Altering milk composition by nutritional and genetic approaches.pdf

Altering milk composition by nutritional and genetic approaches Potential exists in altering milk composition or ‘designing’ milk by nutritional management and through exploiting naturally occurring genetic variation among cattle…... …….to achieve specific health and /or...

Altering milk composition by nutritional and genetic approaches Potential exists in altering milk composition or ‘designing’ milk by nutritional management and through exploiting naturally occurring genetic variation among cattle…... …….to achieve specific health and /or processing opportunities. Emphasis used to be on breeding bigger animals that produce more milk. Now, adding more value to the milk produced and monitor its health implications. Led to ways to produce milk with lower fat and greater amounts of protein or different types of protein. By combining the two approaches, genetic work and the diet studies, could develop milk tailored to consumer preferences or rich in specific milk components that have health implications. Modification of milk composition by genetic technology Milk composition can be dramatically altered using gene transfer. Classical studies: association between lacto-protein variants and milk production traits. DNA technology in dairy science has enabled to identify a new genetic polymorphism. A transgenic animal is defined as an animal that is altered by the introduction of recombinant DNA through human intervention. Process involves a DNA construct be designed and built to express the desired protein in the animal. Construct is then introduced into a single cell embryo to allow incorporation of the transgene into animal genome. “Tailored” milk and nutritional significance Ø Change in milk fat Composition of milk could be altered by feeding lactating dairy cows a controlled diet to obtain a naturally modified component to alter milk fat. Stearic acid and oleic acid act similarly to decrease cholesterol. Although the ‘ideal’ milk fat composition may not be achieved, manipulation of composition of milk is possible through feed practices for dairy cows. Cows fed with fish oil, fishmeal or plankton can produce milk rich in omega-3 fatty acids. Restricted quantities of fish products are added to the cow’s diet of grass or silage to produce omega-3 fatty acids enriched milk. For half-fat milk, the supplement is de-husked oats and for spreadable butter is rapeseed oil. To boost whole milk , natural cancer fighting ability, dietary fats such as corn oil are fed to cows in protected form. The cows produce milk with substantially increased levels of conjugated linoleic acid (CLA). Studies have shown that CLA suppresses carcinogens and inhibits a number of cancers. “Tailored” milk and nutritional significance………cont. Ø Change in milk protein Demand to produce additional proteins and introduce compositional changes. Table 1 Potential changes in milk through genetic engineering. ____________________________________________________________________________________________ Potential modification Change in milk ____________________________________________________________________________________________ Increase casein content Increased protein, better manufacturing properties particularly for cheese making Engineered Casein Better manufacturing properties Remove a β-lactoglobulin Better manufacturing properties, decreased milk allergies Remove fat Easier to produce low fat milk products, decrease the butter surplus. Increase solids content, remove lactase lactose Produce b-galactosidase,Lactose produce antibodies of pathogens Safer food, mastitis prevention ____________________________________________________________________________________________________  Changes in the individual casein content of milk Ø Increasing the alpha S1 or S2 – casein content  high content of alpha S2-casein will enhance nutritional value of casein and increase micelle stability.  Attempts to express the bovine gene have been unsuccessful. Ø Producing milk devoid of beta-lactoglobulin  Cow’s milk is an allergic trigger in a significant fraction of infants and beta- lactoglobulin, not found in cow’s milk, is one of the causes.  Elimination of this protein from cow’s milk might overcome many major allergy problems associated with cow’s milk.  A genetic approach in individuals that carry a null beta-lactoglobulin allele.  The method of choice is the knockout of beta-lactoglobulin gene. Ø Changes in milk sugar  Lactose is the major sugar in milk.  The adult population suffers from intestinal disorders due to lactose maldigestion resulting from the normal drop of the intestinal lactose-hydrolysing enzyme.  Lactase- phlorizin associated with this pathology and lactose intolerance can be limited by dietary changes or through use of low lactose or lactase replacement products.  “Tailoring” milk by genetic modification Ø Modification of protein  Increasing the K-casein content Higher content was associated with smaller micelle size and higher heat stability. Relevant gene is important in transgenesis.  Modification of beta-casein in milk An increase results in increased curd firmness by 50%. Modification to beta-casein in deletion of the plasmin cleavage prevented the bitter flavour in cheese due to plasmin cleavage. Ø Modification of fat  Milk fat quality relate to organoleptic properties of the manufactured product.  The type of fatty acids present in milk fat can influence the flavour and physical properties of dairy products.  Sensory evaluation indicated that butter produced from cows fed with high oleic sunflower seeds and regular sunflower seeds were equal or superior in flavours to the control butter.  The high oleic acid sunflower seed and regular sunflower seed treatment butter were softer, more unsaturated and exhibited acceptable flavour, manufacturing and storage characteristics.  Milk containing naturally modified fat, obtained either by feeding extruded soybean or sunflower seeds, produced blue and Cheddar cheeses enhanced the safety against L. monocytogenes and S. thyphimurium due to accumulation of fatty acids.  “Tailoring” milk by genetic modification……..cont. Ø Increasing total solids and reducing lactose and water content of milk  Mice that produce milk with 33% more total solids and 17% less lactose than normal control mice have been generated by transgene.  Using this technology and increasing the understanding of the mechanisms, could lead to cattle with similar characteristics.  Having a cow with 6.5% protein, 7% fat 2.55% lactose and 50% less water would have many of economic and processing benefits.  Main economic benefit would be 50% reduction in cost of shipping milk.  Less stress on the cow due to producing half the normal volume of milk.  On manufacturing side, after removal of fat, from this type of milk, a skim milk having twice protein content and half the lactose content of normal milk could be produced.  Would make it easier to produce low lactose or lactose free ’hard dairy’ products.  The concentrated milk should lead to better product yields to the same amount of initial input.  The lowering of milk volume and lactose content will reduce the total whey output produced during processing.  The reduction of stress on the mammary gland of the cow and the more viscous milk may also decrease the susceptibility to obtain mastitis infection. Organisms that cause mastitis use lactose as their energy source since reduced lactose decreases available food for the bacteria.  “Tailoring” milk by genetic modification……..cont. Ø Higher levels of beta-casein and K-casein-A  To enhance milk composition and milk processing efficiency by increasing the casein concentration in milk, additional copies of the genes encoding bovine beta and K-casein (CSN2 and CSN3, respectively)were introduced into female bovine fibroblasts.  Laboratory engineered cells to overproduce casein proteins were fused with cow eggs and the resulting embryos were transferred into recipient cows and 11 transgenic calves were born.  Nine were found to produce the enhanced milk.  One protein, , K-casein, increased heat stability in the cheese making process.  The other protein, beta-casein, improved the process by reducing the clotting time of the rennet, which curdles the milk. It also increased the expulsion of whey(watery part of the milk) which remains after cheese is formed.  This allows cheese-makers to produce more cheese from the same volume of milk. The manufacturing process is also quicker and due to faster clotting times associated with higher protein levels.  The cows producing 8-20% more beta-casein and double the normal amount of K-casein, offer big savings for cheese manufacturers.  Cows genetically modified to produce high-protein milk for the cheese industry have been created by a biotech company,AgResearch in New Zealand and marks cow’s milk being engineered to improve quality than contain profitable pharmaceuticals.  “Tailoring” milk by genetic modification……..cont. Ø Tailoring milk to cut cheese costs  Two years old, the clones produce about 13% more milk protein than normal cows.  They carry extra copies of genes for two types of protein casein, key for cheese and yogurt manufacture.  Protein rich tailored milk from cloned ,genetically modified cows could speed dairy processing and cut cheese making costs.  Dairy manufacturers need less milk to make cheddar firm and ice-cream creamy.  Allow milk to have high protein content but to remain watery.  AgResearch now needs to find out whether the increase improves the milk’s calcium content or its ability to coagulate before they seek approval to sell the clones to dairy farmers.  Most scientists believe that milk from cloned cows is no different than normal milk but are less certain about safety of milk from genetically modified cows.