Food Bact Exam 4

Antimicrobial Impacts of Freezing

Osmotic shock

pH, aw impacts from solute concentration

localized dehydration as liquid water migrates to maintain water equilibrium

Impacts of Thawing on Microbial Viability

Oxidative, thermal shock can occur during thawing foods

Repeated cycling of freezing/thawing shows enhanced antimicrobial impacts, stronger food quality damage

Pasteurization

process designed to eliminate/ reduce most process-resistant non-sporulating pathogen of concern and reduce non-pathogenic spoilage

Blanching

application of moderate heating to foods to inactivate enzymes carrying enzymatic spoilage (most frequently applied to plants/produce)

Hot Fill

Non-sterilized container is filled with sufficiently hot food to render final product commercially sterile

Thermal Processing

Sous vide “under vacuum”

Food cooked separately from package and aseptically filled post-process

Aseptic Processing/ Packaging

Food cooked independently of packaging

useful for liquid foods

Impacts of heat on microbes

denatures enzymes

permeabilizes membrane

releases membrane-bound proteins

Heat on microbes allows __ of __ contents, loss of ___ ____

leakage , cytoplasmic, membrane functionality

Heat on microbes enhances ___ activity of chemical _____ or physical ____ (high pressure)

antimicrobial, antimicrobials. processing

Heat on microbes can produce ____ injury if not sustained sufficiently to ____ contaminated____

sub-lethal, inactivate, microbes

Sub-lethal heating exposure can result in ___ tolerance to ____ heat exposure

increased, subsequent

Sub-lethal heating is the result of

heat shock proteins ( HSP’s), DNA chaperone proteins, which protects against more substantial microbial damage

Cross-protection

against other stressors (antimicrobial application, high pressure)

Thermobacteriology

microbial death previously observed to follow 1st order via application of moist heat

Logarithmic Kinetic

the extent of death is equal with certain time increment

(at 5 min, 90% are killed, so at 10 min 99% are killed)

In thermobacteriology, death rate,,,

can be predicted and validated

Decimal Reduction Time

Time in min at constant temperature achieving a 1.0log10-cycle reduction in population of microbe

D=

2.3/ kT

D-Value Determination

do own research

Thermal Resistance Costant (z)

describes impact of changing process temperature on resulting lethality to microbes

Thermal Resistance Constant (z) is defined as

temperature change (F or C) producing a 10-fold change in value of D (all values must be the same temperature)

Thermal Death Time (F-Value)

Time required at constant temperature w known z-value to destroy a desired/ required number of microbial cells

F0

universal reference thermal process, set at 250F with z=18F

Reference F0 used to compare to

lethalities achieved at other temperatures

F-value is specific to a microbe at a

specific D-value

F-value application in Industry Processing

Set a process lethality target and process to achieve the target for every batch

Fermentation

the re-oxidation of a reduced electron acceptor by another metabolite pathway

Fermentation produces low…

energy yields (2 ATP/1 GLC) compared with oxidative phosphorylation in aerobic condition (4 ATP/1 Glc)

Acetic acid bacteria

capable of oxidizing ethanol to acetate

Milk Fermentation

Pasteurized or ultra-pasteurized prior to inoculation

Inactivates background microbiota that may compete with starter cultures

Proteases, lipases can also..

be added to assist fermentative microbes

Raw milk-made products previously associated with

L.monocytogenes transmission to consumers

raw milk requirements (for cheese)

60 dyas aging at >/= 35F

Kraut Fermentation

salt added (2-2.25%), which allows water extraction

Fermentation may be paired with

drying/ageing, salt and cure salt addition, producing an RTE product

Smoking can be used for

mild or full cooking to end fermentation and stabilize product

Fermented meats final pH

<5.0 targeted by USDA

Fermented meats add..

sugar to allow acid fermentation to needed final pH

Fermentation may occur in..

smokehouses due to warmer temperatures

Drying/ Ageing

moisture removal (slow drying is best to avoid too rapid a rate of drying on exterior of sausage which prevents internal moisture from migrating to the surface)

During drying…

mold or other microbes can grow on surface

Like vegetable fermentations, some sausages can be,,

fermented with naturally present microbiota

Back-slopping

use finished batch to inoculate new sausage mix batch

Industrial meat starters

Homo-, hetero-fermentative LAB microbes (Pediococcus, Lactococcus, Streptococcus)