Radio frequency pasteurization and disinfestation techniques applied on low-moisture foods

Abstract

The shelf life of foods is usually limited due to the frequent contamination by pests and microorganisms. Although low risk of pathogen contamination and no growth potential compared to those in high water activity animal- or vegetal-derived products, the low-moisture food has still significantly contributed to the total number of foodborne infections and outbreaks. Radio frequency (RF) treatments can be classified as a dielectric heating, which is a promising technology for achieving effective food pasteurization and disinfestations because of the associated rapid and volumetric heating with large penetration depth. The RF technique could be applied at low-moisture food as both the dipole dispersion and ionic conductivity may play effective roles. It can selectively heat and kill the microorganisms/pests without damaging the agricultural product because of the large difference of dielectric loss factors between target microorganisms/pests and host foods. In this article, the low-moisture foods sterilized and disinfested by RF energy are reviewed through basic theories, dielectric properties, heating effect, and uniformity. The potential research directions for further RF heating applications are finally recommended in low-moisture foods.     

The effect of microwave treatment on the immunoreactivity of gliadin and wheat flour

Commercial gliadins and wheat flour were exposed to microwaves at power distribution of 70, 200, and 500 W for different time periods to achieve a level of applied energy doses up to 150 kJ. Ethanolic extracts (40 vol.% ethanol/water) of microwave treated samples were analyzed by ELISA with the use of either monoclonal antibodies against -gliadin or polyclonal anti-gliadin antibodies and by electrophoresis followed by immunoblotting. A significant increase in reactivity, almost 210% over the untreated control sample, was observed for gliadins exposed to the energy dose of 40 kJ. Gliadins treated with higher energy doses showed a drop in an immune response independent of monoclonal or polyclonal antibodies used in ELISA. Gliadin fractions extracted from wheat flour treated with microwaves demonstrated similar immunoreactivity changes vs applied energy, although the maximum of reactivity appeared at 30 kJ. The increase in immune response of microwave irradiated gliadins was also confirmed by immunoblotting assay with the use of sera of patients susceptible to wheat flour allergy. Reversed phase HPLC elution profiles of treated gliadins showed that the content of all gliadin fractions in microwave treated samples decreased with the increase of the dose of applied energy.     

基于视频目标跟踪算法的储粮害虫活跃程度判别研究

针对储粮害虫杀虫效果评估实验,本文提出了一种多目标跟踪算法,通过跟踪评估区域内多头储粮害虫的运动给出每头害虫的活跃程度,对害虫存活状态进行自动评估。算法基于 Faster R-CNN框架的目标检测技术,融合Mean Shift和Deep SORT目标跟踪算法,实现了对储粮害虫运动位置的连续跟踪,且减少了两头害虫相遇再分离后身份错位问题发生的情况。对于20头以内的同种害虫,平均多目标跟踪准确率为95.89%,多目标跟踪精度为83.18%。而且在目标跟踪算法中记录了每头储粮害虫的速度变化,通过分析一定时长的害虫移动速度,提出了一种评估储粮害虫活跃程度为低、中或高的分级方法,可以辅助实验人员对实验效果的分析。     

Modeling heat transfer for disinfestation and control of insects (larvae and eggs) in date fruits

A space-and-time dependent model describing the impact of heat transfer on insect survival rate was developed for analyzing the heat disinfestation process of dates. A 2D axial-symmetric domain was defined with five sub-domains: the bulk date pulp, a thin air layer and the date pit, a larva (located in the air layer) and eggs (on the date surface). The model included convective heating and microwave heating (915 MHz). Dielectric properties of the date pulp, egg and larvae were measured. The model predictions showed good agreement with experimental results in the case of the “biological model” (Ephestia kuehniella Zeller) in dates subjected to hot air treatment (70 °C). Sensitive analysis showed that the date size and water content greatly affected the heating time process, during hot air and microwave treatments. Moreover, regarding the eggs’ specific surface, it is advisable to combine convective hot air with microwave heating to induce egg mortality on the date surface.     

Toxicity and growth inhibitory activities of methanol extract and the β-carboline alkaloids of Peganum harmala L. against two coleopteran stored-grain pests

Methanol extract and the β-carboline alkaloids were extracted from the seeds of Peganum harmala (Zygophyllaceae). Their toxicity, growth inhibitory and effects on the progeny production of Tribolium castaneum and Rhyzopertha dominica was studied. To assess any additive effects among the extracted β-carbolines, they were tested as binary mixtures (1:1) or as a crude alkaloid fraction. All extracts exhibited a considerable adulticidal effect with increasing activities in response to increased exposure period. Using the contact toxicity bioassay, the crude β-carboline fraction was the most effective (LC_50’s were 20.1 and 36.7) μg/cm², 48 h post-treatment against R. dominica and T. castaneum, respectively. LC_50’s of (harmaline + harmine), (harmaline + harmane), and methanol extract were (31.2, 39.4), (33.7, 47.2), and (39.8, 65.2) μg/cm², 24 h post-treatment against R. dominica and T. castaneum, respectively. At 48 h post-treatment, LC₅₀ of (harmaline + harmine) reached 22.4 μg/cm² against R. dominica. When mixed with the insect’s diets, toxicity of all extracts were increased with the crude alkaloidal fraction the most toxic (LC_50’s were 7.8 and 14.7) mg/kg grains, 48 h post exposure against R. dominica and T. castaneum, respectively. When the 2nd instar larvae were fed sub-lethal doses-treated grains, development and F1 progeny of both insects were significantly affected (P ≤ 0.001). At 3.5 mg/kg grains of the crude alkaloidal extract, percentages of malformed larvae and pupae of T. castaneum were 19.7 and 33.4%, respectively. In this case, a total life span of 81.3 days was recorded for the treated individuals compared to 44.2 for the control. A reduction in the adult progeny of 56.9, 44.0 and 43.6% was obtained with 3.5 mg/kg of the crude alkaloids, (harmaline + harmine) and methanol extract, respectively. Meanwhile, the reduction in adult progeny of R. dominica reached 79.2% with the same concentration of the crude alkaloid extract.     

Combined effect of carbon monoxide mixed with carbon dioxide in air on the mortality of stored-grain insects

A study to determine the effect of carbon monoxide (CO) mixed with carbon dioxide (CO₂) in air on controlling stored-grain insects was conducted in the laboratory. Within modified airtight gas exposure units containing wheat at 15% moisture content wet basis (w.b.), mixed-age adults of rusty grain beetle, Cryptolestes ferrugineus (Stephens), red flour beetle, Tribolium castaneum (Herbst), and granary weevil, Sitophilus granarius (L.) were exposed for 48, 96, 144 or 192 h to three types of gas mixtures in air, 5% CO, or 30% CO₂, or 5% CO + 30% CO₂ at 20 °C and 30 °C, the balance of the gas being air in each case.Carbon monoxide alone had no effect on the mortality of adults of the three insect species. For C. ferrugineus, there was no difference in mortality between by CO₂ alone and the CO₂ + CO mixture at either temperature for all exposures. However, both T. castaneum and S. granarius had higher mortality in the CO₂ + CO mixture than the CO₂ alone at both temperatures. Moreover, S. granarius was more susceptible to CO₂ + CO mixture than T. castaneum. These results suggest that for certain species, CO could be used to increase the efficiency of CO₂, especially at high temperatures.     

微波消解测定食品中金属元素的方法探讨

为了快速、简便、准确地测定食品中的金属元素 ,建立了硝酸微波消解法。本方法需要固体样品 0 2～ 0 5g ,液体样品 0 5～ 3 0mL ,浓硝酸 0 5～ 2 0mL ,加水至 8mL消解 ,定容至 15mL ,用原子吸收光谱仪测定Fe、Mn、Cu、Zn、Pb、Cd ;用原子荧光光谱仪测定Hg。由于所用试剂量大大减少 ,空白值低 ,结果准确可靠。检测国家标准物质GBW 0 85 0 8米粉 ,GBW 0 85 13茶树叶 ,平均回收率为 82 35 %～ 10 8 70 % ,RSD为 0 6 3%～ 7 37% ,测定值与标示值相吻合 ,适于食品中金属元素的测定。     

Delineating the effect of gaseous ozone on disinfestation efficacy,protein quality,dehulling efficiency,cooking time and surface morphology of chickpea grains during storage

Ozone is one of the acceptable and economically viable techniques for treating grains during storage for its residue-free and environment-friendly nature. A laboratory-scale and pilot-scale ozone disinfestation system for chickpea grains was developed. Chickpeas conditioned to different moisture levels (10, 12, 14% wb), infested with Callosobruchus maculatus were stored at different temperatures (15, 23, 31 °C), with varying bed thickness (50, 75, 100 mm), and samples were disinfested by ozone gas at different concentrations (500, 750, 1000 ppm). Ozone concentration, moisture content of the grain, grain bed thickness, and storage temperature had significant (p < 0.01) effects on the disinfestation of C. maculatus insects. 100% insect mortality (adult and egg) and 79% germination were achieved when treated at 1000 ppm ozone for 5 consecutive days. The optimum treatment parameters were tested in pilot-scale bins (250 kg) and the germination ability, protein, milling, and cooking qualities of chickpea grain were evaluated after 6 months storage period. The protein content, germination ability, surface morphological analysis, milling, and cooking time were shown to profoundly deteriorate in the untreated samples as a contrast to that of the ozone-treated samples. Ozonation at higher doses resulted in the crack generation on the surface of the insect eggshell (5–38 μm) and chickpea pericarp (326–711 nm), with added advantages of improved dehulling efficiency of chickpea by 3.1% and reduction in the cooking time by 15 min. The SDS PAGE profiling exhibited major deviations in the protein bands in the stored chickpea. The essential amino acids (EAA) and total amino acids (TAA) decreased in the ozone-treated sample and control sample with storage; however, major deterioration was observed in the control sample stored for 6 months.     

微波对茶叶中霉菌的灭菌效果研究

为解决茶叶中霉菌的污染问题，研究了不同微波条件对茶叶中霉菌的杀灭效果，以达到在茶叶加工中综合利用微波实行加热制作和杀除霉菌的双重目的。试验结果表明：微波对茶叶中霉菌的处理效果随茶叶水分含量的增加而增强，同时与茶叶的处理物料量、容器介质及水分扩散条件有关。使用800W功率的微波炉，处理135s，可将250g茶叶中的霉菌完全杀灭。处理120s，可将鲜茶料和发酵茶料中的霉菌完全杀灭。轻度的微波作用对茶叶中霉菌生长有激活效应，微波加热超过150s，会对茶叶本身的品质造成损害。在茶叶的初制加工过程中，进行微波处理，可有效地控制茶叶中的霉菌，同时实现对茶叶料的热烘干。     

小麦进口急剧增加,国内优质麦供应任重道远

近期我国小麦进口呈现急剧增长势头,对国内小麦市场产生了一定的冲击。本文通过对深圳蛇口南顺面粉有限公司的调查,分析了小麦进口增长的主要原因,并对国内优质小麦生产提出政策建议。     

小麦洗打一体清理机研制

小麦洗打机是在打麦机和洗麦机的基础上开发的一种新型清理设备,具有能耗低,清理效果好,污染小．使用方便的特点．     

Disinfestation of red flour beetle (Tribolium castaneum) present in almonds (Prunus dulcis) using microwave heating and evaluation of quality and shelf life of almonds

Almonds (Prunus dulcis) are one of the high-value nuts facing insect pest infestation predicaments during post-harvest operations and subsequent storage. The red flour beetle (Tribolium castaneum) (Coleoptera: Tenebrionidae) is an economically important and notorious insect pest that globally infest almonds thereby resulting in high storage losses. Currently, the fumigants (hydrogen phosphide and propylene oxide) commonly used during almond storage pose a health hazard to the applicator and consumer as well as the environment. Other disadvantages of chemical methods include chemical residue, high exposure time (2–4 days), pest resistance, the demise of beneficial insects and incomplete disinfestation of the egg stage of the target pest. Among other physical disinfestation methods, the use of microwave as a disinfestation technique offer advantages of less processing time, lower energy consumption, clean technology, and no residues. Therefore to test the efficacy of microwave in pest control of stored almonds, we exposed life stages of T. castaneum to microwave irradiation at different power levels (120–600 W) and durations (30–90 s). Hundred percent mortality of all selected life stages was achieved at 480 and 600 W when infested almonds exposed for 90 and 60 s respectively. The quality attributes of treated almonds such as color difference, water activity, hardness, peroxide value, free fatty acid, and iodine value were measured and found to be acceptable. The fatty acid composition and sensory analysis demonstrated no significant difference (p > 0.05) in control and microwave treated almonds. The storage studies revealed that microwave treated almonds were free from infestation and rancidity for up to 12 months, whereas untreated almonds were spoiled within 3 months.     

一种探管式储粮害虫诱捕在线监测装置的设计研究

为实现对粮仓粮堆内害虫发生的早期监测,本研究基于探管式诱捕器和红外光电传感器研发了一种经济有效、可实时在线监测害虫发生的装置;基于该装置建立了9种主要储粮害虫成虫红外光电序列数据集;通过方差分析和数据可视化方法验证了其数据分布特性与害虫进入诱捕段的位置无关;对红外光电序列建立了高斯核支持向量机模型,通过实验室的测试,对蛀蚀性和粉食性两大害虫类别的判别达到了加权平均分类准确率87.7%、召回率87.5%和F1值87.6%。     

Flameless catalytic infrared radiation used for grain disinfestation does not affect hard red winter wheat quality

The effects of a bench top flameless catalytic infrared emitter at temperatures and times used for disinfesting grain on the physical, chemical, rheological, and end-use qualities of wheat were evaluated in the laboratory. The test weight of wheat was unaffected when 113.5 and 227.0 g of hard red winter wheat were exposed for 45 or 60 s to infrared radiation. However, a slight drop in kernel moisture increased kernel hardness, but these effects were reversed when the wheat was tempered prior to milling. Flour, shorts, and bran yields, and chemical properties (protein and ash) of these fractions from untreated wheat and infrared-treated wheat showed minor differences that were inconsequential. Mixograph and bake test results did not reveal any consistent adverse effects of infrared radiation on the quality parameters studied. Our results show that infrared treatments that provide effective control of stored-grain insects do not affect the physical, chemical, rheological, and end-use qualities of hard red winter wheat.     

小麦淀粉分离方法研究

小麦淀粉通过直接破碎浸泡过的小麦籽粒来分离得到，通过对各种影响因素的研究，总结出一种淀粉分离方法，以此种方法分离制取的小麦淀粉纯度高，破损率低，能够较好地保持其原有的各种特性，利于对小麦淀粉特性进行研究。     

The quality assessment of gari produced by using microwave energy

Summary A novel technique using microwave energy for roasting and drying or garification of fermented cassava mash is investigated. The quality of gari produced using this method compared favourably with the standards quoted in the literature and with those of commercial gari purchased from a London market, in terms of colour, swelling capacity, moisture, pH and total acidity.     

Comparison of crumb microstructure from pound cakes baked in a microwave or conventional oven

Imaging, light microscopy and scanning electron microscopy were used to compare the microstructure of crumbs from pound cakes baked in a microwave or conventional oven. The microwave baking conditions for pound cake (240 W, 5 min) were established in previous research, conventional baked pound cakes were obtained using a swing oven at 180 °C for 40 min. Statistical differences in total cell, cell/cm² and mean cell area (P?0.05) were observed in the image analysis. Cells from microwaved pound cake crumbs were 20% larger. However, factor shape was 0.81 for both microwave and conventionally baked crumbs, and crumbs from both oven types were similar in appearance. Light microscopy revealed birefringence in crumbs from both types of pound cakes. Scanning electron microscopy revealed that the conventionally baked product had a greater amount of protein matrix however; the matrix structure of the crumb was comparable between microwave-baked and conventionally baked pound cakes. In conclusion, our results suggest that the unique aspects of pound cake dough, including its high content of fat, sugar and moisture, make it well suited to microwave baking.     

Disinfestation of stored wheat grain and flour using gamma rays and microwave heating

Samples of wheat grain and flour (20 gm of each) were infested with 20 larvae or 5 pairs of adult insects of Tribolium confusum, Lasioderma serricorne, Corcyra cephalonica or Rhyzopertha dominica. The infested samples were tested as follows : (1) microwave heating at four temperature levels 40, 45,50 and 55 °C, for exposure times from10 to 50 s; (2) gamma irradiation over the dose range of 0.5-4 KGy; (3) gamma irradiation + microwave heating. Complete kill of all stages tested was achieved at 50 °C with an exposure time of 50 s. A dose of 2 KGy induced 100% mortality of R. dominica after three days, but it took up to 7 days for all T. confusum and L. serricorne adults to die after a 4-KGy exposure. All insects died within 24 h when exposed to the combination of 1KGy + 50 °C for 30 s.Biochemical analyses on the samples of wheat grain and flour subjected to those treatments at which high mortality was obtained generally showed no detectable changes in the quality of protein, fat, fiber, carbohydrates or ash. The germination of wheat grain was lowered after treatment with microwave radiation but was not affected by a dose of 1 KGy gamma radiation.     

微波能促进壳聚糖钙离子配合物的制备研究

首次报道了微波加热下壳聚糖钙离子配合物的制备,考察了影响壳聚糖配合物中钙离子含量的主要因素。结果表明,其它条件相同,微波法制备的壳聚糖钙离子配合物钙离子的含量比水浴加热制备的配合物钙离子的含量较高。实验考察了加热时间、不同反应物配比、不同种类的酸和不同浓度的醋酸对配合物钙离子含量的影响。     

Simultaneous microwave heating and three-dimensional MRI temperature mapping

In microwave processing a number of microwave specific factors cause non-uniform heating patterns with hot and cold spots. Hence, the quality and safety of food products can be compromised. Capabilities for creating three-dimensional temperature maps are therefore essential for control, optimisation and validation of microwave heating processes. This paper will discuss the advantages and shortcomings of different techniques for measuring temperatures in electromagnetic fields. The unique possibilities of applying non-invasive magnetic resonance imaging (MRI) for temperature mapping are demonstrated by experiments. In particular, in-situ measurements with three-dimensional isotropic resolution of 1 mm and a reasonable temporal resolution of 13 s are presented and compared with infrared thermography and fibre optic thermometry. Numerical simulations are employed to assess the extent of two kinds of systematic errors involved in the MRI experiment.

Industrial relevance

The presented approach for measuring temperatures volumetrically in-situ during a microwave heating process allows for the determination of three-dimensional temperature distributions; hence hot and cold spots in the products can be detected.Although the experiments in this study have been conducted in a high-resolution MRI tomograph with a small sample diameter, the same approach works in larger scale medical tomographs with bores up to 1 m diameter, making it also relevant for industrial scale applications.The costs of an MRI tomograph are still high; however, having premium products where quality would be adversely affected by overheating and safety compromised by under-processing, the application of such technology would be of great benefit for the food industry. Two approaches for applying this technology in industrial applications are possible:1. In-situ temperature measurement would allow for a feed-back control of the process, which is essential for microwave applications to be applied to processing of high quality products.2. The technology can be used for random tests, which in turn allows for evaluating temperature performance (level and uniformity), as well as fine-tuning of coupled electromagnetics/CFD models to simulate and optimise processing lines.No calibration of such system is needed and only a small amount of unbound water has to be present in the product for the methodology to be applied on or close to an industrial processing line.With a feed-back controlled microwave process, which can be simulations or real processes, the main advantage of such applications, the increase of process rates due to the volumetric heating can be utilised and at the same time the quality of the treated product can be optimised and product safety can be ensured by improving temperature uniformity. Furthermore, regulatory bodies can be satisfied.