Food Preservation--Low-Tech Past, High-Tech Present and Future

Millard Food preservation--in other words, extending shelf life--has been a widely-practiced human endeavor since the days of cave people.  (Forget that sexist term "cave men.")  According to the website PartSelect, cave folk who lived in cold locations froze fish, seal meat, and other small animals by storing them on ice.  In warmer climates, drying was the ancient method of choice for food preservation. Later, to freezing, drying, and fermenting, the Romans added pickling and canning. 


In modern times, science has provided additional ways to extend shelf life, especially techniques, currently widespread, that can keep foods fresh longer in the refrigerator. Now, scientists are working on ways to extend the shelf life of foods that are customarily refrigerated, making them safe and tasty at room temperature for longer periods of time. Read on to discover the "supersandwich" with a shelf life, at room temperature, of 3-5 years!  But let's start with the somewhat high-tech processes that most consumers come in contact with regularly, though they may not realize it.


Reduced Oxygen Packaging (ROP)


 "Air is the enemy of food," a scientist once told me.  Like all generalizations, this one has some exceptions. However, in general, oxygen does increase chemical breakdown and cause microbial spoilage of many foods. What's one modern solution?  Reduced oxygen packaging.  Some examples in your grocery store today are cook-chill, vacuum packaging, and modified atmosphere packaging. 


Cook-chill is a technique that fills a plastic bag with hot cooked food from which the air has been forced out. The product is then closed by using a plastic or metal crimp. 


Vacuum packaging removes air from the package and then seals it so  that a nearly perfect vacuum is created.  The package is hermetically sealed, which prevents gases from entering or escaping.  The most common hermetic packages are foods in metal or glass jars.  However, our supermarkets now carry many foods that are already cooked, on plastic  trays covered with plastic, and not frozen.  Yet, they carry a "use-by" date of a week or two after the date they're  put out for sale.  These foods can be microwave heated in about 3-5 minutes, and, most people will agree, they taste better than frozen foods.


Modified atmosphere packaging (MAP) is another widely-used preservation method.  It replaces some or all of the oxygen inside a food package with other gases, for example carbon dioxide or nitrogen.  This technique can be used to extend the shelf life of many more products such as fish, pre-cut greens, cheese, bakery goods,  dried fruit, and nuts.  MAP has the additional benefit of reducing the amount of additives and preservatives needed to maintain safety and quality. 


There is one problem with reduced-oxygen environments: they can be conducive to the multiplication of some bacteria that don't "like" oxygen, especially the bacteria that cause botulism. To avoid this risk, it's important to keep these foods properly refrigerated.


High Pressure Food Processing (HPP)


When they call this technique "high pressure," they aren't kidding. It utilizes up to 87,000 lbs. of pressure per square inch!  That would crush a marshmallow or a strawberry, but many of the foods sold in today's American supermarkets have been subjected to this treatment, and the result is a tasty product that is safe and of high quality and that lasts (unopened) 2- 4 times longer than its untreated counterpart.


Millard (a company that processes many products using HPP) describes HPP as a "post-packaging, non-thermal, pasteurization method."  Yep, you got it right.  This procedure can actually pasteurize without heat. That's a big advantage because, when foods are heated to kill bacteria, the quality is diminished--for example, taste, texture, appearance, and nutritional value.  Products treated with HPP retain their natural freshness. Another benefit of this method of decontamination is that it cuts down on the need for preservatives and additional chemicals to fight the bacteria that cause spoilage or illness. 


What products have been treated with HPP?  The process has been used on cooked ready-to-eat sliced deli meats, guacamole, tomato salsa, applesauce, orange juice, oysters. (Hormel uses HPP for meat, and Cargill uses it for ground beef.)  The process is extremely beneficial for prepared foods, packaged deli meats, sausages, juices, dips, salsa, seafood, wet salads, salad dressings, fruits, and vegetables. Acidic foods are especially well-suited to HPP technology.  On the other hand, foods that contain no moisture and those that have entrapped air are not candidates for this process.


MAP and vacuum-packed products are HPP-compatible and benefit from the process since HPP provides additional microbial kill and extended shelf life.  The "use-by" date that consumers find on HPP products reflects the extended shelf life resulting from HPP processing. 


HPP cannot yet give us shelf-stable versions (ones that don't require refrigeration) of low-acid foods such as vegetables, milk, or soup because the process does not destroy bacterial spores that could cause illness. 


Here's a summary of the typical HPP procedure as explained by Ohio State University's Department of Food Science and Technology:  The product is packaged in a flexible container (plastic pouch or bottle) and put into a high pressure chamber.  The chamber is filled with hydraulic (pressure-transmitting) fluid, which could be water.  The pressure from the fluid is transmitted through the packaging into the food, usually for 3-5 minutes. (The photo accompanying this article shows Millard HPP equipment.)  After processing, the product is then refrigerated.


HPP has been used on food for a couple of decades now, and it keeps growing in popularity.  In 2008, about 450 million pounds of food treated with HPP was commercially available worldwide. 


Want to see HPP in action?  Click here to watch a video of the operation at the Millard facility.


The Almost Indestructible Supersandwich


"Food that Lasts Forever" is the utopian title of a March 12, 2012 Time magazine article. Why would we want it to last forever?  Considering the ever-expanding world population, many fear that the future food supply will be inadequate.  More immediately, there are many situations today in which it would be a wonderful convenience to have more food that could last, if not forever, at least for several hours or days without refrigeration. More importantly, to provide for the needs of troops in the field, shelf life extension of unrefrigerated foods would be a great advantage.


Lauren Oleksyk, leader of the food-processing, engineering, and technology team at the U.S. Department of Defense Combat Feeding Directorate described for Time "the indestructible supersandwich."  Its bread stuffed with pepperoni or chicken.  Sounds pretty ordinary, doesn't it?  But it's built to last for 3-5 years without refrigeration. To accomplish this feat, it's necessary to control all of these: moisture, atmosphere, and microorganisms.  The researchers accomplished all three by using water-absorbing ingredients and edible polymer film to keep the bread dry and by tucking "packets of oxygen-scavenging chemicals in the outer wrapping."  Furthermore, the packaging is made as impervious as possible, "with layers of heat-resistant polypropylene and metal foil."   This may not sound delicious and nutritious to those who want their sandwiches "natural," but it's progress. Don't be surprised if, eventually, supersandwiches are available to purchase for your supper. 


Time mentions many benefits that today's research on extending shelf life  may bring, for example, cutting the need to grocery-shop to only once a month, rarely having to throw out spoiled food,  and  being able to buy fruits and vegetables at a lower cost.  In the coming years, technology is likely to bring even more convenient, time-saving, (and, hopefully, money-saving) innovations to the goal of extending the shelf life of foods.   




Catherine N. Cutter, Ph.D., Pennsylvania State University, Dept. of Food Science


Time “Food that Lasts Forever” March 12, 2012


MIllard facility "Preserving Food Through High-Pressure Processing"


PartSelect “Food Preservation Basics" "High Pressure Food Processing Lab"


Department of Food Science and Technology, Ohio State University


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