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Journal of Food Science and Technology logoLink to Journal of Food Science and Technology
. 2020 Jul 9;58(4):1238–1246. doi: 10.1007/s13197-020-04633-w

Quality of reduced-fat meat emulsion: effect of pre-emulsified duck skin and hydrocolloids

Hae In Yong 1,#, Tae-Kyung Kim 1,#, Samooel Jung 2, Young-Boong Kim 1, Yun-Sang Choi 1,✉
PMCID: PMC7925752  PMID: 33746252

Abstract

This study explored the impact of reduced-fat meat emulsion with pre-emulsified duck skin and hydrocolloids on physicochemical properties such as cooking loss, emulsion stability, apparent viscosity, protein solubility, and texture profile analysis. Six different reduced-fat meat emulsions were produced: control (pork back fat), T1 (duck skin, DS), T2 (pre-emulsified with duck skin, PDS), T3 (PDS + 2% carrageenan), T4 (PDS + 2% alginate), T5 (PDS + 2% pectin), and T6 (PDS + 2% guar gum). Moisture content, protein content, yellowness, and apparent viscosity of reduced-fat emulsion with PDS and hydrocolloids were all higher (P < 0.05) than control. Cooking loss and emulsion stability of T4 and T6 were lower (P < 0.05) than the control values. Cooking loss and total fluid separation were greatest (P < 0.05) for T5. Fat content of reduced-fat emulsion with PDS was lower (P < 0.05) than that of the control. Meat emulsion comprising PDS with alginate resulted in superior physicochemical properties compared to the other reduced-fat meat emulsion.

Keywords: Pre-emulsion, Reduced-fat, Duck skin, Hydrocolloid, Alginate, Emulsion stability

Introduction

Frankfurters are a globally popular food. The typical emulsified sausage formulation is a source of important animal proteins (Kim et al. 2017). Their widespread consumption has made frankfurters an economically important product in the meat industry (de Oliveira Faria et al. 2015). The fat in frankfurters has an important role and affect cooking loss, emulsion stability, desirable texture, and flavor (Choi et al. 2016). Nevertheless, the typically high fat content (generally 20–30% back fat), which includes saturated fatty acids, poses health concerns that include cardiovascular diseases, obesity, and some kinds of cancer (Kavuşan et al. 2020). Although formulating frankfurters with reduced-fat content could produce healthier products and are desirable, this formulating could induce a undesirable texture, low emulsion stability, and high cooking loss (Choi et al. 2009).

Duck skin by-products are environmental pollutants and pose a significant problem in the duck processing industry (Kim et al. 2018). However, duck skin can be used as a useful resource that contains collagen, lipid, and gelatin (Kim et al. 2018; Lee et al. 2012). Shim et al. (2018) demonstrated that pre-emulsified alginate and duck skin mixed at a 1:1 ratio improved the quality characteristics of duck ham. Kim et al. (2018) described the optimized quality of duck ham by the inclusion of alginate in the ham formulation. Addition of duck skin and alginate improves quality characteristics such as water binding capacity (Kim et al. 2018; Shim et al. 2018). According to these previous studies, pre-emulsified duck skin and hydrocolloids enhance the quality properties of restructured duck ham. However, there combination effect of pre-emulsified duck skin with hydrocolloids on quality properties of meat emulsion has not conducted.

Hydrocolloids generally enhance the emulsion stability, emulsion viscosity, water holding capacity, and texture properties of meat processing (Kim et al. 2017). Additionally, hydrocolloids should be considered as needed for various conditions such as pH, storage stability, viscosity, temperature stability, solubility, and interaction (Kim et al. 2018).

Carrageenan is produced from red seaweeds, as a linear sulfated polysaccharide and generally has been used in meat processing to enhance gel properties (Candogan and Kolsarici 2003; Cierach et al. 2009). Carrageenan has a high water binding capacity due to ionic and hydrogen bond interactions that occur with water molecules and enhances the textural and sensorial analyses of low-fat frankfurters (Cierach et al. 2009).

Alginate has been extensively used as a biopolymer in meat processing due to its distinct colloidal properties, which involve emulsion stabilization and gel formation (Hong et al. 2012). Alginate is the primary element of the cell membranes of seaweed and sea tangle. Addition of alginate can help in enhancing the emulsion stability, water holding capacity, and textural properties of restructured hams (Kim et al. 2018).

Pectin is a water-soluble hydrocolloid that is often used as a stabilizer, gelling agent, thickener, and emulsifier in the food industry (Ren et al. 2019). Pectin is also an acidic polysaccharides with a complex structure that is a component of the cell wall of plants. In plants, pectin lends mechanical strength and flexibility by interacting with other cell wall elements (Chen et al. 2019). Kim et al. (2016) found that the addition of pectin enhanced the textural properties and water holding capacity of meat products. Pectin has been utilized as an effective replacement for fat (Candogan and Kolsarici 2003).

Guar gum is a rich biopolymer extracted from Cyamopsis tetragonolobus seed endosperm. Guar gum emulsions contribute stabilizing and emulsifying properties. Guar gum hydrates easily in aqueous media to produce a viscous pseudo-plastic solution due to low shear viscosity, which is beneficial in emulsion stabilization and gel formation (Guthrie 2019). Park et al. (2008) applied guar gum to pork as a model system as a replacement for phosphate.

This study aimed to determine the effect of pre-emulsified duck skin and hydrocolloids on the physicochemical properties of reduced-fat meat emulsion. Our findings provide comprehensive information that will inform the appropriate application of pre-emulsion with duck skin to achieve reduced-fat meat products that are preferred by consumers.

Materials and methods

Reduced-fat meat emulsion preparation and processing

Fresh pork ham (Musculus semitendinosus, Musculus semimembranosus, Musculus biceps femoris) and pork back fat were obtained from a local processor and kept at 0 °C until used. The pork ham and back fat were chopped through a plate (8-mm) using meat chopper (SMC-22A, SL Co., Korea). A control meat emulsion and six different reduced-fat meat emulsions (T1 to T6 below) were produced (Table 1). The control meat emulsion was prepared with 50% pork meat, 30% ice, and 20% pork back fat. The T1 to T6 reduced-fat emulsions were made ready by substituting 20% pork back fat with 20% duck skin. T1 lacked pre-emulsion. T2 included pre-emulsion. T3 to T6 were prepared using pre-emulsified duck skin, ice, and hydrocolloids as follows: T3: 20% duck skin + 18% ice + 2% carrageenan; T4: 20% duck skin + 18% ice + 2% alginate; T5: 20% duck skin + 18% ice + 2% pectin; T6: 20% duck skin + 18% ice + 2% guar gum. The hydrocolloid levels were reflected the results of previous studies (Choi et al. 2010). To manufacture pre-emulsified duck skin, the skin was cut in ice water containing 2% hydrocolloids using an Nr-963009 silent cutter (Hermann Scharfen GmbH & Co, Germany). The prepared pre-emulsion was kept at − 3 °C for 1 day. The chopped pork lean meat was cut for 20 s in the silent cutter and then chilled in ice, subsequently by the addition of NaCl (1.5%) and sodium tripolyphosphate (0.2%) and homogenization for 40 s. The pork back fat or pre-emulsified duck skin was added after 3 min. Meat emulsions were homogenized (6 min) at a temperature < 10 °C. The reduced-fat meat emulsion processing was accomplished thrice for each treatment. Each emulsion was analyzed as described subsequently using triplicate determinations.

Table 1.

Formulation (%) of emulsified reduced-fat meat emulsion manufactured with pre-emulsified duck skin

Control T1 T2 T3 T4 T5 T6
Pork ham 50 50 50 50 50 50 50
Ice 1 30 30 20 18 18 18 18
Ice 2 (pre-emulsion) – – 10 10 10 10 10
Pork back fat 20 – – – – – –
Duck skin – 20 20 20 20 20 20
Hydrocolloids – – – 2 (carrageenan) 2 (alginate) 2 (pectin) 2 (guar gum)
Subtotal 100 100 100 100 100 100 100
Salt 1.5 1.5 1.5 1.5 1.5 1.5 1.5
Phosphate 0.2 0.2 0.2 0.2 0.2 0.2 0.2
Total 101.7 101.7 101.7 101.7 101.7 101.7 101.7
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Proximate composition

The moisture, protein, fat, and ash contents of cooked meat emulsions with pre-emulsified duck skin were determined using AOAC (2000) methods (indicated below in brackets). The moisture, protein, fat, and ash contents of samples were determined by a drying oven (950.46B) at 105 °C, the Kjeldahl method (981.10), Soxhlet extraction method (960.69), and dry ashing method (920.153), respectively.

pH

The pH values of meat emulsion samples with pre-emulsified duck skin were measured using a pH meter (Mettler-Toledo GmbH, Switzerland). The pH was measured by homogenizing by adding distilled water (20 mL) to the sample (5 g). The pH meter was calibrated with buffer (pH 4, 7, and 10) solutions (Kim et al. 2019).

Color

The color values of meat emulsion samples with pre-emulsified duck skin were determined using a model CR-400 Chroma meter colorimeter (Minolta Ltd., Japan, D65 light source, 8 mm aperture; 0° observer)(Noh et al. 2019). The colorimeter was using illuminate C, and calibrated with a white plate (L* = + 97.83, a* = − 0.43, and b* = + 1.98).

Cooking loss

The meat emulsion samples with pre-emulsified duck skin were stuffed into a conical tube for 30 s, centrifuged for 5 min at 500×g, and boiled (75 °C) for 30 min in a water bath. Cooked samples were cooled (25 °C) for 4 h. After cooling, the weight loss of the cooked samples was measured. The weight difference represented cooking loss, which was expressed as a percentage (Choi et al. 2016).

Emulsion stability

The emulsion stability of meat emulsion samples with pre-emulsified duck skin was determined by the Bloukas and Honikel (1992) method with moderate modifications. Each meat emulsion sample (20 g) was stuffed into a graduated glass tube and heated (75 °C) for 30 min. The total expressible fluid and fat separated from the meat emulsion were measured at the underneath of a graduated glass cylinder (Choi et al. 2009).

Apparent viscosity

The apparent viscosity of the meat emulsion was measured using a model DV3THB rheometer (Brookfield Engineering Laboratories, USA). The meat emulsion was put inside the steel cup and a standard spindle (SC4-29) was used to determine the apparent viscosity of the meat emulsion (Choi et al. 2011). The test speed of apparent viscosity was 10 rpm for 35 s.

Protein solubility

The protein solubility of meat emulsion samples with pre-emulsified duck skin was determined by the Joo et al. (1999) method. Total protein solubility was determined by homogenizing each meat emulsion (2 g) in 20 ml potassium iodide (1.1 mol/l) in phosphate buffer (100 mol/l, pH7.2) and Sarcoplasmic protein solubility was determined by homogenizing each meat emulsion (2 g) in 20 ml of potassium phosphate buffer (25 mM, pH 7.2). The samples and buffer were homogenized (1500 rpm) on ice and left to stand on a shaker (4 °C) at overnight. The overnight mixtures were centrifuged (1500×g) for 20 min and the protein concentrations of the supernatants were determined. Myofibrillar protein solubility was acquired by measuring the difference between the total protein solubility and sarcoplasmic protein solubility (Shin et al. 2019).

Texture profile analysis (TPA)

TPA of cooked emulsion samples with pre-emulsified duck skin was determined using the Bourne et al. (1978) method. The TPA conditions were force 5.0 g, distance 8.0 mm, maximum load 2.0 kg, head speed 2.0 mm/s, pre-test speed 2.0 mm/s, and post-test speed 5.0 mm/s. TPA was conducted with a model TA-XT2i texture analyzer (Stable Micro Systems Ltd., England).

Statistical analyses

All data were obtained at least thrice for each experimental condition and expressed as mean and standard deviation. Statistical analyses were performed using SPSS Ver. 20.0 (SPSS Inc., USA) for the one-way ANOVA (analysis of variance), which included treatment effect and their interaction as main effects. Duncan’s multiple range tests was used to determine differences between treatment means (P < 0.05).

Results and discussion

Proximate composition

Proximate compositions of cooked reduced-fat emulsion with pre-emulsified duck skin and hydrocolloids are shown in Table 2. Moisture content and protein content were higher (P < 0.05) than the control with pork back fat. Fat content was lower (P < 0.05) than the control, due to the addition of more fat. The ash contents of all treatments with cooked emulsion did not differ significantly (P > 0.05). The findings agreed with those of Shim et al. (2018) that the proximate composition of duck ham with pre-emulsified skin differed in moisture content and fat content. The pre-emulsification process influenced the emulsion stability and water holding capacity of the meat emulsion. Pintado et al. (2018) reported that the moisture content and fat content of fresh sausage in which pork backfat was partially replaced by chia and oat emulsion gel was significantly different. The results are also similar to those obtained by Kim et al. (2018) for restructured hams with duck skin and hydrocolloids. However, the latter study showed a similar proximate composition tendency even though the pre-emulsion process did not proceed.

Table 2.

Effect of pre-emulsified duck skin and hydrocolloids on proximate composition of cooked reduced-fat meat emulsion

Traits (%) Control T1 T2 T3 T4 T5 T6
Moisture 65.77 ± 0.79d 65.89 ± 0.57cd 64.95 ± 0.84d 67.07 ± 0.78c 69.85 ± 0.47a 68.38 ± 0.93b 68.89 ± 0.22ab
Protein 14.27 ± 1.44d 19.49 ± 0.54c 20.53 ± 0.91c 25.87 ± 0.66a 22.49 ± 0.94b 20.11 ± 0.97c 24.66 ± 1.09a
Fat 14.04 ± 0.91a 6.58 ± 0.37c 6.69 ± 0.76bc 7.26 ± 0.78bc 7.73 ± 0.32bc 7.95 ± 0.92b 7.36 ± 0.31bc
Ash 2.00 ± 0.06 2.09 ± 0.05 1.99 ± 0.07 1.92 ± 0.48 2.09 ± 0.06 2.13 ± 0.27 2.16 ± 0.08
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Mean ± standard deviation was presented with three replicates

Control, emulsified with pork back fat; T1, emulsified with duck skin; T2, pre-emulsified with duck skin; T3, pre-emulsified with duck skin and carrageenan; T4, pre-emulsified with duck skin and alginate; T5, pre-emulsified with duck skin and pectin; and T6, pre-emulsified with duck skin and guar gum

a–dDifferent small letter in the same row means significant differences (P < 0.05)

pH and color

Effects of the addition of emulsified skin and hydrocolloid and the substitute of pork back fat on the pH of raw and cooked meat emulsions are summarized in Table 3. The pH of raw reduced-fat emulsion with pre-emulsified duck skin and pectin was lower (P < 0.05) than the control and other treatments. The pH of cooked reduced-fat emulsion with pre-emulsified duck skin and hydrocolloids was lower (P < 0.05) than control, with the lowest (P < 0.05) pH displayed by T5. According to previous studies, duck skin had no significant effect on pH of meat product and hydrocolloids could affect pH value of meat products when replace animal fat (Kim et al. 2018; Pintado et al. 2018; Shim et al. 2018). Furthermore, the ratio of meat and fat also affect the pH of meat products (Kim et al. 2017). Therefore, these results might be due to the different pH value of ingredients.

Table 3.

Effect of pre-emulsified duck skin and hydrocolloids on pH and color of emulsified reduced-fat meat emulsion

Traits Control T1 T2 T3 T4 T5 T6
Raw
pH 6.18 ± 0.02a 6.20 ± 0.01a 6.19 ± 0.01a 6.19 ± 0.01a 6.20 ± 0.02a 5.96 ± 0.01b 6.18 ± 0.02a
CIE L* 56.65 ± 0.76e 57.10 ± 0.63e 59.76 ± 0.63d 65.53 ± 0.32b 67.31 ± 0.84a 63.80 ± 0.33c 65.86 ± 0.94b
CIE a* 8.81 ± 0.54b 10.56 ± 0.73a 10.41 ± 0.51a 10.40 ± 0.25a 10.57 ± 0.46a 10.57 ± 0.46a 10.38 ± 0.22a
CIE b* 8.88 ± 0.76e 9.78 ± 0.90d 10.09 ± 0.90d 11.08 ± 0.10c 11.99 ± 0.51ab 11.20 ± 0.34bc 12.14 ± 0.19a
Cooked
pH 6.56 ± 0.04a 6.35 ± 0.07b 6.30 ± 0.03bc 6.26 ± 0.03d 6.29 ± 0.02 cd 5.98 ± 0.01e 6.27 ± 0.02cd
CIE L* 74.10 ± 0.48b 72.89 ± 0.27c 73.09 ± 0.45c 72.97 ± 0.75c 76.38 ± 0.26a 72.68 ± 0.41c 74.08 ± 0.95b
CIE a* 3.78 ± 0.16c 3.53 ± 0.23d 3.66 ± 0.05cd 3.65 ± 0.19cd 3.89 ± 0.15bc 4.19 ± 0.12a 4.09 ± 0.22ab
CIE b* 9.46 ± 0.16e 10.28 ± 0.55d 10.23 ± 0.40d 11.00 ± 0.51c 12.09 ± 0.21a 12.27 ± 0.37a 11.57 ± 0.25b
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Mean ± standard deviation was presented with three replicates

Control, emulsified with pork back fat; T1, emulsified with duck skin; T2, pre-emulsified with duck skin; T3, pre-emulsified with duck skin and carrageenan; T4, pre-emulsified with duck skin and alginate; T5, pre-emulsified with duck skin and pectin; and T6, pre-emulsified with duck skin and guar gum

a–eDifferent small letter in the same row means significant differences (P < 0.05)

Data of the color of reduced-fat emulsion with pre-emulsified duck skin and hydrocolloids are presented in Table 3. The lightness of raw reduced-fat emulsion with pre-emulsified duck skin and hydrocolloid was significantly (P < 0.05) higher than control and treatment with duck skin (T1). The redness and yellowness of raw reduced-fat emulsion with duck skin or pre-emulsified duck skin was higher (P < 0.05) than the control with pork back fat. The lightness and redness of cooked reduced-fat emulsion with pre-emulsified duck skin and alginate were highest (P < 0.05) among all the treatments, and the yellowness of cooked reduced-fat emulsion with pre-emulsified duck skin was significantly (P < 0.05) higher than the control. According to previous studies, each pre-emulsified duck skin and hydrocolloids did not affect color values of duck ham except for lightness (Shim et al. 2018; Kim et al. 2018). The difference value in lightness value might be due to the exudate fluid on surface of sausage and addition of pre-emulsion (Youssef et al. 2011). Because the significant effect of the amount pre-emulsified skin was not observed on redness and yellowness value in study of Kim et al. (2017), significant difference of these values might be due to the difference between pork fat and duck skin. This color changes of reduced-fat emulsion were overall likely associated with difference between pork fat and duck skin, pre-emulsified duck skin, and hydrocolloids, which might relate to the water exudate on the reduced-fat emulsion.

Cooking loss and emulsion stability

Data concerning the change in cooking loss of reduced-fat emulsion with pre-emulsified duck skin and hydrocolloids are displayed in Table 4. Cooking loss of reduced-fat emulsion with pre-emulsified duck skin and alginate (T4) and guar gum (T6) was lower (P < 0.05) than the control with pork back fat, whereas the cooking loss of reduced-fat emulsion with pre-emulsified duck skin and pectin (T5) was highest (P < 0.05) compared to the control and all treatments. Cooking loss of reduced-fat emulsion with duck skin (T1) was higher than the reduced-fat emulsion with emulsified duck skin (T2). These findings show that the pre-emulsion process reduced the cooking loss, even at the same formulations. This is because the pre-emulsion enhanced the emulsification stability of the reduced-fat emulsion. Similar results were presented by Shim et al. (2018), who demonstrated that the cooking loss of hams was affected by the addition of the pre-emulsified skin. Kim et al. (2018) showed that the cooking loss of restructured hams with hydrocolloids was lower than the control; especially, the lowest cooking loss was evident in the restructured hams with alginate. Pintado et al. (2016) noted that frankfurters formulated with pre-emulsified fat with alginate had lower cooking loss than the emulsion gel-free control. Choi et al. (2010) indicated that reducing the animal fat in emulsion type sausages by substitute with pre-emulsion reduced cooking loss. Meat emulsions seem to have ehnanced water holding capacity due to the addition of pre-emulsified duck skin and hydrocolloids, which lowers cooking loss.

Table 4.

Effect of pre-emulsified duck skin and hydrocolloids on cooking loss and emulsion stability of emulsified reduced-fat meat emulsion

Traits (%) Control T1 T2 T3 T4 T5 T6
Cooking loss 9.45 ± 0.43bc 9.84 ± 0.36b 8.91 ± 0.77c 8.66 ± 0.18c 6.90 ± 0.42d 17.85 ± 0.80a 7.65 ± 0.49d
Emulsion stability
Total fluid separation 9.57 ± 0.58b 8.11 ± 1.42bc 7.33 ± 1.52c 2.88 ± 0.98d 0.98 ± 0.02d 11.75 ± 0.93a 0.96 ± 0.83d
Fat separation 0.93 ± 0.42bc 1.37 ± 0.17a 1.04 ± 0.07ab 0.64 ± 0.28c 0.00 ± 0.00d 1.00 ± 0.05bc 0.00 ± 0.00d
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Mean ± standard deviation was presented with three replicates

Control, emulsified with pork back fat; T1, emulsified with duck skin; T2, pre-emulsified with duck skin; T3, pre-emulsified with duck skin and carrageenan; T4, pre-emulsified with duck skin and alginate; T5, pre-emulsified with duck skin and pectin; and T6, pre-emulsified with duck skin and guar gum

a–dDifferent small letter in the same row means significant differences (P < 0.05)

The data for emulsion stability of reduced-fat emulsion with pre-emulsified duck skin and hydrocolloid are shown in Table 4. The total fluid separation of reduced-fat emulsion with pre-emulsified duck skin and hydrocolloid was lower (P < 0.05) than the control, expect for reduced-fat treatments with pectin (T5). Because emulsifying capacity of pectin was reduced under less acidic condition (pH > 3.5), the total fluid separation of T5 was highest (P < 0.05) compared with the control and all treatments(Dickinson 2018). No fat separation was evident for the reduced-fat emulsion with pre-emulsified duck skin and alginate (T4) and guar gum (T6) because all fat contained in duck skin is emulsified and the emulsion stability is pronounced. The stability of meat emulsion can be a prime indicator in the quality of meat products(Beriain et al. 2011; Choi et al. 2007; Pintado et al. 2016). The results agree with the report by Kim et al. (2018) that the total expressible fluid and fat separation of restructured meat batter with hydrocolloids were lower than those of the control. Due to the lower emulsion stability, water and fat holding capacity of hydrocolloids may be limited (Pintado et al. 2016). Shim et al. (2018) reported that the emulsion stability of duck ham batter with different levels of pre-emulsified skin was associated with lower total expressible fluid separation and fat separation compared to the control. Presently, pre-emulsified duck skin using alginate or guar gum was excellent concerning cooking loss and emulsion stability.

Protein solubility

Protein solubility of meat products have been detected because the proteins composed meat such as sarcoplasmic and myofibril, and stromal proteins determine the textural properties and emulsifying capacity and stability (Choi et al. 2011; Kim et al. 2017). The protein solubility data of the reduced-fat emulsion with pre-emulsified duck skin and hydrocolloid are shown in Table 5. Total protein solubility of reduced-fat emulsion with pre-emulsified duck skin and alginate (T4) was higher (P < 0.05) than the control, and the total protein solubility of reduced-fat emulsions treatments with pre-emulsified duck skin and hydrocolloid did not differ significantly (P > 0.05), except for T4. Sarcoplasmic and myofibril protein solubilities of T4 were higher (P < 0.05) than the other treatments and control. Choi et al. (2015) described that myofibrillar protein is important for improving the emulsifying and water holding capacity of meat products. Thus, the solubility of myofibrillar protein affects the textural properties of products made with meat emulsion. Protein solubility of meat emulsion can be used as a measure to evaluate the quality of the final meat emulsion meat products. The present data implicate the T4 formulation as being suitable to prepare high quality meat products.

Table 5.

Effect of pre-emulsified duck skin and hydrocolloids on protein solubility of emulsified reduced-fat meat emulsion

Traits (mg/ml) Control T1 T2 T3 T4 T5 T6
Total protein solubility 9.72 ± 0.19b 10.12 ± 0.25b 10.14 ± 0.21b 10.88 ± 0.25b 14.54 ± 0.85a 10.35 ± 0.19b 10.40 ± 3.47b
Sarcoplasmic protein solubility 5.02 ± 0.10cd 5.11 ± 0.19cd 4.92 ± 0.14d 4.84 ± 0.19d 5.92 ± 0.34a 5.54 ± 0.17b 5.29 ± 0.57bc
Myofibril protein solubility 4.70 ± 0.19b 5.01 ± 0.25b 5.22 ± 0.22b 6.05 ± 0.25b 8.62 ± 0.96a 4.81 ± 0.23b 5.10 ± 3.50b
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Mean ± standard deviation was presented with three replicates

Control, emulsified with pork back fat; T1, emulsified with duck skin; T2, pre-emulsified with duck skin; T3, pre-emulsified with duck skin and carrageenan; T4, pre-emulsified with duck skin and alginate; T5, pre-emulsified with duck skin and pectin; and T6, pre-emulsified with duck skin and guar gum

a–dDifferent small letter in the same row means significant differences (P < 0.05)

TPA

Table 6 presents the TPA data of the reduced-fat emulsion with pre-emulsified duck skin and hydrocolloid formulations. The hardness of reduced-fat emulsion with pre-emulsified duck skin and carrageenan (T3) was significantly (P < 0.05) higher than the control, whereas the hardness of reduced-fat emulsion with pre-emulsified duck skin and alginate (T4), pectin (T5), and guar gum (T6) were all significantly (P < 0.05) lower than the control. The springiness of reduced-fat emulsion with pre-emulsified duck skin and hydrocolloids was higher (P < 0.05) than the control, and the cohesiveness, gumminess, and chewiness of reduced-fat emulsion with pre-emulsified duck skin and carrageenan was higher (P < 0.05) than the control. The textural properties of meat products include hydrocolloids depend on the added amounts and kinds of hydrocolloids (Cierach et al. 2009; Dickinson 2018). The hardness, cohesiveness, gumminess, and chewiness of restructured hams with hydrocolloids were lower than the control without hydrocolloid, likely because the hydrocolloids increased the water retention capacity and water holding capacity of the meat emulsions (Kim et al. 2018). Furthermore, pre-emulsifying processing decreased hardness, chewiness, springiness, and gumminess of duck ham with increasing moisture content (Shim et al. 2018). In this study, alginate, pectin, and guar gum had a significant influence on TPA and addition of pre-emulsified skin tended to reduce the hardness of meat emulsion with increasing the water retention capacity and water holding capacity.

Table 6.

Effect of pre-emulsified duck skin and hydrocolloids on texture profile analysis of emulsified reduced-fat meat emulsion

Traits Control T1 T2 T3 T4 T5 T6
Hardness (kg) 0.26 ± 0.04b 0.25 ± 0.05b 0.23 ± 0.11bc 0.37 ± 0.06a 0.10 ± 0.01d 0.17 ± 0.03c 0.17 ± 0.04c
Springiness 0.86 ± 0.02c 0.95 ± 0.02b 0.95 ± 0.02b 0.98 ± 0.02a 0.97 ± 0.02ab 0.96 ± 0.02ab 0.98 ± 0.02a
Cohesiveness 0.46 ± 0.02bc 0.52 ± 0.02a 0.51 ± 0.03a 0.52 ± 0.03a 0.48 ± 0.03b 0.45 ± 0.03bc 0.44 ± 0.02c
Gumminess (kg) 0.12 ± 0.02b 0.13 ± 0.03b 0.12 ± 0.03b 0.19 ± 0.03a 0.05 ± 0.01d 0.08 ± 0.02c 0.07 ± 0.01c
Chewiness (kg) 0.10 ± 0.02b 0.12 ± 0.02b 0.11 ± 0.03b 0.19 ± 0.02a 0.05 ± 0.01d 0.07 ± 0.01c 0.07 ± 0.02c
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Mean ± standard deviation was presented with three replicates

Control, emulsified with pork back fat; T1, emulsified with duck skin; T2, pre-emulsified with duck skin; T3, pre-emulsified with duck skin and carrageenan; T4, pre-emulsified with duck skin and alginate; T5, pre-emulsified with duck skin and pectin; and T6, pre-emulsified with duck skin and guar gum

a–dDifferent small letter in the same row means significant differences (P < 0.05)

Apparent viscosity

The effect of apparent viscosity for the reduced-fat emulsion with pre-emulsified duck skin and hydrocolloid over 35 s is depicted in Fig. 1. The apparent viscosity of control and all reduced-fat emulsion treatments reached the highest within 5 s, after which it tended to maintain the highest value. The apparent viscosity of reduced-fat emulsion with duck skin (T1) and pre-emulsified with duck skin (T2) was lower (P < 0.05) than the control. The apparent viscosity of the reduced-fat emulsion with pre-emulsified duck skin and alginate (T4) was the highest (P < 0.05). Apparent viscosity of meat emulsions with pre-emulsified skin decreased with the rotation time, and meat batters with increasing pre-emulsified skin displayed increased maximum apparent viscosity(Shim et al. 2018). Similarly, Kim et al. (2018) described that restructured meat batter with hydrocolloids had higher apparent viscosity than that of the control without hydrocolloid, as hydrocolloid improves the binding capacity between moisture and protein. Meat emulsions with higher apparent viscosity had greater emulsion stability, with a strong correlation between emulsion stability and apparent viscosity (Choi et al. 2009). High apparent viscosity of meat emulsions did not break smoothly (Choi et al. 2009, 2019). Thus, here, the apparent viscosity was increased by adding hydrocolloid during pre-emulsified skin processing; the reduced-fat emulsion with pre-emulsified duck skin and hydrocolloid can produce emulsions systems with high emulsion stability.

Fig. 1.

Fig. 1

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Effect of pre-emulsified duck skin and hydrocolloids on apparent viscosity of emulsified reduced-fat meat emulsion. Control, emulsified with pork back fat; T1, emulsified with duck skin; T2, pre-emulsified with duck skin; T3, pre-emulsified with duck skin and carrageenan; T4, pre-emulsified with duck skin and alginate; T5, pre-emulsified with duck skin and pectin; and T6, pre-emulsified with duck skin and guar gum

Conclusion

Reduced-fat meat emulsion with pre-emulsified duck skin and hydrocolloids including carrageenan, alginate, pectin, and guar gum displayed altered physicochemical properties. Cooking loss, emulsion stability, protein solubility, and apparent viscosity of the pre-emulsified duck skin and alginate were better than the other treatments. Because pre-emulsified duck skin with added alginate produces excellent physicochemical properties of meat emulsion, it is preferred for the manufacture of reduced-fat emulsion meat products.

Acknowledgements

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). This research was also partially supported through the High Value-added Food Technology Development Program (118011-03) by the Ministry of Agriculture, Food, and Rural Affairs (Republic of Korea).

Footnotes

Publisher's Note

Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Hae In Yong and Tae-Kyung Kim have contributed equally to this work.

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