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While drinking a glass of freshly made orange juice a little while ago I noticed orange juice is a great vehicle for explaining all sorts of science related phenomenon. This last post in its series is all about orange juice packaging, using some of the principles discussed in earlier posts on spoilage of orange juice and vitamin C oxidation.
Packaging of food by itself is a fascinating science and topic to discuss. Besides it being very important in determining whether someone will actually buy your product (nice bright colours, recognizable logo, trustworthy appearance), it can also greatly improve the quality of a product. A piece of meat without a vacuum pack wouldn’t last as long as an unpackaged piece would, a hermetically sealed pack of crackers will keep them crisp and crunchy for a longer period of time. Orange juice is a great example to discuss this topic on since there are so many processes involved.
There are a lot of reasons orange juice might be considered ‘over date’. It can be due to browning of the juice, which causes it to look less appetizing, clouding of the juice or downright microbial spoilage (growth of micro-organisms). We’ll start by discussing the latter.
Preventing moulding of orange juice
As discussed in my post on moulded orange juice, orange juice can spoil pretty badly. The high sugar content (= food for micro organisms) and sufficiently mild pH make it a great place for, amongst others, moulds to grow. Pakaging plays a very important role in preventing this spoilage.
Most orange juices have been heat treated, pasteurized, to kill off most micro-organisms. A heat treatment is however only effective if there is no chance for micro-organisms to re-enter the orange juice. This is where the choice of packaging starts playing a role.
If a package is heat resistant it can either be filled with the hot orange juice, or the orange juice can be heat treated in the package itself. Metal cans and glass bottles are examples of packaging which can withstand enough heat to do this. By filling the package with hot orange juice of by heating the juice in the package the package itself is heat treated as well, limiting the chance that the package re-introduces micro-organisms which might cause spoilage of the drink again.
If a pack cannot withstand the heat it will have to be filled with cooled juice in an aseptic manner. This is generally the case for cartons or plastic packaging.
Taking oxygen out
Orange juice manufacturers do not like oxygen in their orange juice. There are actually various reasons for wanting to keep it out. The first is that oxygen is required for the oxidation of ascorbic acid (vitamin C), keeping out oxygen will greatly reduce vitamin C losses during storage.
Another reason, which is actually linked to the oxidation of vitamin C, is that oxygen can induce browning of orange juice. This is a non-enzymatic example of browning and has been associated with the Maillard reaction (read more here if you’d like to know more hard-core Maillard chemistry!).
As discussed in my post on using orange zest or orange peel in recipes, oranges contain quite some very aromatic oils. These oils can often also oxidize with oxygen, causing unwanted off flavours, as is the case with olive oil.
All in all, enough reasons to keep oxygen out. Manufacturers start tackling this issue when packaging the oxygen. They will generally de-aerate the juice, taking out all the oxygen. However, taking all oxygen out at the start isn’t sufficient, oxygen shouldn’t be able to come in during storage either.
Keeping oxygen out
You might think that all packaging you’ve seen in the shops will keep out oxygen: glass, cans, cardboard, plastic. This is, however, not the case at all! Glass and metal cans are good in keeping out oxygen, they have advantageous so-called ‘barrier properties’.
Cardboard and plastic on the other hand often aren’t as good in keeping oxygen out. Therefore, manufacturers will use more complex materials, often consisting of several layers of materials. Each material will have its own role in the package. In the case of carboard, a layer of aluminium foil is often used to prevent oxygen migration into the package. Of course, cardboard packaging will generally also contain some sort of plastic layer(s) at the outside.
For plastics the use of aluminium is not always an option since it can interfer with the transparency of the pack. In other cases (such as the flexible drinking packs from CapriSun) it is less of an issue. When no aluminium foil can be used, a combination of different plastic types is used which each have a slightly different property. EVOH (a common ploymer plastic) is considered a good material for imporving the barrier properties of the pack. In the case of PET bottles, multilayer PET is used, which means that various layers of PET have been made into one, which seems to work better than one layer of the same overall thickness.
Did you notice though that a lot of plastic bottles aren’t just closed using a plastic cap, but also by using an aluminium seal? There you go, you now know why that’s there!
Actively keeping oxygen out
Using a suitable pack for keeping out oxygen is often defined as being a ‘passive’ method. However, new developments have led to the discovery of components that can actively bring down the oxygen content in a pack. This could be oxygen that is already there at the start, or oxygen that comes in during storage. These are so-called oxygen scavengers.
There are several known materials which can ‘fight’ oxygen when they are present in the packaging material. However, there are still discussions on whether all of these are safe and the search is continuing for more natural alternatives. Nevertheless, such active components woulds make life a lot easier for orange juice packers.
Importance of the package for marketing & sales
During my search for interesting articles on the topic, I ran into one that isn’t linked to the safety or quality of the product itself. Instead, it focusses solely on the perception of customers when they see a package of orange juice. Apparently Tropicana, a huge orange juice producer in the US, decided the completely overthrow their packaging. They didn’t change the material or type of box (as far as I could find), only the design. However, this resulted in a huge failure, causing a great downfall of the sales of the orange juice and requiring them to switch to the old design within weeks again. Read a more thorough analysis here and here, I found it fascinating.
It shows again that packaging isn’t necessarily there to protect the product, it’s certainly also there to sell the product.
There are some great resources there out on the web on packaging of orange juice, it’s a topic discussed quite often. Here’s some of them which you might find useful:
Research on the use of PET packaging.
Interesting article on why the type of packaging used for juices is a lot hard to get to work for a product like beer.
Robertson, G.L., Food packaging and shelf life – a practical guide, Chapter 10 Packaging and shelf life of organge juice, 2010, CRC Press, link
Trends in packaging: Beverages 2015, 1, 248-272; doi:10.3390/beverages1040248