Yong-g Guan

Changes in the initial stages of a glucose-proline Maillard reaction model system influences dairy product quality during thermal processing

The Maillard reaction always occurs during the thermal processing of dairy products, which significantly influences their quality. In the present study, the initial stages of a glucose-proline model system were investigated in water and different types of buffer solutions. Results showed that phosphate buffer accelerated the reversible degradation of the initial stages of the reaction. The proposed catalysis mechanism was that hydrogenous and dihydric phosphate radical anions simultaneously accepted and donated protons for the conversion of the intermediates into N-glycosylamine. The catalysis mechanism was confirmed via testing and no reducing of hydrogenous and dihydric phosphate radical anions was observed during the reaction. Moreover, both N-(1-deoxy-D-fructos-1-yl)proline and its degradation compounds were analyzed. Results showed that degradation of N-(1-deoxy-D-fructos-1-yl)proline to form 5-hydroxymethyl-2-furaldehyde and formic acid was also accelerated by phosphate buffer. An interesting phenomenon was that citrate decreased 5-hydroxymethyl-2-furaldehyde formation, which might be because Strecker-type degradation occurred more easily than 1,2-enolization reaction in citrate buffer solution. However, this hypothesis has not been confirmed, and element label experiments should be carried out in the future.

Effects of pressure on the glucose-ammonium sulphite caramel solutions.

Effects of pressure on glucose-ammonium sulphite solutions were investigated. The reactant (i.e. glucose), intermediate products content, and browning intensity of advanced stages were tested using an UV-Vis spectrophotometer and a high performance liquid chromatograph to gain a better understanding of the influence of pressure on the glucose-ammonium model Maillard reaction system. This study indicates that pressure could promote the first step of the reaction, i.e. condensation reaction between SO(3)(2-)/ammonium and glucose, but inhibit the increase of A(294), A(420) and 5-hydroxymethyl-2-furaldehyde content. The mechanism of inhibiting the glucose-ammonium model Maillard reaction might be that pressure increases dissociative SO(3)(2-) content in solutions and inhibits the degradation of the Amadori rearrangement product.

Preparation of antioxidants from sugarcane molasses

Supercritical carbon dioxide fluid extraction with piecewise distillation separation was used to obtain antioxidants from sugarcane molasses. Extraction pressure, time, temperature, flow rate of CO2 and ethanol content were selected as the independent variables. Oxygen radical absorbance capacity was used to evaluate the antioxidant activity of the extract. Results showed that conditions to obtain the highest total oxygen radical absorbance capacity value of sugarcane molasses extract were determined to be an extraction pressure of 33.3 MPa, temperature of 43.3 °C, time of 86.7 min, 90% ethanol content of sugarcane molasses and flow rate of CO2 of 20 L/h. Under the conditions stated above, the experimental value was 2584.9. This study indicated that supercritical carbon dioxide fluid extraction with piecewise distillation separation can effectively extract antioxidants from sugarcane molasses.

Simultaneous analysis of Nε-(carboxymethyl)lysine, reducing sugars, and lysine during the dairy thermal process.

A new analytical method allowing the simultaneous quantification of Nε-(carboxymethyl)lysine (CML), lysine, and reducing sugars (glucose, lactose, and galactose) is described. It is based on high performance anion-exchange chromatography with pulsed amperometric electrochemical detection. This method demonstrated a low limit of quantification (0.385 to 0.866 mg/L), excellent linear correlation (R(2)>0.997), and desired calibration range (3.125 to 25 mg/L). In addition, lactose-lysine solutions containing sulfite (4 to 400 mmol/L) were heated at 110°C for 2h. The results showed that sulfite inhibited the formation of CML and promoted the consumption of reducing sugars and lysine in the Maillard reaction model. The method proved to be useful for simultaneous analysis of CML, lysine, and reducing sugars (glucose, galactose, and lactose) in the Maillard reaction system. Moreover, sulfite was an effective inhibitor of CML formation.

Short communication: Simultaneous analysis of reducing sugars and 5-hydroxymethyl-2-furaldehyde at a low concentration by high performance anion exchange chromatography with electrochemical detector, compared with HPLC with refractive index detector

A simultaneous analysis of reducing sugars and 5-hydroxymethyl-2-furaldehyde of the Maillard reaction products was detailed. It was based on a high performance anion exchange chromatography with electrochemical detector system and an HPLC with refractive index detector. Results showed that high performance anion exchange chromatography with electrochemical detector using a CarboPac PA-1 column (Dionex Corp., Sunnyvale, CA) was more suitable for reducing sugars and 5-hydroxymethyl-2-furaldehyde determination, especially for trace analysis. The lowest detectable limit of reducing sugars and 5-hydroxymethyl-2-furaldehyde was 0.00005 mol/L in this experiment. However, HPLC with a refractive index detector always produces a tailing peak for 5-hydroxymethyl-2-furaldehyde, and mannose and fructose cannot be absolutely separated. The results of the present study could provide a more sensitive means for 5-hydroxymethyl-2-furaldehyde and reducing sugar detection.

Short communication: Possible mechanism for inhibiting the formation of polymers originated from 5-hydroxymethyl-2-furaldehyde by sulfite groups in the dairy thermal process

5-Hydroxymethyl-2-furaldehyde can undergo polymerization to form high-molecular weight molecules via the Maillard reaction during dairy thermal treatment. In this study, the effect of sulfite group on polymer formation, especially in inhibiting the formation of high-molecular weight polymers has been described. Results showed that the sulfite group significantly inhibited the increase of polymer molecular weight via prevention of the polymerization of 5-hydroxymethyl-2-furaldehyde. The formation of an intermolecular dimer based on the glucose molecule through Schiff base cyclization can lead to a competitive reaction with 1,2-enolization to reduce 5-hydroxymethyl-2-furaldehyde formation, which might be another factor in reducing the formation of high-molecular weight polymers.

Indirect competitive ELISA based on monoclonal antibody for the detection of 5-hydroxymethyl-2-furfural in milk, compared with HPLC

In this study, a method for rapid detection of 5-hydroxymethyl-2-furfural (HMF) was investigated. Monoclonal antibody (anti-HMF) was prepared and evaluated by an indirect competitive ELISA (ic-ELISA) format. The optimized standard curve was y=-0.2097x+1.0432 [where x is the logarithm (base 10) of the values of the HMF concentration and y is the absorbance of ic-ELISA results tested at 490 nm] and the linear detection range was 0.008 to 32.768 mg/L. The percentage of cross-reactivity of HMF with 5 major furfural derivatives was less than 2.92%. Finally, the established ic-ELISA format was used to test HMF in milk, and compared with the result obtained by HPLC, which produced an error of about 0.3%. Based on the data in this experiment, we concluded that the established ic-ELISA format was reliable with a high specificity.

Developing an effective means to reduce 5-hydroxymethyl-2-furfural from caramel colour.

Supercritical carbon dioxide fluid extraction was used to extract 5-hydroxymethyl-2-furfural from caramel colour (solid content was about 75%). The procedure was carried out by response surface methodology using a quadratic polynomial model. Extraction pressure, time, temperature and ethanol content were selected as the independent variables. Conditions to obtain the highest extraction ratio of 5-hydroxymethyl-2-furfural were determined to be an extraction pressure of 21.65MPa, time of 46.7min, temperature of 35°C and 70% ethanol content of caramel colour. The predicted 5-hydroxymethyl-2-furfural extraction ratio was 87.42%. Under the conditions stated above, the experimental value of 5-hydroxymethyl-2-furfural extraction ratio was 86.98%, which was similar to the predicted value by the model. This study indicated that supercritical carbon dioxide fluid extraction can effectively reduce 5-hydroxymethyl-2-furfural from caramel colour, which can help food industry to improve the safety of the food material, as well as provide more healthy caramel colour for human beings.