Monitoring for nitrate in UK-grown lettuce and spinach

To comply with European Commission requirements, the UK is carrying out a monitoring programme on nitrate concentrations in lettuce and spinach. This paper reports the results obtained between June 1996 and April 1998. A total of 182 samples of protected lettuce, 131 samples of outdoor-grown lettuce and 34 samples of fresh spinach were taken from the main growing areas of the UK. Nitrate concentrations in protected lettuce were influenced by the season with summer-grown crops (mean of 2382mg/kg) having lower levels than those grown in the winter (mean of 3124mg/kg). Weather conditions also affected concentrations in protected lettuces with long hours of sunshine and low rainfall associated with low nitrate levels. Nitrate concentrations in outdoor-grown lettuces were lower (mean of 1085mg/kg) than those in protected lettuces but there were insufficient data to determine if they were affected by the weather conditions or season. Similarly there were insufficient data to determine if weather conditions or season influenced nitrate concentrations in spinach (mean of 1900mg/kg) but regional differences were observed.     

Physico-Chemical Characterization of Oils Extracted from Noni,Spinach, Lady’s Finger,Bitter Gourd and Mustard Seeds,and Copra

The physico-chemical properties of solvent-extracted oil from the seeds of noni (Morinda citrifolia L.), spinach (Spinacia oleracea L.), lady’s finger (Abelmoschus esculentus (L.) Moench), bitter gourd (Momordica charantia L.), mustard (Brassica nigra (L.) Koch), and the dried kernel (copra) of coconut (Cocos nucifera L.) were characterized. Among these sources, spinach seed had the lowest oil content (4.5 ± 0.4%) while coconut kernel had the highest oil content (63.1 ± 2.8%). Palmitic, oleic, and linoleic acids were the major fatty acids for spinach, lady’s finger and noni seed oils, while erucic, eleostearic, and lauric acids were the major fatty acids for mustard seed oil, bitter gourd seed oil, and coconut kernel oil, respectively. All of the oils possessed at least three major peaks in their triacylglycerol profiles except for bitter gourd seed oil which had only one major peak (1-stearoyl, 2,3-dieleostearoyl). The last endothermic peaks were –12.4, –6.0, 6.8, 57.7, 2.7, and 24.3ºC for noni, spinach, lady’s finger, bitter gourd and mustard seed oils, and coconut oil, respectively. Initially, the solid fat content of bitter gourd seed oil decreased gradually, but became rapidly after 50 until 60ºC. Coconut oil had its solid fat content reduced rapidly around 14 to 28ºC.     

Reduction of Escherichia coli O157:H7 viability on leafy green vegetables by treatment with a bacteriophage mixture and trans-cinnamaldehyde

Enterohemorrhagic Escherichia coli (EHEC) O157:H7 has been recognized as a major foodborne pathogen responsible for frequent gastroenteritis outbreaks. Phages and essential oils can be used as a natural antimicrobial method to reduce bacterial pathogens from the food supply. The objective of this study was to determine the effect of a bacteriophage cocktail, BEC8, alone and in combination with the essential oil trans-cinnameldehyde (TC) on the viability of a mixture of EHEC O157:H7 strains applied on whole baby romaine lettuce and baby spinach leaves. The EHEC O157:H7 strains used were Nal^R mutants of EK27, ATCC 43895, and 472. Exponentially growing cells from tryptic soy (TS) broth cultures were spot inoculated on leaves and dried. EHEC cells were placed at low, medium, and high inoculum levels (10⁴, 10⁵, and 10⁶ CFU/mL, respectively). Appropriate controls, BEC8 (approx. 10⁶ PFU/leaf), and TC (0.5% v/v) were applied on treated leaves. The leaves were incubated at 4, 8, 23, and 37 °C in Petri dishes with moistened filter papers. EHEC survival was determined using standard plate count on nalidixic acid (50 μg/mL) Sorbitol MacConkey agar. No survivors were detected when both leaves were treated with BEC8 or TC individually at low inoculum levels after 24 h at 23 and 37 °C. When the EHEC inoculum size increased and/or incubation temperature decreased, the efficacy of BEC8 and TC decreased. However, when the two treatments were combined, no survivors were detected after 10 min at all temperatures and inoculum levels on both leafy greens. These results indicated that the BEC8/TC combination was highly effective against EHEC on both leafy greens. This combination could potentially be used as an antimicrobial to inactivate EHEC O157:H7 and reduce their incidence in the food chain.     

菠菜参考物质中40种元素的中子活化分析

采用仪器中子活化分析和放射化学中子活化分析测定了菠菜参考物质（ＮＩＳＴ－１５７０ａ）中的４０种元素。其中纯仪器分析测定了Ａｇ、ＡＩ．Ｂａ．Ｂｒ、Ｃａ、Ｃｅ、ＣＩ、Ｃａ、Ｃｒ、Ｃａ、Ｅｕ、崐Ｆｅ、Ｈｆ、Ｋ、Ｌａ、Ｍｇ、Ｍｎ、Ｎａ、Ｎｉ、Ｒｂ、Ｒｅ、Ｓｂ、Ｓｃ、Ｓｅ、Ｓｒ、Ｔａ、Ｔｂ、Ｔｈ、Ｖ、Ｚｎ崐和Ｚｒ等３１种元素：采用三个简单的放射化学流程测定了另外９种元素：通过际去主要干扰核素崐测定了Ｃｄ．Ｌｕ,Ｍｏ、Ｓｍ．Ｙｂ和Ｕ;采用ＮａＤＤＴＣ／ＣＨＣＩ３萃取测定Ｃｕ：通过酸性ＡＩ２Ｏ３无崐机交换柱吸附测定Ａｓ和Ｐ．该流程也适用于其它生物样品的多元素分析。还采用ＩＫ０法对２３５Ｕ的裂变干扰和Ｙ能谱干扰进行了校正     

Study of flavonoids in aqueous spinach extract using positive electrospray ionisation tandem quadrupole mass spectrometry

The presence of three flavonols (quercetin, kaempferol, myricetin) and two flavones (apigenin, luteolin) were investigated in the extract of fresh spinach leaves. Aqueous spinach extracts were prepared with a leaf/water ratio of 1:2 at 80 °C for 30 min stirring. Ferric ammonium sulphate method was used for measuring total polyphenols in the extracts and expressed as catechins and tannic acid equivalents. The flavonoids glycosides in the extract were hydrolysed to their aglycons with 1.2 M HCl in boiling 50% water methanol solution. The resulting aglycons were identified and quantified by a C18 reverse phase high-performance liquid chromatography (RP-HPLC). Furthermore, the results were confirmed by HPLC coupled to an electrospray ionisation tandem triple-quadrupole mass spectrometer ESI-MS performing low-energy collision induced dissociation (CID-MS/MS) in the collision cell (HPLC-ESI-MS/MS). Analyses were made in the multiple reaction monitory (MRM) mode. Results showed that total polyphenols contents in fresh spinach leaves were 270 mg kg⁻¹ and 390 mg kg⁻¹ as tannic acid and catechin equivalents, respectively, in which, major flavonoids aglycons were apigenin (170 mg kg⁻¹), quercetin (50 mg kg⁻¹) and kaempferol (30 mg kg⁻¹).     

Inactivation of Escherichia coli O157:H7, Listeria monocytogenes, Salmonella enterica and Shigella flexneri on spinach leaves by X-ray

Several recent foodborne disease outbreaks associated with leafy green vegetables, including spinach, have been reported. X-ray is a non-thermal technology that has shown promise for reducing pathogenic and spoilage bacteria on spinach leaves. Inactivation of inoculated Escherichia coli O157:H7, Listeria monocytogenes, Salmonella enterica and Shigella flexneri on spinach leaves using X-ray at different doses (0.1, 0.2, 0.3, 0.5, 0.75, 1.0, 1.5 and 2.0 kGy) was studied. The effect of X-ray on color quality and microflora counts (mesophilic counts, psychrotrophic counts and yeast and mold counts) of untreated and treated spinach was also determined. A mixture of three strains of each tested organism was spot inoculated (100 μl) onto the surface of spinach leaves (approximately 8–9 log ml⁻¹), separately, and air-dried, followed by treatment with X-ray at 22 °C and 55–60% relative humidity. Surviving bacterial populations on spinach leaves were evaluated using a nonselective medium (tryptic soy agar) with a selective medium overlay for each bacteria; E. coli O157:H7 (CT-SMAC agar), L. monocytogenes (MOA), and S. enterica and S. flexneri (XLD). More than a 5 log CFU reduction/leaf was achieved with 2.0 kGy X-ray for all tested pathogens. Furthermore, treatment with X-ray significantly reduced the initial inherent microflora on spinach leaves and inherent levels were significantly (p < 0.05) lower than the control sample throughout refrigerated storage for 30 days. Treatment with X-ray did not significantly affect the color of spinach leaves, even when the maximum dose (2.0 kGy) was used.     

Simultaneous recovery of bacteria and viruses from contaminated water and spinach by a filtration method

Water and leafy vegetables eaten fresh are increasingly reported as being involved in food-borne illness cases. The pathogenic agents responsible for these infections are mainly bacteria and viruses and are present in very small quantities on the contaminated food matrices. Laboratory techniques used to isolate or detect the contaminating agent differ enormously according to the type of microorganisms, generating time and economical losses. The purpose of this study was to optimize a single method which allows at the same time the recovery and concentration of these two main types of pathogenic organisms. Water and spinach samples were artificially contaminated with the feline calicivirus (FCV), rotavirus, hepatitis A virus (HAV), Escherichia coli, Listeria monocytogenes, Campylobacter jejuni and Salmonella Typhimurium. The principle behind the recovery technique is based on the use of a positively charged membrane which adsorbs both viruses and bacteria present in the water or in the rinse from the vegetables. Using conventional microbiology, PCR and RT-PCR, this filtration technique allowed a detection level superior to 10² CFU/g for S. Typhimurium, E. coli, L. monocytogenes and C. jejuni and to 10¹ PFU/g for FCV, HAV and rotavirus. This combined method can also be applied to other bacterial and viral species for the identification of the responsible agent for food-borne illnesses.     

几种蔬菜在冷藏过程中的品质变化

研究了菠菜、黄瓜、青椒在3种不同冷藏温度（1,5,9℃）下贮藏时的品质变化。通过对这3种蔬菜进行感官评分和含水量,Vc含量及叶绿素含量的测定,发现菠菜、黄瓜、青椒分别在1℃,9℃、5℃下贮藏时的质量变化较慢。     

Determination of oxalic acid in spinach with carbon nanotubes-modified electrode

This work investigated the electrocatalytic oxidation of oxalic acid on multiwall carbon nanotubes (MWNTs) modified glassy carbon (GC) electrode. The result indicated that the oxidation of oxalic acid was greatly improved at the MWNTs-modified GC (MWNTs/GC) electrode as compared with the bare GC electrode. The effects of the MWNTs suspension amount, pH and scan rate on the electrooxidation response of oxalic acid were studied by voltammetry. The surface concentration and diffusion coefficient (D_R) of oxalic acid at the MWNTs/GC electrode were determined by chronocoulometry. This MWNTs/GC electrode presented a wide linear response ranging from 5.0 × 10⁻⁵ to 1.5 × 10⁻² M for oxalic acid. The detection limit (S/N = 3) was estimated to be 1.20 × 10⁻⁵ M. Based on this MWNTs/GC electrode, the content of oxalic acid in spinach was successfully determined.