Sysco Boston LLC, part of a global food-marketing corporation, held an open house at its 650,000-square foot distribution center Sept. 21. The event provided the public with four hours of access to its building located on 133 acres off Route 44 at the Spring Street interchange, which replaced the company's Norton location. The warehouse employs 860 workers and carries more than 14,000 products for restaurant and institutional food service customers, according to company officials.