Measurement of Water Activity

Summary

This video delves into the concept of water activity (aw), which is pivotal for assessing food safety and shelf life by gauging the availability of free water for microbial growth. It introduces four primary methods for measuring water activity: the desiccator technique using sulfuric acid or salt solutions to maintain low humidity, the Winkler method for dissolved oxygen measurement in freshwater systems, the dynamic vapor sorption (DVS) which directly measures vapor pressure for fast and reliable results, and the spring sorption balance method that tracks moisture content changes in a controlled environment. The video underscores the significance of water activity in predicting food spoilage and ensuring product longevity.

Takeaways

• 💧 Water Activity (AW) is a measure of the free water available for microbial growth in a system.
• 📊 AW is defined as the ratio of the vapor pressure of water in a material to that of pure water at the same temperature.
• 🍽️ High AW indicates more water available for bacteria, which can lead to faster spoilage of food.
• 🌡️ AW is crucial for understanding food safety, shelf life, and the longevity of food products.
• 🔬 The desiccator method uses sulfuric acid or salt solutions to maintain a low humidity environment for moisture-sensitive items.
• 🧪 The Winkler method measures dissolved oxygen in freshwater systems, indicating the health and productivity of water bodies.
• 📉 The dynamic vapor sorption (DVS) method directly measures the vapor pressure of a sample to calculate water activity, overcoming traditional method drawbacks.
• 🧬 DVS is useful in various industries including pharmaceuticals, foods, feeds, fertilizers, agrochemicals, fine chemicals, detergents, cosmetics, and electronics.
• 🌱 The spring sorption balance method involves observing the extension or contraction of a calibrated coil spring due to moisture gain or loss in a constant relative humidity atmosphere.
• 📈 By plotting the sorption isotherm with samples of various moisture contents, one can determine the food's water activity.
• 🛡️ Controlling water activity helps predict and prevent food spoilage, ensuring the safety and quality of food products.

Q & A

What is water activity and why is it important?

Water activity, denoted by 'aw', is a measure of the free water in a system available for microbial growth. It's important because it directly impacts food safety and quality, influences microbial growth, shelf life, and chemical reactions within food.

How is water activity defined in the context of food safety?

Water activity is defined as the ratio of the vapor pressure of the water in a material to the vapor pressure of pure water at the same temperature. It's like a water score for food, indicating how much water is available for bacteria to use, which can affect how quickly the food spoils.

What is the purpose of a desiccator in relation to water activity?

A desiccator maintains a low humidity environment for moisture-sensitive items such as fruits and vegetables. It contains substances like sulfuric acid or salt solutions to absorb moisture and preserve the integrity of chemicals, electronics, or hygroscopic materials.

How does the Winkler method measure dissolved oxygen?

The Winkler method involves suspending a sample in a vessel with a saturated salt solution and continuously weighing it. Oxygen reacts with manganese hydroxide to form higher hydroxides, which release iodine upon acidification. This iodine is then titrated by a standard sodium thiosulfate solution using starch as an indicator.

What is the formula used to calculate dissolved oxygen using the Winkler method?

The formula to calculate dissolved oxygen using the Winkler method is: Dissolved Oxygen (mg/L) = (Volume of titrant * Normality of titrant * 8.8). The 8.8 is a conversion factor that helps convert the volume and normality of the thiosulfate solution into the amount of oxygen in milligrams per liter.

What is the dynamic vapor sorption (DVS) method and how does it measure water activity?

Dynamic vapor sorption (DVS) is a method for measuring water activity by directly measuring the vapor pressure of a sample. Water activity is calculated from the ratio of the sample's vapor pressure to that of pure water. DVS is fast, reliable, and overcomes drawbacks of traditional methods.

How does the spring sorption balance method measure water activity?

The spring sorption balance method involves suspending a food sample from a calibrated coil spring. The extension or contraction of the spring, which is caused by moisture gain or loss in a constant relative humidity atmosphere, is followed by a cathetometer or recorded electronically.

What are some applications of the dynamic vapor sorption (DVS) method?

The DVS method is used in various industries such as pharmaceuticals, foods and feeds, fertilizers and agrochemicals, fine chemicals, detergents and cosmetics, and building materials and electronics to measure water activity in materials.

How can water activity measurements be used to predict and prevent food spoilage?

By controlling and measuring water activity, we can predict the conditions under which food is most likely to spoil. This helps in ensuring the safety and longevity of food products by preventing microbial growth and spoilage.

What are some sources that provide more detailed information on water activity measurements?

For more detailed information on water activity measurements, one can refer to reviews by Gal (1967) and To (1973). Additionally, methods of partial pressure measurement using simple manometric techniques are given by Taylor (1961) and Carol (1955).

Outlines

00:00

🧪 Understanding Water Activity and Its Measurement Methods

This paragraph introduces the concept of water activity (aw), which is a critical factor in determining food safety and shelf life. Water activity measures the availability of free water in a system for microbial growth and is expressed as the ratio of the vapor pressure of water in a material to that of pure water at the same temperature. The paragraph then delves into four distinct methods for measuring water activity: 1) The desiccator method, which uses sulfuric acid or salt solutions to maintain a low humidity environment for moisture-sensitive items. 2) The Winkler method, employed for measuring dissolved oxygen in freshwater systems, which involves a chemical reaction that releases iodine, subsequently titrated by a standard sodium thiosulfate solution. 3) The Dynamic Vapor Sorption (DVS) method, a modern and reliable technique that measures the vapor pressure of a sample directly, thus calculating water activity. 4) The spring sorption balance method, which involves suspending a food sample from a calibrated spring to measure its extension or contraction due to moisture gain or loss in a controlled humidity environment. The importance of water activity measurement is emphasized as it influences microbial growth, shelf life, and chemical reactions within food, thereby aiding in predicting and preventing food spoilage.

05:02

📚 Applications and Significance of Water Activity Measurement

The second paragraph discusses the application areas of water activity measurement, which include pharmaceuticals, foods and feeds, fertilizers, agrochemicals, fine chemicals, detergents, cosmetics, building materials, and electronics. It outlines the spring sorption balance method in more detail, explaining how it involves placing a food sample of known moisture content in a sealed enclosure to observe changes in relative humidity levels. The paragraph also highlights the importance of water activity in ensuring food safety and quality by controlling microbial growth and chemical reactions. It concludes with a call to action for viewers to subscribe, like, and comment, emphasizing the significance of understanding water activity measurements for the safety and longevity of food products.

Keywords

💡Water Activity (aw)

Water activity, denoted by 'aw', is a measure of the free water in a system available for microbial growth. It is defined as the ratio of the vapor pressure of the water in a material to the vapor pressure of pure water at the same temperature. In the context of the video, water activity is likened to a 'water score' for food, indicating how much water is available for bacteria to use, which in turn affects the food's shelf life and spoilage rate. The higher the water activity, the more bacteria can grow, leading to faster spoilage.

💡Microbial Growth

Microbial growth refers to the increase in the number of microorganisms, such as bacteria and fungi, in a given environment. The video emphasizes that water activity is a key factor in microbial growth because microorganisms require water to grow and reproduce. Foods with higher water activity levels can support more microbial growth, which can lead to spoilage and a reduced shelf life.

💡Food Safety

Food safety is a critical aspect of ensuring that food is free from harmful contaminants and suitable for consumption. The video script highlights that water activity is a key factor in food safety because it directly impacts the growth of microorganisms that can cause foodborne illnesses. By understanding and controlling water activity, one can predict and prevent food spoilage, thereby enhancing food safety.

💡Shelf Life

Shelf life is the length of time that a product can remain fresh, retain its intended quality, and be safe for consumption. In the video, it is mentioned that water activity helps determine the shelf life of food products. Foods with lower water activity tend to have a longer shelf life because they are less conducive to microbial growth and spoilage.

💡Desiccator

A desiccator is a container used to maintain a low humidity environment for moisture-sensitive items. In the video script, desiccators containing sulfuric acid or salt solutions are mentioned as equipment that can help preserve the integrity of chemicals, electronics, or hygroscopic materials by absorbing moisture from the air inside when sealed shut.

💡Winkler Method

The Winkler method is a technique used to measure dissolved oxygen in water bodies. The video describes the process where oxygen reacts with manganese hydroxide to form higher hydroxides, which, upon acidification, release iodine. This iodine is then titrated by a standard sodium thiosulfate solution using starch as an indicator. The method is used as an indicator of the health of a water body, with higher dissolved oxygen concentrations correlating with high productivity and little pollution.

💡Dynamic Vapor Sorption (DVS)

Dynamic Vapor Sorption (DVS) is a method for measuring water activity by directly measuring the vapor pressure of a sample. The video explains that water activity is calculated from the ratio of the sample's vapor pressure to that of pure water. DVS is noted for being fast, reliable, and overcoming the drawbacks of traditional methods, making it suitable for measuring water activity in various materials, including pharmaceuticals, foods, and cosmetics.

💡Spring Sorption Balance Method

The Spring Sorption Balance Method is a technique where a food sample is suspended from a calibrated coil spring, and the extension or contraction of the spring is monitored to measure changes in moisture content. The video script describes this method as involving samples of known initial moisture content that go through a process of moisture gain or loss in a constant relative humidity atmosphere, which helps in plotting the food's sorption isotherm.

💡Isotherm

An isotherm, in the context of the video, refers to a graph that represents the sorption behavior of a substance at a constant temperature. The script mentions that the equilibrium mass values generated by the DVS method are used to plot the isotherm, which is crucial for understanding the relationship between water activity and the amount of water a substance can absorb or release.

💡Chemical Reactions

Chemical reactions within food are processes that can lead to changes in the food's quality, taste, and safety. The video script explains that water activity influences these chemical reactions, as it affects the rate at which they occur. By controlling water activity, one can manage these reactions to maintain the desired properties and extend the shelf life of food products.

Highlights

Water activity (aw) measures the free water in a system available for microbial growth.

Defined as the ratio of the vapor pressure of water in a material to that of pure water at the same temperature.

Water activity is a key factor in food safety and shelf life, indicating how long food might last before spoiling.

Desiccator equipment maintains a low humidity environment for moisture-sensitive items like fruits and vegetables.

Airtight containers with desiccant materials like silica gel or calcium chloride are used to absorb moisture from the air inside.

The Winkler method measures dissolved oxygen in freshwater systems, indicating the health of a water body.

Dynamic Vapor Sorption (DVS) measures water activity by directly measuring the vapor pressure of a sample.

DVS is fast, reliable, and overcomes drawbacks of traditional methods, providing accurate water activity measurements.

The spring sorption balance method measures changes in a calibrated coil spring due to moisture gain or loss in a sample.

Water activity measurements are crucial for predicting and preventing food spoilage, ensuring food safety and quality.

By controlling water activity, we can influence microbial growth, shelf life, and chemical reactions within food.

The desiccator functions to preserve the integrity of chemicals, electronics, or hygroscopic materials against moisture.

The Winkler method involves a chemical reaction between oxygen and manganese hydroxide to form higher hydroxides.

The amount of dissolved oxygen in a water body is correlated with its productivity and level of pollution.

DVS uses a gravimetric technique varying vapor concentration to measure water activity in various materials.

The spring sorption balance method involves placing a food sample of known moisture content in a sealed enclosure.

Water activity measurements are detailed in reviews by Gal (1967) and To (1973), and Taylor (1961).

Measuring water activity is essential as it directly impacts food safety, quality, and longevity of food products.

Transcripts

in this video I'm going to discuss about

the measurements of water activity but

first what is water activity water

activity denoted by aw is a measure of

the free water in a system available for

microbial growth it's defined as the

ratio of the vapor pressure of the water

in a material to the vapor pressure of

pure water at the same temperature it's

a key factor in food safety and shelf

life

it means water activity is like a water

score for food it measures how much

water is available in the food for

bacteria to use the higher the score the

more bacteria can grow which can make

the food spoil faster so it helps us

understand how long the food might last

before it

spoils now let's proceed to the four

methods of measuring water

activity

first the desiccator this equipment

containing sulfuric acid or Salt

Solutions what are its

functions maintain a low humidity

environment for moisture sensitive items

such as fruits and vegetables next

comprising an airtight container with a

lid they employ descants like silica gel

or calcium chloride to absorb moisture

from the air inside when sealed shut

this dry environment preserves the

Integrity of chemicals Electronics or

hygroscopic materials within it need

periodic replacement or regeneration as

they become saturated ensuring continued

Effectiveness in safeguarding against

moisture second the Winkler

method the sample suspended in a vessel

with saturated salt solution and weighed

continuously by a bottom weighing

balance oxygen combines with Mangus

hydroxide to form higher hydroxides

which acidification liberate iodine

equivalent to that of oxygen in simple

terms when oxygen comes into contact

with manganese hydroxide they react to

form a new compound called a higher

hydroxide if this compound is then

exposed to an acid it releases

iodine this iodine is titrated by a

standard sodium thos sufate solution

using starch as an

indicator this is the formula to

calculate the dissolved oxygen using the

winklers method is equals to volume of

titrant multiply by the normality of the

titrant and multiply to 8.8 and the 8.8

in the formula is a conversion factor it

helps convert the volume and normality

of the titron into the amount of oxygen

in milligram per liter

mgl and where the volume of the titran

is the volume of the thos sufate

solution used to reach the end point and

the normality of titran is the normality

of the Tho sulfate

solution the application of Winkler

method is used to measure dissolved

oxygen in freshwater systems it is used

as an indicator of the health of a water

body where higher dissolved oxygen

concentrations are correlated with high

productivity and little

pollution dissolved oxygen analysis can

be used to determine the health or

cleanliness of a lake or stream the

amount and type of biomass a freshwater

system can support the amount of

decomposition occurring in the lake or

stream next the dynamic method or

dynamic Vapor sorption DVS is a dynamic

method for measuring water

activity it measures the vapor pressure

of a sample

directly water activity is calculated

from the ratio of the sample's vapor

pressure to that of pure water DVS is

fast reliable and overcomes drawbacks of

traditional methods factors like

pre-drying SL weding techniques and time

for moisture uniformity can impact

accuracy

this is the dynamic Vaper sorption

analyzer it measures the rate and amount

of solvent absorbed by a sample it uses

a gravimetric technique varying Vapor

concentration around the sample it uses

to measure water activity in materials

and can work with various solvents the

analyzer ensures gravimetric equilibrium

at each humidity level the equilibrium

Mass values generate the isotherm once

the sample is inserted the DVS device

operates

automatically application of the

method

Pharmaceuticals foods and

feeds fertilizer and

agrochemicals Fine Chemicals detergent

and

cosmetics building

materials

Electronics let's proceed to the last

method the spring sorption balance

method the food sample is suspended from

a calibrated coil spring whose extension

or contraction is followed by a cthomer

or recorded electronically

here's the

illustration these methods involve

samples of known initial moisture

content which go through the process of

moisture gain or loss in a constant

relative humidity atmosphere there is an

approach that is to place the food

sample of known constant moisture

content in a sealed enclosure with a

head

space there is a method that is a

quicker less precise method to

determines relative humidity levels

where samples neither gain nor lose

weight by using samples with various

moisture contents the food's sorption

isotherm can be

plotted

the details of the water activity

measurements are found in reviews by gal

1967 and too

1973 the methods of partial pressure

measurement using a simple manometric

technique is given by Taylor

1961 Carol

1955 is given by using a high gromic

technique

water activity is important because

measuring it is crucial as it directly

impacts food safety and quality it

influences microbial growth shelf life

and chemical reactions within food by

controlling water activity we can

predict and prevent food spoilage uring

the safety and longevity of food

products

make sure hit that subscribe button

smash that like button and make sure to

leave some

comment thanks for watching