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。     

不同贮藏温度对肉制品中亚硝酸盐含量的影响

本文研究不同贮藏条件对腊肉、香肠、火腿肠、西式火腿和熏烤肉中亚硝酸盐含量的影响。比较了5种肉制品在冷冻(-18℃)、冷藏(4℃)、常温(25℃)条件下贮藏时,其亚硝酸盐的含量随着贮藏时间的变化趋势。结果表明:随着贮藏时间的延长,肉制品中的亚硝酸盐含量呈下降趋势,且室温条件下亚硝酸盐的含量比冷藏低,冷藏条件下的亚硝酸盐含量比冷冻低。     

不同条件下蔬菜中亚硝酸盐含量的变化

研究8种蔬菜在室温下(20～25℃)、低温下(4℃)贮藏后水浸泡和不用水浸泡情况下亚硝酸盐含量的变化.试验结果表明:室温条件下贮藏的蔬菜亚硝酸盐含量在1～2 d内会达到高峰,然后出现下降,随着时间继续延长,亚硝酸盐含量会逐渐升高.亚硝酸盐含量低温条件下较室温下低.不论室温下还是低温下贮藏的蔬菜,用水浸泡1 h后,其亚硝酸盐含量都会比不浸泡低.     

不同储存条件对芹菜和豇豆中硝酸盐和亚硝酸盐含量变化的影响

目的:研究不同储存时间、储存温度和包装方式对芹菜和豇豆中硝酸盐和亚硝酸盐含量的影响,为居民储存蔬菜提供科学依据。方法:在不同储存温度(4℃、25℃)、储存方式(敞口包装、密封包装)下储存芹菜和豇豆7d后,采用离子色谱法测定其中硝酸盐和亚硝酸盐的含量。结果:随着储存时间的延长,2种蔬菜中硝酸盐和亚硝酸盐含量会逐渐增加。低温4℃密封储存时硝酸盐、亚硝酸盐含量低,变化幅度最小。25℃密封储存时硝酸盐、亚硝酸盐含量高于25℃敞口储存时的含量。4℃敞口储存时硝酸盐、亚硝酸盐含量高于4℃密封储存时的含量。结论:应尽量食用新鲜蔬菜,如若储存应选择低温密封储存,有助于减少硝酸盐和亚硝酸盐的危害。     

不同处理条件对叶菜类蔬菜亚硝酸盐含量的影响

目的:探明在采用盐酸萘乙二胺可见分光光度法下,测定具有代表性的叶菜类蔬菜中的亚硝酸盐含量在不同前处理条件下的变化。方法:采用常温(25±2℃)、冷藏(4℃)、密封冷藏(4℃)3种不同保存方式测定亚硝酸盐含量随着时间的变化规律;食前采用自来水、食用碱浸泡、果蔬洗涤剂浸泡及漂烫4种前处理方法。结果:3种不同保存方式下,随着时间的延长,亚硝酸盐含量表现为密封冷藏冷藏常温。自来水浸泡20min、5%食用碱浸泡、果蔬浸泡5min及漂烫0.5min 4种前处理方法均在一定程度上降低了蔬菜的亚硝酸盐的含量,且效果较其他清洗的处理条件稳定、明显,亚硝酸盐降低较快。结论:叶菜类蔬菜的亚硝酸盐含量在不同的放置条件下,均随存放时间的延长而增加。不同的食前处理均能降低亚硝酸盐含量,但在漂烫0.5min时,亚硝酸盐含量降低最为明显。建议消费者在选择叶菜类蔬菜时,冷藏储存,合理洗涤,避免长期放置。     

不同加工方式与存放条件对蔬菜中亚硝酸盐含量的影响

目的研究不同加工方式、存放时间及存放温度对蔬菜中亚硝酸盐含量的影响,为减少亚硝酸盐危害提供依据。方法将萝卜、胡萝卜、白菜、芹菜4种蔬菜分别进行炒制和腌制处理,各分两份,分别放置于室温(18~20℃)和冰箱(4℃)保存1,6,12,24,48 h。用盐酸萘乙二胺比色法测定其亚硝酸盐含量,并与亚硝酸钠标准曲线进行对比。结果亚硝酸盐含量由低到高依次为炒制蔬菜生蔬菜腌制蔬菜,炒制蔬菜与生蔬菜亚硝酸盐含量比较无统计学差异(P0.05),与腌制蔬菜有统计学差异(P0.01);生蔬菜、炒制蔬菜亚硝酸盐含量均随存放时间的延长呈现上升的趋势,腌制蔬菜在存放6 h时亚硝酸盐含量最高,之后有所下降,48 h后又呈上升趋势。冰箱存放的蔬菜的亚硝酸盐含量明显低于室温存放的蔬菜,但无统计学差异(P0.05);不同贮藏温度下的蔬菜中亚硝酸盐含量均呈出先升高后降低再升高的态势。结论炒制蔬菜亚硝酸盐含量低于腌制蔬菜;低温贮藏可降低亚硝酸盐含量;各种烹制的蔬菜,不论存放时间还是保存温度均不宜超过48 h。     

大白菜贮藏过程中硝酸盐和亚硝酸盐含量变化分析

在不同贮藏温度（0、10、20 ℃）、贮藏方式（未包装、0.04 mm PE保鲜袋包装）条件下贮藏大白菜（Brassica rapa pekinensis）16 d后,采用高效液相色谱法测定大白菜中硝酸盐和亚硝酸盐含量的变化。结果表明,在不同贮藏温度和贮藏方式条件下,硝酸盐和亚硝酸盐的含量随着贮藏时间的延长均呈现先增加、后降
低、再上升的趋势,其中硝酸盐的含量在整个贮藏期间,均在低于432 mg/kg的安全食用范围内;亚硝酸盐含量在20 ℃贮藏条件下贮藏7 d即超过了4 mg/kg的安全摄入量,而其他贮藏条件均在安全食用范围内。大白菜中硝酸盐与亚硝酸盐的含量在贮藏过程中随贮藏温度的降低而显著减少,到贮藏末期（16 d时）20 ℃和10 ℃贮藏大白菜中硝酸盐含量分别是0 ℃贮藏的1.2 倍和1.1 倍,亚硝酸盐含量分别是0 ℃贮藏的1.4 倍和1.2 倍。PE保鲜袋包装有助于减少大白菜在中、低温（10、0 ℃）贮藏中硝酸盐与亚硝酸盐的含量,但在高温（20 ℃）贮藏中其含量增加。因此,建议贮藏大白菜时最好采用PE保鲜袋包装和0～10 ℃的贮藏温度,以保证其硝酸盐和亚硝酸盐含量不超标。     

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。     

加工青菜贮藏过程中产生亚硝酸盐因素的机制研究

通过对青菜在不同温度下(常温20℃,低温4℃),不同包装条件下(家庭用保鲜膜包装与不包装),不同加工方式的处理下(分为炒蒸煮3种加工处理),研究青菜在加工后的贮藏期间亚硝酸盐、硝酸盐、游离氨基酸、铵态氮等指标含量变化影响特征及其影响因素,探究其含量变化规律,并探究了各变量在贮藏期对产生亚硝酸盐是否具有一定的相互作用影响。研究发现:亚硝酸盐、硝酸盐、游离氨基酸、铵态氮各指标在不同温度下、不同包装方式下和不同贮藏时间均具有显著性差异(P0.01)。其中,亚硝酸盐含量在3种加工方式下,在第1小时内只有炒加工含量有所上升,其余均表现为下降,在之后的贮藏期内含量均保持上升之势,且随时间的延长上升幅度越显著。常温贮藏含量明显高于低温贮藏,有包装的含量高于无包装,以炒加工方式亚硝酸盐含量增加幅度最大,平均增幅1212.9倍,以蒸加工方式亚硝酸盐增加幅度最小,平均增幅92.82倍;硝酸盐含量在常温无包装下呈上升之势,其余处理下均呈下降之势,同样以炒加工组含量增幅最大,蒸加工增幅最小。常温无包装在贮藏第72小时达到峰值11778.933 mg/kg;游离氨基酸含量在3种加工方式下均表现为上升,以常温无包装下的增幅最大,其他三者处理增幅较小。铵态氮含量在3种加工方式下其含量以上升为主,只有在煮加工下有且出现略微下降的趋势。对指标相关性方面研究发现,亚硝酸盐与铵态氮均存在相关系数大于0.3的显著相关性,说明亚硝酸盐在加工蔬菜的贮藏过程中,明显存在与铵态氮之间的相互转化的可能性,而亚硝酸盐与硝酸盐有且仅有在煮加工处理下出现显著的弱性相关,与游离氨基酸之间相关性不明显,要研究他们之间具体转变过程和机制,则需要更深入研究。     

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。     

Chilling injury of fruits and vegetables

Abstract

Chilling injury affects many fruits and vegetables. Most crops of tropical and subtropical origin are sensitive to chilling injury. Some crops of Temperate Zone origin are also susceptible. These crops are injured by low, but nonfreezing, temperatures. At these temperatures, the tissues weaken because they are unable to carry on normal metabolic processes. Various physiological and biochemical alterations occur in the sensitive species in response to low‐temperature exposure. These alterations lead to the development of a variety of chilling injury symptoms, such as surface pitting, discoloration, internal breakdown, failure to ripen, growth inhibition, wilting, loss of flavor, and decay. This review article describes the changes in membrane lipids, permeability, proteins, carbohydrates, energy supply, respiration, ethylene production, and other metabolic processes that are affected by chilling temperatures. Methods for alleviation of chilling injury‐such as temperature preconditioning, intermittent warming, chemical treatments, hormonal regulation, controlled atmosphere storage, genetic manipulation, and other methods—are also discussed.     

Flavor quality of fruits and vegetables

Fruits and vegetables are important sources of vitamins, minerals, dietary fiber, and antioxidants. The relative contribution of each commodity to human health and wellness depends upon its nutritive value and per capita consumption; the latter is greatly influenced by consumer preferences and degree of satisfaction from eating the fruit or vegetable. Flavor quality of fruits and vegetables is influenced by genetic, preharvest, harvesting, and postharvest factors. The longer the time between harvest and eating, the greater the losses of characteristic flavor (taste and aroma) and the development of off‐flavors in most fruits and vegetables. Postharvest life based on flavor and nutritional quality is shorter than that based on appearance and textural quality. Thus, it is essential that good flavor quality be emphasized in the future by selecting the best‐tasting genotypes to produce, by using an integrated crop management system and harvesting at the maturity or ripeness stage that will optimize eating quality at the time of consumption, and by using the postharvest handling procedures that will maintain optimal flavor and nutritional quality of fruits and vegetables between harvest and consumption. Copyright © 2008 Society of Chemical Industry     

Fluorine in leafy vegetables

Two small selective surveys (in 1965/6 and 1968/9) of leafy vegetables in areas known to be exposed to industrial contamination with fluorine compounds are reported. The highest fluorine content (297 p.p.m.) was found in a sample of kale in the Stoke-on-Trnt area. In general the results for cabbage and lettuce in 1965/6 averaged 17 p.p.m. for unwashed and 11 p.p.m. for washed vegetables on a moisture-free basis. In the 1968/9 exercise the corresponding figures were 22 p.p.m. and 12 p.p.m. respectively. The average intake of fluoride from cabbage, lettuce and brussels sprouts in such an area has been calculated as 0·03 mg/head/day with a likely maximum of 0·08 mg/head/day (if all 3 vegetables were contaminated to the maximum levels observed). These figures are compared with the average daily intake of fluoride in the whole diet, and in particular fish, in the West Midlands area.     

Flavonols and flavones of vegetables. V. Flavonols and flavones of root vegetables (author's transl)]

Root vegetables contain flavon(ol) glycosides in tracers up to small amounts, while the level of their leaves are in part considerable (to more than 1 g/kg, calculated as aglycon). Radish, rutabagas, scorzoneras, and beets contain less than 1 mg/kg kaempferol and/or quercetin; carrots less than 1 mg/kg apigenin and luteolin; celery roots ca. 75 mg apigenin/kg and 14 mg luteolin/kg; horseradish about 20 mg kaempferol/kg and small radish 1-10 mg kaempferol/kg, whereby all these flavones and flavonols occur as glycosides in the vegetables. In leaves of small radish, variety "Eiszapfen", we found besides isoquercitrin (quercetin-3-glucoside) a quercetin-3-0-diglycoside and a kaempferol-0-diglycoside, both with the sugars rhamnose and arabinose, by tlc.     

Carotenoids in traditional Portuguese fruits and vegetables

Carotenoids, α-carotene, β-carotene, β-cryptoxanthin, lycopene, lutein and zeaxanthin, were determined in 10 varieties of five fruit species (orange, pear, peach, apple and cherry) and five varieties of four species of vegetables (Portuguese coles, turnip greens, purslane, leaf beet and beetroot leaves) cultivated in Portugal and country traditional, the fruits being of protected designation of origin or of protected geographical indication. The determination was done by high performance liquid chromatography, using two metal free reverse phase columns, an organic mobile phase based on acetonitrile, methanol and dichloromethane and a UV–vis photodiode array detector. Identification was done by retention time and spectral analysis and quantification was based on peak area at 450 nm by external calibration. The analysed leafy vegetables are a very good source of lutein (0.52–7.2 mg/100 g) and β-carotene (0.46–6.4 mg/100 g) while the analysed fruits have a considerably lower content of carotenoids (lutein, 0.0032–0.16 mg/100 g and β-carotene, 0.010–0.17 mg/100 g) and a complex and variable qualitative and quantitative carotenoid composition. Most estimated relative measurement expanded uncertainties were between 0.10 and 0.31. Results indicate that the carotenoid content of the analysed items could vary with species, varieties, geographical place of production (region, site) and time of harvest, and should be addressed in the eventual production of data for food composition data bases.     

切割果蔬保鲜

切割果蔬是指果蔬经清洗、去皮、切割或切片、修整、包装而成的新鲜、方便、营养、无公害的果蔬产品 ,切割果蔬相对于未加工的果蔬由于受到机械损伤而更易腐败变质。从切割果蔬的组织生理、微生物、包装及品质等方面对切割果蔬进行了介绍。     

壳聚糖在果蔬涂膜保鲜的应用

壳聚糖是从海洋生物虾、蟹的外壳中提取的甲壳素脱乙酰基得到,是迄今为止发现的唯一的阳离子动物纤维和碱性多糖。且壳聚糖在2013年经美国食品药物管理局批准(USFDA)称为"普遍认可的安全"(GRAS)食品添加剂。作为食品添加剂,壳聚糖有增稠剂、被膜剂、澄清剂抗氧化剂、风味改良剂、乳化剂等用途。其中,壳聚糖作为被膜剂应用于果蔬保鲜引起了消费者和研究员的广泛关注。其主要原因是壳聚糖具有较好的成膜性,能在水果表面形成一种半透膜,可以用来调节果蔬的内部环境,从而达到延缓果蔬呼吸速率,减少重量损失,保持果蔬整体质量,延长保质期等目的。本综述的主要目的是总结壳聚糖作为被膜剂,保护果蔬产品整体产品质量相关研究进展,为其发展指明了一定的方向。     

Modified atmosphere packaging of fruits and vegetables

Modified atmospheres (MA), i.e., elevated concentrations of carbon dioxide and reduced levels of oxygen and ethylene, can be useful supplements to provide optimum temperature and relative humidity in maintaining the quality of fresh fruits and vegetables after harvest. MA benefits include reduced respiration, ethylene production, and sensitivity to ethylene; retarded softening and compositional changes; alleviation of certain physiological disorders; and reduced decay. Subjecting fresh produce to too low an oxygen concentration and/or to too high a carbon dioxide level can result in MA stress, which is manifested by accelerated deterioration. Packaging fresh produce in polymeric films can result in a commodity-generated MA. Atmosphere modification within such packages depends on film permeability, commodity respiration rate and gas diffusion characteristics, and initial free volume and atmospheric composition within the package. Temperature, relative humidity, and air movement around the package can influence the permeability of the film. Temperature also affects the metabolic activity of the commodity and consequently the rate of attaining the desired MA. All these factors must be considered in developing a mathematical model for selecting the most suitable film for each commodity.