Prediction of CML contents in the Maillard reaction products for casein-monosaccharides model

The effect of lactose and its isomerization product lactulose on functional and structural properties of glycated casein

Lactulose is an isomer of lactose, formed under thermal processing of milk. Alkaline conditions favor the isomerization of lactose. As reducing sugar, lactose and lactulose could participate in the Maillard reaction and cause protein glycation in milk products. In this study, the influence of lactose and lactulose on the functional and structural properties of glycated casein was investigated. The results demonstrated that compared with lactose, lactulose led to severer changes in molecular weight, more disordered spatial structure and decrease of tryptophan fluorescence intensity of casein. Besides, the glycation degree and advanced glycation end products (AGEs) results suggested that lactulose exhibited stronger glycation ability than lactose due to the higher proportion of open chain in solution. Furthermore, higher glycation degree induced by lactulose resulted in lower solubility, surface hydrophobicity, digestibility and emulsifying capacity of casein-glycoconjugates compared with lactose. The results of this study are essential for tracking the effects of harmful Maillard reaction products on the quality of milk and dairy products.

Pterostilbene Improves Insulin Resistance Caused by Advanced Glycation End Products (AGEs) in Hepatocytes and Mice

SCOPE

Increased consumption of modern processed foods rich in AGEs is drawing worldwide concerns because they are related with rising diabetes prevalence. This study aimed to investigate if pterostilbene (PTE) regulates glucose metabolism and insulin signaling, as well as its potential mechanism in the context of AGEs exposure.

METHODS AND RESULTS

In vitro, Lo2 and HepG2 cells are treated with vehicle, AGEs with or without PTE. AGEs exposure directly impair insulin action as evidenced by assays of insulin-stimulated glucose uptake, consumption, and output. However, PTE efficiently rescue the AGE-induced phenotypes in both cell lines, and enhance IRS-1/PI3K/AKT insulin signaling in a dose-dependent manner. In vivo, C57BL6 mice are fed with regular, high AGEs diet and high AGEs plus PTE. PTE administration effectively improves hyperglycemia, glucose tolerance, and impaired hepatic insulin signaling induced by AGEs, consistent with the in vitro experiments. Moreover, PTE reduce AGEs accumulation in liver and serum. RNA-seq data indicate that PTE counteracts several AGEs-induced dysfunctions including diabetes related process, glucose metabolic process, immune response, and so on.

CONCLUSION

PTE treatment prominently reduced AGEs accumulation and alleviated AGEs-associated diabetes symptoms. PTE could be used as a promising glucose-sensitizing agent for nutritional intervention.

Molecular characterization of sequence-driven peptide glycation

Peptide glycation is an important, yet poorly understood reaction not only found in food but also in biological systems. The enormous heterogeneity of peptides and the complexity of glycation reactions impeded large-scale analysis of peptide derived glycation products and to understand both the contributing factors and how this affects the biological activity of peptides. Analyzing time-resolved Amadori product formation, we here explored site-specific glycation for 264 peptides. Intensity profiling together with in-depth computational sequence deconvolution resolved differences in peptide glycation based on microheterogeneity and revealed particularly reactive peptide collectives. These peptides feature potentially important sequence patterns that appear in several established bio- and sensory-active peptides from independent sources, which suggests that our approach serves system-wide applicability. We generated a pattern peptide map and propose that in peptide glycation the herein identified molecular checkpoints can be used as indication of sequence reactivity.

Effect of lotus seedpod oligomeric procyanidins on AGEs formation in simulated gastrointestinal tract and cytotoxicity in Caco-2 cells

This study explored the effects of lotus seedpod oligomeric procyanidins (LSOPC) and their main monomer catechin (CC) on the formation of advanced glycation end products (AGEs) and Caco-2 cytotoxicity during gastrointestinal digestion. Studies have found that LSOPC and CC inhibited the AGEs formation effectively in simulated gastrointestinal digestion and protected Caco-2 cells from AGEs attack. The effect of CC on the inhibition of AGEs formation was significantly better than that of LSOPC. Further, they could effectively inhibit the digestive enzyme activity, reactive oxygen species, RAGE-p38MAPK-NF-κB signaling pathway, inflammatory factors (tumor necrosis factor alpha, interleukin 6), and adhesion factors (intercellular cell adhesion molecule-1, vascular cell adhesion molecule-1) to protect Caco-2 cells.

Impact of methylglyoxal modification of chicken sarcoplasmic protein emulsions on emulsifying properties, rheological behavior and advanced glycation end products

BACKGROUND

Protein modification is used to improve emulsion properties. However, there are limited reports on the effect of methylglyoxal (MGO) modification on emulsifying properties and on the production of advanced glycation end-products (AGEs) in chicken sarcoplasmic protein emulsion (SPE). In this study, MGO solution was dispersed into prepared emulsion (17 mg mL^-1 sarcoplasmic-soybean oil (v/v 5:1)) at 0, 0.5, 5, 10, 30 and 50 mmol L^-1 concentrations. Emulsifying activity index (EAI), emulsifying stability index (ESI), Z-average diameter, polydispersity index (PDI), zeta potential, rheological behavior (thermal condensation characteristics and fluidity) and AGEs in different concentrations of MGO SPE were measured. In addition, the effect of MGO on the levels of AGEs, lipid and protein oxidation of the emulsion as well as their relationship has also been analyzed.

RESULTS

Our findings showed that ESI had the lowest value when MGO was added at a concentration of 10 mmol L^-1 , while Z-average, PDI, carbonyl and AGEs had the highest value at the same concentration. Also, 10 mmol L^-1 MGO played an important role in affecting the rheology of the emulsion. Sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) results showed that the presence of myofibrillar proteins (MPs) in SPE was the main reason for the crosslinking of polymers which could be damaged by high concentration of MGO (>10 mmol L^-1 ).

CONCLUSION

Different concentration of MGO showed varying effects on emulsion properties and on the formation of AGEs in chicken SPE. Pearson's correlation analysis concluded that protein oxidation played a significant positive role during MGO modification. © 2020 Society of Chemical Industry.

N ε-(carboxymethyl)lysine formation from the Maillard reaction of casein and different reducing sugars

Dietary advanced glycation end products (AGEs) are involved in the pathogenesis of diabetic complications, atherosclerosis, and kidney disease. Formation of N ^ε-(carboxymethyl)lysine (CML), a well-known AGEs, was evaluated from the reaction of casein from bovine milk with different reducing sugars (glucose, tagatose, and xylose) at various sugar concentrations and heating temperatures (75 and 120 °C) used in food processing to determine the best sweetener to be used in dairy products. The concentration of CML was measured using an enzyme-linked immunosorbent assay. Additionally, SDS-PAGE was carried out to observe the changes in the molecular weight of casein. The results reveal that tagatose leads to a lower CML concentration at 75 °C than glucose or xylose, whereas no significant differences are observed at 120 °C. We conclude that it would be more appropriate to use tagatose rather than glucose or xylose as a sweetener, considering the AGEs contents in heat-treated dairy products.

Effects of microwave heating on the protein structure, digestion properties and Maillard products of gluten

As a kind of traditional food, gluten is widely studied for its physical and chemical properties after processing, while little attention is paid to the simulation cooking processing, digestion and safety. In this paper, gluten was heated with microwave to study its structural transformations, nutritional efficiency, and food safety under Chinese home cooking (CHC). After microwave treatment, intermolecular and intramolecular cross-linking of gluten were formed to result in more aggregation. The secondary structure of gluten changed significantly as well as the formation of α-helix and β-turn promoted under the high power input. Treated with 1000 W for 5 min, cross-linking between amino acids increased, leading the reduction of total amino acids, in vitro protein digestibility and the increase of high molecular weight peptides, while the proportion of essential amino acids kept the same. In the simulation of CHC, the highest content of 5-hydroxymethyl furfural was observed after adding all condiments under 1000 W for 5 min. In addition, sugar played a major role in Maillard reaction to promote the formation of melanoidin and fructosamine while salt and oil did not significantly affect these two Maillard products. Vinegar inhibited the reaction due to the acidic condition but provided some melanoidin and fructosamine itself.

Influence of Potato Crisps Processing Parameters on Acrylamide Formation and Bioaccesibility

A fractional factorial design was used to evaluate the effects of temperature, frying time, blanching treatment and the thickness of potato slices on acrylamide content in crisps. The design was used on freshly harvested and four-month stored potatoes. The critical factors found were temperature and frying time, and the interaction between blanching treatment and slice thickness. Once frying conditions were selected, an acrylamide content of 725 and 1030 mg kg-1 was found for non-stored and 4-month stored tubers, with adequate textural parameters in both cases. The difference in concentration is related to storage conditions, which must be controlled in order to control acrylamide levels. Bioaccesibility studies demonstrated that acrylamide concentration remained at 70%, and reductions took place mainly at the intestinal phase, as a result of reaction with nucleophilic compounds.

Liquid state fermentation vinegar enriched with catechin as an antiglycative food product

Catechin, a natural antiglycative agent, was incorporated into fermented vinegar, and has high potential to lower the risk of diabetes. In this study, vinegar containing 5% catechin as a substrate for acetous fermentation significantly inhibited the formation of total fluorescent advanced glycation end-products (AGEs), as well as N^ε-(carboxymethyl)lysine (CML)/N^ε-(carboxyethyl)lysine (CEL), especially when added during acetic fermentation. Further study proved that catechin could not only significantly suppress the increase of blood glucose levels, but also inhibit α-amylase, α-glucosidase and β-glucosidase strongly with IC₅₀ values of 0.533 mg mL^-1, 0.307 mg mL^-1 and 0.413 mg mL^-1, respectively. Moreover, 32 volatile compounds were finally identified by headspace solid phase microextraction gas chromatography-mass spectrometry (HSPM-GC-MS) and electronic nose. The flavor of the catechin-vinegars, which possess relatively high ester and low acid contents, was superior to that of traditional vinegar. Therefore, it was helpful to use catechin as a functional food ingredient in vinegar to prevent AGE-associated diseases and alleviate postprandial hyperglycemia, through limiting the digestion of starch and inhibiting the uptake of glucose. Meanwhile, the pleasant flavor and safety of catechin-vinegar were better than traditional vinegar, which represents prominent value to attract consumers.

Effect of fatty acids and triglycerides on the formation of lysine-derived advanced glycation end-products in model systems exposed to frying temperature

Lysine-derived advanced glycation end-products (AGEs), including N^ε-carboxymethyllysine (CML), N^ε-carboxyethyllysine (CEL) and pyrraline, are prevalent in processed foods. The impact of lipids on AGE formation is still contentious and most of our current knowledge is based only on CML. Little is known about how lipids impact the formation of CEL and pyrraline, or their involvement in formation pathways. This study investigated the effect of lipids (fatty acids and triglycerides) on the formation of CML, CEL and pyrraline simultaneously in model systems subjected to frying temperature. The results showed the presence of the lipids promoted the formation of CML, CEL and pyrraline. The promotion effects on CML and CEL were not dependent on the unsaturation degree and addition level (50, 100 or 150 μmol) of lipid, while pyrraline formation depended on lipid type (fatty acids vs. triglycerides) and level. The concentration of CML and CEL was statistically correlated with the concentration of glyoxal (GO) and methylglyoxal (MGO), respectively. The pyrraline concentration was statistically correlated with fructoselysine concentration. These results suggested that lipids promote the formation of lysine-derived AGEs by impacting the generation of Amadori products and α-dicarbonyl compounds. This information may be useful for optimizing the formulation and processing conditions to create tastier and healthier foods.

Fatty acids and triglycerides impact lysine-derived AGE formation through modulating the formation of α-dicarbonyl compounds and Amadori products.

Physicochemical Properties of Bovine Serum Albumin-Glucose and Bovine Serum Albumin-Mannose Conjugates Prepared by Pulsed Electric Fields Treatment

The pulsed electric fields (PEF) treatment is a novel method for obtaining glycated proteins by way of a Maillard reaction between proteins and polysaccharides but its effect on the preparation of protein–monosaccharide conjugate has not been explored. This study aimed to prepare bovine serum albumin (BSA)–glucose and BSA–mannose conjugates using PEF in pH 10.0 at an intensity of 10 or 20 kV/cm, frequency of 1 kHz, pulse width of 20 μs and 73.5 pulses. The conjugates were evaluated for physicochemical properties. The results indicated that PEF not only promoted Maillard reaction between BSA and glucose or mannose but also alleviated the undesirable browning. PEF treatment favored the increased surface hydrophobicity and emulsifying activity in BSA but reduced surface hydrophobicity and foaming stability and improved foaming capacity in BSA–glucose and BSA–mannose conjugates. These findings provided useful considerations in the application of PEF treatment as a potential method to prepare BSA–monosaccharide conjugates by Maillard reaction.

Controlled formation of flavor compounds by preparation and application of Maillard reaction intermediate (MRI) derived from xylose and phenylalanine

An effective method for preparing Maillard reaction intermediate (MRI) derived from xylose (Xyl) and phenylalanine (Phe) in aqueous medium was proposed in this study.