不同因素对同时蒸馏-萃取法(SDE)提取洋葱精油的影响

本实验就加水量、溶剂用量和NaCl溶液浓度三个因素对SDE洋葱精油的影响进行探讨,通过实验确定当洋葱浆液与NaCl溶液(90g/1000ml)的比例为1:2、溶剂用量为15ml时,提取得到的含硫化合物浓度较高。     

Detection of onion postharvest diseases by analyses of headspace volatiles using a gas sensor array and GC-MS

Onion postharvest diseases cause significant losses in storage. Volatile sensing by the gas sensor array technology could be used as a promising alternative method to detect onion diseases. Onions were inoculated with Botrytis allii and Burkholderia cepacia, causal pathogen for Botrytis neck rot and sour skin, respectively. In the first phase of this study, 30 onions with equal number of B. allii inoculated and control healthy onions were measured by the gas sensor array from 8 to 11 days after inoculation (dai) and the principal component analysis (PCA) score plot demonstrated that the gas sensor array responded differently to Botrytis neck rot infected onions from those of healthy onions. In the second phase, 30 onions with 10 for each of the three treatments (Botrytis neck rot, sour skin, control) were measured by the gas sensor array on 5, 6, and 7 dai. The PCA score plot illustrated that three treatments formed three distinct clusters, while a hierarchical cluster analysis dendrogram indicated that the response of the gas sensor array to Botrytis neck rot and sour skin were similar. The correct classification rate of the linear discriminant model for three treatments was over 97.8%. Results from GC-MS showed that total 24 major volatiles were identified from the headspace of three treatments. Sixteen compounds were uniquely present in B. allii and B. cepacia inoculated onion bulbs. Total amount of volatile compounds detected in pathogen inoculated bulbs was one to two orders of magnitude higher than that of control healthy bulbs. This study demonstrated the feasibility of using a gas sensor array to detect two onion postharvest diseases in storage.     

Pressure inactivation of hepatitis A virus in strawberry puree and sliced green onions

Hepatitis A can be acquired by ingesting contaminated produce. To investigate the potential of high-pressure processing as an intervention strategy for virus in produce, strawberry puree and sliced green onions were inoculated with > 10(6) PFU of hepatitis A virus and treated with pressures ranging from 225 to 375 megapascals (MPa) in 25-MPa increments at ambient temperature. Subsequent virus extraction and plaque assay determined that hepatitis A virus was inactivated in strawberry puree and sliced green onions after 5-min exposures to pressures of 375 MPa with log PFU reductions of 4.32 and 4.75, respectively. Hepatitis A virus was equally sensitive in puree and onions at pressures > or = 350 MPa. For treatments of < 325 MPa, the virus was more sensitive to pressure in strawberry puree than in sliced onions with log reductions of 1.2, 2.06, and 3.13 observed for strawberries and 0.28, 0.72, and 1.42 observed for onions after 5-min treatments at 250, 275, and 300 MPa, respectively. Although high-pressure processing may cause some organoleptic alterations to strawberries and onions, results show high-pressure processing will inactivate hepatitis A virus in these foods.     

Analysis of pesticides including chlorine in welsh onions and mushrooms using gas chromatograph with an atomic emission detector (GC-AED)

An analytical method for the determination of 32 kinds of pesticide residues in onions, Welsh onions and mushrooms using gas chromatograph with an atomic emission detector (GC-AED) was developed. The pesticides were extracted with acetone-n-hexane (2:3) mixture. The crude extract was partitioned between 5% sodium chloride and ethyl acetate-n-hexane (1:4) mixture. The extract was passed through a Florisil mini-column for cleanup with 10 mL of acetone-n-hexane (1:9) mixture. Although the sensitivity of GC-AED was inferior to that of GC-ECD, GC-AED has a superior element-selectivity. Therefore pesticide residues in foods could be analyzed more exactly by using GC-AED. Thirty-two pesticides including chlorine in onion, Welsh onion and shiitake mushroom were detected without interference. Recoveries of these pesticides from samples determined by GC-AED were 64-114%, except for a few pesticides.     

Influence of cell integrity on textural properties of raw, high pressure, and thermally processed onions

The integrity of onion cells and its impact on tissue texture after high pressure and thermal processing was studied. The contribution of cell membranes and the pectic component of cell walls on the texture properties of onion tissue were analyzed. Neutral red (NR) staining of onion parenchyma cell vacuoles was used for the evaluation of cell membrane integrity and microscopic image analysis was used for its quantification. The content of methanol in tissue as a result of pectin methylesterase activity was used to evaluate the pectin component of the middle lamella and cell walls and the hardening effect on the tissue after processing. High pressure treatments consisted of 5-min holding times at 50, 100, 200, 300, or 600 MPa. Thermal treatments consisted of 30-min water bath exposure to 40, 50, 60, 70, or 90 °C. In the high pressure treatments, loss of membrane integrity commenced at 200 MPa and total loss of membrane integrity occurred at 300 MPa and above. In the thermal treatments, membrane integrity was lost between 50 and 60 °C. The texture of onions was influenced by the state of the membranes and texture profiles were abruptly modified once membrane integrity was lost. Hardening of the tissue corresponded with pressure and temperature PME activation and occurred after membrane integrity loss. PRACTICAL APPLICATION: The texture of vegetables is an important quality attribute that affects consumer preference. Loss of textural integrity also indicates that other biochemical reactions that affect color, flavor, and nutrient content may occur more rapidly. In this study, we analyzed changes in the texture of onions after preservation with heat and high pressure.     

顶空固相微萃取结合气相色谱-质谱联用法对3种洋葱挥发性风味成分的分析

为研究洋葱挥发性成分,利用顶空固相微萃取法提取洋葱的挥发性风味成分,通过气相色谱-质谱联用法分析测定,以总峰面积和化合物个数为指标考察萃取纤维头、萃取温度、萃取时间和解吸时间4个因素对萃取效果的影响,得出最优萃取条件为:萃取纤维头50/30 μm DVB/CAR/PDMS,萃取温度60 ℃,萃取时间60 min,解吸时间5 min。利用最优萃取条件对三种色泽洋葱挥发性风味成分进行分析鉴定。结果表明:三种色泽洋葱共鉴定得到挥发性风味物质61种,其中白皮、红皮、黄皮洋葱分别测到37、40、49种挥发性成分,相对含量分别占流出组分总量的70.29%、81.92%、79.03%。61种挥发性成分中含硫化合物27种、醛类13种、醇类13种、酮类4种,其他4种。三种色泽洋葱的共有挥发性成分有22种,其中含硫化合物占比较大,特别是二异丙基二硫醚和(E)-1-丙烯基-2-丙烯基二硫醚相对含量的总和在三种色泽洋葱的挥发性成分中占比率都超过了20%,对形成洋葱特征风味贡献较大。红皮和黄皮洋葱的含硫化合物的相对含量远高于白皮洋葱,红皮洋葱中2-甲基-2-戊烯醛相对含量高于白皮和黄皮洋葱。     

Onion cells after high pressure and thermal processing: comparison of membrane integrity changes using different analytical methods and impact on tissue texture

Two different analytical methods were evaluated for their capacity to provide quantitative information on onion cell membrane permeability and integrity after high pressure and thermal processing and to study the impact of these processing treatments on cell compartmentalization and texture quality. To determine changes in cell membrane permeability and/or integrity the methodologies utilized were: (1) measurement of a biochemical product, pyruvate, formed as a result of membrane permeabilization followed by enzymatic activity and (2) leakage of electrolytes into solution. These results were compared to previously determined methods that quantified cell viability and 1H-NMR T(2) of onions. These methods allowed for the monitoring of changes in the plasma and tonoplast membranes after high pressure or thermal processing. High pressure treatments consisted of 5 min holding times at 50, 100, 200, 300, or 600 MPa. Thermal treatments consisted of 30 min water bath exposure to 40, 50, 60, 70, or 90 °C. There was strong agreement between the methods in the determination of the ranges of high pressure and temperature that induce changes in the integrity of the plasma and tonoplast membranes. Membrane rupture could clearly be identified at 300 MPa and above in high pressure treatments and at 60 °C and above in the thermal treatments. Membrane destabilization effects could already be visualized following the 200 MPa and 50 °C treatments. The texture of onions was influenced by the state of the membranes and was abruptly modified once membrane integrity was lost. PRACTICAL APPLICATION: In this study, we used chemical, biochemical, and histological techniques to obtain information on cell membrane permeability and onion tissue integrity after high pressure and thermal processing. Because there was strong agreement between the various methods used, it is possible to implement something relatively simple, such as ion leakage, into routine quality assurance measurements to determine the severity of preservation methods and the shelf life of processed vegetables.     

辐照对大葱粉中挥发性含硫化合物的影响

大葱经过干燥处理后进行60Co-γ辐照处理,利用顶空固相微萃取法萃取大葱粉中的挥发性风味物质,然后采用气质联用法对不同处理中的挥发性含硫化合物进行分离鉴定。结果表明,含硫化合物中以二甲基硫醚的含量最高,葱白中的含硫化合物总量要高于葱叶中的含量。辐照在一定程度上能降低含硫化合物的百分比含量。     

洋葱的抗氧化能力及发酵对其的影响

利用二苯代苦味酰基自由基(DPPH)清除试验,抑制亚油酸氧化试验和还原能力试验评价白皮洋葱、红皮洋葱、黄皮洋葱的抗氧化能力.此外对红皮洋葱加入盐糖进行发酵,检测其DPPH清除能力的变化.结果表明,不同洋葱抗氧化能力从大到小依次为红皮洋葱＞黄皮洋葱＞白皮洋葱,发酵可以使红皮洋葱抗氧化能力提高.     

Free Radical Scavenging and Leukemia Cell Growth Inhibitory Properties of Onion Powders Treated by Different Heating Processes

ABSTRACT: Methanol extracts of onion powder dried by hot air (60 °C), vacuum (35 °C), and lyophilization (35 °C) were used to study the effects of drying method on the quercetin composition and the subsequent antioxi-dative changes. It was found that hot air-dried onion had higher radical scavenging activities in both DPPH and peroxide radicals than those of the freeze- and vacuum-dried onions. HPLC analyses showed that freeze- and vacuum-dried onions contained more quercetin glycosides, whereas hot air-dried onion dominated in aglycone. A strong cell proliferation inhibition activity in hot air-dried onion was observed for leukemia cell lines CEM and U937, whereas freeze- and vacuum-dried onions gave comparatively moderate inhibition. Low cell proliferation inhibition was obtained in 3 dried onions for leukemia cell lines K562, P3HR-1, and Raji.     

Long-term storage of onion and the factors that affect its quality: A critical review

Storage of onions is a multifaceted issue, which involves many preharvest and postharvest factors. One of the major factors that affect onion storage is the selection of the proper cultivar, since there are significant differences in storability between the cultivars and not all of them are suitable for storage. Proper preharvest and postharvest conditions are essential for storability of onion bulbs, whereas they also affect marketability (weight losses, texture and color depth of bulbs) and quality (chemical composition, nutritional value, antioxidant activity). Irrigation and fertilization are essential preharvest factors that substantially affect storability, whereas curing methods and storage conditions (temperature, relative humidity, controlled atmospheres) and processing treatments are postharvest factors. This review article examines the effect of long-term storage on the main quality features of onions, such as the incidence of sprouting and root growth, water losses, and changes in chemical composition (mineral composition, sugar content, nutritional value) and antioxidant activity (phenolic and flavonoid contents, DPPH [2,2-diphenyl-1-picrylhydrazyl] scavenging activity).     

洋葱黄酮类化合物的水提工艺条件研究

采用水浸提法提取洋葱中的黄酮类化合物,用比色法测定洋葱中黄酮类化合物的含量,并对黄酮类化合物提取过程中各因素对收率的影响情况作了研究,其影响的主次顺序为料液比>浸提温度>浸提时间。     

Characterization of Shortday Onion Cultivars of 3 Pungency Levels with Flavor Precursor, Free Amino Acid, Sulfur, and Sugar Contents

ABSTRACT:  This study was conducted to characterize shortday onions of 3 pungency levels with regard to the composition of flavor related compounds. A total of 9 onion breeding lines/cultivars were selected, per each of low, medium, and high pungency level, with pyruvic acid contents of 1.9 to 2.8, 4.8 to 5.4, and 7.2 to 8.3 μmoles/mL, respectively. The contents of flavor precursors (S-1-propenyl-L-cysteine sulfoxide [1-PeCSO] and S-methyl-L-cysteine-sulfoxide [MCSO]), free amino acids, free sugars, soluble solids (SSC), and total sulfur (S) in onion bulbs were measured. The flavor precursor contents ranged from 0.03 to 0.16 mg/g fresh weight (FW) for MCSO, 0.07 to 0.65 mg for 1-PeCSO, and 0.12 to 0.77 mg in total, and precursor contents increased with the pungency levels. Onions of different pungency levels did not differ in the contents of individual or total free amino acids, and the most abundant amino acids were glutamine and arginine. The total sugar contents ranged from 50 to 75 mg/g FW, and total S contents (3.5 to 5.1 mg/g dry weight) were not correlated with the pungency levels. However, pungency levels were correlated inversely with bulb weight and positively with SSC, presumably by the effect of dilution. This study indicates that onion pungency is primarily determined by the content of flavor precursor compounds and not by total S, total sugars, or individual/total free amino acids in shortday bulbs.     

EFFECTS OF PREFRY DRYING METHODS ON THE QUALITY OF DEEP FAT FRIED ONION SLICES

Deep fat fried onion slices are used widely as a condiment for hot-dogs and other types of bread and meat combinations in Denmark, Netherlands and Germany. Since there is a consumer demand for food products, high in both sensory and nutritional quality, the effect of prefry drying on the oil content and the color of the fried product was investigated. In order to reduce the oil content in the fried product, raw sliced onions were prefry dried by (1) hot air in a forced air convection oven, (2) microwaving in an oven with a conveyor belt, or (3) freeze dried. For each of the three methods a series of eight batches ranging from 13–30 % dry matter content in the raw onions were obtained. The product that was dried by hot air before frying was lighter than the product prefry dried by microwaving. The product of the freeze dried material was heterogeneous, and the results were excluded. The fried product from dried raw onions, showed the moisture content to be independent of the manipulated dry matter content. The oil content was reduced from about 55% to about 49%, as a result of increasing the dry matter content; however the surface color became darker (L-value was reduced about 6 point).     

Investigation on the volatile oil of Makó onions

The authors have developed a method for determining the volatile oil content of onions. Using this method they found in the Hungarian Makó onions 0.019—0.031 % volatile oil, depending on storage. The composition of onion oil was studied by GC; GC-MS and TLC methods. GC-MS revealed 20 volatile sulphur compounds identified as 10 trisulphides, 6 disulphides, 3 tetrasulphides, and 1 thiophene derivative as well as one unsaturated aldehyde. Three of these: ethyl cis-1-propenyl trisulphide, ethyl trans-1-propenyl trisulphide, and butyl methyl trisulphide were described for the first time in onions. Carbonyl compounds were studied in the form of derivatives obtained with 2,4-dinitrophenyl hydrazine. On the basis of Rf-values and by addition, propanal, butanal, pentanal and hexanal were identified in the aldehyde fraction, while in the dicarbonyl fraction — beside an unknown compound — glyoxal and methyl glyoxal were identified. The presence of these two compounds in onion oil has been reported for the first time.     

Effects of onion on physicochemical properties,lipid oxidation and microbial growth of fresh pork patties

Onions with or without heating (100 °C, 30 min) were extracted with water or methanol, and antioxidant and antimicrobial activities of onion extracts were evaluated. Product characteristics of fresh pork patties containing various onion extracts were measured during refrigerated storage. Water extracts of onions showed higher extraction yield and iron chelating ability than methanol extracts (P < 0.05), whereas, the latter was more effective than the former in phenolic compounds and reducing power (P < 0.05). The addition of onion extracts [water extract from fresh onion (WEFO), methanol extract from heated onion (MEHO) and their combinations (WEFMEHO)] to pork patties decreased redness, increased yellowness, and inhibited lipid peroxidation (P < 0.05). One per cent of WEFMEHO in pork patties had antioxidant activities as effective as butylated hydroxyl toluene (BHT, 0.01%). Redness and yellowness decreased and increased with the addition of onion extract, respectively (P < 0.05).     

Assessment of the flavour of fresh uncooked onions by taste‐panels and analysis of flavour precursors,pyruvate and sugars

Flavour in fresh onions is dominated by volatile sulphenic and thiosulphenic acids that are liberated once alk(en)yl cysteine sulphoxide (ACSO) flavour precursors are cleaved by the enzyme alliinase after tissue disruption. The levels of pyruvate and ACSOs in over 100 samples of onions marketed in the UK were measured, and compared with assessment by taste‐panels. There was a linear relationship between the content of ACSOs and pyruvate. Measurements of pyruvate indicated that the marketing classification of some types of onion did not correspond to their pyruvate levels. A significant linear relationship was found between a sensory measure of strength and pyruvate over the range 1.2–9.3 µmol pyruvate g^?1 fresh weight. In most cases, when a flavour classification of sweet, mild or strong was applied to a sample of onions based on pyruvate content, the taste‐panels agreed with the categorization. The taste‐panels were unable to identify a sweet flavour in onions, except at low levels of pyruvate. Taste‐panels were able to define a likeability character (attractiveness of flavour) for onions, which correlated with the level of pyruvate. However, for some varieties, the flavour classification or likeability did not correspond to predictions based on pyruvate levels alone. Pyruvate measurements were seen as a suitable method for routine quality control once the characteristics of a variety of onion had been established, but initial evaluations should include well‐designed taste‐panel assessments. Copyright © 2004 Society of Chemical Industry     

氯化钠对鸡肉冷藏过程中肌原纤维蛋白氧化的影响

为探究氯化钠对鸡肉腌制冷藏过程中肌原纤维蛋白氧化的影响,采用不同添加量（0.0%、1.5%、3.0%、4.5%、6.0%、7.5%）的氯化钠处理鸡胸肉,冷藏不同时间（0、2、4 d）后提取肌原纤维蛋白,通过测定其表面疏水性、粒径、羰基、巯基含量等判断肌原纤维蛋白氧化程度。结果表明：随着氯化钠添加量的增加及贮藏时间的延长,鸡肉肌原纤维蛋白羰基含量逐渐增加,巯基含量则显著减少（P＜0.05）;肌原纤维蛋白产生一定的聚集交联现象,平均粒径呈增大趋势;肌原纤维蛋白中α-螺旋相对含量随着氯化钠添加量的增加而降低,而色氨酸荧光强度随氯化钠添加量的增加先升高后降低。综上所述,氯化钠对鸡肉腌制冷藏过程中的肌原纤维蛋白氧化有一定促进作用,其中氯化钠添加量4.5%时对鸡肉肌原纤维蛋白的氧化效果最为明显。     

Effects of cultivar,lifting time and nitrogen fertiliser level on quercetin content in onion (Allium cepa L.) at lifting

Commercial cultivars of onion (Allium cepa L.) were grown at Torslunda research station, Sweden with different levels of nitrogen fertiliser and lifted at different growth stages. Soon after lifting, before any drying or curing, tissue from the fleshy edible part of onions was extracted in ethanol and the raw extracts were analysed by high‐performance liquid chromatography without any previous hydrolysis. It was confirmed that the main flavonoid compounds were quercetin monoglucoside and quercetin diglucoside, whereas only trace amounts of quercetin aglycone and other flavonoids were found. The greatest variation in quercetin content, in the range 100–500 mg kg^?1 fresh weight, occurred between years. The concentration of quercetin glucosides in the onions was strongly correlated (R² = 0.98) with the total amount of global radiation in August. Individual onions with fallen leaves had significantly higher concentrations of quercetin glucosides than individuals in the same row with erect leaves. Only minor differences were found between the three cultivars analysed. Higher levels of nitrogen fertiliser had only minor effects on onion yield and size and resulted in lower or equal amounts of quercetin glucosides. Nitrogen leakage from the soil, a potential source of environmental problems, could therefore be minimised by avoiding high nitrogen fertiliser levels with almost no effect on onion flavonol content. Late lifting of onions (80% fallen leaves) resulted in up to 45% higher concentrations of quercetin glucosides compared with early lifting (50% fallen leaves). Copyright © 2006 Society of Chemical Industry