Millions of pounds of nutrient-rich ice cream are discarded after production each year, according to the International Dairy Foods Association. Nearly 5% of the raw materials used in ice cream production end up as waste—representing millions of dollars in lost product per year. This waste primarily comes from batches discarded because of quality issues and waste generated during equipment cleaning. Regulations aimed at preventing cross-contamination with allergens have also greatly increased the amount of discarded ice cream over the past two decades.

Researchers in Penn State’s College of Agricultural Sciences say one answer may be to recycle the ice cream waste. They found that it is possible to recover a large amount of fat at a potentially economical cost. Recovered fat could replace a pork fat called choice white grease that is mainly used in animal feed, or be transformed into compounds for use in pharmaceuticals, cosmetics and other products, the team said. They published their findings in Cleaner Engineering and Technology.

The researchers found that ice cream waste, which typically has a fat content three to five times that of cow’s milk, doesn’t necessarily need complicated treatment to recover its fat. Simple separation, particularly centrifugation—a mechanical process that uses rapid spinning to separate mixtures of different sizes, shapes and densities—with alkaline treatment as a possible aid, can do the job.

“Here in the Department of Food Science at Penn State, we have a close relationship with the food industry, so it was through our industry partners that we first heard about the magnitude of the ice cream waste problem,” said study senior author Yi Zhang, Frederik Sr. and Faith E. Rasmussen Career Development Professor in Food Science. “After offering the Ice Cream Short Course for over 100 years, we have ties to nearly every major ice cream company in the world, so we wanted to see whether we could help solve the problem.”

In the study, the team worked with Perry’s Ice Cream in Akron, New York, which shipped about 90 pounds (41 kilograms) of frozen ice cream waste per batch—with fat content ranging from 1.8% to 10.3%—from four production batches that had been mixed at the ice cream manufacturing facility.

The first approach researchers tried to collect the milk fat was a process called proteolysis—using enzymes like pepsin, trypsin and bromelain to break down proteins that help stabilize the fat emulsion. The second approach was pH shifting, in which they made the waste strongly acidic (pH 2 or 4) or alkaline (pH 11) to destabilize the emulsion. After treatment, they centrifuged the material to separate the fat.

The team measured fat recovery—how much of the original fat they successfully recovered—and fat purity—how much of the recovered material was actually fat rather than proteins, water and other compounds. The result was somewhat surprising, Zhang noted.

“You might expect enzymes to be essential for breaking up the emulsion, but our study found that you don’t necessarily need them,” she said. “The untreated control, when simply processed by centrifugation, recovered about 95% of the fat and actually improved fat purity compared with the original waste.”

Short enzyme treatments of one to two hours sometimes helped fat separation, but longer treatment, higher temperatures and extensive proteolysis did not increase the total amount of fat recovered and could decrease fat purity. The pH experiments found that pH 11—strongly alkaline conditions—separated fat better than acidic conditions.

To analyze the economic implications of their findings, study co-author Rui Shi, assistant professor in Penn State’s Robert V. Waltemeyer Department of Chemical Engineering, and her team built a techno-economic model to evaluate how the fat recovery approaches could be incorporated into industrial processes. They estimated that the minimum selling price per kilogram—slightly more than 2 pounds—of recovered fat would be about 40 cents. Selling the recovered fat above this price could provide an opportunity for profit, Zhang said.

The economics depended heavily on how much fat was present in the incoming ice cream waste, Zhang explained. Higher-fat waste makes the process more profitable because roughly the same amount of waste is processed to obtain more valuable product. The findings indicated that larger-scale processing operations could improve profitability.

She and her collaborators continue to explore value-added products from recovered fat, recycling and reuse pathways for other recoverable byproducts in ice cream waste, such as proteins and sugars, and potential applications for using ice cream waste as a whole.

Contributing to the research at Penn State were first author Fuad Ale-Enriquez, postdoctoral scholar in the Department of Food Science; Robert Roberts, professor and head of the Department of Food Science; Farhad Zaker Hosseiny, doctoral candidate in the Department of Chemical Engineering; and Zhe Xu, who graduated with a master’s degree in biotechnology. Brian Perry, with Perry’s Ice Cream Company, also collaborated on the project.

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