英文品名:Lactose/Galactose (Rapid) Assay Kit

规格型号:115 assays per kit

For the rapid assay of lactose, D-galactose and L-arabinose in food andplant products. Galactose dehydrogenase can be used to measure bothD-galactose and L-arabinose. Suitable for the analysis of lactose in“low-lactose” or “lactose-free” samples which contain high levels of monosaccharides.


Lactose, or milk sugar, is a white crystalline disaccharide. It is formed

in the mammary glands of all lactating animals and is present in their

milk. Lactose yields D-galactose and D-glucose on hydrolysis by

lactase (β-galactosidase), an enzyme found in gastric juice. People

who lack this enzyme after childhood cannot digest milk and are said

to be lactose intolerant. Common symptoms of lactose intolerance

include nausea, cramps, gas and diarrhoea, which begin about 30

minutes to 2 hours after eating or drinking foods containing lactose.

Between 30 and 50 million Americans are lactose intolerant, with

certain ethnic and racial populations being more widely affected than

others; as many as 75 percent of all African-Americans and Native

Americans and 90 percent of Asian-Americans are lactose intolerant.

The condition is least common among persons of northern European


Enzymic methods for the measurement of lactose are well known and

are generally based on the hydrolysis of lactose to D-galactose and

D-glucose with β-galactosidase, followed by determination of either

D-galactose or D-glucose. In the International Dairy Federation

Method (79B:1991) for the measurement of lactose in “dried

milk, dried ice-mixes & processed cheese”, details are given for

deproteinisation of samples, hydrolysis of lactose with β-galactosidase

and measurement of either released D-galactose or D-glucose.

The measurement of lactose as D-galactose liberated is more

generally reliable than measurement as D-glucose liberated because

preparations generally contain more free D-glucose than free


Enzymic kits for the determination of D-galactose are very slow. This

is due to the low rate of natural chemical “mutarotation” between

the α- and β-anomeric forms of D-galactose. Only the β-form is

recognised by β-galactose dehydrogenase. In incubations containing

NAD+, D-galactose and β-galactose dehydrogenase, there is a very

rapid initial increase in absorbance due to the consumption of β-Dgalactose,

and this is followed by a very slow approach to the endpoint.

This very slow approach results from the very low rate of

chemical “mutarotation” of α-D-galactose into β-D-galactose. Using

technology developed by Megazyme (patent pending), a galactose

mutarotase has now been incorporated into the assay format to

rapidly catalyse this rate-limiting mutarotation step. The result is very

rapid analysis times of approx. 5 min at room temperature (Figure 1).


Kits suitable for performing 115 assays are available from Megazyme.

The kits contain the full assay method plus:

Bottle 1: Buffer (2.5 mL, pH 5.0).

Stable for 大于 2 years at 4°C.

Bottle 2: Buffer (25 mL, pH 8.6) plus EDTA and sodium azide

(0.02% w/v) as a preservative.

Stable for 大于 2 years at 4°C.

Bottle 3: NAD+.

Stable for 大于 5 years at -20°C.

Bottle 4: β-Galactosidase suspension (1.2 mL).

Stable for 大于 4 years at 4°C.

Bottle 5: β-Galactose dehydrogenase plus galactose mutarotase

suspension, 2.4 mL.

Stable for 大于 2 years at 4°C.

Bottle 6: D-Galactose standard solution (5 mL, 0.4 mg/mL in

0.02% w/v sodium azide).

Stable for 大于 2 years at 4°C.