Recovery of valuable protein co-products from meat industry by enzymatic hydrolysis: bovine fleshing and hides

Animal products are not only important in terms of taste and tradition, but they also provide essential nutrients. Presently, around 16% of the global meat consumption takes place in EU, and it increased strongly over the last 50 years. The demand for animal-based food is further expected to increase during the coming decades, due to a growing world population and rising prosperity. In particular, meat consumption in developed countries is expected to increase of about 10% by 2030, but a much larger growth is expected in developing regions. Meat, dairy and fish are all important sources of protein, and they are partly interchangeable and cannot be entirely replaced with vegetable protein sources. Nevertheless, their production is accompanied by huge amount of waste and loss of biomaterial. For example, beef meat specifically accounts for only 44% of total live animal weight, with the highest production of low value products and waste material being generated in the abattoir. This waste is composed of edible (e.g. offal) and non-edible (e.g. Specified Risk Materials) parts. Edible animal co-products are almost completely used in other foods, such as broths, jellies, emulsifiers, fat matter, extracts and concentrates. Beside this, other parts (fat tissue, some internal organs and blood), being protein-rich, are also used in pet food, feed, organic fertilisers and technical applications. Despite all these applications, because of the high production of low value or waste material generated during slaughtering, meat industries anyway keep trying to add value to co-products through the generation of innovative food and non-food products. Then, there is increasing interest in studying these non-meat products with the aim to extract or recover additional value from the meat processing chain. Both reduction and recovery of the food waste have become hot topics and a challenge for the modern society. One possible way to process the waste material is using non-thermal innovative methodologies, which do not affect its quality and the properties. Enzymatic hydrolysis offers indeed a fast and gentle alternative to other mechanical or chemical treatments. The ability of the enzyme to hydrolyse proteins to produce free amino acids and short peptides allows the nitrogen to be more soluble and easily recovered and purified. This PhD project explored different ways to recover two meat industry co-products, bovine hides and bovine fleshing meat, through enzymatic hydrolysis. The first section is focused on the recovery of bovine fleshing, a low quality meat found immediately under the skin rich of collagen fibres and connective tissue, as possible food or feed ingredient. Fleshing is usually discarded by meat industry, even if having the potential to become a new source of proteins. In the present project, different proteolytic enzymes and conditions were tested, demonstrating the feasibility for fleshing recovery in a high quality soluble protein hydrolysate. The most efficient enzyme (Alcalase) was then selected to a further optimisation of the process, in order to scale-up the reaction to a semi-industrial level. In the second section, the efficiency of the enzymatic unhairing methods for hides was studied as alternative to the presently used chemical methods, in order to produce raw material for the leather industry. The enzymatic reaction of unhairing was developed at a pilot scale level in semi-industrial reactors and compared with the chemical-based one. Furthermore the wastewaters obtained from both methods were characterized for a future possible valorisation in feed formulations or as food ingredients. The full recovery of bovine hides through total hydrolysis was then studied in the last section, using and optimizing proteolytic hydrolysis for obtaining high quality hydrolysates. Finally, the techno-functional properties of the hydrolysates were studied as a function of the hydrolysis conditions. The effect of the replacement of the meat part with the bovine hides’ hydrolysates in Irish sausages was also evaluated. In conclusion the enzymatic hydrolysis may be a useful method to obtain hydrolysates with a considerable potential in order to recover meat industry co-products as a source of proteins for food or feed industry.