referring first to fig1 which is the sole drawing figure in this description , there is shown a very simple schematic representation of a prototype system for processing milk based infant formula for aseptic packaging which was used in the experiments which will be described herein . a supply of a milk based infant formula , for example a supply tank 1 is provided . the flow of infant formula is regulated by a valve 2 , and passes through tubing 3 to a feed pump 4 . the feed pump 4 propels the infant formula through tubing 5 towards a heat transfer device 6 in which the low temperature incoming infant formula passes through tubing which is adjacent to tubing containing high temperature outgoing infant formula , such that the temperature of the incoming infant formula is slightly elevated by transferred heat . the infant formula then passes through more tubing 7 to a deaerator 8 which degasses the infant formula . upon exiting the deaerator the infant formula is propelled by a second feed pump 9 through more tubing 10 to a homogenizer 11 . upon leaving the homogenizer the infant formula passes through more tubing 12 to a first heater 13 where the infant formula is heated , by indirect steam , to a temperature of , for example , about 77 ° c . upon leaving the first heater the infant formula passes through more tubing 14 to a second heater 15 where the infant formula is further heated , by indirect steam , to a temperature of , for example , about 121 ° c . upon leaving the second heater the infant formula passes through more tubing 16 to a third heater 17 where the infant formula is further heated , by indirect steam , to a temperature of , for example , about 143 ° c . it is to be understood that the system being described is only exemplary , and that one , two or any other suitable number of heaters may be employed , at any suitable temperatures for the infant formula , and that the heating source could be direct or indirect steam or even electric heating coils . after exiting from the last heater , in this example the third heater 17 , the infant formula passes through a hold tube 18 where the infant formula is held at an elevated temperature of , for example , about 143 ° c . for , for example , about five to ten seconds . it is in this hold tube 18 that the problem of fouling or &# 34 ; burn - on &# 34 ; was measured . after exiting from the hold tube the infant formula passes through a cooler 19 where the temperature of the infant formula is reduced to be , for example , about 77 ° c . after exiting from the cooler 19 the infant formula passes through more tubing 20 to a second homogenizer 21 . after exiting from the homogenizer the infant formula passes though more tubing 22 to the heat transfer device 6 which has already been described . however , this time the warmer infant formula will be considered to be the outgoing infant formula . after exiting from the heat transfer device 6 the infant formula passes through more tubing 23 to a plate cooler 24 where the temperature of the infant formula is reduced , for example , to about 20 ° c . after exiting from the plate cooler the infant formula passes through more tubing 25 to a filling apparatus 26 where the commercially sterile infant formula is placed into commercially sterile containers . there are two types of fouling material that occur in uhtst systems . the first is a type a foulant . this material is a soft , voluminous , curd - like material . it does not adhere to the surface of the uhtst system very strongly and is easily removed by cleaning . the most significant problems with the type a material are its resistance to heat transfer and the reduction in cross - sectional area of the hold tube which reduces the time which the infant formula spends in the hold tube when the flow rate through the system remains constant . the second type of foulant is a type b material . this material is characterized by its gritty nature . it is composed mostly of minerals and is not a significant deterrent to heat transfer or hold tube performance . when a milk based infant formula which was not in accordance with the present invention was processed in the prototype aseptic processing system significant fouling of the uhtst hold tube was observed . in the prototype aseptic processing system the fouling material was a typical type a material . the amount of fouling material in the hold tube is dependent upon the length of the run . steam control valves regulate the amount of steam entering the uhtst heaters ( 13 , 15 and 17 in fig1 ). the degree to which a steam control valve is open depends on how much steam and pressure is needed to maintain the heaters temperature setting . when the aseptic processing system is not fouled it maintains a constant valve setting . however , when the aseptic processing system begins to foul and the heat transfer properties deteriorate the aseptic processing system responds by opening the steam valves to maintain temperature . when processing a milk based infant formula in the exemplary aseptic processing system fouling can be determined by observing the steam control valve that regulates the third heater . the uhtst process is adversely affected by fouling that occurs in the hold tube . as fouling increases the degree of opening of the steam control valve increases . an increase of 25 % over the initial set point was considered complete fouling for the purpose of the experiments described herein . in the experiments described herein monitoring the system for fouling is simply a matter of observing the steam control valves during processing . the absolute amount of fouling was determined in these experiments by weighing the hold tube after processing . in each of the experiments described herein the milk based infant nutritional formula employed in the experiment was similac ® ready - to - feed which is manufactured by the ross laboratories division of abbott laboratories , columbus , ohio , united states of america . the initial efforts to control fouling involved manipulating the steam temperature settings of the heaters . by lowering the temperature differentials between the heaters it was hoped that fouling could be avoided . this approach only marginally improved the length of each run , but it was not by itself enough of an improvement . the next phase of the experiments evaluated the effects of increasing the ph and adding of citrate . although simple adjustment of the ph of a milk based infant formula to a value of 7 . 0 further extended the run time , as shown in table 1 the minimum length of run time of eight hours was not attained . the addition of potassium citrate in combination with a product ph of 6 . 9 to 7 . 1 was found to extend the run time to eight hours . potassium citrate was added at levels of 400 , 200 , and 150 ppm , ( citrate ion levels of 233 , 116 and 87 ppm ) as shown in table 2 . the amount of fouling material decreased with increasing levels of potassium citrate . table 1______________________________________fouling of the uhtst system during processing ofa milk based infant formula after ph adjustments fouling length of material type ofrun no . ph run ( min .) ( g ) foulant______________________________________1 7 . 00 240 25 . 1 a2 7 . 02 85 48 . 6 a3 7 . 00 75 * a4 7 . 01 75 * a avg .= 119 avg .= 36 . 85______________________________________ * foulant material broke loose from hold tube during processing . table 2______________________________________fouling of the uhtst system duringprocessing of a milk based infant formula afterph adjustments and potassium citrate additions ppm added length foulingrun citrate of run material type ofno . ph ions ( min .) ( g ) foulant______________________________________1 7 . 03 233 255 * 6 . 9 b2 6 . 93 233 240 * 1 . 0 b3 6 . 80 233 120 * 6 . 0 b4 7 . 01 233 210 * 8 . 8 b5 6 . 93 116 420 * 33 . 1 a / b6 6 . 87 87 120 ** 50 . 2 a / b______________________________________ * run terminated because no more product was available ** run terminated due to fouling experiments conducted with a prototype aseptic processing system determined that the highest level of potassium citrate ( 400 ppm ) and the higher phs &# 39 ; ( 6 . 9 - 7 . 0 ) produced the best results . when these fortification levels were used the amount of fouling was minimal , and only type b fouling occurred . the 0 - time product quality of selected runs was acceptable . processed mix was obtained from a production facility and was processed in the prototype aseptic processing system with potassium citrate levels of 200 , 300 , and 400 ppm , ( citrate ion levels of 116 , 174 , 233 ppm ) at phs &# 39 ; of 6 . 74 to 6 . 98 . the potassium citrate used to fortify the milk based infant formula was weighed out , dissolved in water , and added slowly with agitation to the mix . after allowing the mix to agitate for 5 minutes 1 . 0n koh was used to titrate the mix to the desired ph . the product was packaged in 8 oz metal cans and enrolled in a physical stability evaluation program . the use of citrate , for example in the form of potassium citrate , to chelate the mineral salts and keep them soluble during uhtst processing of the milk based infant formula has been explored and found to be very effective . the most effective potassium citrate level was found to be a fortification rate of 400 ppm . the optimum ph was found to be between 6 . 9 and 7 . 0 . the amount of fouling material decreased , and the type of foulant changed from a to b as the potassium citrate level and the ph were increased ( table 3 ). a visual examination of the hold tube from the uhtst system in the prototype aseptic processing system demonstrated the same relationship . table 3______________________________________fouling of the prototype uhtst system duringprocessing of a milk based infant formula afterph adjustments and potassium citrate additions ppmraw added length foulingrun product citrate of run material type ofno . batch ph ions ( min .) ( g ) foulant______________________________________ 1 1 7 . 01 233 120 6 . 1 * b 2 1 7 . 03 174 120 0 . 6 b 3 1 7 . 02 116 120 1 . 1 b 4 1 6 . 80 233 55 74 . 5 a 5 1 6 . 90 233 55 ** 2 . 9 b 6 2 6 . 90 233 112 3 . 7 b 7 2 6 . 90 174 120 6 . 5 b 8 2 6 . 90 116 120 31 . 1 a / b 9 2 6 . 80 233 75 5 . 4 b10 2 6 . 80 174 92 69 . 5 a11 2 6 . 85 174 115 14 . 9 a / b12 3 6 . 71 # 174 15 67 . 0 a13 3 6 . 85 174 120 12 . 4 a / b14 3 6 . 90 116 120 13 . 4 a15 3 6 . 80 233 115 4 . 4 b16 3 6 . 85 174 110 5 . 2 b______________________________________ * uhtst system was rinsed with caustic before product run ** run terminated because no more product was available # ph after potassium citrate addition , no ph adjustment the uhtst processed product is much whiter than the retorted product , and has more of a true milk color . this aspect of the aseptically processed product may be very beneficial if the product is packaged in a translucent container . the physical stability of product from this experiment was checked again during an eighteen month period , and it continued to be satisfactory . it was thought that the seasonal variation associated with the condensed skim milk in a milk based infant formula might affect the process of the invention . portions of commercial batches of a milk based infant formula were obtained from a production facility at monthly intervals from january through september . the batches were reprocessed in the prototype aseptic processing system . optimization batches processed under the same conditions were filled from october through december . the results revealed that hold tube fouling was effectively controlled in all batches . no fouling was recorded during any of the approximately 2 hour long runs . the use of 400 ppm of potassium citrate ( 233 ppm of citrate ions ) and a ph adjustment to 6 . 95 ± 0 . 05 to control fouling during uhtst processing appears to be unaffected by seasonal variations associated with milk based products . the replicate batches were processed for two hours with no fouling of the hold tube . the physical stability of the replicate and optimization batches was good . the physical stability results of the replicate batches were in agreement with the results from the optimization batches . the addition of potassium citrate results in potassium levels of approximately 955 mg / liter and citrate levels of approximately 948 mg / liter . the potassium level is well below the united states infant formula act ( ifa ) maximum . the control of fouling during aseptic processing of a milk based infant formula can be achieved with the addition of 233 ppm of citrate ions ( 400 ppm potassium citrate ) and a ph adjustment to 6 . 95 ± 0 . 05 .
a process for aseptically processing a milk based infant formula includes the steps of adding citrate ions to the formula at a concentration of at least 128 ppm and adjusting the ph to be at least 6 . 8 before subjecting the formula to a temperature of at least 132 ° c .