Microbial Spoilage + Public Health Concerns (1) Flashcards
True/False: spoilage means a food is unsafe to eat
False; not always unsafe (but probably unpalatable; and cannot tell if it is unsafe)
meat, poultry, and fish are ____ foods. What implications does this have on spoilage?
muscle rapid spoilage (nutrient rich, protein rich, moist; supports pathogenic growth)
Where does contamination of meats come from?
from skin/guts/equipment; contaminated during slaughter/processing/dressing
True/False: the internal part of meat is usually very low in microbes
True (if from a healthy animal); since not exposed to outer environment
origin of meat contamination can be classified as ___ or ____
natural (from animal: skin, feathers, guts, etc)
external (from equipment, air, soil, humans, etc)
What influences the type and numbers of bacteria on meat?
animal type, hygiene of facility
What is the first step by bacteria in contamination of meat?
attachment to meat surface
What bacteria is the best at attaching to meat surfaces?
Pseudomonas
What is the best way to prevent contamination of meat?
cleanliness of processing facility (less bacteria can attach); rinse meat to prevent attachment of bacteria
What is a major issue in food processing equipment? Why is it such a big issue?
formation of biofilms (combination of spoilage/pathogenic bacteria) - can form on almost any surface! HIGHLY PERSISTANT
can be 10-100x more resistant to sanitizers than planktonic bacteria
____% of meat and ___% of fish are lost due to microbial spoilage
25%; 30%
What species is dominant in cold aerobic conditions in meat? What species is dominant in vacuum packed meat?
enterobacteriaceae (Gram neg)
LAB
How does Pseudomonas affect other microbial species?
inhibit Shewanella (uses up glucose and makes iron-binding siderophores) promote Listeria (hydrolyze proteins and make AA for listeria)
What is spoilage?
development of undesirable sensory characteristics in food that leads to consumer rejection (will depend on personal preferences and socioeconomic differences)
Examples of spoilage characteristics:
off flavors, off colors, off-odors, off-textures, discoloration, slime, putridness (proteolysis), sourness
Non proteolytic spoilage is characterized by a ___ taste/smell, while proteolytic spoilage is very ____.
sour; putrid
the energy source of spoilage bacteria is ____
glucose
In an oxygenated environment, what is the first spoilage bacteria that grows and why?
pseudomonas
best at metabolizing glucose (outcompetes Brochothrix and Shewanella)
What happens after glucose is depleted in food spoilage?
lactate becomes primary substrate; then amino acids (putrid)
When do amino acids become the main substrate in food spoilage? What is the indication that this is happening?
At CFU = 10^7
become slimy, sulfur/ammonia odor, putrid
List the main substrates for spoilage in food in the order they are utilized:
What is an exception to this pattern?
glucose, lactate, amino acids
exception: crustaceans - endogenous enzymes in hepatopancreas will break down tissue upon death
Why must crustaceans be kept alive prior to cooking?
after death -> rapid proteolysis (spoilage) by endogenous enzymes
What factors influence the definition of “spoilage?”
geography
socioeconomic factors
food type
preservation interventions
What are ways to evaluate ‘freshness’ of meat? What are the weaknesses of each method?
sensory evaluation - requires trained experts, subjective
Microbiological tests - destructive, only give general info
develop spoilage indicators (measurable biochemical changes) - still in development
What are examples of substances that could be used as spoilage indicators (meat)?
amines, ammonia, trimethylamine, sulfur
What characteristics make for a good spoilage indicator?
- absent or very little in fresh tissue
- produced by spoilage bacteria
- increase with storage time
- correlate well with sensory analysis
Are AMR bacteria problematic to food spoilage?
Possibly - higher resistance to food processing treatment
What is meat traceability and what is it’s importance?
traceability - maintain credible custody of identification of animals from production to retail
important for human and animal health (outbreaks, welfare)
In products such as _____, traceability is very difficult and may be limited to ______.
ground meat/composite products (many animals)
date, place
where did the demand for meat traceability originate from?
BSE outbreak food fraud (horse meat in IKEA meatballs)
The general microbial control for meat is focused on _____ and ______.
good hygiene
proper storage
What is done to help prevent meat spoilage? (6)
- harvest/ship animals with low contamination
- clean water/environment (reduce microbe transfer to carcass)
- safe decontamination measures
- processing (heat, high pressure, irradiation)
- avoid cross contamination
- store at low temp, proper conditions
Characterize the initial microbial load on fresh meat:
10^2 - 10^7 CFU (surface)
mostly AEROBIC mesophiles - gram neg rods & cocci
(Pseudomonas, Enterobactericeae, Acinetobacter, Staphylococcus, Micrococcus, fecal streptococci)
small population of LAB, Bacillus, Clostridium spores
In meat that is immediately vacuum packed, the spoilage organisms will be Gram _____.
positive
Stressed animals during slaughter will lead to meat that spoils (faster/slower). Why?
faster
stress -> use up glycogen -> less glucose in tissue -> glucose depleted more rapidly -> proceeds to proteolysis (putrid)
Ground meat spoils (faster/slower) than intact meat. Why? What is the dominant microbe type?
faster
more cross-contamination, greater initial load, more surface area
similar to intact meat, but also more LAB (bacteria introduced to anaerobic interior)
What microbes cause spoilage in processed meat? Why?
Lactobacilli (anaerobic) and Micrococci (aerobic)
less water activity; inhibits growth of gram-neg psychrophiles
What are spoilage signs in processed meat?
greening, slime, souring
What causes slime production in processed meat spoilage?
yeast, lactobacillus, enterococcus, B. thermosphacta
What causes greening in spoiled processed meat?
Lb. viridescens, Streptococcus, Leuconostoc
What causes spoilage in dry-cured meat with very low Aw?
yeast and mold (surface spoilage)
In poultry, most of the bacterial load is acquired from:
skin and feathers
At the end of poultry processing the bacterial load is:
10^1 - 10^4 CFU
Acientobacter, Enterobactericeae, Pseudomonas
What are the general steps for processing poultry?
- stun/kill/bleed
- scalding
- picking
- eviscerate
- chill
How is feather removal achieved? What are potential issues? What is an alternative?
scalding -> picking
sprays bacteria, spread to other carcasses and equipment
can use “waxing” - lowers aerobic gram-neg counts, but higher Staph aureus
How can evisceration increase bacteria load?
equipment contamination
rupture tissues -> more nutrients available
rupture intestine -> contamination
What are the chilling methods for poultry? Which one is advantageous and why?
Air chilled (cold room) or water chilled (immerse in bath)
Water chilled -> less psychrotrophic bacteria (spoilage), slight increase in % water (more weight; good for seller but not consumer)
Most common spoilage organism in poultry is _____, but can also involve ____.
pseudomonas
yeasts
True/False: aquaculture fish will have less bacterial load than wild caught
False; crowding and stress increase bacterial/pathogen growth
Foodbourne pathogens associated with seafood:
Salmonella, C. botulinum, Aeromonas, S. aureus, Listeria, Vibrio (cholerae, parahemolyticus, vulnificus)
Why is spoilage in seafood particularly of concern?
high in free AA -> converted postmortem by spoilage bacteria (DECARBOXYLATION) -> BIOGENIC DIAMINES
(ex: histidine -> histamine)
causes SCOMBROID POISONING
what microbe is responsible for histamine production in fish flesh?
Morganella morganii (symbiotic microbe in fish)
True/False: proper cooking can prevent scombroid poisoning
False: biogenic amines not destroyed with cooking
What are examples of biogenic amines?
histamine, cadaverine, putrescine
What is a concern of biogenic amines in cured/smoked fish?
will react with nitrates -> carcinogenic substances
Symptoms of scombroid poisoning:
What can be taken to alleviate this?
onset 10-60 min after consumption
flushed skin, headache, itchy, blurred vision, cramps, diarrhea (similar to allergy rxn)
take antihistamines
True/False: most shrimp that is produced is exported
True; 75% produced in developing countries, and 75% is consumed in developed countries
In shrimp production, colonization of _____ is unavoidable. colonization by ____ may occur with fecal contamination.
pathogenic vibrios (colonize exoskeleton)
fecal contamination -> coliforms, salmonella
What organisms are mainly responsible for spoilage of refrigerated shrimp?
pseudomonas, aeromonas
Why are oysters common sources of outbreaks?
eaten raw; filter feeders (concentrate bacteria)
_____ species are often found in the environment for farming shellfish.
Vibrio (pathogenic and non-pathogenic)
