生菜在贮藏过程中亚硝酸盐、硝酸盐含量的变化及其与微生物生长的关系

主要研究了在25℃室温和4℃冷藏条件下,新鲜生菜和清炒生菜中亚硝酸盐和硝酸盐含量的变化情况,并探讨了微生物对其硝酸盐及亚硝酸盐含量变化的影响.结果表明,新鲜生菜在两种贮藏条件下,其亚硝酸盐和硝酸盐含量在较小的范围内波动.清炒生菜在冷藏条件下贮存亚硝酸盐含量变化较小,远低于国标规定值的4mg/kg,但在室温条件下贮存6h,其亚硝酸盐含量就已经超过国标规定值,贮存24h后,更是超过国标规定值4倍之多.而微生物的生长是导致清炒生菜中亚硝酸盐含量变化的主要原因之一.     

热烫叶菜在冷链储运及微波复热过程中的品质变化

论文以上海青和菜心作为研究对象,探究了叶菜在热烫加工、冷链贮藏和微波复热过程中亚硝酸盐含量、硝酸盐含量、菌落总数、维生素C（Vc）含量等指标的变化。结果表明：因亚硝酸盐易溶于水,热烫处理能有效降低叶菜中的亚硝酸盐含量;冷藏过程前期叶菜中的Vc协助抑制亚硝酸盐增长,而冷藏后期随着Vc的消耗和微生物增长,亚硝酸盐含量逐渐增加,上海青和菜心在4 ℃分别冷藏5 d和4 d后亚硝酸盐含量仍能维持在4 mg/kg的安全标准内,而10 ℃冷藏的只能保证2 d内的安全性;微波复热过程由于水分散失导致硝酸盐和亚硝酸盐的浓度增加,因此复热过程应避免大面积敞口加热。本文探索了热烫叶菜在冷链储运及微波复热过程中亚硝酸盐的累积机理,为其应用于冷链盒饭提供理论依据。     

食品中亚硝酸盐及其含量的调查

本文报道了武汉市四类食品(粮食、蔬菜、鱼肉制品、水)中亚硝酸盐、硝酸盐含量的调查结果。结果表明,四类食品中都含有亚硝酸盐,硝酸盐。在四类食品中,鱼肉制品中亚硝酸盐含量均值(5．75mg/kg)高于其它食品,蔬菜中硝酸盐含量均值(1298．21mg/kg)高于其它食品。肉制品又以香肠中亚硝酸盐、硝酸盐含量的均值(7．79mg/kg、653．44mg/kg)为最高,硝酸盐残留量超标率达33%。蔬菜类食品中,不同的蔬菜,亚硝酸盐、硝酸盐含量不同。亚硝酸盐以黑白菜为高(7．02mg/kg)硝酸盐以菠菜为最高(3874．50mg/kg),其次是芹菜(3368．25mg/kg)藕中亚硝酸盐、硝酸盐含量(0．51mg/kg、27．56mg/kg)均低。根据调查结果,对60公斤体重成人每日亚硝酸盐、硝酸盐的摄入量作了初步估计,亚硝酸盐摄入量为3．37mg,硝酸盐摄入量为671.19mg。硝酸盐摄入量超过了每日允许摄入量(219mg/60kg、b．w)。     

食前处理对几种蔬菜品质的影响

本试验以市售菠菜、苦苣、小白菜和生菜为材料,分别对其进行盐渍、盐渍后水洗和煮沸处理,探究不同处理方式对蔬菜中硝酸盐与Vc含量的影响。结果表明:未处理前,菠菜中的硝酸盐主要集中于茎,而叶片中Vc含量高于茎;煮沸3 min处理可显著降低菠菜茎叶硝酸盐含量,茎叶硝酸盐较煮沸前分别减少79.2%和63%;同时,Vc含量下降。盐渍、盐渍后水洗及煮沸三种方式均可显著降低苦苣、小白菜与生菜中硝酸盐含量,其中,苦苣、小白菜和生菜经煮沸后硝酸盐含量较原样分别减少40.1%,51.9%和66.8%。煮沸是降低硝酸盐含量的有效方法;对于未经处理的原样而言,三种蔬菜中以苦苣的Vc含量较高,硝酸盐含量较低。     

常用蔬菜中铅、镉含量的测定与分析

对购买于当地市场中的8种蔬菜:黄瓜、芹菜、菠菜、油麦菜、大白菜、菜花、生菜等进行Pb、Cd含量状况调查,并研究了蔬菜对Pb、Cd含量的吸收富集分布特点。结果表明:天水市常用蔬菜中Pb含量范围为0.003~1.003 mg/kg,Cd含量范围为0.002~0.091 mg/kg;蔬菜中Pb、Cd的人均日暴露量均低于ADI值,分别为0.064 mg/(d·人)和0.009 mg/(d·人)。     

太原市市售蔬菜贮藏过程中亚硝酸盐含量变化及食用安全评价

以绿叶菜类(生菜、油麦菜、芹菜)、根茎类(胡萝卜、土豆、莲藕)和瓜果类(黄瓜、西红柿、茄子) 9种太原市市售蔬菜为研究对象,研究了亚硝酸盐含量在蔬菜贮藏过程中的影响及食用安全性评价。研究结果表明,在室温和冷藏两种贮藏条件下,在6 d的贮藏期内,亚硝酸盐含量均低于4 mg·kg-1,在食用安全范围内。     

家庭贮藏加工对蔬菜中亚硝酸盐含量的影响

采用比色法检测蔬菜中的亚硝酸盐含量。试验结果表明,不同蔬菜的亚硝酸盐含量在贮藏(常温和4℃冰箱)加工(不同煮沸时间)过程中变化明显,且有"亚硝化峰"现象。两种贮藏温度下,4℃冰箱贮藏可降低蔬菜中亚硝酸盐含量,并使亚硝化峰延迟出现;6种蔬菜中亚硝酸盐含量峰值比较为:菠菜、白菜芹菜、四季豆番茄、白萝卜;按蔬菜中亚硝酸盐限量值4.0mg/kg计,番茄和白萝卜中亚硝酸含量均未超标,而菠菜和白菜中亚硝酸含量均超标。煮沸时间在5 min~20 min内,6种蔬菜中亚硝盐含量均不超过3.5 mg/kg。以菠菜为例,煮熟后室温放置24 h~32 h期间,其亚硝酸盐含量和细菌总数迅速增加,放置至32 h,亚硝酸盐含量达到5.2 mg/kg。     

加工和贮存条件对蔬菜亚硝酸盐含量的影响

以小白菜、青瓜和白萝卜3种蔬菜为研究对象,采用分光光度法检测样品中亚硝酸盐含量,探究加工方法及贮存条件对蔬菜亚硝酸盐含量的影响。结果表明:与室温(20℃)贮存相比,新鲜蔬菜采用冷藏(4℃)方式贮存时亚硝酸盐的增幅较少。沸水烹煮可使蔬菜中的亚硝酸盐含量有所下降,在随后的冷藏贮存中,亚硝酸盐含量回升。煮熟后未吃完的蔬菜,冷藏贮存时间不宜超过24h。晾晒制作蔬菜干制品的过程中,蔬菜中亚硝酸盐含量在第2天前上升速度较快,随后上升得相对较慢。     

添加发酵菠菜液对猪肉灌肠冷藏过程中品质的影响

利用发酵菠菜替代亚硝酸盐的作用,开发新型绿色肉制品。将菠菜打浆后进行自然发酵和接菌(萨科WBL45复合菌株)发酵,发酵过程中分别为不调节pH值和每0.5 h调节pH值至中性,测定发酵过程中硝酸盐和亚硝酸盐含量的变化。然后将加工猪肉灌肠分3组,CK组(不添加亚硝酸钠)、SN组(添加0.15 g/kg亚硝酸钠)、FS组(添加136 g/kg发酵菠菜液),测定猪肉灌肠在冷藏过程中的抗氧化性(TBARs)、色差和亚硝酸盐残留量。结果表明:菠菜打浆后添加10 g/100 g葡萄糖、接种量4.25×10~6 CFU/mL,发酵温度38℃、发酵12 h时,菠菜中的硝酸盐可以最大程度地转化为亚硝酸盐,亚硝酸盐含量达到1100 mg/kg。添加了发酵菠菜液的猪肉灌肠在冷藏过程中TB ARs值明显比CK组低,且与SN组(亚硝酸钠组)差异不显著,亚硝酸盐残留量小于30 mg/kg,符合国标要求,由于菠菜中含有天然叶绿素、叶黄素等,使产品呈现诱人的鲜亮绿色。     

蔬菜中硝酸盐、亚硝酸盐提取与测定的研究

目的:研究蔬菜中硝酸盐、亚硝酸盐对保障人类健康具有重要意义.方法:本实验选择用简便、高效的超声波提取技术提取蔬菜中的硝酸盐和亚硝酸盐,用紫外分光光度法测定其含量.结果:研究表明,利用紫外分光光度法同时测定蔬菜中硝酸盐和亚硝酸盐含量的方法简单、快速、选择性好.结论:硝酸盐测定的相对误差在-2.52％～1.14％之间,亚硝酸盐测定的相对误差在1.98％～4.26％之间,符合定量测定要求.     

Changes in nitrate and nitrite content of four vegetables during storage at refrigerated and ambient temperatures

The nitrate and nitrite contents of four kinds of vegetables (spinach, crown daisy, organic Chinese spinach and organic non-heading Chinese cabbage) in Taiwan were determined during storage at both refrigerated (5 ± 1°C) and ambient temperatures (22 ± 1°C) for 7 days. During storage at ambient temperature, nitrate levels in the vegetables dropped significantly from the third day while nitrite levels increased dramatically from the fourth day of storage. However, refrigerated storage did not lead to changes in nitrate and nitrite levels in the vegetables over 7 days.     

Determination of nitrates by a novel ion chromatographic method: occurrence in leafy vegetables (organic and conventional) and exposure assessment for Italian consumers

A novel ion chromatographic method to detect nitrates in vegetables was developed, and the nitrate contents in green salad (a mixture of endive and prickly lettuce), lettuce, chicory, rocket and spinach were determined from Italian markets in 1996 -2002. These leaf vegetables were included because they are currently supposed to provide most of the nitrate intake in the typical Italian diet. The highest content of nitrate was detected in chicory (6250 mg kg -1 ) and rocket (6120 mg kg -1 ), which are consumed in large quantities in some regions of Italy. Green salad and lettuce contained less nitrate (highest values = 4200 and 3300 mg kg -1 , respectively), but because they are consumed more generally, they provided 60% of the total intake of nitrates. Only a few samples were above the legal limits, with seasonal variation. A significantly higher nitrate content was found in organically grown green salad and rocket than in those conventionally produced. These data indicate that the average intake of nitrates from leafy vegetables is below the acceptable daily intake, i.e. 3.7 mg nitrate ion kg -1 body weight day -1 , but the total intake should be monitored to protect groups at risk, such as children and vegetarians.     

Nitrate and nitrite in vegetables on the Danish market: content and intake

The contents of nitrate and nitrite in lettuce, leek, potato, beetroot, Chinese cabbage and white cabbage on the Danish market were determined for 3 years in the period 1993-1997 as part of the Danish food monitoring programme. These vegetables are supposed to provide the major contribution to the intake of nitrate from the diet. Results for nitrate and nitrite in fresh and frozen spinach are also shown. The highest content of nitrate was found in lettuce followed by beetroot, Chinese cabbage, fresh spinach, leek, frozen spinach, white cabbage and potatoes. For all the products a great variation in the content of nitrate was found. For lettuce a characteristic variation throughout the year is clearly seen with the highest content in the winter period the lowest content in the summer period. Generally, the content of nitrite was low but in spinach high contents were found, probably due to improper storage conditions during transportation. The intake of nitrate and nitrite from these vegetables is calculated on the basis of two different consumption surveys. For both surveys the average intake of nitrate from the vegetables included in the monitoring programme is estimated to be approximately 40mg day^-1, whereas for nitrite the average intake is approximately 0.09mg day^-1. The total intake of nitrate and nitrite is estimated to be respectively 61mg day^-1 and 0.5mg day^-1.     

重庆市菜园土壤与蔬菜硝酸盐和亚硝酸盐含量及相关性研究

研究重庆4 个农贸市场市售3大类19 种蔬菜73 个样品中硝酸盐含量及重庆市13 个主要蔬菜基地土壤和蔬菜的硝酸盐、亚硝酸盐含量及相关性。结果表明,重庆市售蔬菜不同种类及同种蔬菜不同部位的硝酸盐含量差异显著。大小顺序为叶菜类（X =1 619.73 mg/kg）＞茄果类（X =1 327.67 mg/kg）＞葱蒜类（X =
1 078.39 mg/kg）;莴苣叶（X=1 567.91 mg/kg）＞莴苣茎（X=1 871.62 mg/kg）。叶菜类全部超过了一级标准,污染指数高达9.09,污染程度最为严重;茄果类和葱蒜类超过一级标准的样本占81.3%和87.5%,污染指数分别高达8.85和6.56。重庆市13 个主要蔬菜基地不同蔬菜以及同种蔬菜不同部位的硝酸盐含量差异也显著,大小顺序为萝卜叶（X=745.97 mg/kg）＞莴苣茎（X=730.88 mg/kg）＞莴苣叶（X=693.32 mg/kg）＞白菜（X=617.63 mg/kg）＞萝卜根（X=575.74 mg/kg）。土壤中NO3－-N含量差异也显著,大小顺序为种植莴苣的土壤（X=75.24 mg/kg）＞种植白菜的土壤（X=47.05 mg/kg）＞种植萝卜的土壤（X=33.42 mg/kg）。蔬菜可食部分的硝酸盐与土壤中的NO3－-N含量呈极显著正相关关系,线性方程y=407.872＋4.796x。供试重庆市13 个主要蔬菜基地土壤及蔬菜可食部分的NO2－-N含量均较低且差异不显著,蔬菜中的亚硝酸盐含量和土壤中的NO2－-N含量也无显著相关性。     

不同贮藏和食用方式对小青菜中亚硝酸盐含量的影响

采用国标的方法测定室温下贮藏的小青菜的亚硝峰值为10-34mg／kg,大大高于在4℃贮藏条件下的小青菜;4℃不密封和4℃密封两种贮藏方式亚硝峰最高峰都在第4d,分别为6．48nag／kg和5．31mg／kg;浸泡处理30min后,亚硝酸盐的含量仅为1．02mg／kg,比鲜样降低了45％;烫漂90S后亚硝酸盐含量有所降低;小青菜中亚硝酸盐含量会随着食盐添加量增大呈现增加趋势,添加小青菜质量0．8％的食盐使小青菜中亚硝酸盐含量增加了81％;小青菜炒制后贮藏24h,未添加唾液的样品亚硝酸盐含量为2．29mg／kg,添加唾液的样品24h时含量达到2．72mg／kg。通过正交试验,炒小青菜的最佳处理方式为浸泡60min、漂烫120S、食盐添加量为小青菜质量的0．1％。     

Survey of nitrate and nitrite contents of vegetables grown in Korea.

A scientific basis for the evaluation of the risk to public health arising from excessive dietary intake of nitrate in Korea is provided. The nitrate () and nitrite () contents of various vegetables (Chinese cabbage, radish, lettuce, spinach, soybean sprouts, onion, pumpkin, green onion, cucumber, potato, carrot, garlic, green pepper, cabbage and Allium tuberosum Roth known as Crown daisy) are reported. Six hundred samples of 15 vegetables cultivated during different seasons were analysed for nitrate and nitrite by ion chromatography and ultraviolet spectrophotometry, respectively. No significant variance in nitrate levels was found for most vegetables cultivated during the summer and winter harvests. The mean nitrates level was higher in A. tuberosum Roth (5150 mg kg(-1)) and spinach (4259 mg kg(-1)), intermediate in radish (1878 mg kg(-1)) and Chinese cabbage (1740 mg kg(-1)), and lower in onion (23 mg kg(-1)), soybean sprouts (56 mg kg(-1)) and green pepper (76 mg kg(-1)) compared with those in other vegetables. The average nitrite contents in various vegetables were about 0.6 mg kg(-1), and the values were not significantly different among most vegetables. It was observed that nitrate contents in vegetables varied depending on the type of vegetables and were similar to those in vegetables grown in other countries. From the results of our studies and other information from foreign sources, it can be concluded that it is not necessary to establish limits of nitrates contents of vegetables cultivated in Korea due to the co-presence of beneficial elements such as ascorbic acid and alpha-tocopherol which are known to inhibit the formation of nitrosamine.     

不同利用方式对几种根茎类蔬菜亚硝酸盐含量的影响

以山药、胡萝卜、莲藕为实验材料,研究不同贮藏条件、烹饪方法和熟菜保存方式下3种根茎类蔬菜中亚硝酸盐含量的变化。结果表明：无论常温还是低温贮藏,贮藏7d内,3种根茎类蔬菜的亚硝酸盐含量均呈现先增加后降低的趋势,虽然常温贮藏的亚硝酸盐含量高于低温贮藏,但两者均小于4mg/kg。不同烹饪加工可显著降低3种蔬菜的亚硝酸盐含量,煮制、炒制、烤制加工方式的亚硝酸盐含量降幅分别为70%～83%、66%～80%和33%～55%,其中胡萝卜的亚硝酸含量降幅最大,莲藕的最小。低温和常温保存的熟菜,菜体中亚硝酸盐含量随时间延长而增加,保存到48h时,3种菜体的亚硝酸盐含量均小于4mg/kg,且低温远低于常温(前者最大为1.03mg/kg,后者最大为1.98mg/kg),参照食用的亚硝酸盐标准,低温(4℃)和常温(20℃)保存的熟制根茎类蔬菜食用安全期均达48h,且煮制和炒制加工的熟菜优于烤制。     

烹饪过程对空心菜和卷心菜硝酸盐潜在安全风险的影响

研究4种烹饪（油炒、汽蒸、微波和水煮）过程对空心菜和卷心菜中硝酸盐、亚硝酸盐和抗氧化能力的影响,并通过抗氧化性/体内亚硝酸盐比（antioxidant/in vivo nitrite ratio,A/N）值评价其硝酸盐潜在安全风险。结果表明,油炒会同时提升叶类蔬菜的硝酸盐含量（28.03%～49.57%）和铁离子还原能力（108.88%～218.35%）,而水煮则相反。微波和汽蒸在降低蔬菜硝酸盐含量（31.25%～46.61%）的同时提升铁离子还原能力（76.35%～112.99%）。基于可食用性和A/N值评价结果,在烹饪2 min内空心菜和卷心菜分别选择水煮和油炒烹饪对硝酸盐潜在安全风险的控制效果更好。微波是两种叶类蔬菜相对安全的烹饪方式,但不宜超过4 min,而汽蒸更适宜长时间烹饪（>4 min）。     

Antioxidant capacity of fresh‐cut vegetables exposed to ionizing radiation

The effect of ionizing radiation on antioxidant capacity, phenolic content and tissue browning of three vegetables was studied. Midrib and non‐midrib leaf tissues of Romaine and Iceberg lettuce and endive were irradiated with gamma‐rays at 0, 0.5, 1 and 2 kGy, and then stored at 7–8 °C for 8 days. Antioxidant capacity and phenolic content of tissues as well as tissue browning were analyzed at 1, 4 and 8 days of storage. In general, irradiation increased the phenolic content and antioxidant capacity of both tissue types of all vegetables at day 4 and day 8. The rates of the increase were higher in midrib tissues than in non‐midribs, and increased with storage time. Irradiation, however, increased tissue browning of midrib tissues of Romaine and Iceberg lettuce. Our results suggest that irradiation increased nutritional quality of leafy vegetables, but some adverse visual quality changes were encountered. Published in 2005 for SCI by John Wiley & Sons, Ltd.     

Heavy metals in vegetables grown in The Netherlands and in domestic and imported fruits

The contents of cadmium, lead mercury, copper, manganese and zinc in 242 samples of 37 different species of domestic and imported fruits have been determined. Also contents of the same heavy metals, except mercury, have been determined in 205 samples of 7 species of domestic vegetables (lettuce, spinach, endive, beetroots, onions, celeriac and Swedish turnips). The median contents (in mg/kg fresh mass of the edible part) found for fruits are: Cd 0.002; Pb 0.017; Hg 0.002; Cu 0.61; Mn 0.52 and Zn 0.99. In the vegetables median levels have been found (mg/kg) of 0.009-0.073 for Cd, 0.01-0.03 for Pb, less than 0.2-0.3 for Cu, 0.69-1.41 for Mn and 0.95-5.5 for Zn. The contribution of fruits to the tolerable daily intakes of Cd, Pb and Hg is, for an average consumption pattern, less than 1%. On the other hand, the contribution to the recommended amounts of the essential elements Cu, Mn, and Zn is no more than 1%-3%. From the vegetables an average portion of spinach contains 19% and 2.6% of the tolerable daily amounts of Cd and Pb, respectively. For the other species of vegetables these figures are less than 5% for Cd (except for endive, 6.8%) and for lead less than 1%. Spinach contributes considerably to the need for Cu, Mn and Zn, in general more than 10% of the recommended daily amounts. The other species of vegetables contribute only from less than 1% to less than few percents.