In order to reduce the initial bacteria count on the surface of broilers after slaughter and extend the shelf life of chilled chickens, the effects of ozone water treatment (0Z), ultrasonic combined with sodium hypochlorite treatment (SH-US) and ozone combined with ultrasonic combined with low concentration sodium hypochlorite combined (SH-US-0Z) on the bacteria-reducing effect on the surface of chicken legs and the fresh-keeping effect during pallet packaging and storage were investigated. The results showed that the initial microbial number on the surface of chilled chicken legs could be significantly reduced by all the three treatments (P<0.05), and SH-US-0Z combined treatment had the best bacteria-reducing effect. The treatment reduced the total number of initial colonies from 5.72(Ig(CFU/g)) to 4.25(Ig(CFUIg)) with a bacteriogenic reduction rate of 96.6%, which effectively delayed the growth rate of microorganisms during storage, improved the surface brightness value and sensory quality of chicken thigh during storage, and reduced the storage loss and volatile base nitrogen content. Although the combined treatment group increased the lipid oxidation degree and decreased the surface redness value, it did not cause sensory deterioration. Therefore, SH-US-0Z composite treatment has significant bacteria-reducing and fresh-keeping effects on the basis of reducing the use of sodium hypochlorite, effectively maintaining the quality of chicken legs during storage, and extending the shelf life to more than 5 days.
Chilled chicken refers to the fresh chicken that has passed the quarantine inspection and immediately lowered its carcass temperature to 8 ° C after slaughter, to 4 ° C within 12 hours, and to be divided, processed, circulated, stored and distributed at 0~4 ° C. Chilled chicken is safe and hygienic, and has great advantages in taste, flavor and nutritional value. However, chilled chicken is very easy to be contaminated by microorganisms during processing, transportation and storage, resulting in a short shelf life, which restricts the circulation and sale of chilled chicken. Therefore, how to extend the shelf life of chilled chicken has always been the hot spot of industry exploration and meat bacteria reduction technology research. At present, the broiler industry mainly disinfecting chicken carcasses after slaughter by continuously adding sodium hypochlorite to the precooling tank to reduce the initial microbial number on the surface. Sodium hypochlorite is an oxidizing fungicide, which is widely used in food industry because of its wide bactericidal spectrum and low price. However, when sodium hypochlorite is used in large quantities, it can form toxic chlorine byproducts (such as trihalomethanes, chloramines and halogenated ketones). At the same time, the study also found that sodium hypochlorite has a limited effect on the disinfection of meat surfaces and processing contact surfaces. Therefore, with the enhancement of consumer health awareness, the broiler slaughtering industry is in urgent need of green and effective bacterial-reducing technology to replace the traditional chemical bacterial-reducing technology.
The hair follicles on the skin of broilers close for a short time after they are slaughtered and feathered. The hair follicle is easy to retain a large number of microorganisms, difficult to clean, at the same time, the closure of the hair follicle mouth makes it difficult to enter the bacteria-reducing agent such as sodium hypochlorite and can not play a bacteria-reducing effect, further aggravating the perishable characteristics of chicken skin.
Our team’s previous study found that ultrasonic treatment can open the hair follicle again and help sodium hypochlorite to play a role in reducing bacteria in the hair follicle. Ultrasonic sterilization is a common sterilization method in food industry. The shear force and free radicals generated by ultrasonic through cavitation destroy bacterial structure, inhibit microbial growth and prolong shelf life. Duckhouse et al. treated the E. coli bacteria solution with ultrasound combined with sodium hypochlorite, and found that the treatment could effectively reduce the number of E. coli colonies. Sun Yongcai et al. used 30 mg/L sodium hypochlorite combined with ultrasound to effectively reduce the total number of colonies on the surface of chicken breast. At the same time, ultrasound can also open the hair follicle again through the cavitation effect, so that sodium hypochlorite solution can enter the hair follicle, and better play the antibacterial effect.
As a non-thermal bactericidal technology, ozone has the advantages of fast decomposition speed, obvious bactericidal effect, no residue after treatment and does not affect the senses, and has been widely used in the preservation of fruit and vegetable products and aquatic products. Liu Yini et al. treated fresh-cut cabbage with 1.4mg /L ozone water, and found that ozone water treatment could significantly reduce the number of microorganisms in fresh-cut cabbage. At present, the technology has gradually begun to be used in meat preservation. Studies have shown that ozone treatment has a significant bacterial-reducing effect, which can effectively reduce the number and growth rate of microorganisms in meat and its products. Gimenez et al. treated beef with 280 mg/m3 gaseous ozone, and found that ozone treatment could effectively prolong the storage time of vacuum-packed beef, but long-term exposure to ozone (>10 min) would have a negative impact on beef redness (a*) and aggravate oxidative rancidity, which may be due to long-term exposure to ozone. This causes the oxygenated myoglobin in beef to be oxidized to high ferrimyoglobin, resulting in a* reduction. However, the surface structure of chicken skin is complex, so the application of ozone in the surface bacteriological reduction of broilers after slaughter is less. Based on the bacteria-reducing principle of palisade and our previous research on the bacteria-reducing effect of ultrasonic coordination with sodium hypochlorite, this study intends to combine ozone bacteria-reducing technology with ultrasonic coordination with sodium hypochlorite bacteria-reducing technology, aiming to reduce the amount of sodium hypochlorite used, and explore the bacteria-reducing effect of its synergistic effect on the surface of post-slaughter chicken leg products and its influence on the quality and microbial growth during storage. Provide technical support for extending shelf life of chilled chicken products.
method
Experimental design
36 white feather broilers were randomly collected from the production line, and 72 of their whole legs were randomly divided into 4 groups. The following treatments were performed: control group (water soaked for 5 min), smelly water treatment group (4.8mg ozone water soaked for 5 min), ultrasound combined with low concentration sodium hypochlorite treatment (SH-US) group (100 mg sodium hypochlorite was added to clean water at one time and ultrasound treated 25 min), ozone water combined with ultrasound in coordination with low concentration sodium hypochlorite treatment (SH-US-0Z) group (100 mg sodium hypochlorite was added to clean water first and ultrasonic treatment was performed for 25 min, and then 4.8mg ozone water was soaked for 5 min). After adding 100 mg/L sodium hypochlorite, the mass concentration of sodium hypochlorite decreased rapidly and remained at 60-65 mg. Each treatment group consisted of 18 chicken legs. After the treatment, all the chicken legs were drained, packaged in trays, and stored at (2 × 2)℃ for 0, 3, and 5 days. At the corresponding time point, 6 chicken legs were randomly selected from each group for microbial, physicochemical index determination and sensory evaluation. Two chicken legs were taken from each index at each time point for measurement. The experiment was repeated independently for 3 times.
Determination of pH value of chicken leg
The pH value of chicken legs was measured by a portable pH meter at various time points during storage. pH meters are calibrated with standard buffers of pH 7.00 and 4.00 before use. 6 points were randomly selected to determine the pH value of the chicken leg, and the final result was averaged.
Determination of surface flesh color
At different storage time points, after opening the package, the brightness value (L*), a* and yellowness value (b*) of the chicken skin surface were measured with a color difference meter, and corrected before measurement. 6 to 8 parts of each chilled chicken leg were randomly selected for measurement, and the results were averaged.
Determination of loss rate of storage juice
Refer to the method of Wang Shouyin et al. The chicken legs are treated, drained and palletized and refrigerated. The mass before pallet packaging is denoted as m1(g); At each storage time point, unpack and drain the surface juice with absorbent paper, then weigh the quality again and record as m2(g). The loss rate of storage juice is calculated as follows.
Storage juice loss rate /%=(m1-m2)/m2×100
Determination of thiobarbiturate reactants (TBARS)
TBARS value is commonly used to judge the degree of fat oxidation, referring to Siu and other determination methods and slightly improved. At each storage time point, 2g chicken skin (subcutaneous fat removed) and 2g chicken were randomly clipped from the surface of chicken legs into 100mI test tube, adding 20 mL distilled water into the test tube, homogenizing for 1 min(homogenizing for 30s interval after 30s interval and then homogenizing for 30s). Thoroughly mix the homogenized liquid with 20 mL 10 g/100 mL trichloroacetic acid solution, filter with filter paper, and set the filtrate aside. 4 mL filtrate was absorbed into the centrifuge tube, and 1 mL 60 mmoL thiobarbituric acid solution was added into the centrifuge tube and mixed well. Then the centrifuge tube was heated in a water bath at 80 ℃ for 90 min, and then removed and cooled to room temperature. 250µL of the cooled solution was transferred to the 96-well plate and the test solution OD532nm was measured at 532nm wavelength. The TBARS value was calculated by substituting OD532nm into the standard curve equation of 1,1,3, 3-tetraethoxypropane. The result was calculated by the mass of malondialdehyde per kilogram of sample, in mg/kg.
Determination of total volatile basic nitrogen (TVB-N) content
Take 5 g chicken skin without obvious fat attachment and 5 g meat samples on the surface of the chilled chicken legs, chop them and put them into a 100mL conical bottle, add 75mL distilled water, and stir well with a glass stick. After the mixture was soaked for 30 min, the automatic Kjeldahl nitrogen analyzer was used to determine the volatile base nitrogen in food according to the “Determination of Volatile base nitrogen in Food under the National Standard of Food Safety”.
Microbial count culture
Refer to Yang Xiaoyin et al. ‘s method and make some changes. Open the package in a sterile environment, randomly take 10 g chicken skin samples from the top surface of the chilled chicken leg, place them in a sterile beating bag, then add 90 mL 8.5 g sodium chloride solution (containing 0.01% peptone), beat and mix them with a beater at room temperature for 2 min. Absorb 1 mL of mixed bacterial solution for a series of 10-fold gradient dilution, and put diluents with appropriate gradient into different media for plate culture, with 3 parallel groups for each gradient.
Result
It was found that 0Z, SH-US and SH-US-0Z3 bacteria-reducing methods effectively reduced the number of microorganisms on the surface of chilled chicken legs, and had good bacteriostatic effects on enterobacter, Lactobacillus, pseudomonas, thermocyclicide and psychrophilic bacteria. Compared with 0Z and SH-US treatment groups, SH-US-0Z treatment can further reduce the initial microbial quantity on the surface of chilled chicken legs, delay the microbial growth rate during storage, and reduce the TVB-N content and storage juice loss. Although the combined treatment increased lipid oxidation and decreased surface a*, it did not adversely affect the sensory quality of chilled chicken legs. Therefore, the combination of ozone combined with ultrasound and sodium hypochlorite can effectively reduce the initial bacterial count on the surface, delay the quality deterioration during storage, and extend the shelf life to more than 5 days, which can be used as an effective bacterial reduction method in the production of chilled chicken. This study provides an effective technology for reducing bacteria on the surface of broilers after slaughter and extending the shelf life of chilled chickens while reducing the consumption of sodium hypochlorite.
Extract from China Meat Food Comprehensive Research Center 2023, Vol. 37, No. 12 Effect of ozone combined with ultrasound combined with low concentration sodium hypochlorite composite treatment on chilled chicken legs.