Fermentation in Dairy Flashcards
Describe the application of biotechnology post farm.
-
Processing
- Fermentation (e.g., milk to yogurt)
- Non-fermented probiotic foods
- Novel foods
-
Production of specific compounds
- Processing aids (e.g., enzymes)
- Additives (e.g., colour, flavourings)
-
Waste management
- Transformation of waste into environmentally friendly material (biodegradation)
Define: fermentation
Anaerobic (and sometimes aerobic) breakdown of organic materials (mostly carbohydrates) by microorganisms as part of their metabolic process.
Yeasts; moulds; bacteria
List a few fermented food products.
- Kombucha
- Natto
- Cheese
- Kefir
- Sauerkraut
- Kimchi
Fermentation has a long history of use in the human diet. Compare its function in less advanced societies to more advanced societies.
- Desirable microorganisms grow on food and produce
compounds as part of their metabolism- These compounds provide desired characteristics in food by formation of specific metabolites
- Serves as a low cost means of preservation in less advanced societies by preventing the growth of pathogens and spoilage former
- Gives variety in industrialized societies
Describe the resurgence of fermented foods.
- Fermented foods named as the top superfood
- According to “What’s trending in nutrition”
- Cultural shift from heart health to gut health
- Connection to brain function
- Rise in lactose intolerance
- Fermented dairy products are better tolerated
Why do we ferment foods?
Preservation: Fermentation extends the shelf life of perishable foods by creating conditions (e.g., low pH, alcohol, or certain by-products) that inhibit the growth of harmful microorganisms like pathogens and spoilage bacteria.
Flavor and Texture: Fermentation enhances the flavor, aroma, and texture of foods. For example, fermented products like yogurt, sauerkraut, and kimchi have distinct tangy flavors due to the production of acids, while bread and cheese develop unique textures.
Nutrient Enhancement: Fermentation can increase the bioavailability of nutrients, breaking down complex compounds and synthesizing vitamins (such as B vitamins) that our bodies absorb more easily.
Health Benefits: Some fermented foods contain probiotics, which are beneficial bacteria that can support gut health and immune function.
Cultural and Traditional Practices: Many fermented foods are integral to cultural cuisines and traditions, contributing to food diversity and heritage.
What is the outcome of fermentation? [5]
- Formation of metabolites
- Acids; aldehydes; ketones; alcohols; CO2
- Prevention of spoilage
- Inhibition of pathogen growth
- Lowering the total energy (except alcohol producing fermentation)
- Higher nutritive value
Metabolites provide unique sensory quality to fermented foods.
Compare primary and secondary fermentation metabolites.
Primary Metabolites:
- Produced during the active growth phase (log phase) of microorganisms.
- Essential for basic cellular functions, like growth and reproduction.
- Common examples include ethanol, lactic acid, and acetic acid.
- These metabolites are directly involved in the fermentation process and are necessary for the organism’s survival.
Secondary Metabolites:
- Produced during the stationary phase, after the growth phase has slowed.
- Not essential for growth but often have specialized functions, like defense or signaling.
- Common examples include antibiotics (e.g., penicillin), pigments, and toxins.
- These metabolites often help the organism compete in its environment or interact with other organisms.
For a food producer, primary metabolites define the basic quality of the product (e.g., ethanol and lactic acid), while secondary metabolites offer opportunities for added complexity, flavor, and functionality (e.g., nisin - an antimicrobial peptide).
What are the three large categories of fermentation?
- Natural fermentation
- Traditional culture
- Use of pure cultures
What is natural fermentation?
-
Microorganisms arrived by chance in raw food
- Microorganism as part of their ecosystem ( LAB in milk)
- Microorganism as part of processing (yeast in grape and grape crushing equipment)
- Condition provided to compete and outgrow
- Fermentation occurred
- Stabilization in fermented food
- Still being used in home pickling and small scale wine making
What are the problems with natural fermentation? [5]
- Right form of microorganism should be present
- Long time required for processing
- Surprise outcome
- Safety risks
- Unreliable for industrialized production
What is back slopping?
- Sample of successful fermentation used for the next batch of fermentation (e.g., Home made sourdough)
- Large quantities of dominant mixed culture is added as a fermenting source
- Shorter time required compared to natural fermentation
- More predictable results
- Still being used in small scale beer processing, some cheese types and vinegar
Traditional mixed culture
What is the concern with traditional fermentation?
Although more uniform and predictable than natural fermentation, still does not meet the requirements for large scale production to avoid safety and economical risk
Describe the characteristics of the modern fermentation food industry. [9]
- Large scale
- Heat treated medium
- Aseptic condition
- Contained structure
- Automated
- Time sensitive
- Minimal exposure to contaminants
- Consistent quality
- Safety a major concern
What is Koch’s Postulate? [4]
- The microorganism must be found in abundance in all organisms suffering from the disease, but should not be found in healthy organisms.
- The microorganism must be isolated from a diseased organism and grown in pure culture.
- The cultured microorganism should cause disease when introduced into a healthy organism.
- The responsible microorganism can be re-isolated and purified and once re-introduced to the host will have the same disease causing property
Describe the use of Koch’s postulate in fermentation science.
The responsible microorganism for fermentation can be isolated and purified and once reintroduced to raw material it will cause the same fermentation
What is a pure starter culture? [4]
- A selected type of microorganism or mixture of different microorganisms to initiate the fermentation
- Laboratory selected and pre-cultured starters used (first attempt in 1883- isolating brewer’s yeast by Emil Christian Hansen)
- Pure starter cultures are propagated under sterile condition
- The food to be fermented is usually heat treated to minimize the presence of other microorganisms
What are the problems with pure culture fermentation? [2]
- Expensive for small scale producers
- Does not have the same organoleptic properties of natural/traditional fermentation
What are some challenges in fermented product development? [3]
- In cultured/fermented products you deal with both chemistry and microbiology as it pertains to the product’s sensory and physical attributes
- Microorganisms may behave differently due to strain differences
- Slight changes in the conditions (e.g., temperature) may cause a different strain to dominate
Describe lactic acid bacteria.
- “A nontaxonomic classification for a group of Gram-positive non-spore-forming bacteria which ferment sugars to lactic acid”
- Emerged 1.5-2 billion years ago
- Lack pathogenicity
- Ferment lactose and other carbohydrates to lactic acid
- Relatively acid tolerant
- Mostly aerotolerant anaerobe
At this time there are 13 genera established as LAB. Which ones are dairy LAB? [4]
Lactobacillus
Lactococcus (relatively new taxonomic group)
Leuconostoc
Streptococcus
Note that Bifidobacteria have been erroneously included in some older resources, but it is not LAB.
Compare homofermentative vs heterofermentative.
Homofermentative: Produces primarily one main product, usually lactic acid, from fermentation (e.g., lactic acid bacteria in yogurt).
Heterofermentative: Produces multiple products from fermentation, such as lactic acid, ethanol, and CO₂ (e.g., in sauerkraut and kefir).
What metabolites are produced by LAB? [4]
- Lactic acid (major)
- Formic and acetic acid (minor)
- Acetaldehydes (less than 25 ppm)
- Exopolysaccharides (EPS)
What are the ‘OLLDD’ commercial LAB starter culture classifications?
- “O” type
- L. lactis subsp. lactis and cremoris (acid producing)
- “L” type (formerly “B” type)
- “O” type plus Leuconostoc spp.
- “LD” type
- “L” type plus “D” type
- “D” type
- “O” type plus flavour producing strains of L. lactis
What are the LPA commercial classifications?
- “L” type; Aseptic “laboratory” propagated
- Excluding any phages
- Labile to phage
- “P” type; Non-aseptic “practice” propagated
- Develop natural resistance to phages due to constant exposure
- Artisanal or naturally propagated
- Non defined strains propagated by “back slopping”
What is yogurt?
- Semi-solid, live bacterial biomass of lactic acid bacteria namely, Streptococus thermophilus and Lactobacillus delbruekii subsp. bulgaricus, grown in milk
Yogurt does not have a standard of identity in Canada.
What is cheese?
Product of pressed milk curd (coagulated [by fermentation usually] milk protein)
Cheese does have a standard of identity in Canada.
What are the different types of yogurt?
- Plain
- Set (Balkan style) - fermentation takes place in the container; firmer than stirred
- Stirred (Swiss style) - fermentation takes place within the fermenter
- Flavoured
- Set (Fruit at the bottom)
- Stirred (Fruit or other mixed, incubated and packaged)
- Frozen yogurt
- Yogurt drinks
Describe a process flowchart for yogurt making.
Note the start and end point of pH values.
Describe the cheese making unit operation.
There are many different secondary starter cultures added after whey separation for cheese depending on what type of cheese it is.
Bacteriophages are viruses that attack bacteria. How does this happen?
- They have the typical virus structure (head and tail)
- Attach to specific receptor (Ca++ required)
- Channel formation
- DNA penetration
- Degradation of host chromosome
- Synthesis of phage DNA components
- Breach of host cell wall
- Release of phage components
- Transform into complete phage
Describe the lytic pathway of bacteriophage infection.
Not mentioned in this class, but there is also the lysogenic cycle whereby the viral DNA incorporates itself into the host genome and remains dormant for a long time before lysis. Lysogenic may be more efficient since it allows the host cell to replicate with the viral DNA in the meantime.
