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Question 1

Myoglobin

Answer 1

Heme group: aromatic porphyrin ring with ferrous (Fe2+), 16 electrons, space available for 2 more electrons

Question 2

3 heat treatment methods

Answer 2

Sterilization (hospital)
Commercial sterility (food)
Pasteurization/blanching

Question 3

Sterilization

Answer 3

No living forms are alive or biologically active. Using steam to reach 121C for 15mins. Appropriate for tools/hospital but not for food.

Question 4

Commercial sterility

Answer 4

All pathogenic and toxin-forming vegetative organisms and their spores are inactivated to the extent that they cannot reproduce. Mostly the canning process.
Vegetative cells are much more susceptible to heat than spores.
Ex: Botulinum pH>4,6. Has heat-resistant spores, grows anaerobically, produces neurotoxin deadly at microgram quantities, at low ph cannot germinate (be activated to vegetative cells).
For low acid foods, we use steam under pressure to reach 10psi (116), 15psi (121), 20psi(127). Pounds per square inch. To give shelf life of >2years

Question 5

Pasteurization as preservation method

Answer 5

Below boiling point of water.Targets vegetative cells of pathogenic microorganisms like Mycobacterium Tuberculosis that are relatively thermoresistant. Limited shelf life because spores survive and are the source of new vegetative outgrowths.

Question 6

Blanching as preservation method

Answer 6

Short heat process to denature deleterious enzymes in fruits and veggies like polyphenol oxidase (green to olive because of enzymatic browning) and lipoxygenases (off flavors from lipid oxidation). Commonly prior to freezing or other nonthermal processes to minimize enzymatic deterioration.

Question 7

Basic principles of heat processing

Answer 7

Balance between destruction of microorganisms and maintenance of quality. Safety first. Combination of time and T. Heat penetration. Validating efficacy
Ex: C.botulinum is too dangerous to use for validation so we use a less dangerous but more heat resistant spore former like C.sporogenes PA3679(putrefactive anaerobe) or bacillus stearothermophilus. If they are destroyed, Botulinum are destroyed for sure. Time and T combinations can have same effects, but in general shorter time higher T is better for attributes.Ex: 330min 100C = off flavor brown milk and 0,78min at 127C white high quality. HTST is expensive for perfect T and time.
2 types of thermal processing: (1) conventional: canning then heating, (2) aseptic processing: process then package (tetra brick type) suitable for HTST

Question 8

Premise associated with commercial sterility

Answer 8

Assuming that there are 10-6 spores in a can, commercial sterility is reduction by 12 logarithmic cycles to 10--6 = one spore in 10-6 cans. Dvalue = decimal reduction time is heating time at given temperature to reduce by 90% (by one log) every cycle. Dvalue is specific to particular organism and is done by plate count under different T and time. Higher T would have an steeper slope because it would take less time.
Thermal resistance (z-value, reduction of D by one requires how much Tincrease) of the organism is (T2-T1) divided by (logD1 - logD2 or slope)

Question 9

Conventional thermal method: canning

Answer 9

Equipment used: Batch retort which is a large pressure cooker in which steam under pressure is the heat transfer medium (enables T higher than 100C). Shaped in U with steam and water. Put to the psi needed (10,15,20) and retained at the T for a hold time. Retort is then flooded in cold water and cooled at room T. Hold time is determined based of overall lethality of the process with the come up and cool down + thermal resistance of microorganisms targeted (z-value)

Question 10

Heat penetration studies

Answer 10

Thermocouples are inserted in the cans and hooked up to a data logger. Thermocouples are placed at the cold point because each particule must reach the temperature specified and be held at the requisite time to attain commercial sterility. Cold point is the slowest heating zone and depends on the type of heat transfer in the food.
Solid foods: heat is transferred slowly by conduction = from molecule to molecule. Center of the can
Liquid/fluid foods: hotter liquid rises and creates a convection currents: more rapid heat transfer but depends on viscosity(ex: starch gelatinization increases viscosity which slows the rate of heat transfer). Center of the can one-third above bottom.
Most foods have both (canned pineapple) convection syrup and conduction pineapple
When the container changes size, product formulation, package characteristics, thermal investigations are required but for cans there is so much data that it can be used with confidence.

Question 11

Aseptic packaging definition + advantages

Answer 11

Food is thermally processed and filled into pre-sterilized containers and sealed with pre-sterilized closure in an aseptic environment (no m-o). Started with milk pasteurization. Now also used for commercially sterile products. Useful for heat sensitive products not good for HTST processing.
Advantages: continuous, very high and efficient heat transfer rates because not constrained by container.

Question 12

Milk pasteurization with aseptic packaging

Answer 12

1.Batch processing: pasteurization at 62,5C for 30min then package.
2.1930: continuous HTST pasteurization 71C for 15sec with rapid cooling to 2C then packaging
3.1970:UHT (ultra high temperature) higher than 100C for 1sec (by direct steam injection) with rapid cooling and aseptic packaging. Commercially sterile product until package is opened (more than 2 years).
North america processers use plate heat exchange which is very efficient because of high surface area

Question 13

Tetra brick and on-site packaging

Answer 13

Aseptic processing is often combined with on-site package forming = tetra brick = integrated process. Tetra brick is a folded sterile package made with single roll of laminate (cardboard, aluminum and plastic). 20,000packages/h. UV light and hydrogen peroxide are commonly used to sterilize packaging. Huge cost savings because lighter than cans!!Coffee creamers, pouches, plastic bottles or form-filled trays can be formed on-site as well.

Question 14

Summary of thermal processing

Answer 14

Conventional or aseptic processes are determined by economics and produtc characteristics.
All treatment methods require stringent evaluation and validation to ensure commercial sterility/pasteurization. Controled by government regulatory oversight because of the risk
Other types of thermal processing exist:
Microwave heating, ohmic heating, pulsed electric fields

Question 15

Refrigeration

Answer 15

Refrigeration causes few flavor or texture changes. More rapidly chilled, the better the quality and nutritive value. Variables to control are temperature, air circulation, humidity and gas atmospheres. Right after harvest or slaughter. Refrigerators are below <4C (40F). Cold air sinks so lower sections are colder than top sections. Air circulation must be at the right humidity to maintain freshness (too low pulls water away from foods so it dries..) Replacing oxygen with carbon dioxide to slow respiration.

Question 16

Freezing basics

Answer 16

All the water in a food system can only be frozen when the temperature drops to below the eutectic point of the food product, when the residual water and all solutes co-crystallize. Eutectic point for most foods is -50C but for product quality and energy costs balance, we use -18C (99% is under crystalline state).

Question 17

Changes that can occur in a food product after being frozen

Answer 17

Chemical reactions can still occur but very slowly like solubility reduction: crystallization of lactose in ice cream (sandy,grainy) + protein denaturation due to salting loss of water holding capacity in meat + change in pH(inorganic organic acids to cause protein denaturation/coagulation + destruction of sensitive emulsions + loss of gas solubility (beer, soft drinks)

Question 18

Rate of freezing

Answer 18

Slow freezing = large crystals
Fast freezing = small crystals
As airflow increases, the rate of freezing increases
Other factors of freezing rate: Temperature differential, surface area, product shape, air velocity, heat transfer, composition

Question 19

Temperature variation in freezing

Answer 19

Cryogenic freezing = -198C with liquid nitrogen to do a big temperature differential to create fast freezing = small water crystals. But not cost effective. Temperature in freezer vary from -22 to -12C every 2h (4000cycles/year).
Fluctuations cause changes in the ratio of water which cause larger ice crystals because of sublimation of water. Quality deterioration

Question 20

Thawing

Answer 20

Most quality deterioration takes place during thawing. Ice concentrated components (salting out) start to react and microorganisms start to grow. Microwave thawing shortens thawing time which reduces microbial growth.

Question 21

General differences in home and commercial freezing

Answer 21

Home freezing: food is frozen by exposure to still air (not moving), slower
Commercial freezing: exposure to still or moving air. Indirect contact with a cooling medium. Immersion into a cooling medium. Type of commercial freezing: Still air (sharp) freezing, blast freezing, tunnel freezer, indirect contact plate freezer, scraped surface heat exchanger, immersion freezing, cryogenic freezing

Question 22

Still air (sharp) freezing method

Answer 22

Commercial freezing method. Slow and common method, looks like home freezing. Insulated room maintained at -23C to -30C with some air circulation. Used for previously frozen by other means or rate-insensitive products (ice cubes). Not a continuous process!

Question 23

Blast freezing

Answer 23

Commerical freezing method. Use of high-velocity air to speed freezing rate, with high speed fans. 30lbs can of egg yolk freezes in 72h in sharp freezer and 12-18h in blast freezer. Not a continuous process.

Question 24

Tunnel freezer

Answer 24

Commercial freezing method. Product played on trays of mesh belt and run counter current to high-velocity cold air. Typical product is individually quick frozen (IQF) shrimp. Very rapid and efficient but problem of dehydration (freezer burn) because of ice sublimation, can be controlled with spaying a water mist on product to coat so that evaporated water is from the external mist layer and not the food itself. Continuous process

Question 25

Indirect contact plate freezer

Answer 25

Commercial freezing method. Used for flat-packed products like fish, fruits, veggies, hamburger patties. Refrigerated plates is to press package between them using pressure to give good contact and efficient conduction. Not continuous, therefore batch process.

Question 26

Scraped surface heat exchanger

Answer 26

Commercial freezing method. Use ethylene glycol in the exterior jacket as a coolant. Commonly used to freeze pre-concentrated products like orange juice concentrate obtained from evaporator. High surface area,forced convection, excellent heat transfer characteristics and continuous process.

Question 27

Immersion freezing

Answer 27

Commercial freezing method. Packaged products are immersed in refrigerated medium like ethylene glycol (-67C), sugar or salt solution resulting in good contact, good heat transfer, excellent for irregular shaped products (shrink wrapped,turkey, chicken). Refrigerated brine - used in fishing industry to boats to freeze fish.

Question 28

Cryogenic freezing

Answer 28

Commercial freezing method. Between static and immersion freezing. Cryogen is sprayed onto the product (liquid nitrogen (-169C) and liquid CO2(-79C)). N2 provides great cooling force delta T. Latent heat of evaporation from -196C to -195C is 200kj/kg (from liqiud to gas), the additional 186kj/kg is absorbed from -195C to -18C. = 386kj heat/kg. Liquid N2 are sprayed onto the product with continuous wire mest belt and requires no primary refrigerant because produced by direct compression of gas. All advantages except expensive.
CO2 dry ice (solid) can be mixed with product direclty cools product as it sublimes. High pressure liquid CO2 turns to dry ice when sprayed because of reduction of pressure and then it snows and then sublimes to gaseous CO2 which cools the product. On equivalent weight basis, CO2 absorbs twice as much energy as liquid N2.
Continuous process

Question 29

Incoming freezing technologies

Answer 29

Super freezer with temperature lower than -60C, which gives good quality product and eutectic temperature for high value products like tuna

Question 30

Types of reduced water activity processing

Answer 30

Dehydrated, concentrated, intermediate-moisture

Question 31

Food dehydration

Answer 31

Simple drying is limited to reduce food to 15% moisture, Uncontrolled because suceptible to weather patterns + contamination of microbes,etc. Controlled drying technology = food dehydration. Well designed dehydration can reach moisture to 1-5%. Reduction in water activity (Aw). Reduction in weight. Ex: 1/8 of its original weight (lower transportation cost). Challenge is reconstitution = dried product that is similar to original product.

Question 32

Principles of drying

Answer 32

Depends on heat and mass transfer. Heat has to move in of the product so that vapors(mass) can move out.
High surface area = big heat/mass transfer because of Exponential relationship between surface area and particle size.
Product profile: minimize distance of heat to go in and vapors to go out.
Temperature differential between heat medium and product is important.
Relative humidity: amount of moisture air can hold at a particular temperature. The more grams of H2O it can hold, the more efficient it will be because will be saturated less quickly. The bigger the difference between relative humidity or air and food, the quicker it will dry :)

Question 33

Concept of moisture sorption isotherm

Answer 33

Change in weight in relation to RH at a specific temperature.
Aw = RH divided by 100. so for food, we use Aw.
To measure moisture sorption isotherm, we set up a series of hermetically sealed chambers containing different saturated salt solutions and over a few days, each salt will equilibrate to a defined relative humidity (10-100percent RH). It will gain or loss moisture so reweigh the product after and plot the change in weight in relation to relative humidity.
Do it for every temperature (0,20,40,etc)

Question 34

What the moisture sorption isotherm tells us

Answer 34

Shows the expected moisture sorption behavior of a food, expected Aw and RH where no more release or absorption of water occurs, effect of temperature on moisture isotherm, Aw to predict product stability. Important for drying behavior and packaging requirements because of H2O vapors.

Question 35

Factors affecting the drying process

Answer 35

Reducing pressure reduces the temperature difference required in drying process as the boiling point of water is reduced. 
Latent heat (enthalpy) of evaporation: cooling effect due to the phase change from liquid to gas (minimize product damage)
Structure of the product, food products are usually not homogeneous (cellular structure, fat)

Question 36

Factors affecting quality of dried products

Answer 36

For every 15C rise in temperature, air can hold twice as much moisture in vapor form. Faster drying means less change in food quality, but if it happens too quickly, a dry skin forms and traps moisture inside called case hardening
Increase surface area increases exposure to oxygen which causes formation of tannic acid (browning) in foods high in phenols like apples, grapes, tea. Dehydration temperature are not high enough to denature enzymes so foods are pretreated to inactive enzymes

Question 37

Sulfiting and sulfuring

Answer 37

Sulfiting: Sodium bisulfite extends drying time, but may cause breathing difficulties for allergic people. Few/no effect on heat sensitive nutrients, food color or texture.
Sulfuring: Sulfur dioxide - involves exposing fruits to fumes from burning sulfur for up to 4h and for other foods, sulfur dioxide circulates. Shortens drying time, inhibts mold + repel insects.
Both methods destroy thiamin

Question 38

What is considered before choosing a drying method

Answer 38

Type of food, quality desired, how much customer is willing to pay, whether food is whole, divided, pureed or liquid.

Question 39

Tray drying method

Answer 39

Food is on trays with holes in an enclosed cabinet for 20h while air is blown over the food or rises up the trays and moisture-filled air is vented out. Used for small-scale operations for fruits and veggies.

Question 40

Belt drying method

Answer 40

Tunnel dehydrator on moving belts. Foods reach moisture levels of 5-7percent in an hour. Works best with grains, peas and beans
Continuous

Question 41

Drum drying method

Answer 41

Rotating heated drums pick up food and dry it as the drums rotate. The drying time needed determines the size/speed of the drum. Best with heat-resistant foods that are brittle when dry like mashed potatoes, tomato pastes.

Question 42

Spray drying method

Answer 42

Very small drops of the food are sprayed into the top of a heated chamber and dehydrate as they fall. Used with heat sensitive products like milk,eggs, protein powders, flavorings and instant coffee. Fastest drying method (seconds)

Question 43

Vacuum drying method

Answer 43

Heated trays or shelves called platens transfer heat in a vacuum chamber. Lowering atmospheric pressure lowers boiling point to minimize heat damage. Produces highest quality, expensive, fruit juices.

Question 44

Freeze-drying method

Answer 44

Lypholization or dehydrofreezing are synonyms.
Food is frozen and then placed in a vacuum chamber and heated. Food temperatures and atmospheric pressure are lowered until water sublimates. Best one

Question 45

Advantages and disadvantages of concentrates (concentration)

Answer 45

Lowering shipping costs, extended shelflife and better handling ease prior to dehydration. Problems with concentrates are cooked flavors, color changes, gritty texture, denatured proteins, and low acid foods require additional preservation methods to destroy pathogens.

Question 46

Concentration methods

Answer 46

Open kettle: Oldest way, requires frequent stirring, can result in flavor and color changes, because of high heat and long cooking time. Good for jams, jellies, condensed soups
Heat evaporation method: food enters and leaves evaporator in a continuous process, exposed to HTST, fesher flavor than open kettle because heat damage is limited.
Vacuum evaporation method: vacuum is added to evaporator and lowers atmospheric pressure every chamber
Filtration method: smaller particles pass through filters so original food source is isolated in the filter.

Question 47

Intermediate moisture foods

Answer 47

Moisture content of 20-50percent with enough dissolved solutes to prevent growth or microorganisms. Nutrient and calorie dense. May or may not need refrigeration and preservatives or antioxydants to prevent enzymatic activity.