The effect of lactase and formula reconstitution on milk osmolality

These experiments investigated the reaction rate of lactase on milk lactose by measuring milk osmolality; and explored the effect of formula reconstit ution on milk osmolality. The investigations measured milk osmolality with the Fiske Os, freezing-point osmometer, Lactase (Lactaid) incubated with pu re lactose solutions established the validity of the method. Lactase was in cubated for 24 hours with four reconstituted milk formulas (Milumil, and Co w and Gate Nutrilon Plus, Farley's First Milk, SMA Gold). Milk osmolality i ncreased most rapidly in the first 4 hours after the addition of lactase. T he lactase enzyme completed over 90% of the reaction within 12 hours. The m ilk osmolalities ranged from 487 to 591 mosm/kg after 24 hours with 2-4 dro ps of lactase in 240 mi of formula. A clinical guideline osmolality of 400 mosm/kg was reached in 240 mi of formula at 1 to 12 hours depending on the dose of lactase. High milk osmolalities due to prolonged enzyme incubation, or high lactase doses could be reduced to around 400 mosm/kg by dilution o f 240 mi of formula with an extra 60 ml of water. The initial osmolality of formula after reconstitution by paediatric nurses varied widely and usuall y exceeded the manufacturer's quoted osmolality. This initial osmolality wa s a further influence on the final osmolality reached after the addition of lactase. It is concluded that the recommended incubation time for Lactaid of 24 hours is unnecessary as lactase exerts the majority of its effect in less than 12 hours. Adjustment of Lactaid dose and incubation times will ma intain milk formula osmolality within standard guidelines. Dilution with ex tra water will correct inadvertent high enzyme doses and prolonged incubati on times. The normal method of reconstituting milk formulas from powder may be unreliable as the manufacturer's quoted osmolality was not reproduced w hen milk formulas were reconstituted by paediatric nurses.