In vitro measurement of volatile release in model lipid emulsions using proton transfer reaction mass spectrometry

The presence of fat in food plays an important role in the way aroma is released during consumption and in the creation of the overall sensory impression. Fat acts as a reservoir for lipophilic volatile compounds and modulates the timing and delivery of aroma compounds in a unique manner. Despite considerable research, reproducible in vitro methods for measuring the effect of fat on volatile release are lacking. An open in vitro cell was used to simulate the open human naso-oropharygeal system and was interfaced with a proton transfer reaction mass spectrometer (PTR-MS) to examine some of the fundamental effects of fat on dynamic volatile release in liquid fat emulsions. Lipid emulsions with various fat contents (0-20%) and droplet sizes (0.25, 0.5, and 5.0 μM) were spiked with flavor volatiles representing a range of lipophilicity (K(o/w) = 1-1380). Preloaded syringes of spiked emulsion were injected into the cell, and temporal changes in release were measured under dynamic conditions. Significant differences in release curves were measured according to the lipid content of emulsions, the vapor pressure, and K(o/w) values of the volatile compounds. With increasing addition of fat, the critical volatile release parameters, maximum concentration (I(max)), time to maximum concentration (T(max)), and the integrated area under the concentration curve (AUC), were affected. The in vitro curves were reproducible and in agreement with theory and correlated with the preswallow phase of in vivo release data. An exponential model was used to calculate changes in mass transfer rates with increased fat addition.     

Effect of fat nature and aroma compound hydrophobicity on flavor release from complex food emulsions

Complex food emulsions containing either hydrogenated palm kernel oil (vegetable fat) or anhydrous milk fat (animal fat) were flavored by using different aroma compounds. The fats differed by their fatty acid and triacylglycerol compositions and by their melting behavior, while the aroma compounds (ethyl butanoate, ethyl hexanoate, methyl hexanoate, mesifurane, linalool, diacetyl, cis-3-hexen-1-ol, and gamma-octalactone) differed by their hydrophobicity. Application of differential scanning calorimetry to fat samples in bulk and emulsified forms indicated differences in the ratio of solid-to-liquid between temperatures ranging from 10 to 35 degrees C. Solid-phase microextraction coupled with GC-MS analysis indicated that flavor release from food emulsions containing animal or vegetable fat differed depending on both the fat nature and flavor compound hydrophobicity. The release of diacetyl was higher for emulsions containing animal fat, whereas the release of esters was higher for emulsions containing vegetable fat. The release of cis-3-hexenol, linalool, gamma-octalactone, and mesifurane (2,5-dimethyl-4-methoxy-(2H)-furan-3-one) was very similar for the two fatty systems. The above results were discussed not only in terms of aroma compound hydrophobicity, but also in terms of structural properties of the emulsions as affected by the lipid source.     

Mechanism of volatile compound production during storage of sunflower Oil

Volatile compounds formed in the course of the thermal decomposition of hydroperoxides during storage of sunflower oil were analyzed by headspace solid-phase microextraction sampling followed by gas chromatographic separation and mass spectral detection. The determining role of alkoxyl radicals in the process has been proven by electron spin resonance spectroscopic measurements. On the basis of analytical results, the reaction networks and mechanisms were constructed by computer modeling to describe the formation of volatile products of radical decomposition of hydroperoxides. We established that off-flavor aliphatic aldehydes are originated from only the alkoxyl radicals derived from trigliceride of linoleic acid. To find a specific additive, which redirects the formation of these radicals toward production of more stable species, is suggested.     

Trends and uncertainties in volatile organic compound emissions from anthropogenic sources

This paper discusses trends and uncertainties in the anthropogenic emission inventory for VOC. EPA's trend analysis indicates that emissions increased almost across the board until about 1970. After 1970, emissions continued to increase for industrial solvents, but declined for transportation, nonindustrial solvents, and combustion and waste disposal. With the current emphasis on using grid models to define NO_x and VOC control strategies, the uncertainty of emission inventories is becoming increasingly important. However, the volume of data in an emissions inventory makes the detailed assessment of uncertainty difficult if not impossible.     

Impact of destroying the structure of model gels on volatile release

The release of a strawberry aroma from different composite gels taken as models of fruit preparations and from a sucrose solution was investigated. The composition of the model systems differed with regard to the gelling agent, either pectin or carrageenan, and to the rigidity of the gel. With the use of atmospheric pressure chemical ionization-mass spectrometry, the release profiles of the aroma compounds were determined under stirring. At the same time, purge and trap measurements were performed to determine the release profiles of the aroma compounds without stirring. The comparison of the patterns obtained using these two complementary methods made it possible to determine how the structure of the matrix, the mechanical treatment, and the properties of the aroma compound affect aroma release. A far greater proportion of the aroma compounds was retained in the fruit preparation systems than in the sucrose solution. The different release profiles could be interpreted in terms of the volatility of the aroma compounds and of their diffusion through the gels.     

复合微生物菌剂与氨基酸水溶肥组合施用对香蕉土壤理化性质及微生物群落的影响

为了研究复合微生物菌剂和氨基酸水溶肥组合施用后香蕉土壤性质及微生物群落结构变化,在海南省东方市开展香蕉大田试验,以组合施用复合微生物菌剂与氨基酸水溶肥为处理组,在香蕉的苗期、中期、孕蕾期各处理一次,以滴灌清水为对照组,全部处理结束30 d后进行土壤取样,测定土壤理化性状,并提取土壤DNA进行土壤微生物高通量测序,对比研究土壤性质及菌群的变化情况。结果如下:(1)处理组有效地改善了土壤养分,土壤有效磷和速效钾含量极显著上升(P0.01);碱解氮显著增加(P0.05);根结线虫数量显著下降(P0.05)。(2)细菌测序结果表明,在目水平上,对照组土壤中细菌相对丰度≥2%的优势菌目在处理组土壤中都呈下降趋势;在属水平上,物种丰度≥1%的菌属中,处理组土壤的Rhodanobacter(罗丹杆菌属)、Sphingomonas(鞘氨醇单胞菌属)、Dyella(分类未定)的物种丰度都明显升高,其中Sphingomonas呈显著性升高。(3)真菌测序结果显示,处理组土壤中Colletotrichum(炭疽菌属)的丰度明显下降,但Penicillium(青霉菌属)的丰度有所升高。综上,采用复合微生物菌剂和氨基酸水溶肥组合处理,对土壤理化性状和微生物具有明显的改良和改善作用,有利于减少香蕉的病害发生。     

液态缓释复配肥在日光温室蔬菜上的应用研究

节能日光温室蔬菜生产中,在农民自己施肥的基础上,于茄子、黄瓜采收前距离植株10 cm处,打直径为5~7 cm的孔,茄子地适宜孔深为40 cm,黄瓜地适宜孔深为20 cm,灌施液态缓释复配肥,间隔20 d时间灌施1次,连续灌施3次,茄子以每次每株灌施800 mL为宜,其增产率为35.8%。黄瓜每次每株灌施500 mL为宜,增产率为17.2%。茄子高效益期的产量占总计产时段产量的58.3%,而产值占总计产时段产值的71.5%。黄瓜高效益期的产量占总计产时段产量的64.3%,产值占总计产时段产值的86.5%。     

电导率法快速检测缓释复合肥养分释放的探讨

比较两种计算方法获得的缓释复合肥料Osmocote静水培养液中氮、磷、钾3种养分累积释放曲线的差异,探讨缓释复合肥料养分释放的快速检测方法。采用静水溶出率法,在25℃和40℃条件下分别测定溶液中的养分含量和电导率,利用电导率—氮、磷、钾养分浓度标准曲线法(方法Ⅰ)和电导率—实测养分浓度回归分析法(方法Ⅱ)分别求得缓释肥料养分累积释放曲线并进行比较。结果表明,Osmocote包膜缓释肥料的电导率—氮、磷、钾养分浓度标准曲线(方法Ⅰ)都呈二次曲线,相关系数均等于1;电导率—实测氮、磷、钾养分浓度回归分析曲线(方法Ⅱ)也都呈二次曲线,相关系数均达极显著水平;电导率与氮素浓度相关性最好,钾次之,磷最差;方法Ⅰ和方法Ⅱ所得的养分释放率相比,氮的相对误差最小,钾次之,磷相差甚远。因此,电导率—氮素浓度标准曲线法(方法Ⅰ)与电导率—实测养分浓度(方法Ⅱ)相比,既方便快捷,又可以保证较小的相对误差,可以作为氮、磷、钾复合型缓释肥料养分释放快速检测的一种较好的备选方法。     

Effects of bituminous emulsions on retention and release of some chemical elements in two soil samples

The effects of bituminous emulsions on the retention and release of some nutrient elements and heavy metals were investigated in the laboratory for a pair of different soil samples, one from each of Egypt and Belgium. The emulsion was applied at several rates to promote the formation of aggregates, to stabilize them, and to make the soil samples more hydrophobic. The quantities of extractable potassium and trace elements were determined for the untreated and treated samples, as well as for aggregates more than 2 mm in diameter before and after destruction.The results show that addition of bituminous emulsion increases aggregation percentage and aggregate stability, and decreases the extractable amounts of elements. This effect increases with increasing concentration of bituminous emulsion. The extractable amounts of the nutrient elements after destruction of the aggregates were higher than those before destruction. The mechanisms of retention and release of nutrient elements before and after destroying the aggregates are schematically presented and discussed.     

聚合物包膜NPK复合肥料养分释放滞后期的研究

聚合物包膜肥料养分释放的滞后期是指不释放养分或释放量很少的时期,主要由水分进入过程和养分溶解过程组成,滞后期的长短受这两个过程控制;滞后期的主要影响因素为包膜厚度、养分溶解度、养分组成等。以此为理论基础,模拟了聚合物包膜肥料养分释放的滞后期,推导出聚合物包膜肥料滞后期的方程为:tlag=kr/3(l/PhP+1/D),估算了聚亚安酯类物质包膜NPK复合肥料(Multicote)中K+、NO3-、NH4+释放的滞后期。4和H2PO4+由于养分离子本身的溶解性质不同以及养分间的相互作用,不同的养分离子的滞后期存在明显差异,与试验结果一致。同时,该模型还表明,当包膜厚度较薄时,对滞后期起主导作用的是养分溶解过程,只有当包膜厚度足够大时,才会对滞后期起主导作用。该模型将对聚合物包膜肥料的研制和应用提供重要的理论指导。     

Effect of emulsifier on oxidation properties of fish oil-based structured lipid emulsions

The effects of the emulsifiers lecithin, Tween 20, whey protein isolate, mono-/diacylglycerols, and sucrose fatty acid ester on oxidation stability of a model oil-in-water emulsion prepared with enzymatically synthesized menhaden oil-caprylic acid structured lipid were evaluated. Oxidation was monitored by measuring lipid hydroperoxides, thiobarbituric acid reactive substances, and the ratio of combined docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) contents to palmitic acid in the emulsion. After high-pressure homogenization, all emulsions, except those prepared with lecithin, had similar droplet size distributions. All structured lipid emulsions, except for the lecithin-stabilized emulsions, were stable to creaming over the 48-day period studied. Emulsifier type and concentration affected oxidation rate, with 0.25% emulsifier concentration generally having a higher oxidation rate than 1% emulsifier concentration. Overall, oxidation did not progress significantly enough in 48 days of storage to affect DHA and EPA levels in the emulsion.     

Boreal pine forest floor biogenic volatile organic compound emissions peak in early summer and autumn

In boreal forests, canopy-scale emissions of biogenic volatile organic compounds (BVOCs) are rather well characterised, but knowledge of ecosystem-scale BVOC emissions is still inadequate. We used adsorbent tubes to measure BVOCs from a boreal Scots pine (Pinus sylvestris L.) forest floor in southern Finland and analysed the compounds with a gas chromatograph-mass spectrometer. The most abundant compound group was the monoterpenes (averaging 5.04 μg m⁻² h⁻¹), in which α-pinene, Δ³-carene and camphene contributed over 90% of the emissions. Emissions of other terpenoids (isoprene and sesquiterpenes) were low (averaging 0.05 and 0.04 μg m⁻² h⁻¹, respectively). BVOC emissions from the forest floor varied seasonally, peaking in early summer and autumn, with most of the compounds following similar patterns. The emission pattern was sustained throughout the measurement period, suggesting that the main sources of the emissions remained more or less stable. We compared the BVOC fluxes with environmental parameters such as temperature, precipitation and PAR, and with fluxes of other trace gases (CO₂, CH₄, N₂O), as well as with ground vegetation photosynthesis and with litter input. Several of these parameters were correlated with the presence of BVOCs. The sources of soil BVOC emissions are very poorly understood, but our results suggest, that changes in litter quantity and quality, soil microbial activity and the physiological stages of plants are linked with changes in BVOC fluxes.     

缓释复合肥养分释放特性和黄连生物效应研究

采用连续恒温培养和大田试验研究了4种缓释复合肥在种植黄连的土壤(森林黄棕壤)中的养分释放特性及其对黄连产量和药用品质的效应。结果表明,20℃恒温模拟条件下缓释复合肥氮、磷、钾养分缓释性能较佳,3种养分释放的动力学过程可用Elovich方程St=a+blnt、双常数方程lnSt=a+blnt和抛物线扩散方程St=a+bt0.5表征,各方程参数b值均可用于描述缓释复合肥氮、磷、钾养分释放速率。在田间试验中4种缓释复合肥极显著提高3～5年生黄连产量,大幅度提高黄连小檗碱和生物碱产量,并以SRF3、SRF2和SRF13种缓释复合肥的效应大。     

A new insight into the formation of odor active carbonyls by thermally-induced degradation of phospholipids in self-assembly structures

The role of molecular organization in heated aqueous dispersions of egg phosphatidylcholine (PC) and egg phosphatidylethanolamine (PE) was studied with respect to the formation of key odorants. Evidence was found for the crucial role of self-assembly structures adopted by phospholipid molecules on the quantitative composition of volatile constituents. The concentrations of seven aldehydes and one vinyl ketone were determined by isotope dilution assay in heated aqueous dispersions of PC and PE present in various ratios. Addition of PE to PC drastically decreased the amount of (E,E)-2,4-decadienal formed, which cannot be explained by the differences in the fatty acid composition of PC and PE. The free amino group in PE does not explain this phenomenon either, as replacing PE by phosphatidic acid distearylester also reduced the amounts of (E,E)-2,4-decadienal. We suggest that the type of self-assembly structure adopted by phospholipids in water significantly influences the reaction yields. However, the mechanisms leading to the preferred formation of phospholipid-derived odorants in a lamellar phase, as compared to the reversed hexagonal phase, remain unknown.     

淀粉黏结剂对颗粒有机复混肥养分释放的影响

以自制的两种淀粉基黏结剂作为有机复混肥造粒黏结剂，以无机黏结剂硅酸钠为对照处理，以废物堆肥和市售无机化肥作为原料，经圆盘造粒获得3种不同颗粒有机复混肥。3种有机复混肥颗粒平均抗压碎力都达到了中国国家标准(≥6 N)的要求；无机黏结剂C颗粒经24 h的水浸泡后，其崩解率为6.1%；而A和B淀粉黏结剂颗粒保持完好，崩解率为0。通过168 h养分溶出试验发现，有机黏结剂A和B能明显降低颗粒肥中营养元素的释放速率；PVA(聚乙烯醇)改性淀粉黏结剂B作为有机复混肥造粒黏结剂，能明显延缓颗粒肥中NH⁺₄-N、全氮、全磷和全钾释放速率。虽然黏结剂A比黏结剂B延缓颗粒肥无机养分释放的效果差，但与无机黏结剂C相比，其延缓颗粒肥无机养分释放速率的效果要好的多。试验结果表明：用改性淀粉黏结剂作为有机复混肥造粒黏结剂，可以同步实现对速溶无机养分的控制释放，也为新型非包膜控施肥的研制和开发提供新的思路和参考。     

Antioxidant properties of Teaw (Cratoxylum formosum Dyer) extract in soybean oil and emulsions

The antioxidant activity of an extract from Teaw (Cratoxylum formosum Dyer) leaves was studied in soybean oil and soybean oil-in-water emulsions. Samples containing the extract or reference antioxidants including chlorogenic acid, which comprises 60% of the Teaw extract, were stored at 60 degrees C and analyzed periodically for peroxide value (PV) and thiobarbituric acid reactive substances (TBARS) to allow both hydroperoxides and hydroperoxide degradation products to be monitored. Chlorogenic acid and the Teaw extract were more effective than alpha-tocopherol in inhibiting lipid oxidation in bulk oil but were less effective in an oil-in-water emulsion in accordance with the polar paradox. The PV/TBARS ratio for oil samples containing chlorogenic acid was higher than for alpha-tocopherol and BHT because chlorogenic acid inhibits both hydroperoxide formation by radical scavenging and hydroperoxide decomposition by metal chelation. The importance of the metal-chelating activity in retarding hydroperoxide decomposition was confirmed by studying the decomposition of oil samples containing added ferric ions. The PV/TBARS ratio was higher for citric acid than for alpha-tocopherol in the presence of added ferric chloride, but the order was reversed in samples lacking ferric chloride. Samples containing added chlorogenic acid gave the highest PV/TBARS ratios both in the presence and absence of ferric ions. The PV/TBARS ratios for the samples containing antioxidants fell rapidly to lower values in a soybean oil-in-water emulsion than in the soybean oil. This was due to increased hydroperoxide decomposition in the emulsion at the same PV. The Teaw extract contained 12% oil-soluble components, which contributed to a slightly higher oil-water partition coefficient than that of chlorogenic acid. The antioxidant activity of the aqueous phase of the Teaw extract was reduced more than that of chlorogenic acid by partitioning of the oil-soluble components into oil, which showed that the less-polar components contributed to the antioxidant activity of the Teaw extract in aqueous media.     

Modification of volatile compound profile of virgin olive oil due to hot-water treatment of olive fruit

The effect of hot-water treatments of olive fruits before processing on the biosynthesis of virgin olive oil aroma was investigated by quantifying the variation within the major classes of volatile compounds. Data showed that hot-water treatments gave rise to changes in the volatile aroma profile of virgin olive oil from the three olive cultivars under study, Manzanilla, Picual, and Verdial. Different effects by thermal treatments were observed according to cultivar. In general, these changes are mainly due to a decrease in the contents of C(6) aldehydes and C(5) compounds. Contents of C(6) alcohols and esters remained constant or decreased slightly when the temperature of the treatment was increased. Thus, heat treatments seemed to promote a partial deactivation of the lipoxygenase/hydroperoxide lyase enzyme system, whereas other enzymatic activities, within the lipoxygenase pathway, such as alcohol dehydrogenase and alcohol acyltransferase, remained apparently unaffected as a consequence of heat treatments.     

Effect of apple particle state on the release of volatile compounds in a new artificial mouth device

Varying the crushing parameters in a model mouth apparatus gave different crushed apple samples, which were compared to apples crushed in the human mouth by six people. An image analysis method was developed to measure the similarity between apple particles after crushing in the artificial mouth and in the human mouth. Thus, experimental conditions were determined that produced fruit in a state closest to that obtained after mastication in a human mouth. The influence of these different conditions on the quantity of released volatile compounds was then studied.     

三种有机无机复混钾肥钾素的释放与供应特征

在实验室条件下,通过间歇淋洗培养和土壤培养试验研究了不同有机无机复混钾肥钾素的释放与供应特征。在等化肥钾量投入条件下,与化学钾肥相比,供试的3种有机无机复混钾肥没有显著影响到钾素在石灰性土壤中的释放规律;土壤速效钾含量有所增加,糖渣系、糠醛渣系和污泥系有机无机复混钾肥处理的土壤速效钾含量分别比化学钾肥处理增加了13.5%、12.7%和1.6%。与化学钾肥处理相比,糖渣系、糠醛渣系有机无机复混钾肥处理的钾素(K)固定量分别减少了42和39 mg/kg。     

Interactions of soluble peptides and proteins from skeletal muscle on the release of volatile compounds

The ability of skeletal dipeptides (carnosine and anserine) and a sarcoplasmic protein (myoglobin) to interact with key flavor compounds (hexanal, octanal, methional, 2-pentanone, 2-methylbutanal, and 3-methylbutanal) has been studied using the solid phase microextraction (SPME) technique. Conditions for SPME analysis (fiber coating, sampling time, and linearity of detection) were optimized. The effect of pH on the binding was also investigated. Thermodynamic models were applied to evaluate the binding parameters n (number of binding sites), K (affinity constant), and DeltaG (Gibb's free energy) to all of the flavor compounds studied, and they showed an absence of cooperative effect. Carnosine was the peptide with the highest affinity for all of the volatile compounds except 2-pentanone. Its interaction with hexanal and methional was significantly affected by pH. Anserine showed a lower level of interactions with hexanal, methional, 2-methylbutanal, and 3-methylbutanal, whereas myoglobin interacted with only hexanal and 2-methylbutanal. Differences in aroma retention can thus result in different sensory perceptions of muscle foods.