Final Flashcards
Food Processing:
the conversion of raw animal
and plant tissue into forms that are convenient and
practical to consume.
Food Preservation:
the use of specific thermal
and non-thermal processing techniques to minimize the
number of spoilage microorganisms in foods, making them
safe and giving them an extended shelf-life.
Includes canning, refrigeration, freezing, dehydration, high pressure processing, irradiation, addition of food additives, fermentation, etc.
Purposes of Food Processing
• To improve product quality
– Quality: degree of excellence, the sum of acceptability
characteristics, most of which are subjective
• To formulate or manufacture a food product with
specific characteristics
• To improve product consistency
• To improve food shelf-life (the time it takes a product
to decline to an unacceptable level)
• To improve food safety (freedom from harm)
• To maximize output, or to minimize defects
Processed Foods
Any food other than a raw agricultural
commodity, including any raw agricultural
commodity that has been subject to washing,
cleaning, milling, cutting, chopping, heating, pasteurizing, blanching, cooking, canning, freezing, drying, dehydrating, mixing, packaging, or other procedures that alter the food from its natural state.
Processing effect on nutritional content
• Processing of foods, including the addition of
ingredients, may reduce, increase, or leave
unaffected the nutritional characteristics of
raw agricultural commodities.
Processed Foods. Categories
• According to the International Food Information
Council:
1) Minimally Processed Foods
2) Foods Processed for Preservation
3) Mixture of Combined Ingredients
4) Ready-to-eat Foods
5) Convenience
Minimally Processed Foods
Foods that use little processing • Washed, packaged fruits and vegetables • Often simply pre-prepared for convenience ü Bagged spinach ü Cut vegetables ü Roasted nuts
Foods Processed for Preservation
• Processed to maintain freshness and nutrients
ü Canned fruits/vegetables
ü Frozen fruits /vegetables
Mixture of Combined Ingredients
Use of sweeteners, colors, preservatives and other
additives to improve safety, taste, visual appealing
ü Cake mixes
ü Salad Dressings
üCured meats
üArtificially flavored and colored foods
Ready-to-eat Foods
• Foods that require little preparation • Do not need to be cooked before use ü Breakfast cereals ü Lunch meats ü Carbonated beverages ü Dry cereal, nuts
Convenience Foods
• Packaged to keep fresh and save time • More “heavily” processed ü Frozen meals ü Frozen Pizza ü Microwaveable dinners
Processed Foods. Negative Aspects
Controversial additives • GMOs • trans fats • Saturated fats • Added sugar • Sodium • Caloric intake
Processed Foods. Positive Aspects
Food Safety and Preservation • Removal of anti-nutritional factors • Foods for people with special needs • Fortification and Enrichment • Affordable, Convenient
Why is it important to understand Food Processing?
• Food processing methods are used to preserve and
create foods.
• If you understand how something functions, you can
improve product quality
Food Processing and
Food Chemistry
• Controlling chemical reactions that play a role in
food quality and food spoilage:
ü Breakdown of carbohydrates, proteins, lipids, and pigments
ü Browning reactions
ü Starch gelatinization and retrogradation
ü Emulsification and foam formation
ü Gel formation and viscosity-building
ü Lipid oxidation and rancidity
ü Protein denaturation and coagulation
ü Enzymatic reactions
Food Processing and
Food Microbiology
• Controlling microbial growth in foods that affects food quality and food spoilage: Manipulation of: – pH – aw – Oxidative state – Nutrient content – Biological structure – Naturally-occurring inhibitors – Temperature – Gaseous atmosphere – Relative humidity
Unit Operations in Food Processing
• Unit Operations: Categories of common
operating steps practiced in the food industry
• A basic step in a process
• A process may have many unit operations
to obtain the desired product
Unit Operations examples
• Materials handling • Cleaning • Separating • Disintegrating • Pumping • Forming • Mixing v Heat exchange v Evaporation v Drying v Packaging v Non-thermal methods
Materials Handling
• Handling raw or partially processed materials
• Important considerations related to product
quality
Cleaning and Sanitation
• The equipment used will vary depending on
what you want to clean
– Water
– Surfaces of foods
– Surfaces of equipment or processing facilities
Clean:
Remove soil (matter out of place)
Sanitize:
Reduce microbial contamination to a safe level
Disinfect:
Kills 100% of vegetative cells, may not kill bacterial spores and viruses
• Sterilize:
Complete destruction of all forms of life (bacteria, bacterial spores, fungi, viruses)
Soils in food processing facilities are composed of
deposits of
fat, carbohydrates, proteins, and mineral
deposits
• 4 Factors of Cleaning:
– Time
– Action
– Concentration
– Temperature
Spray ball cleaning takes a lot of
time and chemical action
Rotary wetting cleaning takes a lot of
time and chemical action
Boiling out/fill and drain takes a lot of
time, chemical action and temperature
Size Reduction
• Reductions of particle size (cutting, grinding, pulping,
chopping, dicing, grating, homogenizing)
• Equipment selection can play a role in product quality
Pumping
Moving foods from one point to another • Important characteristics in selecting pumps: – Minimize product damage – Ease of cleaning
Mixing
All mixers do “work” on a product and can
affect product quality
Unit Operations in Food Processing examples
ü Pasteurization ü Sterilization ü Evaporation ü Drying ü Freezing ü Frying ü Baking ü Boiling ü Non-thermal methods
Process flow diagrams
• Basic Shapes
– Arrows indicate the Direction of Flow
– Parallelograms indicate Inputs or Outputs
– Diamonds indicate Decision Forks
– Rectangles indicate Processes
The Removal of Water
• Purposes:
– To slow spoilage (shelf-stable aw <0.6)
– To reduce bulk/weight/volume
– To control texture
– To make new products
• Concentration and Evaporation:
– The partial removal of water from
foods to increase its total solids
content
• Drying:
– An extensive approach to moisture
removal in which product moisture
is reduced to a few percent
Concentration and Evaporation
• Methods and Techniques
– Open kettles or pots
– Vacuum evaporator
– Freeze concentration
Volatile partitioning
Volatile compounds are compounds that due to their
high vapor pressure and low water solubility enter the
gas phase (air)
– Freeze concentration:
concentration of a product at the freezing point by ice crystal formation and separation
• The concentrate retains the flavor, color and aroma
• Crystallization: production of ice crystals
• Separation: separation of the ice crystals
The Drying Process
• Constant Rate Period (BC): straight line
– Water evaporates from the surface
• Critical Moisture Content (C)- where flat line turns into slope
• Falling Rate Period (CD):
– Water must be transported to
the surface (diffusion is rate limiting)
Factors That Affect Drying
• Product
-- Composition (water, sugar, CHO, Aw) – Amount of product – Size; Surface Area/Volume Ratio – Product Porosity – Pre-treatments of product (blanching, heat treatment)
Factors That Affect Drying
• Drier
– Type of drier – Temperature – Humidity – Pressure (vacuum) – Air flow – Air volume
Drying
• Methods and Techniques:
– Sun or Oven Drying (fruits and nuts)
– Forced-Air Drying
– Spray Drying (milk powder, instant coffee, eggs)
– Roller or Drum Drying (potato flakes, fruit juice)
– Tunnel Drying
– Freeze-Drying
Freeze drying
Sublimation of solid ice to vapor under vacuum
Physical Effects on Foods and Drying
Loss of structural water • Loss of water between and within cells – Shrinkage – Cell collapse – Surface cracking • Concentration of solutes • Case hardening – Formation of a hard outer layer that traps water inside the product
Food Chemistry and Drying
• Chemical reactions can occur at high drying temperatures
• Development of flavors and colors
– Caramelization
– Maillard Browning (when reactants can come together)
– Enzymatic Browning (when PPO is not denatured)
• Denaturation of proteins
• Loss of volatiles
Food Microbiology and Drying
High drying temperatures can kill bacterial populations
• Heat from drying is insufficient to kill bacterial
endospores
• aw can be altered to preserve foods
– The pathogen of concern in foods with low water activity is
Staphylococcus aureus
• aw ³ 0.85 for toxin production by S. aureus
• aw ³ 0.83 for growth of S. aureus
• Most spoilage organisms grow slowly in dried foods
Intermediate Moisture Foods (IMF)
IMF processing is used to create foods with : ü Moisture contents of 15-20% ü aw values of 0.6-0.85 • IMF foods do not require refrigeration to prevent microbial growth • Hurdle Technology (• Water removal (partial) • Solute concentration • Addition of sugar • Salt • Acid • Other preservatives)
Raisin Manufacture
• Harvested grapes are spread on paper sheets for 2-3 weeks. • The moisture content in the grapes drops from 80% to 15%. • The raisins are rolled up and equilibrate for several more days.
Manufacture of Golden Raisins
Sulfiting agents (sulfites) are used to inhibit enzymatic browning. • Forms of sulfites: Sulfur dioxide (SO2) Sodium sulfite (Na2SO3) Sodium metabisulfite (NaS2O5) Potassium metabisulfite (KS2O5) Sodium bisulfite (NaHSO3) Potassium bisulfite (KHSO3) • Sulfites can also inhibit Maillard browning
• Sulfites
A non-immunological food sensitivity
May cause breathing difficulty within minutes
Other symptoms include sneezing, swelling of the
throat, and hives
• Conduction:
heat transfer occurs between molecules (direct contact with a solid or a non-moving liquid)
The heat moves from one particle to the other
by direct contact
• The food does not move
• Convection:
heat transfer occurs because of a moving fluid (liquid or gas)
• Convention involves the movement of the mass
being heated
• In natural convection the heated portion
becomes less dense and rises
• Radiation:
heat transfer occurs because of light waves (electromagnetic energy)
Electromagnetic waves have different energies
depending on their wavelength and frequency
• Radiation does not involve direct contact
between the particles exchanging heat
Purposes of Heating
• To increase shelf-life • To kill or control microorganisms (including endospores) • To control or denature enzymes • To drive off moisture or gases • To alter texture (dissolve solutes, gelatinize starch, denature proteins, breakdown structures) • To inactivate toxins • To develop flavors • To develop colors
• Indirect contact heating:
food or package not in direct contact with the heating medium
• Heat exchanger
• Steam-jacketed kettle
• Direct contact heating:
food or package in direct contact with the heating medium • Retort or pressure cooker • Fryer • Direct steam injection or infusion • Broiler, toaster • Grill • Microwave
Baking and Roasting
• Use of heated air to alter the eating quality of
foods
• Essentially the same unit operation
• Baking: Flour based foods or Fruits
• Roasting: Meats, cocoa and coffee beans,
nuts and vegetables
• Heated air temperatures: 110 - 240 ˚C (230 –
450 ˚F)
• Heat is supplied by a combination of
radiation, convection and conduction
Chemical Changes:
Baking in an Oven
– Evolution and expansion of gases – Solid fats melt – Sugars caramelize – Proteins denature and coagulate – Starch gelatinizes – Moisture evaporates – Flavors develop – Browning occurs
Contrast Baking with
Boiling or Steaming
• Maximum possible
temperature is ≈100°C
• No Maillard Browning
• Inactivation of enzymes
Frying
• Frying is a process of immersing food in hot oil. • Simultaneous heat and mass transfer • High Temperature: 175- 190 ˚C (345-375˚F) • Oil provides uniform contact with a heating medium. • Frying is a “dry” heating method. • Frying only heats the surface of a food. • Conduction to heat the internal part of the food.
The four stages of Frying
- Initial heating
- Surface boiling
– Vaporization of water
– Forced convection of oil - Falling rate
– Rate of evaporation decreases
– Chemical changes occur in the internal regions
of the food
– Crust thickens - Bubble end point
Physical and chemical changes
in the frying oil
- Hydrolysis
- Oxidation
- Polymerization
- Viscosity Increase
- Thickening of oil
- Development of off-flavors
Acrylamide formation
Acrylamide is formed from food
components during heat treatment
• Maillard Reaction between amino
acids (e.g. asparagine) and reducing
sugars
• Asparagine: major amino acid in
potatoes and cereals
• Potential carcinogenic
• High frying temperature and long cooking times
• Storing potatoes in the refrigerator can result in
increased acrylamide formation during cooking
• Soaking raw potato slices in water for
15-30 min before frying helps minimize
acrylamide production
• Cook to a golden yellow color not brown!!
Broiling
• A heating element emits infrared energy. • Broiling rapidly heats the surface of the food and results in Maillard Browning. • Broiling only acts on the surface of a food. • Broiling is distance-dependent.
Microwave Heating
Microwave energy produces heat in materials that absorb it • Wavelengths of 0.025 – 0.75 m and frequencies of 20,000 to 400 MHz • Food applications: approved microwave frequencies are 2,450 and 915 MHz
Understanding Microwave Heating
- Molecular friction of polar molecules
– Microwaves are very effective at heating foods
because foods contain water, which is polar.
– Microwaves create a fluctuating electrical field
inside a microwave oven, which changes direction
2.45 billion times per second (2,450 MHz). - Ionic polarization
– Dissociated ions cause heat when they collide
• Dielectric Properties of foods
Loss factor (εl): Ability of foods to dissipate
electrical energy. The higher the loss factor, the
more energy is absorbed by the food
– Dielectric Constant (εll): Rate at which energy
penetrates a food
Microwave Heating: depth
• Microwaves penetrate most foods (or are absorbed) to a
depth of 5-7 cm (2-3 in)
• The outer surface is heated by the microwaves and is
followed by inward conduction
• Foods do not heat up equally fast in a microwave
oven
• Polar molecules absorb more energy than non-polar
components of foods
