Effects of sugar, protein and water content on wheat starch gelatinization due to microwave heating

 Understanding the interactions between sugar, starch, protein and water, which are the main components of a baked product, will advance the development of high quality, microwaveable products. This paper presents a mathematical model describing the quantitative relationships between water, sugar and protein on the gelatinization of wheat starch following 20 s of microwave heat as determined by differential scanning calorimetry. Addition of sugar decreased the degree of gelatinization of starch due to microwave heating significantly. Water and protein were not found to be as significant as sugar in delaying gelatinization. The effects of sugar and protein on the gelatinization of starch were pronounced in water-limited systems. The model could be used to describe systems containing 33–67% water, 0–33% sucrose and 0–5.8% protein, with a coefficient of determination of 0.91. Received: 29 June 1998     

Influence of starch sodium octenyl succinate on rheological behaviour of wheat flour dough systems

Experimental and theoretical influence of addition of various amounts of three types starch sodium octenyl succinate (OSA) granules (0–20%): (a) non-physically modified, (b) pregelatinized and (c) hydrolyzed spray-dried on rheological behavior of wheat flour dough systems under oscillatory strain conditions was considered.     

Effects of microwave frying and different flour types addition on the microstructure of batter coatings

In this study, the influences of microwave frying and various flour types on microstructure of batter coatings were investigated. Control batter formulation contained only wheat and corn flour. To determine the effects of different flour types, 30% of the corn and wheat flour mix was replaced with chickpea, rice or soy flours. Frying was performed in microwave oven at 365 W (70%) power level for 1.5 min after bringing the oil temperature to 180 ± 1 °C. Samples were also fried in a conventional fryer at 180 °C for 1.5 and 5.0 min for comparison. Microwave fried samples had higher specific bulk volume and porosity values and also smoother inner surface as compared to conventionally fried samples. Porosity values of different batter formulations were in the range of 0.425–0.484 in 1.5 min microwave fried chicken samples and 0.348–0.392 in 5.0 min conventionally fried ones. Microwave fried samples had comparable or lower hardness values than the conventionally fried ones depending on the flour type used in batter formulation. Microstructure of fried batter was different for different batter formulations. Microwave fried control and chickpea flour containing batter provided formation of larger gas cells on the outer surface. Soy flour containing batter resulted in smallest size gas cells for both frying methods.     

Exploring the heating patterns of multiphase foods in a continuous flow,simultaneous microwave and ohmic combination heater

A continuous flow, simultaneous microwave and ohmic combination heater was designed and fabricated to heat treat particulate foods without leaving solids under-processed. Heating uniformity of the combination heater was examined by numerically analyzing the electric field distribution under microwave and ohmic heating. In addition, to minimize the reflection of microwave power, impedance matching of the microwave cavity was conducted with a vector network analyzer. Performance of the heater was studied using food mixtures containing sodium chloride solutions (0.2–0.5%) and carrot particulates. Heating patterns of liquid–particle mixtures were investigated and compared under individual and combination heating modes. Energy efficiencies were also determined for corresponding heating methods. The results showed that maximum solid–liquid temperature differences under microwave and ohmic heating were about 8.1 and 8.0 °C, respectively. However when microwave and ohmic heating techniques were applied simultaneously, there was no significant temperature difference between solid and liquid phases. Energy efficiency of combination heating was higher than microwave heating and a maximum increase in energy conversion of 12.8% was obtained. The findings opened new and very promising opportunities to thermally process particulate foods with improved uniformity, organoleptic, and nutritional quality in addition to reduced food safety problems.     

微波辐射对玉米淀粉羧乙基化的研究

实验采用Discover微波精确有机合成系统,采用单模聚焦微波辐射技术及电脑微控和空压气体同步冷却技术,以玉米淀粉为原料,并且以丙烯氰为醚化剂,研究了单模聚焦微波辐射对玉米淀粉羧乙基化的影响.通过正交实验确定最佳工艺条件:淀粉4.0g,丙烯腈2.7g,氢氧化钠3.0g,乙醇溶液体积为35mL,微波辐射功率95W,辐射时间4min,最高温度50℃.在此条件下可以快速有效获得较高取代度的羧乙基玉米淀粉.产品经红外光谱仪表征,证实与目标产物完全一致.     

河北产区9个谷子品种淀粉性质的研究

对河北产区9个不同品种谷子的淀粉含量、表观直链淀粉含量、透明度及糊化特性等进行研究,比较其中的差异。测得这9个品种淀粉含量平均为64.52%,表观直链淀粉平均为14.96%;通过对直链淀粉与透光率的研究表明,淀粉透光率与直链淀粉含量存在显著的负相关性;对糊化特性的分析表明:冀谷19具有较高的崩溃值,为2890cP,以及较低的消减值-1234.5cP,同时其直链淀粉含量也较低,为11.97%,说明冀谷19可能具有较好的食味品质。     

Effect of γ‐radiation and microwave heating on endosperm microstructure in relation to some technological properties of wheat grain

Grains of the Polish winter wheat variety Begra were subject to γ‐radiation (⁶⁰Co) within the dose range of 0.05–10 kGy and microwave treatment from 15 to 180 s, the latter resulting in a bulk grain temperature ranging from 28 to 98°C. Both processes were responsible for marked structural changes of wheat kernel endosperm and were pronounced with increasing dose of ionizing radiation or with prolonged time of microwave treatment. Endosperm microstructures of wheat kernels treated with γ‐radiation ranging from 0.05 to 0.5 kGy did not differ from that of untreated ones. Only some changes in the structure of starch granules and proteins were observed at doses of 1, 5 and 10 kGy. Simultaneously at the doses of 5 and 10 kGy a statistically significant decrease of falling number, sodium dodecyl sulfate (SDS) sedimentation values, dough stability and energy were observed, while dough weakening progressed. Microwave treatment longer than 90 s caused marked changes in kernel endosperm structure. Some changes of proteins caused by denaturation created visible fibrils as well as high swelling and deformation of starch granules. This was followed by an increase in the falling number value, decrease in the estimated results of SDS sedimentation test, lowering of the percent of gluten washed out and of the dough energy, respectively. Also a significant decrease in bread quality expressed by volume and score was observed with increasing time of exposure to microwave.     

Biochemical characteristics of Trametes multicolor pyranose oxidase and Aspergillus niger glucose oxidase and implications for their functionality in wheat flour dough

Similar to glucose oxidase (GO), pyranose oxidase (P₂O) may well have desired functionalities in some food applications in general, particularly breadmaking. As its name implies, P₂O oxidises a variety of monosaccharides. P₂O purified from a culture of Trametes multicolor (P₂O-Tm) had high affinity towards d-glucose (K_M = 3.1 mM) and lower affinity to other monosaccharides. GO from Aspergillusniger (GO-An) had a K_M value of 225 mM towards glucose, which points to a significant difference in glucose affinity between the two enzymes. Furthermore, P₂O-Tm had higher affinity towards O₂ (K_M = 0.46 mM) than GO-An (K_M = 2.9 mM). Dehydroascorbic acid did not accept electrons in the reactions catalysed by P₂O-Tm and GO-An. For the same activity towards glucose in saturating conditions, the rate of ferulic acid oxidation in a model system and of thiol oxidation in a wheat flour extract were higher with P₂O-Tm, than with GO-An. The demonstrated differences in properties and functional features between P₂O-Tm and GO-An allow prediction of differences in functional behaviour of the enzymes, in food applications.     

Annual variation of deoxynivalenol in Danish wheat flour 1998-2003 and estimated daily intake by the Danish population

The occurrence of deoxynivalenol (DON) in Danish wheat flour was studied during the period 1998-2003 by either capillary gas chromatography with electron capture detection and liquid chromatography coupled to an ion trap mass spectrophotometer. A total of 151 samples were collected from mills and the retail market in Denmark. Contamination levels varied considerably from year-to-year with the highest concentrations occurring in samples from the 2002 harvest with mean and median concentrations of 255 and 300 µg kg^-1, respectively. Compared to other harvest years, 2002 had the highest amount of precipitation around flowering time, i.e. from the end of June to the beginning of July covering weeks 25-27. The lowest average levels were found in samples from the 2001 harvest, where weeks 25-27 were dry compared with other harvest years. The highest value (705 µg kg^-1) was obtained in a flour sample from the 2002 harvest, but none of the tested samples exceeded the maximum limit of 750 µg kg^-1, which has been recently introduced by the European Commission for DON in flour used as raw materials in food products. Calculation of chronic or usual intake by a deterministic approach showed that intake did not exceed the TDI of 1 µg kg^-1 bw day^-1 either for the whole population or for children. A probabilistic approach also showed that intake in general was below the TDI, but intake for children in the 99% percentile amounted to more than 75% of the TDI. The highest intake is calculated to be 2.5 µg kg^-1 bw day^-1.     

Gas chromatographic detection of d-amino acids in natural and thermally treated bee honeys and studies on the mechanism of their formation as result of the Maillard reaction

Relative quantities of d-amino acids, (%D) calculated from the sum of d- and l-amino acids were determined in bee honeys (n=6) by GC-SIM-MS. Amino acids were isolated by treatment with Dowex 50 W X8 cation exchanger and converted into N(O)-perfluoroacyl amino acid propyl esters. In all honeys d-Ala, ranging from 2.2–6.2% d-Ala, was detected. Other d-amino acids were also found, albeit not in all honeys and approached 5.9% d-Glx, 5.4% d-Lys, 3.0% d-Phe, 2.1% d-Orn, 1.7% d-Asx, 1.5% d-Ser, 0.1% d-Pro, and 0.4% d-Val in certain honeys. Quantities of d-amino acids increased very much on experimental heating of honeys in an oven and on a microwave treatment. Conventional heating of a forest honey (no. 1) at 65 °C for 450 h leads to an increase of d-Ala (2.2–12.5%), d-Pro (0.0–5.0%), d-Ser (1.5–9.1%), d-Asx (1.7–9.8%), d-Phe (0.4–5.0%) and d-Glx (1.5–5.8%); first numbers in parentheses refer to unheated honeys. Relative quantities of other d-amino acids also increased. Experimental heating of another forest honey (no. 2) in a microwave oven for 3 min at 180 W leads to an increase of d-Ala (3.7–11.0%), d-Glx (1.5–13.7%), d-Asx (0.7–10.2%), d-Phe (0.3–4.8%), d-Val (0–4.2%), and d-Pro (0.1–2.3%). Microwave treatment at 700 W for 1 min of a blossom honey (no. 3) leads to an increase of d-Ala (6.2–26.7%) and of d-Phe (3.0–10.9%). Microwave treatments were accompanied by intensive destruction of amino acids. Heating of a model mixture mimicking the major components of honey (d-glucose, d-fructose, and l-amino acids at 20% water content) at pH 2.6–9.0 and at 180 W for 1–3 min leads to the generation of d-amino acids and was also accompanied by intensive decay of amino acids. From the data it is concluded that d-amino acids are formed in honeys in the course of the Maillard reaction. A mechanism is presented based on amino acid racemization of reversibly formed Heyns and Amadori compounds (fructose-amino acids).Parts of the results have been presented at 9th International Congress on Amino Acids and Proteins, August 8–12, 2005, Vienna, Austria, and Euro Food Chem XIII, September 21–23, 2005, Hamburg, Germany.     

Inhibition of fish oil oxidation and the radical scavenging activity of New Zealand seaweed extracts

This study describes the potential use of New Zealand seaweed extracts as antioxidants in fish oils. The extracts from two brown seaweeds (Ecklonia radiata, Macrocystis pyrifera) and two red species (Champia sp. and Porphyra sp.), were added to hoki (Macruronus novaezelandiae) oil and assessed by production of oxidation products in an elevated temperature (60 °C) storage trial. Antioxidant assays ORAC and DPPH were conducted to elucidate the radical scavenging activity of the seaweed extracts. The results showed that all the lipid-soluble seaweed extracts had some antioxidative capacity, with brown algae generally outperforming red algae species. Extracts from E. radiata performed best with significantly lower primary, secondary and total oxidation products, and higher DPPH radical scavenging ability than the commercial antioxidant, BHT. This study demonstrated the potential of brown algae seaweed extracts, in particular E. radiata, for use as antioxidants in fish oil products.     

A rapid microwave-assisted derivatization process for the determination of phenolic acids in brewer’s spent grains

A simple and fast method for the TMS derivatization of phenolic acids in a closed vial using microwave irradiation followed by GC/MS analysis is proposed. A full factorial design was used to investigate the effects of two independent variables, namely, time and power of microwave irradiation, on the yield of silylation reaction. The optimal conditions were tested against the classical heating derivatization procedure. No significant differences were found between the classical heating and microwave-assisted derivatization. Chromatographic separation of the nine phenolic acids examined was achieved in 16 min. The mass spectral fragmentation patterns of the derivatives obtained by the proposed method were identical to those from the classical heating. Four different batches of brewer’s spent grain were extracted and analyzed for the total phenolic acid content. Significant differences between the batches of spent grains were found for all analytes. The total phenolic acid content varied between 2688 and 4884 μg/g.     

Characterisation of an acidic peroxidase from papaya (Carica papaya L. cv Tainung No. 2) latex and its application in the determination of micromolar hydrogen peroxide in milk

An acidic peroxidase isoform, POD-A, with a molecular mass of 69.4 kDa and an isoelectric point of 3.5 was purified from papaya latex. Using o-phenylenediamine (OPD) as a hydrogen donor (citrate–phosphate as pH buffer), the optimum pH for the function of POD-A was 4.6, and the optimum temperature was 50 °C. The peroxidase activity of POD-A toward hydrogen donors was both pH- and concentration-dependent. Under optimal conditions, POD-A catalysed the oxidation of OPD at higher rates than pyrogallol, catechol, quercetin and 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS). The chemical modification reagents N-bromosuccinimide and sodium azide significantly inhibited POD-A activity. The results of kinetic studies indicated that POD-A followed a ping-pong mechanism and had a K_m value of 2.8 mM for OPD. Using CPC silica-immobilised POD-A for the determination of micromolar H₂O₂ in milk, the lower limit of determination was 0.1 μM, and the recoveries of added H₂O₂ were 96–109%.