Effects of wet heating using large-scale cooking equipment on food properties

Abstract

Objectives: To obtain basic data on the effects of wet heating using large-scale cooking equipment on food properties for the selection of suitable large-scale cooking equipment and optimal cooking conditions for vegetables; to improve the palatability and quality of school lunch menus; and to standardize and improve the efficiency of school lunch preparation.

Methods: The food properties of vegetables (potato, carrot, and spinach) wet heated with a pan, a steam convection oven (stecon), and a VarioCooking Center (vario) and those of rice dishes (white rice and pilaf) wet heated with a vario and a gas rice cooker were investigated.

Results and Discussion: Stecon took the longest heating times. In stecon cooking, ingredients were heated by condensing heat transfer and steamed by hot air, leading to a small temperature rise from surface to inside. The vegetables were heated relatively uniformly, and they had higher sugar contents. In vario cooking, rapid temperature rise in the early heating stage and maintenance of uniform temperature all over the pan bottom accelerated starch gelatinization. Vitamin C contents were reserved mostly in potato. Although carrots were heated at high temperatures for longer durations, they had lower vitamin C contents. In spinach, most vitamin C contents were reserved. When residual ratios of vitamin C and the improvement of palatability by removing organic acids were considered, appropriate water exposure times for spinach were considered to be three minutes in stecon cooking and one minute in vario and pan cooking. In vario cooking of rice dishes, vario had smaller moisture evaporation rates during rice cooking, and hence, shorter cooking times till completion of steaming and rice stir-fried times in pilaf cooking.

When rice is stir-fried with fat, free fatty acids increase time-dependently, water content required for starch gelatinization is decreased, firmness of cooked rice is affected, and damaged rice texture induces the absorption of water and seasoning liquids. In a gas rice cooker, cooked rice had a cooked grainy taste and pilaf had a more salty taste and palatability, while in vario cooking, both cooked rice and pilaf were simply soft.