Lesson 5 Food spoilage

Persistence

Microbial contamination remains viable but numbers remain unchanged.

Growth

Microorganisms multiply and increase in numbers.

Death

Microorganisms cannot multiply.

Sporulation

Formation of spores by microorganisms.

Toxigenesis

Production of toxins by microorganisms.

Food Spoilage

Undesirable change in color, flavor, odor, or texture of food that makes it unacceptable for human consumption.

Microbial spoilage

Deterioration of food due to the activity of microorganisms.

Enzymatic spoilage

Undesirable changes in food due to enzyme-catalyzed reactions.

Chemical spoilage

Deterioration of food due to non-enzymatic chemical reactions.

Physical spoilage

Undesirable changes to the physical structure of food.

Hydrolysis and fermentation of proteins

Putrefaction, which releases foul-smelling compounds.

Breakdown of pectin

Pectinolysis, leading to the loss of fruit structure and soft rots.

Hydrolysis and fermentation of carbohydrates

Souring, resulting in the production of organic acids and souring of the food.

Hydrolysis of lipids

Fat degradation, releasing glycerol and fatty acids, causing rancidity and bitterness.

Aerobic spoilage of meat

Predominantly caused by psychrotrophic organisms like Pseudomonas.

Off odors at 107 bacterial growth due to glucose and lactate exhaustion and amino acid metabolism.

Slime at 108 bacterial growth.

Enterobacteriaceae and lactic acid bacteria are also important in aerobic meat spoilage.

Anaerobic spoilage of meat occurs in vacuum packaging and is caused by lactic acid bacteria, Brochothrix thermosphacta, and Clostridium.

Surface slime

Shiny, viscous, moist covering on the surface of meat caused by Streptococcus, Leuconostoc, Brucella, Micrococcus, and some Lactobacilli.

Green discoloration

Caused by some Lactobacilli and Leuconostoc.

Hydrolysis (rancidity)

Caused by Pseudomonas, Achromobacter, and yeast.

Phosphorescence

Caused by Photobacteria and Pseudomonas.

Pigmentation

Red spot caused by Serratia, blue color caused by Pseudomonas.

Stickiness, whiskers, black spots, white spots, green patches, off odors

Caused by molds.

Putrefaction

Caused by anaerobic microorganisms.

Shelf life

Length of time a food remains wholesome without deterioration.

Highly perishable foods

Meat, fish, milk, most fresh fruits, and vegetables.

Semi-perishable foods

Potatoes, apple, yam, some nuts.

Stable (durable) foods

Sugar, flour, grain-legumes, dry products.

Direct determination and monitoring

Samples taken at specified stages in food production and stored until quality becomes unacceptable.

Accelerated estimations

Products stored at raised temperatures to increase the aging process.

Shelf-life determination

Direct method involves monitoring the product at regular time intervals, while indirect methods use accelerated shelf-life studies.

The Rule of Q10

The factor by which the rate increases when the temperature is raised by ten degrees.

Calculation example

Determining shelf life based on Q10 values and rate of deterioration at different temperatures.

Chemical indicators

Glucose, gluconic and 2-oxogluconic acid, lactic acid, acetic acid, ethanol, biologically active amines, and volatile compounds used to indicate meat spoilage.

Microbiological indicators

Storage trials, challenge tests, and predictive modeling used to determine indicators of early food spoilage.