3.1. Body Part Weight-Ratio and Carcass Utilization
Pâté yields were satisfactory, with approximately 100 g of carcass and liver required to produce 72 to 86 g of the different pâté ratios. On a larger scale, one ton of forechest and liver treated as subproducts could result in an average of 820 kg of a product presenting excellent performance and added value, minimizing the amounts discarded from processed carcasses. Compared with other products, 1.2 kg of raw
Piaractus brachypomus meat allows for the production of only about 700 g of processed pâté [
16]. Notably, the entire proposal presented herein employs an efficient use of animal parts with low commercial value, resulting in a final product with low associated costs.
The weight ratio of bullfrog carcasses was determined by relative forechest, thigh, calf, and trunk meat amounts, established as 12.70%, 41.12%, 20.27%, and 25.91%, respectively. The trunk is the second most abundant portion, although it contains relatively little meat compared to the thighs, calves, and forechest, which contain the main edible bullfrog meat portions. A 38.61% carcass yield corresponding to undervalued animal parts was noted, greatly reducing added product value due to underutilization.
Different muscle regions and the liver usually have little or no commercial use and are usually discarded. Remodeling the classification of carcass products marketed for different purposes makes it more economical to use these routinely discarded portions. Similar carcass yields and ratios are noted compared to other studies that evaluate the use of animal cuts and their nutritional composition [
11,
12]. The academic literature consistently affirms the presence of a relationship between a favorable carcass yield and high-quality meat, be it in terms of nutritional parameters or meat quality [
23]. Prioritizing the utilization of the majority of the animal’s anatomical parts enables the incorporation of sections that exhibit favorable meat quality.
3.3. Macro- and Micronutrient Pâté Contents
No significant Aw and pH differences were observed during the processing period, with average Aw values of 0.972 ± 0.04 and pH values ranging from 7.0 to 6.6. Individual parameters are presented in
Table 1 below.
The decreased pH values observed in each treatment are directly associated with the reduced liver percentages added to each formulation. The final product pH is directly associated with the interaction between lipids and the aqueous product portion, as reduced liver amounts result in decreased lipid and aqueous portion interactions. The literature also describes that this interaction varies according to the type of liver during emulsification, where chicken liver exhibits the potential to increase pH product values [
27]. Fat effects on meat and meat product textures have been extensively studied, with higher fat contents associated with less firm and more juicy products [
28].
Food Aw and pH variables are directly associated with rancidity and protein degradation. Fishery meat products are considered a source of desirable fatty acids and valuable nutritional components, with the color deterioration caused by lipid oxidation comprising the main quality degradation factor during food processing and storage [
2,
29].
As mentioned previously, the literature has demonstrated that the association of proteins and lipids during pâté emulsification mainly prevents lipid oxidation, ensuring a greater supply of desired fatty acids for consumers and increasing product shelf lives [
25,
30].
The macronutrient composition values of the prepared products and the bullfrog torso meat and liver paste are displayed in
Table 2.
Frog carcass heating (bleaching) at 60 °C for 15 min followed by deboning allowed for suitable raw meat structure, composition, and nutritional quality, confirmed by the water content, ash, protein, and lipids results. Homogenizing the final product base mass (mixed pulp) for pâté production is noteworthy, as no final product appearance changes were noted. No intrusive odor was noted in the final products, ensuring food quality. Furthermore, all samples were homogeneous and contained no solid residues, which could lead to handling or consumer risks [
1,
8].
Concerning fish pâté products, moisture, lipid, protein, ash, and carbohydrate contents of 61.2%, 22.2%, 11.6%, 2.2%, and 2.8%, respectively, have been reported for white croaker (
Micropogonias furnieri) pâtés and contents of 61.4%, 19.2%, 10.6%, 4.5%, and 4.3%, respectively, for cachama (
Piaractus brachypomus) pâtés [
1].
No significant dry matter differences were observed when comparing C1 with the five pâté treatments. The literature indicates that liver pâté incorporation does not affect dry matter content due to final product emulsification, contributing toward nutrient preservation [
31].
The developed products exhibited low fat and high protein content. However, only a general comparison to other studies was possible, as previous assessments focused on the meat from whole bullfrog legs instead of forechest meat [
12]. In addition, fat contents were slightly higher than reported in other studies, which may be associated with the added liver and the fact that the final products comprised fixed liver and animal back segment ratios. The high water content of bullfrog meat makes this meat more tender and softer than other meats. In addition, bullfrog meat fat content is low, especially forechest meat, thus making it a good choice for people who require low fat but high protein intakes.
The total amino acid and collagen contents reported herein are also noteworthy, with total essential amino acids (EAAs) ranging from 8 to 9% in relation to total crude protein content in the mixed matrix and collagen ranging from 12 to 15%. Most meat properties were maintained, mainly concerning the essential amino acids lysine and methionine. The total amino acid contents of different bullfrog meat parts range from 10.30% to 15.41%, according to Zhu et al. [
12]. Considering the different applied mixture ratios and heat processing, no significant protein loss was observed compared to torso meat and liver samples. Similar EAA ranges have been described in the literature, reinforcing the potential use of bullfrog livers and meat mixtures as high-quality protein sources.
Thigh meat is richer in essential amino acids when compared with bullfrog forechest and calf muscle meat. Amino acids are the most important taste compounds in food, and bullfrog meat is favored in this regard, with a unique flavor. Crude protein contents (17–24%), as well as the mono and dipeptide levels, were similar for the forechest, thighs, and calf (18.61%, 19.04%, and 18.98%, respectively). Zhu et al. [
12] describe a wide distribution of functional monopeptides and essential amino acids in different muscle segments. The addition of liver to the developed pâté, however, allows not only for increased protein levels but also heightened functional product capacity.
High protein foods of animal origin, especially developed from bullfrog carcasses, contain proteins with a high solubilization capacity due to high essential amino acid levels. The development of products from this raw material can also serve demanding consumers interested in foods with added technological value, such as products based on noble parts or by-products, which constitute promising alternatives. In this sense, pâté production is an established alternative in this regard, especially concerning low commercial value materials. Thus, technological development generates an alternative high-quality product developed from this by-product [
12,
16].
The main detected micronutrients were K, P, Na, Mg, Ca, Zn, Fe, Cu, and Mn (
Table 3). Potassium was the most abundant mineral in all samples, followed by P, sodium, Mg, and Ca. Since most micronutrients are involved in biochemical reactions, the forechest meat contains lower K, P, and Mg contents compared to livers (
p < 0.05), albeit non-significantly [
11]. Minerals are an important part of metabolic reaction bioprocesses in living organisms. Potassium, for example, contributes to the intracellular ion balance, while sodium constitutes the main extracellular cation, assuming an important role in acid–base balances. Phosphorus, on the other hand, constitutes phospholipids and phosphoproteins [
24].
Mineral elements within pâté are sourced from bullfrog bones and livers, which undergo a series of processing and heating procedures. After the treatment to achieve a paste-like consistency, enzymatic reactions are initiated but subsequently halted through heat treatment. This paste-like substance is incorporated into meat product formulations, allowing for the enrichment of biologically active calcium, potassium, magnesium, sodium, and phosphorus primarily [
32]. Higher levels of potassium, magnesium, and phosphorus are observed mainly in the liver. However, the limited presence of potassium, copper, manganese, and zinc in the meat-bone paste leads to a reduction in the content of these minerals when the meat-bone paste is used as a substitute for beef liver in reformulated pâtés. Nevertheless, it is noteworthy that the increased addition of liver did not result in a proportional increase in the concentration of these elements in the final pâté product.
3.4. Microbiological and Toxicological Characterizations of the Formulated Pâté
After plate counting using specific media for each microorganism studied, morphotinctorial and biochemical analyses were performed to characterize the colonies found. The microbiological parameters of the developed formulations are depicted in
Table 4 below:
Regarding safety parameters, despite the risk of post-processing contamination, all products were considered safe according to current microbiological and toxicological standards. The choice of applying a quality standard for products aimed at human consumption to raw materials is due to the need to ensure final product safety, as raw material selection is an important factor in highly manipulated products [
17,
20].
Coliforms, enterococci, and staphylococci are common bacterial contaminants in fishery products, originating mainly in the handling stage. Thermotolerant coliforms,
Salmonella spp., and coagulase-positive
Staphylococcus present in the bullfrog raw material were all within Brazilian legislation standards from the handling stage to the storage period [
8,
10,
20]. Adequate heat treatment contributes to significant microbial population reductions in final fish meat preparations [
1].
The total mesophilic counts observed herein demonstrate the efficiency of the applied heat treatment. Total mesophilic counts above 2.95 log10CFU g
−1 were detected in the raw material, undergoing a drastic reduction after thermal processing, present in minimal concentrations in the final products. Despite not being recommended in Brazilian legislation, total mesophilic bacteria counts comprise an important parameter to be evaluated during product development, are directly correlated with the entire processing quality, and may reflect on final product quality [
33,
34,
35].
The microbiological evaluation results following the storage period are presented in
Table 5.
No microbial growths were noted in any of the evaluated treatments after a 30-day storage period, indicating product suitability under adequate storage as a result of heat treatment effectiveness, which was shown as capable of completely inactivating initial viable cells associated with adequate storage, prolonging their shelf life. Heating and chilling processes are applied to food preservation with the aim of inactivating and preventing microbial growth, serving as a basis for shelf life assessments [
36,
37,
38]. They may also, however, result in product quality risks, as they may alter sensorial and nutritional product characteristics [
39].
The toxicological paremeters evaluated are presented in
Table 6 below:
No histamine and sulfur-based compounds were detected in any of the samples, with an established limit of detection of 1.00 µg g
−1, in accordance with the Brazilian standard of 10 mg 100 g
−1 [
17] and the North American standard of 5 mg 100 g
−1 [
40]. A value of 1 mg 100 g
−1 histamine has been previously reported for thermally processed bullfrog meat [
9]. Therefore, both the raw bullfrog materials and the final products formulated herein presented satisfactory hygienic-sanitary conditions, with no significant handling and processing interferences concerning product safety.