Chemicals in My Food

A period of “detox” is probably good for you. Relax, take some light exercise and eat better and you will probably food better. You might feel better yet if you really believe in the healing power of your regime. An exotic macrobiotic smoothie with particular herbs might make you feel great.

Detoxification is just a metaphor though. If there were “toxins” leaving your body (what these molecules are is never specified) then they could be measured. (They can’t). Even if there was a measurable chemical change in urine, for example, you would still need a double-blind clinical trial to show benefits.

The placebo effect is powerful and we should use it to our advantage. Believing the metaphor is a physical reality becomes problematic though if it leads you to promote detox as a ‘remedy’ for real disease. Belief is powerful, but when making medical recommendations belief it must come second to data.

The major sugar in milk is lactose.  Lactose is less soluble in water than table sugar so if you concentrate milk, the lactose can crystallize out.  This is a problem in products like condensed milk (some of the water has been evaporated off) or in ice cream (some of the water is frozen as ice) where lactose crystallization leads to a gritty or sandy texture in the mouth.  The process of crystallization is often slow and can be hard to predict so it can be a challenge to work out if a new formulation is going to give problems.  If there is no reliable theory you have to experimentally measure the progression of crystallization.

Measuring the kinetics of crystallization in a solution is relatively easy; just filter off the crystals and weigh them.  Measuring the kinetics of crystallization in a more complex solid food it is more challenging. This was the motivation behind some work my graduate student Umut Yucel did as part of his MS, and which was recently published in the Journal of Food Science.  This work was supported by a grant from the Center for Food Manufacturing, an industry consortium at Penn State.

Our idea was that ultrasonic waves would be a useful tool to measure the process of lactose crystallization.  Ultrasound is high frequency sound, beyond the range of human hearing.  We can easily measure how fast the sound moves through a sample or how effectively the sample absorbs the sound energy.  We had to design an experiment to see if the ultrasonic measurements would be sensitive to the formation of lactose crystals in a solid matrix.

 We dissolved lactose and gelatin in hot water then cooled the solutions to allow the gelatin to solidify. Initially the gel was clear, but over the next several hours the lactose began to crystallize and the gel became more and more turbid.  Initially the gel absorbed very little sound energy,but over the next several hours the lactose began to crystallize and the gel became more and more attenuating.  Lactose crystals scatter the sound waves leading to high acoustic losses while lactose in solution absorbs much less sound energy.  Ultrasonic attenuation measurements are an effective way to measure the presence and amount of crystals.

Ultrasonic measurements are particularly useful for sensing application, as the waves pass easily through opaque foods or through glass or plastic packaging.  Ultrasonic waves are also very low-energy so don’t damage or otherwise affect the sample.  You can also use them on intact foods so there is no need to separate the crystals for analysis.  Our work demonstrates the potential for ultrasonic sensors as tools to study sugar crystallization in complex foods.

The main practical challenges in this work were to determine appropriate concentrations of gelatin and lactose so that the gelatin would solidify before the lactose began to crystallize but the lactose would crystallize fast enough that the experiment wasn’t impractical. Our methods tied up the instruments for long periods of time so if the crystallization took weeks then the other students would be left waiting.  We also had to be careful that the amount of lactose crystals formed was not so large that all the sound was absorbed and no measurements could be made.  Once we had those details were sorted out the body of the published work only took perhaps six weeks.

Umut wrote up a version of the work for use in his MS thesis, which we later adapted for the Journal of Food Science paper.  The review process was fast and constructive – we had a statistical error in our first version I’m glad was pointed out.  At the moment this thread of work is on hiatus.  I’d like to bring in a new student to look at real products or perhaps build a quantitative relationship between the amount of crystals and the ultrasonic measurements but all of this will have to wait on a suitable grant.

An ice cube on the other hand melts suddenly and completely; it is either a hard solid or a liquid with no intermediate states.  Ice cream melts but melts in an unexpected way, getting progressively softer as it warms then running down the cone and dripping on the floor. The difference is the ice cream is not pure water but a solution of other molecules, importantly sugar. 

A solution, something dissolved in water, always has a lower freezing point than pure water.  The freezing point of a solution decreases as the solution concentration increases.  For example, water freezes at 0°C, a 10% sugar solution freezes about -2°C and a 50% sugar solution about -7°C.  “Freezes” implies complete solidification but what we mean really is that at these temperatures ice is at equilibrium with a sugar solution of that concentration.  So if you cooled a 50% sugar solution to -7°C and dropped an ice cube into it the ice cube would neither melt nor grow larger.  If you cooled a 50% sugar solution to -2°C and dropped an ice cube in it the ice would melt because ice is not at equilibrium with that sugar concentration at that temperature.

Now imagine if you took the 10% sugar solution and cooled it to -7°C it would partly freeze, forming crystals of pure ice. Only water is being frozen into the ice crystals so the remaining liquid sugar solution becomes more concentrated.  At -7°C, ice is at equilibrium with 50% sugar solution so the ice crystals will only grow until the unfrozen solution reaches that concentration.  If you started with 100 pounds of solution to start you would have 10 pounds of sugar and 90 pounds of water.  At -7°C the solution contains all the sugar (10 pounds) and enough of the water to make a 50% solution, i.e., 10 pounds of liquid water.  The remaining 80 pounds of water is frozen into solid ice.  The frozen product is a dispersion of ice crystals in the unfrozen solution.  As I have explained, a high volume fraction dispersion is solid so the large volume of ice means the product is solid and hard..  Next imagine we warm our product up a little.  As temperature increases, the concentration of the solution in equilibrium with ice decreases.  Some of the ice melts to bring the pure frozen ice into equilibrium with a diluted solution.  As the volume fraction of the ice-in-sugar solution decreases the product gets progressively softer.

Ice cream works in just the same way.  The texture of the product changes progressively with temperature rather than melting suddenly.  The ingredients that make the difference are largely the water-soluble small molecules; mainly sugars.  If you add more sugars or raise the temperature the ice cream will soften.

(Image uploaded by flickr user warrenski under the Creative Commons License)