The meat industry generates large amounts of by-products, and their mass represents approximately one-third of the live weight of animals. Most by-products are disposed of and not used for processing, although they meet hygiene requirements and are suitable for human consumption or for the processing of food supplements. The aim of this study was to investigate the effect of lyophilization on the nutritional value and retention of functional ingredients in ovine and porcine by-products: liver, kidneys, hearts, and lungs. For this purpose, meat by-products of the third category were selected in X and Y slaughterhouses and divided into two parts: one part was freeze-dried at −80 °C for 72 h, and the other part was left raw. Fatty acid composition was determined by gas chromatography–mass spectrometry (GC-MS), and amino acid analysis was performed by AccQ Tag technology (Waters Corp., Milford, MA, USA) and HPLC. Our study shows that the lyophilization process did not significantly affect protein and fat content. The largest decrease in the amount of proteins was determined in samples of ovine kidneys, at 0.8%, while the difference in protein in ovine liver samples before and after lyophilization was 0.38%. The composition of essential amino acids did not change after lyophilization, except a decrease in Leu and Thr in porcine samples and Leu, Thr, and Met in ovine samples (p < 0.05). The lyophilization process did not significantly affect the polyunsaturated fatty acid content, including the amounts of omega 3 and omega 6 fatty acids. The optimal ratio of omega 6 and 3 fatty acids was determined in samples of lyophilized ovine livers (2.65), and the largest ratio was found in samples of lyophilized porcine hearts (16.67). The study results show that, after lyophilization, meat by-products of the third category (according to Regulation (EC) No. 1069/2009, Categorization, Article 10), especially ovine liver, can be used as a source of amino acids and polyunsaturated fatty acids for functional food processing. The process of lyophilization is also appropriate for preserving meat by-products without losing the nutritional value and beneficial components.

The results show that seven types of N-nitrosamines: N-nitrosodiethylamine (NDEA), N-Nitrosopiperidine (NPIP), N-nitrosodimethylamine (NDMA), N-nitrosopyrrolidine (NPYR), N-nitrosodipropylamine (NDPA), N-nitrosodibutylamine (NDBA) and N-nitrosodiphenylamine (NDphA) were reduced after heat treatment of pork steaks marinated with L. plantarum MI-LP1, S. carnosus LM-SC1, S. vitulinus LM-SV1. Selected LAB suppressed the formation of putrescine and spermine, lowered acid and peroxide values, which were significantly lower than in the control samples, then P&le;0.05 in all cases. The nitrites and nitrates amounts were significantly decreased in pork steaks samples marinated with L. plantarum MI-LP1 and S. carnosus MI-SV1 strains. These results presented that selected lactic acid bacteria could be used for marinating pork steaks to improve quality characteristics and reduce N-nitrosamine formation during grilling.

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