Chapter 4. Physical measurements of food
Chapter 4. Physical measurements of food
Section 1. Introduction • Physical property of food: ➢ 1) Relative density, refractive, optical rotation ➢ 2) Chroma, viscousness, texture
Section 1. Introduction • Physical property of food: ➢ 1) Relative density, refractive, optical rotation ➢ 2) Chroma, viscousness, texture
Section 2. Physical determination methods • Relative density method • Refractive method • Rotation optical method
Section 2. Physical determination methods • Relative density method • Refractive method • Rotation optical method
1. Relative density method • 1.1 Density and relative density ➢Density ？ 指物质在一定温度下单位体积的质量，以ρ 表示，ρ= mass/volume = m/v(g/cm3)
1. Relative density method • 1.1 Density and relative density ➢Density ？ 指物质在一定温度下单位体积的质量，以ρ 表示，ρ= mass/volume = m/v(g/cm3)
• Relative density？ 定义：指某一温度下物质的质量 与 同体积某一温度下水的质量之比，以 d 表示，是无因次量。 d t1 t2 = t1温度下物质的密度 / t2温度下水的密度
• Relative density？ 定义：指某一温度下物质的质量 与 同体积某一温度下水的质量之比，以 d 表示，是无因次量。 d t1 t2 = t1温度下物质的密度 / t2温度下水的密度
• d20 4 • d20 20 • d20 4= d20 20×0.99823
• d20 4 • d20 20 • d20 4= d20 20×0.99823
1.2 Significance of determining relative density • Determination of density is one of the most simple measurements in food analysis. • Every liquid food has its relative density. Relative density will change, when the composition or concentration of food changes. • Through determining the relative density of food, its purity, concentration and quality can be measured
1.2 Significance of determining relative density • Determination of density is one of the most simple measurements in food analysis. • Every liquid food has its relative density. Relative density will change, when the composition or concentration of food changes. • Through determining the relative density of food, its purity, concentration and quality can be measured
Measuring concentration • Sucrose • Alcohol • Juice: total solids contents
Measuring concentration • Sucrose • Alcohol • Juice: total solids contents
Measuring quality • Milk: normal 1.028-1.032，if adding water to it, d will decrease. • Vegetable oil: 0.9090-0.9295
Measuring quality • Milk: normal 1.028-1.032，if adding water to it, d will decrease. • Vegetable oil: 0.9090-0.9295
1.3 Measurement of density • 1.3.1 pycnometric method (密度瓶法) ➢ The most common method of density determination consists of measuring the weight of a known volume of liquid in a vessel, the volume of which was calibrated in terms of pure water that the vessel holds. This is best done by using a pycnometer
1.3 Measurement of density • 1.3.1 pycnometric method (密度瓶法) ➢ The most common method of density determination consists of measuring the weight of a known volume of liquid in a vessel, the volume of which was calibrated in terms of pure water that the vessel holds. This is best done by using a pycnometer