2_MICROBIAL GROWTH IN FOODS & FACTORS AFFECTING THEM

Microbial growth

is the increase in the number of microorganisms, such as bacteria or fungi, through reproduction.

energy, cellular components, and many end products.

Microorganisms utilize nutrients in foods to obtain ____

Nutrition

Deals with the nutrients required for growth as part of microbial physiology.

Macronutrients and Micronutrients

Types of Nutrients:

Macronutrients

What type of Nutrients:

• Nutrients that are required in large amounts

• Examples: C, N, O, H, P, S, K, Mg, Ca, Na

Micronutrients

What type of Nutrients:

• Nutrients that are required in just trace amounts

• Examples: Fe, Mn, Cr, B, Co, Cu, Mo, Zn

Phenotypes

made up of proteins

spores

Most molds reproduce by producing ____(sexual and asexual)

Asexual spores

• the products of mitotic division of a single parent cell

• reproduction is accomplished through the formation and spreading of ____

• germinate into a hyphae structure under favorable conditions

Sexual spores

• formed through a process involving fusion of the two parental nuclei followed by meiosis, producing haploid offsprings.

• It develops into hyphae and a mycelium that produce more spores

Hypha

Mycelium

yeast

Pseudomycelium

Sporangiospores

Conidiophores

binary fission or budding

A yeast cell can reproduce asexually by

mating

A yeast cell can reproduce sexually by

Budding

Bud separates out from the mother cell to produce daughter cells.

Binary fission

• Yeast cells split into two equal cells.

• is a process where a bacterial cell divides to two new cells. The time required to form two cells is called the generation time

Mating

Fusion of two yeast cells.

hosts

Viruses cannot reproduce by themselves, they need ___

Lytic and Lysogenic

Viral DNA follows 2 cycles in bacterial cells:

Lytic cycle

free phage DNA controls bacterial DNA and converts bacterial cell to bacteriophage-producing cell that starts synthesizing viral particles, nucleic acid, and proteins.

Lysogenic cycle

virus DNA combines with the bacterial chromosome, which can be replicated once the host DNA replicates. Each daughter cell gets a copy of the virus DNA.

generation time

Binary fission is a process where a bacterial cell divides to two new cells. The time required to form two cells is called the

horizontally

Bacteria splits __

Growth Curve

An organism growing in an enclosed vessel, such as tube or a flask (a growth condition called a batch culture), cannot grow exponentially indefinitely. Instead, a typical ___ for the population is obtained.

Batch culture

• An organism growing in an enclosed vessel, such as tube or a flask (a growth condition called a____), cannot grow exponentially indefinitely.

• "may hangganan lang ang source nurients"

Lag, Log/Exponential , Stationary, Death

Growth Phases

viable count

When agar is used, ___ is used to term quantity of bacteria

Turbidity

When broth is used, ___ is used to term quantity of bacteria

Lag phase

What growth phase:

• This happens when a microbial culture is inoculated into a fresh medium

• No replication and immediate increase in cell numbers or mass

• Cells synthesize cellular components such as enzymes and other cellular materials.

Adaptation phase

cells acclimate to the new environment

Log Phase

What growth phase:

• A period of exponential growth: exponential and deceleration phases

• •Cells are actively growing and are dividing at maximal rate

• Healthiest state ideal for assays

• Growth rate is constant but influenced by environmental factors

• Population is uniform in chemical and physiological activities.

Exponential growth

• is a pattern of population increase, where the number of cells doubles during a constant time interval.

Stationary Phase

What growth phase:

• Exponential growth ceases and the population growth plateaus, thus it limits the growth of the population

• No net increase or decrease in cell number, thus the growth rate of the population is zero

• Cells undergo cryptic growth

• two situations that limit growth: ⚬

  • depleting nutrients

  • toxic waste accumulation

Death Phase

What growth phase:

• Population of cells eventuallly die

• The number of viable cells declined

• In some cases, death is accompanied by actual cell lysis

cryptic growth

happens when cells utilizes themselves to survive (growth curve would slightly increase)

Growth parameters

taken from the exponential phase (population is assumed to be physiologically active and uniform)

(𝛍) = dX / dt

Specific Growth Rate:

where X = biomass and t = time of cultivation

Nt = N0 x 2n

Number of Generations (n):

where N0 = initial population number.

Nt = final population number t

n = number of generations at time t

G = t/n

Generation time formula:

where g = time it takes a population to double in size

t = time taken for the cell to divide

n = number of generations

C. MG. SG. SG. C. A. P

(Competition, Metabolic growth, Symbiotic growth, Synergistic growth, Commensalism, Antagonistic, Predation)

Relationships among Microorganisms in Foods

competition

What relationship among Microorganisms in Foods:

• one can predominant and produce changes in food

metabiotic growth

What relationship among Microorganisms in Foods:

• acids produced by a cell can activate the growth of other cells and so on

symbiotic growth

What relationship among Microorganisms in Foods:

• two or more microbes help each other in food

synergistic growth

What relationship among Microorganisms in Foods:

• two types grow together and may bring changes that could not produce alone

• (group is better than individual)

commensalism

What relationship among Microorganisms in Foods:

• one microbe uses the substrate that is produced by others but may not affect each other

antagonistic

What relationship among Microorganisms in Foods:

• microbes can adversely affect each other

predation

What relationship among Microorganisms in Foods:

• one penetrates the cell wall of the other and multiply

NC. A.OR. WA. AC. BS

(Nutrient content, Acidification, Oxidation-reduction potential, Water activity, Antimicrobial content, Biological structure)

Intrinsic factors:

RH. ST. GA. OM

(Relative humidity, Storage temp., Gaseous atmosphere, Presence of other microorganisms)

Extrinsic Factors:

C.M.S.C.A.P

(Competition, Metabiotic, Symbiotic, Commensalism, Antagonism, Predation)

Implicit factors:

PT. UC. C

(Physical treatments, Use of chemicals, Contamination)

Process factors:

pH

Intrinsic Factors:

• The acidity or alkalinity of an environment has an effect on the activity and stability of macromolecules, such as enzyme functions and metabolism and cellular activities

• Optimum pH for growth is based on the environment

• Intracellular pH of cells is near neutral to prevent destruction of macromolecules in the cell

  • Acidophile (internal pH 4.6)

  • Alkaliphile (internal pH 9.5)

Water Activity

Intrinsic Factors:

• is a measure of the availability of water for biological functions and relates to water present in a food in “free” form.

• It ranges bet 0 and 1

• = vapor pressure of food/ vapor pressure of pure water

vapor pressure of food/ vapor pressure of pure water

Water activity =

adding solutes, ions, and hydrophilic colloids, freezing and drying

Water activity in food must be reduced to control microbes through _____

Oxidation

losing of electrons

Reduction

gain of electrons

Oxidation-Reduction Potential

Intrinsic Factors:

• When a substrate loses electron, the substrate is oxidized (+mV), while a substrate that gains electrons becomes reduced (-mV)

between +500 and +300 mV

Aerobic microbes grow ___redox potential

between +300 and -100 mV

Facultative anaerobes grow ___

between +100 and -250 mV

Anaerobes grow

Hydrogen peroxide (H2O2) , Superoxide anion (O2-), Hydroxyl radical (OH•)

The reduction of O2 to H2O in respiration produces toxic by products:

Nutrient Content

Intrinsic Factors:

• Microorganisms can use nutrients in foods to synthesize cellular components and energy

simple sugars (e.g., glucose), complex carbohydrates (e.g., starches and cellulose), nitrogen (e.g., proteins and nucleic acids), fats, alcohols, amino acids, vitamins, growth factors, minerals

Nutrients necessary for growth:

Antimicrobial Content

Intrinsic Factors:

• Many food products contain naturally occurring compounds that have ___, which can extend shelf life of a food product.

Examples of naturally present antimicrobials in foods:

• essential oils of spices (e.g., eugenol, cinnamic aldehyde, etc)

• Cow’s milk (e.g., lactoferrin, immunoglobulin, and lysozyme)

• Eggs (e.g., lysozyme, ovotransferrin)

• Cranberries (e.g., benzoic acid and sorbic acid)

• Garlic and onion (e.g., Isothiocyanates and thiosulfate)

Examples of antimicrobials produced by microorganisms

• Propionic acid by propionic bacteria in cheese inhibits molds

• H2O2, organic acids, and ethanol produced by LAB

• Alcohols produced by wine yeasts

• bacteriocins produced by LAB

• Pediocin produced by Lactococcus lactis can control the growth of Listeria monocytogens in foods.

Temperature

Extrinsic Factors:

• Microorganisms grow over a wide variety of __, having a minimum, optimum, and maximum growth conditions.

• Exposure of microorganisms beyond the maximum and minimum temperatures in foods is important with respect to reducing food spoilage and enhancing safety against pathogens, food bioprocessing, enumeration, and isolation of microorganisms from foods.

minimum, optimum, and maximum growth conditions

Microorganisms grow over a wide variety of temperature, having a __

Relative Humidity

Extrinsic Factors:

• Important for the growth of microbes on the surface area of food.

• __of storage environment has a relationship with aw of foods

• Foods that undergo surface spoilage from molds, yeasts, and bacteria should be stored under low __condition.

• Low __ means low moisture

Gaseous Atmosphere

Extrinsic Factors:

• Increased amount of CO2 alters the atmosphere of food storage and it inhibits the microbial growth in a food package.

• Yeast like Brettanomyces show tolerance to CO2 and dominate as the spoilage microflora of carbonated beverages

• Growth inhibition is usually greater under aerobic conditions than anaerobic, and the inhibitory effect increases with decrease of temperature, since solubility of CO2 at lower temperatures increases

• More oxygen, More contaminants

Brettanomyces

Yeast like ___ show tolerance to CO2 and dominate as the spoilage microflora of carbonated beverages.