Emmanuel Duhoranimana

Preparation and characterization of magnetic molecularly imprinted polymers for the extraction of hexamethylenetetramine in milk samples

Magnetic molecularly imprinted polymers (M-MIPs) were synthesized as the sorbents for extracting hexamethylenetetramine (HMT) from milk samples. Molecular simulations were used to calculate the interaction energies of the template monomers. The physical properties of M-MIPs were characterized. The adsorption isotherms and kinetics were investigated. Gas chromatography coupled with tandem mass spectrometry (GC-MS/MS) was applied to determine the amount of HMT residue in milk samples. In the optimized method, a linear calibration curve was obtained using a matrix-matched standard in the range of 1.0-50.0μgL-1. The limit of detection (LOD) and limit of quantification (LOQ) was 0.3μgkg-1 and 1.0μgkg-1, respectively. The relative standard deviation (RSD) of the intra-day assay ranged from 2.6% to 5.2%, while that of the inter-day assay ranged from 3.6% to 11.5%. The recovery of HMT in milk samples ranged from 88.7% to 111.4%.

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. Maillard reaction products (MRPs) were prepared by Maillard reaction performed under stepwise increase of temperature, and cysteine was added as an indicator. The formation conditions of MRI generated from Xyl and Phe were determined through MRPs browning analysis. The MRI prepared under the determined formation conditions was purified using RP-HPLC, and characterized using UPLC-ESI-mass spectra and NMR. The molecular mass (297.1 Da) and formula (C14H19O6N) were proposed. The capacity of flavor formation of heated MRI was evaluated through GC-MS. Results showed that flavor compounds were formed during the subsequent heat treatment, and MRI could be a great potential substitute of MRPs in preparation of fresh process flavors. Therefore, controlled formation of process flavors could be achieved by preparation and application of MRI.

Synergistic Effect of a Thermal Reaction and Vacuum Dehydration on Improving Xylose–Phenylalanine Conversion to N-(1-Deoxy-d-xylulos-1-yl)-phenylalanine during an Aqueous Maillard Reaction

The synergistic effect of a thermal reaction and vacuum dehydration on the conversion of xylose (Xyl) and phenylalanine (Phe) to a Maillard-reaction intermediate (MRI) was researched. The yield of N-(1-deoxy-α-d-xylulos-1-yl)-phenylalanine was successfully improved and increased from 13.62 to 47.23% through the method combining a thermal reaction and vacuum dehydration. A dynamic process was involved in the transformation of Xyl and Phe (Xyl-Phe) to N-substituted d-xylosamine and in the transformation of N-substituted d-xylosamine to N-(1-deoxy-α-d-xylulos-1-yl)-phenylalanine during the initial stage of dehydration; then, only the transformation of N-substituted d-xylosamine to N-(1-deoxy-α-d-xylulos-1-yl)-phenylalanine occurred during the final stage. Furthermore, the MRI was prepared under optimized conditions (90 °C and pH 7.4), and the obtained MRI was characterized and confirmed by ESI mass spectrometry and NMR.

Sodium sulfite pH-buffering effect for improved xylose-phenylalanine conversion to N -(1-deoxy- d -xylulos-1-yl)-phenylalanine during an aqueous Maillard reaction

The yield of the Maillard reaction intermediate (MRI), prepared in aqueous medium, is usually unsatisfactory. However, the addition of sodium sulfite could improve the conversion of xylose-phenylalanine (Xyl-Phe) to the MRI (N-(1-deoxy-d-xylulos-1-yl)-phenylalanine) in aqueous medium. Sodium sulfite (Na2SO3) showed a significant pH-buffering effect during the Maillard reaction, which accounted for its facilitation of the N-(1-deoxy-d-xylulos-1-yl)-phenylalanine yield. The results revealed that the pH could be maintained at a relatively high level (above 7.0) for an optimized pH-buffering effect when Na2SO3 (4.0%) was added before the reaction of Xyl-Phe. Thus, the conversion of Xyl-Phe to N-(1-deoxy-d-xylulos-1-yl)-phenylalanine increased from 47.23% to 74.86%. Furthermore, the addition moment of Na2SO3 and corresponding solution pH were crucial factors in regulating the pH-buffering effect of Na2SO3 on N-(1-deoxy-d-xylulos-1-yl)-phenylalanine yield. Based on the pH-buffering effect of Na2SO3 and maintaining the optimal pH 7.4 relatively stable, the conversion of Xyl-Phe to N-(1-deoxy-d-xylulos-1-yl)-phenylalanine was successfully improved.

Investigating the optimum conditions for minimized 3-chloropropane-1,2-diol esters content and improved sensory attributes during savory beef flavor preparation

In this study, the effects of enzymatic hydrolysis of tallow and addition of sodium chloride (NaCl) were evaluated on the formation of 3-monochloropropane-1,2-diol (3-MCPD) esters and sensory characteristic of beef flavors. The enzymatic hydrolysis condition had significant effects on 3-MCPD mono/di-esters formation during the beef flavor preparation. Considering the safety and sensory characteristics of beef flavors, the optimal enzymatic hydrolysis conditions were selected as: lipase concentration 75U/g tallow, tallow concentration 80% (w/v) and pH 7.0 at 47.5°C for 9.5h. Using the optimal enzymatic hydrolysis conditions, no 3-MCPD monoesters were detected and 3-MCPD-diesters concentration was strongly dependent on NaCl concentration and its addition moment (before or after thermal reaction) at different temperatures. In conclusion, beef flavor was prepared using the optimal hydrolysis conditions and heated at 110°C for 100min, then 10% NaCl was added when the system was cooled to 60°C.