Tara McHugh, Ph.D.—
New, Incredible Edible Packaging Films!

Tara McHugh, Ph.D., is a research food technologist with the U.S. Department of Agriculture, Agricultural Research Service (ARS), working out of the Albany, California, Western Regional Research Center in the Process Chemistry and Engineering Research Unit. Her lastest project is the development of an edible film food wrapping, made from a puree of fruits and vegetables, which can be used to extend the shelf life of fresh produce while improving its overall nutritional value. Dr. McHugh first became interested in edible film technology at University of California, Davis, where she did her Doctoral dissertation on whey protein edible films.

FoodTechSource: First, can you describe for us the product you’ve developed?

Tara McHugh, Ph.D.: It is an edible food wrap—in sheet form—made from 100 percent fruits and vegetables. What we’re starting with are purees—ground up produce. Normally purees are manufactured commercially in a concentrated form. However, in the lab we dilute them with water and plate them out on flat surfaces and allow them to dry at ambient temperature. The solutions form films that are very flexible and in fact have good oxygen barrier properties. They can be formed from strawberry, peach, apricot, pear, apple, broccoli, or carrots, a whole variety of fruits and vegetables.

FTS: How did you come up with the idea to produce edible wraps in this way?

McHugh: I think it’s best to start with the simplest process and see if it works. So we just tried it out and sure enough it did work. The purees formed nice films, which is apparently because of the long-chain carbohydrates naturally present in the purees—the cellulosic and pectic compounds in there that provide the structural matrix for the films.

“The edible wraps are as thin as paper: 0.1 mil thick. The cellulose compounds provide the structural matrix.”

FTS: How thin are the films?

McHugh: They’re as thin as paper: 0.1 mil or so. They can be thicker as well, but we prefer to work with rather thin film because it is more flexible. This allows us to wrap a wider variety of products.

FTS: How strong are the film wraps?

McHugh: We haven’t quantitatively tested the mechanical properties, but they’re fairly strong. They’re certainly strong enough to maintain their integrity when wrapping a food product with them. They are not as strong as paper, though.

FTS: The obvious comparison would be to some sort of plastic wrap.

McHugh: Right. They’re not as strong as plastic wrap. There are ways that we can strengthen them and we’ve worked a little bit on that by adding substances to improve the mechanical strength. But our role as a government agency is to develop the technology to a certain point and then look for a cooperator to transfer the technology to. We then work on a specific application with them, and we find the specific technology to meet that need. So we don’t necessarily develop final products here, we develop the technology then refine it in cooperation with an outside group.

FTS: I’ve heard of dipping produce in edible coatings. Is this different?

McHugh: Yes. It’s different than most applications of edible films in the sense that previously most edible films or coatings served as invisible barriers, while we feel it will be beneficial for the consumer to know he or she is obtaining additional fruits or vegetables in their diet through this film source. So our films are thicker than what a coating would be, and they are intentionally visible rather than being invisible.

FTS: How does that effect the look of the product?

McHugh: It changes the look of the product. If you are using a strawberry film, which is red, and you wrap it around a food product, the produce is going to be seen through a red tint. With carrot or peach the tint will be orange, and with broccoli, green. So it’s not at all invisible. It’s a different approach.

FTS: As I understand it, the film can also be used as a flavor enhancer, correct?

McHugh: Exactly. You could wrap a steak in it, for example, and potentially the film would melt during cooking and form a glaze. So there are definite advantages: adding new flavor and color to the food product, and extended shelf life due to barrier properties.

FTS: But I thought you said that as a barrier it is not very effective...?

McHugh: It is effective enough to extend shelf life. You see, we’re not looking to replace the synthetic package that would otherwise be protecting your food. That is for food safety reasons. You still want to cover it with packaging because if you want to consume the fruit wrap you wouldn’t want everyone in the store handling it... But potentially the wraps, when used in conjunction with a synthetic film, could enable simplification of the synthetic package into a form where it could be made biodegradable. Often, synthetic packaging is not biodegradable.

FTS: Are there any other benefits?

McHugh: It allows the use of off-grade produce: fruit that is too small for the fresh market or for canning. It also allows you to use mechanically harvested fruit more easily. And since we’re working from a puree, another advantage is that fruit could be processed and held in the stable puree form for many months—until well into the off-season when it could be processed into films. And that can help reduce some of the seasonality of employment in agriculture.

FTS: What are the oxygen barrier properties of the wrap?

“The wraps are comparable to fairly good synthetic oxygen barriers, but they are more hydrophilic so the permeability properties are effected by relative humidity. ”

McHugh: The wraps are comparable to fairly good synthetic oxygen barriers. But they vary from synthetic barriers in that they are more hydrophilic so the permeability properties are effected by higher humidity. As you expose the film to higher humidity the barrier properties lessen. That is different than synthetic film properties. So any test results would need to be qualified depending upon what relative humidity is present.

FTS: So it would be good in Los Angeles but not Hawaii?

McHugh: Well, once again you’re going to have an external package around it so that’s going to provide your primary moisture barrier. The other thing we’ve looked at is adding different lipids, or fats, to help with this. And although the film would no longer be 100 percent fruit or vegetable the lipids improve the water barrier properties and reduce the effect of relative humidity.

FTS: Have most of the tests you’ve run so far been for moisture content?

McHugh: Some of the tests we run are just basic tests, such as to determine how permeable the film is to oxygen or water vapor. We have also done basic application tests in which we wrapped a piece of fresh-cut apple to test for moisture loss of the apple piece and browning of both the wrap and the apple. We found that the films were very good at reducing the amount of browning in the apple. Also, the films are more effective than dipping or spraying the apple with the same solution. In other words, if we add 100 percent puree and dip an apple piece in that, then formed a film from the same solution and wrapped the apple, the wrapped apple piece had a much longer shelf life than the dipped apple piece, and both had a longer shelf life than the uncoated apple piece.

FTS: How quickly does the film wrap brown?

McHugh: Well, these edible wraps will still be wrapped in an external package so that’s going to have an effect. But when exposed to the environment, it only browned a little bit. With fresh produce you’re dealing with a couple weeks’ shelf life, and the film browned a bit but still looked very acceptable.

FTS: Was one wrap more effective than another?

McHugh: In general the vegetables formed a slightly better water barrier than the fruits, but once again by modifying the total composition of the film they’re all in the same ballpark. So depending on the application and the marketing information, you could develop an effective barrier from any of the fruits or vegetables. You just might have to add more lipid or modify it in a certain way. But in general the vegetables were more effective and that’s probably because they contain lower concentrations of sugars.

FTS: Aside from adding ingredients, is there anything else you do in the process that is unique?

McHugh: Well, if we add lipids then we try to mix them in a variety of ways, depending upon the melting point of the lipid—sometimes you need to heat lipids up to incorporate them.

FTS: And to form a puree you just whip it up?

McHugh: Right, you grind up your fruit or vegetable. Then, as I mentioned, you plate it using a casting procedure at ambient temperature. But commercially you wouldn’t go about it that way. In a commercial setting you’d want to, at the very least, dry these films at an elevated temperature so they would be more efficient, and/or look at extrusion to produce the films in a continuous manner—which is one of the things we have taken a look at as well.

FTS: Does that look promising?

“In a commercial setting you’d want to dry these films at an elevated temperature so the process would be more efficient, and/or look at extrusion to produce the films in a continuous manner”

McHugh: Yes, there’s no problem with doing that. But still, in the lab or at home you could do it in this easy casting way.

FTS: Would you mind if I ask you a few questions about the Agricultural Research Service? It’s not often we have the chance to speak to somone who works for the research arm of the USDA.

McHugh: Not at all. I work at the Western Regional Research Center. We have approximately 150 employees working here, so it’s a fairly big center. We’re one of four such centers located across the country.

FTS: At a research level, how does the ARS function?

McHugh: We perform agricultural research that is in the interest of the nation. The project we work on focuses on increasing the utilization of fruits and vegetables, and on trying to help ease the seasonality of employment in agriculture. We also focus on helping the country meet the minimal nutritional requirements as established by the USDA. All of the projects within ARS strive to meet the nation’s needs for agricultural-related research.

FTS: Do you collaborate with universities?

McHugh: Yes, we work in collaboration with universities from time to time, and we’ve also collaborated with the private sector. One of the mechanisms we have to transfer the technologies we develop is through cooperative research and development agreements (CRADA) with private industry and universities.

“One of the mechanisms we have to transfer the technologies we develop is through cooperative research and development agreements (CRADA) with private industry and universities.”

FTS: How do projects get accepted?

McHugh: Some projects come down from a Presidential initiative, and some projects come internally or from growers’ groups. But all of the projects must be written up in fairly extensive project statements and sent out for review by industry, government, and grower’s organizations in the agricultural sector; they’re reviewed for their scientific quality and importance or relevance to the nation’s agricultural needs.

FTS: So, do you have to lobby for a project you might want to work on?

McHugh: No, we’re not allowed to lobby; the project statements are sent out and we don’t know who they go to. It’s a blind review panel that reviews the projects. They come back with feedback, and we modify the project based on that review process.

FTS: Say someone has an idea...

McHugh: What we would do is talk about our mutual interests and then most likely enter into one of these CRADA cooperative agreements. However, we’re not a contract lab, either. So you couldn’t come to us with an idea that didn’t relate to our current research and have us work on that. We can enter into a CRADA but they must relate to a current program.

FTS: What would you do if there was someone who came up with a great idea comparable to a cure for the common cold but they did not have the research facilities? Could they approach the USDA through the ARS?

McHugh: They could come to us and we could try to find someone working in a similar area that would be a better person to talk to about the idea. But we work on projects related to our base program only.

FTS: Thank you for your time.