Functional and instrumental textural properties of reduced-salt meat emulsions with konjac gel: Combined effects of transglutaminase, isolate soy protein, and alginate

ABSTRACT

The functional and instrumental textural properties of reduced-salt meat emulsions (RSMEs) containing konjac gel, with combined transglutaminase (TG), isolated soy protein (ISP), and alginate were investigated to determine optimal quality characteristics. Control groups were produced using 1.2% salt (-) and 1.5% salt (+). RSMEs (1.2% salt) formulations contained T1 (konjac gel), T2 (konjac gel + TG), T3 (konjac gel + ISP), T4 (konjac gel + TG + ISP), T5 (konjac gel + alginate), and T6 (konjac gel + TG + alginate). The moisture content and myofibrillar protein solubility of all RSMEs (from T1 to T6) were significantly higher than that of control (-) (P < .05). T5 and T6 showed the lowest cooking loss and expressible fluid separation (P < .05), which means that T5 and T6 have good emulsion stability. Texture profile analysis of T6 were most similar to those of controls (+) with normal salt (1.5%) levels. in addition, the apparent viscosity of T6 was the maximal. These results indicated that T6 might successfully induce certain technical properties in RSMEs. Consequently, the combination of konjac gel, TG, and alginate are worthy to improve the quality of RSMEs.

KEYWORDS:

• Reduced-salt
• konjac gel
• transglutaminase
• isolate soy protein
• alginate

Introduction

Meat products, which are consumed extensively worldwide, constitute a large and important source of meat protein, and supply essential amino acids required by the human body.^[1] Salt is an important component of meat products, and meat products might generally contain about 2–3% salt.^[2] Since ancient times, salt was added to meat product to improve microbial stability. Furthermore, the addition of salt to meat products has played a substantial role in improving water-holding capacity and emulsion stability, and these were related to desirable texture properties and juiciness.^[3] Desmond^[4] reported that salt has notable effects on the rheological and structural properties of meat products, which are associated with the elution of salt soluble proteins such as the myofibrillar protein. However, high salt diets are associated with a higher risk of heart disease, cancer, hypertension, and obesity.^[5,6] Thus, it is necessary to formulate various strategies for reducing the amount of salt in processed meat,^[7] because the reduction in salt levels results in the deterioration of shelf life and quality characteristics including emulsion stability and texture properties.^[4]

Konjac consists of neutral water-soluble polysaccharides, and has been used since ancient times with a plant native to East Asia.^[8] Konjac has a strong water binding capacity, and thus improves physiological properties and structural stability, by allowing proteins to combine with polysaccharides.^[1] Several researchers have found that the konjac gel can be used advantageously with low-fat meat processing technology.^[19,10]

Transglutaminase (TG) can improve texture by catalyzing the non-sulfur covalent bond between the ɛ-amino group in the peptide residue of the protein and the β-carboxyamide group of a protein bound to the glutamine residue.^[11] Some studies have been conducted on meat products using TG, to improve the texture of low fat or reduced/fat meat products.^[12,13]

Isolated soy protein (ISP) is a non-meat protein containing a high protein concentration of 90% or more. Some studies have reported that isolated soy protein improves quality characteristics such as the water holding capacity, emulsification, emulsion stability, and meat product texture.^[14] Choi et al.^[15] reported that adding isolated soy protein to frankfurter improves the emulsion stability.

Alginate was a negatively charged polysaccharide acquired from sea tangle and seaweed.^[16] Alginate is extensively used in meat processing, mainly to improve viscosity, stability, and gel formation.^[17] Kim et al.^[18] reported that excellent quality characteristics were observed after the addition of alginate into restructured duck ham formulations. They reported that the addition of alginate could improve emulsion stability, water holding capacity, and textural properties of meat products. However, though certain studies have described the addition of TG, ISP, and alginate separately, no study has described the use of a combination of TG, ISP, and alginate. This study aimed to develop a reduced-salt (1.2%) meat emulsion that quality is similar to the meat emulsion with a normal salt content (1.5%). Thus, this study evaluate the effect of a combination of TG, ISP, and alginate on the optimal quality characteristics of reduced-salt meat emulsions with konjac gel.

Materials and methods

Preparation of manufacturing reduced-salt meat emulsion

Fresh pork ham (protein 15.98%, moisture 73.41%, fat 5.07%) and pork back fat (fat 85.12%, moisture 10.21%) were purchased from a local processor, at 48 h postmortem. The visible connective tissue and intramuscular fat within the pork ham was removed. Konjac gel was manufactured using konjac (HuBei konson konjac Co., Ltd., HuBei, China), carrageenan (carrageenan BF-100, ES Food Co. Ltd., Kunpo, Korea), and water in a ratio of 7: 3: 90. The konjac gel preparation containing konjac and carrageen were homogenized in water at 3,000 rpm for 6 min, while maintaining a temperature of below 10°C. Transglutaminase (TG) (ACTIVA TG-B, ES Food Co. Ltd., Kunpo, Korea), isolated soy protein (ISP) (ES Food Co. Ltd., Kunpo, Korea), and alginate (ES Food Co. Ltd., Kunpo, Korea) were purchased from a local market.

Formulation and processing reduced-salt meat emulsions

Trimmed pork ham and slightly frozen pork back fat were grounded through an 8 mm plate. The formulations of eight different reduced-salt meat emulsions are shown in Table 1. Control (-) and (+) formulations were produced with 1.2% salt and 1.5% salt. Reduced-salt (1.2% salt) formulations were prepared using 5% konjac gel. The following konjac gel treatments were used: T1, konjac gel; T2, konjac gel + 1.0% TG; T3, konjac gel + 1.0% ISP; T4, konjac gel + 1.0% TG + 1.0% ISP; T5, konjac gel + 1.0% alginate; and T6, konjac gel + 1.0% TG + 1.0% alginate. Ground pork lean meat, salt, and phosphate were homogenized and mixed for 1 min in a silent cutter (Cutter Nr-963009. Scharfen, Postfach, Germany). Ice water was added during homogenization, to prevent the temperature of the meat emulsion from rising. Pork back fat, konjac gel, TG, ISP, and alginate were added to the meat batter for 3 min. The meat emulsion temperature was observed to be below 10°C, while processing meat emulsions. The final meat emulsion (around 300 g) was placed in collagen casings and then heat treated. The cooking process was performed at 75°C for 30 min in a water bath, and it was ensured that the core temperature of the meat emulsion became 75°C. The cooked samples were cooled using cold water (less than 15°C), and then analyzed to determine their quality characteristics. All treatments groups were replicated three times (1 batch, 3 kg), on three different days.

Table 1. Formulations of reduced-salt meat emulsion with konjac gel and combined TG, ISP, and alginate (Unit: %).

Ingredients	Control (-)	Control (+)	T1	T2	T3	T4	T5	T6
Pork meat	60	60	60	60	60	60	60	60
Pork back fat	20	20	20	20	20	20	20	20
Ice water	20	20	15	14	14	13	14	13
Konjac gel^1)	-	-	5	5	5	5	5	5
Transglutaminase	-	-	-	1	-	1	-	1
Isolated soy protein	-	-	-	-	1	1	-	-
Alginate	-	-	-	-	-	-	1	1
Total	100	100	100	100	100	100	100	100
Salt	1.2	1.5	1.2	1.2	1.2	1.2	1.2	1.2
Phosphate	0.15	0.15	0.15	0.15	0.15	0.15	0.15	0.15

¹⁾Konjac gel was manufactured with konjac powder, carrageenan powder and water (7:3:90) and konjac gel and other ingredient replaced water composition.

Proximate composition

The proximate compositions of cooked reduced-salt meat emulsions were determined using the standard reference methods described by the AOAC.^[19] The moisture (AOAC method 950.46B), protein (AOAC method 981.10), fat (AOAC method 960.69), and ash (AOAC method 920.153) content were determined.

pH

The pH value of each cooked and uncooked reduced-salt meat emulsion was measured using a Model 340 pH meter (Mettler Toledo GmbH, Schwerzenbach, Switzerland) at 21 ± 1°C. The pH meter was calibrated with buffer solutions having a pH of 4, 7, and 10.

Color

The instrumental color values (CIE L*, lightness; CIE a*, redness; CIE b*, yellowness) of each cooked and uncooked reduced-salt meat emulsion were determined using a colorimeter (CR-410 Chroma Meter; Konika Minolta, Osaka, Japan). Illuminant condition, standard observer, and aperture were D65, 2° standard observer, and Ø 50 mm. White calibration plate (lightness, 97.83; redness, −.043; yellowness, 1.98) was used for calibration.

Cooking loss

Reduced-salt meat emulsion samples containing konjac gel were placed into a collagen casing, and boiled (75°C) for 30 min in a water bath (core temperature: 72 ± 1°C). The weight loss in the cooked samples was measured, and was revealed as a percentage value.^[20]

Emulsion stability

The emulsion stability of reduced-salt meat emulsion samples with konjac gel was determined by the previous study method^[21] with reasonable modifications. Each reduced-salt meat emulsion sample (20 g) was stuffed into a graduated glass tube and boiled (75°C) for 30 min. The sample in glass tube was cooled at 4°C until the fat and water layer were completely separated. Then, the fat separation (%) and the total expressible fluid separation (%) were measured as described by Choi et al.^[22] in here, the lower values of total expressible fluid separation and fat separation represents the better the emulsion stability.^[22]

Protein solubility

The protein solubility of reduced-salt meat emulsion samples containing konjac gel was determined by the method described by Joo et al.^[23] with modifications. The total protein solubility was determined by homogenizing (1,500 rpm) each 2 g of meat emulsion samples in 1.1 mol/L of potassium iodide (20 mL) in 100 mol/l phosphate buffer (pH 7.4). The homogenized samples were allowed to stand on a shaker overnight at 4°C. The overnight mixtures were centrifuged at 1,500 g for 20 min and the protein concentrations of the supernatants were determined. The sarcoplasmic protein solubility was determined by dissolving 2 g of each meat emulsion into 20 ml of 25 mM potassium phosphate buffer (pH 7.4). The next sequences of sarcoplasmic protein solubility were the same as those shown above for total protein solubility. Myofibrillar protein solubility was calculated by determining the difference between the total protein solubility and sarcoplasmic protein solubility.^[24]

Apparent viscosity

The apparent viscosity of the reduced-salt meat emulsion was measured using a rheometer (DV3THB, Brookfield Engineering Laboratories, USA). The reduced-salt meat emulsion was placed inside a steel cup, and SC4-29 standard spindle (10 rpm, 60 s) was used to determine the apparent viscosity of the meat emulsion. Then, values were calculated using the Bingham math model by viscosity analysis (Rheocalc T 1.2.19, Brookfield Engineering Laboratories, USA).^[24]

Instrumental texture profile analysis

The texture profile analysis (TPA) of cooked reduced-salt meat emulsion samples containing konjac gel was performed using the method described by Bourne et al.^[25] The reduced-salt meat emulsion samples with konjac gel were placed into a collagen casing, and boiled at 75°C for 30 min. The cooked samples were cooled (at a temperature less than 15°C), and then TPA was performed. TPA was conducted using a texture analyzer (TA-XT2i, Stable Micro Systems Ltd., England). The TPA conditions were as follows: distance: 8.0 mm, maximum load: 2.0 kg, force: 5.0 g, pretest speed: 2.0 mm/s, head speed: 2.0 mm/s, and posttest speed: 5.0 mm/s. The technical replicates for each samples were conducted 10 times.

Statistical analysis

All data were obtained at least thrice at each experimental condition and analyzed with three independent batch (replication). All values were expressed as the mean and standard error values. Significant differences between treatments were calculated using one-way analysis of variance with Duncan’s multiple range test (P < .05), performed using SPSS statistical software (Version 20.0; IBM Corp., Armonk, NY, USA) in a randomized complete block design. For examine, addition amount of salt, konjac gel, transglutaminase, isolated soy protein, alginate and their interaction considered as fixed effects for full models. Random terms for full model contained replicates and other unintended factors, and there were no random effects.

Results and discussion

Proximate composition

Effects of TG, ISP, and alginate on proximate compositions in meat emulsions with konjac gel were shown in Table 2. The moisture content of the control (-) was the lowest (P < .05), and the moisture content of the reduced-salt meat emulsion treated with konjac gel was higher than that of the control (-) (P < .05). The protein content did not differ significantly (P > .05) among the all treatments with control and treatments groups. The fat content of the control (-) was the lowest (P < .05), and the fat content of these controls (+) and all treatments with konjac gel were not significantly (P > .05) different. The ash content of the reduced-salt meat emulsion samples ranged from 1.91% to 2.35%. T2, T5, and T6 showed significantly higher ash content compared to control groups (P < .05). These results are in agreement with those obtained by Kim et al.^[1] in which the moisture content of frankfurter sausages with konjac gel was higher than that observed in treatments performed without konjac gel. Fernández-Martín et al.^[17] reported that the moisture content of pork meat batter with konjac gel was higher than that of batter without konjac gel. Osburn and Keeton^[9] indicated that the low-fat sausage containing konjac gel exhibited higher moisture content, as konjac gel levels were increased from 0% to 20%. Thus, the reduced-salt meat emulsion with added konjac gel appears to play an important role in improving the water content. In addition, reduced-salt treatments with konjac gels tended to be similar to normal salt (1.5%) treatments.

Table 2. Effects on proximate compositions of reduced-salt meat emulsion with konjac gel and combined TG, ISP, and alginate.

Traits (%)	Control (-)^1)	Control (+)	T1	T2	T3	T4	T5	T6
Moisture	59.11 ± 0.28^c	62.25 ± 0.44^ab	63.06 ± 0.40^a	61.42 ± 0.28^b	60.89 ± 0.66^b	61.46 ± 0.37^b	61.70 ± 0.32^b	61.00 ± 0.34^b
Protein	14.91 ± 0.17	15.49 ± 0.10	14.35 ± 0.48	14.77 ± 0.07	15.08 ± 0.19	15.40 ± 0.21	14.64 ± 0.37	15.33 ± 0.17
Fat	14.17 ± 0.28^b	15.60 ± 0.19^a	15.15 ± 0.27^a	15.91 ± 0.13^a	15.05 ± 0.10^a	15.65 ± 0.09^a	15.36 ± 0.13^a	15.04 ± 0.17^a
Ash	1.91 ± 0.06^c	1.93 ± 0.08^c	1.99 ± 0.05^c	2.30 ± 0.11^ab	1.94 ± 0.10^c	2.07 ± 0.03^bc	2.14 ± 0.07^ab	2.35 ± 0.01^a

All values are mean ± standard error of three replicates.

^a-cMeans within a row with different letters are significantly different (P < 0.05).

¹⁾Control (-): reduced-salt (1.2%), Control (+): normal-salt (1.5%), T1: low salt with konjac gel, T2: reduced-salt with konjac combined TG, T3: reduced-salt with konjac combined ISP, T4: reduced-salt with konjac combined TG and ISP, T5: reduced-salt with konjac combined alginate, T6: reduced-salt with konjac combined TG, ISP, and alginate.

pH and color

In Table 3, the pH and color of reduced-salt meat emulsion samples with konjac gel and a combination of TG, ISP, and alginate were evaluated. The pH of the raw meat emulsion ranged from 6.00 to 6.14, and the pH of the raw reduced-salt meat emulsion (T4) with ISP and TG was the highest (P < .05). The pH of the cooked reduced-salt meat emulsion containing konjac gel was higher than that of the control groups (P < .05). Kim et al.^[1] reported that the pH of uncooked and cooked batter was decreased after the pork back fat was replaced with konjac gel. Ruiz-Capillas et al.^[10] indicated that the pH of the fermented sausage was affected by the addition of konjac gel to it. These results may have been observed because the pH of the konjac gel is shown.

Table 3. Effects on pH and color of reduced-salt meat emulsion with konjac gel and combined TG, ISP, and alginate.

Traits		Control (-)^1)	Control (+)	T1	T2	T3	T4	T5	T6
Raw	pH	6.02 ± 0.01^d	6.00 ± 0.01^d	6.02 ± 0.01^d	6.05 ± 0.01^c	6.06 ± 0.01^bc	6.14 ± 0.01^a	6.09 ± 0.02^b	6.09 ± 0.01^b
	CIE L*	76.39 ± 0.54^c	74.83 ± 0.22^d	82.22 ± 0.04^a	82.04 ± 0.13^a	82.62 ± 0.77^a	79.29 ± 0.35^b	82.77 ± 0.23^a	82.90 ± 0.48^a
	CIE a*	8.12 ± 0.14^a	6.39 ± 0.04^b	5.99 ± 0.02^c	6.02 ± 0.04^c	4.60 ± 0.07^e	5.44 ± 0.02^d	4.78 ± 0.09^e	4.79 ± 0.20^e
	CIE b*	12.85 ± 0.13^b	13.16 ± 0.03^a	11.86 ± 0.02^c	11.53 ± 0.03^d	11.46 ± 0.04^d	12.17 ± 0.02^c	12.11 ± 0.05^c	11.53 ± 0.09^d
Cooked	pH	6.07 ± 0.01^e	6.05 ± 0.02^e	6.11 ± 0.01^d	6.18 ± 0.02^c	6.18 ± 0.01^c	6.26 ± 0.01^a	6.24 ± 0.01^ab	6.23 ± 0.01^b
	CIE L*	77.75 ± 0.32^c	76.94 ± 0.40^c	80.63 ± 0.18^a	79.71 ± 0.55^ab	80.51 ± 0.93^a	78.49 ± 0.41^bc	77.65 ± 0.52^c	79.72 ± 0.69^ab
	CIE a*	4.87 ± 0.12^a	4.25 ± 0.11^b	3.69 ± 0.02^d	3.89 ± 0.09^cd	3.61 ± 0.08^d	4.36 ± 0.03^b	5.03 ± 0.11^a	4.04 ± 0.20^bc
	CIE b*	9.60 ± 0.06^d	9.90 ± 0.14^cd	10.06 ± 0.05^bc	10.26 ± 0.07^b	10.62 ± 0.09^a	10.88 ± 0.09^a	10.92 ± 0.16^a	10.74 ± 0.08^a

All values are mean ± standard error of three replicates.

^a-eMeans within a row with different letters are significantly different (P < 0.05).

¹⁾Control (-): reduced-salt (1.2%), Control (+): normal-salt (1.5%), T1: reduced-salt with konjac gel, T2: reduced-salt with konjac combined TG, T3: reduced-salt with konjac combined ISP, T4: reduced-salt with konjac combined TG and ISP, T5: reduced-salt with konjac combined alginate, T6: reduced-salt with konjac combined TG, ISP, and alginate.

The lightness value of raw reduced-salt meat emulsion with konjac gel was higher than that of the control groups (-) (+) (P < .05). However, the redness and yellowness values of the raw reduced-salt meat emulsion with konjac gel were lower than the values for the control groups (P < .05). The lightness values of T1 and T3 with the cooked reduced-salt meat emulsion were the highest (P < .05). The redness values of the cooked meat emulsion ranged from 3.61 to 5.03, and there was no obvious trend between control and treatment groups. The yellowness of raw reduced-salt meat emulsion with konjac gel was higher than that of control groups (P < .05). Kim et al.^[1] reported that the lightness of raw and cooked frankfurters added with konkac gel were higher than control group, and the color values of meat products seem to affected by the color of the konjac gel. Jiménez-Colmenero et al.^[8] reported that the lightness, redness, and yellowness values of treatments with konjac gel were lower than that of control meat products. Thus, the addition of ingredients could shift the color values in meat products. However, the addition of konjac does not always increase the lightness of meat product. Ruiz-Capillas et al.^[10] indicated that the lightness of meat products was not affected by the addition of konjac gel. This result suggests that the amount of konjac gel added in meat product could influence the color values.

Cooking loss and emulsion stability

Table 4 shows the effects of TG, ISP, and alginate on cooking loss, fat separation and emulsion stability in meat emulsions with konjac gel. The cooking loss of control groups (-) (+) was lower than that observed for reduced-salt treatments with konjac gel (P < .05). in particular, the reduced-salt meat emulsion with a combination of konjac gel and alginate (T5, T6) showed the lowest cooking loss (P < .05). Kim et al.^[1] reported that the frankfurter formulated using konjac gel exhibited a significantly lower cooking loss than that of the control. Thus, the meat products containing konjac gel have been shown to inhibit the release of water during the cooking process. Kim et al.^[18] indicated that the cooking loss of restructured ham with hydrocolloids was lower than that of the control without hydrocolloids, and the lowest cooking loss was observed in restructured ham in which 1% alginate was added. Kang et al.^[16] have shown that the cooking loss of meat products with alginate was lower than that of the control. According to Kim et al.,^[26] pre-emulsion made with alginate decrease the cooking loss when it compared to control. Pork meat gels with ISP also showed the low cooking loss compared to control meat gels.^[27] Thus, the cooking loss of meat products was significantly affected by the addition of combined konjac gel and others ingredients.

Table 4. Effects on cooking loss and emulsion stability of reduced-salt meat emulsion with konjac gel and combined TG, ISP, and alginate.

Traits (%)		Control (-)^1)	Control (+)	T1	T2	T3	T4	T5	T6
Cooking loss		9.28 ± 0.14^a	6.97 ± 0.15^b	5.73 ± 0.12^c	5.73 ± 0.06^c	5.38 ± 0.15^c	5.53 ± 0.19^c	4.20 ± 0.15^d	4.60 ± 0.06^d
Emulsion stability	Total expressible fluid separation	13.98 ± 0.26^a	6.89 ± 0.27^b	3.35 ± 0.37^d	5.06 ± 0.24^c	2.40 ± 0.39^de	5.35 ± 0.53^c	1.86 ± 0.24^e	1.60 ± 0.01^e
	Fat separation	1.45 ± 0.12^a	1.31 ± 0.12^ab	0.67 ± 0.13^c	1.34 ± 0.25^a	0.53 ± 0.13^c	1.06 ± 0.26^ab	0.81 ± 0.01^bc	0.80 ± 0.00^bc

All values are mean ± standard error of three replicates.

^a-eMeans within a row with different letters are significantly different (P < 0.05).

¹⁾Control (-): reduced-salt (1.2%), Control (+): normal-salt (1.5%), T1: reduced-salt with konjac gel, T2: reduced-salt with konjac combined TG, T3: reduced-salt with konjac combined ISP, T4: reduced-salt with konjac combined TG and ISP, T5: reduced-salt with konjac combined alginate, T6: reduced-salt with konjac combined TG, ISP, and alginate.

The emulsion stability was affected by the formulation in the konjac gel, and TG, ISP, and alginate levels (Table 4). The total expressible fluid separation of control groups (-) (+) was lower than that in reduced-salt meat emulsions with konjac gel (P < .05), and the total expressible fluid separation of control group (-) (+) treatments with konjac gel and alginate (T5, T6) was the lowest (P < .05). The fat separation was the highest (P < .05) in controls (-) and treatments (T2) with TG. Kim et al.^[28] reported that the stability of meat emulsions was affected by the addition of TG, and the emulsion stability was poor when TG was added. The total expressible fluid separation of reduced-salt meat emulsions tended to be similar to the level of cooking loss. The fat separation in the control (-) was higher than that in reduced-salt meat emulsions with konjac gel (P < .05), except in treatments with TG (T2 and T4). Jiménez-Colmenero et al.^[2] showed that emulsion stability and cooking loss were the highest in meat batter with TG alone, due to poor fat- and water- binding capacity. Thus, they reported that in order to utilize TG in meat products, it was necessary to add an additive to improve the binding force. Kim et al.^[1] reported that the total amount of released fluid and separated fat released was lower in frankfurters formulated with konjac gel than in the control. Kim et al.^[18] indicated that the total expressible fluid and fat separation in restructured meat products with alginate and konjac were lower than that of the control. They reported that alginate increased the strength of binding of water, protein, and fat, resulting in increased emulsion stability. These results are in agreement with those of Fernández-Martín et al.^[17] which showed that the emulsion stability of meat batter with seaweed and konjac gel was lower than that of the control. This can be attributable to the well-known ability of alginate (from seaweed) to bind to water and strongly adsorb oils, because of which emulsion stability was improved. Our study showed improved emulsion stability in konjac gel and alginate, because 0.3% of the salt was replaced.

Protein solubility

The effects of konjac gels and combined TG, ISP, and alginate on the protein solubility of reduced-salt meat emulsions are shown in Table 5. The myofibrillar protein solubility of the control (-) was the lowest among the all treatment groups (P < .05). The normal-salt control (+) showed a higher myofibrillar protein solubility than the reduced-salt control (-) (P < .05), because the myofibrillar protein is a salt-soluble protein. The sarcoplasmic protein solubility of meat emulsion ranged from 16.94 to 21.60 mg/g. Choi et al.^[29] reported that myofibrillar protein solubility plays the most meaningful role in meat emulsions. As more myofibrillar protein is extracted from the muscle meat, emulsion ability increased in meat emulsion. Kim et al.^[28] reported that significant differences were observed between the myofibrillar protein solubility and sarcoplasmic protein solubility of meat emulsions formulated using TG. The myofibrillar protein solubility of emulsions with TG was lower than that of the control without TG, due to the protein aggregation caused by TG.

Table 5. Effects on protein solubility of reduced-salt meat emulsion with konjac gel and combined TG, ISP, and alginate.

Traits (%)	Control (-)^1)	Control (+)	T1	T2	T3	T4	T5	T6
Myofibrillar protein (mg/g)	65.36 ± 0.77^f	76.24 ± 0.82^c	94.82 ± 0.68^a	70.26 ± 0.93^d	85.06 ± 0.57^b	70.14 ± 0.71^d	94.71 ± 0.80^a	69.30 ± 0.63^e
Sarcoplasmic protein (mg/g)	17.78 ± 0.63^c	16.94 ± 0.25^c	19.03 ± 0.13^b	17.31 ± 0.21^c	19.23 ± 0.11^b	17.17 ± 0.24^c	21.60 ± 0.15^a	20.12 ± 0.55^b

All values are mean ± standard error of three replicates.

^a-fMeans within a row with different letters are significantly different (P < 0.05).

¹⁾Control (-): reduced-salt (1.2%), Control (+): normal-salt (1.5%), T1: reduced-salt with konjac gel, T2: reduced-salt with konjac combined TG, T3: reduced-salt with konjac combined ISP, T4: reduced-salt with konjac combined TG and ISP, T5: reduced-salt with konjac combined alginate, T6: reduced-salt with konjac combined TG, ISP, and alginate.

Apparent viscosity

Figure 1 shows the changes in the apparent viscosity of reduced-salt meat emulsions with konjac gel and combined TG, ISP, and alginate during 60 s. The maximum viscosity of the control (-) was the lowest between the control groups and all treatments, while the maximum viscosity of the reduced-salt meat emulsion with konjac gel and combined TG and alginate (T6) was the highest. The apparent viscosity of control groups and all reduced-salt meat emulsion treatments with konjac gel was decreased regularly over time; thus, all samples exhibited thixotropic behavior. Kim et al.^[1] found that the addition of konjac gel could increase the apparent viscosity of emulsion meat products. When alginate was added to pre-emulsion, apparent viscosity was increased compared to control.^[26] Kim et al.^[18] indicated that the apparent viscosity of restructured duck ham batter containing alginate, konjac, and carrageenan was higher than that of the control, because of hydrocolloids reinforcing the capacity of moisture to bind to proteins. These results were in agreement with those of a previous study, which reported that the apparent viscosity of the meat emulsion with TG was higher than that of the control without TG, because the increase in apparent viscosity could be attributed to TG-induced cross-linking. Choi et al.^[15] reported that the apparent viscosity of meat emulsions were related to the emulsion stability, as the higher viscosity of meat emulsions did not become reduced. The results of this study showed that the incorporation of konjac gel and TG into reduced-salt meat emulsions could improve the apparent viscosity and emulsion stability.

Figure 1. Apparent viscosity of reduced-salt meat emulsion combined with konjac gel and combined TG, ISP, and alginate. Control (-): reduced-salt (1.2%), Control (+): normal-salt (1.5%), T1: reduced-salt with konjac gel, T2: reduced-salt with konjac combined TG, T3: reduced-salt with konjac combined ISP, T4: reduced-salt with konjac combined TG and ISP, T5: reduced-salt with konjac combined alginate, T6: reduced-salt with konjac combined TG, ISP, and alginate.

Texture profile analysis

The texture profile analysis results of the reduced-salt meat emulsion containing konjac gel and combined TG, ISP, and alginate are shown in Table 6. The hardness of reduced-salt meat emulsions with konjac gels was lower than that of control groups (-) (+) (P < .05), with the exception of reduced-salt treatments with alginate (T5, T6). The springiness of control (-) and T3, and T5 was the lowest, as compared to values observed with other treatments (P < .05). The cohesiveness of the reduced-salt meat emulsion containing konjac gel and combined TG, ISP, and alginate ranged from 0.46 to 0.53, and the highest cohesiveness was observed for reduced-salt meat emulsions with konjac gels and combined TG and ISP (T4). The gumminess and chewiness of reduced-salt meat emulsions were the highest after being treated with konjac gels, and combined TG and ISP (T4). Osburn and Keeton^[9] reported that the results of texture profile analysis of frankfurters with konjac gel were markedly affected. Additionally, Fernández-Martín et al.^[17] reported that the hardness of heat-processed meat systems was influenced by the addition of konjac gel and seaweed. These results are in agreement with those obtained by Kim et al.^[28] who reported that the hardness, gumminess, and chewiness of meat emulsions with TG was higher than that of the control without TG, because TG aids in the formation of cross-links that contribute to gelation. Park et al.^[30] also reported that the addition of TG to meat batter increase the hardness. Kim et al.^[18] reported that the hardness, cohesiveness, gumminess, and chewiness of restructured meat products with combined konjac + alginate were lower than that of the control, due to their increased water holding and water retention capacity. When ISP was added to pork meat gel, hardness was increased.^[27]

Table 6. Effects on texture profile analysis of reduced-salt meat emulsion with konjac gel and combined TG, ISP, and alginate.

Traits	Control (-)^1)	Control (+)	T1	T2	T3	T4	T5	T6
Hardness (kg)	0.46 ± 0.02^d	0.48 ± 0.02^d	0.59 ± 0.02^c	0.74 ± 0.03^b	0.71 ± 0.03^b	0.93 ± 0.07^a	0.34 ± 0.02^e	0.42 ± 0.02^de
Springiness	0.69 ± 0.06^bc	0.97 ± 0.04^a	0.81 ± 0.06^abc	0.87 ± 0.04^ab	0.61 ± 0.04^c	0.95 ± 0.05^a	0.80 ± 0.03^bc	0.88 ± 0.05^ab
Cohesiveness	0.47 ± 0.01^b	0.48 ± 0.02^b	0.48 ± 0.01^b	0.50 ± 0.01^ab	0.49 ± 0.01^ab	0.53 ± 0.01^a	0.46 ± 0.01^b	0.47 ± 0.01^b
Gumminess (kg)	0.10 ± 0.01^de	0.11 ± 0.01^de	0.17 ± 0.01^cd	0.27 ± 0.01^b	0.25 ± 0.01^bc	0.48 ± 0.04^a	0.05 ± 0.01^e	0.08 ± 0.01^de
Chewiness (kg)	0.30 ± 0.01^cd	0.44 ± 0.01^c	0.46 ± 0.01^c	0.63 ± 0.02^b	0.43 ± 0.02^c	0.92 ± 0.01^a	0.25 ± 0.01^d	0.35 ± 0.01^cd

All values are mean ± standard error of three replicates.

^a-eMeans within a row with different letters are significantly different (P < 0.05).

¹⁾Control (-): reduced-salt (1.2%), Control (+): normal-salt (1.5%), T1: reduced-salt with konjac gel, T2: reduced-salt with konjac combined TG, T3: reduced-salt with konjac combined ISP, T4: reduced-salt with konjac combined TG and ISP, T5: reduced-salt with konjac combined alginate, T6: reduced-salt with konjac combined TG, ISP, and alginate.

Conclusion

Our results showed the technical and functional properties of different reduced-salt meat emulsions containing konjac gel and a combination of transglutaminase, isolated soy protein, and alginate. The cooking loss and total expressible fluid separation values of control groups (-) (+) were higher than those observed for reduced-salt treatments with konjac gel (P < .05), and these values were the lowest (P < .05) for reduced-salt meat emulsions with a combination of konjac gel and alginate (T5, T6). The hardness of reduced-salt meat emulsions containing konjac gels, alginate, and transglutaminase tended to be similar to that of normal-salt treatments (Control (+)). The maximal viscosity was observed in reduced-salt meat emulsions with konjac gel and combined transglutaminase and alginate (T6). Thus, our study showed that the reduced-salt meat emulsion containing konjac gel and a combination of transglutaminase and alginate was observed to exhibit the most similar technical and functional properties to normal-salt (1.5%) meat products. in conclusion, the presence of konjac gel and a combination of transglutaminase and alginate might be used to successfully produce good quality reduced-salt meat products.

Disclosure statement

The authors have no competing interests to report.

Additional information

Funding

This research was supported by Main Research Program (E0187000-03) of the Korea Food Research Institute (KFRI) funded by the Ministry of Science and ICT (Republic of Korea).