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Questions and Answers
What is the primary objective of heat treatment in food preservation?
What is the primary objective of heat treatment in food preservation?
Which factor influences the thermal resistance of microbial cells or spores?
Which factor influences the thermal resistance of microbial cells or spores?
During which phase of growth do bacterial cells exhibit the greatest resistance to heat?
During which phase of growth do bacterial cells exhibit the greatest resistance to heat?
What is pasteurization primarily used for?
What is pasteurization primarily used for?
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What temperature range generally characterizes pasteurization?
What temperature range generally characterizes pasteurization?
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Which of the following methods can supplement pasteurization in food preservation?
Which of the following methods can supplement pasteurization in food preservation?
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What happens to microbial proteins at high temperatures during heat treatment?
What happens to microbial proteins at high temperatures during heat treatment?
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What occurs to the time required to kill cells or spores as the temperature increases?
What occurs to the time required to kill cells or spores as the temperature increases?
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Which method is NOT effective in preventing microbial contamination during food preservation?
Which method is NOT effective in preventing microbial contamination during food preservation?
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What is the primary goal of inhibiting microbial growth in food preservation?
What is the primary goal of inhibiting microbial growth in food preservation?
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Which process is used to inactivate food enzymes as a method of food preservation?
Which process is used to inactivate food enzymes as a method of food preservation?
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Which method is most effective for preserving food by creating unfavorable conditions for microorganisms?
Which method is most effective for preserving food by creating unfavorable conditions for microorganisms?
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What is the objective of extending the lag phase and phase of positive acceleration in food preservation?
What is the objective of extending the lag phase and phase of positive acceleration in food preservation?
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How does prevention of oxidation contribute to food preservation?
How does prevention of oxidation contribute to food preservation?
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Which of the following is NOT a chemical reaction that should be delayed in food preservation?
Which of the following is NOT a chemical reaction that should be delayed in food preservation?
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What is a potential outcome of exposing microorganisms to sublethal heat treatments?
What is a potential outcome of exposing microorganisms to sublethal heat treatments?
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What is the primary purpose of ventilation in food storage rooms?
What is the primary purpose of ventilation in food storage rooms?
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What concentration of carbon dioxide is considered optimal for preserving eggs?
What concentration of carbon dioxide is considered optimal for preserving eggs?
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Which gas combination is typically used for gas storage of food?
Which gas combination is typically used for gas storage of food?
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What does the thermal death point (TDP) measure in microorganisms?
What does the thermal death point (TDP) measure in microorganisms?
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What is a major advantage of combining U.V. irradiation with chilling during food storage?
What is a major advantage of combining U.V. irradiation with chilling during food storage?
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What is the effect of freezing on microbial growth?
What is the effect of freezing on microbial growth?
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What is the D Value in thermal destruction of microorganisms?
What is the D Value in thermal destruction of microorganisms?
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Which microorganism can grow at temperatures as low as 0-3°C?
Which microorganism can grow at temperatures as low as 0-3°C?
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Which method is used to inactivate plant enzymes before freezing vegetables?
Which method is used to inactivate plant enzymes before freezing vegetables?
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What is the typical temperature for common or cellar storage of food?
What is the typical temperature for common or cellar storage of food?
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What happens to chemical or enzymatic reactions at lower storage temperatures?
What happens to chemical or enzymatic reactions at lower storage temperatures?
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Which food item is best stored at a temperature of 13.3 – 16.7°C?
Which food item is best stored at a temperature of 13.3 – 16.7°C?
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What is the main purpose of packing most foods before freezing?
What is the main purpose of packing most foods before freezing?
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How do low temperatures affect the enzyme activity in stored food?
How do low temperatures affect the enzyme activity in stored food?
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What is a potential consequence of high humidity in food storage?
What is a potential consequence of high humidity in food storage?
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Which of the following best describes chilling storage temperatures?
Which of the following best describes chilling storage temperatures?
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What is the correct temperature and time combination for the HTST pasteurization method?
What is the correct temperature and time combination for the HTST pasteurization method?
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Which method of pasteurization uses the lowest temperature for the longest duration?
Which method of pasteurization uses the lowest temperature for the longest duration?
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What does the phosphatase test indicate in milk pasteurization?
What does the phosphatase test indicate in milk pasteurization?
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What temperature is required during boiling to adequately treat food?
What temperature is required during boiling to adequately treat food?
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Which process is referred to as Ultra Heat Temperature (UHT) processes?
Which process is referred to as Ultra Heat Temperature (UHT) processes?
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What is the characteristic temperature and duration that Clostridium botulinum spores can resist?
What is the characteristic temperature and duration that Clostridium botulinum spores can resist?
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What is the role of steam pressure during sterilization processes?
What is the role of steam pressure during sterilization processes?
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What happens during the alkaline phosphatase test if the milk has not been properly pasteurized?
What happens during the alkaline phosphatase test if the milk has not been properly pasteurized?
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What is a characteristic of quick freezing compared to slow freezing?
What is a characteristic of quick freezing compared to slow freezing?
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How long does it take to achieve slow freezing?
How long does it take to achieve slow freezing?
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Which of the following statements is true regarding microorganisms during freezing?
Which of the following statements is true regarding microorganisms during freezing?
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What is a primary advantage of quick freezing over slow freezing?
What is a primary advantage of quick freezing over slow freezing?
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Which change occurs during the preparation for freezing that affects food deterioration?
Which change occurs during the preparation for freezing that affects food deterioration?
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What happens to the metabolic rapport during quick freezing?
What happens to the metabolic rapport during quick freezing?
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How does the freezing process affect lipids in foods?
How does the freezing process affect lipids in foods?
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What is the effect of thawing on quick frozen foods?
What is the effect of thawing on quick frozen foods?
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Study Notes
Food Preservation
- Food preservation aims to prevent or delay microbial contamination and self-decomposition of food.
Principles of Food Preservation
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Prevention or delay of microbial contamination:
- Keeping out microorganisms (sterilization)
- Removing microorganisms (e.g., filtration)
- Inhibiting microbial growth (e.g., low temperature, drying, anaerobic conditions, chemicals)
- Killing microorganisms (e.g., high heat, radiation)
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Prevention or delay of self-decomposition of the food:
- Destroying or inactivating food enzymes (e.g., blanching)
- Preventing chemical reactions (e.g., oxidation using antioxidants)
- Preventing damage caused by insects, animals, or mechanical causes
Application of Food Preservation
- Lengthening the lag phase and the phase of positive acceleration is crucial.
- Reduce the number of spoilage organisms by reducing contamination.
- Avoid adding actively growing organisms to prevent contamination during growth phase of organisms.
- Create unfavorable environmental conditions to slow or stop growth (e.g., temperature, pH, presence of inhibitors).
- Damage organisms through processing methods like heating or irradiation.
Methods of Food Preservation: High Temperatures
- The primary objective of heat treatment is to kill microbes causing food spoilage or posing health risks.
- Heat denatures or clots microbial proteins, inactivating their vital functions, inhibiting metabolism enzymes, and damaging the cell wall.
Factors Influencing Thermal Resistance
- Relationship between temperature and time: Higher temperatures result in shorter times for killing microorganisms.
- Initial concentration: Higher initial numbers require longer or higher temperatures.
- Previous history: Conditions in which cells live & how cells have grown affect the ability of spores or cells to resist heat.
- Growth Phases: Microorganisms, in general, tend to exhibit greatest resistance during the late logarithmic to maximum stationary phases of growth.
Heat Treatments Employed in Processing Foods
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Pasteurization (below 100°C): Kills part of the microorganisms but not all. Used to eliminate pathogens or when higher temperatures might harm quality.
- Methods: steam, hot water, dry heat, electric currents; Cooling immediately after.
- Boiling (around 100°C): Sufficient for killing many microbes but not spores. Suitable for low and medium acid foods.
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Sterilization (above 100°C): Kills all microorganisms (including spores). Achieved via steam under pressure.
- Ultra-Heat Treatment (UHT) involves steam injection or infusion with flash evaporation followed by rapid cooling to achieve high temperatures. Detection of effectiveness involves determining the presence of heat resistant organisms like Clostridium botulinum, resistant to high heat at 120°C for 20 minutes.
Thermal Destruction of Microorganisms
- Thermal death time (TDT): Time needed to kill a given number of microbes at a fixed temperature.
- Thermal death point (TDP): Temperature needed to kill a given number of microbes in a fixed time (e.g., 10 minutes).
- D-value: Time required to decrease the number of live organisms by 90%.
Preservation by Use of Low Temperatures
- Low temperatures slow down chemical reactions, enzyme action, and microbial growth.
Growth of Microorganisms at Low Temperatures
- Freezing prevents the growth of most foodborne microorganisms.
- Refrigeration slows growth rates.
- Specific microorganisms have minimum growth temperatures (e.g. Clostridium botulinum type E 3.3°C; Yersinia enterocolitica 0-3°C)
Temperatures Employed in Low-Temperature Storage
- Common/Cellar Storage: Typically below 15°C for root crops, potatoes and others.
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Chilling/Cold Storage: Temperatures near freezing (-1 to 8°C).
- Holds eggs, dairy, meats, seafood, vegetables and fruits for a limited time.
- Using gas in addition to cold storage may extend storage time.
- Freezing: Freezing prevents all microbial growth and significantly slows enzyme reactions. Methods vary regarding pre-processing and packaging.
- Methods like scalding/blanching are used for vegetables prior to freezing.
Quick Freezing vs. Slow Freezing
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Quick freezing: Forms smaller ice crystals, preserving cell structure.
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Slow freezing: Forms larger crystals. Damages cell structure to a greater degree.
Effect of Freezing on Microorganisms
- Cocci (spherical) bacteria are more resistant to freezing than rods.
- Endospores and toxins are unaffected.
- Low temps impact fatty acids, causing some changes to lipids' unsaturated fatty acids.
Changes during preparation for Freezing
- Conditions at harvesting, slaughter, and handling influence food's deterioration rate. Temperatures and handling will result in different microbial growth and changes.
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Description
Test your knowledge on the principles of heat treatment and food preservation methods. This quiz covers key concepts such as pasteurization, thermal resistance of microorganisms, and the goals of inhibiting microbial growth. Discover how various techniques contribute to extending the shelf life of food.
