Spent hens are laying hens that have reached the end of their first laying cycle. The disposal of spent hens has become an increasing problem in the laying industry due to the high costs involved. Conventional disposal methods such as burial or incineration are neither practical nor environmentally friendly. A better disposal method, especially from an economic point of view, is the composting of spent hens. Spent hens are not attractive to food processors due to their age and small size. They have fragile bones that easily break into the meat during processing. The meat is generally tough due to the collagen content and cross-linking. Therefore, the use of spent chicken meat in whole foods is limited and the market price is low. The rendering industry has been producing protein meal from poultry processing waste for several years. The rendered spent hen meal is a good substitute for fish and soy meal in typical animal feed or pet food. The problem is that the addition of proteins of animal origin to feed for farm animals has been banned in the EU since 2001. In the past, most of the spent hen meat was used in foods such as soups, canned food, minced meat, bouillon cubes and snacks. In recent years, however, the value of spent hens used for human consumption has fallen to almost zero. Due to the decreased demand for spent hens and the need to dispose of the carcasses in an economical manner, there has been increased interest in developing new value-added products from spent hen meat, including biomaterials (e.g. adhesives, bioplastics, adsorbents, etc.) and functional food ingredients (e.g. gelatin, bioactive peptides). Future research is likely to focus on the conversion of biomass from spent hen meat into value-added products.
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