Technical Summary: Lactose Analysis (Bulletin ref. TB058714)
 

A simple two-step enzymatic assay for lactose in aqueous solutions or extracts.
 

Name:
Code:
Size:

Lactose
GMRD-095
50-100 tests

Instruments:
 

All GM8 Series analyzers
 

Principle:

i) Lactose (milk sugar), a disaccharide, is stoichiometrically hydrolyzed by galactosidase to a-D-glucose and galactose in a simple pre-reaction. Under the special buffer conditions used, mutarotation to ß-D-glucose rapidly occurs:
 

ii) In the presence of molecular oxygen, ß-D-glucose is oxidized by the enzyme glucose oxidase to gluconic acid and hydrogen peroxide:

Under the conditions of the assay, oxygen consumption is directly proportional to glucose concentration, which relates directly to the original lactose concentration. Any glucose originally present is measured directly after aqueous dilution as in the pre-reaction.
 

Samples:

Aqueous solutions and extracts

Sample volume:
Analysis time:
 

5 µl or 10 µl
20 seconds
 

Linearity:
 

50 mmol/L total glucose (0.9 %W/V) equivalent to approx. 18 % lactose
 

Reagent Stability:

Shelf-life 9 months unopened stored at 0 - 5°C. Reconstituted ß-galactosidase
7 - 9 days (4 vials) if stored at 0 - 5°C. Aliquots may be frozen for extended life.

Note:

i) Lactose analysis may be performed via the glucose assay on GM7, GL5 and GL6 analyzers.
ii) Sample opacity or turbidity presents no problem since the sensor system is electrochemical rather than spectrophotometric.