“Before I state the details of my process, I ought to observe that it consists principally,
1st. In inclosing in bottle the substances to bepreserved.
2nd. In corking the bottle with the utmost care; for it is chiefly on the corking that the success of the process depends”
3rd. In submitting these inclosed substances to the action of boiling water in a water-bath (BALNEUM MARIAE), for a greater or less length of time, according to their· nature, and in the manner pointed out with respect to each several kind of substance.
4th. In withdrawing the bottles from the water-bath at the period prescribed.”
These observations made by Nicolas Appert described, probably by first time, preservation methods, in his case by heating, of packaged food products. At the same time, he stated in his treatise “The Art of Preserving All Kinds of Animal and Vegetable substances for Several Years”, the importance of packaging when food is preserved post-packaged. Since then, packaging became an essential part of the preservation methodology.
Although his observations were done two centuries ago, the relationship packaging-preservation method (and its impact on food quality) can be applied in current technologies, including High Hydrostatic pressure (HPP).
Cans, glass, paper-board… could be used for HPP?
Packaging in HPP processing is subjected (jointly with the food) to high pressures (around 400 – 600 MPa / 58,000 – 87,000 psi) using water as a pressurization fluid. Thus, packaging materials must (1) be water-resistant. Packaging will contact with pressurization water during the HPP cycle. On the other hand, during pressurization, water reduces 15% – 18% of this volume which is recovered when HPP cycle is finished, therefore (2) the reversible response of the whole package to compression is crucial to the success of the HPP processing.
So, packaging materials are required to be flexible enough to withstand the mechanical stress caused by hydrostatic pressure while maintaining physical integrity. Due to their good flexibility, elasticity and water-barrier characteristics, plastics are commonly used in HPP products. Other materials such as paperboard-based, metal cans and glass bottles are not well suited for HPP: They are not able to recover the shape and size after HPP and because of their lack of water and pressure resistance.
What polymers are HPP suitable?
The performance of plastics under HPP conditions are widely described in literature. Juliano and collaboratorsand Caner and collaboratorssummarized the effect of HPP on polymeric materials. They provide a valuable tool for preliminary selection and evaluation of polymeric-based materials for HPP. However, Hiperbaric encourages testing each packaging at actual/expected HPP conditions in order to assess the suitability of the materials for each food product.
Besides good mechanical, sealing and barrier properties, all packaging material in HPP products must fulfill national or regional regulations about food-contact materials and migration. Food and Health authorities from Europe, USA, Canada and other countries offer guidelines and further information about this topic.
The shape and size doesn’t matter in HPP technology…
In HPP, pressure is transmitted in a quasi-instantaneous manner throughout the food product (known as Pascal’s law). Thus, there are no significant gradients of pressure, regardless of the size and geometry of the product. The latter makes HPP technology suitable for processing different kinds of food products in different types of packaging such as bottles, pouches, trays, cups, bags (even big bags for the foodservice market).
… well, actually they do
Since the technology is effective despite of the design of the packaging (good news for design and marketing teams), size and shape play a relevant role in productivity. The productivity in HPP (as other batch operating mode technologies) is closely related to how many products can be processed per time unit (the more, the cheaper… the better). The quantity of product to be processed in each batch will depend on packaging design, as well. Thus, packaging design will play a primary role in marketing and production decisions, influencing on product’s convenience and attractiveness to consumers and on filling ratio (the proportion of volume of product in one batch divide by the capacity of HPP machine). The higher filling ratio, the higher HPP production per cycle.
What happens with MAP in HPP?
Modified atmosphere packaging (MAP) is a technique used in order to improve shelf-life of foods by replacing air with other gases such as nitrogen, carbon dioxide and carbon monoxide, or their mixtures. Sometimes consumers perceived MAP-packaged food products as fresher, being processed by HPP, as well. The synergy between MAP and HPP remains unclear and strictly product-dependent. However there are available MAP-packaged products processed by HPP in market around the world, mainly meat products, but this choice is mostly made on marketing/product presentation decisions.
Due to the fact that gases are very compressible under high pressure, more headspace involves lower productivity in terms of kg per hour, because part of the volume is occupied by gases which must be compressed. On the other hand, the higher headspace the bigger deformation strains on the packaging materials. Hiperbaric recommends keeping headspace as small as possible.
Hiperbaric considers packaging an essential part of the success of HPP technology, impacting directly on marketing, productivity and product’s acceptance of HPP products. We will be pleased to support you throughout packaging selection and the design of your HPP products.