By John Miller ZURICH, Sept 11 (Reuters) - One of the world's largest bakery companies, Aryzta, has agreed an underwriting deal with five banks, setting the stage for raising 800 million euros ($928.48 million) in new capital to strengthen its balance sheet. Shares in the maker of McDonald's burger buns to Otis Spunkmeyer cookies rose as much as 8 percent after the company named BofA Merrill Lynch and UBS as lead managers, and Credit Suisse, JP Morgan and HSBC Bank plc as joint global coordinators of its capital raising. The Swiss-Irish company has warned on its at least three times since 2017 due to rising distribution and labour costs in North America, problems with undocumented workers at a U.S. bakery, high butter prices and weak consumer spending in some European markets, particularly Britain following its vote to leave the European Union.