FOOD 4150 Lecture 7

Spoilage

• microbial spoilage of foods results from changes in the food composition, and or appearance or structure as a result of the growth and metabolism of microorganisms

• a product is considered spoiled if sensory changes make it unacceptable to the count

Sensory Changes of Spoilage

• color defects

• changes in temp

• development of off flavours

• off odors or slime

• any other characteristic making the food undesirable for consumption

Why Food Spoils

• most spoilage is caused by microorganisms (bacteria, yeast, molds)

• enzymatic activity within the muscle tissues

• physical changes

• insect e.g. worms, bugs, fruit flies cause damage

Perishable Foods

• foods that have shelf life ranging from several days to about 3 weeks are known as perishable

• e.g. milk and dairy products, meats, poultry, eggs, seafood

Non-Perishable Foods

• have indefinite shelf life and can be stored for several years or longer

• e.g. dry beans, nuts, flour, sugar, canned fruits, peanut butter

Semi-Perishable Foods

• can be preserved for a long time (~6 months) under proper storage conditions

• e.g. veggies, fruits, cheeses, potatoes

Are Spoiled Foods a Risk to Health

• probably not, however most people would not eat spoiled foods - unlikely to cause illness

• foodborne pathogens can be present in non-spoiled food

• if pathogenic bacteria are present in spoiled foods, there is a likelihood that the person will become sick

Primary Causes of Spoilage

• prolonged distrubution or storage time

• inappropriate storage temp

• high initial bacterial counts

• rotation of stock: first in first out

• transportation: temps near freezing

Cross Contamination

• occurs when microorganism from one surface are transferred to another surface

  • food to food

  • equipment to food

  • people to food

• common factors in the cause of foodborne illnesses

Ecology of Meat and Poultry

• in healthy live animals the internal tissue (i.e. muscle, blood, etc.) are normally free of microorganisms

• the mixture of microorganisms regularly found in any anatomical site are referred to as the normal flora

Sources of Contamination Meat and Poultry

• digestive tract - during evisceration process

• hide - aerosols during hide removal

• hair/feathers

• hooves

• lymph nodes

• handling

• processing environment equipment, surfaces, etc.

Composition and Spoilage of Meats

• aw: 0.99

• protein content: 15-22%

• lipids: 2.5 - 37%

• carb composition: 0 - 1.2%

• pH: 7.4 pre-rigor, 5.6 post rigor (chemical changes on muscles)

• 24-36h meat should be chilled to 2-4 degrees celcius

Hides and GIT

• pseudomonas

• acinetobacter

• flavobacterium

• micrococcus

• staphylococcus

• yeast and molds

• fecal material and soil

• main source of pathogens

Fresh Poultry Shelf Life

• 10.6 C 2-3 days

• 4.4 C 6-8 days

• 0 C 15-18 days

• number of bacteria needed for spoilage: 10^5cfu/cm²

• bacteria involved in spoilage: pseudomona, aromobakterien

How to Decrease Contamination

• animal health and cleanliness at slaughter

• milk and egg production maintenance for health

• sanitation procedures - SOPs

• good manufacturing practices

• hazard analysis and critical control points (HACCP)

Ecology of Finfish and Shellfish

• sources of contamination:

  • internal tissue muscle sterile-bacteria present in outer slime layer of skin and gills

• environment:

  • season of year

  • harvest conditions

  • handling

  • processing

Fish Spoilage

• 18% protein

• fat: 1-30%

• high in nitrogen

• spoilage microflora: Pseudomonas, moraxella

• spoilage occur in 4 stages

Fish Spoilage Stages

• stage 1: 0-6 days shifting of bacterial populations/ no odor

• stage 2: 7-10 days: bacterial growth become apparent/ slightly fishy odor

• stage 3: 11-14 days: fishy odor/slime

• stage 4: >14 days: proteolysis begins, extremely slime, offensive odor

Shellfish

• crustaceans and mollusks: larger amounts of free amino acids

• crustacean-potent cathepsin like enzymes - breakdown of proteins results in tissue softening and volatile off-odor

• black spots - (shrimp) melanosis (bisulfite wash-sulfite allergies)

• less nitrogen, more carbohydrates-spoilage pattern fermentative - predominance of lactobacillus and streptococci