General microbiologyMeat most often spoils due to

1. chemical change (oxidative rancidity)

or2.microbial growth– fastest on fresh meat, may still be major spoilage

problem for processed depending on product

– when an animal is slaughtered, it becomes a race to see who will get it first

– microbial growth is likely because most meat cuts and products have a high water content (Aw = 0.99) and are highly nutritious

– contamination occurs as soon as the animal is slaughtered so constant intervention and addition of barriers is important to shelf life and safety

Contamination will include

1. mold

2. yeast

3. bacteria

Bacteria are the primary problem because they grow fastest - but yeast and molds also cause problems in specific cases where bacteria are inhibited

Factors important to spoilage control/shelf life

1. initial numbers– most important for inactivation treatments

log.survivors

heating time

Spoilage of Frankfurters

number of bacteria per gram

time (days)

2 4 6 8

102

103

104

105

106

107

108spoilage level

15.5

o C (3

day

s)

10o C (6

days

)

4.5o C (14 days)

0oC (45 days)

15.5

o C (1

day

)10

o C (2 da

ys)

4.5o C (5 days)

0oC (16 days)

2. temperatures

– psychrophiles - can grow at 0oC (32oF)

– mesophiles - 25-40oC (77-103oF)

– thermophiles - 45-60oC (113-140oF)

Temperature Relationships of the Major Groups of Bacteria

Psychrophiles(optimum temp.)

Pseudomonas geniculutaAchromobacter guttatus

-10

0

20

30

10

60

50

40

80

70

90

100oC212oF

140

180

160

200

Facultative thermophiles

Streptococcus thermophilusClostridium perfringens

Mesophiles (optimum temp.)

Escherichia coliBacillus subtilis

Obligate thermophiles (optimum temp.)

Clostridium thermosaccharolyticumBacillus stearothermophilus

Ground Beef Spoilage

number of bacteria per gram

time (hours)

24 36 60 96

108

106

spoilage level

15.5oC 10oC 4.5oC 0-2oC

3. oxygen– aerobes

– Pseudomonas - fresh meat

– facultative anaerobes– lactic acid organisms– salted product

– strict anaerobes

4. Aw

– available water– bacteria grow at about 0.91 or more– molds above ~ 0.75– major role of salt

5. pH– reduced pH slows or inhibits growth– very dependent on organism

6. specific inhibitors– nitrite– diacetate– lactate– sorbate– organic acids– lactoferrin– bacteriocins

For control, processors combine or “stack” as many barriers together as possible to maximize inhibitory effects---Barrier concept

– most are additive, a few are synergistic

Fresh meat spoilage is typically by psychrophilic, gram negative aerobes (Pseudomonas)

or

pychrophilic, gram positive, facultative anaerobes (lactics) - (vacuum-packaged fresh meat)

processed products spoilage is most often by the lactics

Shelf life is an important issue and needs to be measured and understood for every product.

– “accelerated” shelf life testing is the utilization of higher than normal temperature for relative comparisons of shelf life

Microbial pathogens/safety issues

– Centers for Disease Control and Prevention - CDC (Atlanta)– often quoted for “food-borne illness causes 76 million cases per year

of GI tract illnesses, 325,000 hospitalizations and 5,000 deaths per year.”

– national investigative and monitoring organization

– in 1996, CDC, USDA-APHIS and FDA established the food-borne Disease Active Surveillance Network (FoodNet) - internet site to collect food-borne disease information

– over 90% of food-related illness cases are caused by bacteria

– about 60% of food related cases are from meat, poultry and fish

– 82% of cases are due to unknown causes

To help identify likely organisms:

A. Categories of causes for illnesses 1. infection

– live organisms ingested– salmonella

2. intoxication (poisoning)– toxin ingested

– Staphylococcus aureus, Clostridium botulinum

3. intoxification– live organisms which produce toxin after ingestion

E. coli O157:H7

B. characteristics of outbreaks

– onset time< 1 hr. - probably chemical

– chemical causes can include ciguatoxin and scombrotoxin, both from fish as well as any environmental toxins

– onset time may be dose related

1-7 hrs. - Staphylococcus aureus8-14 hrs. - Clostridium perfringensover 14 hrs. - other organisms

– intensity – Staph.

– specific symptoms – paralysis - Cl. botulinum

Specific organisms of concern in meat products1. Staphyloccus aureus

– poisoning (toxin)

– nausea, vomiting, stomach cramps, diarrhea 3 - 6 hrs onset --- severe!

– usually cooked, prepared foods– does not compete well in raw foods (not refrigerated appropriately)

– lowest growth ~ 45oF 60oF for toxin

– killed by 145oF cook, inhibited by acid

– tolerate 17% salt

– toxin is heat-stable

– humans are most common source (at least 50% are carriers)

Prevention: thorough cooking, rapid chilling, rapid acidification (fermentation)

2. Salmonella sp. (2000 types)

– infection

– G.I. upset - diarrhea, cramps, fever, vomiting, diarrhea included (flu-like)

– usually cooked, recontaminated foods (eggs, chicken) or undercooked products

– present on much fresh meat

– separate fresh and finished (packaging) areas

– needs 45oF to grow– killed by 140oF

– very susceptible to salt

– sources poultry ~ 60% pork, beef ~ 20%

– second most common food pathogen ~1.4 million cases

Prevention: cook appropriately, avoid recontamination

3. Clostridium botulinum - poisoning (toxin)

– very potent neurotoxin blocks neuromuscular motor end plate

– 1 tablespoon would kill 1/2 of U.S. population

– impaired swallowing, dizziness, poor coordination, muscle paralysis– botox cosmetic treatments to reduce skin wrinkles

– recoveries improved by using respirators, etc. until effects wear off, still 10-20% mortality

– low acid, vacuum cans/packages

– need 250oF for destruction

– toxin is more heat-susceptible (80oC -10 minutes)

– susceptible to acids (below pH 5.0)

– inhibited by nitrite

– contamination level is low but widespread (outbreaks are rare)

– honey suspected in some cases of infant botulism

Prevention: appropriate cooking (retort), refrigeration, use of nitrite

4. Cl. perfringens

– intoxification (live ingestion toxin)

– G.I. upset - diarrhea, cramps - seldom nausea

– usually cooked products held at warm temperatures

– needs at least 50oF - best@115oF

– most common in foods held on steam tables for extended time

– need 212oF for inactivation

– also susceptible to acid (5.0) and salt

Prevention: appropriate cooking, rapid chilling

5. Listeria monocytogenes

– often found in meat though dairy products are most common problem

– concern is absorption and transport to other vital organs– causing abortions, meningitis, etc.

– flu-like symptoms in normal individuals

– refrigeration is not a safeguard– but needs oxygen for best growth

– commonly found in processing plant environments, widespread in environment

– salt tolerant (to 25%)

– infection

– survives and grows at ~ 32oF very significant

heat sensitive, cooking to 160oF is more than adequate

– not a frequent problem (2,500 cases per year), but high fatalities

Prevention: appropriate cooking, prevent recontamination

6. Yersinia enterocolitica

– infection

– tolerates refrigeration temperature well (to 33oF) survives freezing

– G.I. upset, diarrhea, fever, vomiting --- resembles appendicitis

from all livestock including dogs and cats

but pork is most common source

– acid (pH 4.6), salt and cold tolerant --- also survives vacuum

– does not compete well with other organisms– will survive in fermented sausage but nitrite is quite effective for

control

Prevention: cook appropriately

7. Escherichia coli O157:H7

– first found in 1982 - originally McDonalds (not publicized)

– later Jack-in-the-Box case - 475 people - 3 deaths

- lots of publicity

– intoxification (live ingestion toxins)

– G.I. upset - bloody diarrhea and kidney failure in children

– survives freezing and refrigeration very well but will not grow until about 38-40oF

– heat sensitive– 140oF for less than 1 minute will kill 90%

– now recommend cooking to 155oF-160oF internal temperature rather than 140oF internal for cooked hamburgers

– can survive in fermented sausage

– primarily dairy cattle source (?)

Prevention: appropriate cooking

8. Campylobacter jejuni

– infection

– cramps, diarrhea, headache, muscle pain

– common in animal G.I. tracts

– most frequent cause of bacterial food-borne illness but hasn’t received publicity ( ~ 2 million cases per year in food)

Prevention: appropriate cooking

9. Shigella spp

– intoxification (live ingestion and toxins)– similar to E. coli O157:H7

– believed to be source of genetic pathogenicity of E. coli

– bloody diarrhea, cramps, fever

– typically derived form fecal contamination (water sources) and under cooking - often sea foods

– third most common food-caused illness organisms according to FoodNet

Prevention: avoid contamination, appropriate cooking

10. Bacillus cereus

– toxin ( 2 forms - short onset, - long onset)

– sporeforming organism like clostridia that prefers warm temperatures

– relatively quick onset - 1-5 hours ( may be 15-30 min) - vomiting - 8-16 hours - diarrhea

– generally need high numbers of organism

– common soil organism, sources are usually dirt or dust

– usually occurs in food held warm below 140oF

– long recognized but not one of the “majors”

Prevention: appropriate cooking (thermophile) and appropriate chilling

11. Vibrio spp

– intoxification (live ingestion toxins)

– V. cholera - toxin causing water-borne cholera– frequent world wide but not in U.S.

– V. parahaemolyticus– diarrhea, cramps, fever sometimes nausea and vomiting

– typical source is fish and seafood

Prevention: appropriate cooking

(continued)

Characteristics of Some Pathogens of Significance in Meat Products

Organism oxygen temp.(oC) pH(min) salt(max.) water activity(Aw)

Clostridiumbotulinum anaerobe 10-50 4.7 10-12 0.94

Staphylococcusaureus facultative 6.5-50 4.2 18-20 0.86/0.90

Salmonella spp. facultative 5-47 4.0 3 0.95

Listeria monocytogenes facultative 0-45 5.0 8 0.97

Clostridiumperfringens anaerobe 6.5-50 5.0 8 0.95

Escherichia coli facultative 10-45 3.6 8 0.90

Additional sources of food-borne illness

1. Viruses– more common than bacteria as causes of food-borne illness (31 million cases per year)

– Norwalk virus - flu-like symptoms– 23 million cases per year ( ~ 9 million food-borne)

2. Non bacterial toxinsa. scombroid poisoning

– partially spoiled fish particularly mackerel and tuna

– reason for icing fish ASAP

– bacteria convert histidine (amino acid) to histamine and produce severe allergy-like reactions

– nausea, vomiting, headache, hives, itching, breathing difficulties

– onset may be 10 minutes

Prevention: avoid “aged” fish

b. ciguatera poisoning

– caused by a neurotoxin accumulated in fish (mackerel, snappers, etc.)

– toxin comes from small marine food organisms/algae

– symptoms can include numbness, tingling lips, temperature “switching” sensations, blurred vision, potential respiratory paralysis– usually resolved but can be fatal

Prevention: avoid fish from areas with known marine organisms

c. shellfish poisoning

– shellfish (mussels, clams, etc.) accumulate toxins form food organisms (algae/plankton) as well as high levels of bacteria and viruses from environment (“collectors”)

– nausea, vomiting, tingling, paralysis

Prevention: appropriate cooking for bacteria/viruses– avoid harvest during times when plankton/algae levels are

high

d. tetrodo toxin

– found in organs of puffer fish (blowfish)

– rapid paralysis (neurotoxin) and likely death (4-6 hours)

– requires skilled preparation of fish to avoid toxin contamination