Journal Article Reflection Questions
Journal Article: Horner, T.W., Dunn, M.L., Eggett, D.L., and L.V. Ogden. 2011. -Galactosidase activity of
commercial lactase samples in raw and pasteurized milk at refrigerated temperatures. J. Dairy Sci. 94:3242-3249.
The purpose of this discussion is to understand the goal and methods used to answer the research
question. Focus on the setup of the experiment, including the different variables the authors mention, and
on the data collected. Does the data support their conclusion?
Introduction
1. What do these terms mean? If the term refers to a technique, what is its purpose?
a. Lactose intolerance – inability to digest lactose
b. Lactose hydrolysis – it hydrolyzes lactose into 1 D-glucose and 1 D-galactose
c. Lactase – an enzyme that catalyzes the hydrolysis of lactose
d. HPLC – high performance liquid chromatography, used to separate, and analyze different
components in a mixture
e. Chromatography – a technique used to separate mixtures by passing it through a medium
where different components move at different rates.
2. What research question are the authors trying to answer?
How effective is commercially available lactases in refrigerated milk
3. What is the authors’ hypothesis?
Enzymes with greater activity at cold/refrigerated temperatures would be more beneficial than
commercially available lactases.
4. What is their rationale for conducting the present study?
To make lactose-free milk more accessible for lower income families.
5. Why is lactose intolerance more common for certain ethnic groups?
Because they do not have the gene that codes for dissolution of lactose.
Methods
6. What method did the authors use to determine the activity of the commercially bought enzymes?
They used a modified version of the B-galactosidase assay of Miller to analyze the commercial
enzymes.
7. What method did they use to measure enzymatic activity in their experiments?
HPLC, Percival I-36NL, color analyzed by a spectrophotometer, dumas method and miller’s assay.
8. What was the purpose of using three different kinds of milk?
To analyze the rate of hydrolysis by the enzyme in the different types of milks
9. What variables were constant throughout data collection?
The temperature, time, transfers of 30mL then heated,
a) How do these variables affect enzyme function?
They can cause overactivation or inactivation of the enzyme, affecting the effectiveness of it in
each milk sample.
Results
10. Figure 1 – What is the difference between the results shown in panels A and B?
One shows the assay results, and the other show the protein content.
11. Analyze Table 1. What is the lowest concentration and time for each of the 4 tested enzymes to
achieve at least 90% hydrolysis?
1x -DYL at 24 hrs, and 1x- VYL at 24 hrs
12. Figure 2 – Why would the authors show data for the LYL enzyme and not for the other three
enzymes? The author simply chose one enzyme because all of the enzyme behaved similarly since
fat content did not effect the hydrolysis rate.
