Introduction to Microsoft.Net Session 01 Mata kuliah: M0874 – Programming II Tahun: 2010.
Kuliah Yogurt 2010
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Transcript of Kuliah Yogurt 2010
Yogurt
A form of fermented milk produced in most countries where fresh milk is drunk.
Yogurt
• Yogurt is produced by the controlled fermentation of milk by two species of bacteria Lactobacillus bulgaricus and Lactotococcus thermophilus (also known as Streptococcus thermophilus)
Yogurt
• The sugar in milk (called lactose) is fermented to acid (lactic acid) and it is this that causes the characteristic curd to form.
Yogurt
• Streptococcus thermophilus brings the pH of the milk down to 5.5
• Lactobacillus bulgaricus converts lactose to lactic acid
Yogurt
• The two bacteria have a mutually stimulating effect on one another.
• Proteolytic enzymes from L. bulgaricus break down milk proteins into peptides.
Yogurt
• These peptides stimulate the growth of L. thermophilus which in turn produces formic acid and carbon dioxide
• These are growth stimulants for the L. bulgaricus.
Yogurt
• At the end of the incubation pH may fall to as low as 4.2 – 4.4
• The lactic acid coagulates the remaining milk proteins, causing the yoghurt to thicken.
Yogurt
• Acetaldehyde, a metabolic by product of both species, gives raw yoghurt its characteristic flavour.
Yogurt
• Incubation takes 12 hours at 32o C to reach the set point of natural yoghurt
• Sugar, colour and fruit pulp is often added to increase popularity of product.
Yogurt
• Yogurt is a nutritious dessert and its manufacture is an ideal way of using up Europe’s excess milk production
Yogurt
• Some yoghurts may receive additional heat treatment to kill off any living bacteria before or after packaging for the consumer
Fermentation Principles• Milk and LAB culture (Table 4.3)
– Cultured versus “directly set”• Functions
– Lactose– Precipitate casein (pH4.6)– Flavor compounds– Syneresis
• Separation of water from the coagulated milk• Considered unfavorable; to reduce,
– Increase milk solids– heat well above pateurization temp to denature whey proteins– Incorporate stabilizers– Using strains produce exopolysaccharide
• “Ropy” strain-EPS released or dis-attached• EPS remains attached to the cells surface
Yogurt Cultures
• S. thermophilus and Lb. delbrueckii subsp. bulgaricus• 1:1 ratio• Synergistic growth
– S. thermophilus growth first, use free aa and small peptides in milk, lower pH etc, preferred environment for Lb. delbrueckii subsp. bulgaricus
– Lb. delbrueckii subsp. bulgaricus proteolysis helps S. thermophilus to grow
– Lb. delbrueckii subsp. bulgaricus produce more acid, S. thermophilus will decrease
• So the cultures are grown separately, harvested and mixed
• Lactobacillus genus and Streptococcus thermophilus bacteria are usual starter organisms in yogurt.
• They are considered lactic acid bacteria (LAB).• Gram positive, non-spore forming rods or cock,
and aerotolerant anaerobes.
Introduction (cont.)• Streptococcus
thermophilus is a thermophile (grows at 45°C to 110°C). – Ferments lactose to lactic
acid.– Lactic acid chemically
alters casein, a milk protein, and forms curd.
Introduction (cont.)• Lactobacillus genus
bacteria are mesophiles.– Ferment remaining lactose
from S. thermophilus.
proteins peptides
proteins peptides
Lactobacillus thermophilus
proteins peptides
Lactobacillus thermophilusLactobacillus bulgaricus
Proteolytic enzymes
proteins peptides
Lactobacillus thermophilusLactobacillus bulgaricus
Proteolytic enzymes
formic acid + CO2
proteins peptides
Lactobacillus thermophilusLactobacillus bulgaricus
Proteolytic enzymes
formic acid + CO2
lactic acid
proteins peptides
Lactobacillus thermophilusLactobacillus bulgaricus
Proteolytic enzymes
formic acid + CO2
lactic acid acetaldehyde
Raw milk
Raw milk
Pasteurised Milk
pasteurisation
Raw milk
Pasteurised Milk
pasteurisation
Raw Yogurt
homogenisation
cooling
incubation
add starter
Raw milk
Pasteurised Milk
pasteurisation
Raw Yogurt
homogenisation
cooling
incubation
add starter
Processed Yogurt
(heat treatment)
packaging
(heat treatment)
add fruit/flavour