Composite Composition Structure of Powder Phospholipid Coating Material and Core Material

Liquid phospholipids feature excellent emulsifying activity and nutritional value, yet they face prominent application limitations: susceptibility to oxidative rancidity under light, heat and oxygen exposure, easy viscosity increase and agglomeration during storage, poor dispersibility in cold aqueous systems, and incompatibility with some solid powder formulations. Microcapsule technology converts viscous liquid phospholipids into free-flowing powder phospholipids by constructing a complete core-shell composite structure. The core material concentrates active phospholipid components, while the coating material forms a continuous dense barrier membrane. The matching selection of core raw materials, coating matrix and auxiliary functional additives determines encapsulation efficiency, oxidation resistance, rehydration dispersion performance and shelf stability. This paper analyzes the quality deterioration mechanism of unencapsulated liquid phospholipids, elaborates the classification and structural characteristics of core material and coating material systems for phospholipid microcapsules, discusses the interface interaction mechanism between core and shell phases, compares common preparation molding routes, and summarizes how optimized core-shell composite structures improve the processing adaptability and functional stability of powder phospholipids in food, nutrition and cosmetic formulations.

1. Bottlenecks of native liquid phospholipids without microcapsule encapsulation

Natural liquid phospholipids extracted from vegetable oil degumming sludge exist as viscous oily fluids, and inherent physical and chemical defects restrict large-scale standardized application in powder product systems.

First, strong oxidation sensitivity. Unsaturated fatty acid chains on phospholipid molecules are prone to free radical chain reactions when contacting air, generating peroxides, aldehydes and ketones. Rapid rise in peroxide value produces peculiar rancid odor, resulting in shortened raw material validity period.

Second, poor solid formulation compatibility. Viscous liquid phospholipids cannot be directly mixed with carbohydrates, amino acids and mineral powder materials. Long-term static placement causes oil phase separation, material agglomeration and uneven component distribution, bringing difficulties to tableting, granulation and powder blending processes.

Third, weak cold-water dispersibility. Liquid phospholipids are difficult to form uniform microemulsions in low-temperature water. Large oil droplets float upward, leading to liquid stratification, which cannot meet the production requirements of instant nutritional powder, solid beverages and cold-processed emulsion products.

Fourth, flavor interference risk. Oxidation-derived off-flavors spread freely in mixed systems, contaminating the flavor matrix of finished products. Meanwhile, direct contact between phospholipids and metal ions accelerates lipid peroxidation, further aggravating quality attenuation.

Microcapsule core-shell composite construction effectively isolates phospholipid core materials from external oxygen, light, metal catalysts and moisture, fundamentally solving the above defects of liquid phospholipids.

2. Structural composition of phospholipid microcapsule core material system

The core material is the functional active carrier of microcapsules, mainly composed of phospholipid matrix and compatible auxiliary lipid regulators, which determines the intrinsic functional performance of finished powder phospholipids.

(1) Main active substrate: composite phospholipid mixture

The core base material can adopt liquid soybean phospholipids, sunflower phospholipids or high-purity modified phospholipids including phosphatidylserine enriched phospholipids. The fatty acid chain distribution (linoleic acid and linolenic acid proportion) and phospholipid component ratio directly determine the emulsifying capacity, liposome forming performance and nutritional activity of microcapsule powder. According to terminal demands, high-end formulas can select low-trans-fat refined phospholipids to match clean-label requirements.

(2) Core phase auxiliary regulators

Antioxidants are uniformly dissolved into the phospholipid oil phase as core additives. Natural tocopherol complex, rosemary extract and ascorbyl palmitate are commonly used to block free radical oxidation inside microcapsules. A small amount of medium-chain triglycerides can be added to adjust core viscosity, reduce oil phase viscosity, facilitate uniform atomization during spray drying, and avoid incomplete coating caused by excessive core fluid viscosity.

(3) Functional co-encapsulated active substances

For targeted functional powder products, fat-soluble active components can be co-dissolved in the phospholipid core: DHA/EPA algae oil, coenzyme Q10, fat-soluble vitamins, plant lipophilic extracts. The phospholipid matrix acts as a solubilizer, realizing synchronous encapsulation of multiple lipid active ingredients in one microcapsule particle.

3. Structural composition classification and characteristics of microcapsule coating material (shell material)

The coating material forms a continuous solid barrier film outside the core oil droplets after drying. It is required to have good film-forming property, low oxygen permeability, water solubility or water dispersibility, and form stable interface combination with phospholipid oil droplets. Coating materials are divided into three mainstream categories.

(1) Carbohydrate-based coating matrix

Including maltodextrin, modified starch, gum arabic, cyclodextrin. Maltodextrin has low cost and excellent film-forming ability, widely used in general-grade powder phospholipids. Modified starch improves emulsifying performance at the oil-water interface, enhancing the binding force between shell and core. Cyclodextrin can form inclusion complexes with partial volatile oxidation by-products, assisting odor control. Carbohydrate shells feature low oxygen permeability, effectively blocking oxygen diffusion. The main limitation is poor thermal stability under ultra-high temperature sterilization.

(2) Protein-based coating matrix

Sodium caseinate, whey protein isolate, gelatin. Protein molecules have amphiphilic characteristics, which can be closely adsorbed on the surface of phospholipid oil droplets to form dense interfacial films, greatly improving encapsulation efficiency. Protein shells possess superior barrier performance against oxygen and light, suitable for producing high oxidation-resistant premium powder phospholipids. Restricted by cost and pH sensitivity, they are mostly applied in high-end nutritional raw materials.

(3) Composite compound coating system (mainstream high-end scheme)

Mixed formula of polysaccharide + amphiphilic protein + small-molecule emulsifier. The composite shell combines the advantages of carbohydrate film-forming property and protein interface anchoring capacity. It overcomes the single material defects: pure maltodextrin is easy to crack after moisture absorption, while single protein is sensitive to pH fluctuation. By adjusting the proportion of each component, manufacturers can balance encapsulation rate, rehydration dispersibility and storage moisture resistance, which is the preferred coating formula for industrial production of high-stability powder phospholipids.

(4) Shell phase auxiliary functional additives

A small amount of emulsifiers are added into the aqueous coating phase to reduce oil-water interfacial tension during homogenization; anti-caking agents such as silicon dioxide can be externally added after drying to improve the free-flow property of finished powder; pH regulators stabilize the charge distribution at the oil-water interface and prevent microcapsule particle aggregation before drying.

4. Interface interaction and complete core-shell composite structure morphology

After high-pressure homogenization, phospholipid core oil droplets are uniformly dispersed in the aqueous coating solution to form oil-in-water emulsion. Amphiphilic segments of coating materials spontaneously gather at the oil-water interface to form a tight adsorption layer. After spray drying and rapid water evaporation, the coating material dehydrates and shrinks to form a continuous solid shell, constructing typical core-shell spherical microcapsule structure.

Under ideal preparation conditions, the phospholipid core is completely wrapped inside the shell without oil leakage. The shell forms a physical isolation layer: blocking oxygen penetration to slow phospholipid oxidation; isolating external moisture to prevent core phospholipid viscosity rise and agglomeration. When the powder meets water during application, the coating material hydrates and dissolves, the core phospholipid is released and spontaneously forms tiny emulsion droplets, realizing rapid dispersion.

Unreasonable matching of core and shell materials leads to structural defects: incomplete coating causes surface free oil; mismatched interfacial tension triggers core-shell separation during storage; uneven shell thickness results in partial premature rupture and oil leakage.

5. Main industrial molding technology routes for phospholipid microcapsules based on core-shell composite system

(1) Spray drying microencapsulation (dominant industrial process)

The core phospholipid oil phase and aqueous coating solution are mixed and homogenized to form stable O/W emulsion, then atomized into tiny droplets inside a drying tower. Hot air quickly evaporates water, and the coating material cures into a solid shell. This technology realizes continuous large-scale production, low comprehensive cost, flexible adjustment of core-shell material ratio, suitable for mass production of powder phospholipids for food and nutrition industries.

(2) Coacervation microencapsulation

Utilize polymer phase separation to precipitate coating materials around phospholipid oil droplets to form shells. It can obtain thicker and denser barrier shells with outstanding oxidation resistance, yet the production batch scale is limited, and the cost is relatively high, mainly used for small-batch high-value functional encapsulated phospholipids.

(3) Freeze-drying microcapsule molding

Suitable for heat-sensitive high-unsaturation phospholipid systems. Avoid thermal damage to linoleic acid and linolenic acid chains during drying. The finished microcapsule has loose porous structure with excellent rehydration performance, but high energy consumption restricts wide popularization.

6. Influence of core-shell composite structure matching on key finished product indicators

(1) Encapsulation efficiency and surface free oil content

The matching degree between core phospholipid viscosity and coating material interfacial activity directly determines free oil index. Excessively high proportion of core material easily causes incomplete wrapping; improper selection of shell emulsifier leads to core shedding. Low surface free oil is the core indicator to judge microcapsule quality and oxidation stability.

(2) Oxidation stability during shelf storage

Shell oxygen transmission rate is controlled by coating material composition and shell thickness. Composite protein-polysaccharide shells have lower oxygen permeability than single maltodextrin shells, effectively slowing the rise of peroxide value of phospholipid core materials.

(3) Cold water instant dispersibility

The hydrophilic groups of the outer coating material determine the hydration speed. Well-designed core-shell structure enables powder phospholipids to disperse rapidly in normal temperature and low-temperature water without floating oil, meeting the preparation requirements of solid beverages and instant nutritional powder.

(4) Powder flowability and anti-caking property

The complete spherical core-shell structure avoids direct contact between viscous phospholipid cores. Uniform particle size distribution reduces inter-particle adhesion, so finished powder maintains free-flowing state during long-term storage, suitable for automated weighing, mixing and tableting production lines.

7. Application advantages of structured microencapsulated powder phospholipids

(1) Break the form limitation of liquid phospholipids

Convert viscous oily phospholipids into free-flowing solid powder, compatible with all kinds of solid formulations including nutritional granules, compound premix powder, chewable tablets and solid drinks.

(2) Greatly extend storage life

The core-shell barrier isolates oxygen, moisture and metal ions, inhibiting lipid peroxidation, reducing rancidity risk, lowering transportation and storage requirements, and supporting long-distance cross-regional logistics distribution.

(3) Expand the applicable pH and temperature window

The shell structure buffers environmental interference. Microcapsule powder phospholipids maintain stable performance under conventional UHT sterilization and different formula pH conditions, wider than the application range of original liquid phospholipids.

(4) Realize synchronous compounding of multiple fat-soluble functional ingredients

Multiple lipid active substances can be co-dissolved in the phospholipid core material for one-step encapsulation, simplifying downstream formula development and reducing the number of raw material varieties added by manufacturers.

Phospholipid microcapsules rely on a stable composite core-shell structure system to achieve the transformation from liquid viscous phospholipids to functional powder phospholipids. The core material dominated by phospholipid matrix undertakes emulsification, solubilization and nutritional functions, and can be compounded with antioxidants and fat-soluble active substances to adjust intrinsic performance. The coating material forms a continuous isolation barrier outside the core oil droplets; carbohydrate, protein and composite mixed shell materials have respective advantages and limitations, and composite coating systems become the preferred scheme for high-end powder phospholipid production. The interfacial interaction between core and shell determines encapsulation integrity, surface free oil content, oxidation resistance and rehydration dispersibility. Spray drying technology supports large-scale industrial preparation of microcapsule powder phospholipids. Reasonable design of core material formula and coating material composition can effectively overcome the inherent defects of liquid phospholipids such as easy oxidation, poor powder compatibility and difficult cold water dispersion. As an important processing upgrading technology for phospholipid raw materials, microcapsule encapsulation expands the application boundary of phospholipids in solid nutritional preparations, instant functional beverages and compound premixes, and provides standardized stable powder phospholipid raw material solutions for the high-end nutrition industry.