Abstract: The antioxidant effects of different concentrations of rosemary extracts synergized with chilling on beef were investigated. The antioxidant effects of different concentrations of rosemary extract and chilled beef were investigated. The color difference values (L* and a*), drip loss, shear force, thiobarbituric acid value (TBARS) and sensory indexes were measured on the 1st, 3rd, 5th and 7th days of the storage period using chilled beef, and the distilled water-soaked beef stored at 4 ℃ was taken as control 1, and the distilled water-soaked beef preserved in ice temperature was taken as control 2. The results showed that the beef treated with 0.15 % rosemary extract and chilling had excellent organoleptic properties on the 7th day of storage, with L* value of 36.49, a* value of 17.27, drip loss of 0.62 %, shear force of 4 429 g, TBARS value of 0.18 mg/100 g, and a significant antioxidant effect on chilled beef.
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Cold beef is the beef that adopts scientific slaughtering process and is always maintained at 0℃~4℃ during storage, transportation and sale, which has the advantages of tenderness, juiciness, freshness, deliciousness, high protein, low fat, etc., and is safe and healthy, and has gradually become the main object of meat consumption in recent years. China is the world's third largest beef producer, but compared with the United States, Australia, New Zealand and other beef production powerhouses, the gap is very large, and the trade deficit is increasing year by year. Beef at 0 ℃ ~ 4 ℃ conditions can not completely inhibit the growth of microorganisms, so the shelf life is short. Especially during the storage period, it is easy to be affected by various external environmental factors, resulting in oxidation of lipids and proteins in beef and surface discoloration phenomenon, which directly affects its nutritional value and commercial value[1] , and meat color is an important sensory indicator for consumers to judge the freshness of meat[2] .
Therefore, the development of beef industry in China has been seriously restricted. How to control the color deterioration of chilled beef during storage and marketing has become a hot research point. Ice temperature preservation technology is known as the "third generation of preservation technology" [3], placing fresh beef in ice temperature conditions (above freezing point, below 0 ℃) has a significant effect on maintaining the nutrition, color and quality of beef. In addition, rosemary is a natural antioxidant, which not only has a good antioxidant effect, but also is safe and reliable. The synergistic effect of rosemary extract with chilled beef can be a good antioxidant, which is also in line with the natural and healthy dietary concepts of modern consumers.
In this paper, the antioxidant effects of different concentrations of rosemary extract and chilled beef were investigated. The color difference, drip loss, shear force, thiobarbituric acid value (TBARS), and sensory evaluation of the beef were determined for the beef soaked in distilled water and stored at 4 ℃ as control 1, and for the beef soaked in distilled water and preserved by chilling temperature as control 2, and the most suitable concentration for the antioxidant of beef was optimized. During the storage period, the color difference, drip loss, shear force, thiobarbituric acid value (TBARS) of beef were measured, and sensory evaluation was performed to optimize the concentration of rosemary extract that is most suitable for antioxidant oxidation of beef, which can effectively prolong the shelf-life of chilled beef, and to a certain extent, promote the application of chilled freshness technology in the preservation of meat to provide consumers with safe, tasty, and nutritious chilled beef to meet the market demand and to promote the further development of China's beef industry.
1 Materials and Methods 1.1 Materials and reagents
Beef: Yisai Beef Co., Ltd. of Henan Province, fully ripened after 72 h of acid exclusion, and the parts of cucumber strips were taken and packed, and transported to the laboratory at 4 ℃; rosemary: Shenzhen Hengsheng Biological Science and Technology Co. Ltd.
1.2 Instruments and equipment
Ltd.; 20629 Temperature Recorder: Delta Trak, USA; CR-400 Colorimeter: Konica Minolta Investment Co., Ltd., Japan; CT3 Mass Contouring Instrument: Brookfield, USA; BlueStar B Spectrophotometer: Beijing Laibertechnik Instruments Co: Ltd.; SHA-B Dual-function Water Bath Oscillator: Jintan Jierer Electric Appliance Co.
1.3 Methodology
1.3.1 Meat sample handling
The plates and knives were wiped and sterilized with alcohol cotton balls in a sterile room. The outer package of beef was opened and the surface fat, tendons and fascia were removed. In order to ensure the uniformity of the color of each piece of meat, the surface layer of the meat sample was cut off with a sterile knife, and the meat sample was divided into 72 rectangular pieces of 100 g. The meat samples were exposed to air for 45 min and set aside.
1.3.2 Preparation of rosemary solution
Dissolve rosemary extract in distilled water and stir well to make a solution of 200 mL, put it in a beaker. It is necessary to prepare it as it is used.
1.3.3 Study of antioxidant effect of different concentrations of rosemary extracts on beef
In the aseptic chamber, the treated beef cubes were divided into 6 groups of 12 cubes each. Four groups were immersed in different concentrations of rosemary extract solution for 1 min, then removed with sterilized tweezers, drained, and put into numbered plastic preservation boxes with lids for storage at -1.00 ℃. The changes of color difference, drip loss, shear force, TBARS and sensory indexes of the beef on the 1st, 3rd, 5th and 7th days were measured. The antioxidant effect of rosemary extract in combination with chilling on beef was investigated by using distilled water-soaked beef (4 ℃) as control 1 and distilled water-soaked beef (-1.00 ℃) as control 2, and the antioxidant concentration of rosemary extract was selected as a suitable antioxidant concentration for beef. The experimental arrangement is shown in Table 1.
1.4 Detection indicators
1.4.1 Determination of freezing point
During the freezing process of beef, when the center temperature of beef drops to a temperature below 0 ℃, there will be a rebound, and stabilized at a certain temperature for a period of time, and then the temperature will continue to drop rapidly until freezing, the freezing point of beef that is the temperature[4] . Determination of freezing point is an important part of ice temperature preservation technology. The method was adopted from Sun Tianli et al[5] with slight modification. Fresh beef (cucumber strips) was cut into rectangles of about 100 g. The probe of the temperature recorder was inserted into the center of the beef, placed in the freezer at -18 ℃ and then taken out after freezing. The temperature recorder was removed and connected to a computer to obtain the curve of the temperature of the center of the beef as a function of time, so as to determine the freezing point temperature of the beef (cucumber strips).
1.4.2 Determination of color difference
The quality of chilled beef can be directly reflected by meat color. The method of Guo Xinying et al[6] was used for the determination of color difference with slight modification. The beef was cut into slices of 2.0 cm thickness along the muscle fiber direction, the surface moisture was absorbed by filter paper, and the slices were placed flat on the table, covered with a transparent plastic wrap, and the L* and a* values were measured by a colorimeter. According to NY/T 2793-2015 "Objective Evaluation Methods of Meat Quality" [7], beef with L* values between 30 and 45 and a* values between 10 and 25 were determined to be fresh.
1.4.3 Determination of drip loss
Drip loss is a very important economic indicator for chilled beef, and the larger the value, the poorer the water retention (water holding capacity) of the beef[8] . Water retention is an important index to evaluate the quality of chilled beef [9-10]. The oxidation and decomposition of muscle proteins during storage will affect the water retention. The water retention was determined by cutting the beef into pieces of 3 cm×1 cm×1 cm, drying the surface water with filter paper and weighing accurately as the mass before dripping. The meat was then covered with a plastic bag and hung by a string at the upper end in a chilled warehouse for 24 h. The meat was then removed, drained of surface water and weighed accurately as the post-drip mass. The difference between the two masses as a percentage of the pre-drip mass is the drip loss.
1.4.4 Determination of shear
Shear force is the degree of sustained resistance of beef to chewing [11] and is an indicator of beef tenderness expressed as hardness value. The method of Chen et al [12] was adopted with slight modification. Firstly, the fat, tendon and fascia on the surface of beef were removed, and the meat was cut into 3 cm×2 cm×1 cm strips, and the shear strength of the meat was measured by a texture meter.
Cutting force. TA-SBA shear blade fixture, TA7/TA-VBJ probe was used to determine the test speed of 1 mm/s, each sample was repeated 3 times, and the average value was taken.
1.4.5 Determination of TBARS values
Determination was carried out according to the second method of spectrophotometric method in GB 5009.181-2016 "Determination of malondialdehyde in foodstuffs, national standard for food safety" [13].
1.4.6 Sensory evaluation
The evaluation of the sensory indexes of beef on the 7th day of storage was based on GB/T 17238-2008 "Fresh and Frozen Split Beef" [14], with reference to the scoring scale developed by Sun Kaixuan et al [15] with slight modification, and the evaluation team consisted of 8 food professionals, and a 10-point scale was used. The sensory scoring criteria of beef are shown in Table 2.
1.5 Data analysis
Each test was repeated three times, and the results were expressed as mean ± SD. The graphs were plotted using Sigmaplot13.0, and the statistical analysis of the data was performed using the t-test for independent samples in comparing the means in SPSS Statistics 20.0 statistical analysis software, and the level of significance of the differences was 0.05. The data were analyzed using the t-test for independent samples in comparing the means in SPSS Statistics 20.0 statistical analysis software.
2 Results and analysis 2.1 Freezing point of beef
The curve of beef center temperature versus time is shown in Figure 1.
As can be seen from Fig. 1, after the beef was put into the freezer, with the extension of time, the center temperature of the beef decreased gradually, when the center temperature of the beef reached -1.13 ℃, it was maintained for 2 min and then slightly rebounded to -1.11 ℃, and the temperature was maintained for the longest time of about 14 min, then the center temperature of the beef began to decrease slowly, and began to decrease rapidly when the temperature was reduced to -1.14 ℃, which indicated that the freezing point temperature of the meat sample was about -1.11 ℃. This indicates that the freezing point temperature of the meat sample is about -1.11 ℃. Therefore, -1.00 ℃ was selected as the temperature of ice temperature preservation in this experiment.
2.2 Study of antioxidant effect of different concentrations of rosemary extracts on beef
2.2.1 Effect of different concentrations of rosemary extract on color difference values of beef
The effects of different concentrations of rosemary extract on L* and a* of beef are shown in Tables 3 and 4.
As shown in Table 3, with the extension of storage time, the L* value of beef in each treatment group basically showed a gradual decline, and the L* value of beef in control 1 declined the fastest (p<0.05). The difference between the L* values of beef in control 1 and control 2 was not significant (p>0.05) in the first 3 days, but it was significantly lower than that of control 2 on the 5th day (p<0.05), and it was already lower than 30 as not fresh meat, which indicated that ice temperature preservation was effective in maintaining the brightness of beef.
The difference between the L* values of beef in the rosemary treatment group at 0.05% and control 2 was not significant; the difference between the L* value of beef in the rosemary treatment group at 0.10% was significant from the 3rd day onwards; and the difference between the L* value and control 2 was not significant. The L* values of beef in the 0.10 % rosemary-treated group were significantly lower than those of control 2 from day 3 onwards (p<0.05); the L* values of beef in the 0.15 % rosemary-treated group were not significantly different from those of the 0.20 % rosemary-treated group (p>0.05), and were significantly higher than those of the other treatment groups (p<0.05).
As shown in Table 4, with the prolongation of storage time, the a* of meat samples of different treatment groups showed a decreasing trend. a* of beef in control 1 group was close to 10 on the 5th day of storage, and decreased to 8.98 on the 7th day. The a* of beef in control 1 group was close to 10 on the 5th day of storage, and then decreased to 8.98 on the 7th day, while the a* of beef in control 2 group was significantly better than that of control 1, except for the 3rd day, the difference was significant (p<0.05), the difference was highly significant (p<0.01) in all other storage periods, which indicated that the oxidation of myoglobin was effectively retarded under the condition of freezing, and it played a good inhibiting effect on the formation of high ferric myoglobin. The results indicated that the oxidation of myoglobin was effectively delayed under ice temperature, and the formation of high iron myoglobin was inhibited. The a* values of beef in the first 3 days in the 0.05% and 0.10% dieffenbach treatment groups were not significantly different from those of the control group (p>0.05) because of the low concentration of dieffenbach and the high content of oxygen in the box at the beginning of the storage period, which resulted in the low antioxidant effect.
The a* of beef increased significantly (p<0.05) when the concentration of rosemary was increased to 0.15 %, and was 17.27 at day 7, which is attributed to the fact that rosemary is considered to be one of the plants with the highest content of antioxidants [16], which is capable of maintaining the bright red color of meat by inhibiting the formation of trivalent iron in myoglobin [17], and it has a potent inhibitory effect on oxidization of a variety of complex lipoid species. The increase in a* of beef was not significant (p>0.05) when the concentration of rosemary was increased to 0.20 %.
2.2.2 Effect of different concentrations of rosemary extract on drip loss in beef
The effect of different concentrations of rosemary extract on drip loss of beef is shown in Figure 2.
As shown in Figure 2, the drip loss of beef in each treatment group gradually increased with the extension of storage time. The dripping loss of beef in control group 1 increased the fastest (p<0.05), because the change of muscle water holding capacity is related to temperature, protein hydrolysis degree, pH value and other factors [11], 4 ℃ can not completely inhibit the growth and reproduction of harmful microorganisms, and their secretion of protease caused muscle protein hydrolysis to reduce the water holding capacity.
The drip loss of beef in control 2 was significantly lower than that in control 1 (p<0.05), because the ice temperature effectively inhibited the growth and reproduction of harmful microorganisms, which had a good effect on the hydrolysis of muscle proteins. The drip loss of beef in the rosemary-treated group was lower than that in the control group from day 3 onwards, especially in the 0.15 % and 0.20 % rosemary-treated groups (p>0.05), and was significantly lower than that in the other treatment groups (p<0.05), due to the obvious antibacterial effect of rosemary extract [18-19], mainly due to the diterpene phenolics being able to effectively change the permeability of bacterial cell membranes [19]. The main reason was that the diterpene phenolic compounds were able to effectively change the permeability of bacterial cell membranes and play an antibacterial effect [20], and its active ingredient rosemarinic acid also had a certain bacterial inhibition, which could effectively slow down the hydrolysis of muscle proteins, and maintain a certain degree of water-holding capacity of muscle.
2.2.3 Effect of different concentrations of rosemary extracts on beef shear force
The effect of different concentrations of rosemary extract on beef shear force is shown in Fig. 3.
As shown in Figure 3, the hardness of beef with different concentrations of rosemary increased and then decreased with the extension of storage time, because the texture of muscle is related to the state of water, fat and protein, and the gel network structure of protein is able to lock the water and fat. The texture of muscle changes with hydrolysis of proteins and oxidation of proteins and fats [21]. The shear of beef in control group 2 was significantly smaller than that in control group 1 (p<0.05), indicating that ice temperature preservation was better than 4 ℃ preservation.
As the concentration of rosemary increased, the antioxidant effect was gradually strengthened, which was very effective in maintaining the texture of beef, especially the shear force was significantly reduced in the 0.15 % and 0.20 % rosemary treatment groups (p<0.05), which was attributed to the fact that the plant extract could improve the texture of meat by inhibiting the oxidation of fat and protein [22]; in addition, the acidic components of rosemary extract could also maintain the pH value of beef to a certain extent [23], which increased the expansion of myosin and improved the texture of beef. In addition, the acidic component of rosemary extract can maintain the pH value of beef to a certain extent [23], and improve the texture of beef by increasing the expansion of muscle proteins.
2.2.4 Effect of different concentrations of rosemary extract on TBARS value of beef
The effect of different concentrations of rosemary extract on TBARS values of beef is shown in Figure 4.
2.2.5 Effects of different concentrations of rosemary extract on sensory indexes of beef
The effects of different concentrations of rosemary extract on the sensory parameters of beef are shown in Table 5.
As shown in Table 5, the sensory scores of control 1 beef were significantly lower than those of other groups (p<0.05), indicating that the beef was corrupted due to the oxidation of lipids and proteins as well as microbial growth and reproduction on the 7th day of storage at 4 ℃; in addition, the unstable decomposition of some fat oxidation products would produce volatile components and affect the odor of the beef [23]; and at the same time, the effect of iced preservation was good in delaying the deterioration of the sensory characteristics of beef. At the same time, it also shows that ice temperature preservation has a good effect on delaying the deterioration of sensory characteristics of beef.
In terms of meat color and odor, the rosemary-treated group was significantly better than control 2, indicating that rosemary extract was effective in inhibiting the oxidation of myoglobin and maintaining the color and odor of the meat, especially in the 0.15 % rosemary-treated group, which had the best color (p<0.05), while the color of the beef was significantly deteriorated in the rosemary-treated group at the concentration of 0.20 % (p<0.05), because the rosemary solution was pale yellow in color and the high concentration would affect the color of the meat. The color of beef was significantly (p<0.05) worse when the rosemary concentration reached 0.20%, because the rosemary solution was light yellow and the high concentration would affect the meat color; the odor of beef in the 0.15% and 0.20% rosemary treatment groups did not differ significantly (p>0.05) and was better than that in the other treatment groups, because the rosemary extracts had a certain aromatic odor.
In terms of viscosity, there was no significant difference between the 0.05 and 0.10 % rosemary treatment groups and control 2 (p>0.05), while the 0.15 and 0.20 % rosemary treatment groups showed no significant difference in scores (p>0.05) and were significantly higher than the other treatment groups (p<0.05). In terms of juice volume, the rosemary-treated group was significantly better than control 2 (p<0.05) due to the antioxidant effect of rosemary extract on lipids and proteins, which effectively improved the water retention of beef; the increase in the scores was no longer significant when the concentration of rosemary was greater than 0.10 % (p>0.05).
3 Conclusion
Modern people pursue health and advocate natural food. The safety of synthetic antioxidants is of great concern, while natural antioxidants are characterized by high antioxidant performance, safety and health. Rosemary extract has been recognized by the US Food and Drug Administration (FDA) as a "Public Safety Food". Rosemary extract is a safe and efficient radical scavenger, which can effectively prevent the oxidation of lipids in beef, preventing the deterioration of meat color caused by oxidation, and its antioxidant effect is two to four times higher than that of the synthetic antioxidants tert-butyl hydroxyanisole and 2,6-di(tert-butylhydroxyanisole) and one to two times higher than that of tert-butylhydroquinone.
In this experiment, the antioxidant treatment of beef was carried out by using different concentrations of rosemary extract in combination with ice temperature preservation. The concentration of rosemary extract was selected as 0.15 % for beef antioxidant treatment through the determination of color difference (L* and a* values), drip loss, shear force and TBARS value of the beef during the storage period, as well as the evaluation of sensory indicators of the beef on the 7th day of storage. The L* value was 36.49, the a* value was 17.27, the drip loss was 0.62%, the shear force was 4 429 g, and the TBARS value was 0.18 mg/100 g. Therefore, the antioxidant effect of rosemary extract with chilling on chilled beef is very good, and it has a certain effect on improving the quality of beef.
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