the milk liquid to be evaporated is introduced via pipe 1 into effect 2 . upon leaving pipe 1 , the milk liquid is equally distributed by divider plates 3 over the downpipes 4 . the milk liquid forms a film over the walls of these downpipes 4 , which are heated externally with water vapor introduced via pipe 5 . a two - phase flow of concentrate and vapor enter liquid collector 6 , where product and vapor are separated . the product is pumped through pipe 7 and pump 8 to the divider plate of the next effect . the vapor is directed via line 9 to the next effect to condense on the outside of the downpipes . in the process according to the invention , a fat fraction can be supplied under the downpipes 4 or to the product flow in pipe 7 . 1628 kg liquid containing 81 kg skim milk solids , 24 . 5 kg whey protein solids obtained through ultrafiltration , and 188 kg desalted whey solids , was divided in 2 portions a and b of 814 kg each . the solids content of this liquid was 18 %. to portion a ( comparative example ), 83 kg liquid fat ( stored under nitrogen ) was added with mixing at 50 ° c . this fat had the composition as shown in column c of table i . this fat - enriched liquid was subsequently evaporated to a solids content of 46 % in an evaporator with three effects . portion b ( invention ) was evaporated to the extent where a product flow of a solids content of 35 % was fed into the last effect of the evaporator . under the downpipes of this last effect , 83 kg of the above fat composition was added to the liquid in a constant flow at 50 ° c ., in such a manner that the fat was evenly distributed during the evaporation time that likewise a liquid of a solids content of 46 % was obtained . both portions were subsequently homogenized in a two - stage homogenizer ( 100 + 30 bar ), followed by cooling to 8 ° c . and the addition , with mixing , to the liquid of a number of additives which are conventional for food for premature infants : minerals , except for copper and iron , vitamins , amino acids , taurine , uridine monophosphate , guanosine monophosphate , inosine monophosphate , cytidine monophosphate , adenosine monophosphate . then both portions were spray - dried ( inlet temperature 186 ° c ., outlet temperature 90 ° c .) and a conventional premix ( containing iron and copper ) was admixed to form the desired end product . this product was packaged in cans , under nitrogen or not . from a determination of the peroxide numbers of the fat fraction the powders of batch b possessed a higher stability than the powders of batch a over a storage period of 13 and 26 weeks , respectively . the peroxide numbers of the fat fraction were determined according to a modification of the method of loftus hills and thiel ( loftus hills , g . and thiel c . c ., j . dairy res . 14 ( 1946 ), 340 ; australian standard n 63 , ( 1968 ), p 22 ). according to this method , the fat is extracted from the powder at 55 ° c . with a mixture of 1 - chlorobutane / methanol , whereafter the peroxides present in the extract oxidize fe ( ii ) ions which have been added with a reagent , to form fe ( iii ) ions , whereafter the latter ions are determined spectrophotometrically by means of an ammonium rhodanide stain . the table below presents the results of this peroxide number determination . ______________________________________ peroxide number of the fat ( meq / kg ) in 20 samples storage period at 20 ° c . : 13 weeks 26 weeks______________________________________batch a , not packaged under n . sub . 2 0 . 7 1 . 4batch b , not packaged under n . sub . 2 0 . 02 0 . 6batch a , packaged under n . sub . 2 0 . 3 1 . 4batch b , packaged under n . sub . 2 0 0 . 7______________________________________ a comparable conclusion could be drawn from tests where the fat fraction was enriched with additional antioxidant ( dose 200 ppm ascorbyl palmitate on the fat , and 1000 ppm ronoxan a ® containing 25 % ascorbyl palmitate , 5 % dl - α - tocopherol and 70 % lecithin ), whether or not combined with bringing the powder under nitrogen gas directly after drying . the addition of fat in the last effect of the evaporator led to an improved and optimum result in terms of product stability . in accordance with a known method ( c ), 62 kg soya oil was added with vigorous stirring to a mixture of 390 kg whole milk , 1496 kg low - fat milk , and 107 kg butter serum . this mixture was heated up by known techniques , heated at 120 ° c . for three minutes and evaporated to 7 . 8 % fat and 18 % non - fat milk solids ( nfms ). this product was subsequently homogenized ( 150 + 25 bar , 50 ° c .). this was followed by final standardization to 7 . 8 % fat and 18 % nfms with either water , or different amounts of solutions of na 2 hpo 4 and / or nah 2 po 4 supplemented with water . this was followed by packaging in cans and sterilization at 121 ° c . in accordance with the process of the present invention ( d ), 390 kg whole milk ( 4 . 38 % fat and 8 . 85 % nfms ) was mixed with 1496 kg skim milk ( 0 . 03 % fat and 9 . 24 % nfms ) and 107 kg butter serum ( 0 . 53 % fat and 8 . 44 % nfms ). this mixed milk was heated to 120 ° c . by known techniques , followed by sustained heating for 3 minutes . the hot milk was then transferred onto the first effect of a falling film evaporator ( two effects ) and evaporated to a solids content of approximately 21 %. under the downpipes of the second effect , 62 kg soya oil of 50 ° c ., evenly distributed over the entire required evaporation time , was added in a constant flow . thus a product with 7 . 8 % fat and 18 % nfms was obtained . this evap was subsequently homogenized in the conventional manner ( 150 + 25 bar , 50 ° c .) and standardized either with water or with a solution of na 2 hpo 4 and / or nah 2 po 4 in water . finally , the evap was sterilized in cans , as described with reference to the traditional method ( c ). concentrated milk was produced as in example 2 , except that the butter serum was not mixed with the other milk liquids before evaporation but , after heating to 50 ° c ., was injected into the second effect of the evaporator right beside the soya oil . the evap could be sterilized without addition of phosphates or other milk - foreign stabilizers . concentrated milk was prepared as in example 3 , but the soya oil was replaced with an oil containing 81 % oleic acid ( see oil b , table i ). concentrated milk was prepared as in example 3 , but the soya oil was replaced by fatty mixture c , as indicated in table i . according to the process of the present invention such as it has been illustrated in the examples , oxidation - sensitive fatty acids enter into contact with oxygen to a minimal extent as compared with the process according to the comparative example . as a result , remarkably stable milk concentrates having a prolonged storage life are obtained by a simpler process operation . table i______________________________________fatty acid % soya oil oil b fat mixture c______________________________________c8 : 0 1 . 1c10 : 0 1 . 1c12 : 0 12 . 6c14 : 0 4 . 6c15 ( a ) isoc15 : c16 ( a ) isoc16 : 0 10 . 5 3 . 5 20 . 7c16 : 1ω7c17 anteisoc17 isoc17 : 0c17 : 1ω9c18 : 0 4 . 0 4 . 0 3 . 1c18 : 1ω9 22 81 36 . 5c18 : 1ω7 0 . 1c18 : 2ω6 54 . 5 9 . 0 15 . 80c18 : 3ω6gla 0 . 35c18 : 3ω3 7 . 5 1 . 9c18 : 4 0 . 05c20 : 0 0 . 5 0 . 5c20 : 1ω9c20 : 1ω7c20 : 2ω6c20 : 3ω6c20 : 3ω3c20 : 4ω6 aac20 : 5ω3 epa 0 . 25c22 : 0 0 . 5 1 . 0c22 : 1ω9 / 11c22 : 2ω6c22 : 4ω6c22 : 5ω3c22 : 6ω3 dha 0 . 35c24 : 0c24 : 1ω9other 0 . 5 1 . 0 1 . 50______________________________________
the invention relates to a process for the preparation of milk and milk powders having a long storage life utilizing techniques which are known per se . to that end , a milk liquid is prepared , which is evaporated , and a fat fraction is added to the milk liquid in one or more effects of the evaporator . this process is particularly suitable for the preparation of a milk having a long storage life , in which unsaturated fatty acid chains are present .