Development basics for pasteurised, aseptic and similar products

The underlying objective of any thermal processing of beverages or liquid food is safety. Thermal treatments consist of heating a product and holding it at a desired temperature for a specific length of time in order to either pasteurise or sterilise the product. For many processes, the minimum log reduction of bacteria are set by the regulations. However, these are minimum requirements and are usually exceeded for many reasons, including attaining lower failure rates, longer shelf life, and product quality and image. However, these thermal processes also directly impact the quality and image of the product due to its reactions to heat.

Pasteurised products have the number of pathogens reduced to a level at which they are unlikely to cause disease when handled properly. They are generally processed at temperatures between 81-99°C, filled at refrigerated temperatures and must be kept refrigerated.

Aseptic products are sterilised and packaged into sterile containers under sterile conditions. They are considered shelf stable, meaning that they do not require refrigerated handling or distribution. Aseptic products fall into two categories - high acid and low acid.

High acid products have a pH ≤-4.6 and are typically processed between 102°C and 113°C.

Low acid products have a pH >4.6 and are generally processed at conditions above 138°C. Aseptic products have very long non-refrigerated shelf lives (typically 6-12 months).

In general, thermal processes for aseptic products have shorter hold times than those for pasteurised products (1-10 versus 16-30 s) but this is not a hard and fast rule. Minimum hold times for both pasteurised and aseptic products are determined by the required log reduction of bacteria.

There are also other processes related to but subtly different than traditional pasteurisation and aseptic processing and they can be quite significant. These include:

• ESL or extended shelf life is a process for processing and packaging that falls between pasteurised products and aseptic products. It applies the benefits of near aseptic packaging to limit contamination from that operation and thermal processing conditions optimised to maximise product image and shelf life. In simple terms, the product is virtually aseptically processed and is then filled into a near-sterile container. This results in a fresh-tasting product (product dependent) that must be refrigerated and has a refrigerated shelf life of up to six months. This is independent of product pH and, as a result, ESL products range from juices to soy milks and UHT coffee creamers. Correspondingly, the thermal process conditions used for these products range broadly.
• Hot fill: A process wherein a high-acid product is heated then filled into a container at temperatures of 82-93°C and then kept at this temperature for approximately one minute before being cooled. The combination of the heat and acidity of the product and residence time at these temperatures sterilises both the product and bottle. These products do not need refrigeration. This is often used for isotonics and juices.
• Low-temperature pasteurisation: Some products, such as yoghurt, are pasteurised at very low temperatures (174-85°C) but have very long hold times (often up to seven minutes or longer). This reduces the pathogens, while still maintaining the active yoghurt cultures. Liquid pasteurised eggs are also processed at similar conditions.

Considerations when selecting a processing style

Product market/end use of product (consumer versus institutional)

The desired market for a product is a strong determining factor in the choice of pasteurisation, ESL or aseptic processing. Pasteurised products usually have a fresher product image. Since they are sold in the refrigerated section, they require refrigerated transport and they are generally consumed at home or in facilities where refrigeration is nearby and immediate. ESL products also convey this fresher product image because they are sold in the refrigerator case and the process has been optimised to maintain as much quality as possible. The quality of these products is often very close to that of strictly pasteurised ones but is a function of how well the process was optimised to provide quality and shelf life and it varies widely by product. Aseptic products are often aimed at markets that require more convenience, such as when a meal is to be consumed away from home or to eliminate the need for an expensive refrigerator.

Matching seasonal demands and seasonal supplies

The choice of pasteurising, ESL or aseptically processing a product may be affected by the availability and/or demand of the product throughout the year. For example, the majority of eggnog is consumed within a period of about one month, so producers must build up an inventory prior to the demand. The process for eggnog must ensure its safety and provide the quality and shelf life needed to support the demand. Alternatively, orange juice is consumed year round, but the supply tends to be seasonal. To address this disparity, in addition to importing oranges, suppliers effectively use ESL techniques to process and handle the juice under conditions that ensure very long shelf life, both in refrigerated tanks at the facilities and in finished product containers for the consumer.

Market/distribution distance

If the supply of a product is centrally located but distributed over a large geographic area, there will be long transit times from the plant to many end consumers. Should the product be shipped refrigerated or should the product be aseptic so that it does not need refrigerated distribution? This type of question must be answered before developing a formula to ensure the product has the desired image when it reaches the end consumer.

Strictly pasteurised products provide the shortest refrigerated shelf life and often the best quality because it is a truly minimal process. This results in short distribution and very high quality. ESL products are an extension of these processes in which the overall process, thermal process, handling and packaging have been optimised for shelf life and quality. These products provide very high quality, often close to that of pasteurised products and longer shelf life and correspondingly wider distribution. Aseptic products provide the longest shelf life and widest distribution. Their quality is very good but the processes they require can’t be optimised to maintain the same quality as ESL products.

Ingredient cost versus product price point

An underlying requirement of any product is the ability of the consumer to purchase it at an acceptable price. There have been many excellent pasteurised and aseptic products that are too expensive to make and sell profitably.

Conversely there have been many products that are made cheaply and, thus, do not have an acceptable product image and quality for the market. Thus, when formulating products, researchers must work within a cost structure that enables the product to be purchased and a profit to be made.

Conventionally pasteurised products can use a wider assortment of ingredients than ESL and aseptic products because the process has less impact and it is not as critical to select durable ingredients. This is where a significant advantage of pasteurisation lies. It allows use of a wide assortment of high-quality and lower-cost ingredients to produce a premium product that could be very difficult to make as ESL and aseptic products.

Reactions of a formula to the process

When formulating a new product, or reformulating an existing one, researchers must work towards a goal of a desired product identity. Because the product will be thermally processed and this directly affects the product identity, the process must be integrated into product development. Failing to do so will likely produce a desirable product from the laboratory that requires considerable effort to reproduce at the manufacturing facility.

There are both desirable and undesirable reactions that affect a product’s image.

Desirable reactions include:

• Protein denaturation (eg, enzyme inactivation, trypsin inhibitor inactivation in soy products)
• Starch hydration to generate viscosity
• Gum activation to generate viscosity or suspend solids
• Flavour development (ie, a roasted coffee flavour)
• Texture development

Undesirable reactions may include:

• Protein denaturation
• Improper thickening (too thick or too liquid)
• ‘Off’ or burned flavour development
• Loss of flavour
• Gritty or grainy texture development
• Colour changes or loss of colour
• Loss of nutrients (vitamins, protein content, etc)
• Loss of physical stability

Virtually all ingredients react, to some degree, to thermal processes. However, based on the above-listed reactions, the most reactive ingredients tend to be:

• Starches - hydrate over time when heated and thicken when cooled
• Gums - activate and then thicken when heated
• Nutritional ingredients - vitamins, minerals, proteins, etc
• Flavours
• Colours

Integrating the process

The reactions that influence a product’s image are largely fuelled by the formula’s reaction to thermal processing. Hence, the processes used in product development must truly represent the commercial process. If they do not, the product image at the production plant will not match that of the product developed in the laboratory.

To integrate the commercial process into research, small-scale processing equipment is often used. Purchasing or leasing this type of equipment requires an initial outlay of capital. However, the cost of the alternative processing methods, reformulations and lost time far exceed the cost of the equipment. Considering that trials at the manufacturing level often cost tens of thousands of dollars and require significant administrative efforts and weeks of preparation, selecting the proper and accurate processing system for the laboratory can accomplish considerable cost savings. Bringing the process into the laboratory can greatly accelerate research and provide a decisive competitive advantage.

When considering research processors, the actual process conditions of the entire commercial process (heating time, homogenisation conditions, hold time and temperature, cooling time, etc) not just the hold time and temperature must be taken into account. This is called a time/temperature history. the time/temperature history of the research processor must be able to match the processes of the production plants.

There are also many other important considerations that should be taken into account when sourcing research processing equipment and selecting a vendor, such as:

• The convenience of the equipment and ability to conduct processing trials quickly and make safe samples for taste panels and shelf-life studies.
• The ability of the equipment to process a range of products
• High versus low acid, thick versus fluid products
• The ability of the equipment to conduct a range of processes
• HTST, UHT, direct steam injection versus indirect heating, hot-fill, etc.
• The ability of the equipment to integrate other unit operations
• In-line homogenisation, deaeration, sampling, hydration loops, etc.
• Filling capabilities - ability to simulate aseptic filling
• Maintenance requirements and durability of processing equipment
• The type and extent of technical support offered by the supplier of the equipment
• Other services available from the supplier of the equipment
• The processing experience/knowledge of the product development staff

Equipment suppliers or engineering firms offer products and services to address some of these considerations. Other organisations, such as universities, may be able to address some of the remaining considerations. However, comparatively few specialise specifically in thermal processing. One source of solutions to these issues is MicroThermics. They specialise in continuous thermal process for HTST, UHT and aseptic and ESL processes and process simulation in the food industry. Using advanced mathematical and design techniques, their processors have the ability to provide the heating styles and times (time temperature histories) found in commercial processing plants. Additionally, they offer a range of integrated processes such as vacuum cooling, deaeration, homogenisation, data collection and even custom filling.