Chapter 1 Food Spoilage Flashcards
What are the signs of microbial spoilage? Provide at least 4 signs.
- Visible growth
- Foam Production
- Slime
- Exudate
- Off-flavor
What are the 5 factors that affect microbial spoilage?
- Significance of microorganism (i.e. multiplication rate)
- Microbial load
- Predominant microorganisms
- Food nutrients
- Microbial growth in succession
What are the 4 major causes of food spoilage?
Physical, Chemical, Microorganisms, and Others.
What types of nutrients do microorganisms prefer?
Metabolizable carbohydrates > NPN and small peptides > Large proteins > Lipids
Why does the predominant microbial type and nature of food spoilage change?
Due to the production of metabolites from the predominant m/o. The metabolites changes the environment and may favor certain species while inhibit other species of m/o.
What is the sequence of events in microbial spoilage?
- Introduction of m/o
- Favorable food environment
- Storage time
- Multiplication of m/o
Define the protein-sparing effect.
The protein-sparing effect is when the body utilizes sources other than protein to generate energy.
How does LAB affect the microflora of fresh meat?
When carbs are added, LAB can arrest the growth of many normal microflora that metabolizes NPN and proteinaceous compounds, which prevents putrefaction as proteins are not decomposed into volatile compounds.
What are some (4) examples of carbohydrate degradation?
- Alcoholic fermentation
- Lactic acid fermentation
- Butyric acid fermentation
- Propionic acid fermentation
State the common groups (8) of microorganisms involved in food spoilage.
- Yeasts
- Molds
- Enterobacteriaceae
- Pseudomonas sp.
- Lactic Acid Bacteria
- Bacillus sp. (spore former)
- Clostridium sp. (spore former)
- Alicyclobacillus (spore former)
What are the differences between proteolysis and putrefaction?
Proteolysis is the breakdown of proteins into polypeptides and into peptides; Putrefaction is the breakdown of amino acids into volatile products.
How does lipid degradation contribute to rancidity and off-flavor.
Lipid degradation by lipases produces glycerol and fatty acids. The latter can then degrade into aldehyde and ketone, which is the contributor of rancidity and off-flavor.
Name the three (3) spore former species discussed in this chapter
- Bacillus sp
- Clostridium
- Alicyclobacillus
Give some examples of m/o (4) that can degrade nitrogen compounds.
Pseudomonas, Shewanella, Bacillus, Clostridium.
What are some changes in foods caused by spoilage m/o?
- Color change from m/o growth
- Color change from chemical changes
- Softened texture
- Changes in odor and flavor.
Give some examples of volatile products produced from the breakdown of amino acids.
H2S (Hydrogen Sulfide) Methyl Mercaptans Indole Cadaverine Putrescine Histamine
Define shelf-life
The period of time in which food remains safe and retains desired quality.
Isolation of microorganisms that causes food spoilage is based on Koch’s postulates. Describe the steps involved in the isolation process.
- Isolate m/o from food
- Grow m/o in pure culture.
- Inoculate m/o in another sample of food
- m/o must cause spoilage in the new food.
- Isolate and identify the m/o
There are five(5) major microbial factors that affect the shelf life of food, state and describe them.
pH - Death is rapid in low pH as bacteria uses more energy to maintain intracellular pH.
Water Activity - Low water activity causes dehydration
Microbial interactions - e.g. mutualism or competition may have a positive impact on shelf-life.
Gas tensions - MAP/ vacuum packaging inhibits the growth of aerobes but is less inhibitory to anaerobes.
Storage conditions
What is the purpose of shelf-life test?
To assess if a product is safe and stable during normal production and storage conditions.
What is the purpose of challenge test?
To assess if a food product is likely to be safe if contaminated with undesirable microorganism.
How does ASLT differ from shelf-life test?
ASLT uses an “abuse” condition to speed up the rate of deterioration to predict the shelf-life of a product.
What is predictive microbiology?
Predictive microbiology is the utilization of statistical techniques and computer data analysis to predict the growth and activation of m/o.
What is predictive microbiology?
Predictive microbiology is the utilization of statistical techniques and computer data analysis to predict the growth and activation of m/o.
How to reduce the fishy odor caused by Trimethylamine N-oxide (TMAO)?
Evaporate it by heating it with alcohol.
Some apples rot to become soft and mushy, while some become dry and firm. What is a possible factor that gives rise to the soft and mushy texture of rotten apples?
Microorganisms that produce the enzyme pectinase breaks down the pectin cell-wall of the apple, giving rise to a softened texture.
Why is the microbial number important in food spoilage?
The microbial number must reach the “spoilage detection level” to result in observable changes. For example, formation of lactic acid may be detected at higher microbial load, while formation of H2S can be detected at lower microbial load.
A food is usually spoiled by one or two species of dominant microorganisms. What are the factors that can make a microorganism more dominant than others?
- Suitable growth environment
- Shorter generation time
