Researcher seeks new uses for cull potatoes

A Washington State University scientist is trying to turn cull potatoes into a profitable byproduct for Washington potato growers.

The state’s potato growers harvest about 5 million tons of potatoes every year. Nearly 15 percent of the potatoes, usually known as culls, end up as some form of feed or residual use by-product, according to Melvin Martin of the J.R. Simplot Company.

Culls cannot be sold on the fresh market or processed into french fries or other potato products because they do not meet minimum size, grade or quality standards. Culls often are sent on for further processing, fed to cattle or added to compost piles. Potatoes cost about $70 to $120 per ton to grow while growers generally receive less than $10 a ton for their culls, according to Martin.

Potato processing in the state of Washington also generates waste in the form of solids, peels, unusable potato parts and wastewater. An average processing plant can produce between 1.5 and 3 million gallons of wastewater daily, according to Don Nichols of the Washington Department of Ecology.

Shulin Chen, a scientist with Washington State University’s biological systems engineering department, in conjunction with WSU’s International Marketing Program for Agricultural Commodities and Trade and the Washington State Potato Commission, is developing new uses for culls that would transform them into high-value food and non-food products.

Chen, who will report on his research here Tuesday (Nov. 2) at the annual meeting of the IMPACT Center, said that cull potatoes and wastewater from potato processing can be used to make chitin, chitosan and lactic acid, all which have strong domestic and international sales potential.

Chitin is the second most abundant polysaccharide in nature. It is found primarily in the exoskeletons of crustaceans as well as in the cell walls of some fungi. Studies on the production of lactic acid from potatoes using the fungal strain Rhizopus oryzae NRRL 395 found that a considerable amount of fungal biomass is produced at the same time. The fungal mass has a cellular wall composed primarily of chitin. Chitosan is a substance taken from chitin.

Chitin and its derivatives can be used for clearing wastewater and in the manufacture of cosmetics and in medical applications. Chitin also can be a precursor to numerous chitin derivatives, such as glucosamine, a product used for the treatment of arthritis. Chitosan also has proved useful in promoting tissue growth, accelerating wound-healing and bone regeneration.

Lactic acid is used as a food additive for flavor and preservation and in the development of poly-lactic acid, a product used to make biodegradable plastics and textiles.

Estimates show that the use of poly-lactic acid could grow into a one- billion pound per-year market in the next ten years and that there is a $1.25 billion per year potential biomedical market for chitin, chitosan and their derivatives.

With the wholesale price for lactic acid currently at about 50 cents per pound and $4,500 a pound for pure chitin and chitosan, Chen is confident that the fermentation and separation process he is working on could “warrant increased purchasing points for the farmers’ cull potatoes.”

Research has progressed rapidly and could possibly be implemented in processing plants across the United States within the next five years.

The biggest problem Chen faces is how to make his process economically feasible to potato processors. “It is not a question of if it can be done,” Chen said. “The technology is there. It’s a matter of reducing the associated costs.”

Chen’s technology potentially could reduce the environmental impact of potato waste and the wastewater generated during processing. Wastewater generally is applied to land but because it contains some quantities of starch, protein, nitrogen and phosphate, any form of land application must be closely monitored. The WSU scientist’s technology utilizes the starch and protein from wastewater as well as the culls.

The IMPACT center was established in 1985 to address issues important to the future of Washington’s agriculture, food systems and economy. The center funds research to improve the competitiveness of Washington agriculture in overseas markets.

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