Structural and Instrumental Textural Properties of Meat Patties Containing Soy Protein

Abstract

The effect of two different types of soy protein namely soy protein flour (SPF) and texturized soy protein (TSP); soy protein extender concentration; cooking times; and cooking temperatures on structural and textural properties of pan‐fried patties were studied. Beef patties were formulated using extra lean (10 kg fat/100 kg) ground beef samples, with different concentrations of soy protein (0, 2, 3.5, and 5% kg/kg total mass). They were formed into patties, and cooked on a griddle at different temperatures (177 and 187°C) and cooking times (10, 15, and 20 min). Water holding capacity (WHC) and total cooking loss (TCL) were determined. Instrumental textural profiles of the cooked samples were obtained using a Universal Testing Machine Instron. Porosity and pore size distributions were determined by a mercury intrusion porosimeter. The results indicated that increasing soy protein concentration increased WHC and reduced TCL. Beef patties extended with TSP were harder and more cohesive than those extended with SPF. Total mean porosities at the 5% soy protein extender concentration were 0.42 and 0.40 for the SPF and TSP extended samples, respectively. Samples extended with SPF had up to 84% capillary pores.

Keywords:

• Soy protein
• Pan‐frying
• Meat patty
• Texture
• Porosity
• Pore size distribution

Introduction

Plant base proteins are extensively used as fillers, binders, and extenders in meat systems.[1] Different plant based proteins such as soy protein, corn germ protein, wheat germ protein, and rapeseed concentrate have been used as meat extenders.2–4 Soy proteins contain about 50% protein including the eight essential amino acids and considerable quantities of vitamins and minerals.[5] They are excellent additives in low fat meat systems. They are available in different forms such as coarse grit [texturized soy protein (TSP)] to very fine flour (200 mesh) [soy protein flour (SPF)]. The use of soy protein as an extender enhanced water binding capacity and textural properties;[6] it minimized total cooking loss[7] [8] and minimized shrinkage.[9] Thus, soy protein extension improves the functional characteristics and stability of meat products.

Extension of meat systems with soy protein develops a complex composite heterogeneous and anisotropic structure. It alters the physical and textural characteristics of extended beef patties. This change may upset the microscopic structure of the native material and ultimately the physical properties. Thus meat extension with soy proteins may have significant influence on textural attribute.

Texture in food is closely associated with the structural makeup of the material. The structural matrix is mostly a network of protein strands surrounded by individual muscle pieces and fibers.[10] The eases of mechanical destruction by mastication are a fundamental textural phenomenon of interest in food industries. Food texture is one of the most important quality attributes, which influences consumer preferences of food products. An objective instrumental textural profile analysis (ITPA) attempts to quantify textural parameters using the Universal Testing Machine Instron. The objective method of measurement of meat texture are capable of explaining about 60% of variation in panel scores and the remaining 40% is the inescapable consequence of human error in making judgement.[11] Troutt et al.[2] also reported a strong correlation between objective Instron method and sensory panel texture traits. Many researchers12–17 reported ITPA on beef patties using Instron.

Mechanical and textural properties such as porosity and pore size distribution can significantly influence the mechanical and textural characteristics of cooked and dried foods,[4] [18] [19] these parameters could also be correlated to the mechanical and textural properties.[20] [21] Mercury porosimetry is one of the most commonly used methods to study physical properties of porous materials. The method provides data on densities, porosity and pore size distributions of materials, although the values of porosity measured by porosimetry are usually lower than values measured with a pycnometer,[19] due to the phenomenon of interconnectedness and dead‐end or blind pores.[22] Ngadi et al.[4] used porosimetry data to characterize porosity and pore size distributions in beef patties extended with soy protein. Other authors[19] [23] [24] also used the technique to characterized pore size distribution in food products. The knowledge of physical and textural properties is vital to the design of better quality foods and as well as mathematical model of food systems.[25]

The objective of this research study was to investigate the effect of temperature, cooking time, types of soy protein, and soy protein extender concentration on physical properties of pan‐fried beef patties.

Materials and Methods

Extra lean (10 kg fat/100 kg) ground beef samples were used throughout this study. The samples were purchased from a local grocery chain. Two types of soy protein were used namely: low fat SPF with particle size (100 mesh) and medium grade (3–6.4 mm) particle size TSP (IOWA SOY™, Vinton, IO). Experimental samples were formulated by adding various levels of soy protein concentrations (0, 2, 3.5, and 5% kg/kg total mass) and other ingredients as shown in Table 1, and details as described by Ngadi et al.[4] The same formulation was used for both the SPF and TSP. The formed patties were frozen at −18°C ± 1°C until required for use.

Table 1.  Formulation of ground beef patties extended with soy‐protein (SPF and TSP) at different concentrations

Ingredient	Treatment [composition (g)]
Extender	0	2	3.5	5
Ground beef	82.5	80.5	79.0	77.5
Salt	2.5	2.5	2.5	2.5
Distilled water	15	15	15	15
Total	100	100	100	100

The water holding capacity (WHC) for the uncooked beef patty samples that had been extended with SPF and TSP were determined by centrifugation method. Ten grams of samples were mixed with 40 mL distilled water in centrifuge tubes and were allowed set for 30 min in a water bath (Isotemp 1028S, Fisher Scientific, Pittsburgh, PA) at 22°C prior to the test run. The centrifuge tubes were inserted in the centrifuge (Model HN‐S, International Equipment Company, Needham Heights, MA) holding chambers, and spun at 1200g for 30 min. At the end of the centrifugation the extra water was removed. The new mass of the sample was recorded and hence the WHC determined.[4]

Frozen patty samples were thawed overnight in a refrigerator at 4°C. Cooking was accomplished at 177 and 187°C using a pan fryer (Moffat, Specialites De Cuisine Inc., Montreal). All the patty samples were turned over after the first 5 min of each time variable used. Internal center temperatures of patties were monitored using T‐Type thermocouples that were attached to a data logger (Hotmux, DCC Corporation, Pennsauken, NJ). Cooking loss after each cooking treatment was determined after the samples had equilibrated at room temperature (23°C ± 1°C) as the ratio of the total mass loss after pan‐frying and the original mass of the raw patty.

Instron Universal Testing Apparatus, (model 4502, Canton, MA) was used to obtain textural profile of cooked samples. The patty samples were cut with a cylindrical die (36 mm diameter) into 12 mm thick sizes. A 50 KN load cell and a flat‐headed plunger attachment (19.1 mm diameter) were used. Samples were individually compressed at a crosshead traveling speed of 20 mm/min. The equipment was interface to a microcomputer for the data acquisition, and all the data of the measured ITPA parameters were acquired through the microcomputer for further analysis. Instrumental textural profile parameters obtained by twice compressing the samples to 75% of their original thickness. Hardness is the maximum applied force (N) which was indicated by the height of the first peak in the ITPA curve. Cohesiveness, a measure of the internal strength of the bonds that make up the product, was obtained as the ratio of the area under the second peak and the area under the first peak. Toughness which is the ability of the product to withstand repeated stress before fracture, was measured as the area under the first curve of ITPA.

Porosity and pore size distributions were determined using a porosimeter (Autopore III series 9400, Micromeritics Instrument Corporation, Norcross, GA) following the methods of Ngadi et al.[4] The equipment was designed with the capacity to measure micropores up to 5 nm pore diameter at a maximum pressure of 228 MPa. The samples measured with the porosimeter were vacuum dried prior to the test, using the method described by Ngadi et al.[4] Data on porosity and cumulative volume of intrusion were acquired through a microcomputer interfaced to the porosimeter. Mercury intrusion and extrusion volumes are plotted as a function of pore diameter or pressure. Pore sizes are calculated based on the Washburn equation [Eq. (1)][26] on the assumption that the pores are cylindrical in shape.

where D is the pore diameter, P is the applied pressure at which the mercury is forced into the sample, γ is the surface tension of mercury given as 0.485 N/m, and ϕ is the solid–liquid contact angle (130°). Although the assumption may not represent the actual nature of pores, it is generally accepted in the practical sense of estimation, or else may be too complicated. The pore size distribution are usually computed based on the relationship between pore radius and pore volume as defined [Eq. (2)]

where D _v is the pore size volume distribution function, P is the applied pressure at which the mercury is forced into the sample and r pore radii measure to every corresponding P, v _t is the total pore volume and v is the pore volume.

A factorial experimental design was used for this study. The experimental factors involved and their levels were as follows: type of soy protein extender (control, SPF, TSP); soy protein concentration (0, 2, 3.5, and 5%); cooking time (0, 10, 15, 20 min) and temperature (177 and 187°C) with three replications. Analysis of variance (ANOVA) and the mean comparison using the Duncan's multiple range test (DMRT) was accomplished by statistical analysis system (SAS v.8).

Results and Discussion

Water Holding Capacity and Cooking Losses

Water holding capacity and total cooking losses (TCL) were determined on beef patties extended with SPF and TSP. The ANOVA of data indicated that the type of soy protein (SPF or TSP) and concentration used have significant effect (P < 0.01) on WHC of beef patties. The Duncan's mean comparison test (DMCT) results for WHC is presented in Table 2. The results show that increasing soy protein extension concentrations improved the water holding capacity. Similar results were reported by other authors.[4] [27] [28] No significant difference (P > 0.05) was observed between the control samples and the samples with 2% SPF extension, whereas there was significant difference (P < 0.01) between control samples and 2% TSP extended samples. The mean value of WHC obtained at 5% extender concentration using TSP was higher than the value obtained for SPF. This may be due to differences in the physical characteristics of the extenders. Soy protein flour has a fine powdery texture whereas TSP has a coarse texture that apparently provided pockets for moisture absorption. Water holding capacity correlates to juiciness in meat patties systems.[9] Extension of meat patties with soy protein should improve moisture retention and final product quality.

Table 2.  Mean comparison of types of soy protein used on WHC and TCL on pan‐fried beef patties extended with soy protein

Concentration (%)	WHC		TCL
	SPF (%)	TSP (%)	SPF (%)	TSP (%)
0	9.0a	9.0a	29.5a	29.5a
2	13.9ab	17.1b	26.6ab	20.7b
3.5	20.9c	20.6b	24.0bc	15.6c
5	18.9bc	24.0b	21.6c	13.8c

Note: Means with the same letter and in the column are not significantly different at 5% level.

Analysis of variance showed that there was significant effect (P < 0.01) of the type of soy protein on TCL. The DMCT showed that total cooking loss decreased as the extender concentration increased and as WHC also as shown in Table 2. Other authors[2] [8] [15] [27] [28] have reported similar observations. This could be attributed to the rehydration effect of the soy protein during patty formulation. Cooking time, temperatures also have significant effect (P < 0.01) on TCL. There were increased cooking losses with cooking time and temperature increments. Beef patties extended with TSP incurred less cooking loss as compared to SPF (Table 2). The use of soy protein in beef patty systems has favorable implications because of its moisture retention ability associated with textural attributes.

Textural Analysis

Textural parameters such as compressive force (hardness), cohesiveness, and toughness were determined from the instrumental textural profile analysis (ITPA) using an objective instrumental measurement method. The effects of the temperature, cooking time, soy protein types, and concentration were evaluated for the pan‐fried beef patties. Type of soy proteins used had significant influence (P < 0.01) on the hardness, cohesiveness and toughness of pan‐fried beef patties. The mean comparisons of measured ITPA for samples extended with SPF and TSP are shown in Tables 3 and 4 respectively. It was apparent that increased concentration of SPF significantly decreased (P < 0.05) hardness of the beef patty samples. Montejano et al.[29] reported a hardness value of 41 N for comminuted beef whereas[1] reported maximum compressive force values of 68, 49, 43, and 33 N for ground beef samples extended with 0, 2, 4, and 6% sorghum flour, respectively. Other researchers[12] [30] have also made similar observations using different extenders. The hardness values obtained in this study are higher than the reported values probably due to difference in the extenders. Addition of meat extenders apparently modifies structure of ground meat patties resulting in decreased hardness. The result may be linked to extender influence on WHC of the products. The effect of SPF on meat patties may be attributed to its physical characteristics namely: fine particle texture, uniform size distribution, disparsibility, and water binding capacity. Extension of meat patties with SPF also significantly (P < 0.01) changed toughness of samples. However, there was no significant difference (P > 0.05) between the 2, 3.5, and 5% concentrations of SPF used in this study. Cohesiveness of the samples was not changed (P > 0.05) as a result of SPF extension concentration. Samples extended with TSP appeared to be more cohesive and harder than those extended with SPF. Montejano et al.[29] reported cohesiveness for comminuted beef as 0.31. Brown and Zayas[31] reported a value of 0.70 as cohesiveness for beef patties extended with corn germ protein. The results obtained in this study were close to the value reported by Montejano et al.[29] The integrity of the pan‐fried samples extended with SPF was not compromised by heat treatment as compared to the TSP extended samples. Large particle chunks of TSP grits were visible on the surface of the patties after extension formulation, which could have contributed to their toughness and cohesiveness. Control samples apparently will require greater force to chew than the samples that were extended with soy protein. As a result, samples with soy protein extensions will be more desirable than control samples. The cooking temperatures had no significant effect (P > 0.05) on cohesiveness at different levels of concentrations of patties extended with SPF. Toughness was influenced (P < 0.05) by cooking temperature and time for samples extended with TSP as indicated by the ANOVA. Cooking time affected cohesiveness of samples extended with SPF. Proteins as extender improve the water retention ability while enhancing textural attributes such as juiciness and binding characteristics. Therefore, the addition of soy protein slurries as extenders had a dilution effect on patties and thus enhanced their functional properties.[7]

Table 3.  Mean comparison of extender concentration on textural properties of pan‐fried beef patties extended with SPF

Concentration (%)	SPF
	Hardness (N)	Toughness (MPa)	Cohesiveness	Porosity
0	105.9a	0.036a	0.31a	0.44a
2	69.6b	0.026b	0.35a	0.37b
3.5	68.6b	0.027b	0.31a	0.39b
5	58.8c	0.028b	0.35a	0.42a

Note: Means with the same letter and in the column are not significantly different at 5% level.

Table 4.  Mean comparison of extender concentration on textural properties of pan‐fried beef patties extended with TSP

Concentration (%)	SPF
	Hardness (N)	Toughness (MPa)	Cohesiveness	Porosity
0	105.9a	0.036a	0.31c	0.44a
2	71.6c	0.025c	0.50a	0.40b
3.5	85.3b	0.030b	0.42b	0.40b
5	103.9a	0.038a	0.36bc	0.41b

Note: Means with the same letter and in the column are not significantly different at 5% level.

Porosity and Pore Size Distribution

The effects of the independent parameters (type of soy protein, soy protein concentration, cooking time, and temperature) on porosity were determined using a mercury porosimeter. Total porosities of 0.33 to 0.45 and 0.35 to 0.42 for samples extended with SPF and TSP, respectively were obtained. These values are close to the values reported by Farkas and Singh[23] for air‐dried chicken meat, and reported by Rahman et al.[19] for vacuum dried tuna meat. However, the values are greater than those reported by Ngadi et al.[4] for oven cooked meat patties containing soy protein. The ANOVA showed that type of soy protein significantly (P < 0.01) influenced pore development in pan‐fried beef patties. Mean comparison of porosity data shown in Tables 3 and 4, indicated that control samples exhibited higher porosity (P < 0.05). Formulating beef patties with soy protein decreased porosity of samples. Cooking at high temperature could enhance shrinkage as a result of protein denaturation and thus reduce pore sizes.[32] Pan and Singh[33] attributed shrinkage to structural collapse as a result of severity of heating. There was a significant decrease in porosity when beef patties were extended with 2% TSP. However, increasing the TSP concentration from 2 to 5% did not significantly (P > 0.05) influence porosity of the beef patties. Similar to TSP, extending beef patties with 2% SPF significantly decreased sample porosity. Mean value of porosity obtained with 5% SPF was higher than the values obtained using 2 and 3.5% concentrations and was not different from the mean value obtained for control samples. At the 5% soy protein concentration, mean porosity values of 0.42 and 0.40 were observed for samples extended with SPF and TSP, respectively. The initial decrease in porosity in the patties extended with SPF could be attributed to increased solubility and the filling of pores in the patties matrix by the fine particles of SPF.

Cumulative pore volumes of pan‐fried beef patty extended with 5% soy protein concentration are shown in Fig. 1. The total cumulative pore volume in control samples was 0.416 mL/g. The total cumulative pore volumes in patties extended with SPF and TSP were 0.313 and 0.416 mL/g, respectively. Karathanos et al.[18] reported a cumulative intrusion volume of 0.623 mL/g for Amioca starch. Ngadi et al.[4] reported cumulative pore volumes of 0.33 and 0.20 mL/g for oven cooked beef patties extended with SPF and TSP, respectively. The TSP curves showed coarseness within structural matrix, thus exhibiting a distinct characteristic large voids due to its gritty texture, while it plateau after a cumulative pore volume of 0.416 mL/g when mercury saturation breakthrough at low pressure (207 kPa) was achieved. No pore volume increment was observed as pressure increased further. It was evident that solubility of TSP in ground beef mixture was difficult to achieve because of the structural makeup with large particle sizes (3–6.4 mm). The existence of large planar pore sizes (10–70 µm) and interior matrix pores ranging between 0.01 and 10 µm was observed on the control and samples extended with SPF.

Figure 1.  Cumulative pore volume (mL/g) of pan‐fried beef patties extended with 5% (kg/kg total mass) of soy protein flour and texturized soy protein.

Cumulative pore volume percentages were also used to characterize pore size distribution on control samples and samples extended with SPF and TSP for pan‐fried beef patties. Pore sizes of about 40 µm and smaller were used in this analysis. The effect of type of soy proteins used in patty formulation beef patties is shown in Fig. 2. Up to 84 and 70% of the pores are capillary pores that exist within the samples extended with SPF and the control, respectively. Nearly all pores in the samples extended with TSP are greater than 10 µm in diameter. Farkas and Singh[23] reported that for slowly frozen freeze‐dried chicken white meat have 80% pore volume as micropores. Soy protein flour exhibit better quality attributes due to its smaller particle size (100 mesh) of about 0.149 mm, uniformity and solubility. This characteristic trait contributes to its textural enhancement. The control samples exhibited lower percentage of pore volumes, and the effect of soy protein extension appeared to enhance pore development.

Figure 2.  Pore size distribution of pan‐fried beef patties extended with 5% (kg/kg total mass) of soy protein flour and texturized soy protein.

Conclusions

The type of soy protein extender used in the formulation of pan‐fried beef patties significantly influences (P < 0.05) the WHC and TCL. Extending beef patties with soy protein increase WHC by 42% thus decreases the TCL by 69% at the highest level of concentration level of 5%. The cooking time and temperature negatively influences (P < 0.01) on TCL. The type of soy protein (TSP and SPF) used in the beef patty system had significant influenced (P < 0.05) on textural attributes such cohesiveness, toughness, and hardness. Pan fried beef patties extended with SPF appeared to less hard than those extended with TSP. The use of soy protein had a decreasing effect on porosity. Samples extended with SPF contain over sixty percent of capillary pores within their structural matrix.

Acknowledgment

This study was supported in part by funding from the National Science and Engineering Research Council of Canada.