In the study, there was no effect (p > 0.05) of the addition of a seed mixture in any of the studied groups on the pH of poultry meatballs, which ranged from 6.21 to 6.25 (Table 2). Similar results were obtained/published by Bilek and Turhan [23] for beef cutlets with the addition of linseed flour, Kotecka-Majcharzak [30] in pork meatballs with the addition of hemp cake, and Guo et al. [28] in cooked pork with amaranth seed extract.

Significant differences (p < 0.05) were found in cooking losses (Table 2). Poultry meatballs in the addition of a mixture of linseed, amaranth and hemp seeds were characterized by lower losses after thermal treatment compared to group WR, with the addition of wheat roll, which was probably due to the retention of moisture in enriched products. Among the study groups, the M₂ meatballs in which a mixture of seeds of equal proportions (8%) was used, were characterized by lower cooking losses, which may be of technological importance. The reduction of cooking losses in the ground meat product with the addition of hemp ingredients (hemp flour, hemp protein and whole hemp seeds) was demonstrated by Zając et al. [29]. However, the size of the losses was determined not only by the proportion, but also by the form of the additives used. Similar results were obtained by Bilek and Turhan [23], simultaneously showing the reduction of cooking losses with the addition of linseed flour to beef cutlets, and Longato et al. [21] in poultry burgers with amaranth seeds and Sharoba [40] in sausages with amaranth flour.

The color of the product is an important visual feature, influencing the assessment of its quality, determining the choice and decision about a potential purchase or consumption. Additives and their participation in the recipe play an important role in shaping the color of enriched meat products, in addition to the raw meat [29]. The present author’s study showed a significant (p < 0.05) effect of the additives used in the mixture of linseed, amaranth and hemp seeds on the color of the cross-section of finished products. Meatballs enriched with seeds, regardless of the proportion of additives used, had a brighter color (higher yellow color brightness L* and saturation b* index and lower color saturation towards red a*). The proportion of meat raw material in all groups was the same, so the color changes of poultry meatballs resulted from the type of plant additives used. Also, Novello et al. [11] noted an increase in the brightness and saturation of the yellow color of beef cutlets with the participation of seeds and linseed flour. However, a decrease in red color intensity a* in beef cutlets with the addition of linseed flour was noted by Bilek and Turhan [23]. The color changes could be due to the presence of yellow flavonoids in linseeds [11]. Kotecka-Majchrzak et al. [30] showed that the colour of the meatballs section changed with a greater share of hemp cake towards darker. Zając et al. [29] showed that the color parameters of pork meatballs changed depending on the hemp ingredient used. The studies by Zając and Świątek [41] showed no effect from the addition of hemp and flax seeds on the quality of pâtés.

The tenderness of the meat product is one of the textural partners of importance to the consumer. The changes in texture parameters depend on the type and amount of the ingredient used and the interaction of the additive with the meat stuffing [29]. The present author’s study showed that poultry meatballs with the addition of a mixture of linseed, amaranth and hemp seeds were characterized by poorer brittleness (greater cutting force) compared to the control group (WR). Among the assessed meatballs enriched with plant additives, the highest hardness was found in group M₃ of meatballs with the highest proportion of non-husked linseeds. An increase in hardness (increase in sheer force) of poultry burgers enriched with linseed flour and an increase in the hardness of burgers with an increase in the used additive was demonstrated by Cocaro et al. [42]. The increase in hardness measured by the TPA test of meat products enriched with plant additives (hemp and linseed seeds) was confirmed in the study by Zając and Świątek [41], with hemp ingredients by Zając et al. [29], and with amaranth flour by Faid [26] and Tamsen et al. [10].

The indicator of the microbiological quality of food and the health safety of a meat product is the total number of aerobic bacteria [40]. The study showed that products enriched with the addition of linseed, amaranth and hemp seeds were microbiologically safe. In the study groups M₁ and M₂ with a higher proportion of amaranth seeds, they inhibited the total number of microorganisms on the third day of refrigerated storage (Table 2). Amaranth seeds contain antimicrobial compounds such as alkaloids, polyphenols, terpenoids and squalene. Confirmation of the antimicrobial effect of amaranth seed extract in cooked pork meat was demonstrated by Guo et al. [28] and of amaranth flour in chicken meat burgers by Longato et al. [21] and in beef sausages by Sharoba 40]. Moreover, Sharoba [40] showed that the total number of aerobic bacteria and the value of the TBA index in the finished product, at the first evaluation date, as well as during storage, decreased with an increase in the proportion of amaranth seed flour. In the study by Zając et al. [29], the addition of hemp ingredients (hemp flour, hemp protein and whole hemp seeds) to pork loaves did not inhibit or increase the total number of microorganisms in relation to the control group and between the product variants.

The addition of a mixture (M₂) with equal proportions of seeds as a substitute for a wheat roll (WR) caused a significant (p ≤ 0.05) increase in the ash content in poultry meatballs (Table 3). In studies by Billek and Turchan 23], Nowello et al. [11], and Cócaro et al., [42] the addition of linseed in the form of seeds or flour increased the ash content in meat products.

Proteins are an essential component of the human diet, and the consumption of the right amount of wholesome protein is important for health [43]. In the present study, the use of a mixture of linseed, amaranth and hemp seeds (groups M₁, M₂ and M₃) as a replacement for wheat roll (WR) had a beneficial effect on increasing the protein content (p ≤ 0.05) in poultry meatballs (Table 3). Other authors have also shown similar results. Verma et al. [9] found an increase in the protein content in meatballs with the addition of amaranth; Novello et al. [11] in beef cutlets with the addition of linseed flour, and Novello and Rodrigues Pollonio [20] in patties with the addition of linseed. Poultry proteins contain all of the essential amino acids [44]. In the present study, the amino acid profile of meatballs with the mixture of seeds was better in terms of the content of methionine. Of the nine essential amino acids that cannot be synthesized in the human body (phenylalanine, valine, threonine, tryptophan, methionine, leucine, isoleucine, lysine and histidine) in the amino acid profile of meatballs with a mixture of linseed, amaranth and hemp seeds (M₁, M₂ and M₃), a higher proportion of methionine was found than in meatballs from the control group (WR). The higher methionine content in meatballs with the seed mixture is beneficial and results from the higher methionine content in each of the components of the seed mixtures than in wheat roll. Increasing the proportion of methionine can be considered beneficial for improving the health and nutritional value of poultry meatballs, as methionine has anti-atherosclerotic properties, limiting lipid peroxidation (self-oxidation). In the study by Zeinab et al. [45], the addition of flax seeds to beef sausage did not increase the methionine content in the final product.

In the present study, the modification of the recipe of poultry meatballs resulted in an increase in fat content in all study groups. The fat in enriched meatballs, however, was characterized by a more favorable fatty acid profile than the fat in meatballs with wheat roll (WR). According to Bernacchia et al. [46], linseeds may be a good source of fatty acids in a diet low in marine fish, which is considered the best source of omega-3 fatty acids. The fat of poultry meatballs with seed mixtures compared to the fat of meatballs with wheat roll (WR) contained over 30% less saturated fatty acids (SFA), which significantly improved the health benefits of the meatballs (Table 4). The main ingredient of meatballs is meat, which has a high content of saturated fatty acids [47], considered to be one of the causes of cardiovascular disease. Also, the increase in polyunsaturated fatty acid (PUFA) content in meatballs with the addition of a seed mixture can be considered favorable [48]. In the present study, the proportion of polyunsaturated fatty acids in all study groups was more than 50% higher than in meatballs with wheat roll (WR), which indicates clearly better health benefits of enriched products (Table 4). Among polyunsaturated fatty acids, omega-3 fatty acids play a special role, as in the human body they reduce the concentration of undesirable excess triglycerides in the blood, normalize blood pressure, have anticoagulant and anti-inflammatory effects, inhibit the development of coronary heart disease, support brain function, inhibit excessive immune response, have anti-atherosclerotic properties, support vision processes, and inhibit lipogenesis [49]. Neither omega-3 nor omega-6 acids can be synthesized in the human body due to the lack of enzyme systems capable of creating a double bond in the chain of fatty acids further than C-9 [50]. In the human body, n-3 and n-6 fatty acids are part of the phospholipids of cell membranes, and their mutual proportion in tissues depends to a large extent on the supply in the diet. In our study, the content of n-3 acids beneficial to health was over four times higher (p < 0.05) in M₁ meatballs, five times higher in M₂ meatballs, and about 4.5 times higher in M₃ meatballs compared to meatballs from the group WR, which can be associated mainly with the high content of alpha linolenic acid (C18: 3n-3 ALA) in the seeds of linseed contained in the seed mixtures added. Alpha-linolenic acid (18: 3 n-3, ALA) is not synthesized in the human body and must be supplied with the daily diet. The level of omega-3 fatty acids in the blood thus reflects the amount of ALA consumption. In the human body, ALA is converted into eicosapentaenoic acid (20: 5 n-3, EPA) and docosahexaenoic acid (22: 6 n-3, DHA). In light of the cited data, it is worth noting that the tested poultry meatballs with the seed mixture were characterized by a higher proportion of linoleic acid. An increase in the content of n-3 fatty acids after the addition of linseed to ground beef cutlets was also found by Novello et al. [11]. Zając et al. [29] indicate an increase in the content of polyunsaturated fatty acids in a meat product with the addition of hemp seeds.

One of the indicators of the quality of a healthy human diet is not only the level of consumption of omega-3 PUFAs, but also the proportion of omega-6 fatty acids to omega-3 fatty acids. Although the content of both omega-3 and omega-6 fatty acids in the diet is important, an excess of omega-6 fatty acids may interfere with the enzymes responsible for the desaturation and elongation of omega-6 and omega-3 fatty acids and hinder the conversion of ALA to EPA and DHA [50,51]. In addition, the ratio of omega-6 to omega-3 in the diet affects the functioning of neurotransmitters and the brain. A diet containing excessive amounts of polyunsaturated fatty acids (PUFA) and a high ratio of omega n-6 to omega n-3, increases the susceptibility to cardiovascular diseases, cancer, inflammatory and autoimmune diseases, and an increased level of omega-3 PUFA (low omega-6/omega 3) reduces the risk of these diseases [52,53]. In the present study, the ratio of omegan-6/omega n-3 fatty acids in poultry meatballs with wheat roll (WR) was not favorable and amounted to 10:1, while in meatballs with a mixture of hemp, amaranth and golden linseed seeds it was favorably narrowed to 3:1 in groups M₁ and M₃ and 2:1 in group M₂, respectively, which is the level considered optimal in the human diet. An improvement in the ratio of omega n-6 to omega n-3 was achieved by Bilek and Turchan [23] in beef cutlets with linseed flour; Bilska et al. [54] and Zając and Świątek [41] in pâtés with 20% addition of linseed oil and hemp and linseed seeds, and Zeinab et al. [45] in beef sausage with the addition of linseeds.

The addition of a mixture of seeds (M₁, M₂, M₃) instead of a hydrated roll (WR) did not increase the share (p > 0.05) of trans fatty acids, which are unfavorable to human health, in the finished product. Paying attention to the level of trans fatty acids in poultry meatballs with a mixture of linseed, amaranth and hemp seeds is due to the fact that unsaturated trans fatty acids incorporated into cell membranes, instead of cis isomers, cause changes in membrane permeability, activity and the number of receptors and enzymes associated with membranes, which is associated with the deterioration of the vital functions of these cells. Trans fatty acids have been shown to have a significant impact on the risk of developing atherosclerotic lesions and cardiovascular disease [55].

Fiber is considered a dietary component with a beneficial effect on health and is widely used in modern technologies to improve the functional values of meat products [3,9]. Dietary fiber has a beneficial effect on human health as a factor in preventing many diseases, including cancers of the gastrointestinal tract. It contributes, among other things, to reducing the absorption of cholesterol and triglycerides, lowering blood pressure, slowing down the breakdown of carbohydrates, and lowering blood glucose levels. Fiber accelerates intestinal peristalsis and the passage of contents through the digestive tract, prevents constipation, promotes the development of beneficial intestinal bacteria, and reduces the feeling of hunger [56]. In our study, the addition of a mixture of seeds caused a significant (p ≤ 0.05) increase in the proportion of fiber in poultry meatballs from groups M₁, M₂, and M₃. The possibility of using hemp ingredients in meat processing also drew the attention of Zając et al. [29], who, after adding hemp flour, hemp protein, husked and whole hemp seeds, obtained pork containing fiber. In the study by Verm et al. [9], gluten -free, fiber-rich lumps of goat meat were obtained using amaranth flour (1.5%) and quinoa flour (3%) as a substitute for wheat flour. Zeinab et al. [45] obtained beef sausage with fiber through the addition of linseed and chickpeas.

Among the vitamins found in meat products, vitamin E deserves special attention, which is considered the most important antioxidant soluble in fat, protecting the human body against various pathological processes related to oxidative stress [57]. Oxidative stress is one of the main factors influencing the development of atherosclerosis and its complications, and atherosclerosis is the source of most cardiovascular diseases. Natural vitamin E consists of a family of eight different compounds of tocopherols and tocotrienols, which are powerful antioxidants that trap lipoperoxyl radicals. Moreover, α-tocopherol also has anti-inflammatory and antithrombotic effects [58,59]. The study showed that enriched poultry meatballs from group M₃ were characterized by twice as much (p ≤ 0.05), and from groups M₁ and M₂—almost three times as much vitamin E as compared to the control product (WR). From a nutritional point of view, replacing wheat roll (WR) with a mixture of linseed, amaranth and hemp seeds can be considered as beneficial for increasing the health benefits of poultry meatballs. There is little research work on the use of plant additives to increase vitamin E content in poultry meat products. In the study by Dominguez et al. [60], the increase in the content of α-tocopherol in the meat product was obtained by replacing fat with olive oil.

Sensory attributes are the main determinant of the quality of meat products and their acceptability by consumers. In the production of fortified food, it is important that enriched meat products do not differ from traditional recipe products in terms of sensory characteristics [61]. In our study, the use of the addition of a seed mixture in groups M₁, M₂, and M₃, regardless of the proportion of individual components, had a favorable (p < 0.05) effect on smell and taste desirability, as well as the structure and bonding of the products. However, within the research groups, the M₂ meatballs enriched with 8% of plant additives were rated the best in terms of taste desirability, product binding and general desirability. On the other hand, the tenderness of the enriched meatballs in all study groups was rated lower compared to the product with the addition of wheat roll (Table 5). In the study, the increase in the hardness of the samples in the study groups was probably caused by the use of plant additives with a high fibre content. Fibre, thanks to its characteristic structure and ability to cross-link, allows for strengthening the texture of products with its addition. In the case of meat products made from ground mass, the higher hardness of products does not always reduce their quality, and the consumer expects good bonding and proper structure from such a product [9]. Furthermore, in the studies by Zając et al. [41], the pâté with both hemp seed and linseed and Zając et al. [29] of pork loaves with the addition of hemp seeds, de-hulled hemp seeds, hemp protein and hemp flour was harder than the control product. In the study by Zając and Świątek [41], the overall sensory quality of pâtés with the addition of hemp seeds and golden flax was rated higher compared to the control pâté. Naumova et al. [8] indicate that the 10% addition of hemp flour contributed to the improvement of the taste and aromatic properties of beef cutlets with acceptable consistency and juiciness characteristics; however, the higher proportion of hemp added decreased the sensory characteristics. On the other hand, Kotecka-Majchrzak [30] reported that 10% of hemp cake added causes a significant change in the color and taste of pork meatballs, but it retained acceptable taste characteristics. In studies by Bilek and Turhan [23] it was noted that the addition of linseed flour obtained from linseed seeds had an impact on the assessment of sensory characteristics (appearance, tenderness, juiciness and general acceptability). Verma et al. [9] indicate that the addition of amaranth seeds within the range of 1.5% increased the acceptability of all sensory characteristics of goat meatballs. The results of the study carried out by Sabzi Belekhkanlu et al. [61] showed that the use of amaranth flour in the production of typical meat hamburgers led to a product with good sensory properties acceptable to consumers. On the other hand, Longato et al. [21] showed that amaranth and pumpkin seeds used in the production of poultry burgers did not have a significant effect on sensory characteristics; only burgers with 2% amaranth seeds were rated higher for juiciness and overall acceptability compared to the control burgers. In the study by Zając et al. [29], the overall acceptability of pâtés with the addition of hemp ingredients (hemp flour, hemp protein and whole hemp seeds) was lower for fortified products, and only the taste of the product with the addition of husked hemp seeds was comparable to the control product. Novelo et al. [11] indicate that the addition of 10% golden linseed resulted in a reduction in flavor and texture.

The use of the author’s original mixture of linseed, amaranth and hemp seeds instead of wheat roll for the production of poultry meatballs allowed for obtaining a gluten-free product. Confirmation of the use of amaranth seeds in meat products for people with celiac disease was found in the studies by Tamsen et al. [10], Kerimoglu and Seredaroglu [62].