Food Processing and Engineering

What factors can influence microbial growth during refrigeration?

- Initial micro population - Characteristics of the food - Effect of processing - Refrigeration temp - Refrigerator load/ capacity

What factors contribute to the magnitude of the thermal process?

- Product pH or acidity - Heating and cooling characteristics - Size of container - Heating and cooling medium - Time/temperature relationship - Product composition

How does Refrigeration affect microbial growth and food quality?

- Retard microbial growth - Limit lipid oxidation - Limit non-enzymatic browning and enzymatic browning - Slow down sugar conversion - Reduce respiration reactions.

Starting with 1 atm, how are the following units related: atmosphere, inches of mercury, pascal, psi?

1 atm = 29.92 (~30) in Hg = 760 mm Hg = 101,325 Pa = 14.696 psi

Name five categories of freezing equipment used in the food industry.

1-The air blast freezers / cold storage freezers 2-The cartoon freezers / box freezers 3-The spiral belt freezers 4-The fluidized bed freezer / IQF freezer (or tunnel freezers) 5-The immersion freezers / brine freezers 6-The plate freezers / block freezers 7-The contact belt freezers 8-The impingement freezers / flat product freezers 9-The cryogenic freezers

What are the physio-chemical reactions affecting product quality?

1. Component migration - migration of components in and out of foods. Water - foods can pick up or lose moisture from the environment. 2. Phase change - loss of product quality over time - stale bread due to retro-gradation of starch - slow crystallization of elements of starch.

What are the biochemical reactions affecting product quality?

1. Enzymic browning - occurs in fruits and vegetables after bruising and processing. Phenolic compounds react with phenolases with oxygen to produce yellow-brown pigment. - Vacuum packaging, modified atmosphere packaging, sulphites, citric acid or ascorbic acid reduce the effects of browning. 2. Glycolysis - Breakdown of glycogen in living tissue - happens after harvest/slaughter oxygen causes breakdown of tissue and softening of structure. 3. Proteolysis - Proteases enzymes attack protein matter in food breaking them down to peptides or shorter chain amino acids. 4. Lipolysis - Lipolysis causes loss of product quality. - Lipases cause catalysis of hydrolysis of triacylglycerols into fatty acids and glyceride breakdown."

Name at least four reasons for processing foods.

1. Preserve against deterioration 2. Provide adequate food supply throughout the year 3. Convenience 4. Provide uniform quality of foods on a large scale 5. Create new products to meet specific nutritional needs or changes in technology.

Name three types of drying.

1) Air convection 2) Drum or roller driers 3) Vacuum driers.

Describe two kinds of fluids that require the application of yield stress before any flow occurs.

1) Bingham liquids 2) Plastics

Name four types of mixers.

1) Conical blender 2) Ribbon blender 3) Propeller 4) Turbine 5) Paddle agitators.

Name the methods for direct heating and indirect heating.

1) Direct heating methods: toasting, frying, steam injection, steam infusion, spray drying, baking 2) Indirect heat exchangers: plate, tubular, shell and tube, scraped surface heat exchanger.

What do HTST, PSIG, and CSTR stand for in food processing?

1) High Temperature Short Time 2) Pounds per Square Inch Gauge 3) Continuous Stirred Tank Reactor.

Name four examples of traditional nonthermal processing.

1) Modified atmosphere packaging (MAP) 2) Controlled atmosphere storage (CAS) 3) Nitrogen flush packaging 4) Vacuum packaging

Name four basic principles of food processing.

1) Moisture removal 2) Heat treatment 3) Low-heat treatment 4) Thermal processing 5) Nonthermal processing (traditional & nontraditional) 6) Acidity control

Name types of concentration methods/equipment.

1) Solar evaporation 2) Flash evaporators 3) Ultrafiltration 4) Open kettle 5) Thin-film evaporators 6) Reverse osmosis 7) Freeze concentration 8) Vacuum evaporators.

Name three types of evaporation.

1) Sun drying 2) Heated kettle/open boiling 3) Heated kettle/vacuum evaporation.

What is the overall heat transfer coefficient/ How is it calculated?

1/U = 1/hsteam + L/k + 1/hjuice + Rf; U = overall heat transfer coefficient h = convective heat transfer coefficient k/L = conductive heat transfer coefficient = thermal conductivity/thickness Rf = Fouling factor

In a thermal processing operation, if the D value is 0.5 minutes at 250°F and the initial microbial count is 100,000, what is the microbial count after 2 minutes?

10, a decrease of 4 D values

Assume the temperature of moist air is 60C, and the saturation pressure of water vapor at 60C is 20 kPa. If the measured water vapor pressure is 4.0 kPa, what is the relative humidity of the air?

20% (Relative humidity is the ratio of the partial pressures: RH = 4/20 = 20%)