YOGURT (CURD)
Introduction
Yogurt
is a fermented dairy product obtained by the controlled fermentation of milk
using specific lactic acid bacteria. It is one of the oldest fermented foods
known to humans and is widely consumed across the world due to its nutritional
value, pleasant taste, and health benefits. During yogurt production, lactose
present in milk is converted into lactic acid by starter cultures, resulting in
milk protein coagulation, thick texture, and characteristic sour flavor.
Yogurt is considered a
functional food because it not only provides essential nutrients such as
proteins, calcium, vitamins, and minerals, but also contains beneficial
microorganisms (probiotics) that improve gut health. It plays a significant
role in human nutrition, especially in regions where milk preservation is
challenging.
History of Yogurt
The
word "yogurt" is derived from the Turkish word "yoğurmak",
meaning to thicken or coagulate. Yogurt consumption later spread to Europe
through the Ottoman Empire. In the early 20th century, scientific interest in
yogurt increased after Elie Metchnikoff proposed that lactic acid bacteria in
yogurt could promote longevity by improving intestinal health. Since then,
yogurt has gained global acceptance as a health-promoting dairy product.
Types of Yogurt
Yogurt can be classified
based on fat content, processing method, and microbial composition.
a) Based on Fat Content
Full-fat yogurt –
Prepared from whole milk
Low-fat yogurt – Made
from partially skimmed milk
Fat-free yogurt –
Prepared using skimmed milk
b) Based on Processing
and Texture
Set yogurt – Fermented
directly in retail containers
Stirred yogurt –
Fermented in tanks and stirred before packaging
Drinking yogurt – Thinner
consistency, suitable for beverages
Greek yogurt – Strained
yogurt with high protein content
c) Based on Microbial
Composition
- Conventional yogurt – Contains
standard starter cultures
- Probiotic yogurt – Contains
additional beneficial microbes such as Lactobacillus and Bifidobacterium
4. Methodology of Yogurt
Preparation
The
production of yogurt involves the following steps:
1. Fresh,
high-quality milk (cow, buffalo, or mixed milk) is selected. Milk should be
free from contaminants and antibiotics.
2. Milk
fat and solids-not-fat (SNF) content are adjusted to obtain desired texture and
consistency.
3. Milk
is heated to 85–90°C for 30 minutes or 95°C for 5 minutes. This step:
Destroys pathogenic
microorganisms
Improves yogurt texture
by denaturing whey proteins
4. Heated
milk is cooled to 42–45°C, the optimum temperature for starter culture growth.
5. Starter
culture is added at 2–3% concentration and mixed thoroughly.
6. The
inoculated milk is incubated at 42–45°C for 4–6 hours until pH reaches around 4.5.
7. Fermented
yogurt is cooled to 4°C to stop further fermentation and stored under
refrigeration.
Common Starter Cultures:
- Lactobacillus delbrueckii subsp.
bulgaricus
- Streptococcus thermophilus
These bacteria are used
in a symbiotic relationship and are essential for yogurt fermentation.
Role of Microorganisms in
Yogurt Fermentation
a) Streptococcus
thermophilus
- Initiates fermentation
- Rapidly ferments lactose to lactic
acid
- Produces formic acid and carbon
dioxide that stimulate Lactobacillus bulgaricus
- Contributes to mild flavor
b) Lactobacillus
delbrueckii subsp. bulgaricus
- Enhances acid production
- Produces acetaldehyde, the main
flavor compound of yogurt
- Breaks down proteins into peptides
and amino acids
- Improves aroma and texture
c) Probiotic
Microorganisms (in probiotic yogurt)
- Lactobacillus acidophilus
- Bifidobacterium bifidum
- Lactobacillus casei
Role:
- Improve intestinal microflora
- Enhance digestion and immunity
- Suppress harmful bacteria
Nutritional Applications
- Rich source of proteins, calcium,
phosphorus, and vitamins
- Easily digestible due to reduced
lactose content
Health Benefits
- Improves gut health and digestion
- Helps in lactose intolerance
- Boosts immune system
- Reduces risk of gastrointestinal
infections
Industrial and Culinary
Applications
- Used in beverages, desserts, and
bakery products
- Base material for flavored and frozen
yogurt
- Used in traditional foods and
probiotic formulations
Therapeutic Applications
- Used in dietary management of
diarrhea
- Helpful in cholesterol reduction
- Supports bone health
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