Food Micro - Exam 2

What is food spoilage?

Undesirable deterioration that makes food unacceptable in quality and sometimes unsuitable to eat.

How is a food-safety hazard different from spoilage?

A hazard can cause illness even when food looks, smells, and tastes normal; spoilage is a quality change.

Does mold or a bad odor prove that food contains a pathogen?

No, spoilage organisms and pathogens are different categories.

What is the classic four-phase microbial growth curve?

Lag, exponential (log), stationary, and death/decline.

What is a provisional sequence of spoilage steps?

Contamination, adaptation/selection, growth, metabolite/enzyme accumulation, and detectable spoilage.

What happens during initial microbial growth in food?

A small population adapts and begins growing; early growth may be below sensory detection.

What are microbial metabolic byproducts in food?

Products of microbial metabolism such as acids, gases, and alcohols that may alter food.

How can metabolite accumulation cause food spoilage?

Metabolites build up and change pH, aroma, flavor, gas pressure, color, and texture.

What does sensory spoilage mean?

The food develops detectable unacceptable odor, flavor, appearance, or texture.

What is structural spoilage?

Physical breakdown or alteration such as softening, tissue collapse, or gas pockets.

What is the final stage of spoilage in the five-step scheme?

The food is completely deteriorated and unacceptable.

What is the lag phase?

Cells adjust to the food environment and make needed enzymes; cell numbers change little.

What is the log phase?

Cells divide rapidly at a near-constant rate; numbers rise exponentially.

What is the stationary phase?

Growth slows as nutrients are depleted and waste accumulates.

What is the death phase?

Viable-cell numbers fall because death exceeds new growth.

Define intrinsic food factors.

Properties inherent to the food: pH, water activity, nutrient composition.

Define extrinsic food factors.

Environmental/storage conditions: temperature, atmosphere, humidity, and packaging.

What is water activity (aw)?

A measure of water available for microbial growth, roughly the ratio of water vapor pressure over food to that over pure water.

How is water activity different from moisture content?

Moisture content is total water; aw reflects how available that water is to microbes.

How does low pH affect spoilage?

It inhibits many bacteria; acid-tolerant yeasts and molds may still grow.

Why do nutrient differences change spoilage communities?

Microbes differ in which nutrients they can use; the food selects organisms with matching metabolism.

How does refrigeration affect microbial spoilage?

It slows growth of many organisms, extending shelf life, but does not sterilize food.

How does oxygen availability select spoilage microbes?

Oxygen favors aerobic organisms; restriction suppresses aerobes but selects facultative or anaerobic organisms.

What is vacuum packaging?

Packaging that removes most air and reduces oxygen around the product.

What organisms often dominate aerobically packaged refrigerated meat?

Aerobic psychrotrophic bacteria, especially Pseudomonas.

Which organisms may become important in vacuum-packed chilled meat?

Lactic acid bacteria and other low-oxygen organisms.

Does vacuum packaging guarantee food safety?

No, it may delay aerobic spoilage but can favor anaerobic hazards.

Why can foods stored side-by-side spoil differently?

They differ in pH, water activity, nutrients, and packaging microenvironment.

What is microbial succession in food?

A change in which organisms dominate over time as conditions change.

Why may a late-stage spoilage organism replace an early colonizer?

The early organism changes the environment or consumes preferred nutrients.

What does Pseudomonas commonly do in food?

Causes off-odors, slime, and discoloration in chilled foods.

What can lactic acid bacteria do in foods?

Ferment sugars to organic acids; can cause souring in unintended products.

What is yeast spoilage often like?

Fermentation of sugars can cause gas, alcohol, and off-flavors.

What is mold spoilage often like?

Visible fuzzy colonies, discoloration, softening, and musty odors.

Why should E. coli and Salmonella not be casually listed as typical spoilage organisms?

They are primarily food-safety pathogens; their presence may not cause sensory spoilage.

What is a sensible way to interpret sensory signs?

Treat them as evidence of quality deterioration, not as a definitive safety test.

What is microbial spoilage?

Deterioration caused by microbial growth or enzymes acting in food.

What is nonmicrobial deterioration?

Quality loss driven by chemical or enzymatic reactions rather than microbial growth.

What is oxidation in electron-transfer terms?

Loss of electrons; oxidation is paired with reduction.

What does 'OIL RIG' summarize?

Oxidation Is Loss (of electrons); Reduction Is Gain (of electrons).

How can oxidation affect food?

It can create off-flavors, discoloration, nutrient loss, and changes in texture.

What is lipid oxidation?

Reaction of unsaturated fatty acids with oxygen.

What are primary products of lipid oxidation?

Lipid hydroperoxides, which can break down into smaller volatile compounds.

What secondary compounds can cause rancid flavors?

Aldehydes, ketones, alcohols, acids, and other volatile products.

What is oxidative rancidity?

Rancid odor/flavor arising largely from oxidation of fats.

What is hydrolytic rancidity?

(Incomplete entry, no definition provided.)

What accelerates lipid oxidation?

Oxygen, light, heat, transition metals such as iron or copper, long storage, and high unsaturation.

Name ways to slow lipid oxidation.

Limit oxygen, light, and heat; use suitable packaging and permitted antioxidants; control metal catalysts and storage time.

Is rancidity always microbial?

No, oxidative rancidity is chemical; hydrolytic rancidity may be caused by food enzymes or microbial lipases.

What is enzymatic browning?

PPO-mediated oxidation of phenolic compounds after tissue disruption, followed by reactions that form brown pigments.

What does PPO stand for?

Polyphenol oxidase, an enzyme in many fruits and vegetables.

What substrates and reactant are involved in PPO browning?

Phenolic compounds and oxygen; PPO oxidizes phenolics to reactive quinones that polymerize into dark pigments.

Is enzymatic browning caused by microbes?

No, it is an enzyme reaction in the food, though microbial damage can expose tissues and accelerate it.

Give a common enzymatic-browning example.

A cut apple or potato turning brown after exposure to air.

How can enzymatic browning be slowed?

Reduce oxygen exposure, acidify, chill, use approved antioxidants, or inactivate PPO by a suitable heat treatment/blanching.

What is a mold?

A filamentous fungus that grows as hyphae and forms a network called mycelium; many produce spores.

What are hyphae?

Microscopic thread-like fungal filaments that grow and absorb nutrients.

What is mycelium?

The mass or network of interwoven hyphae that forms the mold body.

What is vegetative mycelium?

Hyphae growing into or across the food/substrate, primarily acquiring nutrients.

What is aerial mycelium?

Hyphae extending above the food surface, often bearing reproductive structures.

What are septate hyphae?

Hyphae divided by cross-walls called septa; septa may have pores.

What are coenocytic hyphae?

Hyphae without regular cross-walls, producing a continuous cytoplasm with many nuclei.

What is a sporangium?

A sac-like structure where spores called sporangiospores form internally.

What is a sporangiophore?

A specialized hyphal stalk that supports a sporangium.

What are conidia?

Asexual fungal spores formed externally, not enclosed in a sporangium.

What is a conidiophore?

A specialized stalk that produces or supports conidia.

What are sclerotia?

Compact, hardened masses of fungal hyphae that help some fungi survive adverse conditions.

What are zygospores?

Thick-walled sexual spores formed after fusion of compatible fungal structures in some groups such as traditional Zygomycete molds.

What are chlamydospores?

Thick-walled resting cells formed from hyphal cells, helping persistence under stress.

What is the key visual clue for Aspergillus?

An upright conidiophore ending in a swollen vesicle with phialides and chains of conidia.

What is the common visual clue for Penicillium?

Branched conidiophores with brush-like or broom-like clusters (penicilli) bearing chains of conidia.

What is the common visual clue for Fusarium?

Septate hyphae and often curved, canoe- or sickle-shaped multicellular macroconidia.

What is the common visual clue for Rhizopus?

Broad, usually nonseptate/coenocytic hyphae; sporangia at sporangiophore tips and root-like rhizoids.

What are rhizoids in Rhizopus?

Root-like hyphae that anchor the mold and help absorb nutrients.

What is the difference between Aspergillus and Penicillium conidiophores?

Aspergillus typically has a terminal swollen vesicle with radiating structures; Penicillium typically branches into a brush-like arrangement.

What useful food role can some Penicillium species have?

Selected strains are used to ripen and flavor cheeses, including blue-veined and soft-ripened varieties.

Why is mold identity important in food?

Different species differ in spoilage behavior, useful fermentation roles, and potential mycotoxin production.

Are all molds harmful?

No, some are useful in foods and biotechnology; some cause spoilage; some produce mycotoxins.

What is a mycotoxin?

A toxic secondary metabolite produced by certain fungi that may contaminate food or feed.

Are mycotoxins required for mold growth?

No, they are secondary metabolites, not essential structural parts of the mold.

Why is visible mold not a reliable test for mycotoxins?

Not every mold produces toxins, toxin production can occur without obvious visible growth.

Why may removing the visible mold not make a food safe?

Hyphae and toxins can extend beyond the visible colony, especially in soft/high-moisture foods.

Why may cooking fail to remove mycotoxins?

Many mycotoxins are chemically stable under ordinary cooking and processing.

Which Aspergillus species are classically associated with aflatoxins?

Certain strains of Aspergillus flavus and A. parasiticus.

What commodities are important aflatoxin concerns?

Corn/maize, peanuts, tree nuts, and some other crops.

What are major aflatoxin health concerns?

Liver toxicity and cancer risk, especially with chronic exposure.

Which toxin is classically associated with Fusarium verticillioides in corn?

Fumonisins.

Which Fusarium toxins are associated with Gibberella ear rot and wheat head blight?

Deoxynivalenol (DON, also called vomitoxin) and zearalenone.

What is ochratoxin A associated with?

Certain Aspergillus and Penicillium species; it is a food/feed contaminant.

Where can mycotoxin contamination arise?

Before harvest in the field, during harvest, drying, transport, or storage.

What stored-grain conditions favor fungal growth?

Elevated grain moisture/water activity, warm or changing temperature, damaged kernels.

How does K-State stored-grain guidance describe water activity?

Most field fungi need very high aw, while some storage fungi can grow at lower aw.

Is 'molds need aw about 0.80' a universal rule?

No, minimum aw varies greatly by species.

What is a key mold-control strategy for stored grain?

Dry promptly and maintain safe, uniform moisture and temperature.

What does FDA do regarding mycotoxins?

FDA monitors and regulates/sets action or advisory levels for certain contaminants.

Why are mycotoxins a supply-chain problem?

They may enter in the field and persist through processing.

What is a bacterial endospore?

A dormant, highly resistant survival structure formed inside certain bacteria.

Why do bacteria form endospores?

To survive unfavorable conditions.

What is sporulation?

The developmental process in which a vegetative cell forms a resistant endospore.

Does endospore formation increase bacterial numbers?

No, one vegetative cell produces one endospore, which later yields one vegetative cell.