The present invention provides a powdered composition for preparing a heat-stable food product that is at least partially gelled, wherein the composition essentially comprises the following ingredients as a percentage by weight with respect to a total of 100% of said ingredients representing 100%: 1) 5% to 50% of sodium alginate; 2) 0 to 50% of a slow-dissolving calcium salt that can react with the sodium alginate to form a calcium alginate gel; 3) 0 to 25% of an agent for retarding the reaction between the sodium alginate and said calcium salt; 4) 20% to 95% of a dispersing agent optionally also constituting a water retention agent, selected from sugars, polysaccharides of vegetable origin selected from maltodextrins, native or modified starches and native or modified celluloses, and vegetable proteins. The present invention also provides a method of preparing a food product that is at least partially gelled, wherein the method comprises bringing a composition of the invention into contact, preferably by mixing, with a raw food material.