SAN FRANCISCO -- Wilbur-Ellis Co. here is recalling all lots of the rice protein concentrate it shipped to pet food manufacturers because the product may be contaminated by melamine. Wilbur-Ellis said it obtained the rice protein from a single Chinese supplier: Binzhou Futian Biology Technology Co. It then shipped it to five U.S. pet food manufacturers located in Utah, New York, Kansas and two in Missouri. Last Sunday, Wilbur-Ellis notified the Food and Drug Administration about a bag in a recent shipment of rice protein that tested positive for melamine. Unlike the other, white-colored bags in the shipment, the bag in question was pink and had the word melamine stenciled on it. Wilbur-Ellis separated that bag and quarantined the entire shipment for further testing, according to the supplier. No further deliveries of rice protein concentrate have been made. Samples of the white bags, tested by the FDA, came back positive for melamine, according to Wilbur-Ellis, leading it to issue the voluntary recall. Rice protein concentrate is believed to be the source of melamine in Natural Balance, Pacoima, Calif., products. Earlier this week the company recalled its venison dog products and its dry venison cat food.