Understanding Food Spoilage

Definition of Food Spoilage

• Spoiled food is food that has been damaged or injured
• Damage renders the food undesirable for human consumption

Common Causes of Food Spoilage

• Insect damage
• Physical injury such as bruising or freezing
• Enzyme activity
• Microorganisms

Foods Affected by Spoilage

• Fresh meats and poultry
• Processed meats
• Fish and shellfish
• Eggs
• Bakery products
• Milk
• Fruits and vegetables

Spoilage of Fresh Meats and Poultry

• Meat is the most perishable food due to its high water activity (aw) and abundant nutrients
• Protein-based foods are high-risk due to fast microbial growth, which can lead to food poisoning
• Beef studies are the basis for meat spoilage patterns, with similar patterns observed in pork, lamb, and other meats

Sources of Microorganisms in Fresh Meats

• Stick knives
• Animal hide
• Non-sterile containers
• Overall environment
• Hands of handlers
• Lymph nodes, such as in hamburgers
• Gastrointestinal tract (GIT)

Biochemical Events Leading to Rigor Mortis

• Respiration stops, halting ATP synthesis
• Circulation ceases, impeding ATP resynthesis which leads to a lack of ATP
• Lack of ATP causes actin and myosin to combine into actomyosin, resulting in muscle stiffening
• Oxygen supply decreases, leading to the growth of anaerobes
• Nervous and hormonal regulation stops, temperature drops, and fat solidifies
• Glycolysis begins, converting glycogen to lactic acid, pH drops from 7.4 to 5.6, denaturing proteins

Effects of Glycogen on Spoilage

• Glycogen, a glucose polymer stored in muscles and the liver, serves as an energy reserve
• In a living animal, circulatory systems supply O2 to muscle cells, converting glycogen into energy, CO2, and H2O
• Post-mortem, O2 supply to muscles is cut off, respiration stops, but glycogen breakdown continues.
• Glycogen converts to lactic acid, lowering pH until glycolytic enzymes are inactivated
• Stressed animals use glycogen to deal with stress, resulting in less glycogen and acid production post-mortem
• Reduced acid leads to higher pH (above 6.2), promoting microbial growth, resulting in dry, firm, dark (DFD) meat and quicker spoilage

Fresh Meat Spoilage Factors

• Majority of refrigerated meat spoilage occurs on the surface from external sources, it depends on water activity
• Internal spoilage bacteria become active when the temperature is not properly reduced, the main bacteria are Clostridium perfringens and Enterobacteriaceae family
• Pseudomonas grow the fastest where Eh has high O/R, moisture, and low temp
• Molds dominate spoilage of beef cuts when the surface is too dry for bacteria to grow

Mold and Yeast Spoilage of Fresh Meats

• Molds will fail to thrive on meats when bacteria consume oxygen faster than what the molds can use
• Fungal spoilage includes Thamnidium, Mucor, and Rhizopus (whiskers on beef), Cladosporium (black spot), Penicillium (green patches), Sporotrichum, and Chrysosporium (white spots)
• Molds do not grow on meat below -5°C
• Yeast spoilage includes Candida and Rhodotorula

Ground Meat Spoilage

• Ground meat's smaller particle size and higher surface area promote the growth of aerobes
• Spoilage is exclusively caused by bacteria like Pseudomonas, Acinetobacter, Alcaligenes, and Aeromonas

Spoilage of Meat Near Bone and MDM

• Deep spoilage
• Mechanically deboned meats (MDM) have a higher pH (6-7) due to marrow incorporation
• Spoilage in these areas is caused by Clostridium and Enterococcus

Detection of Meat Spoilage

• Microbial spoilage cannot be recognized without special testing, with the exception of raw milk
• Early spoilage is detected through off-odors, particularly in vacuum-packaged meats
• Off-odors are present in meat and aerobically stored vegetables
• Slime develops, which is especially noticeable under aerobic conditions
• Definite structural changes occur in the product

Slime layers and Biofilm in Spoilage

• The first sign of spoilage is off-odor, the measurement is at log 7 to 7.5/cm²
• Slime develops, measured at log 7.5 to 8/cm²
• The slime layer is a biofilm
• It grows bacteria, fungi, and protozoa bound by an extracellular matrix that adheres to an object
• Example dental plaque
• The biofilm protects microbes, making them hard to destroy
• The sliminess has a mass of bacteria growth + softened meat proteins

Smell of Spoiled Meat

• Meat that spoils at low temperatures emits off-odor compounds: ammonia, H2S, indole, and amines.
• Putrefaction is the decomposition of organic material, primarily protein, due to microorganisms, producing foul odors
• Cadaverine and putrescine are diamines that indicate spoilage
• Putrescine is mainly produced by Pseudomonas, and cadaverine is produced by Enterobacteriaceae

Spoilage at Fridge Temperatures

• When fresh meat (pH ~5.6) is stored at fridge temperature, Pseudomonas grows the fastest and utilizes glucose
• Brochotrix thermosphacta also uses glucose and glutamate but grows slower, making it a poor competitor

Spoilage Phases

• Off-odor becomes evident when simple carbohydrates are depleted, thus it switches to amino acids and nitrogen compounds
• Off-odor and off-flavor develop specifically when amino acids are consumed by bacteria.
• Initial signs of spoilage are a rise in pH and increases in bacterial numbers

Spoilage of Poultry Characteristics

• Poultry skins support spoilage bacteria better than muscle tissues
• Spoilage biota typically starts on the surfaces, originating from water, processing, or handling
• The inner parts of poultry are rather sterile with very few microbes
• The main indication of spoilage is surface sliminess.
• Visceral cavities develop sour odors that are a 'visceral taint'

Spoilage of Poultry Microbes

• Pseudomonas causes primary spoilage given a high surface humidity, a high content of oxygen, and low temperature
• Fungi does not affect poultry unless when antibiotics are used and bacterial growth goes unchecked
• Yeast is produced when Candida, Rhodotorula become present

Carcass Sanitizing/Washing Methods

• Trimming
• Washing with plain water
• Using organic acids (acetic, citric, lactic acid) at 2-5%
• Using other chemicals like hydrogen peroxide, chlorine dioxide, or chlorhexidine
• Steam treatment for 5-10 seconds at 80°C

Spoilage of Eggs Protection

• Protective: Intrinsic factors
• Fresh eggs:

Components of Fresh Eggs

• Outer waxy shell membrane helps block microorganisms
• Shell helps block microorganisms
• Barriers to m/o: A, B, C,D
• Inner shell membrane helps block microorganisms

Egg White Spoilage

• Effective barriers against gram-positive bacteria, lysozyme
• Avidin forms a complex with biotin
• Conalbumin forms iron complex
• High pH 9.3
• Antimicrobial

Egg Yolk Spoilage

• Nutrient contents favor m/o growth
• pH 6.8
• m/o is present

Egg Microbial Entry and Growth

• Generally fresh eggs are sterile
• After having laid eggs, numerous m/o might appear
• ie. Pseudomonas, Acinetobacter, Serratia, Enterobacter, Eschericia, Salmonella (esp. Salmonella Enteritidis.)
• M/o might penetrate shells, then they enter -> grow -> spoil
• The speed of entry depends on the temperature, age of eggs, level of contamination and the humidity

Spoilage Signs in Eggs

• Prolonged storage causes white will lose water to the yolk making the white shrink and the yolk gets thin

• The yolk could come in direct contact with a membrane leading to bacterial infection

• Bacteria leads to foul smells as H2S is released

• Molds grow first in the air sac region that has high O2 percent

• High humidity - mold grows

• Low humidity - loose H2O

Processed Meats

• These meats are cured, smoked, and cooked

About Curing

• It produces flavor and color

NaCl Properties

• Prevents m/o growth

Nitrate and Nitrite Properties

• They stabilize red meat color, flavor, retard rancidity and prevent clostridial spores from germinating
• Sugar: Color stabilization, and flavoring also gives a substrate for fermentation
• Such as sausage, bacon, ham

About Smoking

• Develops color, aroma and flavor

Preservation Methods

• Ingredients are preserved by heat and smoking
• Woods and liquids are smoked

3 Types of Spoilage in Processed Meats

• a) Sliminess is confined to outer casing, caused by Lactobacillus, Enterococcus and B. thermosphacta, Weissella viridescens
• It's favored by moist surface
• b) Souring
• Happens to ingredients underneath the skin
• Lactobacillus, Enterococcus cause it
• Occurs due to utilization of m/o carbs
• Acidity is the product of this
• c) Greening
• (i) H2O2
• Popular in cured meats
• Air exposure causes it, it was usually stored in an aerobic environment
• Upon exposure, H2O2 reacts with nitrosohemochrome
• Green oxidizing porphyrin is produced
• Created by Weissella viridescens, Leuconostocs and Enterococcus

Greening by H2S

• Common in container storage where the temp is 1-5’C
• Forms greenish sulphmyoglobin
• Can prevent this in under PH6.0 meats
• Pseudomonas and Lactobacilli

Other facts about spoilage of processed meats

• B. thermosphacta most dominant in sausage
• Condiments and spices could result in a bad m/o

Bakery Products

• Spoilage from bakery occur
• Lower moisture inhibits fast m/o and encourages mold growth
• High humidity causes it
• Wraps increases it

About Bread Mold

• 'Bread mold’ – Rhizopus stolonifer
• Red bread mold’ – Neurospora sitophila

About pastry

• High PH in low aw cakes inhibit spoilage, however sugary pastries are still prone though
• The molds are destroyed via baking, but it can come from handling, toppings, and air
• Milk*
• The high PH 6.4-6.6 raw milk content produces m/o growth
• m/o indicates contamination

Facts About Spoilage

• M/O is always present
• Raw milk kept at low temps allows growth

Types of Bacteria

• Enterococcus, Lactococcus, Streptococcus, Lactobacillus, Pseudomonas, Bacillus, Listeria - Less than 10^2 - 10^3 cfu are initially produced
• Pasteurization kills thermoduric, however types of bacteria include Streptococcus thermophilus, lactobacilli, Bacillus, Clostridium persist
• Streptococci produces milk curd, converts PH to 4.5

About Mildew

• Can exist in milk
• PH is raised at neutrality allowing bacteria production
• Pseudomonas converts milk as the PH changes

Detection of Milk Contamination

• Off-flavor, odor indicated that it's soured

Fish and Shellfish

• Inner-flesh is normally sterile in C) Spoilage of Fish and Shellfish
• Gills & Intestines have many pathogens such as Pseudomonas, Psychrobacter, Vibrio, Flavobacterium, Coryneforms and Micrococci.
• Biota: Temperature indicates if the water is fresh or warm

What to look for in waters regarding bacteria

• Mesophilic GM and water temp
• Psychrotophic Gm is water temp

Notes on Marine Fish

• High salt
• Fatty - Less low carbs, higher polyunsaturatd
• Low connective contents

Additional Facts

• Damage the fish to result in earlier spoilage
• A cooling agent should be used for catches to remain sanitary

Postmortem Signs

• There tends to be increased ph with no acids

Bacteria Growth

• It uses nitrogen after the process

Detection of Spoilage for Fish and TMA

• Find microbial organisms for infection

What is TMAO +Where is TMA found?

• TMAO: Marine fish, osmoregulation

• Not present freshly

• Bacterial origin

• If its unbalanced indicates the ph

Types of Fish Contamination

• Is histadine decarboxylase in microbial organisms converts fish.

Fish Warning Signs

• Off odor smells from examining the gill of a fish
• Evicerating fish can quickly spread bacteria
• Autolysis tends to speed it upp
• Most common for skin