Effects of Jet-Milled Defatted Soy Flour on the Physicochemical and Sensorial Properties of Hamburger Patties

Food-grade DSF was obtained from Ho-Kyoung Tech (Korea). Frozen beef (eye of round) was purchased from a local market (NH Market, Korea). Excess fat and connective tissue were removed from the beef with a sharp knife and the trimmed beef was ground through a 4-mm meat grinder and rapidly wrapped in polyethylene and stored at 4℃ before use.

The DSF powder was sieved twice (150- and 63-µm testing sieves; Nonaka Rikaki, Japan) to obtain coarse and fine fractions. Those powders that could not pass through the 150-μm sieve were collected as the coarse DSF. The powders that passed through the 150-μm sieve, but that were retained by the 63-μm sieve were collected as the fine DSF. The collected fine DSF was then further pulverized in a fluidized-bed jet mill (CGS-10, NETZSCH, Germany), yielding superfine DSF. Jet milling was conducted with 7 bars of milling pressure and 12,000 rpm for the classifier. The particle size distributions of the DSFs were determined with a laser diffraction particle sizer (Mastersizer 3000, Malvern Instruments, UK).

The hamburger patties were prepared as follows, using the traditional method: 1) the control hamburger patty was made from 95% lean ground meat and 5% water; 2) the hamburger patty with coarse DSF was composed of 90% lean ground meat, 5% water, and 5% coarse DSF; 3) the hamburger patty with fine DSF was composed of 90% lean ground meat, 5% water, and 5% fine DSF; and 4) the hamburger patty with superfine DSF was composed of 90% lean ground meat, 5% water, and 5% superfine DSF.

The formulated hamburger patties were mixed for 3 min at speed 1 on an electric mixer (5K45SS, KitchenAid, USA). Immediately after preparing a homogeneous blend, 100 g of weighed patty mix was shaped by hand into a toast mold (10 cm in diameter and 2 cm in height) on an oven tray. Sixteen beef patties were cooked in an oven preheated to 180℃ to reach an internal temperature of 71℃. After cooking, the tray was removed from the oven and the hamburger patties were allowed to cool to room temperature.

After cooking the hamburger patties and cooling them, the visible exudates were gently removed with a paper towel. The cooking loss was calculated as follows:

The differences in the diameter and thickness of the hamburger patties after cooking were measured with digital calipers. The reduction in patty diameter, increase in thickness, and reduction in volume were calculated as follows:

The color of the patties was determined based on the CIE L* (lightness), a* (redness/greenness), and b* (yellowness/blueness) values using a colorimeter (UltraScan Pro, HunterLab, USA). A standard white plate with L* = 97.4 9, a* = 0.13, and b* = 0.04 was used for calibration. Each sample was measured three times. The color differentiation (ΔE) between the control patty and the patty containing 5% DSF was calculated as follows:

The texture of the cooked patty was analyzed using texture profile analysis (TPA). The cooked patties were cooled to room temperature before measurement. Each patty was cut into 2 × 2 × 1.5-cm cubes. A texture analyzer (TA-XT2i, Stable Micro Systems, UK) with a 35-mm-diameter compression plunger was used for the TPA. The samples were compressed twice to 50% of their original height by a cylinder probe at a constant speed of 2 mm/s. The TPA curve was recorded and the hardness, adhesiveness, springiness, cohesiveness, gumminess, and chewiness were calculated automatically (Bourne, 2002).

The sensory properties of the hamburger patty samples were evaluated using the quantitative descriptive analysis (QDA) method, which was specifically developed for meat products (American Meat Science Association, 1995; Selani et al., 2016), with some modifications. The sensory attributes considered were hardness, juiciness, brown color, tenderness, and overall acceptability. Eight panelists were trained using previously identified standard references (Table 1). Cooked patty samples were cut into 2 × 2 × 1.5-cm cubes and assigned random numbers. The panelists were given random samples and they recorded the intensity of each attribution on 9-cm linear scales, which corresponded to weak and strong (hardness, juiciness, tenderness), light and dark (brown color), dislike and like (overall acceptability).

All experiments were conducted in triplicate and the results are expressed as the mean ± standard deviation. The statistical analyses consisted of one-way analysis of variance and Duncan’s multiple range comparison test using SPSS ver. 20.0 software (IBM, USA). p-values < 0.05 were considered of significant.

Table 2 shows the particle size distributions of the DSF samples. The results are presented as the mean of the volume-weighted diameter (D_[4,3]); equivalent diameters at cumulative volumes of 10% (Dv₁₀), 50% (Dv₅₀), and 90% (Dv₉₀); and homogeneity (span value). The average particle size can be expressed as either D_[4,3] or Dv₅₀. Coarse, fine, and superfine DSF had Dv₅₀ values of 259.3±0.6, 91.5±0.5, and 3.7±0.2 µm, respectively. The prepared DSF powders had relative homogeneous size distributions, as indicated by the small span values. Although the DSF samples were prepared as described previously (Muttakin et al., 2015), there were some differences in the average particle size due to the different batches of DSF material used. Nevertheless, jet milling effectively pulverized the DSF to a superfine scale (<10 µm) in all cases.

Fig. 1 shows the appearance of the hamburger patties made with different DSFs before and after cooking. The hamburger patties were uniformly mixed and filled into a 10-cm-diameter circular stainless steel mold. Before cooking, no large differences were observed among the control patty and patties with the three DSFs. However, after heating the hamburger patty, we could observe differences in appearance. The control patty decreased in size and a relatively large amount of meat juice drained from the patties. For the hamburger patties made with fine and superfine DSF, the decrease in size was small, as was the amount of juice produced.

Fig. 1. The appearance of hamburger patty made with 5% DSF powder.

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Table 2 shows the effect of DSF particle size on the color of the cooked patties. The lightness (L* value) of the control patty was 50.78±0.62, and it decreased to 44.25±1.48 with the addition of 5% coarse DSF. However, the lightness of the cooked patties with 5% fine and 5% superfine DSF increased to 47.45±0.25 and 47.32± 0.74, respectively, which were similar to that of the control patty. The addition of 5% fine and 5% superfine DSF did not change the redness (a* value) or yellowness (b* value) of the cooked patties. The only change was in the a* value of the patty containing 5% coarse DSF. These results indicate that the addition of 5% fine and superfine DSF minimally affects the color of the cooked patty, which can be confirmed by the small DE values. Similarly, it has been reported that the addition of oat fiber and carrageenan had little effect on the color of cooked hamburger patty (Mittal et al., 1992; Hughes et al., 1997), while the addition of rice bran fiber changed the cooked color of meat batter (Choi et al., 2009).

Table 3 presents the cooking loss, reduction in diameter, increase in thickness, and reduction in volume of the hamburger patties made with the different DSFs. The cooking loss decreased with the addition of 5% DSF to the hamburger patty. The cooking loss of the control patty was 34.4%. The addition of coarse and fine DSF to the hamburger patty reduced the losses to 26.4% and 27.2%, respectively. The cooking loss of the patty with superfine DSF was the lowest at 24.8%.

Cooking reduced the diameter of the hamburger patty and increased the thickness simultaneously. The reductions in patty diameter with coarse, fine, and superfine DSF were 18.8%, 18.0%, and 15.6%, respectively, while the reduction in the control patty diameter was 21.2%. The thickness of the patty increased after cooking. Thickness of the control patty increased by 5%, while the thicknesses of the patties with coarse, fine, and superfine DSF increased by 14.3%, 23.2%, and 30.0%, respectively. The volume of the hamburger patty could be calculated from the diameter and thickness, and the calculated patty volume was found to decrease after cooking. The volume loss of the control patty was 34.7%. The addition of coarse and fine DSF to the hamburger patty reduced the losses to 24.6% and 17.3%, respectively. The volume loss of the patty with superfine DSF was the lowest at 7.5%.

The cooking loss reflects the moisture and lipid losses after cooking, which are important determinants of the juiciness and mouth feel of cooked meat (Abdel-Naeem and Mohamed, 2016). The cooking loss is affected by different variables, such as the composition, additives, cooking methods, oven temperature, and sample dimensions (Vittadini et al., 2005). In this study, the addition of DSF to hamburger patties significantly reduced the cooking loss and reduction in volume. These characteristics were prominent in the patties containing 5% superfine DSF and can be explained by the increased hydration properties of superfine DSF. Our previous research indicated that superfine DSF has increased water-holding capacity and swelling capacity of 24% and 32%, respectively, compared with those of coarse DSF (Muttakin et al., 2015).

Table 5 shows the results of the texture profile analysis of the hamburger patties after cooking. The addition of 5% coarse DSF increased the hardness of the cooked patty significantly from 19.84±2.55 to 26.34±2.26. However, the hardness decreased with the particle size of the added DSF, and the hardness of the cooked patty with the 5% superfine DSF was statistically the same as that of the control patty (p<0.05). The hardness of a cooked patty was explained by moisture and fat retention after heating (Choi et al., 2009; Selani et al, 2016). As shown in Table 3, the patty with 5% superfine DSF showed less cooking loss and volume reduction, which indicates that more moisture and fat were retained within the patty after heating, resulting in the reduced hardness value.

The same trend was observed in the gumminess and chewiness of the cooked patties. The addition of coarse DSF increased the gumminess and chewiness significantly, but the gumminess and chewiness decreased with the particle size of the added DSF. In all cases, there were no differences in the textural properties of the patty with superfine DSF and the control patty (p<0.05). Springiness and cohesiveness were not affected by the addition of DSF. Previous reports showed that gumminess, springiness, and chewiness decreased when the usage level of vegetable fibers increased, while the addition of 5% rice bran increased only springiness of pork patty (Choi et al., 2008).

The sensorial properties of the control patty and patties with DSF were analyzed using the QDA method (Table 6). Table 1 shows the five sensorial attributes (hardness, juiciness, tenderness, brown color, and overall acceptability) with the previously identified standards.

The addition of 5% DSF reduced the hardness of the cooked patties. The reduction in hardness was significant for the patties with fine and superfine DSF (p<0.05). The hardness measured using the sensory evaluation showed a different tendency from the hardness measured with the TPA due to differences in the measurement methods where the hardness was judged by the amount of force required to bite through the sample during the 1^st and 2^nd chews in the sensory test versus the first down-stroke in the TPA test.

The addition of 5% coarse DSF reduced the juiciness of the cooked patty from 4.6±1.5 to 1.6±0.5. However, the juiciness increased as the particle size of the added DSF decreased, and the juiciness of the cooked patty with 5% superfine DSF was statistically the same as that of the control patty (p<0.05). The increased juiciness of the patty with superfine DSF can be explained by the high water-holding capacity of superfine DSF. Tenderness did not change with the addition of 5% coarse DSF, while it increased significantly in the patties with fine and superfine DSF (p<0.05).

The patties with coarse and fine DSF showed reduced overall acceptability, while the patty with 5% superfine DSF had the same overall acceptability as the control patty (p<0.05). The hamburger patty containing superfine DSF was found to be significantly juicier and tenderer than the patties with coarse and fine DSF. The reported overall acceptability of beef patties is mostly affected by juiciness and tenderness (Pinero et al., 2008; Yi et al., 2012) which is in accordance with our result.