High‐pressure processing of Manuka honey: brown pigment formation,improvement of antibacterial activity and hydroxymethylfurfural content

This work was undertaken to assess the effects of high‐pressure processing on brown pigment formation, antibacterial activity and hydroxymethylfurfural (HMF) content in Manuka honey. The honey was subjected to different pressures (200–600 MPa) at ambient temperatures (25–33 °C) and with moderate temperatures (53–74 °C) for holding times (10–30 min). The brown pigment formation in high‐pressure‐treated sample showed a significant increase (0.16–0.17, P < 0.05), whereas maximum percentage inhibition of Staphylococcus epidermidis (84.34 ± 7.62%) was achieved when honey was subjected to 600 MPa as compared to the control (64.15 ± 5.86%). The percentage inhibition in high‐pressure‐treated samples correlated linearly (r = 0.941) with brown pigment. No significant increase in HMF as affected by high pressure was found (P > 0.05). Thus, high‐pressure processing has no adverse effect on the honey quality because it can control HMF concentration during process. Increasing brown pigment formation is associated with the enhancement of antibacterial activity.     

Effect of drying conditions on bioactive compounds and antioxidant activity of broccoli (Brassica oleracea L.)

The effect of air‐drying parameters on antioxidant activity and changes in antioxidant compounds of broccoli (Brassica oleracea L.) were studied. Broccoli samples were dried to 70 g kg^?1 moisture content using temperatures ranging from 50 to 100 °C and air flow‐rates from 1.20 to 2.25 m s^?1, resulting in drying times from 25 to 90 min. Temperature, owing to its positive effect on the oxidation kinetics, was negatively correlated with ascorbic acid and free and total polyphenol contents but not with kaempferol, even though the sample dried at the highest temperature showed the lowest kaempferol content. The air flow‐rate was positively correlated with the total (TPP) and free (FPP) polyphenol contents because it led to a reduction in the drying time. No correlation was found between air flow‐rate and kaempferol content. Air flow‐rate and temperature positively affected the antioxidant activity by reducing the drying time. High‐temperature, short‐time processes maximised the antioxidant activity of broccoli owing to the negative effect of drying time on antioxidant activity. The antioxidant activity of broccoli was positively and significantly correlated with the FPP content but not with TPP and kaempferol. The evaluation of hydroxymethylfurfural content as an indicator of the occurrence of a Maillard reaction in dried broccoli did not support the hypothesis of a contribution of MRPs to the antioxidant activity of dried broccoli. Copyright © 2006 Society of Chemical Industry     

高效液相色谱法测定浓缩果汁及水果果糖中5-羟甲基糠醛

建立了浓缩苹果汁、浓缩梨汁和水果果糖中的5-羟甲基糠醛的高效液相色谱（HPLC）检测方法。样品用甲醇溶解后,经水稀释,Inetrsil ODS-3 C18（250mm×4．6mm,5μm）色谱柱分离,紫外检测器在282nm处进行检测;5-羟甲基糠醛在1．0-25．0mg／L范围内线性关系良好,相关系数为0．9998,回收率为82．2％～103.3％,精密度（RSD）为0．62％-1．25％,方法的检出限（LOD）为0．2mg／kg。本方法具有快速、简单、灵敏度高、适用范围广等特点,可以满足果汁中5-羟甲基糠醛的分析要求。     

Prediction of 5–MF Formation in an Industrial Apple-Juice Evaporator

The rate of formation of 5-hydroxymethylfurfural (5-HMF) in apple juice with soluble solids ranging from 15 to 69°Brix at 100, 104, 108 or 112°C was experimentally determined. Different mechanisms of reaction were proposed and corresponding kinetic models were derived. The model that provided the best fit to experimental data corresponded to a first-order initiation step, followed by an autocatalytic period limited by consumption of reactants. The resulting kinetic equations were incorporated into the mathematical model of a triple-effect apple-juice evaporator. The simulation values obtained for the content of 5-HMF in the concentrated apple juice were in good agreement with observed industrial levels. From simulation runs 5-HMF generation was strongly related to the temperature level at the first evaporation effect.     

Synthesis of 2,5‐Diformylfuran and Furan‐2,5‐Dicarboxylic Acid by Catalytic Air‐Oxidation of 5‐Hydroxymethylfurfural. Unexpectedly Selective Aerobic Oxidation of Benzyl Alcohol to Benzaldehyde with Metal=Bromide Catalysts

The alcohol group of hydroxymethylfurfural (compound 1, HMF) is preferentially oxidized by dioxygen and metal/bromide catalysts [Co/Mn/Br, Co/Mn/Zr/Br; Co/Mn=Br/(Co+Mn) = 1.0 mol/mol] to form the dialdehyde, 2,5‐diformylfuran (compound 2, DFF) in 57% isolated yield. HMF can be also oxidized, via a network of identified intermediates, to the highly insoluble 2,5‐furandicarboxylic acid (compound 5, FDA) in 60% yield. For comparison, benzyl alcohol gives benzaldehyde in 80% using the same catalyst system. Over‐oxidation (to CO₂) of HMF is much higher than that of the benzyl alcohol but can be greatly reduced by increasing catalyst concentration.     

A new approach for the production of 2,5-furandicarboxylic acid by in situ oxidation of 5-hydroxymethylfurfural starting from fructose

The production of 2,5-furandicarboxylic acid (FDCA) starting with fructose as substrate via acid-catalyzed formation and subsequent oxidation of 5-hydroxymethylfurfural (HMF) was investigated. It was shown that an effective separation of the oxidation catalyst from fructose in combination with extraction and derivatization of formed HMF in methyl isobutyl ketone (MIBK) leads to formation of FDCA as final product. Two systems were developed to realize the concept, one by phase separation with a membrane, the other by encapsulating the oxidation catalyst in silicone beads. This revised version was published online in June 2006 with corrections to the Cover Date.     

Impact of an integrated process of hot pressurised liquid extraction–macroporous resin purification over the polyphenols,hydroxymethylfurfural and reducing sugars content of Vitis vinifera ‘Carménère’ pomace extracts

Thermal degradation and generation of objectionable compounds such as hydroxymethylfurfural have been observed in hot pressurised water extraction of polyphenols. Addition of small amounts of ethanol can reduce process temperatures and retain extraction efficiencies. However, ethanol may reduce the recovery of polyphenols in the subsequent purification stage. The overall effect of increasing amounts of ethanol (0–15%) and reduced temperatures (90, 75, 60 °C) in the extraction stage, as well as increasing amounts of ethanol in the desorption eluent (60–80%) were analysed in a combined hot pressurised liquid extraction–resin purification grape pomace polyphenols process for the first time. Without decreasing the polyphenols recovery (~24 mg GAE g^?1), ethanol addition (15%) reduced the extraction temperature (from 130 to 90 °C) which not only decreased the reducing sugar extraction (~25%) but also avoided the hydroxymethylfurfural generation in the extraction stage. Additionally, the combined hot pressurised liquid extraction–resin purification process preserved the proanthocyanidin oligomeric distribution and was selective to polyphenols. The operating conditions found for the combined process, efficiently produced purified polyphenols extracts (11 mg GAE g^?1), free of hydroxymethylfurfural and reducing sugars.     

2‐Furoylmethyl amino acids,hydroxymethylfurfural, carbohydrates and β‐carotene as quality markers of dehydrated carrots

BACKGROUND: Processing of vegetables in the food industry usually includes dehydration as a preservation process. Industrial convective air drying of carrot can involve steam blanching of the raw product after peeling and cutting, and different stages of dehydration (first space, second space and final drying). Although the shelf‐life of carrot is significantly extended, important changes in its chemical composition can take place during dehydration since high temperatures and long times are used. This research is a preliminary study to evaluate the usefulness of β‐carotene, carbohydrates, hydroxymethylfurfural (HMF) and 2‐furoylmethyl amino acids (2‐FM‐AA) as quality markers of dehydrated carrots. RESULTS: A considerable decrease in β‐carotene and reducing carbohydrates was observed during dehydration. HMF, absent in raw carrots, increased during the whole drying process and the highest formation was found during the steam blanching stage. 2‐FM‐AA of lysine, arginine, γ‐aminobutyric acid and alanine were progressively originated up to the second space and decreased during the final drying. CONCLUSION: The combined use of HMF and 2‐FM‐AA seems to be advantageous for the assessment of the optimal processing conditions to obtain high‐quality dehydrated carrots. Copyright © 2008 Society of Chemical Industry     

High yield production and purification of 5‐hydroxymethylfurfural

Conversion of carbohydrates to 5‐hydroxymethylfurfural (HMF) will provide a new step toward achieving renewable biomass‐based chemicals and fuels platform. Recently, the excellent yield of HMF (91.0%) in dimethyl sulfoxide (DMSO) catalyzed by sulfonated carbon was demonstrated, but the separation of HMF from the reaction mixture remains challenging because of the high boiling point of DMSO. As a solution, herein, low boiling point solvent tetrahydrofuran (THF) mixed with DMSO was used for the fructose dehydration and high yield of HMF (98.0%) was still obtained. Besides, the stability of the sulfonated carbonaceous catalyst was also confirmed. More importantly, HMF from the reaction solution was successfully separated by using simple extraction method, and high purity of HMF (ca. 96.4%) was obtained. Compared with pure DMSO solvent, the combination of low boiling point THF with DMSO not only gives higher yield of HMF, but also improves the separation efficiency and reduces environmental risk. © 2013 American Institute of Chemical Engineers AIChE J, 59: 2558–2566, 2013