Red apples

High pressure processing, pulsed electric fields, microwaves — these technologies (collectively referred to as “advanced processing technologies”) aren’t widely commercialized in the United States…yet. But, as processors work to meet the demands of consumers who want high-quality, natural foods without unpronounceable ingredients, interest in advanced technologies is growing.

To learn more about these three technologies and what they offer for fruit and vegetable processors, we spoke with Diane Barrett, a recently retired fruit and vegetable extension specialist whose career spanned many decades and multiple continents. “My career was like a big circle,” she says. “I was born and raised in California and got my bachelor’s degree in food science at the University of California, Davis. Then, I left California for 15 years, until I came back as a faculty member in the same department where I was a student.”

Those 15 years took her many places, starting with a master’s degree in food chemistry from the University of Wisconsin, Madison. “I wanted to work overseas in developing countries, specifically looking at how to reduce postharvest loss,” she says. “People put a lot of work into growing fruits and vegetables, and then half of the products are lost before they can be eaten.”

Dr. Barrett’s work took her to Indonesia for several years, where she focused on reducing loss during transportation and storage for crops like fruits, vegetables, and rice. “After four years, I realized I didn’t know enough about the raw materials, meaning the plant tissues,” she says.

So, she went back to school, earning a Ph.D. from Cornell University. There, she studied how plant tissues change with maturity, the effects of the environment on growth, and many other factors that affect the quality of fruits and vegetables. Her research focused on the enzymatic reactions that cause browning in Red Delicious apples.

Following her PhD, Barrett took a job at Oregon State University. She worked half in research and half in extension, exploring solutions for the fresh, fresh-cut, and processed fruit and vegetable industry. In 1992, she returned to UC Davis, where she served on the faculty for 25 years as an extension specialist, also leading a research lab and teaching short courses on topics like fruit processing, juice processing, and tomato processing. She also spent 10 years as the UC Davis Site Director for the Center for Advanced Processing and Packaging Studies (CAPPS), a unique research collaboration among industry, university, and government that has been instrumental in advancing new technologies for the food and beverage industry.

Advantages of advanced technologies for fruit and vegetable processing

Barrett’s interest in advanced technologies arose from her work aimed at retaining quality in fruits and vegetables.

“Quality means four things,” she explains, “color, texture, flavor, and nutrient content. When preserving food, the goal is to maximize all four of them. Seeing losses is horrible, and if you can preserve these things, it translates to a lot of savings. A number of studies, including my own research, show that the four quality attributes are better using advanced versus traditional processes. With advanced technologies, we have the potential for improved nutrient content, better color and flavor, and the ability to manipulate the texture.”

By “traditional processing,” Barrett means approaches like thermal processing, sterilization, freezing, pickling, and fermentation. Most of these processes rely on heat, and the quality parameters of fruits and vegetables are very sensitive to heat. The result is a reduction in nutrient content, color and texture changes, and flavor and aroma changes (sometimes for the better). “Years of looking at the effects of how we’ve preserved fruits and vegetables made me want to find another way,” she says.

The first “other way” Barrett had the chance to work on was high pressure processing (HPP).

About 20 years ago, the head of R&D at Avomex (which later became Fresherized Foods, now part of the MegaMex group) called Barrett about a problem with their signature product: guacamole.

Fresherized Foods pioneered the use of HPP in the U.S. food industry. Their process was to put the guacamole into its plastic package, seal it, and process it by immersing it in hydraulically pressurized water. The pressure ruptures the microbial cells, making it safe to eat.

As long as the guacamole was in the package, it retained its attractive green color. But, as soon as you opened the package and exposed the product to air, it started to turn brown. This was the result of the same kind of oxidative reaction that causes browning in Red Delicious apples and other products Barrett had studied. So, she worked with the company on a method to preserve the product’s color while retaining its all-natural character. (Don’t forget to thank Barrett the next time you enjoy some bright green Wholly Guacamole.)

This project led to additional research and collaboration in the areas of HPP and beyond. You can read more about Barrett’s and her colleagues’ work in her PROCESS EXPO Expert in Residence articles:

Which advanced technology is right for you?

Advanced processing technologies have some distinct advantages for processors. As mentioned earlier, they help retain the quality of the raw materials. They are also all uniform processes that affect the product evenly, compared with using traditional heat which often results in the outside of the product being overcooked in order to make sure the inside is safely cooked.

But, the capital cost of equipment can be high, especially for HPP, so processors need to be sure the advantages justify the investment. Here’s Barrett’s take on which advanced technologies provide the most benefits for different applications.

High pressure processing (HPP)

There’s a reason the first commercial use of HPP in the United States was for guacamole. This technology is best for high-value, higher-priced products where you really want to retain color and flavor. This extends to high-quality juices — Starbucks’ Evolution Fresh juices are processed using HPP. In Japan, HPP is commonly used for jams and similar product to retain the natural fruit flavor.

HPP is used outside of the fruit and vegetable industry as well. Hormel uses this technology to pasteurize deli meats. And there’s a unique market for HPP in seafood and oyster processing. (The process actually shucks the oysters for you!) In both cases, HPP is a crucial component in ensuring food safety — once the product is in the package, it’s not opened again until it’s in the hands of the consumer.

HPP also has a few limitations that processors should be aware of.

First, delicate products, like strawberries, don’t stand up well under HPP. As soon as you release the pressure, the product disintegrates.

Second, HPP is currently a batch process, which limits the throughput. You put a batch of products into a cylinder, fill the cylinder with water, and then apply pressure. Barrett notes that OEMs are working hard to figure out how to do it continuously, but the technology isn’t quite there yet.

Pulsed electric field processing (PEF)

In PEF, the product is passed through an electric field that kills pathogenic organisms by causing their cell membranes to rupture.

At the moment, PEF is more widely used in Europe than it is in the United States. But there are a few intrepid companies that have adopted the method.

Genesis Juice, a company in Eugene, OR, was the first U.S. company to use PEF. Juice is an ideal product for this technology because the liquid can flow evenly past the electrodes and directly into a bottle.

Another major application of this technology is in the potato industry. Barrett notes that all of the big potato processors in the Pacific Northwest use PEF to pre-treat their potatoes before frying. A benefit of this treatment is that it reduces the oil uptake, resulting in lower-fat chips. Barrett has also worked with manufacturers to create processes for using PEF with solid tissue products like onions, mangoes, and tomatoes. To learn more about the current PEF landscape, check out the work of Stefan Toepfl, who has been researching and working in the area for more than 10 years.

Microwave processing

Microwave processing can currently done in a couple of different ways.

Like PEF, continuous microwave processing got its start in the potato industry, when sweet potato growers in North Carolina needed a solution for handling excess product at harvest time. This method works well with products that are pumpable, meaning fluids or a semisolid. So, the growers formed a company, Yamco, and created a pureed sweet potato product that they feed through a continuous microwave process. Today, they process carrots and other root crops this way as well.

Another type of microwave system is currently being studied at Washington State University, under the leadership of Juming Tang. It’s called microwave assisted thermal sterilization (MATS), and it can be used for a variety of products, including fish, meat, and ready meals.

Barrett describes the MATS process as “like a TV dinner.” Processors fill plastic trays with product, seal them, put them on a belt, and pass them through a microwave tunnel for pasteurization. The military is particularly interested in this process because it has the potential to provide soldiers with meals that look and taste homemade. MATS is currently commercialized exclusively by 915 Labs, which has a unit capable of producing 30 8-oz trays per minute.

The future of advanced technologies

All of these technologies are pretty new — at least in terms of their commercial and industrial applications. So, what might the future look like? Will we see mass adoption of any or all of these methods?

Barrett thinks that, of the three, microwave processing may have the most opportunity because it’s the most approachable. Everyone knows what a microwave is, so there at least aren’t any psychological barriers to its adoption. She believes that for HPP to reach its potential, equipment manufacturers will need to figure out how to make it more continuous (“They’re working on it, but it’s a challenge,” she says). Finally, while PEF has advantages, she thinks more research is needed into specific applications.

In any case, she speculates that any new trend might start in the military, which has always been a force for innovation in processing. (Did you know that Napoleon offered a prize to improve food preservation so he could feed his troops? The result was the process for canning that we still use today.)

If you’d like to learn more about any of these advanced technologies, check out Barrett’s Expert in Residence articles — at the bottom of each article, she provides a great list of resources so you can catch up on the latest research. To see what’s new in the food and beverage processing and packaging industries, join us next month at PROCESS EXPO. The show will feature new innovations, working production lines for meat and bakery, and much more.