Physical methods to preserve food Flashcards
Physical methods are the most common in food preservation: TRUE OR FALSE
TRUE
What are the 6 physical methods for food preservation?
- High-temperature treatment (cooking)
- Low-temperature preservation (freezing)
- Decreasing water availability (drying, salting)
- Ionizing irradiation
- High-Pressure Processing (HPP)
- Pulsed Electric Field (PEF)
What happens when the temperature exceeds the optimal temperature for an organism ?
Cell multiplication slows and eventually stops, additional temperature may result in cell death
Factors affecting heat transfer
1) Product Type: Liquids absorb heat faster than solid foods.
2) Container Material: Glass containers heat more slowly than metal containers
3) Container Shape: Tall and narrow containers heat more quickly than other shapes
4) Container Size: The center of small containers get reached more quickly than the center of large containers
5) Agitation: Agitation and mixing help to increase heat transfer especially in viscous or semi-viscous products
6) Temperature of Heating Medium: The greater the difference in temperature between the heat transfer medium and the product, the more rapid the rate of heat transfer to the product
What do survivor plot depict ?
the logarithmic nature of population inactivation over time
What is decimal reduction time (D-value) ?
as the time it takes of a 10-fold reduction in the number of survivors at a given temperature
The D value of a microorganism (decreases/ increases) as the processing temperature increases?
decreases
D value is plotted against temperature, it is known as a ___________, it is generally linear
thermal resistance plot
The ___________ represents the change in temperature required to change the D value of a microorganism by an order of magnitude (10-fold)
z -value, large z value indicates a more heat resistant organism
The _______ is the time, in minutes, at a specified temperature, required to achieve a targeted reduction in a homogeneous population having a specific z value
F-value
F-value is important in __________
the commercial canning industry
What is the key pathogen of concern for canned low acid foods
Clostridium botulinum
Sterilization vs commercial Sterilization
Sterilization: Sterilization is the process of rendering a product free of any living organisms
Commercial Sterilization: Commercial sterility of food products is the application of heat that renders the food free of:
1) Microorganisms capable of reproducing in the food under normal non-refrigerated storage and distribution temperatures
2) Viable microbial cells or spores of public health significance
* Commercially sterile foods are heat treated just enough to produce a safe and shelf-stable product
Water can be bound by:
- Hydroxyl groups
- Carbonyl and amino groups of proteins
- Salts
Formula for water activity
aw= P/P0
-For pure water, aw = 1.0
aw is directly related to the equilibrium relative humidity (ERH) in the air surrounding the food:
ERH (%) = aw x 100
High-moisture Foods
Foods with aw above 0.9, foodborne microbes can readily grow in these foods
Intermediate-moisture Foods
Foods with an aw 0.65-0.90, such as raisins or jam, because of the moderately low aw these foods are relatively resistant to microbial spoilage (think of how long a jar of jam will last in the fridge)
Dry foods
Foods with an aw < 0.65, such as milk powder or crackers, these foods do not support the growth of foodborne microorganisms and have a very long shelf life
What type of food is maple syrup
intermediate-moisture food
How is maple syrup prepared?
by boiling the sap from sugar maple trees until the boiling temperature is 4.1C higher than that of pure water (which will vary based on air pressure but is around 100C)
_________ has the lowest water requirements and can grow with an aw of >0.86. However, it cannot produce toxins at this level
Staphylococcus aureus
Yeasts have higher or lower aw requirements compared to bacteria?
Lower
_________ are xerotolerant and grow at lower moisture contents than the other types of spoilage microorganism
Molds
Molds can produce __________, but ________ production is restricted under xerophilic conditions
Mycotoxins
How does glycerol act as a humectant to lower aw ?
glycerol can permeate the bacterial membrane and may have a different inhibitory effect than that of sodium chloride or sucrose.
What does Pulsed Electric field eliminate?
vegetative bacterial cells
PEF processing is designed to treat what type of food?
pumpable food and involves the application of a short burst of high voltage to a product between two electrodes
Drying
the process of mobilizing water present in a food matrix to its surface and then removing it from the surface by evaporation. It often involves simultaneous heat and mass transfer. Most drying operations involve converting liquid water in the material to vapor and then removing it by passing hot air over the product (i.e. beef jerky).
Freeze-drying
During freeze-drying the product is frozen first and the moisture is removed via sublimation. Freeze-drying has a minimal impact on the structure and flavor of the food compared with other drying techniques, but has a relatively high cost, and is therefore used as a value added technique (i.e. camp dinners, instant coffee, infant formulas).
Osmotic dehydration
is a procedure that involves removing water from fresh food using a hypertonic solutions (sucrose, salts, glycerol). It relies on the ability of the food cells to selectively permit the passage of water out of the food without allowing surrounding solutes to enter these cells. As a result food is dehydrated. It cannot remove all the moisture from the food, so it is mainly used as a pretreatment to other methods of dehydration. Primarily used for dehydrating fruits and vegetables (apples, blueberries, pineapples, mangoes etc.).
Electromagnetic radiation with _______ wavelengths (gamma radiation) has lethal effects on microorganisms
shorter
Longer wavelengths (microwaves) just generate _____ and are not as effective
heat
Ionizing radiation includes _____ and _____ radiation
X Rays
gamma
___________ is the primary target of ionizing radiation
The cell’s DNA
the smaller the genome, the ______ the resistance to ionizing radiation
greater
How is DNA caused in Ionizing Radiation?
By the reaction of reactive oxygen species that are generated during radiation
How are X rays produced?
When an electron beam strikes a metal (tungsten or stainless steal)
X-ray sources used to irradiate food are restricted to maximum energies of ______ or less, which is effective at treating fresh fruit and vegetables for microbial lethality
5MeV
Drawback is that X-rays have ______________________
a high power requirement, and have a high requirement for cooling treatment (most of the energy is lost as heat)
In gamma radiation, the radiation sources used for food are : (2)
cobalt-60 and cesium-137
What are the advantages or gamma radiation?
- high penetration power
- energy is constant over the duration of the treatment
- continuous source that doesn’t need to be turned off
The process of gamma radiation usually consists of exposing
exposing the prepackaged food material to a radiation dose for a certain time
Gamma radiation is emitted by:
an excited nucleus of a radioisotope, which permits the nucleus to go to its lowest energy or ground state
Redappertization:
-involves a high dose (10-75 kGy) to produce commercial sterility
Radicidation:
-involves medium dose (1-10 kGy) to produce the equivalent of pasteurization effect - effective against vegetative bacteria but spores are not inactivated
Radurization:
-involves low dose irradiation (0.05-1.0 kGy) to control the presence of insects in grains or stop the sprouting of potatoes or fruit ripening
HPP involves:
treating food with pressures in the range of 100-600 MPa which will inactivate most bacteria, yeasts, molds and viruses (spores survive)
