detoxification during food fermentation processing. 5. Nutritional and physiological benefits such as
a. Promotion of growth and digestion b. Settling effect on the GI tract by deceasing harmful bacteria. c. Improvement of bowel movements d. Suppression of cancer. e. Suppression of blood cholesterol f. suppression of tumours g. Catering to the needs of lactose intolerant people.
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LESSON – 2 Role, Function and Classification of Starter Culture

2.1 INTRODUCTION
Starter cultures consist of microorganisms that are inoculated directly into food materials in order to bring about desired and predictable changes in the finished product. As a result the food may have enhanced preservation property, improved nutritional value, modified sensory qualities, and increased economic value. Although many fermented foods can be made without a starter culture, the addition of concentrated microorganisms, in the form of a starter culture, provides a basis for insuring that products are manufactured on a consistent schedule, with consistent product qualities.

2.2 DEFINITIONS

Starter cultures are bacterial or fungal strains either pure or mixed, used to initiate a fermentation process. The culture include selected strains of food-grade microorganism of known and stable metabolic activities and that is used to produce fermented foods of desirable appearance, body, texture and flavor. Stater culture means the microoganims that are selected based on their ability to produce lactic acid for curd production and a low pH to prevent spoilage, produce metabolites that give desirable flavours or produce enzymes that ripen the dairy product.

2.3 ROLE/FUNCTIONS OF STARTER CULTURES.

The primary function of lactic starters is the production of lactic acid from lactose. In addition to lactic acid production the starter cultures are also useful in different ways as stated below.

Table 2.1 : Functions of starter cultures (Agrimoon.com)

Function Acid production

Result o Gel formation o Expulsion (syneresis) of whey for texturing o Preservation of milk o Helps in the development of flavor

Flavour Preservation

Gas formation

Stablizer formation

lactose utilization

Lowering of potential Proteolysis lipolysis Miscellaneous compounds

redox and

o Formation of flavor compounds like diacetyl and acetaldehyde
o Lowering of pH and redox potential o Production of lactic acid o Production of antibiotics o Production of H2O2 o Production of acetate o Eye formation in certain cheeses o Production of open texture Ex. blue veined cheese o Development of body and viscosity o Ex. Polysaccharide materialas o Reduces the development of gas and off flavours o Suitable for lactose intolerant people. o Helps in preservation o Helps in development of flavor o helpful in the ripening/maturation of cheeses
o Production of alcohol in kefir and kumis

2.4 CLASSIFICATION / TAXONOMIC GROUPS AS PER BERGEY'S MANUAL

Starter cultures are generally classified based on their ability to utilize the lactose as shown in Fig. 2.1

Classification of starter cultures

RODS Lactobacillus

COCCI Lactobacillus Streptococcus Leuconostocs Pediococcus

BACTERIA Bifidobacteria Brevibacterium linens Acetobacter acetii

YEASTS Candida kefir Kluyveromyces Toruloxpora Saccharomyces

MOLDS Penicillium camembertti Penicillium roquefortii Aspergillus

Propionibacteria

oryzae Mucor rasmusen Geotricum candidum

2.4.1. Bacteria

2.4.1.1 Genus Lactococcus : Bergey's Manual or Systematic Bacteriology (1986), combined all the mesophilic lactic acid bacteria (LAB) with Lactococcus lactis to form a single species as they posses.

1. Identical isoprenoid quinines and the enzyme phosphotase

2. Indistinguishable lactic dehydrogenase

3. Identical percentage of guanine and cytosine.

4. High DNA homology

The only properties that distinguish them are plasmid controlled.

ILactococcus lactis subsp lactis Lactococcus lactis subsp cremris Lactococcus lactis subsp lactis diacetylactis

biovar

Acid producer but non flavor producer Acid producer but non-flavour producer Both acid & flavor producer

All the above organisms are mesophilic in nature and their optimum growth temperature is between 25-300C. all are homofermentative organisms.
2.4.1.2.Genus Streptococcus : The members of the Streptococcus are Gram positive organism that usually form paris or chains. In 1937, Sherman separated the genus according to physiogical and growth characteristics, especially with regards to temperature limitations on growth. Four general groups designated by Sherman are (1) Pyogenic. (2) Viridians (3) Enterococcus and (4) lactic. This categorization has become somewhat obsolete as

relationships between species have been shown to overlap. The only species used as starter culture is Streptococcus salivarius subsp themophilus. This is a yoghurt culture, which is thermophilic in nature with optimum growth temperature of 38.420C. All are homofermentative organisms.
2.4.1.3. Genus Leuconostoc : All are heterofermentative organisms capable of producing lactic acid, CO2 and aromatic compounds (ethanol and acetic acid) from glucose. These organisms are normally used along with lactic acid bacteria (LAB) in multiple or mixed strain cheese starter cultures, which produces flavor compounds.
Leuconostoc creamoris
Leuconostoc citrovorum
Leuconostoc dextranicum
2.4.1.4 Genus Lactobacillus : Lactobacillus delbruekii subsp bulgaricus is used for the preparation of yoghurt along with Streptococcus salivarius subsp thermophilus. These two organisms exhibit a symbiotic relationship. Lactobacillus acidophilus is a probiotic culture, used for preparation of acidophilus milk and other probiotic milk products like Bifighurt, Bioghurt, etc. The members of lactobacillus are classified based on fermentation of glucose into 3 groups as shown in Figure given below:

Obligate Homofermentative Group-I Orla Jensen Group
Growth at 15℃ Growth at 45℃ Pentose Fermentation CO2 from Glucose CO2 from Gluconate

Facultative Homofermentative Group II Thermobacterium
+ _ -

Obligate HeteroFermentative GroupIII

Streptobacterium
+ + +

Betabacte rium + ± + + +

Phosphoketolase
FDP aldolase Example

Absent
Present Lactobacillus acidophilus

Inducible by pentose
Present
Lactobacillus caseii

Present
Absent Lactobaci llus brevis

Fig. 2.2 Classification of Lactobacillus based on glucose fermentation.
2.4.1.5 Genus Bifidoacterium : Found in the gut of infants, intestines of man, various animals and honeybees. These organisms are generally used in preparation of therapeutic fermented milk products in combination with yoghurt, acidophilus milk or yakult starter cultures.
Eg: Bioghurt, Biograde, Bifighurt, Cultura 'AB, Yakult, Miru-Miru.
Bifidobacterium bifidum, Bifidobacterium longum, Bifidobacterium infantis, Bifidobacterium breve, etc.
The optimum growth temperature is 370C-100C. Anaerobic conditions are essential for optimum growth. Milk fermtneted with bifidobacteria has a distinctive vinegar taste due to the production of acetate plus lactate from the metabolism of carbohydrates.
2.4.1.6. Genus Propionifacterium : Propionibacterium, freuderveichii and Propionibactrium shermanii are used in swiss cheese. It has the ability to produce large gas holes in the cheese during ripening/maturation period. P. jensenii, P. thoeii and P. acidipropionici are other organisms present in these genera.
2.4.1.7. Genes Brevebacterium : Brevebacterium lines is used a as starter culture in preparation of bacterial surface ripened cheese. It imparts distinctive, reddish orange color to the rind of (or formation of smear on) Brick and Limburger cheese or Camembert cheese.
2.4.2. Molds
Moulds are used for the manufacture of some semi soft cheese varieties and in some fermented milk products. Moulds enhance the flavor and modify slightly the body and texture of curd.

2.4.2.1. White mold is used in manufacture of surface mould ripened chees like camembert and Brie cheese. Eg; Penicillium camemberti, Penicillium caseicolum, Penicillium condition 2.4.2.2. Blue mold is used in manufacture of internal mould ripened cheeses like Roquerfort, Blue Stilton, Danish blue, Gorgonzol and mycella cheeses. Eg; Penicillium, roquefortii 2.4.2.3 Other molds Mucor rasmusen – used in Norway for the manufacture of ripened skim milk cheese. Aspeigillus oryzae _ used in Japan for the manufacture of Soya milk cheese. Geotricum candidum – used in the manufacture of villi a cultured product of Finland. The mould grows on the surface of the milk to form the white velvety layer. 2.4.3 Yeasts : Yeasts are used in the manufacture of Kefir and Kumiss 2.4.3.1. Kefir grains : kefir grains consist of a mixture of different microorganisms such as Candida kefir, Kluyeromyces marxianus, Saccharomces kefir, Torulopsis kefir. 2.4.3.2 Kumiss : the important starter microflora of kumiss include Torulopsis spp. Khuyeromyces marxianus var lactis, Saccharomyces cervisiae. 2.5 TYPES OF STARTERS Starters are grouped under different categories based on compositon of microflora, growth temperature, type of products, flavor production and type of termentation into the following categories. 2.5.1. Based on the Composition of Microflora/Organisms a. Single : Used of only single organism in the preparation of dahi or cheese. Disadvantage of using single coulture is that there may be sudden failure of starter due to bacteriophage attack which leads to heavy loss to the industry. b.Paired Compatible Strain : Two strains of cultures having complementary activities in know proportion are used. This will reduce chances of culture failures. In case of

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Starter Cultures and Fermented Milks