Microbial food spoilage Flashcards
(66 cards)
- the undesirable deterioration of food quality that may result in changes in odor, taste, and appearance of food
- to destroy the value or quality of a food
- refers to the process of decay itself
Food spoilage
Criteria for acceptable foods:
- It should be at a stage of development or maturity.
- It must be free from pollution at any stage in the production.
- It must be free from undesirable biological, chemical, and physical changes.
- It must be free from pathogenic microorganisms.
Types of agents causing food spoilage (chemical, biological, or physical)
- Growth and activity of microorganisms: bacteria, yeasts, and molds.
- Insects, rodents, or animals.
- Action of the enzymes naturally present in the plant or animal food, such as degradation of vegetables by pectinases and fish by proteinases.
- Reactions in the food, such as browning and oxidation.
- Changes, such as changes from freezing, burning, drying, and pressure.
- Presence of foreign material in the food, such as heavy metals, toxins, and nonfood materials.
- Presence of parasites or their eggs.
Undesirable changes that can occur in foods
Texture
- loss of solubility
- loss of water-holding capacity
- toughening
- softening
Flavor
- development of rancidity, cooked or caramel flavors
- other off-flavors
Color
- darkening
- bleaching
- development of other off-colors
Appearance
- increase in particle size
- decrease in particle size
- non-uniformity of particle size
Nutritive value
- loss or degradation of vitamins, minerals, proteins, lipids
Safety
- generation of toxic substances
3 most important types of spoilage:
- Microbial
- Chemical
- Physical
Type of spoilage:
- due to physical damage to food during harvesting, processing, or distribution
- increases the chance of chemical or microbial spoilage and contamination because the protective outer layer of the food is bruised or broken and microorganisms can enter the foodstuff more easily
-example: staling of baked products, physical separation of components, moisture loss or gain by foods
Physical spoilage
Type of spoilage:
- when foods are removed from its natural source, chemical changes begin with the deterioration of food structure
- chemical reactions alter edible quality, including deterioration in color, appearance, texture, aroma, flavor, nutrition, safety, and functional properties
Chemical spoilage
2 types of chemical spoilage
- Nonezymatic browning - occurs during the roasting, baking, grilling, and frying of many foods
a. Maillard reactions - the reaction of carbonyl groups (such as reducing sugar, aldehydes, ketones, and lipid oxidation products) and amino compounds (such as lysine, glycine, peptide, amine, and ammonia proteins)
Protein + Sugar + Heat = Color, flavor, and aroma of baked bread.
b. caramelization or pyrolysis of food carbohydrates due to heat treatment above the melting point of sugar under alkaline or acidic conditions.
c. browning of ascorbic acid: the thermal decomposition of ascorbic acid
d. lipid browning (rancidity), which is oxidation of lipids
e. reaction between the food and the packaging material
e. not changing frying oils - Enzymatic Browning - can occur when the apples, potatoes, and some other fruits and vegetables are cut and exposed to air
- enzymes present in the cells of food carry out an oxidation reaction, such as colorless compounds converted to brown-colored compound
- enzymatic browning does not occur in cooked fruits and vegetables since the enzymes are destroyed by heat
a chemical that can form naturally in starchy foods, like potatoes and grains, during high-temperature cooking processes such as frying, roasting, and baking, and is also found in cigarette smoke.
Acrylamide
How to prevent enzymatic browning
Treat fruits and vegetables with acids like lemon juice to prevent them from turning brown
Don’t soak in water because it will make them soggy
Examples of few polyphenol compounds
Quercetin
Myricetin
Caffeic acid
a condition characterized by excessive pigmentation of body surfaces due to the accumulation of melanin
Melanosis
Signs of microbial spoilage
- rotten egg smell from sulfur-producing microbes
- other off-odors from nitrogenous compounds, such as ammonia and amines
- sliminess from overgrowth of microbes
- gas formation and bubbling
- sponginess in meats
- greening from sulfide-producing bacteria
- rainbow sheen from fluorescent pseudomonads
- souring from acid production
- other off-tastes
Frozen meat microbial agents of concern
Cladosporium herbarum
Penicillium hirsutum
Cryptococcus
Trichosporon
Candida
Raw, comminuted meat microbial agents of concern
Gram-positive bacteria and LAB
Dried meat microbial agents of concern
Aspergillus glaucus
Raw, cured meat microbial agents of concern
Enterobacteriaceae
Clostridium
LAB
Cooked, uncured meat microbial agents of concern
Gram-negative psychrotrophic bacteria
LAB
Cooked, cured meat microbial agents of concern
Heat resistant psychrotrophs, Bacillus spp.
LAB
Frozen raw poultry microbial agents of concern
Cladosporium herbarum
Perishable, cooked poultry microbial agents of concern
LAB, Aeromonas spp.
Psychrotrophic clostridia
Chilled raw poultry microbial agents of concern
Psychrotrophic bacteria
Heat-processed or cured poultry microbial agents of concern
Psychrotrophic bacteria or molds, respectively
Irradiated poultry microbial agents of concern
Moraxella
Enterococci
LAB
