Let's Learn Food Science - Water Activity

Summary

Highlights

• Water activity is a critical factor in food safety, impacting spoilage and microbial growth. 🦠
• Amy emphasizes the difference between moisture content and water activity. Moisture isn't always "available" water. 💧
• Water activity measurement involves understanding vapor pressure and humidity. 📏
• Learn about calibration and why investing in a good water activity meter is crucial. 🛠️
• Water activity affects food quality attributes like crispness and browning, crucial for product development. 🥖

Key Takeaways

• Water activity is key to understanding food safety and preservation. 🌊
• Water activity isn't the same as moisture content. It's all about available water. 💧
• Learn to measure and modify water activity for better food quality and safety. 📏
• Water activity influences bacterial growth and spoilage in food products. 🦠
• Proper water activity is crucial for controlling microbial growth in foods. 🍏

Overview

Chapters

• 00:00 - 01:00: Introduction to Water Activity The chapter introduces the concept of water activity, its significance in food processing, and food quality. The presenter mentions a specific model of a water activity meter used in their lab and teaching, clarifying that there is no preference for one brand over another.
• 01:00 - 03:00: Water Activity Principles and Measurement The chapter introduces the concept of water activity as a straightforward but powerful technique, particularly in the context of food safety. It emphasizes the importance of water activity in determining the safety of food products. Additionally, while the video does not provide a hands-on demonstration, it encourages viewers to refer to machine manuals to gain a practical understanding of measuring water activity.
• 03:00 - 05:00: Implications of Water Activity in Food This chapter covers the basics of water activity in food products, including how to calculate water activity and understand the mathematical principles behind it. Different methods to modify water activity in food products are discussed, along with an introduction to the concept of moisture sorption isotherms. The chapter also emphasizes the importance of setting appropriate water activity targets for microbial control, discussing the logistical considerations involved.
• 05:00 - 07:00: Factors Affecting Water Activity The chapter, 'Factors Affecting Water Activity,' focuses on measuring water activity using standard equipment. It highlights the importance of understanding the specific machine available and reading its manual. The chapter concludes with a discussion on the mechanics of these machines, particularly the dew point calculations involved in water activity meters.
• 07:00 - 10:00: Water Activity and Microbial Growth This chapter discusses the concept of water activity and its importance in microbial growth. It explains that water activity refers to the availability of water to participate in chemical and biological reactions. This is significant in the context of food products, as water activity targets are often established as part of quality control or food safety management. These targets are crucial to prevent spoilage or bacterial growth. The chapter emphasizes the relationship between water activity and the degree to which water is bound in food, impacting how it can interact in reactions.
• 10:00 - 12:00: Water Activity Measurement Devices This chapter discusses the concept of water activity in foods. It explains how water can be bound in the cells of fruits, vegetables, and meats, being physically contained within cell walls and membranes. The text also introduces the concept of macromolecular bindings, which can involve substances such as gels, gelatin, pectin, or glucomannan that affect how water is retained within the food matrix.
• 12:00 - 17:00: Dew Point Detection System Explanation This chapter explains the concept of a dew point detection system, which focuses on understanding how networks can bind up water through colligative properties. It emphasizes the difference between molecular-level binding and solute interaction, influencing water's availability for chemical and biological reactions. These factors are crucial for the effective functioning of a dew point detection system.

Let's Learn Food Science - Water Activity Transcription

• 00:00 - 00:30 [Music] hello everyone today we're going to talk about water activity and its implications for food processing and food quality this just happens to be the model of water activity meter that I use in my lab and in my teaching on any given day and it I don't want to show preference to one meter or another but
• 00:30 - 01:00 the nice thing about water activity it's a pretty straightforward technique with a lot of very powerful implications in food safety so after watching this video you will be able to determine the water activity of a food product now again I can't physically hold your hand and walk you through how to use a machine but I can strongly encourage you to read up the manuals and you'll have the scientific understanding of how water
• 01:00 - 01:30 activity functions you'll also see that it is pretty straightforward to do you'll understand the mathematical principles behind water activity calculation you'll be able to identify appropriate methods to modify water activity in a product and think about the colligative properties and how it interacts with net moisture for what we call a moisture sorption isotherm you'll be able to identify appropriate targets for water activity for microbial control again we'll talk about the logistics of
• 01:30 - 02:00 performing water activity measurements using standard equipment again the fun of teaching using online videos is that I'll walk you through the process but in the end you're going to have to identify what is the machine available to you and read the manuals specific to that machine but it's not too complicated with this and then last but not least we'll talk about the mechanics and those machines what's called dew point calculations that are done in those water activity meters so what is water
• 02:00 - 02:30 activity well it's the availability of water to interact and participate in chemical and biological reactions in many cases food products have water activity targets as par the quality control or food safety management that's necessary to ensure that those products don't spoil or don't promote the outgrowth of bacteria and water activity is really linked to how much the water is bound up in a food and
• 02:30 - 03:00 so in some foods water is bound in cells think of fruits and vegetables think of meat and it's physically partitioned within the cell membranes or the cell walls but it's only partly bound in other cases you could have macro molecular bindings so just the use of gels gelatin or pectin or glucomannan some of these large macro molecules are
• 03:00 - 03:30 able of creating networks that can bind up water but again it's not quite the same as where you have molecular level binding this is where you have the colligative properties of the solutes that are binding up that water and its availability to participate in chemical or biological reactions and so these are all considerations that we take into
• 03:30 - 04:00 effect when thinking about water activity colligative properties I have another video where I'll be talking about how we modify colligative properties but usually how we see this in food products is where we're changing the salt or sugar concentration in a food because salts and sugars are really good at binding up water into unavailable forms and that changes the water activity in very quick fashion
• 04:00 - 04:30 so here's some math for you water activity is expressed as a with a subscript W water activity and it is the vapor pressure of water from the sample that you're analyzing divided by the vapor pressure of pure water and it is expressed as you can tell by the math here it is expressed in a unitless dimension so it doesn't have grams or centimeters
• 04:30 - 05:00 cubed or watts per whatever it is it is a unitless expression and it is always going to be expressed as one or a decimal and so you will see water activities getting like 0.99 or sometimes you will see products that have a water activity of 1.0 but you will never see a product that has of
• 05:00 - 05:30 water activity of two because you can never have a vapor pressure of water in a food product that's going to be greater than the vapor pressure of water so it's going to become vapor pressure of water divided by V professor of water which equals one now that said most food products are going to be in some bracketed ranges and we'll see a table in a couple slides here now when I say
• 05:30 - 06:00 water activity I'm not saying moisture content and then I have a different video that talks about moisture content moisture content is where we're looking at the gravimetric content of evaporated substances within that food product water activity you could have a lot of water in a food product but it could all be bound up in colligative property based binding such that that water isn't available for reactions what we have
• 06:00 - 06:30 very commonly so again water activity is expressed in unit lists values up to one point zero as our maximum bacteria for the most part to grow in the range of 0.8 eight or so to one point zero bacteria typically are going to be growing in biological systems so our if you were to take the water activity of
• 06:30 - 07:00 me cut cut my arm open or cut my hand open my water activity is pretty close to one bacteria thrive in that space now there are some nice that are capable of growing at slightly water activity and some fungi or molds that are capable of growing at even lower water activities we get to that threshold of 0.6 and very few things are capable of growing from a microbial spoilage perspective but that said
• 07:00 - 07:30 pulling water activity lower doesn't necessarily increase quality you pull it to below and you start to lose other quality attributes such as you you start a water to a certain extent contributes to crispness or kicking or the collapse of food products in some cases where you need that water bound in the food product to provide structure browning reaction so caramelization and Maillard
• 07:30 - 08:00 reaction are very much linked to water activity and available water so that you have this peak of browning reactions at 0.6 but they reduce at lower water activities and they reduce at higher water activities and lipid oxidation again there's a sweet spot in this 0.3 to 0.5 range where lipid oxidation reduces to its lowest point but pull it lower and lipid oxidation increases or
• 08:00 - 08:30 pull it higher in lipid oxidation increases down here it's going to be because water actually has a coating effect on some of the lipids systems within foods and now you are losing that protective effect and just direct exposure to oxygen whereas up here you are having additional enzyme activity and oxidation could be occurring from lipolysis in the food product under enzymatic conditions so typical water
• 08:30 - 09:00 activities that we see in foods fresh meats and fish we're pushing really really high close to that theoretical water activity of water itself most bread when it's fresh has a high water activity and think about the shelf life of many of these products again we're pushing lower and lower in the less likelihood of these products to be boiling on their own we hit this point 82.6 and we are this is where we're seeing really only very what are called
• 09:00 - 09:30 zero philic or Osmo philic yeasts and molds being able to grow because again these organisms have to be adapted to be able to free up some of the water that is otherwise linked at a molecular level to the solutes the sugars or salts or other solutes within the system now here's a table of microorganisms most most bacteria that are pathogenic again
• 09:30 - 10:00 are growing in very high water activity environments because again they're there they're going to be pathogenic in biological systems and most living breathing mammals which are where the pathogens that we see most these are going to be in those biological ranges most other bacteria are able to grow in that range where we're once we're
• 10:00 - 10:30 hitting the 0.88 we're starting to hit the limit at which bacteria are able to grow but again there's always exceptions to the rule and so you can't just go out there and say well Amy showed me a PowerPoint and said point eight eight was the cutoff no there are other considerations think about pH think about total moisture content think about oxygen lots of different reasons and so again you want to go back to some validated information either from a
• 10:30 - 11:00 processing authority a government resource or some sort of blue-ribbon study from an industry group that says here is an appropriate water activity that's going to prevent microbial growth or pathogen growth in the product that you're working on what do water activity meters look like well they come in a wide variety of different shapes and sizes but typically from an industry standard we're seeing a very small approximately 3 centimeters
• 11:00 - 11:30 in diameter plastic dish and usually with a small lid that goes on it these are then placed into the reader device or the reader device is placed on top in the case of this with what they call a pocket which is a pocket water activity meter these are very common for quality inspectors who need a device that can be easily portable and taken out onto the manufacturing floor but you'll notice on
• 11:30 - 12:00 this pocket here for example it only has two decimal places where some of these other larger meters are going up to three or in this case the Aqualab up to four decimal places of accuracy that said if we go back to this table in general within regulatory limits we are seeing them expressed at two decimal points and so take that into consideration when you are purchasing a device because something that like this
• 12:00 - 12:30 with less accuracy it's going to cost a little bit less but it may not give you the level of accuracy in control that you need so you may require more decimal points for really strict process control it is the sort of thing where you do likely need to buy something in some of my other videos you may have seen me discuss opportunities for using a bootstrapping approach and what can you do with minimal technology to be able to
• 12:30 - 13:00 approximate the sorts of analytical results in this case it is worth the money because of the importance that it is played yes there are old-school methods where you can take different concentrations of salt and weigh the amount of humidity or hygroscopic of a sample when put into an environment with a saturated salt solution but it's
• 13:00 - 13:30 really not practical for most food manufacturers be doing that this is the sort of thing where you are they're going to buy a meter or you are going to find a lab that has a meter and you can send out samples for advice on a contract basis so how do you do it oh you're gonna take that little sample cup and fill it about half full you don't want it to have it overfilled because that sensor on the toe on the top and the case on in the pocket on the bottom of the device you
• 13:30 - 14:00 do not want the food sample to be in touch in contact with that sensor it can mess up the ability of that sensor to read accurately and so avoid over filling the sample cup so that you don't mock up your machine be patient some of the missing meters will take some time to equilibrate we'll talk about the mechanics of equilibration in a moment and there are calibration discs available for calibrating each of these
• 14:00 - 14:30 different units those calibration discs as I mentioned are filled with a saturated salt solution of different different salts and those different salts when in a saturated solution we'll have very precise water activity cut-offs and so there are ways of calibrating these devices again go back to the user manual of the device that you've ended up selecting for your analysis and most manufacturers anymore are posting their user manuals online so
• 14:30 - 15:00 do not be afraid of googling it looking it up on your search engine of choice and finding those manuals to identify how do you calibrate and how do you use it better how do these meters work well most of them are using what's called a dew point detection system and so if I can summarize it using my fun little diagram here imagine inside that device there's a mirror well there is a mirror and that mirror is slowly but surely on
• 15:00 - 15:30 this thermostat changing temperature and that mirror just like when you're taking a shower in your washroom and the mirror fogs up what we're hitting is the dew point the level of relative humidity is going to eventually condense on that mirror depending on the relative humidity in the in the closed atmosphere around this food sample and the temperature of the mirror so that mirror is on a thermostat and the temperature slowly slowly slowly changes meanwhile
• 15:30 - 16:00 there's a little light sensor and so it is pinging off a beam of light onto the mirror and the mirror is then reflecting it back on to a sensor and the sensor says okay the mirror is still clear the temperature of this sample is compared to the room temperature hasn't hit the dew point but bit by bit by bit is measuring the the temperature of the atmosphere around and it's measuring the temperature of the mirror bit by bit the
• 16:00 - 16:30 temperature is going to ramp down to the point that mirror gets condensation yeah I don't know how to draw condensation so I just I made it looked like it was marred up and the light that's coming from the emitter gets scattered and the light sensor down here then says aha thermostat that was the temperature at which the dew point was hit and it will stop the device and you now know the water it will go through its own algorithm to identify what the water
• 16:30 - 17:00 activity was based off of the relative humidity off of this sample now it is going through using a psychrometric table to be able to do that calculation and we will do a different presentation at a different time to talk about psychometrics and at the relative humidity but in general going back to those water activity measures it will give you out that number and that's all
• 17:00 - 17:30 you need to do you do not need to do any further analysis you take that number and that will be recorded in your control document or it will be part of your product specification if you're doing product development short and simple take care and we'll talk to you soon