Cronobacter Support
07-14-2009, 10:18 AM
5.3.1 Manufacture
Dry infant formula is manufactured according to three process types:
a. Wet-mix process: all ingredients are handled in a liquid phase and heat-treated (critical control point [CCP]), e.g. pasteurized or sterilized, and then dried.
b. Dry-mix process: individual ingredients are prepared, heat-treated as appropriate, dried and then dry-blended.
c. Combined process: part of the ingredients are processed according to (a), in order to produce a base powder to which the rest of the ingredients are added according to (b).
5.3.2 Control of ingredient quality
The main microbiological issues of current public health concern associated with powdered infant formula are related to the presence of Salmonella and other Enterobacteriaceae (coliforms) including E. sakazakii. The presence of these microorganisms may occur as a result of:
• contamination through ingredients not submitted to a heat treatment during the powdered infant formula manufacturing process (this applies for dry-mix and combined processes).
• contamination from the processing environment during the dry steps of the process, i.e. contamination post-thermal processing, presumably acquired from the processing environment during drying or packing (this applies for dry, wet and combined processes).
It must be emphasized that dry-mix ingredients are not “raw”; they are processed by the suppliers to fulfil the same requirements as the finished powdered infant formula. The presence of Enterobacteriaceae is due to post-heat-treatment recontamination. The results of an unpublished industry survey of ingredients are summarized in Table 2 (J.L. Cordier, personal communication, 2004). In order to ensure that ingredients are microbiologically suitable, a number of factors need to be considered:
• The likelihood of occurrence in ingredients – some are considered to have a high risk of containing Enterobacteriaceae (e.g. starch) while others have a low risk (e.g. oils). The rating may depend on the local situation (Table 2).
• Selection of the supplier according to stringent criteria (e.g. appropriate control measures, good hygienic practices [GHPs], verification and release procedures in place).
• Testing of the ingredients to verify effectiveness of the above measures (not to ensure safety).
5.3.3 Processing
Powdered infant formula is produced from ingredients that may include milk, milk derivatives, soy protein isolates, carbohydrates, fats, minerals, vitamins and some food additives. These ingredients, in either liquid or powdered form, are typically mixed with water to form a liquid mix, which is then dried to a powder (aw < 0.3) in large spray dryers. Prior to drying, the liquid mix is heated (pasteurized at 71.6°C for 15 seconds or 74.4°C for 25 seconds [for products containing starches or thickeners] or at higher temperatures [e.g. 105°-125°C for at least 5 seconds]), homogenized, in some cases
Table 2 (attached). Industry survey for the presence of Enterobacteriaceae and E. sakazakii in ingredients used in dry mixing operations for all types of powdered formula (up to 3 years).
evaporated and sometimes stored in large, chilled holding tanks. Vitamins are added just prior to drying. During the drying process, the liquid mix is heated to approximately 82°C and is pumped under high pressure to spray nozzles or an atomizer mounted in a large drying chamber through which flows filtered, high-temperature air. Inlet air temperature ranges from 135° to 204°C, and the exhaust temperature ranges from 45° to 80°C. The liquid mix is dried nearly instantaneously in the hot air and the resultant powder falls to the bottom of the dryer for collection. Alternatively, it is collected from the exhaust stream in cyclone collectors or bag houses. The powder then passes from the drying chamber to a fluidized cooling bed where it is quickly cooled to below 38°C using cool, high efficiency particulate air (HEPA) > EU 10.1 Next, the powder is sifted and pneumatically or mechanically transported to storage silos, tote bins or big bins, or directly to filling operations.
In some cases, manufacturers produce infant formula by first drying a wet mixture of the major ingredients (protein, fat and carbohydrate). This is typically called infant formula base powder. Then, in large mixers or blenders, the dry minor ingredients, such as vitamins, minerals and additional carbohydrates, are blended into the base powder to produce the final product formulation. This option allows for longer drying campaigns and reduces the frequency of changeovers between different product formulations. Another option is to blend all of the pre-dried ingredients together to make a finished infant formula powder. This process is more efficient from an energy standpoint and provides more flexibility in formulation modifications. In the dry-blending process, it is essential that the dry ingredients meet the same microbiological standards as the final product because they receive no additional heat treatment. Because incoming “raw” material testing alone does not guarantee conformance to the high quality standards required by the industry, manufacturers employing these processes maintain close relationships with their “raw” material suppliers and require strict adherence to good manufacturing practices (GMPs) and Hazard Analysis Critical Control Point (HACCP) principles.
On completion of the drying or blending steps, the final product is conveyed from the storage silos or blenders to filling machinery where it is filled into cans or flexible containers. The containers are flushed with inert gas, sealed, coded, labelled and packed into shipping cartons. The finished product is typically held until it undergoes final testing, including nutrient content, uniformity and microbiological analysis.
5.3.3.1 Heat treatment
It has been suggested that the high thermal resistance of E. sakazakii strains in comparison to other members of the Enterobacteriaceae can possibly explain their high prevalence in powdered and prepared formula milk (Nazarowec-White and Farber, 1997a). However, recent studies suggest that the osmotolerance of the organism may be more important in this latter regard (Breeuwer et al., 2003). The ability to be osmotolerant may increase the risk of the organism becoming more dominant in the environment, thus increasing the risk of post-processing contamination of powdered infant formula. Previous work done by Nazarowec-White and Farber (1997b) and others (Nazarowec-White, McKellar, and Piyasena, 1999; Iversen, Lane, and Forsythe, 2004) showed that standard pasteurization practices are effective for the inactivation of E. sakazakii. Edelson-Mammel and Buchanan (2004) showed that a greater than 4-log reduction can be obtained by rehydrating dried infant formula with water pre-equilibrated to > 70°C. This implies that preparing reconstituted formula using the latter approach (using 70°C for rehydration) is likely to result in a high probability that a serving would not contain this organism. Interestingly, there appeared to be two distinct phenotypes of E. sakazakii, and heat resistance varied as much as twentyfold (Edelson-Mammel and Buchanan, 2004). Figure 3 illustrates the difference in heat resistance and provides a comparison with other Enterobacteriaceae (Edelson-Mammel and Buchanan, 2004). A complete listing of D- and z- values can be seen in Table 3. In summary:
• There appears to be substantial diversity in thermal resistance among strains.
• Inactivation of the organism can occur very quickly at temperatures above 70°C. This suggests that the use of relatively mild thermal treatments is a potential risk reduction strategy that can be directed towards reducing or eliminating E. sakazakii in reconstituted powdered infant formula.
1 The Eurovent 4/4 standard has classified HEPA (high efficiency particle air) and ULPA (ultra low particle air) filters in five different classes, EU 10 – EU 14, based on the efficiency determined by using the Sodium Flame test. EU 10 exhibits 95–99.9% efficiency, while EU 14 exhibits >99.999% efficiency.
Dry infant formula is manufactured according to three process types:
a. Wet-mix process: all ingredients are handled in a liquid phase and heat-treated (critical control point [CCP]), e.g. pasteurized or sterilized, and then dried.
b. Dry-mix process: individual ingredients are prepared, heat-treated as appropriate, dried and then dry-blended.
c. Combined process: part of the ingredients are processed according to (a), in order to produce a base powder to which the rest of the ingredients are added according to (b).
5.3.2 Control of ingredient quality
The main microbiological issues of current public health concern associated with powdered infant formula are related to the presence of Salmonella and other Enterobacteriaceae (coliforms) including E. sakazakii. The presence of these microorganisms may occur as a result of:
• contamination through ingredients not submitted to a heat treatment during the powdered infant formula manufacturing process (this applies for dry-mix and combined processes).
• contamination from the processing environment during the dry steps of the process, i.e. contamination post-thermal processing, presumably acquired from the processing environment during drying or packing (this applies for dry, wet and combined processes).
It must be emphasized that dry-mix ingredients are not “raw”; they are processed by the suppliers to fulfil the same requirements as the finished powdered infant formula. The presence of Enterobacteriaceae is due to post-heat-treatment recontamination. The results of an unpublished industry survey of ingredients are summarized in Table 2 (J.L. Cordier, personal communication, 2004). In order to ensure that ingredients are microbiologically suitable, a number of factors need to be considered:
• The likelihood of occurrence in ingredients – some are considered to have a high risk of containing Enterobacteriaceae (e.g. starch) while others have a low risk (e.g. oils). The rating may depend on the local situation (Table 2).
• Selection of the supplier according to stringent criteria (e.g. appropriate control measures, good hygienic practices [GHPs], verification and release procedures in place).
• Testing of the ingredients to verify effectiveness of the above measures (not to ensure safety).
5.3.3 Processing
Powdered infant formula is produced from ingredients that may include milk, milk derivatives, soy protein isolates, carbohydrates, fats, minerals, vitamins and some food additives. These ingredients, in either liquid or powdered form, are typically mixed with water to form a liquid mix, which is then dried to a powder (aw < 0.3) in large spray dryers. Prior to drying, the liquid mix is heated (pasteurized at 71.6°C for 15 seconds or 74.4°C for 25 seconds [for products containing starches or thickeners] or at higher temperatures [e.g. 105°-125°C for at least 5 seconds]), homogenized, in some cases
Table 2 (attached). Industry survey for the presence of Enterobacteriaceae and E. sakazakii in ingredients used in dry mixing operations for all types of powdered formula (up to 3 years).
evaporated and sometimes stored in large, chilled holding tanks. Vitamins are added just prior to drying. During the drying process, the liquid mix is heated to approximately 82°C and is pumped under high pressure to spray nozzles or an atomizer mounted in a large drying chamber through which flows filtered, high-temperature air. Inlet air temperature ranges from 135° to 204°C, and the exhaust temperature ranges from 45° to 80°C. The liquid mix is dried nearly instantaneously in the hot air and the resultant powder falls to the bottom of the dryer for collection. Alternatively, it is collected from the exhaust stream in cyclone collectors or bag houses. The powder then passes from the drying chamber to a fluidized cooling bed where it is quickly cooled to below 38°C using cool, high efficiency particulate air (HEPA) > EU 10.1 Next, the powder is sifted and pneumatically or mechanically transported to storage silos, tote bins or big bins, or directly to filling operations.
In some cases, manufacturers produce infant formula by first drying a wet mixture of the major ingredients (protein, fat and carbohydrate). This is typically called infant formula base powder. Then, in large mixers or blenders, the dry minor ingredients, such as vitamins, minerals and additional carbohydrates, are blended into the base powder to produce the final product formulation. This option allows for longer drying campaigns and reduces the frequency of changeovers between different product formulations. Another option is to blend all of the pre-dried ingredients together to make a finished infant formula powder. This process is more efficient from an energy standpoint and provides more flexibility in formulation modifications. In the dry-blending process, it is essential that the dry ingredients meet the same microbiological standards as the final product because they receive no additional heat treatment. Because incoming “raw” material testing alone does not guarantee conformance to the high quality standards required by the industry, manufacturers employing these processes maintain close relationships with their “raw” material suppliers and require strict adherence to good manufacturing practices (GMPs) and Hazard Analysis Critical Control Point (HACCP) principles.
On completion of the drying or blending steps, the final product is conveyed from the storage silos or blenders to filling machinery where it is filled into cans or flexible containers. The containers are flushed with inert gas, sealed, coded, labelled and packed into shipping cartons. The finished product is typically held until it undergoes final testing, including nutrient content, uniformity and microbiological analysis.
5.3.3.1 Heat treatment
It has been suggested that the high thermal resistance of E. sakazakii strains in comparison to other members of the Enterobacteriaceae can possibly explain their high prevalence in powdered and prepared formula milk (Nazarowec-White and Farber, 1997a). However, recent studies suggest that the osmotolerance of the organism may be more important in this latter regard (Breeuwer et al., 2003). The ability to be osmotolerant may increase the risk of the organism becoming more dominant in the environment, thus increasing the risk of post-processing contamination of powdered infant formula. Previous work done by Nazarowec-White and Farber (1997b) and others (Nazarowec-White, McKellar, and Piyasena, 1999; Iversen, Lane, and Forsythe, 2004) showed that standard pasteurization practices are effective for the inactivation of E. sakazakii. Edelson-Mammel and Buchanan (2004) showed that a greater than 4-log reduction can be obtained by rehydrating dried infant formula with water pre-equilibrated to > 70°C. This implies that preparing reconstituted formula using the latter approach (using 70°C for rehydration) is likely to result in a high probability that a serving would not contain this organism. Interestingly, there appeared to be two distinct phenotypes of E. sakazakii, and heat resistance varied as much as twentyfold (Edelson-Mammel and Buchanan, 2004). Figure 3 illustrates the difference in heat resistance and provides a comparison with other Enterobacteriaceae (Edelson-Mammel and Buchanan, 2004). A complete listing of D- and z- values can be seen in Table 3. In summary:
• There appears to be substantial diversity in thermal resistance among strains.
• Inactivation of the organism can occur very quickly at temperatures above 70°C. This suggests that the use of relatively mild thermal treatments is a potential risk reduction strategy that can be directed towards reducing or eliminating E. sakazakii in reconstituted powdered infant formula.
1 The Eurovent 4/4 standard has classified HEPA (high efficiency particle air) and ULPA (ultra low particle air) filters in five different classes, EU 10 – EU 14, based on the efficiency determined by using the Sodium Flame test. EU 10 exhibits 95–99.9% efficiency, while EU 14 exhibits >99.999% efficiency.