An urgent global problem is the effective and rational management of secondary meat processing resources, the number of which in 2024 amounted to about 155 million tons [1, 2]. They are considered as raw materials for the production of food, medicines, animal feed, cosmetics [3, 4], pharmaceuticals, and biologically active peptides with antihypertensive, antioxidant, antidiabetic, antimicrobial [5, 6], opioid, and antithrombotic effects [7–9]. Preference is given to technologies for products with high demand, low costs, and minimal environmental impact, which ensure the sustainable development of the meat industry and the transition to bioeconomics, and lagging behind in this issue leads to resource loss, increased recycling costs, and environmental problems [10, 11]. Similar programs are being developed in China [10] and Kazakhstan [11]. Meat by-products have a high content of protein, essential amino acids, lipids, biologically available iron, potassium, phosphorus, sulfur, and sodium [12, 13], so they can be used to overcome malnutrition and anemia [14, 15].

The main problem with the use of by-products is their high microbial contamination, which is observed in 15–40% of carcasses of slaughtered animals and can range from 1.42 to 1.82 Lg CFU/g [16].

The authors note certain obstacles to the use of by-products related to their appearance and smell. The characteristics “unsightly appearance”, “viscous”, “fluffy texture”, and “unpleasant odor” were used to describe the sensations, especially in relation to raw offal. Negative olfactory characteristics have a stronger effect on food perception than on taste [17, 18]. This odor is created by 16 characteristic volatile compounds, which include E,E-2,4-nonadienal, E,E-2,4-decadienal-1-al, hexanal, (E)-2-octenal and decyl aldehyde found in the heart; 1-nonanol, ethyl hexanoate, 2-octanone and dodecyl aldehyde in the liver; 3-heptylacrolein in the lungs; heptaldehyde, octanal, p-cresol and 1-nonanal in the rumen; and 1-octen-3-ol and E-2-nonenal in the intestine [17]. To eliminate unpleasant odors in by-products, they are cleaned, boiled, soaked in alkaline or phosphate buffer solutions, and washed [19], soaked in mustard solution, fermented with kefir grains [20].

The main component of by-products is collagen, which has both positive biological and functional properties (high moisture-binding, moisture-retaining and texturizing properties, as well as the content of biologically active peptides) and an unbalanced composition of amino acids with an excess of glycine, proline and hydroxyproline, but with a lack of methionine, isoleucine, threonine, cysteine and tryptophan [21]. Thus, collagen has a low ratio of essential and nonessential amino acids [22, 23] and a low digestibility index, which limits its use in food systems [24]. This can be improved by moving the pH value away from its isoelectric point (pH 6.0 to 6.75), which improves water binding and facilitates fermentolysis.

After disinfection, deodorization, increased digestibility, drying, and grinding it is proposed to obtain and use lyophilized powders from the spleen, lungs and heart, which increase moisture binding and emulsification of meat systems, increase the content of copper and zinc, reduce fat content, improve texture and stability, and also increase the shelf life of meat products without deterioration of taste. These technologies make meat offal a promising additional raw material for the production of fermented sausages, cutlets, emulsified products, minced meat, and pastes [13, 25–29].

Lactic acid bacteria (LAB) are able to solve the problems of by-products due to their adaptability, safety, biological activity, biotechnological value, and high antagonistic activity; therefore, they are used in food and agricultural biotechnology for the production of fermented meat products and animal feed with functional and probiotic properties [30, 31]. Bifidobacteria are also known as probiotics; they are resistant to acids and bile, synthesize vitamins and amino acids, and have antianemic, anti-rickety, and anti-allergic effects. In addition, they produce neuroactive compounds such as gamma-aminobutyric acid, which improve mental health by reducing anxiety, depression, and stress [32–35].

The antagonistic activity of LAB and bifidobacteria is manifested in their ability to suppress the growth of technically harmful and pathogenic microorganisms by such methods as pH reduction, synthesis of organic acids, antibiotics, hydrogen peroxide, diacetyl, reuterin, and bacteriocins [33–40].

Effective multi-strain probiotics not only suppress pathogenic microorganisms more effectively and balance the intestinal microflora [41], but also have anti-inflammatory, immunomodulatory, hypoglycemic, and hypocholesterolemic effects, and improve the quality of the final meat product by synthesizing metabolites that form a favorable taste and aroma (acids, aromatic substances, polysaccharides) [42–45].

These achievements confirm the ability of lactic acid fermentation to enhance the safety, biological value, and sensory properties of meat offal.

This article presents the results of comparing a number of bacterial strains of various genera and origin according to one of the important indicators—antagonistic activity against opportunistic and pathogenic microorganisms. Another unresolved task is to select simple and affordable methods for measuring antagonistic activity from a large number of possible alternatives, and to justify their interchangeability.

The presented article examines the antagonistic activity of bacterial strains, both included in commercial meat starter and medicinal preparations, as well as newly isolated from silage and fermented dairy products. Two in vitro methods, agar diffusion (disk agar diffusion) and co-cultivation in liquid media, demonstrated their significant antimicrobial activity against 8 strains of pathogenic and opportunistic microorganisms. The results obtained highlight the high antimicrobial potential of these strains, especially L. plantarum 8P-A3. This strain, and especially the medicinal drug Lactobacterin created on its basis, is widespread in Russia, its large-scale production has been established, and it is widely used to treat a number of health disorders, which once again confirms its effectiveness. Strains and poly-strain compositions included in commercial meat starter cultures, for example, Pediococcus acidilactici, part of Christian Hansen Safe Pro B-LL-20, Staphylococcus carnosus, and Latilactobacillus sakei, part of Christian Hansen Bactoferm F-SC-111, composition Latilactobacillus curvatus, Pediococcus pentosaceus, Staphylococcus carnosus, part of Schaller Start Star, have also shown high efficiency. The effectiveness of these commercial starter cultures has also been confirmed.

It is clear from experimental data that the strength of antagonistic activity is primarily determined by the genus and type of microorganisms that make up the preparation or starter culture. For example, Texel DCM-1 starter culture, which has the lowest antibacterial activity, contains only Staphylococcus carnosus and Staphylococcus xylosus, while all other starter cultures (except Safe Pro B-LL-20) contain Lactiplantibacillus. This gives us reason to believe that it is the representatives of the genus Lactiplantibacillus that most actively inhibit the growth of pathogenic microorganisms.

Our approaches to the isolation of new active LAB strains from various sources, including fermented dairy products, such as yoghurts, are well in line with the approaches presented in the previously published work [41].

However, this study has certain limitations, primarily because the antagonistic activity of the newly isolated strains is clearly inferior to that of commercial meat starters and medicinal preparations. Additional screening of active strains from various natural sources will be required. It is more effective to produce microorganisms with high antagonistic activity, active synthesis of bacteriocins, and tolerance to stress through mutagenesis, directed evolution, and genetic engineering methods [66, 67]. Productivity will be ensured by high-performance approaches described earlier [60], such as microplates (microtiters) and co-cultivation in liquid media, which allow testing hundreds of strains while simultaneously determining the GII. Screening based on hydrogel emulsions in oil with FACS sorting and bacteriological cytological profiling (BCP) has proven itself well [68, 69].

The second limitation of the presented article is the fact that antagonistic activity is not the only requirement for microorganisms to be used as a commercial starter culture. There are other important requirements specific to different product groups. Thus, for meat products, the key properties are the reduction of nitrites and nitrates (to increase the safety of the finished product), antioxidant activity (to prevent lipid peroxidation and color stabilization during storage), proteolytic and lipolytic activity (to improve taste), and acid-forming ability (to accelerate coloring and increase moisture loss during fermentation). In Russia, the microorganisms Staphylococcus carnosus, Latilactobacillus sakei, and Pediococcus pentosaceus are widely used as starter cultures for fermented sausages and dried foods.

For fermented milk products, the preferred growing temperature (mesophilic 28–32°C, thermophilic 40–46°C), maximum acidity (95–350°T), milk protein coagulation activity, and probiotic properties are important criteria. The most common are Lactococcus lactis subsp. lactis/cremoris, Streptococcus thermophilus, and Lactobacillus delbrueckii subsp. bulgarian and bifidobacteria.

Baking strains are selected based on their ability to form sensoric properties, accumulate acid, and be active against potato bread disease; L. plantarum and Pediococcus in combination with Saccharomyces yeast with high acidity best meet these criteria.

This information suggests the following promising areas of our work related to the experimental determination of the presence and severity of these desired abilities in both strains included in commercial starter cultures and newly isolated strains.

It is also useful to study the antimicrobial properties of strains in relation not only to pathogenic and opportunistic microorganisms that can be considered models, but also those present in real samples of meat offal from various animal species.

It is also interesting to study the mechanisms of the antagonistic activity of LAB, which may be based on their ability to synthesize different organic compounds useful for food technologies and pathogen control [70]. The inhibitory and anti-biofilm efficacy of Lactobacillus rhamnosus GG and Lactobacillus casei against Escherichia coli, Salmonella, and Listeria monocytogenes were investigated. Two control mechanisms have been identified and studied: co-adhesion on surfaces and protection against pathogens by biofilm formation from LAB cells [71]. Finally, it is relevant to study the spectrum of synthesized metabolites, including organic acids, hydrogen peroxide, and bacteriocins that inhibit the growth of pathogens [72–74].

An important aspect of the study is to address the issue of the interchangeability of various methods for determining the antagonistic activity of microorganisms. To assess the comparability of antagonistic activity data obtained by two alternative methods, the Pearson linear correlation coefficient r between the two datasets is used. The overall correlation is r = 0.43, which indicates an average positive correlation.

When estimating the correlation of the average values across the columns, i.e., when comparing the sensitivity of the tested pathogenic and opportunistic strains, the correlation is 0.71, which corresponds to a strong positive relationship. Similarly, the correlation of the average values across the lines, reflecting the assessment of the effectiveness of the studied newly isolated strains, starter cultures, and preparations, is also high and amounts to 0.75.

These results indicate that these methods are not completely interchangeable, and further research is required.