How to Improve the Stability of Lycopene Powder?

Lycopene is a natural carotenoid that is widely found in plant fruits such as tomatoes, watermelons, pink grapefruit, etc. [1], but its main source is tomatoes and tomato products. Lycopene has an isoprene structure (Figure 1, all-trans lycopene), and its molecule contains 11 conjugated double bonds and 2 non-conjugated double bonds. This special structure gives lycopene extremely strong antioxidant activity, which gives it a variety of physiological functions [2]. Lycopene can efficiently quench singlet oxygen [3,4], scavenge peroxyl radicals [5], regulate intercellular communication [6], enhance immunity [7] and regulate cholesterol synthesis [8], etc.

Lycopene can also prevent and treat atherosclerosis, cardiovascular disease, cancer and other diseases [9]. Studies have shown that compared with various carotenoids, lycopene has the best inhibitory effect on the proliferation of human cancer cells such as endometrial (Ishikawa), breast (MCF-7) and lung (NCI-H226) cancer cells [10]. Lycopene has been recognized as a Group A nutrient by the Food and Agriculture Organization of the United Nations, the World Health Organization and the United Nations Additives Committee[11] and is increasingly used in food, pharmaceuticals and cosmetics[12]. However, the multiple conjugated double bonds in the structure of lycopene are susceptible to heat, light and oxygen, which can cause the bonds to break, resulting in degradation and loss of lycopene[13].

Shi [14] and others found that lycopene loss under heat treatment reached 76%. According to a study by Gao Li [15], lycopene loss reached 50.00% after 6 h of direct sunlight. Therefore, the development of highly stable lycopene preparations, which are easier to store and use [16], is of great significance for the popularization and application of lycopene. At present, the main common dosage forms of lycopene preparations are mainly encapsulates, microcapsules, microemulsions and liposomes (Table 1). These preparations differ in composition, preparation methods and stability. Therefore, this paper reviews the latest research progress in the preparation methods and properties of these lycopene preparations, with a view to providing theoretical support for the development and utilization of highly stable lycopene preparations and promoting the application of lycopene in the food, pharmaceutical, cosmetic and materials industries.

1 Lycopene preparation methods

1.1 Lycopene solid inclusion complex preparation methods

Lycopene solid inclusion complexes are usually in the form of powders, granules and tablets with dextrin, starch and the like as the carrier. Lycopene solid inclusion complexes can be prepared using chemical solvent methods and physical milling methods.

1.1.1 Preparation of lycopene inclusion complexes by the solution method

The solution method involves mixing the object with the carrier substance, dissolving it, stirring at a specific temperature for a certain period of time, and then centrifuging and settling or performing other separation operations to obtain the product. This method includes the saturated solution method and the ultrasonic solvent method. Wang Shaofeng et al. [17] used lycopene crystals and β-cyclodextrin as raw materials (molar ratio 1:200) to prepare lycopene complexes using the saturated solution method, with an encapsulation rate of 71.87%. Jin Xueyuan et al. [18] used the ultrasonic solution method to improve the preparation process of the lycopene β-cyclodextrin complex, the encapsulation rate of the complex reached 73.60%; and Lian Xiaohong et al. [19] optimized the preparation process of lycopene-β-cyclodextrin complexes by the solution method to prepare lycopene complexes, and the encapsulation rate can reach 91.04%.

1.1.2 Preparation of lycopene complexes by grinding

Lycopene-dextrin complexes can also be prepared by the milling method. The milling method involves mixing the core material to be encapsulated with the wall material, adding water or other solvents, and then grinding the mixture until it becomes a paste. The resulting preparation is in the form of a lump or powder. Currently, the milling method is mostly used to prepare lycopene-dextrin complexes using different cyclodextrins. Andrea et al. [23] mixed α-cyclodextrin (α-CD) β-cyclodextrin (β-CD) were mixed with lycopene and ground separately to prepare orange-white complexes. Yang Kun et al. [24] used the grinding method to prepare a lycopene-2-hydroxypropyl-β-cyclodextrin (2-HP-β-CD) complex. An Cuicui [25] and others mixed and ground β-cyclodextrin, hydroxypropyl-β-cyclodextrin and lycopene oleoresin (15.00% content) were mixed and ground to prepare lycopene mixed cyclodextrin complex tablets.

1.2 Method for preparing lycopene liposomes

1.2.1 Preparation of lycopene liposomes by spray cooling

Lycopene liposomes can be prepared by spray cooling. Spray cooling involves atomizing a large amount of molten lipids emulsified with a core material to form droplets, which solidify rapidly upon contact with cold air or nitrogen without the need for additional processing [26]. Spray cooling is convenient and economical for producing particles. In addition, spray cooling does not require high temperatures and can encapsulate heat-sensitive ingredients (such as lycopene).

Spray-cooling preparations are already widely used in the food industry. They were first used to prepare preparations such as vitamins, minerals, enzymes, peptides and free amino acids [27]. UmurOnala [28] used methyl palmitate, low-melting point wax and riboflavin as raw materials to prepare liposomes by spray cooling. and the particle size was 18.3±6.4 μm, which was easily absorbed by the larvae of fish. Pelissari et al. [29] used spray cooling to prepare lycopene preparations. Lycopene nanolipid preparations were prepared using shortening (cottonseed oil, soybean oil and palm oil) and lycopene oil solution as raw materials. It was found that the crystal structure of these liposomes is non-uniform. This heterogeneous crystal structure can prevent lipid recrystallization and promote the release of lycopene from the particles, which is beneficial for its digestion and absorption in the body.

1.2.2 Preparation of lycopene liposomes by the film method

Lycopene liposomes can be prepared using the film method. The film method involves dispersing and dissolving a membrane material in a round-bottomed flask using ultrasound. After removing the organic solvent by rotary evaporation, a lipid membrane forms on the round-bottomed flask. After adding the core material and continuing to hydrate by rotary evaporation, the lipid membrane peels off the round-bottomed flask to form liposomes [30].

Lycopene liposomes can be prepared using the film method. Phospholipids and sterols are often used as membrane materials. Fan Yuanjing [31] and others used lecithin, cholesterol and lycopene as raw materials and trichloromethane as a solvent to prepare lycopene nanoliposomes using the film method. It was found that the formed liposomes had the characteristics of small particle size, good water solubility and good bioavailability. Some studies have also used complex lipids as raw materials to prepare lycopene liposomes. Tan [22] et al. used lycopene and egg yolk phosphatidylcholine as raw materials, chloroform as a solvent, and a thin-film method to prepare lycopene liposomes. It was found that when the initial concentration of lycopene was 0.25% to 0.75%, the entrapment rate of the liposomes was higher than 80.00%, while beyond this range, the value decreases significantly, which is related to the oxidative loss of lycopene due to the lack of protective conditions during the preparation process.

1.3 Lycopene microcapsule preparation methods

1.3.1 Spray drying method for preparing lycopene microcapsules

Lycopene microcapsules can be prepared by spray drying. Spray drying is a method of drying by atomization, in which fluid materials (solutions, dispersions and pastes) are broken down into small droplets in the presence of hot air to remove water to obtain a dry powder [20]. This method is commonly used to prepare microencapsulated preparations, such as anthocyanin microcapsules, carotene microcapsules and lycopene microcapsules.

The spray drying method is often used to prepare lycopene microcapsules, with β-cyclodextrin and modified starch as the wall material. Itaciara [21] et al. used β-cyclodextrin and lycopene crystals (molar ratio 1:4) as raw materials to prepare lycopene microcapsules by spray drying. The study found that the encapsulation rate of this microcapsule was 94.00% to 96.00%. Rocha [20] et al. used modified starch as the wall material and 10.00% lycopene oleoresin as the core material to prepare microcapsules by spray drying. It was found that when the proportion of lycopene in the core material was 5.00%, the microcapsules had a maximum encapsulation rate of 29.00%. Other studies have used a variety of materials to encapsulate lycopene, such as Shu Bo [32], who used gelatin and sucrose as wall materials and lycopene oleoresin as the core material to prepare lycopene microcapsules using spray drying. It was found that the encapsulation rate of such microcapsules was 44.33%.

In addition, because lycopene is not water-soluble, an emulsifier was added during the preparation of the lycopene emulsion to ensure better dispersion. Jing Siqun [33] used β-cyclodextrin and modified starch as wall materials, a single coating of lycopene microcapsules as the core material, and monoammonium succinate and soy lecithin (1:1) as emulsifiers to spray-dried to obtain double-coated lycopene microcapsules. Studies on the in vitro release of lycopene from single- and double-coated microcapsules have found that double-coated microcapsules have better sustained release than single-coated lycopene microcapsules.

1.3.2 Preparation of lycopene microcapsules by complex coacervation

Lycopene microcapsules can be prepared by complex coacervation. The composite coacervation method is to adjust the pH or lower the temperature of the system after the raw materials are combined to allow them to settle, thereby obtaining microcapsules. This method requires a mild temperature, which can reduce the oxidative degradation of lycopene during preparation. Silva [34] et al. used gelatin, pectin and lycopene as raw materials to prepare microcapsules by the composite coacervation method, and found that when the pH was 3.0, the agglomeration effect was optimal and the product entrapment rate was greater than 89.50%. Rocha-selmi[35] et al. prepared lycopene microcapsules using the composite coacervation method, with an entrapment rate of greater than 93.08%. The yield of the microcapsule preparation prepared by this method was better than that of the spray drying method, which is related to the loss of lycopene due to the high temperature of the spray drying process.

1.4 Lycopene microemulsion preparation method

Lycopene microemulsions are mostly prepared using the solution method. Salvia [36] and others used a phosphate buffer, corn oil, Tween and tomato juice as raw materials to prepare lycopene microemulsions using the solution method. The mixed raw materials were homogenized at high pressure to obtain nano-microemulsions. The lycopene content in this microemulsion preparation was low (<0.10%); Zhao Guanghua et al. [37] emulsified lycopene, edible oil, Tween 80 and glycerin were mixed and emulsified to prepare lycopene microemulsion, and the lycopene content in the obtained lycopene microemulsion was 0.30%; while Yan Shengkun et al. [38] used high-purity lycopene (90.00%), medium-chain triglycerides, Tween 40 and ethanol as raw materials to prepare lycopene microemulsion using the solution method, The lycopene content in the microemulsion can reach 2.50%.

Lycopene microemulsion preparations prepared by the solution method generally have good solubility and water dispersibility, and the preparation materials are readily available at a low cost. However, the preparation process by the solution method is time-consuming. For example, Wang Shaofeng et al. [17] obtained lycopene β-cyclodextrin inclusion complexes only after 12 h of refrigeration and precipitation.

1.5 Lycopene microparticle preparation method

Lycopene microparticles were prepared by combining supercritical CO2 with supercritical fluid enhanced solution dispersion (SEDS). The principle is to dissolve the solute in an organic solvent to form a solution, and use the mutual solubility of the organic solvent and supercritical fluid to rapidly promote the precipitation of the solute in the form of particles [39]. E. Franceschi [40] and others used supercritical CO2 in combination with the SEDS precipitation method to prepare β-carotene particles; Hazuki Nerome [41] and others prepared lycopene-dextrin complexes by spraying a solution of lycopene and β-cyclodextrin in a supercritical CO2 stream. Lycopene particles prepared in this way can protect lycopene from oxidation while also making the particles small and uniform, thus providing the advantages of high stability and high lycopene content.

2 Stability of lycopene preparations

2.1 Stability of lycopene complexes

Most lycopene preparations are prepared using cyclodextrin as the wall material. The principle is to use the rigid cavity in the molecular structure of cyclodextrin to encapsulate the guest molecule. Lycopene complexes can protect lycopene from oxidation and improve its stability. In addition, β-cyclodextrin is easily hydrated with water to form a hydrate, which can improve the solubility of lycopene.

Lycopene inclusion compound formulations can enhance the stability of lycopene. Lian Xiaohong [19] studied the storage stability of the prepared inclusion compounds. After being stored under aerobic conditions for 8 days, all the lycopene in the lycopene crystals was lost, while the retention rate of lycopene in the microcapsules was 52.28%. This indicates that the formation of inclusion compounds is beneficial to the stability of lycopene. Jin Xueyuan [18] studied the storage stability of lycopene in lycopene-β-cyclodextrin complexes prepared by the method described above. He found that the retention rate of lycopene was as high as 92.20% after 60 days of storage under normal room temperature conditions, indicating excellent stability of lycopene in this complex. Pai Yufen [42] prepared lycopene-encapsulated tablets and studied the stability of the lycopene-encapsulated tablets and lycopene crystals. It was found that the lycopene-encapsulated tablets had good light and heat stability compared with lycopene crystals. In addition, the lycopene-encapsulated tablets improved the solubility of lycopene, which is beneficial to the absorption and utilization of lycopene in organisms.

2.2 Stability of lycopene liposomes

Nano-liposome is a nanoparticle formed by one or more layers of lipids encapsulating a small molecule drug, with an orderly arranged bilayer structure. Liposomes have the advantages of being non-toxic, having good biocompatibility and being easy to target [43]. Applying this technology to the research on the preparation of lycopene dosage forms can improve the stability and solubility of lycopene, which is positive for improving the bioavailability of lycopene.

Lycopene nanoliposomes are nanoparticles formed by encapsulating lycopene in lipids. After being encapsulated in lipids, the stability of lycopene is enhanced. Liu Huixiao et al. sealed the prepared lycopene nanoliposomes in a bottle and stored them in a constant temperature incubator away from light for 30 days. It was found that the retention rate rapidly decreased to 85.00% in the first 10 days of storage, However, the retention rate decreased slowly in the latter 20 days, maintaining at about 80.00%, which indicates that lycopene nanoliposomes exhibit good storage stability during short-term storage [44]. Pelissari et al. studied the degradation kinetics of the prepared lycopene nanoliposomes and found that the use of shortening combined with gum arabic can result in nanoliposomes with good stability. However, the degradation rate of these liposomes reached 60.00% after 90 days of storage, indicating that lycopene liposomes have limited effect on improving the stability of lycopene. This is related to the fact that the chain length of lycopene is too long, resulting in incomplete encapsulation by lipids [29].

2.3 Stability of lycopene microcapsules

Microcapsules are made by embedding small molecules or other core materials with natural or synthetic polymeric materials with encapsulation functions as wall materials. They are available on the market in the form of hard capsules and soft capsules. Lycopene microcapsule preparations can improve the stability of lycopene and enhance its solubility, which is of great significance for the application of lycopene in the food and pharmaceutical industries.

Lycopene microcapsules can improve the stability of lycopene. Lin Weiting [45] and others used whey protein isolate and the Maillard reaction product of xylooligosaccharides as wall materials to prepare lycopene microcapsules. A study of the retention rate of lycopene in the microcapsules found that after 24 days of storage at 4 °C in the dark, the retention rate was 78.25%, and after 24 days of storage at room temperature in the dark, the retention rate was 47.91%, while the lycopene outside the capsule was completely lost under both conditions, indicating that the stability of lycopene was greatly improved after microencapsulation. Shu et al. [46] prepared lycopene microcapsules using gelatin and sucrose as wall materials, and found that the lycopene in these microcapsules exhibited good stability. However, some results show that microencapsulation of lycopene does not significantly enhance its stability. Silva [34] et al. prepared lycopene microcapsules with a good encapsulation rate using a complex coacervation method. The stability of these microcapsules was studied, and it was found that when lycopene was stored at 10 °C and 25 °C, there was a linear degradation loss of lycopene, with an average loss of 14.00% per week.

2.4 Stability of lycopene microemulsions

Microemulsions were first proposed by Schulman in 1943. A microemulsion is a thermodynamically stable and homogeneous oil-water mixed system, generally formed by two immiscible surface liquids under the action of a surfactant interfacial film. Microemulsions can be divided into O/W, W/O and bicontinuous types according to the different oil-water ratios [47]. The use of emulsifiers guides the formation of lycopene with lipids, water, etc., to form a homogeneous dispersion system, i.e., a lycopene microemulsion. This food-grade microemulsion containing lycopene and having biocompatibility can exhibit good solubility in aqueous and non-polar media, and can improve the bioavailability of lycopene to promote absorption by the organism.

Yan Shengkun et al. prepared lycopene microemulsions and studied the effects of factors such as different temperatures, different emulsifiers, different co-emulsifiers, and different oil varieties on the stability of the microemulsion system. The study found that when medium-chain triglycerides, Tween 40, and ethanol are used as raw materials, the stability of the lycopene microemulsion is better when stored at 37 °C, and the lycopene content can reach 2.50%. The product has a natural color and good stability. It can be mixed with water in any ratio and has broad application prospects [38]. Quan Lichan [48] and others studied the factors affecting the stability of lycopene in water-dispersible microemulsions and found that 4 h of light exposure can completely degrade lycopene. Temperature is negatively correlated with lycopene stability, and alkaline conditions are more conducive to maintaining lycopene stability. Iron and and copper ions are detrimental to lycopene stability. This indicates that lycopene should be stored in the dark, at low temperatures, and in alkaline conditions, and that iron and copper containers should be avoided.

3 Other properties of lycopene preparations

3.1 Bioavailability of lycopene preparations

The proportion of a pharmaceutical preparation that reaches the site of action via the body's circulatory system under normal physiological conditions is known as the bioavailability. Different processing methods can affect the bioavailability of lycopene. Tang et al. [49] showed in human feeding intervention experiments that the bioavailability of several types of tomato products is: tomato sauce > tomato juice > tomato. The bioavailability of lycopene varies depending on the type of preparation. Zhu Jinfang [50] and others studied the intestinal absorption characteristics of lycopene liposomes and lycopene raw materials. The results showed that lycopene in lycopene liposomes is more easily absorbed in the small intestine, which indicates that the liposome dosage form increases the bioavailability of lycopene, which is consistent with the research of Colle [51] and others. Hu Linlin prepared lycopene nanocapsules and found that the bioavailability of this dosage form could reach 72.50%. Kong Xianghui et al. [52] studied the bioavailability of self-made lycopene liposomes and found that the bioavailability of lycopene liposomes was 154.42%, which was close to the 205.03% of commercially available lycopene microcapsules, using oil-soluble lycopene as the reference dosage form.

3.2 Antioxidant activity of lycopene preparations

The antioxidant activity of lycopene is one of its important biological activities. In vivo antioxidant animal experiments on lycopene crystals have shown that lycopene crystals can significantly increase the activity of superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) in mice and significantly reduce the content of malondialdehyde (MDA), indicating that lycopene crystals have antioxidant activity [53,54]. Lycopene still has antioxidant activity after formulation. Liu Yong et al. [55] conducted an in vivo antioxidant experiment on lycopene soft capsules prepared by humans, and found that lycopene soft capsules can increase the SOD and GSH-Px activities in human serum, indicating that this dosage form has antioxidant properties. In addition, some dosage forms may exhibit stronger antioxidant activity than lycopene raw materials. Chai Xingxing et al. [56] studied the in vitro antioxidant activity of lycopene nanodispersions and found that the IC50 values for the scavenging of H2O2 by lycopene nanodispersions and lycopene tetrahydrofuran solutions were 29.70 μg/mL and 34.42 μg/mL, respectively, indicating that lycopene nanodispersions have better antioxidant activity.

3.3 Configuration transformation and stability of lycopene preparations

Lycopene has poor structural stability and temperature affects its configuration. Li Hong et al. [57] found that the combination of heat reflux and recrystallization can be used to convert all-trans lycopene into an isomer with a cis proportion of 78.00% to 85.00%. During the preparation of lycopene preparations, the lycopene configuration may undergo a change from the trans configuration to the cis configuration. Wang Xiaowen et al. [58] identified the change in lycopene configuration in a lycopene microemulsion preparation and found that during the preparation of the microemulsion, all-trans lycopene can isomerize to four different structures of cis lycopene (x1-cis, x2-cis, 9-cis and 13-cis); further studies on the stability of cis-lycopene and trans-lycopene in this preparation found that when the microemulsion was stored at 25 °C for 40 days, the retention rate of cis-lycopene was 47.9%, while the retention rate of trans-lycopene was as high as 91.00%, indicating that lycopene has poor conformational stability during preparation of microemulsions and that its stability is also reduced after conversion to the cis configuration.

4 Research outlook

Lycopene preparations can enhance the stability of lycopene. At the same time, lycopene preparations retain the good antioxidant activity of lycopene and have better bioavailability. However, the existing lycopene preparations still have the following problems: (1) microcapsules and complex preparations are not suitable for use in food systems; (2) some preparations contain organic solvent residues; (3) microemulsion preparations have strict storage and transportation conditions and are restricted in their use in the food industry; (4) there is still degradation and loss of lycopene during preparation of the preparations. Therefore, in order to enhance the stability of lycopene, improve its bioavailability and solve the problems with the existing dosage forms, in the future development of lycopene preparations: (1) safe and edible carriers such as starch, protein and edible oils and fats should be selected to complex with lycopene in order to expand the application of the preparations in the food system; (2) gentle and efficient methods such as the composite coacervation method, supercritical CO2 extraction method combined with the SEDS precipitation method, etc., to reduce the loss of lycopene during preparation and the residual organic solvent in the preparation. A lycopene preparation with good safety and which is convenient and economical can be prepared, thus promoting the wider application of lycopene preparations in the food, biological, pharmaceutical, materials and other industries.

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