STARTER CULTURES AND FERMENTED MILK PRODUCTS

Module 6. Causes of slowness of starters

Lesson 9
PROBLEMS ASSOCIATED WITH STARTER ITSELF, WITH CONTROL OF STARTERS, WITH MILK AND WITH PRODUCTION METHOD

9.1 Starter Defects

1. Insufficient acid production

2. Insufficient flavour production

3. Flavour defects

4. Body and texture defects

9.1.1 Insufficient acid production or non-acid curd

One of the most common defects in lactic acid starter cultures. A good starter should produce lactic acid at vigorous and steady rate. The slowness in starters may occur with dramatic suddenness or starter culture may slowly lose its viability. The reasons for the insufficient acid production could be

a) Spontaneous loss of vitality inherent in starter itself : starter strain variation or genetic instability usually associated with plasmids, loss of lac’ plasmid

b) Incompetence in the control of starters

i. allowing the starters becoming contaminated

ii. Frequent sub-culturing

iii. Use of unsuitable media

iv. Use of wrong incubation temperatures

c) Causes of slowness inherent in milk itself

i. Use of Milk of abnormal quality i.e. mastitis milk or colostrums milk or late lactation milk or silage milk or winter milk

ii. Milk containing antibiotic residues

iii. Milk contaminated with bacteriophage

iv. Milk containing residues of detergents and sanitizers

v. Milk shaving inhibitory bacteria

vi. Seasonal variations in milk composition

vii. Milk containing natural inhibitory substances like leucocytes, antibiotics etc.,

viii. Excessive aeration of milk

d) Changes in the method of making fermented milk : Sudden change in the methods adopted for the preparation a particular fermented milk causes slow acid production

9.1.2 Insufficient flavour production

Factors that affect the acid production also affect flavour production. In addition to these the following factors also affect the flavour

• Improper acid production

• Milk having low citrate ions

• Milk containing high Gram negative organisms that reduce diacetyl content by

• Producing diacetyl reductase

9.1.3 Flavour defects

a) Sharp acid taste : this is due to the over ripening of the culture which maybe due to increased inoculum or higher incubation temperature or prolonged incubation period.

b) Malty flavour: This is due to the variants of Lactococcus lactis ssp. lactis var maltigenes

c) Metallic flavour: This is due to over ripening of the culture or due to the use of poorly maintained containers with metallic contamination or due to the over growth of Leuconostoc sp.

d) Green flavour: This is due to under development of Leuconostocs as result of repeated transfer of culture before adequate development

e) Flat flavour: Due to small amounts of citrates in milk or due to under development of aroma culture

f) Bitterness : due to the activity of proteolytic contaminants

9.1.4 Body and texture defects

a) Weak body : It is due to insufficient acid production or milk with low total solids or milk subjected to severe heat treatment

b) Hard and lumpy: It is due to over ripening

c) Wheying off: It is due to over ripening or due to low total solids in milk resulting in fracturing, defective starters, use of un-homogenized whole milk, agitation or vibration of culture soon after curd begins to form. Whey may collect on the surface or at the bottom of the culture or beneath the cream layer

d) Ropiness : due to the contamination of starter with Alcaligenes viscosus or due to the ropey strains of starters like Leuconostocs or L. lactis ssp lactis var hollandicus .

e) Gassiness: Production of CO₂ by the coli forms or yeast. CO₂is also produced by certain strains of Leuconostocs and in case of cottage cheese these may contribute to the floating curd defect. In cheddar cheese gas production may be troublesome because it results in eye formation or bulging of cans.

9.1.5 Problems with starter itself

Spontaneous loss of vitality inherent in starter itself i.e. starter strain variation or genetic instability usually associated with plasmids

9.1.6 Problems with control of starters

These are due to incompetence in the control of starters

i. Allowing the starters becoming contaminated

ii. Frequent sub-culturing

iii. Use of unsuitable media

iv. Use of wrong incubation temperatures

9.1.7 Problems with milk-antibiotics, abnormal milks etc

Milk with abnormalities or other contaminants can create problems for starters

1. Use of abnormal Milk i.e. mastitis milk or colostrum milk or late lactation milk

2. Milk containing antibiotic residues

3. Milk contaminated with bacteriophage

4. Milk containing residues of detergents and sanitizers

5. Milks having inhibitory bacteria

6. Seasonal variations in milk composition

7. Milk containing natural inhibitory substances

9.1.8 Problems with production method

Many problems will be encountered during the production of fermented milk products

1. Use of abnormal milk

2. Use of poor quality starter cultures

3. Use of improperly cleaned utensils and equipment

4. Use of milk subjected to improper heat treatment

5. Use of unhygienic production practices

6. Handling persons with unclean habits and unhealthy persons

7. Use of improperly cleaned and sterilized packaging material

8. Use of improper storage conditions and temperatures.