UPDATE 1-Shares of WhiteWave open at $19

Olivia Oran and Martinne Geller

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Oct 26 (Reuters) - WhiteWave Foods Co shares rose almost 12 percent in their New York Stock Exchange debut on Friday, as investors bet on the growth of the organic foods sector.

Shares of the Dallas, Texas-based Dean Foods Co spinoff opened at $19, up 11.8 percent, after pricing at $17, above the expected range. WhiteWave sold 23 million shares in an upsized deal, raising $391 million in its initial public offering.

WhiteWave, which sells Silk soy milk and Horizon organic dairy products, had expected to sell 20 million shares within a range of $14 to $16 per share.

Dean Foods announced in August it was spinning off its WhiteWave segment, whose brands appeal to health-minded consumers. The company also confirmed in September it is selling its Morningstar division, which sells Friendship cottage cheese and private label dairy products such as creamers, ice cream mix and sour cream.

Natural and organic foods and drinks have been a growing bright spot for packaged food and drink makers, who have sought to capitalize on consumers' growing interest in natural ingredients.

Dean's other businesses, including regional brands of fresh milk, have gotten squeezed in recent years by higher dairy costs, the weak economy and cheaper private label brands.

Passing on higher commodity costs is difficult in the milk business because there is little brand loyalty and consumers often choose the cheapest brand.

The WhiteWave business, which is profitable and growing, has long been seen as the most attractive part of Dean. That view has been bolstered by the fact that Dean Chief Executive Gregg Engels will lead the company following the spin-off.

Dean Foods is selling a 12 percent stake in the WhiteWave unit.

WhiteWave's IPO comes after the success of other recent offerings from organic foods companies including Annie's and Natural Grocers by Vitamin Cottage Inc.

Shares of Annie's have more than doubled since the company's March IPO to close Thursday at $39.45. Shares of Vitamin College closed at $20.11 after pricing at $15 in July.

WhiteWave's net sales rose 12 percent from the year prior to $1.9 billion in 2011.

WhiteWave Foods said it would use the proceeds of the offering to pay back debt owed to Dean Foods.

Underwriters for WhiteWave's IPO include J.P. Morgan, Credit Suisse and Bank of America Merrill Lynch.

(Reporting By Olivia Oran and Martinne Geller in New York; Editing by Gerald E. McCormick and Phil Berlowitz)