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Global consumption of meat products established an enormous and constantly growing industry. By-products generated from this industry have a high biological oxygen demand, and if they are not treated properly, then they can have serious implications for the environment. Meat products, such as fish, chicken, beef, sheep, and pork all result in similar waste products. These include carcasses, intestines, feathers, fish bones and scales, as well as blood. Although these can be seen as waste from the meat producer, they become much more valuable after rendering. A variety of products exist, such as gelatin from hooves, meat-and-bone meal from carcasses and intestines as well blood, feather, and fish meal. These are mainly used as animal feed supplements because of their high protein content, but the nutritional properties vary dramatically, and in some cases, further processing is required. In this chapter the sources and properties of animal-based proteins are discussed of their biological composition as well as their physicochemical properties.

Congruent to a rapidly growing population is the generation of horticultural and agricultural by-products and waste. The modern-day food cycle includes agricultural production, postharvest handling and storage, food processing and packaging, and distribution and retail, ending with consumption and waste disposal. Of these, agricultural production and postharvest handling and storage result in unintended losses and by-products whereas the other steps generally result in food waste. Approximately one-third of the worldwide food production is wasted each year. Although it is most desirable to prevent waste and by-product formation, followed by reuse or recycling, the formation of by-products and waste is inevitable, and management options must be innovative and also meet legislative requirements. However, management options are mostly a compromise between what is viewed acceptable based on legal requirements and local perceptions, and what is deemed technologically and financially feasible.