Provena Foods of Santa Ana, a specialty food-processing company serving the pizza and pasta industries, posted a net income of $779,640 for 1987, up 2% from the $766,398 reported a year earlier. Net sales rose 26% to $31.2 million, from the $24.8 million recorded the previous year. During the fourth quarter, Provena's net income dropped to $92,395, down 58% from the $218,398 posted in the same period a year earlier. Company officials attributed the decline to the start-up costs of a new pasta plant in Chino. Sales during the quarter increased 11%, to $7.6 million from $6.9 million.