Review/Oorsig Volume 22, Issue 05 - Page 13

Volume 22 • Issue 05 • 2018 the predominant glycolipid in the glycosylation of complex molecules such as myelin in the Leloir pathway. As a result Galactose is often referred to as the “brain sugar”. Galactose is also a component of the molecules present on blood cells that determine the ABO blood types. There is evidence that it may play a role in the absorption of minerals such as calcium, copper and zinc. However, the suspicion exists that osteoporosis in Lactose-intolerant individuals may be the result of avoidance of dairy products in their diet, rather than as a lack of Lactose. If Lactose is not digested in the small intestine it may be used as a prebiotic by certain large intestine bacteria. Most notably it promotes the growth of bifidobacteria which may play a life- long role in countering the ageing-associated decline of some immune functions. LACTOSE HAS MANY USES Despite its significant commercial value, the majority of milk processors do not have the ability to “harvest” Lactose. As a result, dairy farmers are not paid a premium based on their Lactose levels, as is the case for protein and butterfat levels. Lactose plays a crucial role in determining milk volume and has significant value in its own right. During the cheese and butter manufacturing process lactose remains in the whey fraction. Whey acts as the primary commercial source of lactose through a process of crystalizing an oversaturated whey solution. Lactose has many commercial uses, especially in the food and pharmaceutical industry: • • • It is used when excessive sweetness is undesirable. Especially in milk formulas for babies where it reduces the sensation of appetite and prevents cravings for sweet foods and overeating. Lactose is also less cariogenic (causing less tooth decay) than other sugars. Reducing the sugar content in foodstuffs can be problematic since sugar affects the flavour, colour and texture of several foods. Especially in the confectionary industry. Lactose is commonly used as a substitute because of its low sweetness and excellent bulking properties. Because lactose has low sweetness and low water solubility it is commonly used as an excipient in the pharmaceutical industry to coat tablets. Estimates puts its use as high as 70%. It also has excellent tablet forming qualities and is used as a bulking • • • agent. Lactose in tablets is only present in milligrams and therefor not present in sufficient quantities to cause symptoms in lactose -intolerant individuals. Lactose is sometimes added to cow’s milk to simulate the high lactose content of human breastmilk. Lactose is sprayed onto silage to increase acid formation during the fermentation process. Lactose can also be used to produce ethanol. LACTOSE SYNTHESIS Lactose synthesis is initiated in the secretory vesicles of the Golgi apparatus. Glucose is converted to UDP- Galactose and through the action of the enzyme lactose-synthetase a Glucose and UDP-galactose combine to form a Lactose molecule. The milk protein, beta-lactalbumin, must be present for Glucose and UDP-galactose to combine. As a result, beta-lactalbumin is a major limiting factor in the production of Lactose and hence milk volume. As the Lactose is produced, water flows into the vesicles through osmosis to try and dilute the lactose and maintain equilibrium. Lactose accounts for approximately 50% of the osmotic pressure of milk. The balance is made up by ions, citrate and proteins. Consequently, the vesicles swell, move to the cell membrane and break open to release the milk into the lumen of the milk ducts. The milk ducts are impermeable to the constituents of milk. No re-absorption of milk constituents or water takes place in the milk ducts. The ducts are merely conduits and storage vessels for the milk to flow to the teats until such a time as the milk is extracted. rBST increases the availability of Glucose to the alveolar cells by increasing the blood flow to the udder. As a result, more Lactose is produced and through the osmotic effect of Lactose more water is drawn into milk production and increases the volume of milk produced. The increased volume of milk is proportional to the levels of Lactose, therefor there will be no change in the milk Lactose concentration. Serotonin is also produced in mammary tissue and is under partial control of prolactin. Delayed milking will increase serotonin levels which down-regulates the synthesis of Lactose, which in turn will reduce milk production. Milk yield can thus be increased through more frequent milking or by increasing the photoperiod. Once again, the Lactose remains proportional to the milk production and therefor there is no change in the lactose concentration in the milk 13