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Questions and Answers
What is one of the learning outcomes of the course related to water in foods?
What is one of the learning outcomes of the course related to water in foods?
- Identify the nutritional values of water.
- Determine the caloric content of hydration.
- Explain the concept of water activity (aw) in food systems. (correct)
- Describe various cooking methods for water-based foods.
Which statement accurately describes the role of water in food?
Which statement accurately describes the role of water in food?
- Water is not important for food characteristics.
- Water contributes to the taste but not to the texture of food.
- Water influences chemical reactions and microbial growth in food. (correct)
- Water solely acts as a solvent in food products.
Which of the following is a physicochemical property of water relevant to food technology?
Which of the following is a physicochemical property of water relevant to food technology?
- Absence of any electrical conductivity.
- Density variability only at boiling point.
- High specific heat capacity. (correct)
- Insolubility of any solutes.
What aspect of water does the course focus on regarding its characteristics in food?
What aspect of water does the course focus on regarding its characteristics in food?
Which of the following best defines 'water activity' (aw)?
Which of the following best defines 'water activity' (aw)?
What does water activity (aw) measure in food?
What does water activity (aw) measure in food?
Which type of water is characterized as free water that can be easily evaporated?
Which type of water is characterized as free water that can be easily evaporated?
What is the defining characteristic of chemically bound water?
What is the defining characteristic of chemically bound water?
What describes physically bound water in food?
What describes physically bound water in food?
Which water type has water molecules that can form hydrogen bonds with other water molecules?
Which water type has water molecules that can form hydrogen bonds with other water molecules?
What moisture content is typically associated with Type 3 water when removed from food?
What moisture content is typically associated with Type 3 water when removed from food?
What property distinguishes Type 4 water in food?
What property distinguishes Type 4 water in food?
How is absorbed water defined in the context of food?
How is absorbed water defined in the context of food?
What is one of the roles of water in food systems?
What is one of the roles of water in food systems?
Which food type is categorized as highly perishable?
Which food type is categorized as highly perishable?
What is the moisture content of fresh tomatoes?
What is the moisture content of fresh tomatoes?
What is the molecular composition of a water molecule?
What is the molecular composition of a water molecule?
Which process involves water acting as a heat transfer medium in food production?
Which process involves water acting as a heat transfer medium in food production?
What does moisture content (MC) describe in food?
What does moisture content (MC) describe in food?
In terms of physicochemical properties, what is the pH value of pure water?
In terms of physicochemical properties, what is the pH value of pure water?
Which of the following statements about hydrogen bonds in water is correct?
Which of the following statements about hydrogen bonds in water is correct?
Which food category is considered non-perishable?
Which food category is considered non-perishable?
What type of energy is associated with the change of state in water?
What type of energy is associated with the change of state in water?
Which of the following is NOT a role of water in chemical reactions?
Which of the following is NOT a role of water in chemical reactions?
What is the boiling point of water at 1 atm?
What is the boiling point of water at 1 atm?
What is the significance of water activity (aw) in food systems?
What is the significance of water activity (aw) in food systems?
In the context of food storage, what aspect does moisture content primarily determine?
In the context of food storage, what aspect does moisture content primarily determine?
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Study Notes
Chemical Structures and Physicochemical Properties of Water
- Water is a polar molecule with H atoms having a positive charge (δ+) and O atoms having a negative charge (δ-).
- The hydrogen bond formed between water molecules due to the difference in electronegativity contributes to its high boiling point (100°C) and flowability.
- Water has a pH of 7.0 when pure, a molecular weight of 18.0153, a melting point of 0°C, and a boiling point of 100°C at 1 atm.
Water Activity and its Importance in Food Systems
- Water activity (aw) is a measure of the free water available for chemical reactions and microbial growth.
- Water activity ranges from 0 to 1 with 1 representing pure water.
- Water activity is lower in foods with high solute concentrations like salt or sugar as these solutes bind to water molecules.
- Moisture content relates to the water content in food, expressed as a percentage.
- Relative humidity is the percentage of water vapor content in the air.
Role of Water in Chemical Reactions and Microbial Growth
- Physically bound water includes capillary water, trapped water, and absorbed water.
- Chemically bound water consists of water molecules forming hydrates with other molecules containing O and N atoms, and water molecules integral to other compounds like proteins and carbohydrates.
- Free or mobile water is not bound to any other molecules.
- Water acts as a universal solvent for various substances including salts, vitamins, sugars, and pigments.
- Water acts as a heat transfer medium in food systems, particularly during cooking and preservation processes.
- Water can be involved in chemical reactions like protein hydrolysis (breaking down proteins into amino acids).
- Water is essential for the growth and survival of microorganisms, impacting food safety and stability.
- High water activity increases the risk of microbial growth, leading to spoilage.
Food Categories by Perishability
- Highly perishable foods include beef, chicken, fish, milk, and eggs, with high water activity prone to spoilage.
- Moderately perishable foods like vegetables, fruits, bread, and cake have a moderate amount of free water.
- Non-perishable foods like seeds, sugars, dried spices, and legumes have very low water activity, resisting microbial growth and spoilage.
Application: Drying Process in Food Industry
- Hot air drying removes water from liquid to vapor at normal pressure.
- Vacuum drying removes water from liquid to vapor at lower pressure.
- Freeze drying removes water from solid phase to vapor at very low pressure.
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