Effect of Different Processing Methods and Salt Content on the Physicochemical and Rheological Properties of Meat Batters

Abstract

The physicochemical and rheological properties of raw and cooked batters produced by a chopping or beating process with various amounts of salt content were studied. Various meat batters were made up for this purpose: the batter processed by chopping with 2% salt, by beating with 1% salt and 2% salt, respectively. Compared with the chopping, the beating cooked batters had higher L* value, hardness, G’ value at 80°C, and lower cooking loss. Using the beating process, the batter with 1% salt had lower L* values, hardness, springiness, and higher cooking loss than the 2% salt. From the micrographs, the batters produced by beating process exhibited more uniform and compact microstructure than the chopping. The result of low-field nuclear magnetic resonance exhibited that the batters of beating had higher water holding capacity than the chopping. Overall, the beating process enabled lowering of the salt content, cooking loss, and making the cooked batter more hard and elastic.

Keywords:

• Beating
• Dynamic rheological
• Meat batter
• LF-NMR
• Cooking loss

INTRODUCTION

Mincing and mixing of raw meat and other materials is a key stage procedure in manufacturing finely comminuted meat products, it influences the properties of meat systems.^[1,2] The bowl cutter (Fig. 1 can be used for industrial mincing and mixing of meat and other materials, and stability of the product was maximized,^[3] that depends on a rotating bowl with a series of rotating sharp knives running. The beating machine (Fig. 2 disrupts the connective tissues and myofibrillar structures with blunt blades (200 rpm) using a crushing force at variable speed, thus enhancing the friction forces and exchange of soluble components in the processed meats. This simulated the development of a traditional Asian product, kung-wan.^[4,5] Kang et al. reported that compared the chopping, the kung-wans and frankfurters produced by beating had better texture, higher cooking yield.^[5,6] However, few studies have reported the effects on physicochemical and rheological properties of meat batters produced by chopping or beating.

FIGURE 1 The cutting machine and knives.

FIGURE 2 The beating machine showing blunt paddles.

The salt is a key step in the swelling of myofibrillar proteins, the depolymerization of myofilaments, and the dissociation of actomyosin complex.^[7] Thus it stronger influences the texture, cooking yield, flavor, and shelf life of comminuted meat products.^[1] However, excessive dietary salt intake can raise blood pressure, which is a major cause of cardiovascular disease.^[8] How to reduce salt without sacrificing product quality is a challenge for the meat industry. The salt content of comminuted meat products could be reduced by using salt substitutes, masking agent, flavor enhancers, processing techniques, but few processing techniques could be used to reduce the salt level, except high pressure.^[9] It is necessary to find a new processing technique to decrease the salt content. Therefore, the objective of this work was to determine the physicochemical and rheological properties of pork batters by the chopping or beating with various amounts of salt to obtain the mechanism of lowering salt by the beating.

MATERIALS AND METHODS

Preparation of Meat Batter

Pork lean meat (semitendinosus, biceps femoris, mesoglutaeus, after 24 to 48 h of slaughtering, pH 5.78, 71.18% moisture, 20.47% protein, 7.14% fat) were purchased three times in 3 days from a local meat market (Nanjing, China). After the trimming of visible connective tissues, the lean meat was processed through a grinder (MM-12, Guangdong, China) using a 6 mm sieve. The ground meat (1.0 kg each) was packaged in nylon/PE bags and stored at –20°C until analyses (within 2 weeks).

The meat batters by different process were prepared with four replications at different occasions. The base ingredient consisted of pork leg meat (1000 g), added salt were denoted as follows: chopping with 2% (C), beating with 1% (T₁), and 2% (T₂). Meat batters were produced by either beating or chopping. For the beating method, the thawed ground meat was processed using a beating machine according to the process below: the thawed ground meat was beat with salt for 15 min (200 rpm; final temperature less than 10°C). For the chopping method, the products were prepared using a vacuum bowl cutter (Stephan UMC-5C, Germany) as follows: the thawed ground meat was chopped (1500 rpm) with salt for 75 s, then finished with a high speed (3000 rpm) for 60 s (final temperature less than 10°C). Then the prepared meat batters of beating and chopping were shaped into meatballs of 30 mm diameter, and cooked at 80°C water for 20 min (internal temperature 72°C), then cooled to room temperature; packed Nylon/PE bags and stored at 0–4°C until machine evaluation within 2 days.

Color Measurement

The color of raw and cooked batters was measured using a Minolta chromameter (illuminant: pulsed xenon arc lamp; CR-40, Minolta Camera Co., Japan), calibrated with a white calibration board CR – A43 (L* = 96.86, a* = –0.15, b* = 1.87). Five samples from each formulation or processing method were evaluated for internal color. A mean of five measurements was obtained for each L*, a*, and b* values.

Cooking Loss

After cooling at 2°C overnight, the cooked batters were weighed and the percentage weight loss was calculated using the following formula:

Instrumental Texture Profile Analyses (TPA)

After cooling at 2°C overnight, the cooked batters were kept at room temperature for 2 h. The hardness attributes of the cooked batter was determined using a texture analyzer (TA-XT.plus, Stable Micro system Ltd., Surry, UK) at room temperature. TPA parameters were determined using five cooked cores (each diameter 20 mm, height 20 mm). The conditions were as follows: test speed 2.0 mm/s; strain 50%, time 5.0 s; and trigger force 5 g. The cylinder probe (P/50, 50 mm stainless cylinder) of the texture analyzer mold was used. Attributes were calculated as follows: hardness, springiness, cohesiveness, chewiness, and gumminess.^[10]

Dynamic Rheological Measurement

Dynamic rheological studies were performed on a MCR301 dynamic rheometer (Auton. Paar. Ltd, Austria) using a procedure of Kang et al.^[6] A 50 mm parallel steel plate geometry with a 0.5 mm gap was used. The raw batters were heated at a rate 2°C/min from 20 to 80°C. During this heating process, the sample was continuously sheared in an oscillatory mode at a fixed frequency of 0.1 Hz. Changes of the G’ was measured during the heating. Each sample was measured in triplicate.

Scanning Electronic Microscopy (SEM)

Microstructure of cooked batters was determined using SEM (Hitachi-S-3000N, Hitachi High Technologies Corp., Toyoko, Japan), with the procedure reported by Haga and Ohashi.^[11] Cubic samples (3 × 3 × 3 mm³) obtained from cooked batters were fixed for 24 h at 4°C in a 0.1 M phosphate buffer (pH 7.0) containing 2.5% glutaraldehyde. The fixed samples were washed in 0.1 M phosphate buffer (pH 7.0) for 10 min, then post-fixed for 5 h in the same buffer containing 1% osmium tetroxide. The post-fixed samples were washed three times with 0.1 M phosphate buffer (pH 7.0) for 10 min, and then dehydrated in a graded series of 50, 70, 90, 95, and 100% ethanol for 10 min in each ethanol concentration followed by dehydration twice with 100% acetone for 10 min.

Nuclear Magnetic Resonance (NMR) Measurements

NMR relaxation measurements were performed according to the method of Han et al.^[12] with slight modification. Approximately 2 g of the sample was placed in a 15 mm glass tube and inserted in the NMR probe of a PQ001 Niumag Pulsed NMR analyzer (Niumag Electric Corporation, Shanghai, China). The analyzer was operated at resonance frequency of 22.6 MHz at 32°C. Spin-spin relaxation time (T₂) was measured using the Carr-Purcell-Meiboom-Gill (CPMG) sequence. T₂ was measured made a τ-value of 350 μs. Data from 10,000 echoes were acquired as 32 scan repetitions. The repetition time between subsequent scans was 8000 ms. Post processing of NMR T₂ data distributed exponential fitting of CPMG decay curves were performed by Multi-Exp Inv Analysis software (Niumag Electric Corp., Shanghai, China). Each measurement was performed at least triplicate.

Statistical Analysis

The data was analyzed using the one-way analysis of variance (ANOVA) program. The difference between means was considered significant at p < 0.05. Significant differences between means were identified by the Least Significant Difference (LSD) procedure using the statistical software package SPSS v.18.0 (SPSS Inc., USA).

RESULT AND DISCUSSION

Color Measurement

The color of the raw and cooked meat batters, formulated with various salt contents, prepared by either the chopping or beating process is presented in Table 1. At the same salt content (2%) and the color of the raw meat batters were significantly (p < 0.05) different produced by the chopping and beating process. Compared with the chopping treatment, the beating had greater L*, b*, and a* values. Kang et al.^[5] who reported that compared with the chopping process, the raw kung-wan batters produced by beating with 2% salt had higher L* value, and similar a* and b* values. The differences were made by either adding pork backfat or not adding it. However, in the cooked meat batters, T₂ had higher L* and b* values, and lower a* value than C. Different processing methods had different effects on the myoglobin structure in the meat batter. Such as pressure processing affects the myoglobin structure and decreases the content of meat.^[13–15] Due to the beating treatments having a longer processing period, resulting in more local denaturation and myoglobin oxidation, and greater discoloration in the beaten product.^[13] C and T₁ had similar L* and a* values in the raw meat batters. However, in the cooked batters, T₁ had greater L* and b* values, and lower a* value than C. The result implied that low-salt cooked batter (1%) produced by beating had greater lightness than the high-salt chopping batters.

TABLE 1 Color (L*, a*, and b* values) of raw and cooked meat batter preparations by chopping or beating with various amounts of added salt

Sample	Raw meat batter			Cooked meat batter
	L*value	a* value	b* value	L* value	a* value	b* value
C	50.12 ± 1.08^b	13.67 ± 0.91^b	8.31 ± 0.59^b	63.18 ± 0.40^b	7.08 ± 0.20^a	7.81 ± 0.15^c
T1	49.97 ± 0.92^b	12.69 ± 1.26^b	7.27 ± 0.81^c	66.84 ± 0.51^a	6.56 ± 0.22^b	9.15 ± 0.15^a
T2	55.26 ± 0.99^a	14.41 ± 0.61^a	10.25 ± 0.44^a	66.74 ± 0.45^a	6.30 ± 0.23^b	8.14 ± 0.17^b

Each value represents the mean ± standard deviation.

^a–cDifferent parameter superscripts in the same column indicate significant differences (p < 0.05). C: chopping with 2% salt; T1: beating with 1% salt; T2: beating with 2% salt.

The L*, a*, and b* values of the raw meat batters significantly (p < 0.05) increased with increasing salt contents in the beating treatments. T₂ had a higher (p < 0.05) L*, a*, and b* values than T₁. Kang et al. reported that the L* value of raw batters prepared by the chopping and beating increased with increasing salt content.^[5] However, the beating treatments had higher salt soluble protein (SSP), β-sheet, β-turn, and random coil content and more protein crosslinking than the chopping, and after thermal treatment, could form a better gel network.^[5,6] In the cooked meat batters, T₁ and T₂ had the similar (p < 0.05) L*and a* values, T₁ had higher (p < 0.05) b* value than T₂. A similar result was found by Tobin et al. in frankfurters which contained 1.5 and 1% salt had darker colors than the 2, 2.5, and 3% salt.^[16] Due to the different formulas, frankfurters contented backfat and other materials, Crehan et al.^[17] reported that no changes in L* value of frankfurters and significantly reduced the redness and yellowness when reduced the NaCl concentration from 2.5 to 1.5%. Sofos^[18] also reported that the reduction of salt content from 2.5 to 1.5% significantly decreased the yellowness of frankfurters. Overall, the L* value of raw batter improved with increasing salt content, there were no changes in the cooked batters.

Cooking Loss

The cooking loss of the meat batters, formulated with various salt contents, prepared by either the chopping or beating process is shown in Fig. 3 The processing and salt content had significant effects (p < 0.05) on cooking loss. T₁ and T₂ had lower (p < 0.05) cooking loss than C. The result was in agreement with Kang et al.^[5] who reported the beating processing could cause more myofibrillar protein extract and denaturation than the chopping after added salt, thus these changes lessened the cooking loss. The beating process could enhance the functional characteristics of the SSPs, and improve the water holding capacity.^[19,20] T₂ had lower (p < 0.05) cooking loss than T₁. Salt content in the meat batter determines the effects of the water binding and gelling capacity.^[21] Higher salt enhanced myofibrillar swelling and SSP extraction, and higher SSP concentration significantly decreased the cooking loss. It is known that the more SSP extracted from the meat would form a more stable gel, which would result in a lower cooking loss.^[22,23] Therefore, the use of the beating process and improving the salt content could improve the water holding capacity of gel and lessen the cooking loss.

FIGURE 3 Cooking loss (%) of raw batters when produced by chopping or beating with various amounts of added salt.

TPA

Both the processing and salt content had significant (p < 0.05) effects on the TPA (Table 2). In the beating treatments, the texture was better as the salt content was increased. When the salt content was increased, the amount of extracted SSP improved.^[22] Salt could activate the SSP to increase hydration and water-binding capacity, ultimately increasing the binding properties of proteins to improve texture.^[9] Reduced salt content lead to a decrease in solubilized myosin and actin, which further lowered the gel network and meat matrix formation.^[24–26] Compared with the treatment C, the hardness, springiness, adhesiveness, gumminess, and chewiness of T₁ were significantly improved (p < 0.05). Kang et al. reported that the use of the beating process with 1% salt in kung-wan resulted in a better texture than the chopping with 2% salt, as more SSP extracted and β-sheet formed when using the beating processing.^[5] Moreover, the processing speed and time also effected the mixing of salt in minced meat.^[2] The beating batters had longer process time, that improved the SSP dispersed or aggregated and formed good gel matrix.^[27] Therefore, the batter with low-salt content by beating could form the harder, more elastic, and stronger gel than the chopping one.

TABLE 2 Texture profile analysis of cooked meat batters preparations by chopping or beating process with various amounts of added salt

Sample	Hardness	Springiness	Adhesiveness	Gumminess	Chewiness
	(N)			(N)	(N mm)
C	68.80 ± 1.50^c	0.872 ± 0.014^b	0.681 ± 0.014^c	46.72 ± 1.10^c	41.64 ± 2.54^c
T1	73.56 ± 1.39^b	0.886 ± 0.016^a	0.720 ± 0.017^b	49.81 ± 1.30^b	43.10 ± 1.55^b
T2	76.83 ± 1.03^a	0.891 ± 0.013^a	0.738 ± 0.021^a	52.42 ± 1.43^a	46.23 ± 1.52^a

Each value represents the mean ± standard deviation.

^a–cDifferent parameter superscripts in the same column indicate significant differences (p < 0.05). C: chopping with 2% salt; T1: beating with 1% salt; T2: beating with 2% salt.

Dynamic Rheological Measurement

The effects of different salt levels and processing ways of raw meat batters on changes in G’ during the heating process were determined (Fig. 4). C involved three phases during the heating process because of protein denaturation. When heating from 20 to 42°C, G’ decreased slowly, and then a slight increase from 42 to 52°C, because the meat protein denaturation occurred, and gelation at 45–50°C was initiated after protein–protein interaction had taken place.^[28,29] The changes caused by the denaturation of the myosin tails could disrupt the protein network previously formed at lower temperatures, G’ had a moderate decline from 53 to 56°C,^[27,30] the result was similar with Kang et al.^[31] who reported the raw kung-wan batters produced by chopping (1 and 2% salt) had a slightly decline in G’ from 54 to 58°C. This was immediately followed by a phase where a rapid increase in G’ occurred as the temperature approached 80°C, because of the transformation of the viscous sol into an elastic gel network. T₁ and C had similar heating curves, but they had different transformation temperatures. The differences were caused by the different processing methods and salt level. Compared with the chopping process, beating could cause more meat protein denaturation, such as a decrease of α-helix content and an increase of β-sheet content.^[31] The T₁ had a higher G’ (26.5 KPa) than C (24.7 KPa), that indicated increased β-sheet content could improve G’. The similar result was reported that the higher β-sheet and β-turn contents present before heating could improve G’ of fish myosin at 90°C.^[19] T₂ involved three phases during the heating process. In the first phase, G’ exhibited a moderate increase as the temperature increased from 20 to 47°C, because the beating process resulted in a great number of unfolded myofibrillar and protein aggregation.^[27,32] In the second phase, G’ exhibited a slight decrease as the temperature increased from 48 to 50°C, because of the denaturation of the myosin tails. A rapid increase in G’ occurred at approximately 58°C as the temperature approached 80°C. Compared with C and T₁, T₂ had the lowest G’ of decline which caused by the myosin tails denaturation. The result indicated that using the beating process with 2% salt could decrease the effect of denaturation of myosin tails in the batter when heating. G’ of T₁ and T₂ was higher than C, and T₂ had the highest G’ (31.2 KPa) in the treatments, indicating that T₁ and T₂ had a denser protein network and better texture than C.^[33]

FIGURE 4 Changes in dynamic storage modulus (G’, Pa) with increasing temperature (T, °C) for different meat formulations. C: chopping with 2% salt; T1: beating with 1% salt; T2: beating with 2% salt.

Microstructure

Micrographs of the cooked meat batters demonstrated that salt content and processing method affected several properties of gel structure (Fig. 5). C presented a spongy structure with numerous uniform and dense cavities, these were the characteristic of thermal pork gel.^[16,34] When using the beating, the batters had higher SSP extract, formed more β-sheet content, and protein–protein crosslinking,^[5,6] T₁ and T₂ also had a spongy appearance, but the cavities were more uniform, compact, and smaller than C. Compared with T₁, T₂ had a higher salt content (2%) that was a benefit of the solubilization and swelling of the myofibrillar proteins, the depolymerization of myofilaments, and the dissociation of the actomyosin complex during the bearing.^[7,35] Meanwhile, salt alters the protein structure and increases SSP extract, hydration, consequently forming a stable gel and improved water holding capacity,^[9] thus the gel of T₂ was clearly morphologically different (denser and smaller) from the T₁.

FIGURE 5 Scanning electron micrographs of cooked meat batters. C: chopping with 2% salt; T1: beating with 1% salt; T2: beating with 2% salt.

Low-Field Nuclear Magnetic Resonance (LF-NMR)

Tables 3 and 4 show the distribution of LF-NMR T₂ measurements after multi-exponential fitting of raw and cooked meat batters. There were typically three relaxation populations centered at approximately 0–10, 30–60, and 100–400 ms, which defined T_2b, T₂₁, and T₂₂, respectively, except cooked C.^[36] T_2b is assigned to water tightly associated to protein and macromolecular constituents, and represents about 1–4% of the total water in the meat system. T₂₁ is a major component and considered to intra-myofibrillar water and water within the protein structure. T₂₂ was possibly corresponds to extra-myofibrillar water.^[37–39] The relaxation populations centered at approximately 30–60 ms. In the raw batters, due to T₁ contained lower salt, the initial relaxation time of T_2b was quicker (p < 0.05) than C and T₂. We increased the mean T₂ relaxation times with increasing pH and ionic strength, because the myofibrils swelling and thereby increased spacing between filaments.^[40] C had a greater NMR proportion of T_2b than T₁ and T₂, the reason was that compared with the chopping process, the beating could make more muscle myofibrils, endomysium, and perumysium were breakdown stronger and protein denaturation, and cause the water which tightly associated to decreased protein and macromolecular constituents. Compared with the treatment of C, T₁ and T₂ had a lower initial relaxation times of T₂₁, but T₁ had a higher NMR proportion of T₂₁ than C and T₂. The results indicated that C had more complete muscle myofibrils, and T₁ had more swelling state SSP, that could hold more intra-myofibrillar water.^[41] The initial relaxation times of T₂₁ were not significant different (p > 0.05) in the beating process treatments. However, T₂ significantly declined (p < 0.05) NMR proportion of T₂₁, because of the used beating process with high-salt (2%) made more muscle myofibrils solution, declined the space which hold water of intra-myofibrillar.^[37]

TABLE 3 Effect on relaxation time (ms) and peak ration (%) of raw meat batters preparations by chopping or beating process with various amounts of added salt

	Relaxation time (ms)			Peak ration (%)
Sample	T2b (ms)	T21 (ms)	T22 (ms)	T2b (%)	T21 (%)	T22 (%)
C	0.66 ± 0.08^a	29.55 ± 2.13^b	336.62 ± 14.09^a	2.96 ± 0.06^a	96.75 ± 0.18^b	0.29 ± 0.15^b
T1	0.59 ± 0.11^b	32.75 ± 0.00^a	346.57 ± 15.82^a	2.64 ± 0.06^b	97.15 ± 0.09^a	0.20 ± 0.12^b
T2	0.76 ± 0.09^a	32.75 ± 0.00^a	364.26 ± 16.29^a	2.79 ± 0.19^b	96.77 ± 0.20^b	0.46 ± 0.15^a

Each value represents the mean ± standard deviation.

^a–cDifferent parameter superscripts in the same column indicate significant differences (p < 0.05). C: chopping with 2% salt; T1: beating with 1% salt; T2: beating with 2% salt.

TABLE 4 Effect on relaxation time (ms) and peak ration (%) of cooked meat batters preparations by chopping or beating process with various amounts of added salt

Sample	Relaxation time				Peak ration (%)
	T2b1 (ms)	T2b2 (ms)	T21 (ms)	T22 (ms)	T2b1 (%)	T2b2 (%)	T21 (%)	T22 (%)
C	0.53 ± 0.04	1.89 ± 0.24^c	25.70 ± 1.85^a	285.50 ± 12.97^c	0.52 ± 0.17	0.76 ± 0.19^a	87.50 ± 0.30^c	10.97 ± 0.47^a
T1		7.23 ± 1.82^a	20.84 ± 1.40^b	377^.41 ± 10.36^a		0.47 ± 0.3^b	88.89 ± 0.78^b	10.63 ± 0.58^a
T2		4.89 ± 1.03^b	22.35 ± 1.61^b	328.25 ± 16.40^b		0.71 ± 0.25^a	92.01 ± 0.65^a	7.28 ± 0.58^b

Each value represents the mean ± standard deviation.

^a–cDifferent parameter superscripts in the same column indicate significant differences (p < 0.05). C: chopping with 2% salt; T1: beating with 1% salt; T2: beating with 2% salt.

In the cooked batters, C had four relaxation populations (two located in 0–10 ms), and the initial relaxation times of T_2b were quicker (p < 0.05) than T₁ and T₂, the result indicated that both the chopping and beating processes produced different effects of the meat protein. This was in agreement with some papers that reported that whenever kung-wan batters were raw or cooked, the β-sheet content of samples produced by beating process was higher than the chopping.^[4,31] T₁ had the smallest NMR proportion of T_2b, that indicated salt level also effect on SSP characteristics.^[40] The initial relaxation times of T₂₁ in T₁ and T₂ were quicker than C, indicated T₁ and T₂ had a better gel network than C. A similar result was reported by Han et al.,^[12] the gel with various amounts of microbial transglutaminase had better texture and quicker initial relaxation times of T₂, because of the changes of fast relaxing protein and slowly relaxing water protons. The initial relaxation times of T₂₂ in T₁ and T₂ were slower, and T₂ had smaller NMR proportion of T₂₂ than T₁ and C, that indicated T₂ had less water out the gel.^[37] The result was similar to the cooking loss (Fig. 3). Therefore, the use of LF-NMR could determine cooking loss, texture, and other physicochemistry properties in the raw batter and thermal gel.

CONCLUSION

The study exhibited that the use of different salt contents and processing methods significantly influenced the physicochemical and rheological properties of both raw and cooked batters. Compared to chopping with 2% salt, the raw and cooked batters produced by the beating with 1 and 2% salt had higher L* values, better texture, and lower cooking loss. With beating, the sample with 2% salt (T₂) had higher L* values and texture, and lower cooking loss than the 1%. They all had three phases during the thermal treatment, but T₂ had the highest G’ value at 80°C, that implied having the best texture. Compared to chopping, the cooked batters produced by beating had more uniform and compact microstructure. The results of LF-NMR indicated that the beating processing could improve the water holding capacity in the cooked batter. Overall, the results demonstrated that by using a beating process it was possible to produce low salt meat batter, and having desired qualities with lower cooking loss.

FUNDING

This study was supported by National Natural Science Foundation of China (NSFC, Grant No. 31501508) and program for Innovative Research Team (in Science and Technology) in University of Henan Province (13IRTSTHN006).

Additional information

Funding

This study was supported by National Natural Science Foundation of China (NSFC, Grant No. 31501508) and program for Innovative Research Team (in Science and Technology) in University of Henan Province (13IRTSTHN006).