Peptic hydrolysis of bovine beta‐lactoglobulin under microwave treatment reduces its allergenicity in an ex vivo murine allergy model

In this study, the in vivo allergenicity of bovine beta‐lactoglobulin (BLG) in peptic whey protein hydrolysates generated during microwave and conventional heating treatments was assessed. The allergenicity of the hydrolysates was explored by studying the reaction of the murine jejunum from previously immunised Balb/c mice to treated BLG in an Ussing chamber. Intestinal anaphylactic reactions after stimulation of the gut‐associated immune system are a good indicator of potential in vivo allergenicity of whey hydrolysates. Fifty‐two per cent of BLG was hydrolysed by pepsin after only 3 min of microwave irradiation at 200 watts (W), yet it remained intact under conventional heating. Far‐ and near‐UV circular dichroism spectra indicated significant changes in BLG secondary and tertiary structures with microwave irradiation at 200 W. Pepsin whey protein hydrolysates obtained with microwave irradiation at 200 W for 3 min did not stimulate secretion of chloride in the Ussing chamber, as shown by the intensity of the short current values recorded (27.86 μA cm^?2), compared to the conventional pepsin hydrolysates (68.21 μA cm^?2). This demonstrates the low allergenicity of whey protein hydrolysates generated in this manner. These results confirm that microwave treatment combined with peptic hydrolysis could be applied to produce low allergenicity milk peptides.     

Efficient microwave processing of oil–water emulsion cylinders with lateral and radial irradiations

A detailed theoretical analysis has been carried out to assess the role of lateral and radial irradiations on the microwave heating of 2D cylinders for both o/w and w/o emulsion samples. Lateral irradiation represents the sample incident at one direction with the source at infinity whereas radial irradiation represents the situation where the sample is incident with microwave radiations from the coaxial cylindrical cavity at infinity. For both of lateral and radial irradiations, the effective microwave incidence from the source is assumed to be identical. A preliminary analysis on the microwave heating of samples has been carried out via average power within a sample vs. sample diameter for emulsions with various values (volume fraction of the disperse phase). The samples with smaller diameter are found to have larger average power with radial irradiation for both o/w and w/o emulsion samples. The hot spot formation within a sample is found to be a strong function of lateral/radial irradiation for various emulsion compositions. The radial irradiation or conventional microwave heating with turntable rotation in ovens is not favorable especially for large w/o samples as the hot spot occurs at the center resulting in larger thermal gradient. The present work provides guideline on the heating policy based on either lateral or radial irradiation depending on the sample size and emulsion dielectric properties.     

微波强化浸取天然色素机理的探讨

利用扫描电子显微技术和透射电了显微技术，分析了微波强化浸取天然色素和传统加热浸取天然色素过程中的柚皮细胞结构，发现微波强化浸取的机理与传统加热浸取的机理不同，在此研究的基础上提出了细胞壁的“电穿孔”机理。     

Accelerated texture softening of some root vegetables by Ohmic heating

Effects of different thermal processing methods (Ohmic heating, high and low power, microwave and conventional heating) on textural properties of cylindrical pieces of root vegetables of carrot, red beet and golden carrot were investigated and compared with conventional and microwave processes. The samples were subjected to different processing methods and textural parameters of the processed samples were analyzed using texture profile analysis (TPA) at different processing times. Texture parameters-processing time data were fitted into a previously suggested equation and texture softening rate (K) and residual constant (A) values were calculated. From the K and A values it can be concluded that not only Ohmic heating resulted in greater softening rates but also the final hardness of the samples treated by Ohmic heating was significantly lower than those of other samples treated by either conventional or microwave methods. Negative correlations were found between texture hardness and weight loss of all samples undergone different processing methods.     

高频电磁场下柚皮中天然食用色素的浸取

以柚皮为原料,以水为介质,在微波条件下直接从柚皮中提取天然色素。微波浸取与传统方法相比,具有提取率高、节省时间、能源消耗小、安全无污染等特点。扫描电子显微技术分析证明,微波固液浸取的机理与传统加热浸取的机理是不同的。     

Acid resistance and verocytotoxin productivity of enterohemorrhagic Escherichia coli O157:H7 exposed to microwave

Abstract: We examined the acid resistance and verocytotoxin (VT) productivity of enterohemorrhagic Escherichia coli O157:H7 irradiated by microwave with a domestic microwave oven and a commercial microwave radiator equipped with a thermo‐regulator. When the cell suspension (5 mL) chilled at 0 °C was treated with a domestic microwave oven at weak power (2.45 GHz, 100 W) for 60 s, the living cell number was reduced by 2 orders (final temperature, about 65 °C). The surviving cells showed lower acid resistance and VT productivity than nonirradiated cells. To examine the nonthermal effect of microwave on acid resistance and VT productivity, the cells in Luria‐Bertani medium were intermittently irradiated to keep the culture temperature at 37 °C with the microwave radiator (2.45 GHz, 0.6 W/mL). The intermittent radiation slightly reduced the acid resistance, but clearly suppressed the VT productivity. Microwave oven is probably useful for reducing not only the living cell number but also the acid resistance and VT productivity of EHEC O157:H7.     

Changes in the antigenic and immunoglobulin E-binding properties of hen's egg albumin with the combination of heat and gamma irradiation treatment

This study was carried out to evaluate the changes in the allergenic and antigenic properties of hen's egg albumin (ovalbumin [OVA]) with the combination of heat and gamma irradiation treatment. OVA solution samples were treated by (i) heating (sample 1), (ii) irradiation after heating (sample 2), and (iii) heating after irradiation (sample 3). Samples were isothermally heated and irradiated at the absorption dose of 10 kGy. Competitive indirect enzyme-linked immunosorbent assays (ELISAs) were performed with blood serum to test the ability of treated OVA to bind to immunoglobulin E (IgE) and mouse murine monoclonal antibody (IgG). OVA's ability to bind to mouse IgG changed upon heating at 75 degrees C, and its ability to bind to egg-allergic IgE changed upon heating at 80 degrees C. The ELISAs showed that egg-allergic IgE did not recognize OVA very well when heated at > or = 80 degrees C, while mouse IgG retained better activity under these conditions. Egg-allergic IgE binding was low both for OVA samples treated by heating and for samples treated by irradiation followed by heating. These results show that allergies induced by OVA could be effectively reduced by the combination of heat and gamma irradiation treatment.     

Effects of microwave heating on the migration of substances from melamine formaldehyde tableware

Melamine formaldehyde (MF) tableware, after undergoing repeated heating in a microwave oven for 1, 2, 3 or 5 min, was tested for migration into 3% (w/v) acetic acid, a food simulant. Overall migration (OM) consistently increased with an increasing number of heating/washing cycles, while formaldehyde was found at low concentrations or was not detectable. Unexpectedly, the 1-min series caused the most rapid increase in OM; the European Union regulatory limit of 10 mg dm^–2 was exceeded after 25 cycles. The number of cycles required to reach the OM limit rose to 29 and 67 for the 2- and 3-min series, respectively. Only 37 cycles were needed in the case of the 5-min series; however, the cumulative exposure time to microwave irradiation was relatively close to that of the 3-min series. These findings indicate that microwave heating affects the migration of MF in a significantly different manner as compared with conventional heating reported in previous studies. Fourier transform infrared spectroscopy (FTIR) spectra of MF after completing the microwave heating series show that the plastic was not fully cured, as evidenced by the absence of methylene linkages. The majority of migrants obtained from OM tests consisted of low molecular weight methylol melamine derivatives. The results indicate that microwave heating allowed demethylolation, addition and condensation reactions to occur, which was not the case when using conventional heating. This study demonstrates that microwave heating for 1–2 min in a repeated manner is of high concern in terms of consumer health. It was found that the service terms of melamine ware under microwave heating were drastically reduced, by more than 10-fold, as compared with the service terms under conventional heating. Hence, it is strongly recommended that manufacturers of MF articles provide instructions for use, e.g. “Do not use in microwave”, which should be clearly visible to consumers and not easily detachable.     

微波加热缬氨酸和葡萄糖的棕化反应

研究了微波加热下pH值、反应时间、溶剂配比对缬氨酸与葡萄糖的棕化产物反应深度的影响,以及微波加热和普通加热的棕化产物的差异,并进行了棕化产物的卷烟加香试验及其醚溶性成分的分析。结果表明:①微波能加速棕化反应进程,在相同反应时间内微波反应产物的一些主要成分含量要大于普通加热产物;②温度对棕化反应影响大于加热方式;③相同体系,普通加热和微波加热棕化产物成分基本相同,只是在含量上有差别;④体系的pH值对微波棕化反应进程及反应产物都有较大影响,酸性和碱性环境都能加速反应进程;⑤微波加热的缬氨酸与葡萄糖产物中共鉴定出5种重要的吡嗪类化合物和1种呋喃类化合物,没有鉴定出醛类、吡咯类等常见的普通棕化反应产物;⑥在微波加热,pH6·35,反应时间30min,溶剂为丙二醇-水(1∶1体积比)条件下,缬氨酸与葡萄糖的棕化反应产物加香效果较好。     

微波辐射合成羊毛用壳聚糖胍盐酸盐抗菌剂

采用微波辐射技术合成了一种羊毛用的壳聚糖胍盐酸盐抗菌剂。微波加热法合成壳聚糖胍盐酸盐可以简化合成工艺流程,显著提高了反应速率,在极短的时间内可以获得较常规加热法同样的产率,从而提高了合成效率。探讨了微波辐射合成时的热效应、特殊微波效应和非热效应,并将合成的壳聚糖胍盐酸盐整理剂用于羊毛织物的抗菌整理,取得了很好的抗菌和耐洗效果。     

EFFECT OF FAR-INFRARED HEATER ON THE PHYSICOCHEMICAL CHARACTERISTICS OF GREEN TEA DURING PROCESSING

ABSTRACT

The green tea leaves (Camellia sinensis var. sinensis) were irradiated by a far‐infrared (FIR) heater during the roasting and drying step, resulting in three different treatments produced. Green tea was extracted by soaking the leaves in water, and the components were analyzed. FIR irradiation, combined with fryer heating during the roasting step and additionally applied after the drying step, increased total phenolic contents of green tea from 116.30 to 171.77 mg/g, and total flavanol contents from 17.54 to 24.76 mg/g, compared with the non‐irradiated control. Ascorbic acid contents also increased from 3.07 to 4.20 mg/g. The amounts of epicatechin gallate and epigallocatechin gallate were significantly increased from 2.41 to 4.59 mg/mL and 20.61 to 28.54 mg/mL, respectively, compared with the non‐irradiated control. FIR irradiation increased Nitrite Scavenging Ability of green tea at pH 3.0 and pH 4.2, while there was no significant difference at pH 6.0. Sweetness, umami and aroma of green tea were enhanced by FIR irradiation, while bitterness and astringency were decreased compared with those of the control. These results show that FIR heating during the green tea process affected the chemical properties of green tea, and the FIR heater can be applied to increase the physicochemical qualities of green tea.

PRACTICAL APPLICATIONS

Green tea, a widely consumed drink, has received much attention because of the beneficial biological effects attributable to its excellent antioxidant activity. In this article, a far‐infrared (FIR)‐heater for industrial application was used during the processing of green tea leaves, and the chemical characteristics and quality of FIR‐treated green tea were determined. FIR irradiation, combined with fryer heating during the roasting step and additionally applied after the drying step, significantly increased phenolic, flavanol, ascorbic acid, epicatechin gallate, epigallocatechin gallate contents and nitrite‐scavenging activity compared with non‐irradiated control. Sensory evaluation also showed a positive effect of FIR irradiation. The results indicated that FIR heater could be easily applied to increase the quality of green tea in the processing line.     

The irradiation of spices, packaging materials and luncheon meat to improve the storage life of the end products

Spices and packaging materials were exposed to γ‐irradiation at a dose of 10 kGy. Luncheon meat was prepared with irradiated or non‐irradiated spices and packaged in irradiated or non‐irradiated packaging materials. Packaged luncheon meat was treated with 2 kGy. Irradiated and non‐irradiated packaged luncheon meat were kept in a refrigerator (1–4 °C) for 12 months. Microbiological, nutritive and chemical characteristics of luncheon were evaluated after processing and during storage; whereas, sensory quality was evaluated only after irradiation. γ‐Irradiation decreased the microbiological counts of spices, packaging materials and packed products and increased its shelf‐life. No significant differences in moisture, protein, fat, pH value, total acidity, lipid peroxide and volatile basic nitrogen were observed as a result of irradiation. Sensory evaluation showed that all the combinations of treated luncheon meats were acceptable. However, the taste, odour, appearance and texture scores of irradiated packaged products were significantly lower than those of non‐irradiated samples.     

Lethality and quality evaluation of in-packaged ready-to-eat cooked Jasmine rice subjected to industrial continuous microwave pasteurization

The use of the pasteurization unit as a measure of the lethal effect of heating processes and overall quality of ready-to-eat Jasmine rice was determined in order to compare the conventional and microwave technology. Cooked Jasmine rice was packed in a polypropylene plastic cup and sealed with a lidding film, then subjected to a continuous microwave system (eight 800 W; 2450 MHz) and conventional steamer. The pasteurization unit, log reduction, microorganism count, color, instrumental textural property, and sensory attributes were investigated over a 30-day storage at 8°C. The pasteurization process time was reduced from 420 s under the conventional process to 216 s under the microwave process for a 5-log reduction of L. monocytogenes. The microwave heating showed greater effectiveness for shelf life, extending the product from 7 days (conventional) to 30 days. Cooked rice after heating by microwave was whiter and showed lower hardness than the conventional heated sample. Throughout storage, sensory attributes of the pasteurized product heated by microwave were acceptable by panelists. The addition of 15% trehalose or 1% soybean oil into the rice before cooking decreased the hardness of the cooked rice during storage. This study successfully demonstrated that the continuous microwave pasteurization process, compared to the conventional process, required less process time for ready-to-eat cooked Jasmine rice and extended the shelf life while providing better product quality.     

Effect of microwave heating on optical and thermal properties of rice starch

This study used the oil bath to imitate the high heating rate of the microwave heating (MV) and evaluated the effects of conventional and MV on optical and thermal properties of rice starch at the same heating rate. The results indicated that the time–temperature profiles for microwave and rapid conventional heating fitted well, with a correlation coefficient of 0.9989. During both conventional and MV starch granule did not swell until 60°C, and granule swelling and loss of granule birefringence occurred simultaneously. DSC revealed a 50% decrease in enthalpy when temperature rose from 60 to 65°C, and a further decrease in enthalpy until 70°C. Therefore, microwave irradiation had no effect on the optical and thermal properties of starch during gelatinization.     

Microwave irradiation under different pH conditions induced a decrease in β-lactoglobulin antigenicity

Whey proteins adjusted at pH values 2, 4.6, 9 and at the natural milk pH (pH 6.8) were subjected to microwave irradiation at 300 W for 20 min or 700 W for 10 min. The protein composition of treated and native whey proteins were evaluated by Lowry’s method and sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). The ability of treated whey to bind IgG polyclonal antibody was determined by an enzyme-linked immunosorbent assay (ELISA) using sera obtained from rabbit immunized to β-Lactoglobulin (β-Lg). Significantly higher losses in soluble protein concentrations were observed for microwave irradiated whey proteins at pH value 4.6 (35.6% at 300 W and 44.33% at 700 W) (P < 0.0001) compared with those irradiated at the natural milk pH (26% at 300 or 700 W). The electrophoretic patterns of these proteins revealed a considerable decrease in intensity of the band corresponding to α-lactalbumin but only a slight modification was observed for the electrophoretic profiles of β-lactoglobulin. The data obtained with a rabbit anti-β-lactoglobulin immunoglobulin indicated a low antigenic response for microwave-irradiated whey proteins at the natural milk pH (up to 29.32% as well as 300–700 W) (P < 0.001). The lowest antigenicity was observed for samples adjusted to pH 4.6 followed by microwave irradiation at 300 or 700 W (46.99% at 300 W and 41.16% at 700 W) (P < 0.0001).     

Microwave Finish Drying of Diced Apples in a Spouted Bed

The combination of a spouted bed with microwave heating to improve heating uniformity was evaluated. Experiments were performed on a laboratory system in which evaporated diced apples of about 24% moisture were dried to about 5% at 70°C air temperature using four levels of microwave power density (0 to 6.1 W/g). With the combination method, temperature uniformity in diced apples was greatly improved as compared to that with a stationary bed during microwave drying. Products had less discoloration and higher rehydration rates as compared to conventional hot air drying or spouted bed (SB) drying. Drying time could be reduced by >80% compared with SB drying without microwave heating.     

Microwave vs. convection heating of bovine Gluteus Medius muscle: impact on selected physical properties of final product and cooking yield

The aim of this study was to investigate the impact of two convection–microwave heating (M100 and M30) on texture and colour properties, cooking yield and thermal shrinkage of bovine product (gluteus medius muscle) as compared with conventional roasting at constant temperature (P180 and P80) and roasting with ΔT program (Δ80 and Δ40). The product processed by the M100 method was characterised by high shear force (WBSF) and high compression force (TPA). The reduction of microwave intensity to 30% (roasting M30) could improve the tenderness of final product. In addition, microwave heating at the intensity of 30% shortened the roasting time, and the produced sample exhibited comparable process loss and heat shrinkage extent compared to those treated by the high‐temperature conventional roasting method (P180). The study indicated that combining of convection and low‐intensity microwave heating could be successfully used in catering business for beef roasting due to the shorter cooking time, reduced cooking loss and higher tenderness of meat.     

Effect of γ‐radiation and microwave heating of wheat grain on some starch properties in irradiated grain as well as in grain of the next generation crops

Grains of the Polish winter wheat variety Begra were subjected to γ‐radiation (grain harvested in 1996) within the dose range of 0.05–10 kGy and microwave heating (grain harvested in 1997) from 28°C to 98°C. Later the grains were divided into two parts, the first was used for direct analyses after treatment. The second part was sown on the experimental fields. The obtained crop was described as the first generation and divided into two parts. One part was destined to determination of starch properties and the second part was sown in order to obtain the second generation crop. The same pattern was conducted in order to achieve the third generation crop. γ‐Irradiation directly applied on the wheat grain reduced statistically significant falling number values and gelatinisation enthalpy (ΔH) of the grain treated by 5 and 10 kGy. Calculated linear regression correlation coefficient between the falling number values and the gelatinisation enthalpy was equal to 0.94 (p ? 0.001) and showed that these two starch characteristics are well correlated in the case of directly irradiated wheat grain. The falling number values, peak temperatures (T_p) and gelatinisation enthalpy (ΔH), in three generations of wheat grain crop studied, did not show any statistically significant differences as a result of indirect effect of γ‐irradiation. Microwave direct heating of wheat grain to 98°C caused a statistically significant increase in the falling number value and decrease in starch gelatinisation power expressed by the enthalpy of gelatinisation (ΔH). The statistically significant changes in the falling number values, slight changes in the peak temperatures (T_p) and enthalpy of gelatinisation (ΔH) were found in all three generation crops as an indirect effect of microwave heating.     

Low‐Dose Irradiation Can be Used as a Phytosanitary Treatment for Fresh Table Grapes

Grapes (Vitis vinifera var. Sugraone and Vitis labrusca var. Crimson Seedless) were treated with 400, 600, and 800 Gy and the effects on physicochemical factors were measured alongside sensory testing during 3 wk of storage. Significant changes in texture and color with irradiation and age were measured but little visual difference was seen between control and irradiated grapes. However, age had a greater effect on firmness than irradiation for Sugraone grapes. Irradiation did not significantly (P ≤ 0.05) affect the SSC/TA ratio, which increased during storage. The trained panel detected significant changes in the berry texture and rachis color but rated sweetness and flavor significantly higher (P ≤ 0.05) for irradiated Sugraone as compared to the control. Consumers liked both the untreated and 800 Gy treated Sugraone grapes, but liked the untreated grapes more for texture (P ≤ 0.05). However, there was no difference in liking between irradiated (600 Gy or 800 Gy) and control samples of Crimson Seedless for any attribute. The results show that there are varietal differences in response to irradiation but the overall maintenance in quality of irradiated grapes during 3 wk of storage indicates that irradiation can serve as a viable phytosanitary treatment.     

Carboxymethyl Starch Octenylsuccinate: Microwave‐ and Ultrasound‐assisted Synthesis and Properties

The synthesis of water‐soluble octenylsuccinates of carboxymethyl starch (OS‐CMS) was performed with octenylsuccinic anhydride by assistance of microwave and ultrasound irradiation using the dimethyl sulphoxide/p‐toluenesulphonic acid system and DMSO as solvents for activation of CMS as well as reaction medium of the following esterification. The prepared OS‐CMS derivatives were characterized with regard to their structural, surface‐active and performance properties. The application of both microwave and ultrasound irradiation as energy sources permitted to shorten the esterification time to several minutes from 24 h of the previously reported conventional heating [33], whereby the reaction efficiencies were high and the water‐soluble derivatives exhibited excellent emulsifying efficiency as well as surfactant performance properties tested by washing power and antiredeposition efficiency. The results indicate also the high potential of both microwave and ultrasound energy sources to innovate and increase the efficiency of technological polysaccharide esterification processes.