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Formation of Advanced Glycation End Products in Simulate Canned Saury Fish Models: Effects of Process Methods, Formulations and Correlation Analysis with Nutritive Substances

Shanshan Zhao, Yudong Guan*

The First Affiliated Hospital (Shenzhen People’s Hospital), Southern University of Science and Technology, Shenzhen 518055, China

Abstract: Nɛ-(carboxymethyl)lysine (CML) and Nɛ-(carboxyethyl)lysine (CEL) are two important and well-known Advanced glycation end products (AGEs) in food, which is directly related to many disease, and the levels of CML and CEL are often used as important markers to indicate the level of AGEs. The effects of different processing methods (boiling, air-drying, deep-frying) and process formulations (oil-less, salt-less, sugar-free, no pepper, no cooking wine) on the levels of AGEs in simulatinge canned saury fish models, as well as the interaction between nutritive substances and AGEs were investigated. The results showed that the content of CEL was much higher than that of CML in the same set of fish model. Lower levels of CML and CEL were observed in different process formulations simulatinge deep-fried saury canned fish models. The correlation between proteins and amino acids and AGEs showed that amino acids content > is not always larger than proteins content in amino compound. The results indicated that the process formulates, such as oil, salt, sugar and cooking wine can play inhibitory effect on the level of AGEs in the same deep-fry simulate model.

Keywords: Nɛ-(carboxymethyl)lysine, Nɛ-(carboxyethyl)lysine, advanced glycation end products, correlation analysis

Received May 08, 2022; Revised June 11, 2022; Accepted June 23, 2022

Citation: Shanshan Zhao, Yudong Guan, Formation of Advanced Glycation End Products in Simulate Canned Saury Fish Models: Effects of Process Methods, Formulations and Correlation Analysis with Nutritive Substances. Journal of Food and Nutrition Research, 10 (6). 425-436. January 2022. doi:10.12691/jfnr-10-6-6

1. Introduction

As predicted by FAO, the most promising protein source for humans in the future ia aquatic products. [1] As one of the most popular aquatic products, which canned fish products contain high levels of protein, when they undergo a high-temperature processing. In this respect they are a typical model for studying of the Maillard reaction- induced chemical hazards, such as advanced glycation end products (AGEs). AGEs are a group of complex and heterogeneous compounds that are formed through the Maillard reaction, a nonenzymatic reaction between reducing sugars and free amino groups. [2]

Up to now, more than 20 kinds of AGEs have been identified in foods and biological models, and Nɛ-(carboxymethyl)lysine (CML) and Nɛ-(carboxyethyl)lysine (CEL) have been used as the markers of AGEs formed in foods. [3] CML and CEL can be formed in foods by different pathways. Diet is a significant source of exogenous AGEs. Studies have shown that the diet-derived AGEs may pose a risk to human health. [4]

In addition, long-term cooking procedures can increase AGEs content in food. [5] Chan reported that the concentration and types of AGEs in cooked meat depend on cooking methods, cooking temperature, length of cooking time and the presence of protein and fat. [6] Ames has also reported that changing the cooking methods can induce AGEs. [7] Addition, Yu found that in terms of content for AGEs in the same weight of chicken breast, the different processing methods were, in descending order: oven fried, deep fried, roasted, and boiled fish models. [8] However, the effects of hot processing methods (boiling, air-drying, deep-frying) and process formulations (oil-less, salt-less, sugar-free, no pepper, no cooking wine) on the formation of AGEs in Canned fish ramain unknown.

The main purpose of this study was to quantify CML and CEL in canned fish chromatography-tandem mass spectrometry (LC-MS/MS) in order to investigate the effects of hot processing methods (boiling, air-drying, deep-frying) and process formulations (oil-less, salt-less, sugar-free, no pepper, no cooking wine) on the formation of AGEs in simulated canned saury fish models. Additionally, the formation of AGEs in different kinds of canned fishes and their connection with nutritive substance of canned fish and AGEs was also investigated. The results can be used as a guideline for evaluating the risk associated with AGEs consumption and for providing some reasonable advice about dietary habits for consumers.

2. Materials and Methods

2.1. Reagents

Trichloroacetic acid, chloroform, sodium borohydride, sodium borate, boric acid, sodium hydroxide, hydrochloric acid, hexane and methanol were purchased from Sinopharm (shanghai, China). Four AGE standards including CML (>98%), CEL (>98%), and their isotope-labelled compounds d4-CML (>98%) and d4-CEL (>98%) were purchased from Toronto Research Chemicals Inc. (Toronto, Ontario, Canada).

Stock solutions of CML (400 mg/mL), CEL (300 mg/mL), and d4- CML (100 mg/mL) were prepared by dissolving each of the chemicals in methanol-water solution (80:20, v:v), and stored at -20°C. The AGEs standard mixture (CML 300 ng/mL, CEL 300 ng/mL, and d4-CML 400 ng/mL) and the internal standard d4-CML (10 μg/mL) were prepared by diluting stock solutions right before being used for sample analysis.

2.2. Simulated Canned Saury Fish Models Preparation

The fresh saury fishes were purchased from RT-Mart in Jiangxi province. Fresh saury fishes were dissected with heads split, and cut into fish cubes of the same size (3*5 cm), they are salted in 15% saline solution for 10 min, flushed with water for at least 10 minutes and get the spare.

2.2.1. Canned Boil Saury Fishes

The spare saury fish cubes were put into a cooking pot and bolied for 5-8 min. Then, the saury fish cubes were rubbed with oil (5%), salt (3%), sugar (6%), pepper (3%) and cooking wine (6%) to infuse flavor, and the ingredients became opaque and thickened during cooking. The fish cubes were packed in high temperature retort pouches a standard package weight of 100g per pack. The vacuum packing machine was used to automatically extract the air in the packaging bag and complete the sealing process after reaching a predetermind vacuum. (vacuum degree reaching 0.1 Mpa, within 3-4 s). Saury is suitable for the high temperature and high-pressure sterilization for packaged food (121°C, 12 min) and run it under cold water to cool.

2.2.2. Canned Air-dried Saury Fishes

A drum wind dryer was applied to dehydrated saury fish cubes for 8 h. Then, the saury fish cubes were rubbed with oil (5%), salt (3%), sugar (6%), pepper (3%) and cooking wine (6%) to infuse flavor, and the ingredients became opaque and thickens during cooking. The fish cubes were packed in a high temperature retort pouch a standard package weight of 100g per pack. The vacuum packing machine was used to automatically extract the air in the packaging bag and complete the sealing process after reaching a predetermind vacuum. (vacuum degree reaching 0.1 Mpa, within 3-4 s). Saury is suitable for the high temperature and high-pressure sterilization for packaged food (121°C, 12 min) and run it under cold water to cool.

2.2.3. Canned Deep-fry Saury Fishes

The saury fish cubes were fried in fryer at 180°C for 3-5 min, before being mixed with oil (5%), salt (3%), sugar (6%), pepper (3%) and cooking wine (6%) to infuse flavor, with the ingredients becoming opaque and thickenings during cooking. The fish pieces packed in a high temperature retort pouch with a standard package weight of 100g per pack. The vacuum packing machine was used to automatically extract the air in the packaging bag and complete the sealing process after reaching a predetermind vacuum. (vacuum degree reaching 0.1 Mpa, within 3-4 s). Saury is suitable for the high temperature and high-pressure sterilization for packaged food (121°C, 12 min) and run it under cold water to cool.

2.2.4. Canned Deep-fry Saury Fishes in Different Process Formulations

The deep-fried simulated canned saury fish model was given the top rating through sensory evaluation, and an array of canned fish commercially available are fried products. Therefore, to build various saury canned fish models for research of nutritive substances, CML and CEL, adjusting process formulations for the deep-fry simulated saury fish model by means of adding the oil, salt, sugar, pepper or cooking wine (similar to the other heat treatment processes 2.2.3) can help us analyze the mechanism of AGEs on deep-fried canned fishes in a more comprehensive manner.

2.3. Composition

2.3.1. Analysis of Protein, Reducing Sugar, Fat, Amino Acid and Fatty Acid in Canned Saury Fishes

The canned saury fishes from each of the three batches of tins was analyzed for its protein, recovery sugar, amino acid and fatty acid based upon a Kjeldahl method, [9] 3, 5-dinitrosalicylic acid method, [10] and a solvent extraction method. [11]

The amino acid analysis in simulated canned saury fish models was performed on Sykam S-433D system (Germany) equipped with an LCA K06/Na type chromatography column using an acid hydrolysis method. [12] The mobile phase were sodium=0.12N, pH3.45:0.2N pH1 (v/v) and he flow rate was elution pump 0.45 mL/min + derivative pump 0.25 mL/min, with the injection quantity set at 50 μL. A standard hydrolysis analysis was constructed after 45 min at the column temperature which was 58-74°C gradient control.

The fatty acid in simulated canned saury fish models was prepared as previously described. [13] It was analyzed using Agilent 6890 system (Agilent Technologies, Palo Alto, CA, USA), which was equipped with a flame ionization detector (FID) and a CP-Sil 88 type capillary chromatography column (100m *0.25mm* 0.39mm, 0.20μm, Varian Inc., USA). The GC system was analyzed with injection volume of 1 μL, using high purity hydrogen as carrier gas, with injection port temperature set at 250°C and detector temperature at 250°C. The experiment procedure and setting for GC analysis were in constant flow mode, with a split ratio of 10:1, a hydrogen flow rate of 30 mL/min, a air flow rate of 300 mL/min, a makeup gas flow rate of 20 mL/min and a carrier gas the linear velocity of 26 cm/s. The details of the temperature program of the GC analysis are as below: The initial temperature was set at 60°C and kept for 5 min. Then the temperature was increased to 170°C at a rate of 11°C/min and stayed stable for 25 min. Next, it was raised to 200°C at a rate of 5°C/min stayed stable 5 min, before it finally reached 215°C at a rate of 2°C/min and stayed stable for 20 min.

2.3.2. Sample Preparation for Analysis

For the analysis of CML and CEL in simulated canned saury fish models was prepared as previously described by [14]. The method of Sun requires reducing AGEs in the sample with sodium borohydride for 12h, and defatting and precipitating proteins with n-hexane hydrolysis of protein at 110°C for 24 h. [14] While approximately 500 μL of the diluted acid hydrolysate was dried under a stream of nitrogen gas at 50°C, d4-CML, and d4-CEL were added to the dried samples and reconstituted in water. The reconstituted sample solutions were vortexed for 30 s and then subjected to solid-phase extraction (SPE). For SPE, Oasis MCX column was loaded onto a pre-activated (60 mg/3mL, Shanghai ANPEL Scientific instrument Co., Ltd., Shanghai, China) were preconditioned with 3 mL water and 3 mL methanol in sequence. Finally, the target compounds were eluted with 4 mL 5% ammonia in methanol. 1 mL of sample solution was filtered through a 0.22 μm membrane before being subjected to liquid chromatography with tandem mass spectrometry detection (LC-MS/MS) analysis. All of the experiments were repeated three times and in each experiment a different batch of simulate canned saury fish models was used.

2.4. LC-MS/MS Analysis

The amounts of AGEs in simulated canned saury fish extracts were determined using the ultra-performance liquid chromatography coupled to quadrupole time of flight mass spectrometry (LC-MS/MS) analysis. The column used for the LC system was an Atlantis hydrophilic interaction liquid chromatography silica column (2mm×150mm, 4 μm; Hydro-RP 80A LC). Methanol and water = (1:99 (v/v) were used as the mobile phase. The product ions included CML quantitative ions at m/z 205→84, and qualitative ions at m/z 205→130, D₄-CML quantitative ions at m/z 209→88, and qualitative ions at m/z 209→134, CEL quantitative ions at m/z 219→84, CEL qualitative ions at m/z 219→130, D₄-CEL quantitative ions at m/z 223→88, and D₄- CEL qualitative ions at m/z 223→134, respectively. The column temperature was set to 25°C. In the experimental procedure and setting for mass spectrometric analysis was the flow rate set to 0.2 mL/min and injection quantity was set to 1μL. The detection was conducted using Electrospray ionization mass spectrometers (ESI) and multiple reaction monitoring. In positive mode of ESI, the dry temperature was set to 350°C and a drying gas flow rate to 10 L/min. With the atomizer pressure set to 25 Psi and the sheath temperature to 350°C. In addition, the sheath gas flow rate was set to 9 L/min, Capillary voltage to 3500 V and nozzle voltage to 400 V. Multiple reactive ion detection mode (MRM mode). Comparing between the retention times and standard to achieved the identities of CML and CEL peaks. A typical standard curve was constructed by plotting the MS area ratio of CML, CEL and lysine against the d4-CML, d4-CEL and d4-lysine amount ratios, respectively. The CML and CEL in simulate canned saury fishes were based on the ratio of its response factor to standard response factor.

2.5. Statistical Analysis

A one-way analysis of variance (ANOVA) with at least three independent replicates was carried out to detect for any significant differences. The amounts of AGEs in simulated canned saury fish model samples were reported as the average of the three measurements. SPSS software (version 21.0, IBM Corp. Armonk, NY, USA) was used for statistical analysis, and a value of p≤0.05 is considered statistically significant.

3. Results and Discussion

3.1. Different of AGEs in Simulatde Canned Saury Fish Models among Different Processing Methods

The contents of Nɛ-(carboxymethyl)lysine (CML) and Nɛ-(carboxyethyl)lysine (CEL) were determined using Liquid Chromatography-Tandem Quadrupole Mass Spectrometry (LC-MS/MS). This study explained that the level of CML and CEL in simulated canned saury fish models varied greatly among difference processing methods (Figure 2a). In addition, processing methods significantly affected the CML and CEL levels in canned saury fishes. Afterwards, the average levels of CML (between 250.32 and 1608.12 mg/kg sample; n=3) and CEL (from 721.83 to 3653.67 mg/kg sample; n=3) in canned saury fishes different processing methods of (Table 1). The CEL content was higher than CML content in each simulated saury model. At high temperatures, the reaction rate of MGO with lysine was usually faster than that of GO with lysine. [15] In the simulated deep-fried canned saury, the content of lysine content and fatty acid content were the lowest, but the contents of CML and CEL were the highest. On the one hand, violent oxidation reactions of fats at high temperatures, generated a large number of free radicals, creating conditions for the derivation of CML and CEL, which have the highest content of reducing sugars in the deep-fried fish model, and the ability to generate AGEs in the reducing sugar system is relatively high. It was shown that fatty acid and amino acid contents alone do not determine the final AGEs level. The highest level of CML and CEL were detected in the deep-fried simulated canned saury fish model. Roldan reported salmon had the highest level of CML in fried fish. [16] However, the CML content was not consistent with those of salmon and tilapia as indicated by Chen, who noted that the CML content were 12.23 μg/g and 11.24 μg/g by broiling (232°C), 2.05 μg/g and 3.43 μg/g by frying (204°C), and baking (177°C) with CML contents of 8.59 μg/g and 9.72 μg/g. [17] A study by Uribarri also showed that frying (230°C) and baking (177°C) increased the CML content in meat by 10 to 100 times. [18] The inconsistent results may be due to the different conditions of the raw samples and the processing conditions, pasteurized treatment (121°C, 10 min) is a must in our experiments.

In terms of the effects of different processing conditions on the formation of CML and CEL, deep-fried (180°C) simulated canned fish models was followed by air-dried (50°C), and boiled (100°C) ones. The results showed that the content of CML and CEL were convincing evidences to prove that the processing conditions came into play. The content of CML in chicken breasts is related to the heat processing method, with broiling, topping grilling and boiling in descending order. [19] The boiling temperature increases step by step, with the highest temperature much lower than the decoction temperature (180°C), and a relatively slower rate of Maillard reaction, which has great effect on CML and CEL contents during thermal processing, and thus showing the signs of the low level of CML and CEL. It suggests that temperature and cooking methods seem to be more critical to AGEs than cooking time. Goldberg reported that AGEs were higher in samples which were baked or grilled at 230°C for a short period of time in comparison with to samples boiled for a longer period of time (chicken breast boiled for 1 h yielded 1000 kU AGEs, while chicken breast boiled for 15 min yielded 5250 kU AGEs). [20] A 50°C air-blast drying oven was used for drying sample of the air-dried canned saury fish model for 6-8h, and the long-time thermal processing conditions created certain conditions for the accumulation of CML and CEL. Hot fried saury canned fish had the highest amount of CML and CEL. During frying, there might exist a violent oxidation reaction of fat during frying, fat producing a large number of free radicals, which may affect the formation of CML and CEL. Han showed that hydroxyl radicals generated during lipid oxidation could promote the conversion of fructose lysine and glyoxal toward CML formation. Methylglyoxal (MGO) can be promoted under high temperature conditions, and can be generated from CEL as a precursor substance, which can accelerate the formation of CEL. [15,21] All of these oxidation reactions resulted in high levels of CML and CEL in simulated deep-fried canned saury fish modesl. The effect of treatments on CML and CEL levels in this study was consistent with the results of Niu on AGEs using fish with different heat treatments methods, and was also similar to the results of Cheng on CML under different conditions during baking cookies. [22,23] Jiao also pointed out that the content of CML and CEL in tea is influenced by different tea processing methods. [24] The results of this study suggested that different processing conditions may indeed significantlyaffect the formation of CML and CEL.

3.2. Different of AGEs in Simulated Canned Saury Fish Models among Different Process Formulations

The addition of different technological prescriptions in canned saury fish can significantly affect the CML and CEL contents which vary with different process formulations of simulated canned saury fish models (Table 1). The average levels of CML (from 6.16 to 12.55 mg/kg sample; n=3) and CEL (from 10.29 to 61.27 mg/kg sample; n=3) in different process formulations (Figure 2b). Among all the deep-fried samples, the lowest level of CML was found in the simulated canned saury fish model (6.16 mg/kg) with no cooking wine, which also featured the highest level of lysine and the lowest protein content. Therefore, it is presumed that NaCl acts as an antioxidant to block the formation of some AGEs. Followed by the salt-less model (6.32 mg/kg), the pepper contained antioxidants (such as phenolics) that could block the formation of some AGEs. In comparison, less content of CML and CEL was derived the pepper-free model, where NaCl inhibit the production of CML and CEL. Some studies have shown that sodium chloride in meat products has antioxidant effects, which are generally considered to be either pro-oxidant or an antioxidant effects, depending on factors such as the concentration of salt. [25,26] Therefore, it is presumed that NaCl plays an antioxidant role in meat products when the salt concentration is 3% in the simulated deep-fried saury cans. Nonetheless, no studies have reported on the effects of NaCl on CML or CEL formation in muscle foods, let alone the mechanism associated with the effects of NaCl. [27] The contents were noticeably higher for CEL than for CML. Wu also reported that the mean CEL content in egg whites and yolks was significantly higher than that of CML. [28] The levels of CEL in beef, pork, chicken and fish were also higher than that of CML. [8] The content of CML and CEL in oil-less canned saury fish model were the highest, yet it was surprisingly far less than boil canned saury fish models using different processing methods. By comparing the difference of different process formulations, this study found obvious diversity in CML and CEL content.

3.3. Protein Reducing Sugar, Amino Acid and Fatty Acid Contents in Canned Saury Fish Using Different Processing Methods

The canned fish models using different processing methods contained 19.59-20.82% of protein and 38.92-51.55% fat, with reducing sugar of 200.99-214.01 mg/g. The canned fish models using process formulations contained 19.35-21.12% of protein and 27.04-55.96% fat, with reducing sugar of 172.31-265.86 mg/g (Table 1). The difference in protein content among the different processing methods simulated canned saury is within 1.23%, which is 1.49%-2.92% higher than 17.90% of commercially canned saury. [29] It is possible that compared to simulated canned saury the commercially canned saury has been blended with a larger variety of ingredients, which resulted in larger differences in the amount of protein fish model categories and the protein content determined in this study was similar to that of Niu, who reported that the protein content of grass carp muscle was 19.1% of the sample weight on average. [22] In fact, protein content in salmon was 18.59% and protein content in tilapia was 17.98%, as reported by Chen. [17] In contrast, the protein content in egg yolks and egg whites averaged 16.3% and 11.8%. [28] The difference in protein content between different process formulations of simulated fried and commercially canned saury ranged from 1.45% to 3.22%. Compared with the influence of more ingredient factors in commercially canned saury, the influence of oil, salt, sugar, pepper and cooking wine on the protein content in canned saury was not decisive, where among the process recipes, salt had the most significant effect on the protein content in deep-fried simulated canned saury with different process formulations of simulated canned saury fish model, followed by cooking wine, oil, sugar, pepper. [29] Canned saury fish with no cooking wine showed the lowest content of fat (27.04%), followed by boiled canned (38.92%), while the rest of canned saury fishes had the content fat between 44.22% and 55.96%. The content of reducing sugar in saury in different processing conditions also varied greatly. Canned saury fish with no pepper contained the highest reducing sugar of 265.86 mg/g. There was significant difference in the reducing sugar content in canned fishes among different process formulations, with the contents range from 172.31 mg/g to 265.86 mg/g. The reducing sugar content obtained by adding all the ingredients in different processing methods was 214.02 mg/g, which was 41.71-51.84 mg/g different from the reducing sugar content in the canned fish after adjusting the process recipe. The order of single factors affecting the reducing sugar content in different process recipes was pepper, cooking wine, sugar, salt and oil in different process formulations of simulated canned saury fish model.

Table 1. Protein, reducing sugar, fat, Nɛ-(carboxymethyl)lysine (CML) and Nɛ-(carboxyethyl)lysine (CEL) from different canned saury fishes

Figure 1. The distribution of amino acid composition (a), amino acid scores (b), fatty acid saturation composition (c), as well as PUFA (d) in different hot treatment simulated canned saury fish models (n=3). Monounsaturated fatty acid (MUFA), polyunsaturated fatty acid (PUFA) and saturated fatty acid (SFA).The y-axis represented L-Threonine (Thr), Valine (Val), DL-Methionine (Met), L(+)-Cysteine (Cys), Leucine(Leu), Phenylalanine (Phe), Tyrosine (Tyr), Lysine (Lys), Tryptophan (Trp), polyunsaturated fatty acids (PUFA), docosahexenoic acid (DHA) and eicosapentenoic acid (EPA)

Table 2. Amino acid contents of canned saury fishes with different processing methods and process formulations (mg/kg)

18 amino acids were detected in all samples (Table 2). In each of the simulation models Tryptophan content is the highest, amino acid content varied greatly among the simulated canned saury fish models. The lysine content in deep-fried canned saury fish models and fish models with no cooking wine were 1.33mg/kg and 0.75 mg/kg, respectively. The differences in proline content were detected among simulated canned saury fishes processed with different methods, with boiled canned fish showing the highest proline content of 53.73mg/kg, while the proline content of the rest range from 1.23mg/kg to 1.89mg/kg. Figure 1a shows the distribution of amino acid composition in different simulated canned saury fish system. The total essential amino acids (TEAA) in different simulated canned fishes accounted for 44%-53% of the total amino acids (TAA). Respectively, it basically conforms to the ideal protein pattern recommended by FAO/WHO and the content of umami amino acid (aspartic acid + glutamic acid) in different simulate canned fishes accounts for 14%-17% of the total amino acid content (TUAA/TAA). Figure 1b shows the essential amino acids content in simulated canned fish models, which was scored according to the WHO/FAO/WHO (2007) recommended demand patterns for essential amino acids in adults. The tryptophan (Trp) in different simulate canned saury fish models all satisfied Amino Acid Score (AAS) > 100.

Fatty acid content in canned saury fishes using different processing methods and process formulations are shown in Table 3. Regarding fatty acid composition, different canned saury fishes contains different proportions of monounsaturated fatty acid (MUFA) and polyunsaturated fatty acid (PUFA) (Figure 1c). In different canned saury fish models, the proportion of MUFA and PUFA detected ranged from 32% to 45% and from 55% to 68%, respectively, while the saturated fatty acid (SFA) was not detected. The composition of PUFA in different canned saury fish models is shown in Figure 1d. Eicosapentenoic acid (EPA) have found in almost all simulated canned saury fish models except canned saury fishes no-pepper and no cooking wine, however it reflects the under-representation of EPA in PUFA. While the docosahexaenoic acid (DHA) exist in every simulated model, and the proportions of DHA explained by the models ranged from 17% to 26%. Yu investigated that unsaturated fatty acid (UFA) content in oil was positively correlated with the content of CML, and that linoleic acid would be more likely to derive CML. [30] Ma showed that PUFA leads to the formation of rather unsaturated primary oxidation products and further reactions that result in a series of compounds of aldehydes, ketones, and acids, which trigger nutritional reduction. [31] This study discovered that different levels of nutrients in various heat treatments can produce AGEs in different levels, and when sugars or their oxidation products react with proteins, the ε-amino group of lysine on the side chain mixes with sugar adducts to form AGEs. In addition to resulting in the formation of AGEs-from glycans, lipids also serve as precursors of CML. [32] Moreover, AGEs are formed not only because of lysine, but also as a result of high temperatures between their glycated components and α-dicarbonyl compounds. [33]

Table 3. Fatty acid contents of canned saury fishes with different processing methods and process formulations (mg/kg)

Figure 2. The distribution of CML and CEL content by different processing methods (a) and the different process formulations (b) in simulated canned saury fish models

3.4. Correlation Analysis between Nutrients and AGEs

3.4.1. Different Processing Methods for Simulated Canned Saury Fish Model

Nutrients showed varying degrees of correlation with CML and CEL (Figure 3a). Among the amino compounds, there is a difference in the rate of browning between protein and amino acid for the occurrence of the Maillard reaction, which generally shows that amino acid > protein. The correlation between amino acids and CML and CEL in the boiled model showed that most amino acids were stronger than proteins. On the contrary, the protein correlates more strongly correlated with CML and CEL than almost any of the amino acids in the simulated deep-fried canned saury model. The secondary bonds of proteins break at excessive oil temperatures, leading to the denaturation and coagulation of the proteins into an irreversible insoluble state, producing more pathways for AGEs. In general, higher lysine content in the food matrix would provide more lysine-derived AGEs for the formation of late glycosylation end products. However, this pattern does not correspond to the simulated canned saury fish models processed by different processing methods, suggesting that the extent to which the lysine content of the matrix contributes to the production of AGEs is influenced by the processing method. Similarly, the higher the fat content in the food matrix is, the more carbonyl compounds will be formed after fat oxidation, which will lead to the generation of higher levels of AGEs. It has been shown that the reaction temperature has an effect on the loss of sugars by accelerating the oxidative degradation as the temperature increases and that the structure of sugars changes at high temperatures, thus affecting the reactivity. [34,35] Among the simulated canned saury fish models processed by different processing methods, the deep-fried model, which has the highest processing temperature, showed the weakest correlation between reducing sugars and AGEs (Table S1).

3.4.2. Different Process Formulations for Simulated Canned Saury Fish Model

All models showed a negative correlation with AGEs, except the sugar-free model where a large positive correlation between nutrients and CEL existed (Figure 3b). A strong correlation (value of 1) between nutrients and AGEs was observed in each of the simulation models. The proteins in the model strongly correlate with the production of AGEs. It shows that under the same heating conditions, the adjustment of the process formulation leads to a higher level of AGEs produced by the protein source. The correlation between reducing sugars and AGEs was unevenly influenced by different recipe adjusted food matrices in different process formulations of simulated canned saury fish model. Probably due to the effect of reaction temperature on the oxidative degradation, structure as well as reactivity of the sugar in the deep-fried model, sugar was combined with different flavouring prescription to produce different effects on the generation of AGEs. The resulting date showed that there was almost no correlation between reducing sugar and CML and CEL (<0.3) in simulated no-pepper canned saury (Table S2).

Figure 3. The correlation between nutrients and CML, CEL in different processing methods. (a) and different process formulations (b)

4. Conclusions

The processing methods and process formulations have significant interaction effect on the levels of CML and CEL in simulated canned saury fish models. CML and CEL content in different process formulations for canned fish models was significantly lower than different processing methods models. Furthermore, the difference level of CML and CEL also reflected in different process formulations in the same processing method model, which indicated the complexity of CML and CEL formation in the canned fishes. Processing methods and process formulations have significantly affected on the levels of CML and CEL in canned fishes. Nutrients in different simulated saury canned fish models have correlation between and AGEs has distinct difference. Among the amino compounds, there is a difference in the rate of browning between protein and amino acid for the occurrence of the Maillard reaction, and it is not always true that amino acid > protein. The correlation between reducing sugars and CML and CEL will be weakened by the gradual oxidative degradation of sugars due to the accelerated loss of sugars at the reaction temperature, and the structure of sugars will be changed at high temperature in a way to affect the reaction activity. The results indicated the complexity of AGEs formation in canned fishes during heating and the strong impact of biological variation of individual fish on AGEs formation.

Conflicts of Interest

The authors declared that they have no conflicts of interest to this work.

Acknowledgements

We would like to thank KetengEdit (www.ketengedit.com) for its linguistic assistance during the preparation of this manuscript.

Abbreviation

AGEs: Advanced glycation end products;

CML: N ɛ-(carboxymethyl)lysine;

CEL: Nɛ-(carboxyethyl)lysine;

LC-MS/MS: Liquid chromatography-tandem mass spectrometry;

SPE: Solid-phase extraction

MUFA: Monounsaturated fatty acid;

PUFA: Polyunsaturated fatty acid;

SFA: Saturated fatty acid;

UFA: Unsaturated fatty acids;

EPA: Eicosapentenoic acid;

DHA: Docosahexenoic acid;

TEAA: Total essential amino acids;

TAA: Total amino acids;

TUAA: Total amino acid content

References

Graphical Abstract

Table S1. The correlation between different processing methods and CML and CEL

Table S2. The correlation between different process formulations and CML and CEL

Highlights

• Different simulate canned saury fish models were established.

• Compare difference of nutrient and AGEs content in simulate treatment conditions.

• Interaction between nutrients and AGEs in simulate models were investigated.

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