chemrox - 6-2-2007 at 15:26
EXPERIMENTAL PROCEDURES
Isolation of Lactose from Milk
Sweet skimmed milk (Note I), 200 ml, is warmed to about 40°, and dilute acetic acid (I part glacial acetic acid to to parts water) is added dropwise
from a pipette with continuous stirring. This process is continued until casein no longer separates. An excess of acid should be avoided, for it may
cause some hydrolysis of the lactose. The casein is worked into a mass, removed with a stirring rod, and discarded. Immediately, 5 g of finely divided
calcium carbonate (precipitated chalk) is added, and the mixture is stirred for a brief period and then heated to boiling for about to minutes.
Heating causes almost complete precipitation of the albumin. The hot mixture is filtered by suction, and the filtrate is concentrated in a beaker to
about 30 ml (Note 2). To the hot solution are added 175 ml of 95% ethyl alcohol (NO FLAMESI) and 1-2 g of decolorizing carbon; after it has been mixed
well, the warm solution is filtered by gentle suction through a layer of filter aid wet with ethanol (d. Chap. 14, Notes 2, 3, and 4). The clear
filtrate (Note 3) is allowed to stand overnight or longer in a stoppered Erlenmeyer flask. In some cases, several days wilI be re¬quired for complete
crystallization. Hard crystals of lactose separate, usu¬ally on the walIs and bottom of the flask. The crystals are collected by suc¬tion filtration
and washed with a few milliliters of 25% alcohol. The average yield is 5-7 g.
Taste the product. Any material not oxidized as below is turned in as a product.
NOTES
I. This material should not be allowed to stand too long before being used in this experiment. Even under refrigeration bacterial attack takes place,
and the lactose is converted to lactic acid.
The most convenient jorm oj starting material jor this experiment is pow¬dered skimmed milk. In the case of one brand termed "Instant Dry Milk
(non¬fat)," the manufacturer recommended 5 lbs. of the dried milk per gallon of water;
therefore, 23.9 g in 200 ml of water was used for isolation of lactose. The yield of lactose was about 6 g.
2. In some cases, precipitation of proteins during the concentration will cause bumping in the boiling solution. The solution may also tend to froth
out of the beaker if boiling is quite vigorous. Blowing on the froth will break it and allow faster concentration. It is important that the final
volume be rather accurately 30 ml (:1=2 ml); otherwise, lowered yields result.
3. If the filtrate from the suction filtration is not brilliantly clear, especially if it has the dark appearance caused by traces of decolorizing
carbon, it is de¬sirable to add about 1 g of filter aid and refilter by gravity. Lactose is unlikely to crystallize unless the solution is
brilliantly clear; however, one may be deceived by cloudiness caused by rapid crystallization oj lactose ajter the suction filtration. If the
cloudiness increases relatively rapidly on standing, especially if reflecting surfaces of crystals become evident, further filtration should be
avoided since it will remove the product.
Ozone - 6-2-2007 at 16:15
I know of many interesting uses for lactose, but what is your intended purpose?
Immobilized lactosidase comes to mind...
Curious,
O3
chemrox - 8-2-2007 at 20:41
Hahaha!
Actually-I like it for column chromatography ... better than Tide soap.