Microbial spoilage

Question 1

is spoiled food unsafe?

Answer 1

NOT NECESSARILY. spoiled food is mostly an economic issue, but also a food security issue.
-understanding mechanisms of food spoilage helps minimize losses and provide high-quality food supply with adequate shelf-life

Question 2

why do meat, poultry and seafood have different spoilage even though they are all meats?

Answer 2

they have different “original” microbiotas leading to a different succession of microbial spoilage bacteria
-have different handling and storage requirements, which leads to a different micriobial succession

Question 3

how is contamination origin classified?

Answer 3

natural: originating from the animal ie GI, skin
external: originating from the processing environment ie air, soil, human workers
-the abundance of microbes on the food vary depending on the type of animal, and the hygiene of the processing facility

Question 4

what is the first step by bacteria to spoiling food?

Answer 4

attachment: best way to preserve meats is to have a very clean processing facility so that minimal numbers of bacteria are able to attach to the surface of the meat.
- biofilms: = BAD

Question 5

what microbe dominates anaerobic conditions? aerobic

Answer 5

LAB

enterobacteriaceae

Question 6

spoilage*

Answer 6

• def: consumers rejecting a food based on undesirable sensory characteristics
• definition will differ based on socio-economic factors

Question 7

what is the substrate or energy source of spoilage bacteria?

Answer 7

1. glucose
   -glucose is more rapidly metabolized by aerobic bacteria
2. lactate (second best)
   -occurs at 10^7 CFU and proteolysis becomes sensoially evident
   Crustaceans are an exception to these rules because they have enzymes in their hepatopancreas that cause rapid postmortem muscle breakdown that is independent of microbes (kept alive until cooking)

Question 8

Because it is subjective: The ideal spoilage indicator should

Answer 8

1. be absent or present in very low levels in fresh tissue
2. be produced by the spoilage microflora
3. increase with storage time
4. correlate well with sensory analysis

Question 9

traceability*

Answer 9

def: the ability to maintain credible custody of the identification of animals and their products from production to retail
- essential tool in the protection of human and animal health
- traceablility of meat derived from a single animal is quite good, but much more complicated for compound products (ground beef) and may be limited to date and place
- important with the discovery of horse meat in IKEA meatballs

Question 10

6 important ways to control microbes in meat?

Answer 10

1. harvest, or ship animals for slaughter with low contamination
2. reduce the potential for transfer of microbes to carcassess, meat, and seafood from water and the environment
3. apply safe and effective decontamination interventions
4. apply processes to reduce or eliminate microbes
5. avoid cross contamination at all stages
6. store products at low temperatures and use packing conditions that discourage bac growth

Question 11

red meat: when and which organisms cause spoilage?

Answer 11

hygiene of the animals before and during slaughter

• aerobic mesophiles
• common microbes: Gram-neg rods and micrococci (Pseudomonas!!, Enterobacteriaceae, Staph)

Question 12

red meat: spoilage

Answer 12

• if meat is vacuum packed, Gram-pos bac will dominate the population
• If the animal is stressed or exercised before slaughter it will lead to decreased levels of glucose in the tissue - faster degradation of AA and detection of spoilage at lower cell densities
• LAB may dominate interior of ground meats because of limited oxygen

Question 13

why do intact meats spoil more slowly than comminuted meats (ground beef)

Answer 13

• higher levels of initial contamination
• larger surface area
• cross contamination during grinding
• release of fluids for bacterial growth media due to cells rupturing during grinding

Question 14

what orgnisms cause spoilage in processed meats

Answer 14

• low water activity tolerating bacteria - lactobacilli (anaerobic or micrococci (aerobic)
• characteristics: slime - surface, yeasts, souring, greening - H2O2 production
• dry-cured meats mostly spoil because of yeasts or molds that tolerate extremely low water content

Question 15

how/where is poultry spoiled?

Answer 15

• acquired from the bird’s skin and feathers or during processing
• After processing: 10-10^4 CFU, Gram-neg bac
• during refrigeration Psudomonas becomes predominant
• each step in the processing of raw poultry will affect the level and type of spoilage bacteria, with some steps leading to an increase in population and some leading to a decrease

Question 16

what are steps of poultry processing?

Answer 16

1. stunning/killing/bleeding
2. scalding (birds placed in hot water to ease removal of feathers
3. picking: this process aerosolizes bacteria and can spread them to other carcasses or equpiment
4. Evisceration: intestinal tract is mechanically removed: sometimes ruptures tissue - nutrients available for spoilage, intestine rupture increases bacterial load
5. chilling: air chilling or cold water, psychotropic spoilage bacteria reduced on water chilled birds

Question 17

Which organism is responsible for poultry spoilage?

Answer 17

Pseudomonas

yeasts may be involved

Question 18

which foodborne pathogens are associated with seafood?

Answer 18

Salmonella, Clostridium botulinum, Aeromonas, S. aureus, L. monocytogenes, Vibrio cholerae, Vibrio parahaemolyticus, and Vibrio vulnificus

Question 19

what factors enhance the spread and growth of bacteria

Answer 19

crowding and stress found in aquaculture systems

-aquacultured fish have higher bacterial load than their wild counterparts

Question 20

what is produced by fish postmortem

Answer 20

biogenic diamines including histamine*

• produced via *decarboxylation of specific free amino acids
• decarboxylation (removal of C) occurs via the release of decarboxylase from various microbes growing on the food product

Question 21

is histamine destroyed by cooking?

Answer 21

NO, properly cooked spoiled fish can result in poisoning
-histidine is an AA that exists naturally. At temps above 16C, histidine is converted to histamine via the histidine decarboxylase enzyme produced by M. morganii (symbiont in fish)

Question 22

scombroid food poisonings*

Answer 22

caused by consuming biogenic amines

• foodborne intoxication resulting from eating spoiled fish
• symptoms: flushed skin, headache, itchiness, blurred vision, diarrhea
• anti-histamines can be taken to alleviate symptoms
• Mechanism: inappropriate storage, microbial growth, production of biogenic amines - histamine

Question 23

Shrimp

Answer 23

• coliforms and salmonella are common in shrimp rearing environments
• Psudomonas, Aeromonas
• Pathogenic vibrios are routinely present in the water where shrimp are raised. Can attach to and colonize the exoskeletons of shrimp

Question 24

Shellfish

Answer 24

• Vibrios (both pathogenic and non-pathogenic) are found as native organisms in the estuarine environments where bivalves are collected and farmed
• Oysters are filter feeders that can concentrate the native water microbiome, and since oysters are often consumed raw they are associated with several outbreaks
• Mussles also concentrate bacteria and are not recommended to be eaten raw