lecture 3 notes

Classical growth curve

A curve that represents the four phases of bacterial batch culture growth - lag, logarithmic growth, stationary, and logarithmic death.

Exponential growth rule

The rule that states that during the exponential phase of growth, the number of cells doubles at a steady rate.

Lag phase

The phase of bacterial growth where there is no apparent growth, but viable cells produce necessary enzymes for the use of a new medium.

Exponential phase

The phase of bacterial growth where there is a doubling of cells at a steady rate, limited by the absence of nutrients or an increase in harmful metabolites.

Stationary phase

The phase of bacterial growth where there is no net increase in microbial population, very little cell division, variation in cell morphology, and the production of spores and toxins.

Death phase

The phase of bacterial growth where there is a rapid decline in population, marked by a difference between viable and total count.

Intrinsic factors

Factors that affect microbial growth and survival in foods that are inherent to the food itself, such as moisture content, pH, nutrient content, biological structure, redox potential, and antimicrobial barriers and constituents.

Extrinsic factors

Factors that affect microbial growth and survival in foods that are external to the food itself, such as processing factors, implicit parameters, relative humidity, temperature, time, gaseous atmosphere, and types of packaging/atmospheres.

Moisture content (water activity)

The amount of water available for microbial growth in a food, measured as water activity (aw).

pH

The measure of acidity or alkalinity of a substance, which affects microbial growth by influencing energy requirements, cell membrane integrity, enzyme activity, and the ionization of nutrients.

Oxygen concentration

The presence or absence of oxygen in the environment, which determines the types of microorganisms that can grow.

Water activity (aw)

A measure of the availability of water for microbial growth in a food, influenced by solute concentrations and affecting the growth of microorganisms with different aw requirements.

Minimum levels of aw permitting growth at near optimum temperatures

The minimum water activity levels required for the growth of specific microorganisms at their optimal temperatures.

Redox potential (Eh)

A measurement of the ease by which a substance gains or loses electrons, which affects microbial growth by categorizing microorganisms into different groups based on their Eh requirements.

Cardinal temperatures

The minimum, optimum, and maximum temperatures at which microorganisms can grow, which vary depending on the organism.

Reduced oxygen packaging

A packaging method that reduces the amount of oxygen available to microorganisms, preventing their growth and spoilage.

Vacuum packaging

A packaging method that removes air from the package, reducing the oxygen available for microbial growth and extending the shelf life of the product.

Modified atmosphere packaging (MAP)

A packaging method that replaces the air in the package with a gas mixture containing CO2, O2, and N2, which inhibits microbial growth and maintains product stability.

Nitrogen

The use of nitrogen to prevent pack collapse during packaging and storage of food.

CO2 Inhibition

The inhibitory effect of carbon dioxide on aerobic microorganisms.

Bacteriostatic Effect

The mechanism by which carbon dioxide exerts a bacteriostatic effect on microbial cells.

Gas Mixtures

Examples of gas mixtures used in modified atmosphere packaging (MAP) of food to control microbial growth.

Controlled Atmosphere Storage

The use of impermeable packaging for bulk storage and transport of food to create a controlled atmosphere.

CO2 Impact

The effect of carbon dioxide on microbial cells, including its impact on cell membrane, solute transport, enzymes, and proteins.

Implicit Factors

The influence of organism properties, growth rate, substrate affinity, physiological state, history, stress response, competitive microflora, and microbial interactions on microbial growth.

Specific Growth Rate

The importance of microorganism's specific growth rate in determining its dominance in food microflora.

Dominance of Bacteria

The dominance of bacteria over molds at low pH in food.

Substrate Affinity

The impact of substrate affinity on growth competition among microorganisms.

Physiological State

The sensitivity of exponential phase cells to heat, low pH, and antimicrobials, and the relationship between growth rate and sensitivity to treatments.

History and Stress Response

The pre-adaptation of microorganisms to adverse conditions and the increase in resistance through culturing or pre-exposure to specific factors.

Microbial Interactions

The role of cell-to-cell communication and induction of stress response in nearby cells through molecules secreted by stressed cells.

Mutualism

The effects of mutualism on growth stimulation and the safety implications in certain food products.

Nutrient Availability

The impact of microbial interactions on nutrient availability and removal of inhibitory components.

Antagonistic Interactions

The antagonistic behavior of microorganisms towards each other, including the production of inhibitory compounds or sequestering essential nutrients.

Processing Factors

Various processing factors such as comminution, slicing, packing, irradiation, pasteurization, mixing, washing, and storage that can influence microbial growth in food.

Ecosystem of Food

The ecosystem of food, including the direct and indirect influence of process factors, intrinsic factors (microflora and implicit parameters), and extrinsic factors (temperature and relative humidity) on microbial growth.