LONDON (Reuters) - Anglo-Dutch consumer group Unilever ULVR.L has invited private equity bidders to submit tentative offers for its $8 billion margarine and spreads business by a deadline of Oct. 19, two sources close to the matter told Reuters.

FILE PHOTO: The company logo for Unilever is displayed on a screen on the floor of the New York Stock Exchange (NYSE) in New York, U.S., February 17, 2017. REUTERS/Brendan McDermid/File Photo

The sale of the business, which makes Flora and Stork margarines, officially kicked off in late September with Unilever’s banks sending out confidential information to a series of heavyweight buyout funds which have been working on this deal since the start of the summer, the sources said.

The auction has been dominated by private equity firms which have been lured by the unit’s strong profit margins. But the valuation might prove difficult, as Western consumers cut back on bread and margarine, the sources said.

International investors have teamed up in three rival consortiums consisting of Bain Capital and Clayton Dubilier & Rice (CD&R) as part of one group, Blackstone BX.N and CVC Capital Partners [CVC.UL] as part of a rival group, and KKR joining forces with Singapore's sovereign wealth fund GIC.

U.S. investment fund Apollo was instead looking to bid alone, the sources said.

Industry players including U.S. agricultural trader Archer Daniels Midland Co ADM.N have decided against bidding, the sources added.

Blackstone, CD&R, Bain, CVC, KKR and Apollo declined to comment, while Unilever and GIC were not immediately available for comment.

The sale, which is led by Morgan Stanley and Goldman Sachs, could fetch as much as 6 billion pounds ($7.87 billion) and was expected to wrap up toward the end of 2017, the sources said.

In its bid to exit from the shrinking margarine business, Unilever agreed last month to exchange its spreads unit in South Africa for Remgro's REMJ.J 26 percent stake in Unilever's South African subsidiary, a deal worth $900 million.

The consumer giant has been working hard to boost its margins and performance after rebuffing a surprise $143 billion takeover bid from Kraft Heinz KHC.O this year.

Unilever’s underlying operating margin improved 180 basis points to 17.8 percent in the last six months, helped by an acceleration of cost-savings programmes, and a 130 basis point drop in brand and marketing spending.

On Sept. 25, Unilever made a 2.27 billion euro swoop on fast-growing cosmetics company Carver Korea in a bid to build a global beauty business.