Lecture 4

Question 1

Large group of potential spoilage organisms

Answer 1

Pseudomonas spp, Lactobacillus, Moraxella, Acinetobacter, Brochothrix Clostridium, yeasts andmoulds

Question 2

Food environments:

Answer 2

Intrinsic factors: rich in NPN, peptides and proteins but low carbohydrates, high Aw, pH 5.5 - 5.9
Extrinsic factors: Typically stored refrigerated (<5 degrees), aerobic and anaerobic microenvironments

Question 3

Spoilage defects occur at ….

Answer 3

~10^7 cfu/cm, gets an odour, bone taint and greening

Question 4

Lactobacillus curvatus

Answer 4

• Metabolises glucose to lactic acid, leucine and valine to isovaleric and isobutyric acid
• Metabolise cysteine to H2S

Question 5

Facultative anaerobic e.g. enterobacter, serratia, hafnia, proteus spp

Answer 5

Metabolise amino acids to amines, ammonia, and mercaptans - cause putrefaction

Question 6

Shewanella putrefaciens

Answer 6

Metabolise amino acids to H2S

Question 7

Abundance of bacterial species in meat

Answer 7

Pseudomonas and enterobacteriaceae significantly higher in meat samples

Question 8

Abundance of bacterial species in environmental samples

Answer 8

Brochothrix, staphylococcus, lactic acid bacteria, and psychrobacter

Question 9

Case study: chilled lamb from NZ to europe by ship (70+ days)

Answer 9

• Minimise microbial contamination
  Minimise growth e.g. LAB use glucose anaerobically - growth limited by glucose supply
• Vacuum packaged permeability <20

Question 10

Shelf life model

Answer 10

Shelf-life decreases by 10% for every 1 degree increase above - 1.5 in the 1.5 to 5 degree range, predicts loss of shelf-life of 15, 35 and 65% respectively at 1, 2 and 5