Associate Professor Tang Wenting from Qingdao Agricultural University published research results on active peptide liposome precursors in Food Chemistry

Research background and purpose

Functional polypeptides have promoting effects on human health, such as anti-fatigue, antioxidant, anti-cancer, antimicrobial, anti-hypertensive, cell-modulating and immunomodulatory activities
.
However, food processing and digestion may affect its efficacy, which limits its application in the field of functional foods
.
Therefore, it is necessary to construct a suitable carrier to protect the functional polypeptide from the external environment
.
Liposome precursors are solid powders with good flow properties that can be hydrated to form liposomes
.
Can encapsulation of functional peptides in liposome precursors effectively enhance peptide stability and maintain its biological activity? Accordingly, Wang Fuli, Pu Chuanfen, Tang Wenting*, Sun Qingjie and others from the School of Food Science and Engineering, Qingdao Agricultural University constructed walnut peptide liposome precursors with sucrose, trehalose and mannitol as carriers and lyoprotectants.
The walnut peptide liposome precursor without freeze-drying protective agent was used as a control, and its physical and chemical properties such as scale and morphology were analyzed; the antioxidant and antibacterial activities of the three walnut peptide liposome precursors were tested and compared; The in vitro digestion and release behaviors of walnut peptide liposome precursors in simulated gastrointestinal fluid were investigated
.
This work provides a reference for the development of bioactive peptide delivery systems based on liposome precursors
.
The results were published in the journal Food Chemistry
.

Main research content

01Physicochemical properties of walnut peptide liposome precursor

The average particle size of walnut peptide liposome precursors with sucrose, trehalose and mannitol as freeze-drying protective agents/carriers is about 200 nm, the absolute value of zeta potential is greater than 30 mV, and the encapsulation efficiency is higher than 60% , indicating good stability after hydration
.
The walnut peptide liposome precursors with sucrose, trehalose and mannitol as lyoprotectants/carriers were observed by transmission electron microscopy and atomic force microscopy to be spherical, with a smooth surface without dents
.
Spectral analysis showed that walnut peptides could form hydrogen bonds with lyoprotectants/carriers and phospholipids
.
The addition of lyoprotectant/carrier can enhance the ordered alignment of the bilayer and reduce membrane fluidity
.

02Environmental stability of walnut peptide liposome precursors

The walnut peptide liposome precursor was stored at 4 °C for 25 d in the dark
.
The absolute value of the zeta potential of all samples was >30 mV
.
Overall, the system is stable
.
After storage for 25 d, a significant increase in particle size was observed at both 4 ℃ and 25 ℃; the particle size change at 25 ℃ was more significant than that at 4 ℃
.
The walnut peptide liposome precursor with sucrose, trehalose and mannitol as lyoprotectant/carrier exhibited good stability at pH 2 and 9, while at pH 3, 4, and 5 , the electrostatic repulsion decreases and the particle aggregation increases
.
The absolute potential is lowest at pH = 3, where the aggregation effect is also most pronounced
.

03Antioxidative effect of walnut peptide liposome precursor

After being sealed and stored at 4 ℃ for 25 d, compared with the freshly prepared samples, the DPPH free radical scavenging rate of walnut peptide liposome precursors with sucrose, trehalose and mannitol as carriers decreased by 28.
6%, 19.
7% and 30.
7%, respectively.
% and 24.
4%
.
The DPPH free radical scavenging rate of the positive control ascorbic acid decreased by 4.
5% after 25 days of storage, but still maintained a high antioxidant capacity (> 90%)
.
Compared with the free walnut peptide (DPPH free radical scavenging rate was 23%), the DPPH free radical scavenging rate of the four walnut peptide-loaded liposome precursors remained at about 60.
0% after storage for 25 d
.
Therefore, the walnut peptide liposome precursor showed a good antioxidant effect during the 25 d storage period
.

The antioxidant activity of the four walnut peptide liposome precursors was further analyzed with iron reducing power as an index
.
The newly prepared sucrose-supported walnut peptide liposome precursor has stronger iron reducing ability than other liposome precursor samples
.
There was no significant difference between the peptide-loaded liposome precursors stored for the same time, indicating that the addition of the carrier had no effect on the iron-reducing ability
.
At the same time, it was also found that the antioxidant capacity of walnut peptide was lower than that of walnut peptide liposome precursor, which may be related to the antioxidant activity of liposome components
.
There was no significant difference in antioxidant activity between the walnut peptide liposome precursor and the three carrier-containing liposome precursors, indicating that the addition of the carrier did not affect the antioxidant activity of the liposome precursor
.

04Antibacterial properties of walnut peptide liposome precursors

The four walnut peptide liposome precursors showed antibacterial activity against Escherichia coli and Staphylococcus aureus
.
The inhibition zone sizes of walnut peptide liposome precursor, sucrose, trehalose and mannitol as carrier against Escherichia coli and Staphylococcus aureus were 16.
7±0.
31 and 16.
3±0.
21 mm, respectively , 20.
6±0.
67 and 19.
3±0.
42 mm, 17.
3±0.
30 and 17.
7±0.
25 mm, and 22.
3±0.
55 mm and 18.
6±0.
31 mm
.
Combined with the results of the minimum inhibitory concentration, the walnut peptide liposome precursor, the walnut peptide liposome precursor with sucrose as the carrier, and the walnut peptide liposome precursor with trehalose as the carrier were more effective against Gram-positive bacteria, while The walnut peptide liposome precursor with mannitol as carrier showed higher antibacterial activity against Gram-negative bacteria
.

05Simulated digestion test of walnut peptide liposome precursor in different stages

After 60 min of simulated gastric digestion, the average particle size of the four liposome precursor samples was not significantly different from that before digestion
.
The absolute value of the potential of gastric digestive products was lower than the initial value, but did not affect the stability of PDI
.
After entering the simulated intestinal digestion stage, the absolute values ​​of particle size, PDI, and zeta potential increased, and the structure of liposomes was disrupted, leading to aggregation, fusion, and increased particle size
.

The above conclusions were further confirmed by atomic force microscopy
.
Compared with the samples without carrier, most of the liposome precursors in the gastric phase were intact, while the liposome vesicle structure was damaged and aggregated after 120 min of simulated intestinal digestion
.
The release of free fatty acids from the four samples increased sharply within the first 10 min of simulated intestinal digestion; after 120 min, the free fatty acid release of walnut peptide liposome precursor, sucrose, trehalose and mannitol as carriers The fatty acid release rates were 45.
8%, 46.
7%, 43.
2% and 55.
1%, respectively
.

Main conclusions

About the corresponding author

Associate Professor Tang Wenting

School of Food Science and Engineering, Qingdao Agricultural University

Associate Professor Tang Wenting, master tutor, visiting scholar at Western Research Center of USDA, mainly engaged in grain and oil food processing and research on the stabilization and slow-release technology of functional food ingredients

Introduction of the first author

Wang Fuli Postgraduate

School of Food Science and Engineering, Qingdao Agricultural University

Wang Fuli, a 2019 graduate student in Food Processing and Safety, School of Food Science and Engineering, Qingdao Agricultural University