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Dr. Ted Labuza on Slime, Bombs and Rot

The views expressed are those of the author and are not necessarily those of Scientific American.


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It’s not that I thought food science was boring before I interviewed Ted Labuza, Morse Alumni Distinguished Teaching Professor of Food Science and Engineering at University of Minnesota, but let’s just say that before our phone conversation last week, I had no idea how fascinating, nor dangerous and important, some of the food issues he’s devoted his life to have really been.

He’s an expert that NRDC has consulted with in preparation for our most recent report on food waste, The Dating Game, which comes out today. The premise of the report is that a confused dating system for foods in the US leads consumers to prematurely discard edible food. I talked to Dr Labuza in pursuit of some more information about why food rots, and more importantly, how to get the most bang for my buck by how I store and take care of my food.

What exactly is food science? What is food engineering? How did you get into that line of inquiry?

I went to MIT as an undergraduate. I started out with nuclear physics. I wanted to learn how to make a big bomb. I had a laboratory in the basement of my house where I synthesized trinitroglicerina and mercury. Today that would put you in jail. In those days there was no such thing as terrorism. I got a job working in a Cobalt 60 irradiation facility and met some people from the military who were studying, with a professor in the food engineering program, the irradiation of beef. This was in 1958. He offered me a scholarship for the next three years so I switched into food engineering. Sort of serendipity.

Going from bombs to food.

Right. Food science, food engineering is the study of the chemistry, microbiology, and the processing and engineering of foods. It’s a very broad field. When somebody gets a degree in food science, they take basic physics, organic chemistry, math, calculus courses and so they become, possibly, a jack of all trades.

What kind of stuff have you studied during your career?

Right now there are two major areas I’m working in. One is protein aggregation, the reaction that causes proteins to bind together. In foods and in drugs, when that occurs, say for a protein bar, it causes the bar to harden over time without any change in moisture content, and then becomes too hard to eat.  I worked with a company that was making dry inhalation insulin so you wouldn’t have to inject yourself. Over time, the insulin molecules reacted with each other and would not dissolve in the lung, and were causing granulosus. The FDA had to take that product off the market until we solved that problem.

The other area is working with the Department of Homeland Security on how we can inactivate bioterror agents. Let’s say a milk silo is intentionally contaminated with anthrax spores. How can we process that milk not to be eaten, but to get the product to disposed of? With Homeland Security we’ve been developing rapid testing so a plant could test in 20 minutes to see whether there’s a bioterror agent in it.

What happens in food when it rots? Why does food go bad in the first place? What, scientifically, does refrigeration do to food that helps it keep longer?

Rotting happens in high-moisture foods; the meat, fish, vegetables, fruits, nuts. The products we keep in a refrigerator. There’s two mechanisms to rot. Once you slaughter or cut the plant off the tree, its metabolic processes are still going- it needs to use up all the sugars within the plant itself, and once those sugars are gone then it goes into anaerobic metabolic process that produces acids that produce soft, thick tissue. An apple is no longer nice and crisp because enzymes are breaking down connections between cells, which produces off-flavors. That whole process is called senescence. It’s like us as we get older- we senesce.

The other main mechanism is when you cut up things or take them off the tree or the vine, there’s a potential for microorganisms to get on the surface and cause the product to begin to rot from the outside. You get slime production on meat or fish- organisms growing on the surface and producing bad odors you can smell. Most of those organisms are not pathogens; as they grow faster they actually prevent pathogens from growing. You can control these by pasteurizing or sterilizing. The safest foods around are canned foods- they have at least seven years shelf life but nobody wants to keep a can around for 7 years.

Why do they have such a long shelf life?

You sear them at a temperature that kills all microorganisms. The most important are the ones that create spores- these are microorganisms that save their DNA in a little hardbody that looks like a dust particle. At some point after a heat shock or a stretch, those spores regenerate into a cell; the bad ones produce a toxin that can kill. We process canned foods to a temperature necessary to inactivate 1 million times 1 million spores- 10 to the twelfth spores. Nothing else can grow; you’ve inactivated all the enzymes that would cause senescence, you’ve taken out most of oxygen from the can. The main thing that will cause it to go bad is if it’s hanging around in a human environment, rust can go from outside to inside or somebody can dent the can.

Any processing decreases nutrients from food- the worst is a 20% loss in nutrients. If you don’t process, it’ll rot, so you have a wastage of food. It’s a tradeoff. When people started moving into cities, that’s when food processing began. You had to have food that was available all year round. It started in Rome. Food has an interesting history.

Can people get sick from drinking milk or eating yogurt that is past their “best by” dates?  What about other foods?

I have a personal experience with that. I went to a fast food place in downtown Minneapolis in a mall area, and ordered a roast beef sandwich and a container of milk. I didn’t smell it or anything and tossed it down, and it was spoiled badly. The odor caused a reaction that caused me immediately to throw it up all over the table and all over myself. That doesn’t kill you or make you ill, but the odor response the brain gets causes an immediate reaction. If the food rots generally, the microbiology is such that microbes that spoil are outgrowing anything that could be a food poisoning organism. If the bad microbes are there, the fact that you throw it right up means everything comes right up and you’re not going to get ill.

A yogurt company recently had to recall their product because there was a mold that made it through the process and was fermenting the stuff- it was fizzy like beer or champagne. Nobody got ill, but the company did take it off the marketplace. If people ate it they threw it up.

There’s certain organisms that cause official “food poisoning”. The major ones are salmonella, e coli 015787, campylobacter, etc. We’ve learned in the last twenty years that listeria can grow in the refrigerator, and can grow to just below the freezing point, -1 degree C. It’s a dangerous one because there’s a chance of dying from consuming it, depending on your immune system. If a pregnant woman gets ill with it, there’s a high chance it will kill the foetus.

What do you recommend people do to ensure the safety of their food?

People should keep their refrigerator below 40 degrees Fahrenheit. I keep mine at 34 degrees, and I can get a six week shelf life on an unopened container of milk, and I can keep steak in there without having to freeze it for 14 days. This is VERY temperature dependent. One hour outside the refrigerator is equivalent to 24 hours in a refrigerator. The lower the temperature, the better.

What got you interested in the Dating Game food waste report in the first place? What’s your position on our current food labeling system? (Dr. Labuza has done work on this his entire career. Check out his webpage for backstory on developing testing models, working with Teddy Kennedy, and more.)

When I came to Minnesota, I partnered as a consultant with 3M to come up with a tag that you could put on a package that would have a color change mimicking the same rate at which the food spoils as a function of temperature and time. They decided not to continue in that area because people would think the tag was related to food safety, and we have to separate food safety from the shelf life of food.

How do companies arrive at the dates on their food?

I would say 80% of the dates are guesses or based on what competitors are putting on. There’s two ways to measure end of shelf life: you have a marker- for example one food company found a certain compound was produced by food that they could measure, and when it reached a certain amount it would have a negative impact on consumer acceptance of the product. They generate a “best if used by” date based on that point in time when it will start to have a negative impact. The other option is to do century testing, which is very expensive. I developed a procedure which is a better method- it gives you a graph of the percentage of consumers who would be displeased as a function of time in the distribution. You could make that a decision point. How many consumers do you want to displease? How do we improve distribution so product gets to market sooner in other cities? If a grocery store in Ann Arbor, 50 miles from Battle Creek, ordered cereal, it would take eight weeks to get there, because it’s being stored at various points in time along the way. That’s the nature of distribution: you can’t send something directly, it’s way too expensive.

Are there better ways for food companies to communicate the freshness and/or safety of their product, besides just dates?

Our education of the consumer at grade school and high school level is important. I teach a big course: Food: Safety, Risk and Technology. Moderation is very important. For instance, consuming large quantities of food fried at high temperatures can cause an accumulation of carcinogenic compounds in the body. I’ve gotten myself down to eating french fries only once a year. That’s very difficult to do.

~~~~

This is Part 1 of a two-part series. See Part 2 here: Forty Percent of Food in the US Never Gets Eaten

Perrin Ireland About the Author: Perrin Ireland has been a doodler her entire life, a learner who visualizes concepts in order to understand them. She currently serves as Senior Science Communications Specialist at the Natural Resources Defense Council, where she helps tell the story of how science plays a part in NRDC's work. Follow on Twitter @experrinment.

The views expressed are those of the author and are not necessarily those of Scientific American.

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