Why does processed meat shrink so much when cooked at home, and how does sodium tripolyphosphate help?

Why does processed meat shrink so much when cooked at home, and how does sodium tripolyphosphate help?
Sodium tripolyphosphate (STPP) is widely used in the food industry as a water retention agent, especially in braised meats, sausages, and seafood. It helps maintain muscle tissue plumpness, improves surface gloss, and prevents shrinkage during cooking. In China, food-grade STPP is legal under GB 2760, with typical usage of 2-5 g per kg of meat. However, street vendors may exceed limits because STPP is extremely cheap—retail compound water retainers cost only 10-20 RMB per kg—and overuse can significantly increase product weight and shelf life. Regulatory compliance varies, and excessive intake of phosphates has been linked to calcium absorption interference and cardiovascular risks, particularly for elderly populations.