Science Buddies: "Ask an Expert"

My daughter is doing the Experiment
https://www.sciencebuddies.org/science- ... ntolerance

She is trying to do Experimental Procedures step #9-#16 and is testing 2% Cow's Milk, 2% Organic Cow's milk, 2% Lactaid Milk, Goat Milk, and Soy Milk. During this step of the experiment she should be getting a glucose reading when testing at step #11. I did see someone else's question on this so I am answering the questions from that as well. Can you please help us figure out why we cannot get a glucose reading and some ideas of how we can change these steps so we can get a reading?

The supplies for this experiment were purchased at Home Science Tools and I confirmed by looking at their website that we were in fact using the correct materials.

Below are some questions asked to another family with the same problem, but they never responded back. I have answered with our experience under each question.

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Here are some questions that may help identify the problem. Please answer these if you can; some questions may require using materials you don't have readily available, but answer as many as you can.

1. Were you using glucose strips for urinalysis or for blood?
We are using glucose strips for urinalysis
2. Do the test strips work if you add the milk to the glucose tablets? (check for interference)
We tested 100mL of 2% Cow's milk and dissolved 2g glucose powder and tested it. At 30 seconds, it read .5% glucose
3. Do the test strips work with commercially available lactose-free milk (which should contain lactose that has been hydrolyzed to glucose and galactose).
Yes, with Lactaid milk the glucose test strips show 2% glucose
4. How long did you incubate the lactose pills or drops with the milk sample? What was the temperature?
Per the procedure #10 we warmed the milk for 2 minutes by hand. The temperature was not a very significant change. We tested a new sample by warming the milk (with added lactase) to 100 degrees and testing it with the glucose strip. We still got a negative 0% reading.

Hi Zundel - I talked with one of our scientists about what your daughter is observing with her project. Other Experts may have additional feedback for you, but we are concerned that there may be an issue with the lactase drops you are using. I have some troubleshooting steps for you that may help sort out where the problem is occurring.

As a benchmark, she should be seeing glucose develop in the 2% milk. To troubleshoot, we suggest:

1) Let's first make sure it isn't the batch of glucose strips. This is unlikely, but it's easy to test. Dissolve 4 grams (measured on a kitchen scale) of glucose (from kit) in 200 mL of water (water can be measured with the graduated cylinder in the kit). That is a 1% solution of glucose. Dip the glucose test strip in the 1% solution of glucose for 1-2 seconds. Remove and wait 30 seconds, then match to the bottle. It should look close in color to the 1% color.
2) If that (#1) works as expected, we can assume the lactase is the issue. Lactase is an enzyme and will degrade over time or if left at high temperatures for too long. Unfortunately, there isn't a test that can be done (other than using the lactase on 2% milk and seeing that glucose is created) to test the effectiveness of the enzyme.

A couple of questions and suggestions:
- What brand lactase are you using? In our testing, we know that some brands have higher enzymatic activity than others, but a batch of any brand could go bad if it was transported/stored improperly.
- Is the lactase still within the expiration date? (Should be marked on the bottle.)

Buying another batch of Lacteese drops might be necessary. We would even suggest you buy from a different source/store so you get a different lot for sure.

Amy
Science Buddies