Method for degrading residual heavy metals in livestock and poultry byproducts

Abstract

The invention belongs to the technical field of food processing, and discloses a method for degrading residual heavy metals in livestock and poultry byproducts. The method comprises the following steps: soaking the livestock and poultry by-products in light salt brine, transferring the soaked livestock and poultry by-products into pickle liquid with the pH value of 3.5-3.6, carrying out staged variable-temperature soaking, and then carrying out two-stage spin-drying treatment. According to the method, the degradation effect on residual heavy metals in the livestock and poultry byproducts is remarkably improved, the total degradation rate can reach 85%-100%, meanwhile, the quality of the livestock and poultry byproducts is kept to the maximum extent, the pickle processing waste liquid is recycled, and the cost is saved.

Description

Technical Field

[0001] The present invention relates to the technical field of food processing, and in particular to a method for degrading residual heavy metals in livestock and poultry by-products. Background Art

[0002] With the rapid development of animal husbandry, the production of livestock and poultry by-products has increased annually. These by-products have high edible and developmental value, making them high-quality ingredients for preparing pre-prepared dishes. For example, tripe can be prepared as a hot pot ingredient, and chicken feet can be used in marinades and pickled chicken feet. However, these by-products are prone to residues of the heavy metals lead, arsenic, and cadmium. These residues may even exceed the requirements of GB 2762-2022, "National Food Safety Standard for Limits of Contaminants in Food," which stipulate that lead levels should be ≤ 0.5 mg / kg, arsenic levels should be ≤ 0.2 mg / kg, and cadmium levels should be ≤ 0.2 mg / kg. According to the applicant's test results, some livestock and poultry by-products contain significant levels of heavy metals, with lead levels reaching 0.8 mg / kg and arsenic and cadmium levels reaching 0.4 mg / kg. Long-term consumption of livestock and poultry by-products containing excessive levels of heavy metals can lead to accumulation of these metals in the human body through the food chain, potentially causing chronic poisoning, damage to the nervous and digestive systems, and even other health problems. Minimizing heavy metal residues is crucial for ensuring food safety.

[0003] Heavy metals in livestock and poultry byproducts can be degraded through physical, chemical, or biological methods. For example, these methods involve separating liquid or solid residues containing heavy metals from livestock and poultry byproducts through physical means such as centrifugation or drying, converting heavy metal ions into less toxic forms or separable complexes using hydrochloric acid or oxidants, and utilizing microorganisms such as denitrifying Thiobacillus to metabolize and transform heavy metals. However, these existing methods suffer from high costs, suboptimal degradation effects or efficiency, and the tendency to degrade the quality of livestock and poultry byproducts, potentially leading to re-contamination. Finding natural, safe, low-cost, efficient, convenient, and practical methods for degrading heavy metals will help promote the sustainable development of livestock and poultry byproduct resources.

[0004] In view of this, the present invention is proposed. Summary of the Invention

[0005] The present invention aims to provide a method for degrading residual heavy metals in livestock and poultry by-products. The method can significantly improve the degradation effect of residual heavy metals in livestock and poultry by-products, and the degradation rate can reach 85%-100%.

[0006] In order to achieve the above objects, the technical solution adopted by the present invention is: A method for degrading residual heavy metals in livestock and poultry by-products comprises: soaking the livestock and poultry by-products in light salt water, transferring the livestock and poultry by-products to a kimchi solution with a pH value of 3.5-3.6 for staged temperature-changing soaking, and then performing a two-stage drying process.

[0007] Preferably, the concentration of the light salt water is 0.8-1%, and the amount used is 2-3 times the mass of livestock and poultry by-products.

[0008] Preferably, the livestock and poultry by-products are soaked in the light salt water at a temperature of 18-22° C. for 6-8 hours.

[0009] Preferably, the staged temperature-variable soaking includes soaking at a lower temperature first and then soaking at a higher temperature. Preferably, the lower temperature soaking is at a temperature of 2-4°C for 40-48 hours, and the higher temperature soaking is at a temperature of 15-20°C for 20-24 hours.

[0010] Preferably, the higher temperature soaking further includes lower temperature soaking, and the lower temperature soaking temperature is 2-4°C and the time is 20-24 hours.

[0011] Preferably, the mass ratio of the livestock and poultry by-products to the kimchi liquid is 1:2-2.5.

[0012] Preferably, the two-stage drying process is first drying at a low speed and then drying at a higher speed.

[0013] Preferably, the low-speed spin drying has a rotation speed of 600-650 rmp and a time of 2-3 min.

[0014] Preferably, the rotation speed of the relatively high-speed spin drying is 950-1000 rmp, and the time is 2-3 min.

[0015] Compared with the prior art, the present invention has the following beneficial effects: The present invention significantly improves the degradation effect of heavy metals in livestock and poultry by-products through soaking in light salt water, soaking in kimchi liquid at varying temperatures in stages, and two-stage drying treatment. The total degradation rate can reach 85%-100%, and the heavy metal residue in the product is significantly lower than the national limit standard.

[0016] The present invention controls the soaking temperature of livestock and poultry by-products in light salt water to 18-22°C, and the soaking temperature in pickle liquid to 2-4°C and 15-20°C, and combines a two-stage drying process to effectively remove residual heavy metals while maintaining the quality of livestock and poultry by-products to the greatest extent.

[0017] The present invention is the first to use waste kimchi liquid for the treatment of livestock and poultry by-products. By utilizing the low pH of the kimchi liquid and the adsorption and conversion effects of the microorganisms and high salt concentrations contained in the kimchi liquid on heavy metals, the heavy metals remaining in the livestock and poultry by-products are effectively removed in a natural way, so that the waste liquid can be reused.

[0018] The use of the waste kimchi liquid in the present invention improves the efficiency of kimchi production and reduces the cost of processing livestock and poultry by-products. Compared with the degradation method of adding lactic acid bacteria and edible acid, the processing cost can be saved by about 3 million yuan per year based on the processing of 10,000 tons of livestock and poultry by-products. DETAILED DESCRIPTION

[0019] To make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are described clearly and completely below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer are used. Where the manufacturer of the reagents or instruments is not specified, all are conventional products that can be purchased commercially.

[0020] An embodiment of the present invention provides a method for degrading heavy metals in livestock and poultry by-products, comprising: soaking the livestock and poultry by-products in light salt water, transferring them to a kimchi solution with a pH value of 3.5-3.6 for staged temperature-changing soaking, and then performing a two-stage drying process.

[0021] After industrial kimchi production, kimchi liquid is typically treated as waste and discharged after environmentally friendly filtration. This waste kimchi liquid contains a variety of organic acids, such as lactic acid, tartaric acid, acetic acid, oxalic acid, and ascorbic acid, produced by fermentation, resulting in a low pH. It also contains a variety of microorganisms, such as Lactobacillus plantarum and Lactobacillus acidophilus, as well as high concentrations of salt. In long-term experimental research, the applicant discovered that soaking livestock and poultry by-products in kimchi liquid, combined with its low pH, microorganisms, and high salt concentrations, can synergistically adsorb or convert heavy metals, effectively degrading them. Furthermore, it was found that soaking at higher temperatures, such as 25-30°C, can effectively degrade heavy metals within livestock and poultry by-products, but it can also easily breed harmful microorganisms, affecting their quality. Excessively low soaking temperatures reduce degradation efficiency. Lowering the soaking temperature to 2-4°C only degrades heavy metals on the surface of livestock and poultry by-products, but this temperature is within the cold preservation temperature for meat products and effectively maintains their quality.

[0022] Therefore, in an embodiment of the present invention, the livestock and poultry by-products are first soaked in light salt water to promote the subsequent adsorption and conversion of heavy metals by the kimchi liquid; then the kimchi liquid is used to soak the livestock and poultry by-products in a staged temperature-changing manner to fully exert the adsorption and conversion effects of heavy metals inside and on the surface of the livestock and poultry by-products; finally, a two-stage drying process is performed to fully remove the liquid adsorbed with heavy metals remaining in the livestock and poultry by-products, thereby effectively degrading the heavy metals inside and on the surface of the livestock and poultry by-products while maintaining the quality of the livestock and poultry by-products to the greatest extent, achieving a heavy metal degradation rate of 85%-100%.

[0023] The pickle liquid used in the embodiments of the present invention is obtained from waste pickle liquid, which has been clarified and filtered to remove impurities such as small pickled vegetables and precipitates. This waste pickle liquid is the liquid discharged from large-scale Sichuan pickle processing, and its pH is typically between 3.4 and 4.0. Sichuan pickle processing utilizes traditional techniques and recipes. For example, the recipe includes: 1000 kg of fresh vegetables (such as cabbage, radish, chili peppers, and ginger), 24-29 kg of salt, 4-5 kg of sugar (brown sugar, rock sugar, or white sugar), 150-200 g of Sichuan-style compound spices (star anise, cinnamon, bay leaves, Sichuan peppercorns, and dried chilies), 2-2.5 L of baijiu (Chinese liquor), and 100-150 g of a pickle-specific bacterial inoculant (such as Lactobacillus plantarum and Lactobacillus brevis). The processing flow includes raw material pretreatment, brine preparation, inoculation and filling, controlled fermentation, seasoning and post-fermentation, sterilization and packaging, and waste liquid disposal.

[0024] The pH value of kimchi liquid is the key to determining the degradation rate of heavy metals. Only when the pH value is 3.5-3.6 can the heavy metal degradation rate reach 85%-100%. However, of the waste kimchi liquid discharged from large-scale processing of Sichuan kimchi, usually only about 60% has a pH value of 3.5-3.6, and the remaining kimchi liquid has a slightly higher pH and a slightly lower pH. For kimchi liquid with a pH value higher than 3.6, citric acid is used to lower its pH value; for kimchi liquid with a pH value lower than 3.5, food-grade sodium bicarbonate is used to increase its pH value, ensuring that the pH value of the kimchi liquid is between 3.5-3.6, which can also achieve the effect of the present invention.

[0025] The concentration of the salt water should be between 0.8% and 1%. Too low a concentration will reduce the pickle liquid's ability to adsorb and convert heavy metals. Too high a concentration will affect the sensory quality of livestock and poultry by-products. The amount of pickle liquid used should be 2-3 times the mass of the livestock and poultry by-products. The livestock and poultry by-products should be soaked in the salt water at a temperature of 18-22°C for 6-8 hours. Too short a soaking time will also affect the efficiency of heavy metal removal, while too long a soaking time will negatively impact the sensory quality of the livestock and poultry by-products. It is understood that soaking in the salt water also includes rinsing with clean water and draining.

[0026] Staged temperature-variable soaking involves soaking at a lower temperature followed by a higher temperature soak. The lower temperature soak is performed at 2-4°C for 40-48 hours, while the higher temperature soak is performed at 15-20°C for 20-24 hours. For livestock and poultry by-products with excessive heavy metal residues, such as lead levels exceeding 0.7 mg / kg or arsenic / cadmium levels exceeding 0.3 mg / kg, the higher temperature soak can be followed by a further lower temperature soak at 2-4°C for 20-24 hours to further enhance the degradation of residual heavy metals. Stirring can be used during the soaking process to facilitate the adsorption and conversion of heavy metals, and post-soaking rinsing with running water is also recommended. Preparing a higher temperature soak followed by a lower temperature soak can compromise the degradation of heavy metals.

[0027] The two-stage spin drying process involves first a low-speed spin followed by a higher-speed spin to completely remove liquids containing heavy metals. The low-speed spin is performed at 600-650 rpm for 2-3 minutes, while the higher-speed spin is performed at 950-1000 rpm for 2-3 minutes. The low-speed spin is followed by a rinse with running water.

[0028] In order to make the present invention clearer, examples for implementing the present invention and corresponding comparative examples will be disclosed below to demonstrate the relevant technical effects of the present invention.

[0029] The waste pickle liquid used in the following examples is the pickle liquid discharged from the large-scale processing of Sichuan pickles; the tripe and chicken feet are provided by the production line of an enterprise of the applicant of the present invention.

[0030] The heavy metal indicators and detection methods involved in the examples are as follows: Lead: GB 5009.12-2023 "National Food Safety Standard - Determination of Lead in Foods" Method 1: Graphite Furnace Atomic Absorption Spectrometry, with microwave digestion as the sample pretreatment method; Cadmium: GB 5009.15-2023 "National Food Safety Standard - Determination of Cadmium in Foods" Method 1: Graphite Furnace Atomic Absorption Spectrometry, with microwave digestion as the sample pretreatment method; Arsenic (total and inorganic arsenic): GB 5009.11-2024 "National Food Safety Standard - Determination of Total and Inorganic Arsenic in Foods" Method 1, Hydride Generation Atomic Fluorescence Spectrometry, with microwave digestion as the sample preparation method; Method for determining the pH value of kimchi liquid: pH meter glass electrode rapid determination method.

[0031] Example 1 The method of the present invention is used to degrade heavy metals in tripe, and the residual amounts of heavy metals in the tripe raw materials are as follows: lead 0.8 mg / kg, arsenic 0.1 mg / kg, and cadmium is not detected.

[0032] Experimental Group 1: The waste pickle liquid was clarified and filtered to obtain a pH value of 3.8, and food-grade citric acid was added to adjust the pH value to 3.5 to obtain pickle liquid; The tripe was placed in 1% light salt water with an amount three times the mass of the tripe, soaked at 20°C for 6 h, rinsed with clean water and drained, placed in kimchi liquid 2.2 times the mass of the tripe, soaked at 2°C for 48 h, stirred three times during the period, then heated to 20°C, kept warm for 20 h, stirred once during the period, and then soaked at 4°C again for 20 h. After soaking, it was washed with running water, dried at 600 rpm for 2 min, washed again with running water, and dried at 950 rpm for 3 min to obtain the treated tripe.

[0033] Experimental group 2: The treatment method was the same as that of experimental group 1, except that the third stage of soaking in kimchi liquid (4°C) was omitted.

[0034] On the basis of the above experimental group 2, the following control group was set up: Control group 1: no light salt water immersion; Control group 2: saline concentration was 0.4%; Control group 3: saline concentration was 1.5%; Control group 4: The soaking temperature of kimchi liquid was 20℃; Control group 5: The soaking order of the first stage (2 ℃) and the second stage (20 ℃) during the kimchi liquid soaking process was exchanged; Control group 6: The soaking temperature of the kimchi liquid was 4℃.

[0035] The processed tripes obtained from the experimental and control groups were tested for heavy metals and the processing costs were calculated. The processing costs included the consumption of organic acids and lactic acid bacteria, the electricity cost for drying, etc. The results are shown in Table 1.

[0036] Table 1 Degradation effects of heavy metals in tripe by different treatments .

[0037] Example 2 The method of the present invention is used to degrade heavy metals in chicken feet. The residual amounts of heavy metals in the raw materials are: 0.15 mg / kg of lead, 0.1 mg / kg of cadmium, and 0.05 mg / kg of arsenic.

[0038] Experimental group: The pH value of the waste pickle liquid was measured to be 3.4 after clarification and filtration, so the pH was further adjusted to 3.6 using food-grade sodium bicarbonate to obtain pickle liquid; Chicken feet were soaked in 0.9% light salt water (2.5 times their weight) at 18°C for 8 hours. Rinse with clean water, drain, and soak in kimchi solution (2 times their weight) at 4°C for 40 hours, stirring three times. The mixture was then heated to 18°C and kept warm for 24 hours, stirring once. After soaking, the chicken feet were rinsed with running water and spin-dried at 600 rpm for 2 minutes. Rinse again with running water and spin-dried at 9500 rpm for 3 minutes to obtain the processed chicken feet.

[0039] On the basis of the above experimental groups, the following control groups were set up: Control group 1: the order of the two-stage drying treatment during the exchange drying process; Control group 2: drying treatment was omitted; Control group 3: only the first drying treatment was performed; Control group 4: The use of food-grade sodium bicarbonate was omitted, and the pH value of the kimchi solution was 3.4; Control group 5: kimchi liquid with a pH of 3.9 after clarification and filtration; Control group 6: The kimchi liquid was replaced with an organic acid solution. The organic acid solution was prepared by adding 1 / 3 each of lactic acid, acetic acid, and oxalic acid, and 1 / 4 each of Leuconostoc, Lactobacillus, Pediococcus, and Lactococcus. The pH of the solution was 3.6.

[0040] The treated chicken feet from the experimental and control groups were tested for heavy metals and the treatment cost was calculated. The treatment cost included the consumption of organic acids and lactic acid bacteria, as well as electricity costs for drying. The results are shown in Table 2.

[0041] Table 2 Degradation effects of heavy metals in chicken feet by different treatments .

[0042] The embodiments described above are some embodiments of the present invention, rather than all embodiments. The detailed description of the embodiments of the present invention is not intended to limit the scope of the invention as claimed, but rather merely represents selected embodiments of the present invention. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without creative effort are also within the scope of protection of the present invention.

Claims

1. A method for degrading residual heavy metals in livestock and poultry by-products, characterized in that: The method comprises: soaking livestock and poultry by-products in light salt water, transferring the mixture into a kimchi liquid with a pH value of 3.5-3.6 for staged temperature-changing soaking, and then performing a two-stage drying process.

2. The method according to claim 1, wherein The concentration of the light salt water is 0.8-1%, and the dosage is 2-3 times the mass of livestock and poultry by-products.

3. The preparation method according to claim 1, wherein The temperature of livestock and poultry by-products soaked in light salt water is 18-22 ℃ and the time is 6-8 hours.

4. The method according to claim 1, wherein The staged temperature-changing soaking includes soaking at a lower temperature first and then soaking at a higher temperature.

5. The method according to claim 4, wherein The lower temperature soaking is performed at a temperature of 2-4°C for 40-48 hours, while the higher temperature soaking is performed at a temperature of 15-20°C for 20-24 hours.

6. The method according to claim 4, wherein The higher temperature soaking further includes lower temperature soaking, wherein the lower temperature soaking temperature is 2-4°C and the time is 20-24 hours.

7. The method according to claim 1, wherein The mass ratio of the livestock and poultry by-products to the kimchi liquid is 1:2-2.

5.

8. The method according to claim 1, wherein The two-stage drying process is first drying at a low speed and then drying at a higher speed.

9. The method according to claim 8, wherein The low-speed drying has a rotation speed of 600-650 rmp and a time of 2-3 minutes.

10. The method according to claim 8, wherein The higher speed spin drying has a rotation speed of 950-1000 rpm and a time of 2-3 minutes.