Enzymes are used in Dairy Industry
present at concentrations of about 4.7% (w/v) in milk and the whey (supernatant)
left after the coagulation stage of cheese-making. Its presence in milk makes it
unsuitable for the majority of the world's adult population, particularly in
those areas which have traditionally not had a dairy industry. Real lactose
tolerance is confined mainly to peoples whose origins lie in Northern Europe or
the Indian subcontinent and is due to 'lactase persistence'; the young of all
mammals clearly are able to digest milk but in most cases this ability reduces
after weaning. Of the Thai, Chinese and Black American populations, 97%, 90% and
73% respectively, are reported to be lactose intolerant, whereas 84% and 96% of
the US White and Swedish populations, respectively, are tolerant. Additionally,
and only very rarely some individuals suffer from inborn metabolic lactose
intolerance or lactase deficiency, both of which may be noticed at birth. The
need for low-lactose milk is particularly important in food-aid programmes as
severe tissue dehydration, diarrhoea and even death may result from feeding
lactose containing milk to lactose-intolerant children and adults suffering from
protein-calorie malnutrition. In all these cases, hydrolysis of the lactose to
glucose and galactose would prevent the (severe) digestive problems.
problem presented by lactose is its low solubility resulting in crystal
formation at concentrations above 11 % (w/v) (4°C). This prevents the use of
concentrated whey syrups in many food processes as they have a unpleasant sandy
texture and are readily prone to microbiological spoilage. Adding to this
problem, the disposal of such waste whey is expensive (often punitively so) due
to its high biological oxygen demand. These problems may be overcome by
hydrolysis of the lactose in whey; the product being about four times as sweet (seeTable
1), much more soluble and capable of forming concentrated, microbiologically
secure, syrups (70% (w/v)).
be hydrolysed by lactase, a b-galactosidase.
it may be prepared from the dairy yeast Kluyveromyces fragilis (K. marxianus
var. marxianus), with a pH optimum (pH 6.5-7.0) suitable for the treatment of
milk, or from the fungi Aspergillus oryzae or A. niger, with pH optima (pH
4.5-6.0 and 3.0-4.0, respectively) more suited to whey hydrolysis. These enzymes
are subject to varying degrees of product inhibition by galactose. In addition,
at high lactose and galactose concentrations, lactase shows significant
transferase ability and produces b-1,6-linked galactosyl oligosaccharides.
Lactases are now used in the production of ice cream and sweetened flavoured and condensed milks. When added to milk or liquid whey (2000 U kg-1) and left for about a day at 5°C about 50% of the lactose is hydrolysed, giving a sweeter product which will not crystallise if condensed or frozen. This method enables otherwise-wasted whey to replace some or all of the skim milk powder used in traditional ice cream recipes. It also improves the 'scoopability' and creaminess of the product. Smaller amounts of lactase may be added to long-life sterilised milk to produce a relatively inexpensive lactose-reduced product (e.g. 20 U kg-1, 20°C, 1 month of storage). Generally, however, lactase usage has not reached its full potential, as present enzymes are relatively expensive and can only be used at low temperatures.