The fundamental design principles of hygienic systems remain the same whether producing pharmaceuticals, vaccines or food and drinks. Controlling product quality and possible contaminants is foremost in the processing and engineering design approach to ensure that the product is safe for use.
Contamination sources can be grouped into three main categories: physical contaminants, chemical contaminants and biological contaminants which includes microbial contaminants.
Physical contaminants may be introduced to the process via raw materials, packaging, the surrounding environment or from the manufacturing equipment.
The simplest barrier to physical contamination is to use closed process systems wherever possible. Separation techniques such as filtration, sieves and centrifugation are used routinely to control this. Additionally, human interventions are ideally kept to a minimum to avoid contamination from hair, skin particles and contact with clothing.
Nuts, bolts and equipment seals are commonly captured by strainers and filtration steps; however, particles of glass or ceramics are more difficult to control, so should be strictly avoided within the processing environment.
The simplest barrier to physical contamination is to use closed process systems wherever possible
Chemical contaminants may arise from a number of sources such as raw materials, lubricants, materials of construction of the process equipment or components failures.
Raw materials are routinely tested against their specification before use, but contamination is not uncommon. From an engineering perspective, chemical segregation of storage vessels and the design of offloading goods should protect against mix-ups, and this is normally achieved by a mixture of procedural steps, physical elements (e.g. dedicated hoses and storage vessels for each chemical) and automation checks to monitor process operations and parameters.
When selecting equipment and instrumentation, a key consideration is that the materials of construction do not contaminate the process and are suitable for the processing conditions. This is one of the reasons why stainless steel and elastomers such as EPDM are used extensively due to their chemical resistance and inert nature.
Instruments filled with lubricants and oils should be selected to be food grade in case the instrument fails, and the lubricant enters the foodstuff.
316 L Stainless steel is primarily used for product contact parts due to its good chemical resistance to corrosion and cleanability; although it may not be suitable for use in systems where high concentrations of chloride ions are present routinely (e.g. from salt or hypochlorite solutions). 304 stainless steel is routinely used for non-product contact parts such as skid frames and furniture but is much more susceptible to corrosion from cleaning chemicals.
In this instance alternative alloys such as AL-6XN or Hastelloy may be used, or polymers such as PTFE which do not leach chemicals into the process over time.
Microbial contamination is probably the major concern when processing foodstuffs. Organisms including Salmonella, Listeria, E. coli and Clostridium must be stringently controlled at all times. Hazard Analysis and critical control point (HACCP) evaluation of processes is used to identify the critical processing steps and parameters. In most cases a combination of osmolality, pH, temperature and physical separation techniques are used to control microbial levels within the product.
Plant ‘cleanability’
Plant ‘cleanability’ is foremost when designing a food facility. Cleaning is used to ensure there is segregation between each step of the process and between each individual batch of product.
To avoid cross-contamination, the equipment is selected so that it can easily be cleaned and drained between batches. Pipework is normally constructed from stainless steel and is smooth and crevice-free to ensure that microbes and processing materials are guaranteed to be cleaned-out between batches.
Hygienic pipework fittings, valves and instruments are all designed so that they can be subjected to cleaning with hot solutions of alkalis and acids; and provide a suitable barrier to microbial contamination from the external environment via their seal design.
Cleaning is used to ensure there is segregation between each step of the process and between each individual batch of product
Many of the hygienic systems such as triclamp, IDF and ISS have been established for many years as they were developed for use
in the traditional bioprocessing industries such as dairy, brewing and drinks manufacturing.
Clean in place (CIP) and steam in place (SIP) are routinely used to clean and sanitise plant. CIP relies on pumping hot water and chemical solutions through the equipment at a sufficiently high velocity to ensure turbulent flow which, in-turn scours the soiling materials from the pipework and removes any biofilms that may have become established.
Spray devices such as Sprayballs and high-pressure rotating spray nozzles are used extensively within equipment and vessels. These are selected to ensure all parts of the equipment product contact surfaces are consistently in contact with cleaning solutions. Large variations in pH are used during cleaning cycles and achieved by using strong acids and alkalis, which destroy and remove microbial contaminants, so this must be considered when selecting equipment materials of construction.
SIP and ultra-heat treatment (UHT) steps may require temperatures up to 140 degrees C and pressures of 1 to 3 Barg; so, the equipment systems must be designed to safely operate at these physical conditions.
The time-temperature heating and holding cycles for these systems have been developed over may years based on the kinetics to consistently denature (i.e. kill) the spores for an exceptionally heat-tolerant microbial organism Bacillus Stearothermophilus with the level of microbial kill being measured in the log reduction of viable organisms post heat-treatment.
Both CIP and SIP rely on there being no ‘dead-legs’ or crevices within the equipment and pipework where the cleaning and sanitisation cycles are not able to reach, or fluids may collect between batches. Hygienic equipment, valves, instruments and fittings are used to combat this, and all pipework and equipment is designed to fully drain between process steps to avoid stagnant pools of liquid where microbial growth can occur, or uncontrolled fluid or material carry-over into the next process step or batch.
In summary, hygienic process design has evolved over many decades from the traditional bioprocessing industries such as dairy and drinks manufacturing.
For the food industry the accepted design standards are set out by the EHEDG, but more widely the ASME BPE Bioprocessing standards are used across all the related sectors of bioprocessing such as food, pharmaceuticals, biotech and vaccines manufacturing.
Hygienic design is rooted by fundamental physical, chemical and biologic scientific and engineering principles to robustly control unwanted product contamination; and ensure that product safety can be consistently guaranteed batch after batch.
