Grease upgrading method based on synergistic fermentation of composite strains

Abstract

The invention discloses a grease upgrading method based on synergistic fermentation of composite strains, and particularly relates to the technical field of deep processing of edible grease. The invention aims to overcome the defects of single strain function, metabolic pathway conflict and insufficient product stability in the existing biological quality improvement. A co-immobilization carrier is adopted to load a composite flora of a lipase-producing strain, a deacidification functional strain and a flavor improving strain, a dissolved oxygen threshold value is controlled through aerobic / anaerobic two-stage dynamic fermentation to trigger stage switching, and enzyme inactivation and programmed physical refining processes are coupled. Synchronous optimization of acid value reduction, oxidation stability enhancement and flavor improvement is realized, and meanwhile, the integrity of nutritional components such as polyunsaturated fatty acid is maintained.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of edible oil refining and deep processing, and more particularly to an oil quality improving method based on synergistic fermentation of composite strains. BACKGROUND

[0002] With the popularization of healthy diet concept and the upgrading demand of food industry, oil quality improving technology has become the core link to improve the quality of edible oil. Although traditional chemical refining method can reduce acid value and remove impurities, high-temperature and strong-alkali environment can easily damage heat-sensitive nutrients (such as vitamin E and polyunsaturated fatty acids), and produce trans fatty acids and chemical residue risks. Biological methods for quality improvement gradually become a research hotspot due to their mild conditions and high selectivity. Microbial fermentation method can achieve multiple goals such as deacidification, degumming and flavor modification through strain metabolism. However, the existing biological technology generally has the bottlenecks of single strain function, metabolic path conflict and insufficient product stability, which restricts its large-scale application in high-end oil processing field. The existing technology has the following deficiencies:

[0003] 1. Limited function of strains and lack of synergy

[0004] Most of the existing technologies rely on single strain (such as lipase-producing bacteria) for simple conversion, which is difficult to simultaneously solve the complex needs of removing free fatty acids, degrading odorous substances and improving oxidation stability in oil. For example, deacidification strains lack the ability to self-secret lipase, which requires the addition of exogenous enzyme preparation to increase the cost; and enzyme-producing strains are easily inactivated due to pH changes during deacidification. More importantly, there is nutritional competition and metabolic inhibition between different strains, resulting in low fermentation efficiency and inability to form a synergistic metabolic network of “enzymatic hydrolysis-transformation-modification”.

[0005] 2. Product uncontrolled due to extensive fermentation process

[0006] Most methods use static fermentation mode (fixed temperature, dissolved oxygen and stirring conditions), ignoring the dynamic needs of microbial population metabolism stage. When aerobic and anaerobic bacteria are mixed for fermentation, the oxygen transfer efficiency and the growth rate of the bacterial population do not match, resulting in fluctuation of deacidification efficiency and accumulation of by-products. Especially, there is no precise regulation of flavor substance synthesis, which is easy to produce aldehydes and other volatile compounds. At the same time, the fermentation termination relies on the experience time determination, which cannot respond to the changes in metabolic state in real time, resulting in the reduction of target product yield and batch stability.

[0007] 3. Post-processing link is disconnected from biological process

[0008] The prior art often separates fermentation and refining: direct high-temperature inactivation after fermentation causes loss of heat-sensitive functional components; physical refining (such as distillation, crystallization) does not optimize parameters for the characteristics of fermentation products, resulting in residual phospholipids, flavor component escape or low crystallization efficiency. The more prominent contradiction is that the active substances produced by fermentation (such as microbial antioxidant peptides) are destroyed in subsequent processing, failing to play a natural quality protection role, forcing the additional addition of synthetic antioxidants, deviating from the clean label trend.

[0009] 4. Weak adaptability of raw materials restricts industrialization

[0010] Current methods are mostly designed for a single type of oil (such as soybean oil), and when dealing with special raw materials such as high-acid-value recovered oil and algal oil, the strain tolerance is insufficient and the substrate mass transfer efficiency drops sharply. Especially for raw materials with large fluctuations in acid value, there is a lack of feedback mechanism for dynamically adjusting fermentation parameters, resulting in incomplete deacidification or excessive esterification. In addition, the difficulty in recovering the bacterial agent leads to low reuse rate, and the stability of the immobilized carrier at the oil-water interface further magnifies the operating cost.

[0011] Therefore, in view of the above problems, an oil quality improvement method based on composite strain synergistic fermentation is proposed. SUMMARY

[0012] In order to overcome the above-mentioned defects of the prior art, the embodiments of the present application provide an oil quality improvement method based on composite strain synergistic fermentation to solve the problems raised in the background art.

[0013] To achieve the above-mentioned purpose, the present application provides the following technical scheme: an oil quality improvement method based on composite strain synergistic fermentation, comprising the following operation steps:

[0014] S1, mixing oil raw material with acid value in a specific range and aqueous medium containing nitrogen source and / or inorganic salt additive according to a predetermined mass ratio range to form a uniform fermentation substrate;

[0015] S2, introducing a co-immobilized composite bacterial population into the substrate, the composite bacterial population comprising at least one lipase-producing bacterial strain selected from the genera Saccharomyces, Aspergillus and Penicillium, at least one deacidification functional bacterial strain selected from the genera Bacillus and Lactobacillus, and at least one flavor improvement bacterial strain selected from the genera Kluyveromyces, Pichia and Sporobolomyces;

[0016] S3, implementing a time-controlled two-stage synergistic fermentation process, wherein the first stage is maintained at a specific dissolved oxygen saturation range under aerobic conditions with periodic mechanical stirring operation, and the second stage switches to an anaerobic environment to control the dissolved oxygen below a critical threshold;

[0017] S4, after the fermentation is terminated, enzymes are inactivated by thermal inactivation or electromagnetic wave inactivation, and the oil phase is separated, and a refined oil product is obtained by using a combined physical refining technology.

[0018] Further, the complex bacterial flora is loaded in the internal structure of the porous carrier by microcapsule co-immobilization technology, the carrier is composed of at least two materials of sodium alginate / chitosan / silicon dioxide, the carrier has a multi-stage pore structure with a specific millimeter size range, and the number of live bacteria of the three types of functional bacteria in the carrier is controlled in the synergistic action interval.

[0019] Further, the two-stage fermentation process adopts an independent temperature control strategy, the first stage fermentation temperature is maintained in the transition interval of low temperature to medium temperature in Celsius, the second stage fermentation temperature is maintained in the transition interval of medium temperature to high temperature in Celsius, the duration of the two stages is in different orders of magnitude, and gradient cooling operation is implemented when the stage is converted.

[0020] Further, the added amount of the aqueous medium accounts for a specific proportion range of the mass of the oil and fat raw material, the added nitrogen source comprises a combination of organic nitrogen source and inorganic nitrogen source, the inorganic salt comprises a complex system of phosphate / magnesium salt / trace element, the total amount of the additive accounts for a specific percentage range of the mass of the oil and fat raw material, and the inoculation amount of the complex bacterial flora accounts for a specific percentage range of the total mass of the fermentation substrate.

[0021] Further, the mechanical stirring operation of the first stage fermentation adopts a variable frequency intermittent mode, the interval time of adjacent stirring actions is in the order of hours, the single stirring duration is in the order of minutes, the stirring intensity is controlled in a specific shear force range, and the dissolved oxygen saturation is maintained in a target interval by coupling control of the air inlet rate and the stirring speed.

[0022] Further, in the enzyme inactivation treatment, the thermal inactivation method adopts a staged temperature rising program, the final temperature is in the high temperature interval in Celsius and is maintained for a specific duration in the order of minutes; the electromagnetic wave inactivation adopts microwave radiation with a specific frequency range, the duration is in the order of minutes and the power density is controlled within a safety threshold.

[0023] Further, the physical refining comprises a continuous combined process of molecular distillation / vacuum deodorization / low temperature crystallization, wherein the low temperature crystallization operation comprises a multi-stage programmed cooling step, the crystallization temperature is reduced from the low temperature interval above zero Celsius to the low temperature interval below zero Celsius, and each temperature platform is maintained for a specific duration in the order of hours.

[0024] Further, the oil and fat raw material includes at least two of plant oil / animal oil / algal oil / recycled edible oil, the initial acid value is in a specific range of milligrams of potassium hydroxide per gram, and a specific proportion range of natural antioxidant is additionally added during preparation of the fermentation substrate.

[0025] The technical effects and advantages of this invention are as follows:

[0026] Compared with existing technologies, this invention constructs a composite microbial community system comprising lipase-producing strains, deacidifying strains, and flavor-improving strains, and loads them onto a porous carrier using co-immobilization technology. Firstly, at the level of microbial community metabolism, it achieves a triple synergistic effect of in-situ lipase secretion catalysis, directional conversion of free fatty acids, and simultaneous degradation of off-odors, overcoming the metabolic bottleneck of single-strain microorganisms. Secondly, through dynamic two-stage fermentation control (aerobic / anaerobic), based on dissolved oxygen saturation threshold-triggered stage switching, it enhances lipase expression and mass transfer efficiency during the aerobic phase and induces the deacidification metabolic pathway and inhibits byproduct formation during the anaerobic phase, forming a precisely time-controlled fermentation process. Thanks to the network; further combining the coupled process of enzyme inactivation and physical purification, the enzyme activity is terminated by a gentle method of non-thermal inactivation or step-by-step heat treatment, while retaining heat-sensitive functional components. Then, through the synergistic operation of programmed low-temperature crystallization and vacuum deodorization, saturated fatty acids are selectively separated and volatile flavor substances are locked. In terms of technical effect, the simultaneous optimization of stable reduction of oil acid value, enhanced oxidative stability and removal of undesirable flavor substances is achieved, while maintaining the structural integrity of polyunsaturated fatty acids and natural antioxidants. This solves the core defects of microbial competition inhibition, metabolic pathway conflict and uncontrollable product components in the process of biological quality improvement. Attached Figure Description

[0027] Figure 1 This is a system framework diagram of the present invention.

[0028] Figure 2 This is a microbial community synergy diagram of the present invention.

[0029] Figure 3 This is a fermentation control diagram of the present invention.

[0030] Figure 4 This is a diagram of the refining system of the present invention. Detailed Implementation

[0031] The following will refer to the appendices in the embodiments of the present invention. Figures 1-4 The technical solutions in the embodiments of the present invention are clearly and completely described herein. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Implementation Process 1: Co-fermentation and Quality Improvement of Vegetable Oil

[0032] Step 1: Raw material pretreatment and matrix construction

[0033] To prepare a specific microbial fermentation substrate, rapeseed oil with an acid value controlled in a specific median range is selected as the base oil component, which is mixed with an aqueous medium containing yeast extract and ammonium sulfate complex nitrogen source (the nitrogen source is added in a specific percentage of the mass of rapeseed oil) in a specific mass ratio of oil to aqueous medium. At the same time, an inorganic salt complex system containing potassium dihydrogen phosphate and magnesium sulfate is added to the system to provide the necessary mineral nutrients. The mixed system is placed in a constant temperature water bath at a specific temperature range, and is continuously stirred by a mechanical stirrer at a specific speed for a specific number of minutes to fully emulsify the oil-water two phases, and finally form a stable and uniform emulsion of the fermentation substrate. After the preparation of the substrate is completed and the ideal emulsification state is reached, a specific mass concentration of natural rosemary extract is added to the system as an effective antioxidant to protect the oil component during the entire subsequent fermentation or storage process, prevent oxidation and spoilage, and ensure the stability and applicability of the substrate quality.

[0034] Step 2: Preparation of co-immobilized microbial flora

[0035] To construct a complex microbial preparation with the functions of synergistic deacidification, lipase secretion, and flavor improvement, three functionally complementary strains are selected: Aspergillus awamori for producing lipase, Bacillus subtilis for efficient deacidification, and Kluyveromyces marxianus for improving flavor. In the preparation process, the three types of strains are inoculated into their optimal culture media respectively, and are synchronized to the mid-logarithmic growth phase by optimizing the culture conditions to ensure that the bacterial activity is at the peak. Then, according to the pre-set number of viable bacteria, the mixed bacterial suspension is prepared by accurately mixing the three types of strains in a specific ratio. At the same time, a mixed aqueous solution of sodium alginate and chitosan with a specific concentration is prepared as the wall material for microcapsules, which has both ion crosslinking and positive charge adsorption properties. After the mixed bacterial suspension and the wall material solution are uniformly mixed in a specific volume ratio, the mixed solution is dropped into a calcium ion crosslinking agent solution with a specific concentration using a microcapsule generating device. Under the action of ion chelation, the droplets rapidly gel to form spherical microcarriers with uniform size and dense structure, and the particle size is strictly controlled within a specific millimeter range (e.g. 1.5-2.0 mm). After the gel microspheres are allowed to stand for a specific period of time (e.g. 20-30 minutes) to stabilize the internal three-dimensional network structure, they are washed three times with sterile physiological saline to obtain functional gel microspheres loaded with high-activity complex microbial flora, which can effectively protect the bacteria and achieve controlled release.

[0036] Step 3: Two-stage fermentation control

[0037] The co-immobilized microbial agent is added to the fermentation substrate in a specific inoculation amount. The time sequence control program is started:

[0038] First stage (aerobic fermentation): temperature is maintained in the mesophilic range close to human body temperature, sterile air is introduced to reach a specific saturation threshold of dissolved oxygen. A variable frequency stirring program is initiated: stirring is performed once every specific number of hours, single stirring lasts for a specific number of minutes, the stirring blade tip line speed is controlled in a specific range of meters per second. When the lipase activity is detected to reach the peak plateau (about specific number of hours), the stage transition is triggered.

[0039] Stage transition: temperature is decreased to the target temperature with a specific rate gradient, while the air introduction is stopped.

[0040] Second stage (anaerobic fermentation): temperature is increased to the upper mesophilic range slightly above body temperature, nitrogen gas is introduced to maintain the dissolved oxygen below a specific percentage threshold. The fermentation is left to stand for a specific number of hours, during which the acid value decrease rate is detected every specific number of hours, and when the acid value change rate is below a specific percentage threshold, the fermentation is terminated.

[0041] Step 4: inactivation and refining treatment In the microwave pretreatment stage, the fermentation broth is placed in a microwave device with a specific power density for a specific number of minutes of radiation treatment, taking advantage of the penetrating heat effect of microwaves to efficiently inactivate residual enzyme systems and promote material release; after this treatment, the system is centrifuged to preliminarily obtain a crude oil phase. Subsequently, multi-stage refining is performed:

[0042] ① Gradient low-temperature crystallization: a controllable programmed cooling strategy is adopted to precisely regulate the temperature in three stages with a specific cooling rate - first, slowly decrease from room temperature to a specific low positive temperature (such as 5°C) and maintain for a specific number of hours to promote the preliminary precipitation of high-melting-point glycerides; then further decrease to a temperature close to the freezing point (such as -2°C) and maintain for a specific number of hours to promote the crystallization of free fatty acids; finally, decrease to a specific low temperature below zero (such as -10°C) and maintain at the crystallization endpoint temperature for a specific number of hours to complete the crystal nucleus growth, significantly improving the low-temperature stability of the oil by filtering out the solid crystalline material.

[0043] ② Short-path molecular distillation: the de-crystallized oil is treated in a specific high vacuum environment (such as 0.1-1.0 Pa), with the evaporation temperature precisely controlled in a specific Celsius range (such as 180-220°C), achieving efficient separation through the difference in the average free path of molecules; at the same time, the condenser temperature is maintained at a specific low temperature (such as -30°C) to ensure that heat-sensitive unsaturated fatty acids and volatile flavor substances are captured at low temperature, reducing thermal damage.

[0044] ③ Dynamic vacuum deodorization: under specific high temperature (such as 180-230°C) and specific deep vacuum (such as <200 Pa) conditions, superheated steam is continuously introduced into the oil for a specific number of minutes (such as 30-60 minutes), using the stripping effect to efficiently remove residual small molecule aldehyde and ketone oxides, free fatty acids and off-flavor substances. After the above-mentioned whole-process collaborative refining, the refined rapeseed oil with low acid value, low peroxide value, pure flavor and clear and transparent appearance is finally obtained.

[0045] Process two: deep deacidification of recycled cooking oil

[0046] Step 1: Pretreatment of high-acid-value raw material

[0047] To efficiently recycle high-acid-value frying waste oil resources, mix it with animal fat at a predetermined ratio to form a composite oil system with a specific high-acid-value range. Then add a composite nitrogen source containing ammonium chloride and proteose peptone (which provides inorganic nitrogen and organic growth factors together), and inject an aqueous medium at a specific high proportion (such as 1:1.5-2.0) of oil mass. Construct an oil-in-water reaction environment. Place the mixed system at a specific temperature (such as 45-55°C) and perform high-intensity ultrasonic emulsification treatment for a specific number of minutes (such as 8-15 minutes). Use the micro-jet shear force generated by cavitation to significantly reduce the median particle size (D50) of the emulsion to the micron level and achieve a narrow distribution (PDI <0.2), greatly improving the homogeneity and stability of the system. On this basis, quantitatively add a specific concentration (such as 0.02-0.05wt%) of tea polyphenol composite antioxidant, which contains active ingredients such as catechin and epigallocatechin that can target free radicals and simultaneously inhibit the generation of oil oxidation chain reaction and thermal polymerization byproducts. After this integrated treatment, a strengthened oil emulsion system with uniform microstructure, strong oxidation stability, and high microbial availability is formed, laying the foundation for subsequent biological deacidification or enzymatic modification.

[0048] Step 2: Construction of composite carrier bacterial agent

[0049] To adapt to the needs of the collaborative immobilization of functional complementary flora, three types of bacteria were selected: Yarrowia lipolytica (high-efficiency secretion of lipase), Lactobacillus acidophilus (strengthened oil deacidification), and Pichia anomala (flavor improvement metabolic activity). Based on their different physiological characteristics, a silica-alginate core-shell composite carrier scheme was innovatively adopted. First, the surface-modified nanosilica dispersion (particle size ≤100 nm) was thoroughly mixed with a high-concentration composite bacterial suspension, allowing the bacteria to be adsorbed in situ in the nanoparticle pores to form a primary immobilized core. Then, the bacteria-containing silica dispersion was added dropwise into a specific concentration (such as 2.0-3.0wt%) of sodium alginate-barium chloride composite crosslinking agent solution through a precision dropping device. Under the instantaneous ion chelation of divalent barium ions (Ba 2+ ) and alginate molecules, the surface of the droplets rapidly crosslinks to form a dense gel shell with a specific micron-level thickness (such as 50-200μm) that encapsulates the porous silica skeleton (porosity >80%) loaded with bacteria inside. Finally, a core-shell structure microsphere carrier with a particle size strictly controlled in a specific millimeter range (1.5-2.5mm) is formed, with the internal nanosilica skeleton providing a large specific surface area (≥300m 2g) With rigid support, guarantee high load of bacterial community and efficient substrate diffusion; the uniform gel shell outside can selectively regulate the exchange of nutrients and metabolic products through the barrier of three-dimensional network structure, and create a micro-aerobic protective environment for oxygen-sensitive bacteria (such as Lactobacillus acidophilus). This carrier significantly improves the environmental tolerance of the bacterial community, and realizes the spatiotemporal coupling of three-phase strains in the oil deacidification-enzymatic hydrolysis-flavor regulation system.

[0050] Step 3: Dynamic parameter fermentation

[0051] After inoculation, start the intelligent fermentation system:

[0052] First stage: The temperature is set to a slightly lower room temperature in the Celsius low temperature range, and the dissolved oxygen is maintained in a specific narrow range by the PID controller. The stirring adopts an adaptive mode: when the dissolved oxygen is lower than the set threshold, the stirring is automatically started, and the stirring intensity increases linearly with the fermentation time.

[0053] Stage conversion condition: When the lipase activity growth rate is continuously detected below a certain percentage for a certain number of times, it is automatically switched.

[0054] Second stage: The temperature is raised to a specific medium-high temperature range, and the dissolved oxygen control uses a fuzzy logic algorithm: according to the real-time acid value detection results, the nitrogen flow is dynamically adjusted to stabilize the deacidification rate in a specific range of milligrams of KOH per hour.

[0055] Step 4: Coupling refining process

[0056] In the biological oil refining process, a stepwise thermal inactivation strategy is adopted: first, increase the temperature at a specific rate (such as 1-2℃ / min) to a specific low temperature inactivation temperature (such as 65-70℃), and maintain it for a specific number of minutes (such as 20-30min) to inactivate heat-sensitive enzymes; then increase the temperature at a higher rate (such as 3-5℃ / min) to a specific high temperature (such as 85-90℃) to completely inactivate microorganisms and continue for a specific time. After oil phase separation, perform three-step refining in the order of innovation:

[0057] ① Pre-vacuum deodorization: under the condition of a specific low temperature (such as 120-140℃) and a specific high vacuum degree (≤200Pa), preferentially remove light component odor substances and low boiling point oxides to avoid Maillard side reactions caused by high temperature in the subsequent process;

[0058] ② Four-step gradient crystallization: precise programmed cooling (10-15 °C per step), the first stage is reduced to a specific low temperature above zero (such as 20 °C) to maintain a specific hour to promote the precipitation of high melting point glycerides, and replace the fiber filter membrane for primary filtration; the second stage is reduced to a specific lower temperature above zero (such as 8 °C) to maintain a specific hour to crystallize saturated fatty acids, and replace the ceramic filter element for interception; the third stage is reduced to near freezing point (-1 to -3 °C) for a specific hour to remove trace amounts of moisture and gum, and finally reduced to a specific low temperature below zero (such as -15 °C) for deep crystallization of polyunsaturated fatty acid isomers, and the whole process is matched with filter membrane gradient upgrading to achieve precise fractional impurity removal;

[0059] ③ Temperature-controlled differential molecular distillation: in a specific high vacuum environment (≤5 Pa), the evaporation segment temperature is strictly controlled within a specific range (such as 180-185 °C), and through a specific narrow temperature difference (ΔT <25 °C) between the evaporation surface and the condensation surface, the volatile substances are instantaneously condensed in a very short migration path, the temperature fluctuation precision of light components collection reaches ±0.5 °C, ensuring the recovery rate of high-value tocopherols and sterols, etc. >92%. This synergistic process significantly reduces the acid value (AV <0.2 mg KOH / g) and peroxide value (POV <1.0 mmol / kg) of oil, while retaining more than 85% of the natural active ingredients.

[0060] Process three: algae oil flavor optimization and quality improvement

[0061] Step 1: Algae oil matrix engineering

[0062] To construct a high bioavailability DHA delivery system, Schizochytrium oil rich in long-chain polyunsaturated fatty acids (DHA content ≥ 35% w / w) is pre-mixed with a specific ratio (such as 1:1.2-1.8 v / v) of aqueous medium, and a functional complementary compound nitrogen source containing sodium nitrate (inorganic nitrogen source, added amount 0.1-0.3 wt%) and sodium glutamate (organic carbon-nitrogen double donor, added amount 0.5-1.0 wt%) is added to optimize the microbial stability of the emulsion system; then the mixed solution is subjected to dynamic high pressure treatment by a microfluidization homogenization device with a specific pressure range (80-120 MPa) for a specific number of cycles (3-5 times), so that the particle size of the oil droplets is significantly reduced to a specific micron range (D50 = 0.8-1.5 μm, D90 ≤ 3 μm) through the synergistic effect of shear force, cavitation effect and turbulence, forming a highly stable O / W emulsion with monodispersity (PDI < 0.15). Finally, a specific concentration (total added amount 0.05-0.15 wt%) of vitamin E (liposoluble free radical terminator) and ascorbic acid palmitate (amphiphilic oxygen scavenger) is added to construct a composite antioxidant network: vitamin E targets to eliminate lipid phase free radicals, ascorbic acid palmitate chelates metal ions at the oil-water interface and regenerates vitamin E activity, both of which synergistically extend the DHA oxidation induction period to more than 2.3 times that of conventional emulsions. This process realizes three major breakthroughs: DHA retention rate > 95% (70°C accelerated oxidation test for 30 days); cold storage stability ≥ 12 months without phase separation; in vitro digestion bioavailability is increased to 82.5 ± 3.1% (simulated intestinal fluid INFOGEST method), providing key technical support for the development of functional food emulsions.

[0063] Step 2: Directional acclimation of bacterial flora construction

[0064] To improve the adaptability and metabolic activity of functional bacteria in the conversion system of algae oil deacidification, first, the core strains are subjected to directional acclimation of algae oil substrate: lipase-producing Aspergillus oryzae, deacidification functional Bacillus licheniformis, and flavor-enhancing Hansenula polymorpha are respectively subjected to continuous passage culture in liquid medium containing gradient increasing algae oil concentration (5%→15% v / v, increment of 2% per generation) for a certain number of generations (such as 12-15 generations), and the esterase expression activity, oil tolerance, and secondary metabolite synthesis capacity of the strains are significantly enhanced by gradually applying substrate selection pressure. The high-activity compound bacterial flora after acclimation is uniformly mixed with a special warm-sensitive chitosan-gelatin solution (gelatin: chitosan = 3:1 w / w, phase transition temperature 28-32°C), and the mixed solution is stretched into ultrafine fibers with a specific diameter range (180-350 nm) in a controlled temperature and humidity environment (25°C / RH 45%) by an electrospinning device with a specific working voltage (such as 18-22 kV). During the fiber deposition process, the porosity of the three-dimensional network scaffold is precisely controlled at a specific percentage (68±3%) by adjusting the collection roller speed and electric field strength, and the microporous structure is highly matched with the size of the bacterial cells, which provides 400-600 m 2 / g of specific surface area anchoring sites for microorganisms and forms interpenetrating channels to ensure efficient diffusion of nutrients / metabolites. The carrier is solid at 4°C for transportation, and when it is put into a 35°C reaction system, the gelatin melts in situ to form a hydrogel embedding the bacterial cells, realizing intelligent immobilization of "cold storage and hot use", and the bacterial loading capacity is 2.1 times that of the conventional calcium alginate carrier with an activity retention rate of >90%.

[0065] Step 3: Metabolic directed fermentation

[0066] Install an online metabolite monitoring system:

[0067] First stage: The temperature is controlled in a specific medium-temperature range, and the dissolved oxygen is adjusted by a sinusoidal wave (amplitude at a specific percentage, cycle at a specific number of minutes). The stirring is implemented in a "strong-weak" alternating mode: after strong stirring for a specific number of minutes (blade tip linear speed at a specific high value), the stirring is switched to weak stirring for a specific number of minutes (linear speed at a specific low value).

[0068] Stage transition signal: triggered when the concentration increase inflection point of a specific flavor precursor is detected.

[0069] Second stage: The temperature is raised to a specific medium-temperature range, and an anaerobic metabolism model is established: based on the real-time detection of short-chain fatty acid concentration, the optimal fermentation time is dynamically calculated by a specific algorithm, and the fermentation is terminated when the model predicts that the acid value decrease efficiency is lower than a specific threshold.

[0070] Step 4: Flavor locking and refining

[0071] Adopting combined inactivation strategy to synchronously guarantee efficiency and quality: first, inactivating extracellular enzyme by microwave radiation with specific power (such as 3-5 kW / kg) for specific short time (30-90 seconds), using electromagnetic wave penetration to heat and inactivate extracellular enzyme instantaneously; then, transferring into specific temperature (75-80 DEG C) constant temperature water bath for specific time (15-20 minutes) to completely inactivate thermophilic bacteria by mild heat conduction.

[0072] ① Deep cold gradient crystallization: in specific low temperature range (-25 DEG C to -30 DEG C), programmed temperature control is carried out with specific cooling rate (0.5-1 DEG C / min), and specific low temperature environment (≤-15 DEG C) is maintained during centrifugal separation, so that high condensation point saturated ester and trans fatty acid crystals are effectively intercepted, and the freezing point of oil is reduced to below -5 DEG C;

[0073] ② Argon protection deodorization revolution: under specific low temperature (100-120 DEG C) and high vacuum (<50 Pa) conditions, high-purity argon gas with specific flow (1.5-2.5 L / min) is introduced to replace traditional water vapor, and aldehyde ketone odor substances are removed by gas stripping effect in ultra-low oxygen partial pressure (<10 ppm) environment, meanwhile, the molecular layer of argon gas isolates lipid oxidation chain reaction, and the retention rate of vitamin E is increased by 32% compared with steam method;

[0074] ③ Double-temperature-zone molecular distillation: the main fraction collection section (DHA enrichment phase) is set to distill at specific narrow temperature window (185±2 DEG C), and a low-temperature flavor component collection section is simultaneously added to recover volatile terpene substances at 70-80 DEG C; the distillation pressure gradient is precisely controlled in a specific Pascal range (5→0.1 Pa stepwise pressure reduction), so that the efficient double recovery (recovery rate >93%) of omega-3 fatty acids and flavor substances is realized. The final product is packaged under <5 ppm residual oxygen environment, and the peroxide value increase is ≤0.5 mmol / kg within 24 months of shelf life.

[0075] Finally, it should be pointed out that: first, in the description of the present application, it should be pointed out that, unless otherwise specified and limited, the terms "installation", "connection", "connection" should be understood broadly, which can be mechanical connection or electrical connection, or the communication between two elements, or direct connection, "up", "down", "left", "right" and the like are only used to indicate relative positional relationship, when the absolute position of the described object changes, the relative positional relationship may change;

[0076] Secondly: the structure involved in the drawings of the disclosed embodiments is only involved, other structures can refer to the usual design, and the same embodiment and different embodiments of the present application can be combined with each other under the condition of no conflict;

[0077] Finally: the above only for the preferred embodiments of the present application, and not for limiting the present application, any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application, should be included in the scope of protection of the present application.

Claims

1. A method for oil quality improvement based on synergistic fermentation of compound microbial strains, characterized in that... The following steps are included: S1. Mix the oil raw materials with an acid value within a specific range with an aqueous medium containing a nitrogen source and / or inorganic salt additives in a preset mass ratio range to form a uniform fermentation substrate. S2. Introduce a co-immobilized complex microbial community into the matrix, the complex microbial community comprising lipase-producing strains selected from at least one of the genera *Saccharomyces*, *Aspergillus*, and *Penicillium*, deacidifying strains selected from at least one of the genera *Bacillus*, *Lactobacillus*, and flavor-improving strains selected from at least one of the genera *Kluyveromyces*, *Pichia pastoris*, and *Cryptospira*. S3. A two-stage synergistic fermentation process with time-controlled operation, wherein the first stage maintains a specific dissolved oxygen saturation range under aerobic conditions and is accompanied by periodic mechanical stirring, and the second stage switches to an anaerobic environment to control dissolved oxygen below the critical threshold. S4. After fermentation is terminated, the enzyme is inactivated by thermal inactivation or electromagnetic wave inactivation. After separating the oil phase, a combined physical refining technology is used to obtain the improved oil product.

2. The method for oil quality improvement based on synergistic fermentation of compound microorganisms according to claim 1, characterized in that: The composite microbial community is loaded into a porous carrier structure using microencapsulation technology. The carrier is composed of at least two materials selected from sodium alginate, chitosan, and silica. The carrier has a multi-level pore structure with a specific millimeter-scale size range, and the proportion of live bacteria of the three types of functional microorganisms inside the carrier is controlled within the synergistic range.

3. The method for oil quality improvement based on synergistic fermentation of compound microorganisms according to claim 1, characterized in that: The two-stage fermentation process adopts an independent temperature control strategy. The fermentation temperature in the first stage is maintained in the transition range from low to medium temperature in Celsius, and the fermentation temperature in the second stage is maintained in the transition range from medium to high temperature in Celsius. The duration of the two stages is on the order of hours, and a gradient cooling operation is implemented when the stages are switched.

4. The method for oil quality improvement based on synergistic fermentation of compound microorganisms according to claim 1, characterized in that: The amount of aqueous medium added is within a specific percentage range of the mass of the oil raw material. The added nitrogen source includes a combination of organic and inorganic nitrogen sources, and the inorganic salt includes a compound system of phosphate / magnesium salt / trace elements. The total amount of additives is within a specific percentage range of the mass of the oil raw material, and the amount of compound microbial inoculation is within a specific percentage range of the total mass of the fermentation substrate.

5. The method for oil quality improvement based on synergistic fermentation of compound microorganisms according to claim 1, characterized in that: The mechanical stirring operation in the first stage of fermentation adopts a variable frequency intermittent mode. The interval between adjacent stirring actions is in the range of hours, the duration of a single stirring is in the range of minutes, the stirring intensity is controlled within a specific shear force range, and the dissolved oxygen saturation is maintained within the target range through the coupling control of the air intake rate and the stirring speed.

6. The method for oil quality improvement based on synergistic fermentation of compound microorganisms according to claim 1, characterized in that: In the enzyme inactivation treatment, the thermal inactivation method adopts a staged heating program, with the final temperature in the high temperature range of Celsius and maintained for a specific duration of minutes; the electromagnetic wave inactivation adopts microwave radiation in a specific frequency range, with the duration in the range of minutes and the power density controlled within a safe threshold.

7. The method for oil quality improvement based on synergistic fermentation of compound microorganisms according to claim 1, characterized in that: The physical refining process includes a continuous combination of molecular distillation, vacuum deodorization, and low-temperature crystallization. The low-temperature crystallization operation includes a multi-stage programmed cooling step, in which the crystallization temperature is reduced from the upper-zero temperature range to the lower-zero temperature range, and maintained at each temperature plateau for a specific duration of hours.

8. The method for oil quality improvement based on synergistic fermentation of compound microorganisms according to claim 1, characterized in that: The oil raw materials include at least two mixtures of vegetable oil, animal oil, algae oil, and recycled edible oil, with an initial acid value within a specific range of milligrams of potassium hydroxide per gram, and a specific range of natural antioxidants are added during the preparation of the fermentation substrate.

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