Heavy metal levels in leafy vegetables and some selected fruits

The aim of this study was to determine the levels of Cu, Zn, Fe, Pb and Cd in various fruits (tomato, cherry, grape, strawberry) and vegetables (parsley, onion, lettuce, garlic, nettle, peppermint, rocket, spinach, dill, broad bean, chard, purslane, grapevine leaves) grown in Manisa region. Flame and Graphite Furnace Atomic absorption spectrometry was used to estimate and evaluate the levels of these metals. Detected levels ranged from 0.56 to 329.7, 0.01 to 5.67, 0.26 to 30.68, 0.001 to 0.97 and 0 to 0.06 μg/g for Fe, Cu, Zn, Pb and Cd, respectively. While the highest mean levels of Cu and Zn were detected in grapevine leaves, the lowest mean levels of Fe and Pb were detected in nettle. Cd was not detected in most of the fruits and vegetables studied. The estimated daily intakes of Cu, Zn, Fe, Pb and Cd through fruits and vegetables were found to be below the maximum tolerable levels recommended by FAO/WHO. The element concentrations of fruits and vegetables analyzed in this study were within safety baseline levels for human consumption.     

Antioxidant and micronutrient quality of fruit and root vegetables from the Indian subcontinent and their comparative performance with green leafy vegetables and fruits

Commonly consumed, fruit vegetables (12) and root vegetables (15) in the Indian subcontinent in cooked and uncooked states assessed for inhibition of thiobarbituric acid reactive substances (TBARS), superoxide radical scavenging activity (SOSA), ferrous iron chelating ability (FICA) and nine micronutrients, exhibited large variability in these parameters. SOSA and FICA were significantly associated (r = 0.803, p < 0.001) with each other. Inhibition of TBARS showed marginal correlation with both FICA (0.38, p < 0.05) and SOSA (0.29, p > 0.05). There were significant cooking losses for each of the assessed antioxidant capacity parameters (p < 0.05). Contents of ascorbic acid, per 100 g of cooked fruit and root vegetables were high (61.9 and 31.3% of recommended daily allowance (RDA)). However, both the food classes were not good sources of beta‐carotene, riboflavin and thiamine (1.66–5.26% RDA). When compared with our data on 30 cooked green leafy vegetables (GLV) and 30 fresh fruits, root vegetables showed significantly (p < 0.05) higher levels of zinc and selenium. Cooked root vegetables were comparable with cooked GLVs but uncooked GLVs gave the highest values for inhibition of TBARS (0.73 ± 0.21 mM vitamin E/100g). SOSA (40.7 ± 15.6 mM tannic acid/100g) and FICA (41.6 ± 14.9 mM EDTA/100g) were highest for uncooked fruit vegetables. Root vegetables had the highest levels of polyphenols (251.4 ± 107.3 mg/100g). For the present study, popular fruits and vegetables such as guava, spinach, bitter gourd (Momordica charantia), yam, ginger and beetroot, and also less common ones like bael (Aegle marmelos), kokum (Garcinia indica) and mango‐ginger (Curcuma ameda), showed potential in vitro to combat oxidative stress. Copyright © 2005 Society of Chemical Industry     

Heavy metal levels in leafy vegetables and some selected fruits

The aim of this study was to determine the levels of Cu, Zn, Fe, Pb and Cd in various fruits (tomato, cherry, grape, strawberry) and vegetables (parsley, onion, lettuce, garlic, nettle, peppermint, rocket, spinach, dill, broad bean, chard, purslane, grapevine leaves) grown in Manisa region. Flame and Graphite Furnace Atomic absorption spectrometry was used to estimate and evaluate the levels of these metals. Detected levels ranged from 0.56 to 329.7, 0.01 to 5.67, 0.26 to 30.68, 0.001 to 0.97 and 0 to 0.06 μg/g for Fe, Cu, Zn, Pb and Cd, respectively. While the highest mean levels of Cu and Zn were detected in grapevine leaves, the lowest mean levels of Fe and Pb were detected in nettle. Cd was not detected in most of the fruits and vegetables studied. The estimated daily intakes of Cu, Zn, Fe, Pb and Cd through fruits and vegetables were found to be below the maximum tolerable levels recommended by FAO/WHO. The element concentrations of fruits and vegetables analyzed in this study were within safety baseline levels for human consumption.     

Quality of Green Beans, Bell Peppers and Spinach Stored in Polyethylene Bags

Quality attributes of packaged and unpackaged vegetables generally decreased nonlinearly during storage at 10°C or 20°C, and most of the decrease was greater at 20°C than at 10°C. Packaging reduced weight loss of green beans and spinach kept at 20°C; and reduced chlorophyll loss of green beans at 10°C and of spinach at 20°C. Ascorbic acid (vitamin C) benefited by packaging of green beans and spinach kept at 10°C. Packaging had an effect on thiamin (vitamin B₁) of only spinach held at 10°C and 20°C and had no effect on riboflavin (vitamin B₂). Loss of these quality attributes appears to be enhanced with water loss.     

REACTION AT LIMITED WATER CONCENTRATION. 2. Chlorophyll Degradation

SUMMARY— Chlorophyll degradation was studied as a function of water activity (A_w) in freeze-dried blanched spinach puree and in model systems containing cellulose-citrate buffer and chlorophyll a. At 37°C and A_w higher than 0.32, the most important mechanism of chlorophyll degradation is conversion to pheophytin. The rate of chlorophyll a transformation is 2.5 times faster than for chlorophyll b. The relation between A_w and log time for 20% chlorophyll degradation is linear and the chlorophyll/pheophytin ratio is useful for storage prediction as a function of A_w (down to A_w 0.32). At A_w lower than 0.32, the rate of pheophytin formation in spinach is low. New products are formed which can interfere with spectrophotometric determination of chlorophylls and pheophytins. The possibility of removal of Mg from the porphyrin ring of chlorophyll a was shown in model systems even at A_w below BET (Brunnauer-Emmet-Teller) monolayer coverage.     

Studies on freezing of partially dehydrated spinach

Spinach (Spinacea oleracea) was dehydrated at 70 °C, partially dehydrated frozen (dried to its critical moisture ratio and frozen at ?20 °C) and frozen at ?20 °C. Results indicated that the time required for spinach dehydration was 7 h. Thus, the moisture ratio was 10.1 and 0.054 for the fresh and dried spinach, respectively. The critical moisture ratio during dehydration process was 2.20 after 2.65 h of drying time. Reducing sugars, free amino nitrogen, ash, iron and magnesium were slightly decreased in the partially dehydrated frozen spinach relative to the fresh samples. Dehydration markedly degraded the total chlorophyll, chlorophyll a, chlorophyll b, carotenoides and ascorbic acid whereas the freezing of partially-dehydrated spinach and freezing process were less effective. On the other hand, freezing of partially dehydrated spinach increased phaeophytin. There were no changes in pH-values of studied preserved samples. Freezing of partially dehydrated spinach improved the reconstitution of product at 100 °C and at room temperature (25 °C) comparing to dehydration. The drip loss of frozen spinach was 16.4% after 105 min of thawing time. Cooked fresh and frozen spinach were better in colour, flavour, texture, appearance and shape and over-all acceptability than that of dehydrated cooked one. Moreover, freezing of partially dehydrated spinach improved the aforementioned properties.     

Study of Antioxidant Activity of Biologically Active Compounds Isolated from Green Vegetables by Coupled Analytical Techniques

This study was carried out to determine the total antioxidant activity of selected green vegetables like kale and spinach. The antioxidant activity was expressed in radical scavenging activity (RSA). The generation of the DPPH· (1,1-diphenyl-2-picrylhydrazyl) free radical forms the basis of one of the spectrophotometric methods that has been applied to the measurement of the total antioxidant activity of extracts and solutions of pure substances. Among examined vegetables, spinach showed the highest total antioxidant activity. RSA values for samples of frozen spinach varied from 16.2% to 42.6%, but RSA for fresh spinach did not exceed 19.8%. Kale extracts were obtained by use of supercritical fluid extraction. The highest antioxidant activity was found for the first fraction of extracts, and it was 14.2% (for fraction obtained at pressure 258 bar and 5% methanol addition). Afterwards, lutein belonging to carotenoid group was determined in plant extracts by means of HPLC–UV-VIS. The concentration values of lutein ranged between 0.43 and 0.88 mg/g for three frozen spinach samples and 0.83 mg/g for fresh spinach. Lutein, has also antioxidant properties; therefore, RSA was determined for the standard solutions of lutein. However, the influence of lutein on the RSA values of spinach and kale is relatively low. Spinach, more than other analysed plants had an exceptionally high total polyphenol and flavonoid content.     

硼酸镁晶须制备工艺研究进展

硼酸镁晶须作为一种高性价比的增强增韧剂,正在复合材料制备中获得越来越广泛的应用。文章主要介绍了硼酸镁晶须的制备工艺研究进展,对当前硼酸镁晶须的制备方法进行了分析和评述,并对今后的发展方向进行了展望。     

基于叶绿素的果蔬护绿方法研究进展

叶绿素是存在于绿色植物中的一种独特而重要的营养物质,在果蔬贮藏与加工过程中,如何保护叶绿素是一大难题.本文对叶绿素的性质、叶绿素稳定性的影响因素及果蔬护绿技术等进行了综述.     

粮食及果蔬中叶酸含量分析

对日常食用的主要粮食及果蔬的叶酸含量进行测定与评价,为人体科学合理补充叶酸提供理论依据。在山西省各农户及市场搜集11 种主要粮食、17 种常见蔬菜、8 种常见水果。粮食样品研磨全部过100 目筛子备用,市售新鲜果蔬样品将可食用部分随机多点采样,切碎混合。食物叶酸用磷酸二氢钾溶液恒温水浴浸提,加苯胺处理过的活性炭吸附,用体积分数3%氨-70%乙醇洗脱,采用高锰酸钾氧化-间接荧光法测定。结果显示,主要食物叶酸含量存在差异,叶酸含量较高的粮食种类有：大豆、花生、绿豆、小米、燕麦、玉米和苦荞,含量均在1.56 μg/g（以干质量计）以上;含量较高的蔬菜有：菠菜、油菜、香菇、油麦菜、生菜、卷心菜、青椒、芹菜、白菜和南瓜,含量均在1.53 μg/g（以湿质量计）以上;人们日常食用的水果叶酸含量均在1.74 μg/g（以湿质量计）以上;只要合理调整膳食结构,粗细搭配,多摄食蔬菜水果,就有望通过食疗来补充人体所缺乏的叶酸。     

Comparison of 3 Spectrophotometric Methods for Carotenoid Determination in Frequently Consumed Fruits and Vegetables

ABSTRACT: Carotenoids are C-40 tetraterpenoid compounds with potential health beneficial effects. Major dietary sources include a variety of fruits and vegetables. Rapid screening methods are therefore desired, but their accuracy varies depending on the carotenoid profile and the matrix of the plant food. In the present study, 3 different methods were compared, all based on a rapid extraction protocol and spectrophotometric measurements to determine the total amount carotenoids present in fruits and vegetables (n = 28), either with or without chlorophyll. Published methods (a) Lichtenthaler and (b) Hornero-Méndez and Mínguez-Mosquera were compared with a newly developed method (method c) based on the average molar absorption coefficient (135310 Lcm⁻¹mol⁻¹) and wavelength (450 nm in acetone), for the 5 predominant carotenoid species (beta-carotene, zeaxanthin, lycopene, lutein, beta-cryptoxanthin) in the investigated foods. All results were compared to HPLC (method d). To avoid overestimating carotenoid concentrations due to chlorophyll A and B presence, the effect of saponification was studied for all methods. Overall, saponification led to significant carotenoid losses (12.6 ± 0.9%). Methods a, b, c, and d yielded 5.1 ± 0.4 mg/100 g, 4.6 ± 0.5 mg/100 g, 4.3 ± 0.5 mg/100 g, and 4.2 ± 0.5 mg/100 g total carotenoids, respectively, with method a leading to significant higher mean concentrations compared to all other methods (P < 0.001, Bonferroni) with methods b and c being not significantly different and highly correlated compared to HPLC (> r = 0.95). Similar results were found when stratifying for chlorophyll content and fruits compared with vegetables, however, accuracy varied for individual fruits, highlighting the limitation to use the same method for all plant foods. Practical Application: This study presents a comparison of various rapid spectrophotometric measurements to determine total carotenoid content in various fruits and vegetables and could aid in the selection of the appropriate method for individual plant foods with different carotenoid profile and matrices.     

超高效液相色谱-串联质谱法测定果蔬中氟啶虫胺腈、Pyrifluquinazon和螺虫乙酯残留量

建立超高效液相色谱-串联质谱同时测定蔬菜和水果中氟啶虫胺腈、Pyrifluquinazon和螺虫乙酯残留量的分析方法。样品经乙腈均质提取,混合使用乙二胺-N-丙基硅烷和十八烷基硅烷基质分散净化剂净化,以C18色谱柱分离待测物,采用电喷雾离子化,正离子扫描和动态多反应监测模式检测,基质匹配标准溶液外标法定量。氟啶虫胺腈在0.2～100?μg/L之间,Pyrifluquinazon在0.02～10?μg/L之间,螺虫乙酯在0.1～10?μg/L之间的范围内线性关系良好,相关系数均大于0.999?0。在4个添加水平进行氟啶虫胺腈、Pyrifluquinazon和螺虫乙酯添加回收率实验,平均添加回收率在79.9%～103.9%之间,相对标准偏差在3.3%～8.8%之间。氟啶虫胺腈、Pyrifluquinazon和螺虫乙酯的方法定量限分别为0.334、0.040?5?μg/kg和0.378?μg/kg,检出限分别为0.100、0.012?2?μg/kg和0.133?μg/kg。该方法快速简便、定量准确,可满足多种蔬菜和水果中氟啶虫胺腈、Pyrifluquinazon和螺虫乙酯3?种杀虫剂的残留检测要求。     

镁与人体健康

由于镁与人体健康关系密切，有关镁代谢的研究特别是关于镁缺乏所引起的各种疾病的研究已引起各方面的重视并取得丰硕的成果。本文仅就镁在人体内的分布，吸收，生理功能，异常代谢及其食物来源等作一简要介绍。     

Magnesium in h?heren Pilzen

Zusammenfassung Der Magnesiumgehalt von 402 Arten (1047 Proben) wildgewachsener höherer Pilze, die zwischen 1967 und 1977 vorwiegend in Süddeutschland gesammelt worden waren, wurde durch Atomabsorptionsspektroskopie in einer Luft/Acetylenflamme bestimmt. Er lag zwischen 390 und 4640 mg/kg Trocken-substanz, entsprechend 20 und 1060 mg/kg bzw. 60–180 mg/kg Frischpilz. Dabei enthielten fast 75% der Proben 800–1800 mg/kg Trockensubstanz bzw. 80–180 mg/kg Frischpilz. Der Magnesiumgehalt war art- und gattungsabhängig und in der Trockensubstanz im Mittel am höchsten bei denCoprinaceae, am niedrigsten bei denBoletaceae. Er war entweder ebenso hoch wie oder niedriger als im Boden. Im einzelnen Fruchtkörper (10 Arten) war Magnesium folgender maßen verteilt: Lamellen- bzw. Röhrenschicht > Stiel = Hutfleisch = Sporen. Die Lamellen enthielten maximal doppelt so viel Magnesium wie die anderen Gewebe. Zwischen dem Magnesiumgehalt junger und alter Fruchtkörper bestand kein signifikanter Unterschied. — Der Magnesiumgehalt der Pilze liegt in der gleichen Größenordnung wie der anderer Gemüse.

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Magnesium content of higher fungi

Summary The magnesium content of 402 species (1047 samples) of wild mushrooms, collected mainly in southern Germany from 1967 to 1977, was determined by atomic absorption spectroscopy in an air/acetylene flame. It ranged from 390 to 4640 mg/kg dry weight, equivalent to 20 and 1060 mg/kg fresh weight. Nearly 75% of the samples contained 800–1800 mg/kg dry weight and 60–180 mg/kg fresh weight respectively. The magnesium content depended on species and genus. On average it was highest inCoprinaceae and lowest inBoletaceae. It equalled the magnesium content of the soil or was even lower. In single fruit-bodies (10 species) magnesium was distributed as follows: gills or tubes > stem = flesh of the cap = spores. The gills contained at most twice the magnesium of the other tissues. No significant differences were observed between the magnesium content of young and old fruit-bodies (6 species). — Thus, the magnesium content of mushrooms is in the same order of magnitude as the magnesium content of other vegetables.

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Mit Unterstützung der Deutschen Forschungsgemeinschaft

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Unter technischer Mitarbeit von Rosemarie Nützel und Ulrike Dill     

大气压冷等离子体处理对果蔬表面E.coli O157:H7生物膜的清除作用

本文探究了大气压冷等离子体(ACP)处理对E. coli O157:H7生物膜清除作用的最佳处理功率和处理时间,并进一步探究了ACP处理对E. coli O157:H7生物膜的抗菌机制,利用场发射扫描电镜观察了ACP处理前后生物膜形态的变化,最后将ACP处理应用到四种果蔬表面E. coli O157:H7生物膜的清除上。结果表明,在最佳处理功率400 W,最佳处理时间3 min下,ACP通过抑制胞外聚合物中多糖及蛋白质的合成与分泌来抑制生物膜的形成,并在处理当天分别对户太葡萄、圣女果、维多利亚青提及生菜这四种果蔬表面清除98.99%±0.38%、99.92%±0.20%、96.84%±0.18%、99.80%±0.23%的E. coli O157:H7生物膜,在5 d内仍表现出了较好的抑制效果,延长了四种果蔬的贮藏期。结合感官评定结果,ACP处理虽对四种果蔬的色泽和感官品质略有影响,但仍能被大家所接受。综上,ACP处理可在基本不影响四种果蔬的色泽及感官品质前提下,对果蔬表面的E. coli O157:H7生物膜有明显的清除效果。     

镁盐晶须的研究进展

镁盐晶须是新型的阻燃、增强纤维材料,有着广阔的应用前景。文章较详细地介绍了常见镁盐晶须的种类、用途及制备方法。     

Effects of cooking methods on chlorophylls, pheophytins and colour of selected green vegetables

The effect of microwave and conventional cooking methods on chlorophyll pigments and colour properties of squash, green beans, peas, leek, broccoli and spinach were studied, by HPLC and colorimetry, respectively. In five of six vegetables, chlorophyll a was found more heat resistant compared with chlorophyll b, except in peas. Chlorophylls in peas were retained to the 80–90%, the highest in all vegetables evaluated. Chlorophylls were retained to 19–100%, depending on the vegetable type and cooking method. Pheophytins increased in all vegetables after cooking. Highest chlorophyll a and chlorophyll b losses were observed in boiled leek while microwaved peas and boiled peas retained the most chlorophyll a and chlorophyll b, respectively. Pheophytin a and pheophytin b formation was highest at boiled squash and boiled green beans, which were fifty‐ninefold and twenty‐onefold compared with fresh ones, respectively. Most of the pheophytin formations occurred in boiled and the least in microwaved vegetables. Surface colour changed depending on the type of vegetable and cooking method.     

Retention of quality and nutritional value of 13 fresh-cut vegetables treated with low-dose radiation

Improving the microbial safety while maintaining quality of fresh fruits and vegetables will increase consumer confidence in fresh produce. This study was conducted to investigate the effects of irradiation at 1 kGy, a dose that potentially inactivates E. coli O157:H7 by 5 logs, on the quality of 13 common fresh-cut vegetables: iceberg, romaine, green and red leaf lettuce, spinach, tomato, cilantro, parsley, green onion, carrot, broccoli, red cabbage, and celery. The results showed that the appearance of irradiated samples was similar to the nonirradiated ones except that irradiated carrots, celery, cilantro, and green onions had higher appearance scores than corresponding nonirradiated vegetables. There was no difference in the instrumental texture between irradiated samples and nonirradiated ones. The aroma of several irradiated vegetables was significantly better than controls after 14-d storage, because these control samples decayed or senesced. The 1 kGy irradiation did not affect vitamin C content of most vegetables; however, irradiated green and red leaf lettuce had 24% to 53% lower vitamin C contents than the controls. Our results suggest that most fresh-cut fruits and vegetables tested can tolerate up to 1 kGy irradiation without significant losses in any of the quality attributes.     

Levels and congener distributions of PCDDs, PCDFs and Co-PCBs in Japanese retail fresh and frozen vegetables

To evaluate dioxin contamination in retail vegetables, congener analyses of polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs) and coplanar polychlorinated biphenyls (Co-PCBs) were performed on sixty varieties of fresh vegetables including cereals and mushrooms, obtained from Japanese supermarkets in 2002. The toxic equivalent quantity (TEQ) levels for dioxins in samples ranged from < 0.001 to 0.089 pg-TEQ/g wet weight, when undetected and trace were taken as zero. Among the samples, dioxins were generally detected in green leafy vegetables. The highest TEQ value was for mulukhiya (0.089 pg-TEQ/g), followed by spinach and komatsuna (Japanese mustard spinach) (0.077 and 0.074 pg-TEQ/g, respectively). Additionally, the dioxin levels in seventeen varieties of frozen vegetables were also determined, and showed TEQ values ranging from < 0.001 to 0.080 pg-TEQ/g. The total TEQ in commercial vegetables mainly reflected the levels of 1,2,3,7,8-PeCDD, 2,3,4,7,8-PeCDF and 3,3',4,4',5-PeCB (#126) (the sum of them represented 63% of the total TEQ).     

EFFECT OF DEHYDRATION ON PHYSICOCHEMICAL PROPERTIES OF MUSTARD, MINT AND SPINACH

Mustard, mint and spinach were dehydrated in a sun and cabinet drier and were subsequently studied for rehydration characteristics. Dehydration ratio ranged from 12.37:1.0 to 23.37:1.0, while rehydration ratio varied from 1.0:2.84 to 1.0:3.76 for three green leafy vegetables. The bulk density of dried vegetables varied from 55.1 to 171.5 kg/m³, whereas the angle of repose was in the range of 33.2–52.4°. Color values L, a, b and ΔE were reduced with blanching and drying. Retention of chlorophyll, β‐carotene and ascorbic acid in dehydrated products varied from 41.87 to 61.35%, 22.26 to 55.16% and 13.36 to 37.53%, respectively. On rehydration, the ascorbic acid retention was further reduced to 4.17–11.55%.