Comparing the Effects of Different Additives on the Physicochemical and Textural Characteristics of Pork Batter

SPI and SC were purchased from Dongbang FoodMaster (Eumseong, Korea). Whole porcine blood and backfat were acquired from a local slaughterhouse. Ethylenediaminetetraacetic acid (EDTA) was purchased from Sigma-Aldrich (St. Louis, MO, USA). Fibrous casings were obtained from Kalle (Wiesbaden, Germany).

To prepare plasma, 1 L of whole porcine blood was added to 2 g of EDTA. The mixed blood samples were centrifuged at 8,000×g for 15 min at 4°C. Thereafter, the obtained BP was stored at –50°C. Fresh leg of pork and backfat were diced and ground to 5-mm-diameter using a mincer. Pork emulsions were prepared according to the formula presented in Table 1. The basic ingredients of the pork emulsion were as follows: 72.4% meat, 11.2% backfat, 14.9% ice, and 1.5% refined salt. The following samples were prepared: T1 (commercial pork emulsion), T2 (0.5% SPI), T3 (1.0 % SPI), T4 (1.5% SPI), T5 (0.5% SC), T6 (1.0% SC), T7 (1.5% SC), T8 (0.5% BP), T9 (1.0 % BP), and T10 (1.5% BP). The minced meat was ground for 1 min using a bowl cutter; subsequently, half of the ice, 1.5% refined salt, and an additive (SPI, SC, or BP) were mixed for 2 min. Thereafter, fat was added and emulsified for 1 min, and the remaining half of the ice was placed in a batter and further mixed at a high speed (bowl speed: 24 rpm; knife shaft speed: 2,840 rpm) for 3 min to obtain emulsion batters. The emulsified batters were subsequently stuffed into fibrous casings (70-mm diameter) using a stuffer (IS-8, Sirman, Pieve di Curtarolo, Italy) and cooked in a cooking chamber (Thematec Food Industry, Seongnam, Korea) until the internal temperature reached 75°C. After cooling, the samples were stored at 4°C for further analysis.

Emulsion stability was measured using a method described previously, with modifications (Serdaroğlu and Özsümer, 2003). Emulsified pork batter samples were placed in pre-weighed 50-mL centrifuge tubes and centrifuged at 3,000×g for 2 min at 4°C. Each tube was heated in a water bath for 30 min until reaching 75±1°C, cooled to 4±1°C, weighed, transferred to a pre-weighed crucible, and dried for 16 h. Total loss (%) was measured based on the total fluid released from the centrifuged pork batter, and moisture (%) and fat (%) loss were evaluated based on the magnitude of the total loss. These emulsion stability-related factors were calculated as follows:

The shear force of each sample was estimated using an Instron 3343 tensiometer (US/MX50, A&D, Ann Arbor, MI, USA) attached to a Warner-Bratzler shearing device, providing a 100-mm/min crosshead speed. Five cores (2×2×1 cm) of each emulsion were analyzed at a crosshead speed of 100 mm/min. A texture analyzer (TA-XTZ-5, Shimadzu, Kyoto, Japan) was employed under the following conditions: a 5-mm-diameter cylindrical plunger, 60-mm/min depression speed, and 500-N load cell. Texture property analysis of each sample was replicated five times.

Statistical analysis was performed using the PROC MIXED procedure of SAS (SAS Institute, Cary, NC, USA). All data were carried out using a completely randomized design. Each replicate was considered as the experimental unit for all analyses. Outlier data were checked using the UNIVARIATE procedure of SAS (Steel et al., 1997). The LSMEANS procedure was used to calculate treatment means and the PDIFF option of SAS was used to separate the means if the difference was significant. The effects of different additives were compared with those of control based on the contrast test. In addition, the effects of additional SPI and SC were also than those of BP based on the contrast test. Orthogonal polynomial contrast tests were also performed to verify the linear and quadratic effect of increasing inclusion levels of SPI, SC, and BP. Significance for statistical test was considered at p<0.05.

The physicochemical characteristics, including pH and CIE color (CIE L*, CIE a*, CIE b*, W, C, and h) values, of pork emulsions with the different additives (SPI, SC, and BP) at varied concentrations (0.5, 1.0 and 2.0 g) are compared in Table 2. The pork emulsion pH values of the different additive treatments (T2–T10) significantly decreased compared with that of T1 (the control, p<0.05). Among the treatments, pH significantly decreased in the following order of magnitude: SPI>SC> BP; in addition, pH decreased with increasing additive levels (linear and quadratic, p<0.01).

The pH value of meat products depends on the inherent pH of the raw meat and any included additives, which in turn can influence various physical and chemical properties, such as meat color, texture, water-holding capacity, and gel stability (Puolanne et al., 2001). Dàvila et al. (2007) reported that the addition of porcine BP (2 g/100 g) and SC to pork gel was affected by pH, especially that in the 5.3–6.2 range, influencing water-holding capacity via gel formation-related protein aggregation (Dàvila et al., 2007). In addition, the viscosity of the BP-added emulsion at pH 6.5 and 7.0 was significantly greater than that at pH 5.0. At high pH levels, SPI addition resulted in the formation of more disulfide-mediated aggregates, leading to tertiary structure loss and reduced solubility. In contrast, SPI at pH 6 displayed better storage stability than at other pH levels (Guo et al., 2020). This study also revealed that within a pH range of 6.2–6.6, the different additives potentially enhanced emulsion stability and texture properties.

The pork emulsion CIE L* values of the different additive treatments (T2–T10) significantly decreased (p<0.001) compared with that of T1 (control). Further, the CIE L* values of the pork emulsions significantly increased in the following order of magnitude: BP>SC>SPI; in addition, these values increased with increasing SPI and SC levels (quadratic association, p<0.01). However, CIE L* was not influenced by increasing BP levels in pork emulsion. The pork emulsion CIE a* values of T2–T10 significantly decreased (p<0.001) compared with that of T1. Moreover, the CIE a* values of the pork emulsions significantly increased in the following order of magnitude: SPI>SC>BP; in addition, these values increased with increasing SC levels (linear and quadratic, p<0.05). The CIE a* of the pork emulsions increased with increasing BP level (quadratic association, p<0.01) but was not influenced by SPI level. The pork emulsion CIE b* values of T2–T10 significantly increased (p<0.001) compared with that of T1. The CIE b* of the pork emulsions significantly increased in the following order of magnitude: SPI>SC>BP. Significant differences were noted upon increasing SPI and BP addition levels; nonetheless, no significant difference was observed after SC addition. The pork emulsion W values of T2–T10 significantly decreased (p<0.001) compared with that of T1. No significant differences in whiteness were noted among the different additive treatments. A quadratic increase (p<0.05) in the pork emulsion W values occurred with SC and BP level increases of 40.67–42.99 and 38.40–43.82, respectively; however, increasing the SPI level of the pork emulsions decreased their W values (linear and quadratic, p<0.05). The pork emulsion C* values of T2–10 were significantly lower than that of T1 (p<0.001). Further, no significant differences in C* values were observed after SPI and BP addition; nevertheless, C* significantly decreased with SC addition (p<0.01). The C* values of the pork emulsions significantly increased with increasing SPI level (linear and quadratic, p<0.01); however, these values significantly decreased with increasing BP level (quadratic association, p<0.001). The hue angle of the pork emulsions significantly increased in T2–T10 (p<0.001) compared with that in T1. Moreover, it significantly increased in the following order of magnitude: BP>SC>SPI; in addition, it exhibited a linear and quadratic increase (p<0.05) with SPI and SC level increases of 68.73–69.98 and 70.13–70.41, respectively. BP influence the pH and water holding capacity in food products (Polo et al., 2009; Silva and Silvestre, 2003), especially the pH alteration and improved water holding capacity affect color stability and the overall appearance (Qiao et al., 2001). Thus, the addition of BP can attribute to enhance the color intensity, leading to an increased hue angle.

Non-meat ingredients are typically used in meat products to enhance color or influence color variation. This study’s results are not entirely consistent with those of Cofrades et al. (2000), who found an increase in plasma protein addition level (0%–5%) to significantly increase CIE L* and CIE b* in pork sausage (Cofrades et al., 2000). In addition, soy protein concentrate has been found to provide protection against oxymyoglobin oxidation, which leads to metmyoglobin having a brown color compared with that of the control (Wanasundara and Pegg, 2007). Moreover, BP proteins in emulsion-type pork sausage have been found to exhibit reduced CIE L* (Soriano et al., 1997). Meat color changes are presumably induced by raw material fibers in meat products, according to previous studies (Claus and Hunt, 1991; Troutt et al., 1992). In a prior study, Turkish meatballs with various inclusion levels (5%, 10%, 15%, and 20%) of dietary fiber yielded higher CIE b* values (Yasarlar et al., 2007). Notwithstanding, this study could not clearly establish relationships between the three additives and color parameters; hence, further studies are required to compare and analyze potential factors influencing meat color parameters in non-meat proteins.

The emulsion stability of the pork emulsions after adding the different additives (SPI, SC, and BP) at varying concentrations (0.5, 1.0, and 2.0 g) are compared in Table 3. On comparing emulsion stability between T1 and T2–T10, total and moisture loss were lower (p<0.01) in the additive-treated groups than in the control, indicating superior stability. However, fat loss was higher (p<0.01) in the additive-treated groups, indicating decreased stability. Protein extracts isolated from meat have been found to stabilize O/W emulsions at pH 3–11 (Li et al., 2020). SPI has two main components: 7 S (β-conglycinin) and 11 S (glycinin), both possessing emulsifying properties (Peng et al., 2020). SPIs are amphiphilic in nature, enabling them to play important an role in thickening and surfactivity, thus forming stable O/W emulsions (Lu et al., 2017). SC is a commercial product obtained from milk casein aggregates, and it serves as an excellent emulsifier in O/W interfaces because of its amphiphilic nature (Zhou et al., 2022). Additionally, SC comprises two proteins, namely, αs1-casein and β-casein, which can induce the formation of a stable emulsion by covering fat globules (Dickinson et al., 1998). The significantly high solubility of SC has been observed at pH 7.0–8.0 (Duarte et al., 1998). Amphiphilic structures possess hydrophilic main chains with a small amount of branched hydrophobic chains. The presence of hydrophobic groups enables the amphiphilic polymers to reduce the interfacial tension between oil and water, resulting in the effective emulsification of oil (Abidin et al., 2012). Additionally, intermolecular hydrophobic interactions among the polymers lead to the formation of a network structure, significantly increasing the viscosity of the amphiphilic polymers (Lu et al., 2017). BP can also be used as an emulsifier or fat replacer in meat products. Bovine BP has demonstrated considerable hydrophobicity and a high emulsifying activity index at pH 3.0 and 7.0, respectively (Silva and Silvestre, 2003). The viscosity of a porcine plasma protein-stabilized gel-like emulsion at pH 6.5 and 7.0 was found to be significantly higher than that at pH 5.0 (p<0.05); in addition, after 48-h storage, the emulsion exhibited stability higher than 91.07% (Li et al., 2017). On comparing emulsion stability among the three different additives, BP, SC, and SPI exhibited superior stability in that order. In particular, total loss decreased as additive level increased (linear and quadratic, p<0.01), suggesting an influence on stability enhancement. Moisture loss was only reduced (linear and quadratic, p<0.01) by BP, confirming its impact on stability. Thus, these observations indicate that the amphiphilic structures and emulsifying activities of the three additives can induce high emulsion stability, and the effects of additives on emulsion stability may be influenced by pH.

Shear force is an indicator influenced by tenderness, affecting texture characteristics. It was significantly higher in all additive-treated groups than in the control group (Table 4). On comparing the additives, BP and SC exhibited significantly higher shear force than SPI. However, no significant differences in shear force were noted among the additive-treated groups based on treatment level.

The textural characteristics (including hardness, cohesiveness, springiness, gumminess, chewiness, and adhesiveness) and tenderness of the pork emulsions treated with the different additives (SPI, SC, and BP) at varied concentrations (0.5, 1.0, and 2.0 g) are compared in Table 4. All textural characteristics did not display significant differences between the treatments (T2–T10) and control (T1). Moreover, the gumminess of the pork emulsions significantly increased (p<0.05) after BP and SPI addition compared with that after SC addition; however, no significant difference in other textural characteristics was observed among treatments with different additives (T2–T10). Furthermore, hardness significantly increased with increasing SPI levels. Comprehensively, among the three additives, BP notably influenced shear force and gumminess. The structural characteristics of heat-treated plasma protein gels have been found to impact the hardness strengthening effect in the pH range of 5.0–7.0 (Li et al., 2017).

Previous research has also demonstrated that adding plasma protein at a concentration of 1 g/100 g or higher significantly increases the mechanical force and binding strength of ground beef (Seideman et al., 1979; Suter et al., 1976). Wang et al. (2023) also concluded that plasma protein improved the gumminess of restructured ground chicken patty (Wang et al., 2023). Hydrophilic amino acids in plasma proteins facilitate their involvement in the gelation process alongside salt-soluble proteins, such as myosin and troponin (Bai et al., 2020; Gao et al., 2023). Moreover, the structure of myofibrillar and plasma proteins tends to unfold, enhancing their ability to interact under the influence of ultrasound. Plasma proteins also serve a crucial role in modifying the unique structure of myofibrillar proteins (Wang et al., 2023). Consequently, BP addition in this study resulted in the formation of a more stable protein structure in the emulsion, potentially enhancing texture properties. Consequently, relative differences were noted among the additives in certain texture properties; however, the other texture properties did not significantly differ among the additives. Thus, compare the texture properties of SPI, SC, and BP in the pork emulsion samples.