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. 2023 Nov 29;20:101015. doi: 10.1016/j.fochx.2023.101015

Effects of different roasting temperatures on rabbit meat protein oxidation and fluorescent carbon nanoparticle formation

Xue Li a, Yunlong Song b, Lisa Huangfu b, Sheng Li d, Qingyang Meng f, Zhicheng Wu b, Jinggang Ruan b, Jie Tang b,c, Dong Zhang b,c,⁎, Hongjun Li e
PMCID: PMC10740113  PMID: 38144813

Highlights

  • •

    High roasting temperature leads to significant oxidation of rabbit meat protein.

  • •

    Protein oxidation of rabbit meat is accompanied by CNPs formation during roasting.

  • •

    The increase in roasting temperature does not change the elemental composition of CNPs.

  • •

    The carbonization degree of CNPs increases with the increase of roasting temperature.

Keywords: Roasting, Rabbit meat, Oxidation, Fluorescent carbon nanoparticles

Abstract

This study explores the oxidation of rabbit meat proteins and the physicochemical properties of the resulting fluorescent carbon nanoparticles (CNPs) under various roasting temperatures (180, 210, 240, 270, and 300 °C). The determination of sulfhydryl content, along with the results from UV and fluorescence spectroscopy, indicates that the protein structure undergoes changes during the roasting process, and the degree of oxidation shows an increasing trend with rising roasting temperatures. The CNP solution obtained exhibits a typical blue fluorescence. Moreover, as the roasting temperature increases from 180 °C to 300 °C, the relative content of the three elements in CNPs, namely C, N, and O, increases by 12 %, −3%, and −9 %, respectively. The surface of the obtained rabbit meat CNPs contains hydrophilic and polycyclic groups, such as carbonyl, hydroxyl, and amide bonds. Correlation analysis reveals a significant positive correlation between the degree of protein oxidation and the fluorescence intensities of CNPs.

1. Introduction

Roasting is a cooking method that involves subjecting food to high-temperature heating, such as grilling and baking (Bao et al., 2020). It can impart appealing color, unique flavors, and a crispy exterior to meat products, resulting in delightful sensory characteristics (Jin et al., 2021). Rabbit meat is highly favored by many consumers due to its characteristics, including being high in protein, lysine, and digestibility, as well as containing high niacin content, low fat, low cholesterol, and low calories (Li et al., 2018). Despite roasting being a common cooking method for rabbit meat, systematic research on the impact of roasting on the quality characteristics of rabbit meat is relatively limited. Most studies have only focused on the changes in the conventional physicochemical characteristics of rabbit meat.

Rao et al. (2022) investigated the effects of different cooking methods on the edibility, nutritional quality, and volatile flavor compounds of rabbit meat. The results revealed significant differences in the physicochemical characteristics of cooked rabbit meat among various cooking methods. Rabbit meat samples prepared using microwave, roasting, and deep frying exhibited stronger antioxidant activity after in vitro digestion compared with other cooking samples. Abdel-Naeem, Sallam, and Zaki (2021) examined the effects of different cooking methods on the physicochemical characteristics, fatty acid profile, microbial quality, and sensory attributes of rabbit meat. The results indicated that oven roasting was the preferable cooking method for rabbit meat because it obtained the highest sensory scores and exhibited favorable fatty acid composition, lipid oxidation parameters, microbial quality, and nutritional value. Furthermore, other researchers have also investigated the effects of different cooking methods on the physicochemical characteristics of rabbit meat (Rasinska et al., 2019, Siddique et al., 2021).

With the increasing pursuit of a healthy lifestyle and growing awareness of the hazards of chronic diseases (Zhang, Luo, Zhang, Robinson & Wang, 2022), scholars have shown a growing interest in “disease enters by the mouth”. This research includes studying foodborne particles and chemical substances generated from various food processing methods. Scholars have discovered the presence of nanomaterials in heat-processed food. These nanomaterials exhibit excellent water solubility and fluorescence characteristics and are referred to as fluorescent carbon nanoparticles (CNPs). Zhao et al. (2019) discovered the presence of CNPs in roasted pork. Furthermore, through animal experiments, they found that these CNPs were widely distributed in the bodies of mice, with significant accumulations observed in the liver, kidneys, testes, and brain. Song, Song, Guo, and Tan (2022) extracted CNPs from roasted chicken meat and analyzed their biological effects on the digestion of soy protein isolate by gastric protease. The research revealed that CNPs formed a nanoparticle-protein corona structure with gastric protease, which might affect the digestion of soy protein isolate. In addition, other researchers have extracted CNPs from heat-processed meat products and suggested that they might influence biological functions (Cong et al., 2018, Song et al., 2018). However, whether CNPs exist in roasted rabbit meat and whether their formation exhibits temperature dependence remain unexplored to date.

This study aims to investigate the effects of different roasting temperatures on rabbit meat protein oxidation and the formation of CNPs. Additionally, we aim to explore the relationship between protein oxidation and CNPs formation through correlation analysis under various roasting conditions. The ultimate goal is to provide theoretical guidance for selecting the appropriate roasting temperature for rabbit meat, thereby enhancing the nutritional quality and safety of rabbit meat products and improving the economic efficiency of the meat industry.

2. Material and methods

2.1. Materials

The slaughtered rabbits were purchased from Century Baisheng Supermarket (Pixian District, Chengdu, China), the slaughtering method was stick-beating method. The rabbits belonged to the Sichuan White Rabbit breed, with an average weight of 1.3 kg each. After slaughter, the samples were promptly transported to the laboratory within 1 h using a sampling box at approximately 6 °C (80 L, Ningbo Three Ants Outdoor Products Co., Ltd., Ningbo, China). The pH value of the samples was measured to be 5.91 ± 0.04. The rabbit meat used in the experiment came from three rabbits, and the whole experiments were repeated three times.

2.2. Sample handling

The purchased rabbit was segmented, and the bones were removed. Then, it was minced to make rabbit meat patties, each weighing approximately 40 g. Five roasting trays were lined with aluminum foil, and three portions of rabbit meat patties were placed on each tray. After preheating the oven for 30 min, the five roasting trays were placed in five corresponding ovens at temperatures of 180, 210, 240, 270, and 300 °C, and roasted for 30 min. After roasting, the patties were cooled, placed in bags, and labeled. The entire experiment was repeated three times.

2.3. Product yield

The product yield was determined following the method described by Wang et al. (2021). The calculation method for product yield was based on the fresh weight (M1) and roasted weight (M2) of the samples before and after roasting.

Yield(%)=M2M1×100%

2.4. Salt-soluble protein extraction

The extraction of salt-soluble proteins from rabbit meat followed the method used by Ruan et al. (2023). Approximately 30 g of minced rabbit meat was taken and placed in a 250 mL centrifuge tube. Then, 150 mL of 50 mmol/L phosphate buffer solution (PBS) at pH 7.0 was added. The mixture was homogenized (FSH-2A, Shanghai Jipad Instrument Co., Ltd, China) at 10,000 rpm for 1 min and subsequently centrifuged (LC-LX-HLR210D, LICHEN, China) at 4 °C and 4000 ×g for 15 min. The supernatant was discarded, and 150 mL of 50 mmol/L PBS containing 0.6 mol/L NaCl at pH 7.0 was added to the pellet. The mixture was homogenized at 10,000 rpm for 1 min and centrifuged at 4 °C and 4000 ×g for 15 min. The salt-soluble protein extract is the resulting supernatant. The protein concentration was measured using the kit method.

2.5. Sulfhydryl content

The sulfhydryl content was determined based on the method used by Pu et al. (2023). 1 mL of 5 mg/mL salt-soluble proteins was taken and diluted with 9 mL of 0.05 mol/L PBS (8 mol/L urea, 0.6 mol/L NaCl, 0.01 mol/L EGTA, pH 7). Then mixed 3 mL of diluent with 0.4 mL of 0.1 % 2-nitrobenzoic acid and reacted for 25 min in dark at 40 °C. The absorbance of the treated sample solution was measured at 412 nm, and the sulfhydryl content of the salt-soluble protein was calculated based on the molar extinction coefficient.

Sulfhydrylcontentnmolmg=A×10713,600×C,

where A is the absorbance, and C is the salt-soluble protein concentration.

2.6. UV spectroscopy and endogenous fluorescence spectrum

The UV spectroscopy and endogenous fluorescence spectrum were determined following the method of Wu et al. (2023). The UV spectroscopy of the salt-soluble protein was measured using a UV spectrophotometer (1900, Suzhou xiaotianyuan Instrument Equipment Co., Ltd, China). The concentration of the salt-soluble protein was set at 1 mg/mL, and the wavelength range was set from 200 nm to 400 nm. The scanning speed was set at medium, with 1 nm intervals, and the measurement was performed three times. The sample testing temperature was maintained at 25 °C throughout. The fluorescence spectrum of the salt-soluble protein was measured using a fluorescence spectrometer (FLUOROMAX-4cp, HORIBA Jobin Yvon, USA). The concentration of the salt-soluble protein was set at 1 mg/mL, and the temperature was maintained at 25 °C. The excitation wavelength was set at 280 nm, and the emission wavelength was scanned with a 1 nm step, ranging from 290 nm to 450 nm. The slit width was set at 2.0 nm and 1.5 nm for excitation and emission, respectively.

2.7. Fluorescent CNP extraction

The method described by Cong, Bi, Song, Yu, and Tan (2018) was used for the extraction of CNPs. The extraction steps involved leaching (The rabbit meat sample was mixed with anhydrous ethanol in a ratio of 1:2 (w/v), the mixture was stirred in dark for 24 h, and then the mixture was subjected to ultrasonic treatment (SB-5200DTN, Ningbo Xinzhi Biotechnology Co., Ltd, China) for 15 min), filtration (The mixture was filtered to remove larger impurities), concentration (RE-5285A, Shanghai Nenggong Industrial Co., Ltd, China) (The filtrate was concentrated by rotary evaporator at 65 °C, and stopped when the ethanol was completely removed), extraction (The concentrated substance was redissolved in distilled water, then extracted by ethyl acetate for three times, and finally the upper aqueous phase substance was extracted), dialysis (A dialysis bag with a molecular weight of 3,500 Da was used for dialysis), concentration (The dialysate was collected, and the dialysate was concentrated by rotary evaporator at 65 °C), and lyophilization (FDU-1100, Shanghai Jizhou Chemical Technology Co., Ltd, China) (The concentrated dialysate was freeze-dried by a freeze-drying machine, and finally the powdered sample was obtained). The resulting freeze-dried powder sample should be used as soon as possible, or it can be sealed and stored at a low temperature.

2.8. Elemental composition of fluorescent CNPs

The elemental composition of CNPs was determined following the method described by Bi et al. (2017) with slight modifications. An appropriate amount of CNPs was subjected to X-ray photoelectron spectroscopy (XPS) (NEXSA X, Shanghai Yuzhong Industrial Co., Ltd, China) to measure the percentage of C, N, and O elements. The acquired spectrum data were analyzed using XPSPEAK41 software. The C1s, O1s, and N1s peaks were referenced at 285.0, 531.8, and 398.4 eV for peak fitting and quantification of the elemental composition, respectively.

2.9. Fluorescence and fluorescence spectrum

Fluorescence and fluorescence spectrum were measured using a previously described method by Song, Cao, Cong, Song, and Tan (2018). Different CNP powder samples were prepared at a concentration of 1 mg/mL using deionized water. The fluorescence of CNPs was observed under an UV lamp, and its fluorescence intensity was calculated using ImageJ software. For the fluorescence spectrum measurement, 2 mL of each solution was transferred into a quartz cuvette. A fluorescence spectrometer (FLS1000, Shanghai Diguan Industrial Co., Ltd, China) was used to scan the fluorescence spectrum. The excitation and emission slits were set at 5 nm. The excitation wavelength range was set from 300 nm to 420 nm, whereas the emission wavelength range was set from 200 nm to 600 nm. The detection range was set from 200 nm to 700 nm. The scanning speed was set at 1500 nm/min, with a voltage of 400 V and a response time of 2 s.

2.10. Surface structure of fluorescent CNPs

The surface structure of CNPs was characterized using the method referenced from Wang et al. (2017). Fourier transform infrared spectroscopy (FT-IR) (Spectrum Two, Shanghai Shuangxu Electronics Co., Ltd, China) was employed for the characterization. First, 100 mg of dried potassium bromide (KBr) was taken and placed into an agate mortar. The KBr was thoroughly ground under an infrared lamp. Second, the ground KBr was placed into a mold and pressed for 3 min using a press machine at 20 MPa to create a blank background for scanning. Third, 1 mg of CNPs powder was taken and mixed thoroughly with 100 mg of KBr. The pressing procedure described earlier was repeated to create a sample pellet. Finally, the sample pellet was scanned using FT-IR to obtain the Fourier infrared spectrum of the CNPs.

2.11. Statistical analysis

All experiments were repeated three times, and the results were presented as mean ± standard error. Statistical analysis of the data was performed using SPSS 21.0 software. Data visualization and plotting were conducted using Origin 2022 software (OriginLab Corporation, MA, USA).

3. Results and discussion

3.1. Product yield

As shown in Fig. 1(a), the yield of roasted rabbit meat significantly decreases with increasing roasting temperature (P < 0.05). At a roasting temperature of 180 °C and a roasting time of 30 min, the highest yield reached 67 %, whereas at a roasting temperature of 300 °C, the yield was only 36 %. This reduction in yield is attributed to the increased evaporation of water at higher roasting temperatures within the same roasting time, leading to a greater loss of water content in the meat. Wang et al. (2021) also found in their study that high processing temperatures result in remarkable water loss in meat, leading to a reduced product yield. Furthermore, higher roasting temperatures can cause the loss of more soluble substances, which can affect the yield of rabbit meat. Wang et al. (2021) also emphasized that the loss of soluble substances in meat during thermal processing could contribute to a decrease in yield.

Fig. 1.

Fig. 1

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Effects of different roasting temperatures on rabbit meat yield (a) and sulfhydryl content of rabbit meat protein (b). Notes: The different superscripts (a-e) of yield at different roasting temperatures indicate significant differences (P < 0.05). The different superscripts (a-b) of sulfhydryl content at different roasting temperatures indicate significant differences (P < 0.05).

3.2. Sulfhydryl content

Sulfhydryl groups are the most reactive functional groups in proteins, and their changes in content can be used to assess the degree of protein oxidation (Zhang et al., 2022). As shown in Fig. 1(b), the sulfhydryl content of salt-soluble protein in fresh meat was about 65 nmol/mg, and the sulfhydryl content of salt-soluble protein in rabbit meat roasted at different temperatures was about 12 nmol/mg, the sulfhydryl content of rabbit meat salt-soluble protein after roasting at different temperatures is significantly lower than that of fresh meat salt-soluble protein (P < 0.05). However, no significant differences were observed in the sulfhydryl content among rabbit meat salt-soluble protein roasted at different temperatures (P > 0.05). The reason is that at higher temperatures, the rate of free radical chain reactions accelerates, leading to increased oxidation and denaturation of rabbit meat proteins, which results in a significant decrease in sulfhydryl content. Wang et al. (2023) and Pu et al. (2023) also found in their studies that high-temperature cooking led to the oxidation of sulfhydryl groups on meat protein cysteine, thereby forming disulfide bonds and resulting in a significant decrease in sulfhydryl content. The lack of significant differences in sulfhydryl content among rabbit meat proteins roasted at different temperatures is attributed to the fact that during the prolonged roasting process, various roasting temperatures cause changes in the structure of rabbit meat proteins, but the level of exposed sulfhydryl groups inside the proteins does not differ significantly, resulting in the indistinct differences in sulfhydryl content. Zhu et al. (2019) also found that within a certain range of different roasting temperatures, the differences in the sulfhydryl content of meat proteins were insignificant.

3.3. UV spectroscopy

The endogenous protein fluorescence is closely related to the UV absorption characteristics of aromatic amino acids, and changes in the UV spectrum can reflect alterations in protein structure (Zhang et al., 2020). As shown in Fig. 2(a), different roasting temperatures lead to varying degrees of reduction in the UV spectrum intensity of rabbit meat salt-soluble protein. This result indicates that the microenvironment of aromatic amino acids, such as phenylalanine, tyrosine, and tryptophan, in rabbit meat salt-soluble proteins undergoes changes. Zhang et al. (2022) highlighted that the oxidative modification of tyrosine and tryptophan residues in proteins could reduce the maximum UV absorption peak intensity of proteins. Chen et al. (2023) also suggested that during the heating process, protein structures gradually unfold due to stretching, leading to an increase in the exposure of amino acid residues. At higher temperatures, amino acid residues are more susceptible to attack by free radicals (Xia et al., 2022), resulting in changes in protein structure and ultimately leading to a decrease in the maximum UV absorption peak intensity of the protein.

Fig. 2.

Fig. 2

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Effects of different roasting temperatures on UV spectrum (a) and fluorescence spectrum (b) of rabbit meat protein.

3.4. Endogenous fluorescence spectrum

Tryptophan, located in the core of protein folding structures, has a high quantum yield and exhibits strong fluorescence. Therefore, the loss of tryptophan fluorescence can be used as one of the indicators to assess the degree of protein oxidation (Soladoye, Juárez, Aalhus, Shand & Estévez, 2015). As shown in Fig. 2(b), with increasing roasting temperature, the fluorescence intensity of rabbit meat salt-soluble proteins significantly decreases. Zhang et al. (2020) pointed out that tryptophan residues were situated in the core of natural protein structures. When oxidation occurs, the unfolding of the protein structure exposes tryptophan residues to oxidation, ultimately leading to a decrease in fluorescence intensity. Jiang et al. (2023) suggested that the decrease in protein fluorescence intensity with increasing heating temperature was related to the protein structure and spatial hindrance. The unfolding of the protein structure and exposure to hydrophilic environments result in a decrease in fluorescence intensity. High temperature causes protein aggregation, increases spatial hindrance, and also leads to a reduction in fluorescence intensity. Other researchers have also noted that the formation of protein aggregates can result in the shielding of some nonpolar aromatic amino acid residues, leading to a decrease in endogenous fluorescence intensity (Wang et al., 2017).

3.5. Element composition of CNPs

As shown in Fig. 3, the XPS spectrum of the CNPs extracted from rabbit meat baked at 180 °C reveal three major peaks. The peak at 284.8 eV corresponds to the C1s peak, the peak at 399.5 eV corresponds to the N1s peak, and the peak at 531.0 eV corresponds to the O1s peak. Evidently, the C1s and O1s peaks have much higher intensity compared with the N1s peak. The XPS spectrum of the four other samples in Fig. 3 also exhibit the same information, indicating that the CNPs derived from rabbit meat surfaces contain three elements, namely, C, O, and N, with higher C and O contents and lower N content. Similar findings were observed in the research performed by Bi et al. (2018), where the CNPs from Roasted Pike Eel also exhibited prominent C, N, and O peaks, with a N content of 16.39 %, suggesting its origin from proteins. Cong, Liu, Qiao, Song, and Tan (2019) also reported similar observations in their study on CNPs from roasted duck meat, where the main elements present were C, followed by O, with a small amount of N. The results indicate that the CNPs from roasted rabbit meat are C-based nanoparticles, with C being the predominant element, and the higher O content may be attributed to the oxidation reactions of proteins during the roasting process, resulting in an increase in O from the surrounding air.

Fig. 3.

Fig. 3

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Effect of different roasting temperatures on the XPS full spectra of FNDs in rabbit meat.

As shown in Fig. 4, for CNPs extracted from rabbit meat roasted at 180 °C, the relative content of C, N, and O elements is 60 %, 14 %, and 26 %, respectively, while for CNPs from rabbit meat roasted at 300 °C, the relative content of the three elements is 72 %, 11 %, and 17 %, respectively. With increasing roasting temperature, the content of the C element continues to increase. Similar results were reported by Liu, Song, and Tan (2020), who roasted beef at 280 °C for 30 min and extracted CNPs that were roughly spherical, mainly composed of C (68.68 %), N (10.6 %), and O (15.98 %), with C being the highest, followed by O, and N the lowest, which is consistent with the results of this study. From the changes in the content of the three elements, the variation in roasting temperature does not cause a reversal in the relative content ranking of the three elements, which all maintain a pattern where C is the highest, followed by O, and N the lowest. This finding suggests that roasting temperature does not alter the elemental composition of CNPs, but the increase in C content indicates an elevated degree of carbonization of CNPs with the rise in roasting temperature.

Fig. 4.

Fig. 4

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Effect of different roasting temperatures on the relative contents of C, N and O elements in FNDs in rabbit meat.

3.6. Fluorescence of CNPs solution

Under UV light, the blue fluorescence of the CNPs solution is clearly visible, which is a classic photoluminescence phenomenon, indicating that CNPs possess unique optical characteristics (Li, Yuan & Liu, 2021). As shown in Fig. 5, significant differences in the blue fluorescence are observed among different roasting temperature groups. With increasing roasting temperature, the blue fluorescence intensity of the CNPs solution exhibits a significant increasing trend. This result suggests a significant correlation between the production of CNPs and roasting temperature. Similar phenomena were also observed by Cong, Liu, Qiao, Song, and Tan (2019), who found that higher roasting temperatures result in higher CNPs yield.

Fig. 5.

Fig. 5

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Effect of different roasting temperatures (180 °C, 210 °C, 240 °C, 270 °C, 300 °C) on the fluorescence phenomenon of FNDs aqueous solution in rabbit meat.

As shown in Fig. 6, as the excitation wavelength gradually increases in the range of 300–420 nm, the emission wavelength intensity of CNPs first increases and then decreases. The maximum fluorescence emission wavelength of CNPs from rabbit meat roasted at 180, 210, 240, and 270 °C is 391 nm, with the maximum excitation wavelength at 320 nm, while the CNPs from rabbit meat roasted at 300 °C exhibit a maximum fluorescence emission wavelength around 395 nm, with the maximum excitation wavelength at 310 nm. The increase in roasting temperature may cause a blue shift in the maximum emission wavelength (Wang et al., 2019), which is related to the structure of CNPs, because higher roasting temperatures can alter the structure of CNPs. From the figures, all CNPs exhibit significant excitation-dependent fluorescence, with the maximum emission peak gradually red-shifting as the excitation wavelength increases. Additionally, the positions and fluorescence intensities of the emission peaks of CNPs at different temperatures also change correspondingly with the variation in the excitation wavelength. Wang et al. (2019) found that the maximum emission peak of CNPs from baked lamb red-shifted as the excitation wavelength increased. Li, Cao, Li, Yu, and Tan (2019) also discovered that the maximum emission peak of CNPs from roasted mackerel red-shifted from 425 nm to 480 nm as the excitation wavelength increased. The red-shift phenomenon in the maximum emission peak with the increase in excitation wavelength is likely due to the influence of surface states that affect the band gap of nanoparticles (Tan et al., 2016, Hill et al., 2016).

Fig. 6.

Fig. 6

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Effect of different roasting temperatures on the fluorescence spectra (180 °C (A), 210 °C (B), 240 °C (C), 270 °C (D), 300 °C (E)) and normalized fluorescence profiles (180 °C (a), 210 °C (b), 240 °C (c), 270 °C (d), 300 °C (e)) of FNDs in rabbit meat.

3.7. Surface structure of CNPs

The surface functional groups of CNPs from rabbit meat at five different roasting temperatures were further characterized using FT-IR, and the results are shown in Fig. S1. From the figure, the functional groups of the five groups of CNPs are similar, but differences are observed in the peak positions and vibrational intensities. In the spectrum, typical absorption bands are observed around 3300 cm−1, which are related to the stretching vibrations of N—H and O—H bonds. Peaks exist near 2900 cm−1, corresponding to the vibrations of C—H bonds, and the vibrational intensity of C—H bonds gradually increases with temperature, indicating the formation of methyl groups on the surface of CNPs (Zhang et al., 2021). Additionally, the spectrum bands around 1680 cm−1 and 1590 cm−1 correspond to the stretching vibrations of C Created by potrace 1.16, written by Peter Selinger 2001-2019 O bonds and the bending of amide N—H bonds, respectively. With the increase in baking temperature, the relative intensity of the spectrum band around 1680 cm−1 gradually increases, whereas the spectrum band around 1590 cm−1 weakens. This result suggests the formation of some C Created by potrace 1.16, written by Peter Selinger 2001-2019 O bonds and the subsequent cleavage of N—H bonds, indicating that rabbit meat undergoes more oxidation reactions with increasing temperature, leading to the adsorption of more oxygen-containing functional groups on the surface of CNPs. The characteristic absorption peaks at 1417–1454 cm−1 correspond to C Created by potrace 1.16, written by Peter Selinger 2001-2019 C or C—N bonds, and the absorption band at 1245 cm−1 is attributed to the aromatic structure of C—O bonds. The intensities of these two peaks gradually decrease with increasing temperature, suggesting that under higher roasting temperatures, the thermal decomposition reactions of rabbit meat may intensify, leading to a greater extent of decomposition of CO-NH bonds on CNPs. Based on the combined analysis of XPS results, the surface of CNPs from rabbit meat contains hydrophilic and multi-ring groups, such as carbonyl, hydroxyl, and amide bonds. Zhao et al. (2019) also found a significant amount of hydroxyl, carboxyl, and amino groups on the surface of CNPs from roasted pork. Similarly, Li, Yuan, and Liu (2021) studied CNPs from fried pork and discovered abundant hydroxyl, carbonyl/carboxyl, and nitrogen-containing groups on their surface.

3.8. Correlation analysis

As shown in Table S1, significant correlations are observed among various indicators. The temperature is significantly negatively correlated with the yield of roasted rabbit meat (−0.988), sulfhydryl content (−0.913), UV spectrum intensity at 280 nm (−0.921), and fluorescence spectrum intensity at 340 nm (−0.952), while it is significantly positively correlated with the fluorescence intensity of the CNPs (0.850). This result indicates that an increase in roasting temperature leads to a decrease in the yield of roasted rabbit meat, an increase in the oxidation level of proteins, and a rise in the generation of CNPs. Additionally, the correlation coefficients between the protein sulfhydryl content, UV spectrum intensity at 280 nm, fluorescence spectrum intensity at 340 nm, and the fluorescence intensity of the CNPs are −0.621, −0.615, and −0.681, respectively. This result indicates that an increase in the oxidation level of proteins during high-temperature roasting is accompanied by an increase in the generation of CNPs. However, whether the oxidation of proteins during high-temperature roasting affects the generation of CNPs and its mechanism requires further systematic research in the future.

4. Conclusion

This study analyzed the protein oxidation and the physicochemical characteristics of CNPs generated in rabbit meat at different roasting temperatures (180, 210, 240, 270, and 300 °C). With the increase in roasting temperature, the yield of rabbit meat significantly decreased, and the oxidation level of rabbit meat proteins showed an increasing trend. Specifically, compared with fresh meat, the sulfhydryl content of rabbit meat proteins significantly decreased after roasting. Additionally, as the roasting temperature increased, the maximum UV absorption peak intensity and fluorescence intensity of rabbit meat proteins generally decreased. The prepared CNPs solution exhibited typical blue fluorescence under UV light. In the CNPs extracted from rabbit meat roasted at 180 °C, the relative content of C, N, and O elements was 60 %, 14 %, and 26 %, respectively. In contrast, in the CNPs from rabbit meat roasted at 300 °C, the relative content of these three elements was 72 %, 11 %, and 17 %, respectively. The increase in roasting temperature did not cause changes in the elemental composition of CNPs but led to an increase in the degree of carbonization. Furthermore, the higher roasting temperature resulted in a blue shift in the maximum emission wavelength of the CNPs solution. Combined with the XPS results, the surface of rabbit meat CNPs contained hydrophilic and polycyclic groups, such as carbonyl, hydroxyl, and amide bonds. Correlation analysis revealed a significant positive correlation between the level of protein oxidation and the formation of CNPs. However, whether protein oxidation during high-temperature roasting promotes the formation of CNPs and its underlying mechanisms require further systematic exploration in future research.

5. Ethical Guidelines

Ethics approval was not required for this research.

CRediT authorship contribution statement

Xue Li: Methodology, Investigation, Writing – review & editing. Yunlong Song: Methodology, Investigation, Writing – review & editing. Lisa Huangfu: Methodology, Investigation, Writing – review & editing. Sheng Li: Formal analysis. Qingyang Meng: Formal analysis. Zhicheng Wu: Formal analysis. Jinggang Ruan: Formal analysis. Jie Tang: Methodology. Dong Zhang: Conceptualization, Supervision, Funding acquisition. Hongjun Li: Methodology.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgments

This research was funded by the Science and Technology Department of Sichuan Province, China (23ZDYF3100), Chengdu Science and Technology Bureau, Sichuan Province, China (2022-YF09-00018-SN), Natural Science Foundation of Sichuan Province, China (2022NSFSC1758), and Xihua University Talent Introduction Project (grant number Z211046).

Footnotes

Appendix A

Supplementary data to this article can be found online at https://doi.org/10.1016/j.fochx.2023.101015.

Contributor Information

Sheng Li, Email: lsheng1990@126.com.

Dong Zhang, Email: dongzhang@mail.xhu.edu.cn.

Appendix A. Supplementary data

The following are the Supplementary data to this article:

Supplementary data 1
mmc1.docx (210.4KB, docx)

Data availability

The data that has been used is confidential.

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