Liquid egg continuous microwave pasteurization method based on spiral resonant cavity and quality regulation and control system

Abstract

The invention discloses a liquid egg continuous microwave pasteurization method based on a spiral resonant cavity and a quality regulation and control system. The system comprises a microwave cavity, a spiral tube, a four-magnetron array and a temperature control unit. The high dielectric loss characteristic of whole egg liquid and the secondary flow effect of a spiral pipe are utilized, microwaves penetrate through, reflect and absorb liquid eggs to achieve the rapid heating and heat preservation functions, the basic physical and chemical functions are guaranteed, meanwhile, germs are reduced, and the system adopts a Log-Logistic model to accurately predict and compare the inactivation behaviors of microorganisms under specific treatment conditions. The method is suitable for the field of industrial liquid egg product production.

Description

Technical Field

[0001] This invention relates to the field of liquid egg product processing technology, specifically to a method and dedicated system for pasteurizing liquid eggs such as whole egg liquid, egg white, and egg yolk using continuous microwave heating with a spiral resonant cavity. It is particularly suitable for efficient sterilization and quality maintenance of viscous, heat-sensitive fluid foods. Background Technology

[0002] Whole egg liquid, egg white, and egg yolk are liquid egg products made from fresh eggs through crushing and homogenization. They are widely used in the food industry, including baking and condiments. Liquid eggs have a pH of 6-7 and are rich in high-quality protein, making them an excellent culture medium for foodborne pathogens such as Salmonella and Escherichia coli. Salmonella is the second most common bacterial pathogen after Campylobacter; therefore, pasteurization is essential to ensure microbial safety.

[0003] Pasteurization is a relatively mild heat treatment method used to kill major pathogens and inactivate nutrient bacteria and enzymes in food, making it safe for consumption. As the primary sterilization method in liquid egg processing, pasteurization requires minimal steps to eliminate pathogens and ensure the safety of whole egg products. In the 1990s, many countries enacted a series of strict pasteurization standards for liquid egg products; for example, the US standard was 60°C for 3.5 min, and the UK standard was 64.4°C for 2.5 min. Commonly used sterilization conditions for whole egg liquid are 58–65.5°C (2.5–5.0 min), for egg white liquid 55–57.2°C (1.0–8.0 min), and for egg yolk liquid 58–63°C (2.5–4.0 min). Traditional pasteurization uses plate heat exchangers for conduction heating, which has several drawbacks, including uneven temperature distribution (to ensure that the center of the pipeline reaches the sterilization temperature, the material in the pipe wall area is overheated, resulting in heat redundancy), severe quality deterioration (prolonged high-temperature treatment causes denaturation of heat-sensitive proteins, loss of foaming / emulsification function, increased viscosity, and deterioration of flavor), difficulty in cleaning equipment due to coking (high temperature on the pipe wall exacerbates protein coking, increasing cleaning difficulty and energy consumption), and low thermal efficiency (relying on steam / hot water medium, with a long energy transfer path and slow response).

[0004] Existing novel sterilization technologies (high-voltage pulsed electric field, ozone, UV-C, ultrasound, etc.) suffer from high equipment costs, limited penetration depth, and potential generation of harmful byproducts, making industrial application difficult. While microwave heating offers the advantage of volumetric heating, current research has largely focused on low-viscosity fluids such as milk and juice. Research on continuous microwave sterilization systems for high-viscosity, heat-sensitive materials such as liquid eggs is insufficient, and systematic solutions for process parameter optimization and quality control are lacking. Summary of the Invention

[0005] This invention addresses the shortcomings of existing technologies by researching a continuous microwave pasteurization method and quality control system for liquid eggs using a spiral resonant cavity. This achieves rapid and uniform heating (by utilizing the dielectric properties of whole egg liquid and the flow field characteristics of the spiral tube to shorten heating time), efficient sterilization (reducing E. coli by 5 log CFU / mL), improved quality (compared to untreated samples, foaming ability is increased by 5%, and emulsification ability by 0.1%), and no risk of coking (the tube wall temperature is lower than the material center, avoiding protein thermal aggregation).

[0006] This invention is achieved through the following technical solution: In a first aspect, the present invention provides a continuous microwave pasteurization system for liquid eggs with a helical resonant cavity, comprising: 1. A rectangular microwave resonant cavity (0.4 m × 0.4 m × 0.4 m) with cavity walls that are perfect electrical conductors (PEC) boundaries; 2. Spiral conveying pipeline: inner diameter 10 mm, outer diameter 15 mm, with a 3.5-turn spiral structure inside the cavity, pitch circle diameter (PCD) 120 mm, pitch 30 mm, and effective pipeline length 2.56 m; 3. Microwave generating unit: 4 WR-430 standard rectangular waveguides, operating frequency 2450 MHz, single-port power 800W (efficiency 80%), power density adjustable range of 8-16 W / mL; 4. Fluid drive unit: peristaltic pump, volumetric flow rate 0.56-1.38 L / min, corresponding Reynolds number Re=200-300 (laminar flow state), Dean number De=50-75; 5. Temperature monitoring unit: FOT-L-SD fiber optic temperature sensor, placed at the center of the spiral tube outlet section, with an accuracy of ±0.1℃; 6. Temperature maintenance unit: The microwave cavity outlet is connected to a constant temperature water bath to maintain the sterilization temperature at 56-64℃ for 1-3 minutes; 7. Cooling unit: Rapid cooling to below 4°C using an ice-water bath.

[0007] Secondly, the present invention provides a continuous microwave pasteurization method for liquid eggs, comprising the following steps: 1. Material pretreatment: Fresh liquid eggs (taking whole egg liquid as an example) are passed through an 80-mesh sieve to remove impurities and cooled to 4℃ for storage; Bacterial culture preparation (for verification): E. coli activated to the logarithmic phase is centrifuged at 4℃ and 6000×g for 5 min, and the bacterial sludge is resuspended in the whole egg liquid to achieve an initial bacterial concentration of 10. 7 -10 8 CFU / mL; 2. Continuous microwave heating: Start the peristaltic pump to pre-circulate the whole egg liquid in the pipeline until it reaches a steady state; turn on the microwave source and adjust the power density P and volumetric flow rate Q to make the whole egg liquid reach the target temperature T at the outlet; 3. Temperature maintenance: After the whole egg liquid flows out of the microwave cavity, immediately take a 200 mL sample under sterile conditions; place it in a constant temperature water bath for 1-3 min to ensure that the microbial lethality rate is greater than 5 log CFU / mL; 4. Rapid cooling: After the heat treatment is completed, quickly transfer the product to an ice-water bath to cool it to below 4°C, and then terminate the heat treatment. 5. Quality testing: foaming ability, foam stability; emulsifying ability, emulsification stability index; free thiol content, proportion of α-helices and disordered structures in secondary structure; protein aggregation, etc.

[0008] In this process, a microwave pasteurization kinetic model (Log-Logistic model) was established, and regression fitting analysis was performed to predict and compare the inactivation behavior of microorganisms under specific treatment conditions. The Log-Logistic model is as follows: logS(t) = α + , Where α and ω are the upper and lower asymptotes of the curve (log CFU / mL), respectively, σ is the maximum inactivation rate of microorganisms (i.e., the maximum slope of the sterilization curve), and τ is the logarithm of the sterilization time corresponding to the maximum inactivation rate of microorganisms. Attached Figure Description

[0009] Figure 1 Continuous microwave pasteurization method for liquid eggs.

[0010] Figure 2 Schematic diagram of a continuous microwave pasteurization system.

[0011] Figure 3 Quality of whole egg liquid before and after continuous microwave pasteurization in a spiral resonant cavity. Detailed Implementation

[0012] Example 1: Low-power microwave pasteurization process for liquid eggs in a spiral resonant cavity: Start the peristaltic pump to pre-circulate the whole egg liquid in the pipeline until it reaches a steady state of flow; Turn on the microwave source and adjust the power density P and volumetric flow rate Q to make the material reach the target temperature T at the outlet. Low-power processing (LPT): P = 8 W / mL, Q = 0.562-0.687 L / min, T = 60℃; Heating time: 28.8-37.2 seconds; Materials: 10 L of fresh whole egg liquid, initial temperature 20℃, inoculated with 10 μL of E. coli 7 CFU / mL (Group A), no E. coli inoculation was the control group and Group B; Parameters: microwave power density 8 W / mL, volumetric flow rate 0.687 L / min, target temperature 60℃; Sterilization effect and quality: heating time 32.4 s, outlet temperature 60.3±0.8 ℃, E. coli decreased by 5 log CFU / mL after water bath incubation for 3 min; foaming ability increased by 5% and emulsification ability increased by 0.2.

[0013] Example 2: Application of the dynamic model The data from Example 1 were fitted using a Log-Logistic model, yielding the following E. coli parameters: α = -10.5412, ω = 0.0027, σ = -6.7586, τ = -0.5538. The resulting regression equation was y = 0.9916x + 0.0826 (R²). 2 (0.999), predicting a 5 log reduction in microbial population. 10 The required time t 5d =2.94 min, measured value 2.94 min, deviation 0.8%, model accuracy 1.0427, which can be used for process scale-up design.

[0014] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A spiral cavity based continuous liquid egg microwave pasteurization method and quality control system, characterized in that, Comprise: Rectangular microwave resonant cavity (0.4 m x 0.4 m x 0.4 m), wall is perfect electric conductor; Spiral conveying pipeline, inner diameter 10 mm, 3.5 turns of spiral, pitch circle diameter 120 mm, pitch 30 mm; Four WR-430 rectangular waveguides, working frequency 2450 MHz, single-port power 800 W, power density 8-16 W / mL; Peristaltic pump, volumetric flow rate 0.56-1.38 L / min; Temperature monitoring unit, optical fiber sensor is placed in the center of the outlet cross section of the spiral tube.

2. A continuous microwave pasteurization method of whole egg liquid characterized by, Comprise: Whole egg liquid is preheated and circulated under the drive of the peristaltic pump; Microwave power density is 8-16 W / mL, so that the outlet temperature reaches 56-64 DEG C, and the temperature rising time is 16.8-37.2 seconds; The temperature is maintained for 1-3 minutes; Rapidly cooled to below 4 DEG C in ice water bath.

3. The method of claim 2, wherein, Log-Logistic model to predict microbial inactivation behavior: logS(t) = a + b log(t) , Wherein, alpha and omega are the upper and lower asymptotes of the curve (log CFU / mL) respectively, sigma is the maximum inactivation rate of microorganisms (i.e. the maximum slope of the sterilization curve), and tau is the logarithmic value of the sterilization time corresponding to the maximum inactivation rate of microorganisms.

4. The method of claim 2, wherein, After treatment, the E. coli in the whole egg liquid is reduced by 5 log CFU / mL, the foaming capacity is increased by 5%, and the emulsifying capacity is increased by 0.2.

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