Joseph H. Hotchkiss, Ph.D.
The Guru of Active Packaging

Professor Joseph Hotchkiss is one of the nation’s leading experts in the relatively new field of active food packaging. Director of Graduate Studies in the Field of Food Science and Technology at Cornell University, Hotchkiss’ research efforts focus on the introduction of biotechnology to food packaging in order to improve the quality, taste and/or safety of the product within. Among the most recent successes of Hotchkiss’ research team: the development of a juice container that removes the bitterness from grapefruit juice while the product is enroute to the grocer’s shelf.

FoodTechSource: What is active packaging?

Joseph Hotchkiss, Ph.D.: There have been a tremendous number of technological advancements in food packaging over the last 15 years. For the most part they’ve concerned the development of better or more suitable barriers—and by barrier I mean a system of separating a food product from its environment to ensure freshness and quality. These innovations have allowed us to have all kinds of new products, such as single-strength, high-quality refrigerated orange juice—which would not have been possible without some real breakthroughs in packaging. It looks like a milk carton, but it’s actually very high tech. Nonetheless, these packaging innovations have all been passive in that they were simply an improvement of the barrier concept. Active packaging, on the other hand, focuses on the development of materials which in some way interact with the product to improve its quality, safety, shelf life and useability.

FTS: How long has the concept of active packaging been around?

Hotchkiss: It’s only gained any popularity in the last three or four years. So, it’s really quite a new area and not on the dinner table or in the grocery stores yet, except in some limited ways. But we believe it is the future of packaging.

FTS: It sounds very cutting edge.

Hotchkiss: We’re always trying to push the envelope. Right now we are concentrating on what we call bio-active packaging, in which we are combining advances in biotechnology with advances in material science, to bring some potentially innovative ideas to the packaging realm.

“Right now we are concentrating on what we call bio-active packaging, which combines advances in biotechnology with advances in material science.”

FTS: Such as impregnating polymers in the packaging with certain enzymes?

Hotchkiss: Yes. Adding enzymes to the interior packaging is a great example of that. Enzymes are very useful in processing foods, and in many cases they can improve the product. Our initial demonstration of this was to put an enzyme in a film material used in packaging in order to reduce the bitterness in a citrus juice.

FTS: How did that develop?

Hotchkiss: It was just an idea we had: How could we demonstrate that active packaging could improve the quality of a product during storage? We knew that citrus products generally have a problem with bitterness. So, we got the idea of introducing an enzyme that degrades the bitter compounds in grapefruit juice onto a film which was used to line the inside of the juice carton. To reduce bitterness, we introduced naringanase, which is an enzyme-derived fungus.

FTS: Why naringanase?

Hotchkiss: It turns out that the bitterness in grapefruits is due primarily to a common plant compound that has sugar molecules attached to it. Naringanase clips off those sugar molecules, effectively making the juice taste sweeter.

FTS: What kind of problems did you run into?

Hotchkiss: The main problem we faced was getting sufficient activity at refrigeration temperatures, which juices are commonly held at. We needed to increase activity per unit area of film in order to get sufficient interaction between the enzyme and the juice.

FTS: What sort of things did you try?

Hotchkiss: We focused on immobilization—tried a number of different supporting films that immobilized and held the enzyme, plus were economically viable and were approved for food contact. It was pretty much just trial and error. We were ultimately successful to the extent of demonstrating that you can incorporate an active enzyme into a film, and when that film contacts the product—even at refrigeration temperatures—it can improve the product vis-a-vis its taste, over what would be considered a normal shelf life for that product.

FTS: How precise was your control over the levels of reactivity? And are there scenarios in which too much of a reaction could prove undesirable—such as might occur if the product remained on the shelf too long?

Hotchkiss: I can’t think of one but I’m sure there are. But you can control that by controlling the amount of enzyme you attach to the film.

FTS: It’s more a function of area than time?

Hotchkiss: Yes. It’s a function of area, of loading of enzyme into the film. Of course, temperature plays a role, as does the nature and the pH of the product. So, you’ve got to look at each case. For example, if you wanted to remove lactose from milk, for people who are lactose intolerant, without adding the enzyme directly to the milk, you could incorporate lactase into the wall of the container and package the milk. If you had sufficient activity you could reduce the lactose concentration of the milk during shipment.

“If you wanted to remove lactose from milk without adding the enzyme directly to the milk, you could incorporate lactase into the wall of the container.”

FTS: What would the benefits be of adding it to the packaging?

Hotchkiss: For it to work, you have to add lactase directly to the milk. It’s always a problem adding something directly to foods because then people consume it. Or, instead, you could use an immobilized enzyme reactor, but those systems have not been particularly successful because they have problems with fouling and clogging up, and with bacterial growth, and relatively frequent regeneration times. So, active packaging might prove a beneficial alternative.

One could talk about controlled cholesterol reduction or adding other types of flavor-enhancing enzymes...you can think of lots of potentially good uses for enzymes in food. And with active packaging there’s no need to add the enzymes directly.

FTS: You can reduce a food’s cholesterol content with active packaging?

Hotchkiss: Well, there are enzymes that metabolize cholesterol, so, at least in theory it’s possible. I don’t know if anyone’s done it, but you could put a cholesterol-consuming enzyme in packaging material that, in theory anyway, would reduce the cholesterol of a product like milk.

FTS: Without altering the taste?

Hotchkiss: The beauty of enzymes is that they’re very, very specific in their activity. Typically they do not affect other components.

FTS: Are there cost-saving benefits to active packaging?

Hotchkiss: Cost is a funny thing when talking about enzymes and other products of biotechnology. Proctor and Gamble has put an enzyme system into a laundry detergent which breaks down cellulose so that it makes your clothes appear brighter because it takes away the fuzz that develops on cotton-based fabrics. If you can put that much cellulase in detergent and still sell it at a reasonable cost, through biotechnology it seems to me you can do almost anything.

FTS: What other research are you conducting?

Hotchkiss: The largest part of our work is in anti-microbial food packaging materials—packaging materials that do not add things to foods but in fact kill microorganisms in food. For example, we have worked with an enzyme called lysozyme which is most common to hens’ egg white. Lysozyme also occurs in human saliva and tears, and is fairly common in the biological world as an anti-bacterial enzyme. We have immobilized that enzyme into films and in fact it does kill certain kinds of microorganisms. Unfortunately it’s fairly selective in its activity, so we have been working with a biotechnology expert who’s altering its structure to try to improve its activity and its immobilization potential.

“The largest part of our work is in developing anti-microbial packaging materials that kill microorganisms in food.”

FTS: What are the potential applications?

Hotchkiss: Deterioration of foods is microbiological. So, if you had a good anti-microbiological packaging material, you might be able to influence the process for everything from E coli in apple juice, to spoilage microorganisms in milk, and on the surface of cheese, and in juice products and other beverages.

FTS: You only find spoilage on the surface of cheese?

Hotchkiss: For most three-dimensional solid foods, spoilage is a surface problem. For example, meat from a healthy animal is sterile. The microbiological spoilage is the result of contamination during handling. So, most meat contamination is a surface phenomenon.

FTS: So, theoretically an anti-microbial shrink wrap film could hold in check—or reverse—any mild contamination?

Hotchkiss: And you might stop the molds from growing on the surface of cheese.

FTS: Is this what they mean by scavenger systems?

Hotchkiss: I believe you are referring to oxygen scavengers, which are used to remove the oxygen inside the food container. That’s a fairly new technology. They also have systems to reduce moisture content.

FTS: How do they work?

Hotchkiss: If you want to reduce the oxygen inside of a package, the material most commonly used is compounded iron, which is placed in a packet and put in the container. The iron rusts, and as it does it absorbs oxygen. There’s a more sophisticated technology based on redox chemistry using certain chemicals that are incorporated either directly into films or sometimes bottle cap liners, such as those used to remove traces of oxygen from beers.

FTS: So, it slows the growth of microorganisms by reducing oxygen?

Hotchkiss: Yes. Oxygen poses a serious threat of food. One of the goals of active packaging is to try to come up with ways to stop oxygen from deteriorating foods.

FTS: How long it takes for your research to reach the grocery shelves?

Hotchkiss: As I said, we are in the business of answering the “what if” questions. Some of our ideas take a long time to develop and they never see the light of commercial interest. Other ideas, people pick up on and if they dedicate sufficient resources, within a year they can have a product on the market. For example, we developed systems for adding CO2 to dairy products, and that’s become standard practice in a very short period of time.

FTS: How does that system work?

Hotchkiss: Carbon dioxide is an inhibitor for certain kinds of microorganisms. So, we developed a system for injecting carbon dioxide directly into products like cottage cheese—below the level that you can taste, but still sufficient to be mildly anti-bacterial—in order to increase the shelf life.

FTS: By how much? Double?

Hotchkiss: By up to four times, depending upon the product.

FTS: What is the next development consumers are likely to see?

Hotchkiss: Time-temperature indicators will be the most obvious. There has already been a commercial system introduced by Allied Chemical as I recall; 3M has introduced some systems.... Most commonly they indicate, through color change, the temperature and time history of a product, and alert food handlers or consumers to the possibilities that food has been abused.

FTS: It’s an ingenious concept.

Hotchkiss: The idea is, they integrate time over temperature, which is really what you care about with food. At one temperature, food will last a certain period of time; raise the temperature a little bit and the food will not last as long. So, for example, as a consumer you may be buying a carton of milk without knowing that during transport it was stored for several hours unrefrigerated in the sun—which could cause problems. But if you add a TTI to the packaging you get a clear history of what happened to the product prior.

“None of this is really so important if you’re talking about canned green beans, which are made sterile during packaging. But the marketplace is moving away from that kind of food, and toward so-called fresh product.”

FTS: That’s probably more important today than in past because of growing consumer preference for non-frozen entrees and produce.

Hotchkiss: Exactly. We call these “extended shelf life refrigerated foods,” which are not sterile. In other words, none of this is really so important if you’re talking about canned green beans, which are made sterile during packaging. But the marketplace is moving away from that kind of food, and toward so-called fresh product, such as modified-packaged, high-moisture pasta. And it’s a trend that’s going to continue, because a lot of these products are simply better than their counterparts.

FTS: It certainly is an improvement over most microwaveable frozen food, which never quite made it up to home cooking standards.

Hotchkiss: I’m not so sure anything is ever going to equal grandma’s home cooking. On the other hand, grandma had a lot more time to cook than we have.

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