Zinc-binding mechanism of synthetic oyster peptides and their taste sensory characteristics: Insight into umami and saltiness perception

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Zinc-binding mechanism of synthetic oyster peptides and their taste sensory

characteristics: Insight into umami and saltiness perception

Xuening Yu

, Guang Li

a,b

, Xiaoyang Liu

a,*

, Xiangbo Zeng

, Fawen Yin

, Deyang Li

Ningbo Qin

, Dayong Zhou

SKL of Marine Food Processing & Safety Control, National Engineering Research Center of Seafood, Collaborative Innovation Center of Seafood Deep Processing,

Liaoning Province Key Laboratory for Marine Food Science and Technology, School of Food Science and Technology, Dalian Polytechnic University, Dalian 116034,

China

School of Food and Biological Engineering, Hefei University of Technology, Hefei 23060, China

ARTICLE INFO

Keywords:

Zinc-binding synthetic peptide

Chelation mechanism

Molecular docking

Receptors

Taste mechanism

ABSTRACT

Oyster-derived synthetic peptides (ILAPPER and DGKGKIPEE) formed IZn and DZn by chelating with zinc ions

(97.8 % and 98.9 %), resulting in conformational changes. Molecular docking and NMR analysis revealed that

carboxyl oxygen at C-terminal of Arg-7 and Glu-9, as well as amide bond oxygen atoms of Pro-5 and Ile-6, served

as zinc-chelating sites. DZn exhibited superior in vitro digestion stability and absorption characteristics (21 %)

compared to IZn (18.2 %). The protein expression levels of ZnT1 and ZIP4 were 35.3 % and 52.7 % for IZn, and

28.5 % and 53.8 % for DZn. The synthetic peptides eliminated bitterness (OPH: 3.11; I: -0.93; D: −0.8) while

enhancing salty (I: 6.77; D: 6.25) and umami (I: 2.11; D: 1.81) taste proles. Additionally, peptides I and D

primarily interacted with Glu, Arg, and Gln residues of TIR1, TIR3, TMC4, and TRPV1 receptors. Hydrogen

bonding facilitated interactions with umami taste receptors, whereas hydrophobic interactions were linked to

saltiness perception.

1. Introduction

Zinc plays a crucial role in the synthesis of various enzymes and

serves as an essential catalytic cofactor. A deciency in zinc can impair

the human immune system (Li et al., 2019); therefore, maintaining zinc

homeostasis is vital. Food-derived peptides can function as carriers for

dietary zinc, enhancing the intestinal absorption of zinc ions. Due to

their structural specicity, synthetic peptides can often be more pre-

cisely localized using advanced techniques such as frontier orbital

analysis and molecular docking to identify metal ion binding sites.

Moreover, synthetic peptides generally exhibit a higher binding capacity

for metal ions than enzymatic hydrolysates and demonstrate greater

retention rates. As a result, they are promising raw materials for

developing functional foods aimed at promoting metal ion absorption.

The amino acid composition and sequence within peptide structures

signicantly inuence their zinc-binding capacity (Zhu et al., 2015).

Specic metal-binding ligands, such as histidine, cysteine, aspartic acid,

glutamic acid, serine, and phosphorylated serine, can form soluble zinc

complexes, thereby improving mineral absorption and preventing the

formation of insoluble complexes with phytates (Udechukwu et al.,

2018). For instance, a synthetic peptide derived from sea cucumbers

(WLTPTYPE) was shown to enhance zinc absorption and remain stable

in the gastric environment, with the zinc-binding site identied on the

carboxyl group of glutamic acid (Wang, Sun, et al., 2022). Thus, un-

derstanding the underlying mechanisms of zinc–peptide interactions is

critical for characterizing peptide structures and evaluating their po-

tential to enhance zinc absorption in the gastrointestinal tract. Unlike

conventional methods for identifying binding sites, molecular docking

enables a more intuitive visualization of binding modes between pep-

tides and metal ions through computational modeling (Yu et al., 2023).

In one study, the zinc-binding geometry of the Ala-Ser-His (ASH) peptide

from rapeseed was analyzed using density functional theory, revealing a

bridge bond (O21-Zn41-O32) between the serine and histidine residues

(Wang et al., 2023). Similarly, chickpea-derived peptides participated in

zinc chelation via the C-terminal carboxyl group, the nitrogen atom in

the amino side chain, the imidazole ring of histidine, and the N-terminal.

Molecular docking results for hydrophobic oyster peptides indicated

that aspartic acid, glutamic acid, and leucine may also play key roles in

* Corresponding author.

E-mail address: liuxiaoyang0213@126.com (X. Liu).

Contents lists available at ScienceDirect

Food Chemistry

journal homepage: www.elsevier.com/locate/foodchem

https://doi.org/10.1016/j.foodchem.2025.145077

Received 28 November 2024; Received in revised form 24 April 2025; Accepted 4 June 2025

Food Chemistry 490 (2025) 145077

Available online 7 June 2025

zinc binding (Wang et al., 2021).

Currently, there is a growing appreciation for the sensory experience

of food, accompanied by an increasing focus on health. As a result, taste-

active peptides that enhance umami and mellowness, as well as sodium

salt substitutes, have become key areas of research. Molecular docking

has been widely used to explore interactions between food components

and human receptors, offering a valuable tool for understanding the

mechanisms underlying the binding of avorful compounds to taste

receptors (Dang et al., 2014). Among these, T1R1/T1R3 receptors are

considered the primary umami receptors involved in interactions with

umami peptides (Zhang et al., 2023). Transmembrane channel-like

protein 4 (TMC4), a channel protein, is believed to play a role in low-

salt (low NaCl concentration) taste perception, particularly in taste

cells, where it may regulate sodium ion (Na

) ow. TMC4 is frequently

utilized in studies exploring the mechanisms of salty taste perception

(Zhang et al., 2024). Transient receptor potential vanilloid 1 (TRPV1), a

non-selective ligand-gated cation channel, also contributes to salt taste

perception. It is activated by high concentrations of NaCl and protons,

triggering intracellular signal transduction (Le et al., 2022). Interest-

ingly, unlike TMC4, TRPV1 is also responsive to spicy stimuli, which can

alter taste receptor or channel protein conformations, modulating taste

bud sensitivity through neurotransmitter production. When multiple

taste sensations occur simultaneously, such stimulation can enhance

salty avor perception at certain concentrations (He et al., 2023).

Therefore, exploring the taste characteristics of peptides and their

interaction mechanisms with taste receptors is of signicant interest.

Metal supplements that contain inorganic salts often impart a

metallic aftertaste (Ecarma & Nolden, 2021). However, peptide–metal

chelation can reduce this undesirable avor. Evaluating the taste char-

acteristics of peptides, especially synthetic ones, is essential, as the

amino acid composition, sequence, and three-dimensional structure can

strongly inuence taste. A deeper understanding of synthetic peptide

structures allows for more precise analysis of the mechanisms behind

taste perception.

In this study, two newly identied absorbable peptides (I: ILAPPER,

D: DGKGKIPEE) derived from oyster protein hydrolysate (OPH) were

used to synthesize zinc–peptide complexes (IZn and DZn). This repre-

sents the rst attempt to investigate both the binding and taste mecha-

nisms of synthetic peptides and their zinc chelates with intestinal

absorption potential. The properties of peptides I and D, as well as their

corresponding complexes IZn and DZn, were characterized using UV

spectroscopy, circular dichroism, FTIR, particle size analysis, zeta po-

tential measurements, Raman spectroscopy, scanning electron micro-

scopy (SEM), and differential scanning calorimetry (DSC).

The novelty of the binding mechanism analysis lies in the combi-

nation of molecular orbital bandgap analysis, molecular docking, and

validation through two-dimensional nuclear magnetic resonance (2D-

NMR). Digestive stability and soluble zinc content in the supernatant of

IZn and DZn were assessed. Furthermore, their absorption efciency was

evaluated using the everted rat intestinal sac model and immunohisto-

chemical analysis. For the rst time, the taste proles of I, IZn, D, DZn,

OPH, and OPH-Zn were examined using an electronic tongue to evaluate

their potential as oral zinc supplements. Finally, molecular docking was

applied to explore zinc–peptide interactions, peptide absorption mech-

anisms, and the binding behavior of peptides and hydrolysates with taste

receptors on the tongue. This study provides a theoretical foundation for

the development of marine-derived peptide–zinc complexes as func-

tional food ingredients.

2. Materials and methods

2.1. Materials

The synthetic peptide (ILAPPER, DGKGKIPEE) was synthesized from

Shanghai Apeptide Biotechnology Co., Ltd. (Shanghai, China). Zinc

sulfate purchased from Shanghai Macklin Biochemical Technology Co.,

Ltd. (Shanghai, China). Chromatographic methanol purchased from

Shanghai Macklin Biochemical Technology Co., Ltd. (Shanghai, China).

Pepsin and trypsin were purchased from Sigma Aldrich (Merck KGaA,

Darmstadt, Germany). Hydrated chloral purchased from Shanghai

Macklin Biochemical Technology Co., Ltd. (Shanghai, China). TSQ zinc

ion uorescent probe was purchased from AAT Bioquest, Inc. (Pleas-

anton, CA, USA).

2.2. Preparation of peptide I&D and IZn&DZn

On the basis of previous experiments, the absorbable peptides of

oyster hydrolysates were identied, and two peptides (Peptide I&D)

were selected for synthesis (Liu et al., 2023). To further investigate the

binding mechanism and effects of Peptide I&D on zinc ions, a zinc sul-

fate solution concentration of 400

M was prepared. The concentration

of peptide I&D was set at 2 mg/mL. The two solutions were mixed in a

1:1 (v/v) ratio and placed in a water bath. The incubation time in the

water bath was 30 mins at a temperature of 40 ◦C.

2.3. Determination of zinc-chelating capacity

200

L peptide solution (I&D) was uniformly mixed with 200

L zinc

sulfate solution and allowed to react at 40 ◦C for 30 mins. Following the

reaction, 20

L of 2 mM solution of 4-(2-pyridylazo) resorcinol was

added as previously reported (Jakob et al., 2000), and the optical den-

sity (OD) at 500 nm was measured. The zinc-chelating capacity (%) was

calculated as follows:

Zinc−chelating capacity (%) = [( ODzinc −ODpeptide −ODsample)/ODzinc ]

×100

where OD

zinc

represented total amount of zinc, OD

peptide

represented

samples only contained Peptide I or D, OD

sample

represented IZn and

DZn.

2.4. Determination of UV–vis spectra

I, IZn, D, and DZn were dissolved in deionized water, where the

concentration of peptides in each group was 0.1 mg/mL. Ultraviolet-

visible photometers (Lambda 35, Perkin Elmer Instruments Co, Ltd.,

Waltham, Massachusetts, USA) were used for full-wavelength scanning

in the wavelength range of 190 to 450 nm.

2.5. Determination of circular dichroism (CD)

I, IZn, D, and DZn were dissolved in deionized water at a peptide

concentration of 0.2 mg/mL and analyzed using CD spectroscopy

(JASCO J-1500, JASCO, Tokyo, Japan). Nitrogen purging was main-

tained throughout the test at room temperature. The circular resolution

was set to 0.2 nm, with a data pitch of 1 nm, and the thickness of the

quartz tube used was 1 mm.

2.6. Measurement of FTIR

I, IZn, D, and DZn (1 mg each) were mixed with 50 mg of dry KBr.

The resulting sample was then laminated and analyzed using Fourier

infrared spectroscopy (Spectrum 2, Perkin Elmer Instruments Co., Ltd.,

Waltham, Massachusetts, USA). A spectrum was recorded over the range

of 4000 to 400 cm

−1

, with a resolution set at 4 cm

−1

2.7. Determination of zeta potential and particle size

The average particle size and zeta-potential of I, IZn, D and DZn were

determined by Zeta potential and particle size analyzer (NanoBrook

90plus PALS, Brookhaven Instruments, Nashua, NH, USA). The pH of the

solution was set to 7.5. The experimental group was tested three times.

X. Yu et al.

Food Chemistry 490 (2025) 145077

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