保鲜技术在鲜切果蔬中的应用

简要介绍了鲜切果蔬的发展现状,重点分析了鲜切果蔬常见的保鲜技术及存在的问题,提出了新型保鲜技术在鲜切果蔬的应用构想,展望了鲜切果蔬的应用前景。     

A rapid multi-residue method for the determination of pesticide residues in choi sum, yardlong beans and aubergines

A rapid multi-residue modified QuEChERS method has been developed to analyse 20 pesticide residues in choi sum, yardlong beans and aubergines by gas chromatography with flame photometric and electron capture detectors. Primary secondary amine in dispersive form was omitted in the extraction step but instead packed in a Pasteur glass pipette for column cleanup. The recoveries for all 20 pesticides except chlorothalonil at 10-500 μg kg⁻¹ fortification levels ranged from 74.0% to 117%. Similar recoveries of 81.7-117% were obtained for all organochlorine and pyrethroid pesticides including chlorothalonil using silica gel cleanup. The relative standard deviation obtained was below 14.9%. The limit of quantification was in the range 1-10 μg kg⁻¹. The method has high selectivity for pesticides in vegetables containing high amount of chlorophyll, pigment and coloured compounds such as in choi sum and aubergines. The method was used to analyse 132 vegetable samples from residue survey.     

Development of vegetable composition databases based on available data for probabilistic nutrient and contaminant intake assessments

Dietary intake assessment can be considered as a two-step process consisting of collecting and evaluating food composition data, and combining these data with food consumption data. The purpose of this study was to develop databases of nutrient and contaminant concentrations in organic and conventional vegetables and potatoes based on internationally available secondary data. Databases, as described here, are important in (1) comparing the composition of similar foods (organic versus conventional) and (2) assessing probabilistically the combined intake of nutrients and contaminants when nutritional and toxicological dimensions of food consumption are being studied simultaneously.     

COMBINED INNOVATIVE HEAT PUMP DRYING TECHNOLOGIES AND NEW COLD EXTRUSION TECHNIQUES FOR PRODUCTION OF INSTANT FOODS

There is an increased demand for convenient foods including ready-to-eat and instant products. These products are desired with minimum concentration of synthetic chemicals. This creates challenges for the food industry and dryers manufactures to develop new technologies to process difficult-sensitive materials and to supply final products with high quality and improved properties. Fruits and vegetables are mainly composed of water, carbohydrates, proteins and lipids. Due to modification of chemical and physical bonds the compounds the material becomes viscous and sticky during processing. Conventional dryers have limitations in handling such sensitive materials. Heat pump dryers have been applied in the production of a diversity of ready-to-eat foods and dried instant products for the last five years at SINTEF-NTNU. Besides being energetically efficient and environmentally friendly, the heat pump drying technology provides a wide range of drying conditions as required to produce powders with improved characteristics. This work describes the new technologies and processing line for the production of instant foods as well as the measurements on the properties and quality attributes for raw, intermediate and final instant products.     

Chlorophyll changes in some green leafy vegetables during cooking

Five green leafy vegetables commonly consumed in Nigeria (Talinum triangulare, Corchorus olitorius, Celosia argentea, Amaranthus hybridus and Vernonia amygdalina) were examined for their chlorophyll contents. These varied between 0.038% for Talinum triangulare and 0.137% for Vernonia amygdalina, with chlorophyll-a constituting between 68 and 75% of the total chlorophyll. By bringing the temperature of the leaves to 100°C, at least 56% of the total chlorophyll was lost, the rate of loss decreasing with the initial total chlorophyll content. When the leaves were blanched by immersion in boiling water, they showed a greater rate of chlorophyll loss. This was reduced when the pH was adjusted to 6.     

Phytochemical phenolics in organically grown vegetables

Fruit and vegetable intake is inversely correlated with risks for several chronic diseases in humans. Phytochemicals, and in particular, phenolic compounds, present in plant foods may be partly responsible for these health benefits through a variety of mechanisms. Since environmental factors play a role in a plant's production of secondary metabolites, it was hypothesized that an organic agricultural production system would increase phenolic levels. Cultivars of leaf lettuce, collards, and pac choi were grown either on organically certified plots or on adjacent conventional plots. Nine prominent phenolic agents were quantified by HPLC, including phenolic acids (e. g. caffeic acid and gallic acid) and aglycone or glycoside flavonoids (e. g. apigenin, kaempferol, luteolin, and quercetin). Statistically, we did not find significant higher levels of phenolic agents in lettuce and collard samples grown organically. The total phenolic content of organic pac choi samples as measured by the Folin-Ciocalteu assay, however, was significantly higher than conventional samples (p < 0.01), and seemed to be associated with a greater attack the plants in organic plots by flea beetles. These results indicated that although organic production method alone did not enhance biosynthesis of phytochemicals in lettuce and collards, the organic system provided an increased opportunity for insect attack, resulting in a higher level of total phenolic agents in pac choi.     

杭州下沙地区农民自种蔬菜中镉、铜重金属污染状况调查分析

实验目的是调查分析杭州下沙地区所种植的蔬菜中的重金属的含量,通过对20个蔬菜样品的检测,并对实验结果进行处理分析,对该地区的蔬菜中重金属含量做出客观真实的解读。采用湿式消解—火焰原子吸收法对蔬菜中的镉、铜的含量进行定量分析。所选20个蔬菜样品中测得的镉、铜含量范围分别是0.018~0.214 mg/kg,0.035~0.436 mg/kg,根据实验结果可得,采用湿式消解—火焰原子吸收法可以简洁方便地测出重金属元素的含量,但对混合酸(浓硝酸:双氧水)的配比要求比较高。     

Decontamination by ultrasound application in fresh fruits and vegetables

Changes in consumer eating habits, health concerns, and convenient and practical foods have led to an increased demand for fruit and vegetable products. Food safety is essential considering that there are reports of outbreaks involving the consumption of fruits and vegetables contaminated with pathogens. Washing associated with sanitizer procedure is considered as a critical step to satisfy hygienic and sanitary requirements and maintain the sensory and nutritional characteristics of fruits and vegetables. Chemical compounds are widely applied to clean and sanitize fresh fruits and vegetables, and some of these chemicals, such as the inorganic chlorine compounds, produce by-products that are dangerous to human health. The use of ultrasound is a technology that is gaining ground in the food industry. Ultrasound is a form of energy generated by sound waves at frequencies that are too high to be detected by the human ear. In ultrasound, the removal of dirt and food residues from surfaces and the inactivation of microorganisms occur as a consequence of cavitation, which is the formation, growth and collapse of bubbles that generate a localized mechanical and chemical energy. There are indications that this technology can be used in the food industry, alone or associated with chemical sanitizers. In this paper, we discuss the principles, mechanisms and effects of ultrasound on fruits and vegetables as a sanitization technology.     

Characteristics of Escherichia coli from raw vegetables at a retail market in the Czech Republic

A large epidemic caused by shigatoxigenic Escherichia coli (E. coli) in spring 2011 in Germany resulted in reduction of trust in the health safety of raw vegetables and sprouted seeds. This study focused on the detection and characterization of E. coli in raw vegetables and sprouted seeds sold in the Czech Republic. Out of 91 samples, 24 (26.4%) were positive for the presence of E. coli. Resistance to antimicrobial agents was determined by the disk diffusion method and E-test. Polymerase chain reaction was used for the detection of selected genes encoding virulence — eaeA, hly, stx₁, and stx₂ and genes encoding resistance to tetracycline — tet(A), tet(B), tet(C), and tet(G) and to β-lactams — bla_TEM, bla_SHV, and bla_CTX. The bla_TEM gene was detected in two isolates, the tet(B) gene in three and tet(A) in one isolate. No hly, stx₁, or stx₂ genes were present, but the eaeA gene was found in three (11.1%) isolates from imported vegetables. These isolates can be considered as potentially enteropathogenic. Results of this study show that raw vegetables and sprouted seeds sold in the retail market can represent a potential risk for consumers.     

Quick and reliable screening of compatible ingredients for the formulation of extended meat cubes using Plackett-Burman design

“Extended meat products” is an important concept which involves judicious utilization of other agricultural/animal produce as well as providing meat-like products. Selection of compatible ingredients from among numerous alternates is a daunting task. Of the several methods available, Plackett-Burman design was used to screen 11 potential ingredients to formulate extended meat cubes. Twelve formulations were evolved and their evaluation as rehydrated and stewed meat cubes were carried out by a sensory panel. The attributes of firmness, juiciness, meaty aroma and overall quality were rated by an intensity ranking test followed by appropriate statistical analysis provided regression coefficients for individual ingredients for each attribute. Based on the direction of change (increase or decrease over control) for each attribute and its relation to the overall acceptability of the ingredients for their compatibility in formulating the product was provided. The overall rank sums for each ingredient and the attributes provided a reliable means to select the most compatible ingredients for further optimization work.