14-Physical Preservation ew Flashcards

Question

Why aren’t microwaves used in processing, and why aren’t they a good idea for foods that require cooking for safety?

Answer 1

Microwaves cause rotation of water molecules in foods, and these rotations generate friction and therefore heat. Unlike convectional heat, which penetrates from the outside inward, microwaves generate heat throught out the material leading to faster heating and shorter processing times Distribution of the heat is very uneven, leading to uneven lethality of microorganisms (don’t microwave your chicken fingers) This has hindered the use of the microwave in commercial food processing.

Answer 2

freezing stops metabolic activity of most food borne microorganisms, although cryophillic, psychrophillic, and psychotropic food microbiota will still alter foods at sub zero temps. toxins are not affected by freezing Freezing also retards chemical and biochemical deteriorations like lipid oxidation, enzymatic browning, proteolysis and lipolysis. Freezing also decreases aw

Answer 3

Freezing also decreases the aw therefore, only cold-tolerant and xerotolerant microorganisms can grow, but some yeast and fungi have these characteristics Gram-positive bacteria survive freezing better than Gram-negative bacteria Parasites are readily destroyed via freezing Trichinella spiralis (pork worm) is eliminated if the raw product is held briefly at -23C Rapid freezing produces smaller ice crystals (cells don’t get punctured), and exposes cells to osmotic stress for shorter time periods, therefore, microbial cells are more susceptible to injury and death during slow freezing (like in your home freezer)

Answer 4

unbound and bound, water can be bound by hydroxyl, amino and salt groups. Unbound water is essential for microbial growth and survival. Removing or restricting unbound water can preserve the food by supressing microbial activity and extending product shelf life.

Answer 5

when a moist food is contained within a package with headspace the water molecules will eventually leave the food and enter the surrounding atmosphere until a state of equilibrium is obtained with the air and surrounding food.

Answer 6

1. high moisture; aw> 0.9 2. intermediate 0.65-0.9 3. dry foods; less than 0.65 - dont support growth of food born microorganisms and have long shelf life

Answer 7

0.91 and 0.95

Answer 8

xerotolerant and grow at lower moisture contents

Answer 9

for nutrient acquisition, waste removal, and as a medium for metabolic reactions to take place in

Answer 10

True; glycerol can permeate the membrane and have diff inhibitory effect

Answer 11

F; inhibits microbial growth but may not kill the microorganisms in the food. These microbes may remain dormant until the food is rehydrated and then resume their metabolic activity and multiply (i.e. Salmonella in chocolate bars)

Answer 12

: is 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).

Answer 13

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).

Answer 14

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.).

Answer 15

involves treating food with pressures in the range of 100 to 600 MPa, which will inactivate most bacteria, yeasts, molds, and viruses (spores survive) Food materials containing air pockets may be deformed due to the differences in compressibility between the air and food material Appropriate packaging must also be chosen

Answer 16

processing is designed to treat pumpable food and involves the application of a short burst of high voltage to a product between two electrodes The treatment time is between microseconds and milliseconds This treatment will eliminate vegetative bacterial cells The success of the treatment relies on food composition, pH, and electrical conductivity Air bubbles are also poor conductors and can create process non-uniformity (i.e. pumpable food)

Answer 17

electromagnetic radiation wiht shorter wavelengths have lethal effects on microorganisms. The cells DNA is the primary target so the smaller the genome, the greater resistance to ionizing radiations.

Answer 18

by the reaction of reactive oxygen species (ROS) that are generated during radiation

Answer 19

gamma and x rays

Answer 20

- produced when electron beam strikes metal - irradiate food like fruit and veg - high power requirement

Answer 21

is emitted by an excited nucleus of a radioisotope, which permits the nucleus to go to its lowest energy or ground state The radiation sources used for food are cobalt-60, and cesium-137 The source is stored under water, but during treatment it is contained in a concrete and steal structure to protect workers The advantage is radiation has a high penetration power, and the energy is constant over the duration of the treatment, it is a continuous source that doesn’t need to be turned off The process usually consists of exposing the prepackaged food material to a radiation dose for a certain time

Answer 22

1. Redappertization. Involves a high dose (10 to 75 kGy) to produce commercial sterility 2. Radicidation. Involves medium dose (1 to 10 kGy) to produce an equivalent effect to thermal pasteurization – effective against vegetative bacteria but spores are not inactivated 3. Radurization. Involves low dose irradiation (0.05 to 1 kGy) to control the presence of insects in grains or stop the sprouting of potatoes, or delay fruit ripening

Answer 23

food composition, pH and electrical conductivity. If there are air bubbles than poor conduction and create process of non uniformity.

14-Physical Preservation ew Flashcards

(50 cards)