Webinar: Analysis of Food Products by Dynamic Vapour Sorption

Everyone, thank you for joining us for today's Surface Measurement Systems Online webinar. Today we'll be exploring the topic of analysis of food products by dynamic vapor sorption. Today's session will be a live presentation with our very own Meishan Gao, followed by a live Q and A with Mei Shan as well. Meijan started working as an application engineer and is now an application scientist at Surface Measurement Systems, and Since joining in 2018, she has been working on surface characterization of solid materials, including fiber, powder and film samples, using dynamic vapor absorption and inverse gas chromatography as her primary techniques. Mei Xian obtained her master's degree in Chemical Engineering at Imperial College London in December 2017. Her research project was focused on investigating the properties of fragrance molecules with solid substrates by diffusion and sorption. She also received her Bachelor's degree in Chemical Technology at the Hong Kong Polytechnic University and in Chemistry at Sun Yat sen University in June 2016. So, without further ado, I would like to pass over to Ms. Shen, but just before I do, I'd like to remind everyone of a few of the house rules for the session and how you can take part in the live Q and A. We ask everyone to keep their mic muted throughout the course of the live presentation just to avoid any audio interruptions or background feedback noise that might ruin the audio quality for any of the other people listening. And we will, as mentioned, have a live Q and A at the end of today's session. This can be engaged in in two ways. If you would like to submit your question in writing, you can do so in the Questions tab on the webinar Control panel, and then I will ask Mei Shan your question at the live Q and A section. Or alternatively, if you would like to unmute your microphone and ask the question yourself. If it's maybe a bit of a longer question or you need to provide any elaboration on it, you can raise your hand in the dashboard and then I will let you know when you can unmute your microphone and you can ask the question yourself through your microphone. So once again, you could submit your questions in writing for me to ask, or you can raise your hand and I will let you know when you can ask the question yourself. So without further ado, I will now hand over to Meshan to begin today's presentation.

Thank you, John. Let me share my screen so I hope all of you can see it now.

Yes, we can, Michelle.

Okay, that's great. So first, hello everyone. I'm Maishan, and welcome to Today's Webinar in this presentation I will just focusing on the food products and let's talk about how the DVS technique can be applied in the food sample analysis. So here are some topics we will cover today. We will first have an introduction about the moisture sorption process. Then we will talk about the DBS technique and we can go through some applications related to the shelf life or the stability stories of the food sample including for example the isotherm determination, the vapor induced phase change, the permeability measurement of some packaging material, as well as we can measure the water activity determination with our pain cell assessor as well. So water is everywhere in the real world and the relative humidity can vary in different areas. So the interaction of the moisture with the solid material will have a great impact over a wide range of industries including the pharmaceuticals, food, proteins, packaging material, also personal care products and especially in the food industries. Moisture will cause lots of different problems like the powder caking that will affect the powder flowability in the final application or the instability of the product both physically or chemically and the moisture induced phase change for example like dissolution or the deliquising of the sugar sample at higher humidity environment. So it's very important to study this kind of moisture absorption behavior for the prediction of the stability for the food products. And one of the popular properties we will mirror especially in the food industry is the water activity which measures how tightly the water molecule is bond to the solid material at certain temperature. So we can get this kind of information from the water sorption isotherms and also calculate some other property like the monolayer content, the heat absorption diffusion constant or the permeability of the packaging materials. So there are some commercially water activity meters in the market which are simple and quick analysis, but it only mirrors the free water in the material, not the total moisture content. And a relatively large sample amount is also needed for the analysis with certain meters like several grams of the sample. And of course the experimental condition is not under control so we cannot study the factors that will affect the water activity. So these are not suitable to measure the moisture transmission rate for the packaging material as well. Therefore, we are looking some other method for the material characterization of this kind of moisture solption for the food materials. So for the characterization of the solid material generally we will have used energy as a probe like the spectroscopy method where we can get the analytical and structural information of the solid material, or we can use heat as a probe like the TGA method to get some thermodynamic information of this solid. And in Case of the dynamic wave resorption technique. It's a sorption technique that we are using molecules as a probe. And based on the interaction of the probe molecule and the solid material, we can get all the property of the solid related to the structure chemistry as well as thermodynamics. So when we talk about a molecule interact with solid, it will be either absorbed on the surface of the material or absorbed into the bulk of the material. So by studying the kinetics of the absorption and desorption, we can then easily predict some behavior of of this solid sample in the bottom here, at certain conditions, at a certain temperature and relative humidity. And then we can calculate the property of this sample, for example, the V2 surface area, the stability of the material or the shelf life of this material at certain condition. So when we talk about molecules absorbed on the surface, it can be either by physics option or chemist option. So physics option is a kind of weak interaction that the probe molecules are not chemically bonded on the surface. And it's more like a reversible process. And the property we can measure with the physics option here is more like some property on the surface, for example, the surface area, the surface energy process distribution or heat absorption. And another kind of stronger interaction is the CAM absorption that the probe molecule will form some covalent bond on the surface. And this kind of interaction is more for some special material, like you want to have a particular interaction with some probe molecule. And the property we can measure, for example the active surface area or the catalyst dispersion. And in case of the absorption, it will be either by bulk absorption that the pro molecule will penetrate the surface and then go to the bulk of the material. So in this case the desorption is usually a diffusion limited precise. And the kinetics of this box option will be much slower compared to the physicption. So the property can be measured here. For example, the vapor induced phase change that we can get the glass transition temperature and humidity from the sample or some other property like the total suction capacity, the solubility parameter or even the diffusion coefficient and the permeability for the thin film samples. The last kind of interaction is the absorption into the lactate structure, which means the material will change the structure in the presence of any kind of vapor, like water vapor or organic solvent. And this will lead to the formation of hydrate or solvate. So from the DBS data we can study the structure of this hydrate as well as the kinetic information about this hydrate formation or dehydration. So we can get all those kind of interaction from different pro molecule and solid interaction. And from the DBS experiment we can calculate those kind of properties. And in case of the food industry, we usually use water as the molecule to measure different interaction between the water molecule and food material by the soption desorption isothermic from the DBS data. So DBS is for the dynamic wave assumption, which is basically a braving metric method that we can measure the change of mass for the sample at different concentrations of moisture or organic vapor. So we will based on ultra balance based resolution of 0.1 microgram. And we just need to use very small amount of sample because this system has very good sensitivity, typically just around 10-20mg of the sample if the uptake of the sample is good. And as a dynamic system we have a continuous flow of the pro molecule to the sample so we can achieve a much faster equilibrium compared to the static method. And all the experiment can be performed at ambient temperature and pressure. So it will be more close to the properties we will apply in the real world that simulates the real world conditions. So here is the schematic of one of our system, the DBS resolution. This system can measure the soption of water and organic vapor as well as the competitive sorption of two different components. So in the middle of the system here we have the micro balance. It's connected to both the sample pan and the reference pan. We will then put the sample in the sample pan and keep the reference pan empty. And as you can see, there are two bottles at the back of the system. So one bottle is for water, the other bottle for the organic vapors. The carrier gas for the system could be nitrogen or dry air. And there were different mass flow controllers to control the flow of the carrier gas and the saturated vapor in ratio to reach a certain level of relative humidity or partial pressure. And this mixture will be detected by the sensor here. So the rotronic probe for the water and our speed of sound sensor for the organic vapors. And we will make sure the actual generation of the vapor is matching with the target concentration. And this mixture will flow to both the sample chamber and the reference chamber at a constant rate. And the sample inside the chamber here will pick up the moisture and the mass change will be recorded by the balance. So the whole stand like this one will be set in an incubator with the temperature range from 5 to 85 degree. That means we can perform the experiment exactly from 5 to 85 degrees. But in some cases we might need to precondition the sample at higher temperature. And in that case we can install a preheater under the sample chamber at this location. And this will allow you to precondition sample before the experiment in situ up to 200 degrees. We can also combine the DVN system with some other accessory, for example, some camera also at this location, to take the sample images at different humidity along with DBS data. So for example, here with some sucrose sample at dry condition, the data image shows a powder form and then it goes through the glass transition crystallization at a higher point and also the deliquiscence that go to the liquid form at high humidity. So this setup just with the video camera and the DBS give us a good idea about how the sample will change the structure or change in the nature or change into different color along with the DBS data. And another option with the accessory is we can integrate the Raman spectroscopy with our DBS system that we can take the Raman spectra at the end of each humidity step. And in that case we can get both the Raman spectra and and the DBS data at the same time. So, for example, here the example is a amorphous lactose sample. We did the water suction experiment at 25 degree. So here the blue line indicates the partial pressure of each step. We increase from 0 to 95% RH with 10% steps. And the right line is the change of mass for the sample. So at each stage the sample is picking up the moisture, it's reaching a perfect equilibrium and then jump to the next stage automatically. But as you can see, at 60% RH here, there is a significant decrease in the mass for the sample. And this is due to the amorphous to the crystalline phase change, because the crystalline state material has smaller surface area as well as less suction capacity. And this kind of amorphous to the crystalline phase change is an irreversible phase change, as you cannot see the same effect in the second cycle here. So that's something we can get from our DBS data. And we took those Raman spectra at the end of each stage menstruation equilibrium. And here the Raman Spectra at 0 and 40% RH is a very broad peak showing the amorphous state. And exactly above 60% RH there are some new peaks showing up here that indicates of the crystalline state. So this Raman spectra just confirming with our observation in the DBS data that the sample goes through the amorphous to the crystalline phase change and 60% RH. So the whole setup here raised the deviance as well as the Raman and the video camera. Just give us a full idea about these material changes at different humidity. And then we will go through some kind of application with the DBS technique. So we basically have two very typical method for the DBS measurement. The first one is the step method just we introduced in the previous slide that we increase the humidity step by step. So here's an example with the rice starch sample showing the kinetics information about this moisture absorption. So the same here. The blue line is the target partial pressure or relative humidity at each stage. And the red line is the change of mass for the right starch sample. So at each stage the sample reaching equilibrium and then jump to the next stage automatically. And it's a two cycle experiment with both sorption and desorption. And this time as you can see, the second cycle can go up to the same level as the first cycle and go back at the 0% RH and 0% change and mass change. That means this moisture sorption for the red starch sample is a perfectly reversible process. There is no molecular like water molecule trapped inside the material. At the end of desorption steps and we can take the mass equilibrium mass content of the material at each humidity and then we can plot this mass change equilibrium mass change against this target red humidity. Then we will get this water isotherm for the red starch moisture sorption desorption. So the red line is for the absorption branch and the blue line is for the desorption branch. Some kind of information we can get from this water isotherm. For example, at 90% rhythm this sample can pick up about 20% change in the mass. That means this sample has very good affinity with water. So the water capacity for the sample is about 20% and there is a gap between sorption desorption. This is called the hysteresis gap. And this is because it has very high uptake of the water molecule and those water molecules and not just on the surface, it will penetrate the surface and go to the bulk of the material. So during the desorption part, when the water molecule disruption from the bulk is a diffusion limited precise. So this hysteresis gap, just confirming with this moisture sorption mechanism is a box absorption dominating mechanism. So this is a typical, the shape of this isotherm is a quite typical type 2 isotherm widely found for the food material which shows a monolayer region to begin with and then a multiple layer region. For lightly bond water and then free water region at higher humidity conditions. The free water is used for the growth of bacteria, yeast or mold that will destabilize the material. So we can use this water isotherm to optimize the shelf life or the stability of the food products. So based on the classification, There are different six types of isotherm. So type 1 isotherm is typical for some macroparrous material. Type 2 and type 4 isotherm are typical for the food samples. Where the water molecule will interact with the surface forming the monolayer first. And then it will further interact with the first layer to form some multiple layers. And from the type 2 and type 4 isotherm we can calculate the bet surface area of the material. The type 3 and type 5 isotherm is more like some condensation of the probe molecule on the surface that the prop prop interaction is too strong, that will form some cluster on the surface. And rather than cover the whole surface with the monolayer. So we can use the isotherm to predict or to optimize the shelf life conditions. And one of the equations we can use is the Young and Nelson equation, which gives the constant about how much monolayer and multiple layer from the full isotherm. And the other constant is gives the idea about the degree of the interaction between the pro molecule and the solid surface. So these are some very useful parameters for the shelf life and stability of the food materials. And the other method we widely use is the ramping method, which is a quicker and much easier way to measure the stability of the solid material. So it's very similar to the DSC temperature ramp. In case of the DBS technique, we will ramp the humidity from 0 to 90% RH at a constant rate. So the blue line here and here's the result for the lactose sample again. And the red line is the change of mass for the sample. So the sample is losing mass because of the drying stage, just the flow of the carrier gas. And at very beginning of the humidity the increase is quite slow. It's due to the surface option of the material. And then after a certain point of humidity, the increase of the mass will become dramatically increased. That's because of water molecule not only on the surface this time, but also penetrate the surface and go to the bulk of the material. So before and after, well, the change in the middle here is called for the glass transition of the material. And with the slope before and after this change, we can then calculate the glass transition humidity for the sample at certain temperature. And as we keep increasing the humidity, this sample also goes through the crystallization that the mass will drop dramatically due to the crystalline state has smaller surface area as well as less option capacity. So with this single experiment at 25 degree, we can get first point for the blast transition of the material and then the second point for the crystallization of the material. And this is the experiment we perform at 5% per hour ramping rate. And if we change the ramping rate, we can then get a correlation between the ramping rate and the glass transition humidity. And from the intercept of this line we will then get a critical glass transition humidity at 0% ramping rate. And this is important for the storage of the lactose sample. So above this humidity the sample will go through the crystallization, sorry, the blast transition and the previous experiment just at certain temperature 25°. And if we do a series of the ramping experiment at different temperature, then we can get the stability mapping of the meta stable material. So at each temperature we can get two points, one for the glass transition, the other for the crystallization. So with the increasing of the temperature we can get a blue line for the crystallized glass transition and then the red line for the crystallization. So from this stability mapping we can easily predict at a certain condition of the material, at a certain combination of the temperature and the humidity, the sample is at a stable amorphous state, or the crystalline state, or just unstable state to change the structure at any time. So this stability mapping is very important or very useful to predict the stability of the material at different conditions. Another ramping experiment we performed with the coffee granule which we expose the sample with the humidity ramping first from 0 to 90% RH and then decreased to 40% RH. And we also took some photo image during the soption and desorption steps. So during the soption process you can see up to 60% RH. There is no much difference uptake for the moisture sorption. But after that there is a sharp increase at 90% RH. The in situ image also shows the sample already changed the color for the sample at 90% RH compared to 60% RH. And during the desorption step it keeps increasing mass uptake and then reach maximum at 75% RH. So the delinquency point is somewhere between 90% RH and 75% RH. And this is a stability mapping for the coffee granule. And we can perform similar experiment for other sample as well to study the stability at different humidity at certain temperature and another Example is the protein sugar interaction to stabilize the sugar sample. Where we have the right line is 100% sugar sample and the black line is 100% protein sample. And the other lines for the mixture between different ratios of the protein and the sucrose sample. So where we notice is around 25% RH. All the sucrose containing sample goes through the glass transition. And this meets quite well with the literature report value for the glass transition of sucrose. And then at about 50% RH for the sucrose 100% sucrose sample it will crystallize at about 50% RH. But with increasing of the protein concentration this crystallization point is shifting to the higher humidity range. That means this protein is behaving as the stabilizer that stabilize the protein sugar mixtures. So this is probably due to the protein sugar interaction may delay the sugar nucleation that will result in the inhibited crystallization. And all the sucrose can TV sample also go to the deliquis point above maybe 85% rhythm. So here just shows a very simple XRD based the DBS technique to measure this kind of phase change about circle sample. Another parameter we can use for the prediction of shelf life is the heat absorption. So to calculate the heat absorption we need to do the experiment at at least two different temperatures. So. So here we use the fresh and aged meat sample at 25 degree and 35 degrees. The aged meat sample is the same sample after one week time in the fridge. And the fresh sample shows very similar like almost overlapping of two different temperatures. For the aged meat sample it shows a quite large difference in the uptake at 35 degrees compared to 25 degrees. So from the isotherm we can calculate the heat absorption with our macros is summarized in the table here. So the heat absorption is much higher with the fresh meat sample compared to the aged meat sample. And the heat absorption is also increasing with the increasing of the coverages for the fresh meat sample which indicates the interaction between the water and fresh meat sample is also increasing. Well for the HME sample the value is much smaller and it doesn't increase at all. That means it's also close to the evaporation heat of evaporation for the water molecule. So in the fact the PRO molecule in this case is water is interacting with only the other water water molecule resulting some condensation on the surface rather than interact with the meat sample itself. So that's how we use the heat absorption parameter to predict the behavior of fresh meat and aged meat Sample. The last kind of case study is about the diffusion measurement of the packaging material. So the moisture transmission rate is also very important to mirror in the food industry. And we do have a special device called Pincel to measure the diffusion rate and the permeability of some thin film sample. So this Pincel is composed of three part. We have the lid of the cell, the cup of the cell and two rubber O ring to seal the sample in the middle and the yellow atom here is the thin film sample. So with the Pincel we can measure the moisture transmission rate, the water activity as well as the diffusion or the permeability of the thin film sample. So to start the experiment we will first to put some drying agent inside the cup here and then we will seal the cup with the film of interest and we change the outside concentration with our DBS instrument for different concentration. So the vapor molecule will just penetrate the surface from the top to the bottom with one way direction only. So we can measure the one way diffusion coefficient as well as the permeability of the film sample. So according to the Fick's law, we have the thickness of the film sample and we have the mass at equilibrium and we do the fitting for different humidities and and then we can get the diffusion coefficient of the film sample at certain humidity. And from the slope we can also calculate the permeability of the thin film sample. So the case study here we have the diffusion study. Actually it's a co diffusion study for the packaging material. Here we use caption film sample as an example and we married one water as well as the methanol diffusion on this film sample at different temperatures. And this methanol just represents a kind of flavor molecule used in the food industry. So it can be any kind of organic vapors. And we designed this method basically in three different parts. So the first stage is the methyl only stage has 50% methanol flowing to the vapor through the film. And then we have the second stage is the water only stage. So 20% water. And the last stage is the combination of two components. So we introduce 50% methanol in the presence of 20% water as the background. And we want to study the effect of the background humidity on this methanol deficiency. So we perform the experiment. Actually I don't have the data here, but basically we performed the experiment at two different temperatures. So what we get from the result is with the math node only diffusion. For the first stage, the diffusion coefficient we calculated is quite similar to each other. So temperature has very little impact on the methanol diffusion in this case. But temperature has a very huge impact on the water diffusion. Where we calculated for the water only stage. And for the last stage where the presence of water, the diffusion rate of methanol also improved at higher temperature, where we got from the diffusion rate at two different temperatures. So that's how we calculate or mirror the temperature factor as well as the background humidity factor on the diffusion rate for the packaging material. And we can also use this pencil to study the water activity for the material as well by doing a calibration curve with the separated salt sample. And then we can put the sample of interest into the cell and then we measure the moisture or water activity content inside the food material. So for example, here we get the result for the honey sample, the ketchup sample as well as a milk powder. And it has really good agreement with the literature reported values. And similarly, we can also put some flavor molecules, some liquid inside the cup by putting and then seal the cell with the storage bag. Then we can measure the mass loss of this liquid sample to calculate the vapor flux of certain kind of flavor molecules. So I just gave you an idea about how the DBS technique can be applied in the food industries. So we can measure the moisture sorption behavior to determine the shelf life of the material. We can also use a combination of the video and also the Raman spectroscopy to get a complete understanding about these material changes at different humidity. So I hope you will find DBS useful in your future research and I hope it's clear for this presentation. But if you have any questions, just let me know. And thank you very much for listening. Thank you.

Thank you, Mei Shan, that was a great presentation. We have a few questions right off the. So just before we go into those, I just wanted to remind the audience that they can either submit the questions in writing in the questions panel or they can raise their hand to ask the question themselves over the microphone. So the first question we have is someone has asked what is the typical sample size for D measurement.

Okay, thank you for the question. So basically we have two different configurations of the balance. So the low mass balance is more accurate, has smaller resolution. So we can put up to 1 gram of the sample. And we also have a high mass balance to put up to 5 gram of the sample. But as you know, we have a really sensitive balance. So if the sample can represent is very homogeneous sample, can represent a whole part of the sample. We just need to use about 10 to 20 milligram of the sample. If the uptake is up to 1% change in the mass. But if the uptake is quite low, the surface option we might need to increase the sample mass up to 100 milligram to get a good noise to signal ratio. The more the sample you use, the longer the equilibrium time it will take. So we typically just use the optimized amount to get a quicker experiment then.

Thank you. Another question come in here and they ask is it possible with the modular accessories to use the camera and the Raman at the same time?

Okay, thank you for question. Yes, I think maybe in the previous slide I show a stand so the camera will go to the same location as the preheater is in the bottom of the sample chamber and the Raman there will be a simple port on the top of the sample chamber. So we can basically use the Raman gun and as well as the photo image at the same time during the experiment. But the camera and the preheater will share the same location, cannot be used at the same time. Great.

Thank you. Just wait a moment or two for any other questions to come in. I don't think there's any other questions coming by Shan, so we may crack up for that today before we wrap up for the day. Is there anything else you'd like to add for the audience?

Yeah, so basically actually we have lots of different application notes for the food applications. It's in much details compared to this presentation. So if you're interested in any slide or any applications, you are welcome to contact us and we can send you the application note or we can go through some specific specific application based on your product in details. And if you want we can also share this presentation after meeting with you.

Brilliant. Thank you so much and thank you as well to all of our audience for attending today. We have other webinar and educational content coming up. Our next webinar would be exploring moisture content and pharmaceutical ingredients. That's taking place on Thursday 9th September. And of course we have our headline event, the Zorchin Science Symposium 2021 online taking place at the end of September. This is a fantastic event that's going to be offering a full dedicated Zorption science agenda populated by some of the leading experts from around the world and it will explore a range of topics across both ICC and DBS with a range of industrial applications being discussed. So I strongly recommend you go to our website, check out the agenda and get your ticket. Today there will also be some fantastic networking opportunities to reconnect with the global audience and make some new connections, some new research partners and catch up with some old peers and colleagues. So if you'd like more information about our upcoming work, webinars, or the sort of symposium, Please go to www.surfacemeasurementsystems.comwebinars. thank you all again for attending today, and we hope to see you soon. Thank you.