The microbial spoilage and mechanism of meat

By

Assoc.Prof.Dr.Narumol Matan

Meats Poultry

1. Post mortem change of muscle to meat

• 1 pH : glycogen pyruvate (C6H12O6)

– Respiration

– PSE (pale soft exudative)

– DFD(dark firm dry)

C6H12O6+ 6O2+38 (ADP+Pi) 6CO2+ 6H2O + 38 ATP

2C6H12O6 +2(ADP+Pi) 2CH3CHOHCOOH + 2ATP+6H2O

Lactic acid

2. Rigor mortis actin+myosin

3. Autolysis

Lipid glycerol+free fatty acid

lipase or fat spiting enz.

Protein peptide+actin+myosin

proteolytic enz , cathepsin

Contamination from equipment such as knife, chopping board

Contaminated from humans such as

hand, costume

Contamination from animals

Contamination from storage environment

• spoilage of meats at low temperature is accompanied by the production of off-color compounds such as ammonia, H2S, indole and amines.

2. Meat spoilage mechanisms

• Cadaverine > Putrescine

• Putrescine occurred at levels from 0.4-2.3 ppm และ cadaverine from 0.1-1.3 ppm

Lysine H2N(CH2)5NH2

Cadaverine

Ornithine / arginine H2N(CH2)4NH2

Putrescine

decarboxylase

Detection and mechanism of meat spoilage

Spoilage of fresh livers

• The content of carbohydrate in livers is high and mean pH around 6

• The predominant flora at spoilage consisted of lactic acid bacteria

• The main spoiled flora such as Pseudomonas, Alcaligenes, Escherichia, lactic streptococci, B. thermosphacta

• Among the determining factors are the following; – Whether the product is raw or cooked

– Concentration of nitrites present

– Relative load of psychrotrophic bacteria

– The degree to which the vacuum-package film excludes CO2

– Product pH

The dominant flora :Lactobacilli, B. thermosphacta

Spoilage of vacuum-packaged meats

Spoilage of Frankfurters, bologna, sausage, luncheon meats

Frankfurters Bologna

Sausage Luncheon

1. Slimy spoilage occurs on the outside of casings. From the slimy material may be isolated yeasts, lactic acid bacteria of the genera Lactobacillus, Enterococcus, B. thermosphacta, L. viridenscens produces both sliminess and greening.

2. Souring; the souring results from the utilization of lactose and other sugars by the organisms with the production of acid. Lactobacillus produces souring

3. Greening occur on stored and processed red meats, one cased by H2O2 . It generally appears after an anaerobically stored meat product is exposed to air.

H2O2 Nitrosohemochrome

A greenish oxidized porphyrin

* The second type of greening occurs generally on fresh red meats that are help at 1-5 °C and stored in gas-impermeable or vacuum-packaging containers. This type of greening usually dose not occur when meat pH is below 6.0.

*Microorganisms that cause spoilage such as Lactobacillus

sake, S.putrefaciens

H2S Myoglobin

Sulphmyoblobin

4. Yellow discoloration of vacuum-packaged luncheon-style meat was caused apparently by Enterococcus casseliflavus. The discoloration appeared as small spots on products stored at 4.4 °C, and it was fluorescent under UV. Between 3 and 4 weeks were required for the condition to develop, and the responsible organism survived 71.1 °C for 20 min. The other yellow-pigmented enterococcal species is E. mundtii.

• The nature of these products and the procedures employed in preparing certain ones such as smoking and brining. Therefore, the most common is moldiness, which may be due to Aspergillus, Alternaria, Fusarium, Mucor, Rhizopus, Botrytis, Penicillium

Spoilage of Bacon and Cured Hams

Bacon Cured Hams

• The sugars are fermented to produce conditions referred to as “sours” of various types, depending on their location within the ham. A bacteria have been implicated as the cause such as Acinetobacter, Bacillus, Pseudomonas, Lactobacillus, Proteus, Micrococcus and Clostridium

• Gassiness occur in cured hams by the genus Clostridium.

Spoilage of poultry

• The bacteria flora of fresh poultry by many investigators have revealed over 25 genera.

• When these meats undergo low-temperature spoilage, almost all workers agree that the primary spoilage belong to the genus Pseudomonas. Moreover, in the study were found Acinetobacter, Flavobacterium and Corynebacterium

• Fungi are of considerably less importance in poultry spoilage except when antibiotics are employed to suppress bacteria growth. When antibiotics are employed , however, molds become the primary agents of spoilage. The genera Candida, Rhodotorula are the most important yeasts found on poultry. The essential feature of poultry spoilage is sliminess at the outer surface of the carcass or cuts.

• Fish contain comparatively high levels of proteins and other nitrogenous constituents such as amino acid, ammonia and uric acid etc.

• The microorganisms know to cause fish spoilage are indicated by to reduce Trimethylamine-N-oxide (TMAO) to Trimethylamine (TMA)

Spoilage of fish and shellfish

• Histamine, diamines, and total volatile substances are used also as fish spoilage indicators.

• Measure the total volatile compounds include total volatile bases (TVB), total volatile acid (TVA), total volatile substances (TVS) and total volatile nitrogen (TVN)

Histidine Histamine decarboxylase

- Histamine is produced from the amino acid also as fish spoilage indicators. Histamine is produced from the amino acid histidine by microbially produced histidine decarboxylase. Histamine is associated with scombroid poisoning.

• People who take excessive amounts of histamine will cause an allergic reaction to rash, redness, burning in the mouth. Some people may have nausea, vomiting and diarrhea.

• There are no more than 100-200 ppm (depending on the laws of country).

• Shrimp have higher amino acids than fish and have cathepticlike enzymes that cause rapid breakdown of proteins.

• The genera of bacteria have been recovered from spoiled such as Pseudomonas spp., Proteus

• Most predominant bacteria I shrimp hold to spoilage Temperature Days Held Organisms pH

0 13 Pseudomonas 6.2-5.9 Good

5.6 9 Moraxella 5.8 Off

11.1 7 Moraxella 5.7-5.5 Musty

16.7 5 Proteus <5.2 Sour/putrid

22.2 3 Proteus