Lipid oxidation in milk, yoghurt, and salad dressing enriched with neat fish oil or pre-emulsified fish oil

This study compared the oxidative stabilities of fish-oil-enriched milk, yoghurt, and salad dressing and investigated the effects on oxidation of adding either neat fish oil or a fish-oil-in-water emulsion to these products. Milk emulsions had higher levels of a fishy off-flavor and oxidized faster, as determined by the peroxide value and volatile oxidation products, than fish-oil-enriched yoghurt and dressing, despite the fact that dressings had a higher fish oil content and were stored at room temperature. Additionally, fish-oil-enriched yoghurt generally had higher oxidative stability than fish-oil-enriched dressings, irrespective of the mode of fish oil addition. Yoghurt thus seemed to be a good delivery system of lipids containing n-3 polyunsaturated fatty acids. Different effects of adding fish oil either as neat fish oil or as a fish-oil-in-water emulsion were observed for milk, yoghurt, and dressing. Yoghurt and dressing enriched with neat fish oil were more stable than those enriched with a fish-oil-in-water emulsion, whereas milk enriched with neat fish oil was less stable than milk enriched with the fish-oil-in-water emulsion. Overall, it seemed that application of neat fish oil was a good option for preserving the final quality in yoghurt and dressings, but a pre-emulsion may still be considered for the fish oil enrichment of certain food products, for example, milk.     

Infusion of volatile flavor compounds into low-density polyethylene

Supercritical fluids can extract components from some matrixes (e.g., fat and flavors from food) as well as infusing additives into synthetic polymer matrixes. To study the feasibility of infusing flavors into matrixes as a potential flavoring mechanism, a wide range of volatile flavor compounds was infused into a well-defined synthetic polymer (low-density polyethylene) using supercritical carbon dioxide. The polymer was then extracted, and the amount of infused compound was determined. The effects of time, temperature, pressure, rate of depressurization, volatile concentration, and volatile properties on the degree of infusion were studied. Infusion with supercritical carbon dioxide achieved much higher loadings of the polymer (0.01 to 6.87 mg/g LDPE, depending on the volatile molecule being infused) compared to those achieved by static diffusion. Forty-five volatiles were infused, from which a model was developed to predict infusion as a function of certain physicochemical properties.     

Homogenization conditions affect the oxidative stability of fish oil enriched milk emulsions: lipid oxidation

In this study fish oil was incorporated into commercial homogenized milk using different homogenization temperatures and pressures. The main aim was to understand the significance of homogenization temperature and pressure on the oxidative stability of the resulting milks. Increasing homogenization temperature from 50 to 72 degrees C decreased droplet size only slightly, whereas a pressure increase from 5 to 22.5 MPa decreased droplet size significantly. Surprisingly, emulsions having small droplets, and therefore large interfacial area, were less oxidized than emulsions having bigger droplets. Emulsions with similar droplet size distributions, but resulting from different homogenization conditions, had significantly different oxidative stabilities, indicating that properties of significance to oxidation other than droplet size itself were affected by the different treatments. In general, homogenization at 72 degrees C appeared to induce protective effects against oxidation as compared to homogenization at 50 degrees C. The results thus indicated that the actual composition of the oil-water interface is more important than total surface area itself.     

Sorption of volatile flavor compounds by microcellular cereal starch

Wheat starch based microcellular foam (MCF) forms of (dry) starch possess a significant percentage of micropores in the range of 5-14 A. The present study confirmed earlier preliminary studies that MCF starch (in a 0.25-1.0 mm diameter bead form) is effective in sorbing and lowering the headspace partial pressure of many volatile compounds in a manner similar (although less efficient) to that exhibited by other microcavity sorbants such as charcoal. It was found that the proportion of polar compounds sorbed was much greater than the proportion of nonpolar compounds. A major portion of the sorbed volatile compound was readily displaced from the MCF microcellular starch by the addition of water. These properties make this form of edible starch a potential useful carrier of flavor compounds for dried foods.     

Modeling the partition of volatile aroma compounds from a cloud emulsion

Parameters determining the partitioning behavior of volatile compounds between a cloud emulsion and the gas phase were measured under static equilibrium headspace conditions, using volatiles (e.g., ethyl hexanoate, cymene, and octanol) representing different volatilities and different degrees of hydrophobicity. The significant factors were the molecular characteristics of the volatile and the concentration of the oil phase. The nature of the lipid (C8 and C12 triglycerides), particle size, and emulsifier type (modified starch and gum arabic) did not significantly alter volatile partitioning. An empirical model based on the partition behavior and physicochemical parameters of 67 volatile compounds was produced. This predicted the partition of volatiles (R(2) = 0.83) in cloud emulsions as a function of lipid content. The significant terms (P < 0.05) in the empirical model were Log P, Log solubility, the dipole vector, and the oil fraction.     

Analysis of volatile compounds and their contribution to flavor in cereals.

Recent developments in methods for isolation and measurement of volatiles from cereals are reviewed. The main types of isolation methods, namely, direct extraction, distillation, and headspace, have recently been complemented by solid phase microextraction. Direct solvent extraction provides efficient recovery of compounds with a broad range of polarities and volatilities, whereas headspace techniques provide relatively clean extracts. Supercritical fluid and solid phase microextractions have not yet been fully evaluated for cereals. GC and GC/MS remain the dominant techniques for measurement of the extracted compounds, although new electronic noses show promise. Relating these results to human perception requires careful control to ensure valid comparisons and, in this respect, aroma extract dilution analysis is a useful procedure.     

Study of light-induced volatile compounds in goat's milk cheese

Light-induced volatile compounds in goat cheese were studied by a combination of solid phase microextraction (SPME)-gas chromatography (GC)-mass spectrometry (MS), headspace oxygen depletion, and sensory evaluation. Samples stored under fluorescent light for 2 days at 30 degrees C had 90% more volatile compounds and 4 times more headspace oxygen depletion than samples stored in the dark at 30 degrees C. The volatiles 1-heptanol, heptanal, nonanal, and 2-decenal were formed and increased only in the light-stored samples, which may be formed from singlet oxygen oxidation of unsaturated fatty acids. Sensory evaluation showed that samples stored under light had significantly more off-flavor than samples stored in the dark at 30 degrees C (P < 0.05), and 1-heptanol, heptanal, nonanal, and 2-decenal increased the goat cheese off-flavor significantly (P < 0.05).     

Effect of ascorbic acid on iron release from the emulsifier interface and on the oxidative flavor deterioration in fish oil enriched mayonnaise

This research examines the effect of ascorbic acid (0-800 ppm) on the sensory perception of mayonnaises containing 16% fish oil and on the levels of iron and copper in the aqueous phase. Ascorbic acid increased the formation of fishy off-flavors in fresh mayonnaise. Simultaneously, the iron concentration increased from below the detection limit (1.8 microM) to 34 microM in the aqueous phase of mayonnaises. Model mayonnaises with various concentrations of egg yolk (1-7% w/w) and ascorbic acid (0-8000 ppm) were prepared. Iron concentrations in the aqueous phase increased with increasing ascorbic acid levels, whereas iron concentrations in the assumed interfacial layer decreased. It is proposed that ascorbic acid is able to complex and reduce Fe(3+) to Fe(2+) from phosvitin in the egg yolk, whereby iron is released from the interface. The ascorbic acid-iron complex subsequently reacts with lipid hydroperoxides, resulting in increased lipid oxidation and in the immediate formation of rancid and fishy off-flavors.     

Virgin olive oil volatile compounds from lipoxygenase pathway and characterization of some italian cultivars.

Fruits from seven different varieties of Olea europaea L., grown in the same environmental conditions, were harvested in two succeeding years at the same ripening degree and immediately processed. The oils obtained were submitted to gas chromatographic determination of the volatile compounds extracted by dynamic headspace technique. The results demonstrated that the accumulation of the different metabolites in the oils obtained from the various cultivars were strictly connected with the varietal parameter because of the enzyme differences genetically determined. This feature made possible the differentiation of the examined cultivars on the basis of the percent of each metabolite from the enzymatic transformation of 13-hydroperoxides of linolenic acid. Oils from Picual and Koroneiki varieties cultivated in Spain and Greece, respectively, showed contents of volatiles very similar to those detected in the oils of the same varieties cultivated in Italy, proving that they were not significantly influenced by the environmental conditions.     

Solid-phase microextraction method development for headspace analysis of volatile flavor compounds

Solid-phase microextraction (SPME) fibers were evaluated for their ability to adsorb volatile flavor compounds under various conditions with coffee and aqueous flavored solutions. Experiments comparing different fibers showed that poly(dimethylsiloxane)/divinylbenzene had the highest overall sensitivity. Carboxen/poly(dimethylsiloxane) was the most sensitive to small molecules and acids. As the concentrations of compounds increased, the quantitative linear range was exceeded as shown by competition effects with 2-isobutyl-3-methoxypyrazine at concentrations above 1 ppm. A method based on a short-time sampling of the headspace (1 min) was shown to better represent the equilibrium headspace concentration. Analysis of coffee brew with a 1-min headspace adsorption time was verified to be within the linear range for most compounds and thus appropriate for relative headspace quantification. Absolute quantification of volatiles, using isotope dilution assays (IDA), is not subject to biases caused by excess compound concentrations or complex matrices. The degradation of coffee aroma volatiles during storage was followed by relative headspace measurements and absolute quantifications. Both methods gave similar values for 3-methylbutanal, 4-ethylguaiacol, and 2,3-pentanedione. Acetic acid, however, gave higher values during storage upon relative headspace measurements due to concurrent pH decreases that were not seen with IDA.     

鸡油组织中的磷脂对鸡油挥发性风味化合物形成的影响

磷脂是肉类特征性风味的重要前体物质。鸡油具有浓郁的脂香和鸡汤香气,磷脂可能对其风味有重要作用。该研究采用去除鸡油组织中的磷脂,以及在鸡油中添加磷脂等处理方法,结合顶空固相微萃取-气相色谱-质谱联用技术和感官评价方法研究经不同处理鸡油中的挥发性风味物质相对含量和风味的变化。结果表明添加了磷脂的鸡油,其特征性风味成分显著增加,特别是（E,E）-2,4-癸二烯醛和1-辛烯-3-酮分别增加了4.5倍和10.4倍;而去除磷脂鸡油的挥发性风味物质种类和丰度显著减少;感官评价结果也表明添加磷脂鸡油的风味最浓郁,而去除磷脂鸡油的风味最弱。因此,该研究证明鸡油组织中的磷脂对鸡油的风味具有重要的贡献作用,添加磷脂可显著增加鸡油的香气。该研究结果为浓香鸡油的开发提供理论依据和参考工艺。     

Characterization of volatile compounds contributing to naturally occurring fruity fermented flavor in peanuts

Published research has indicated that ethyl 2-methylpropanoate, ethyl 2-methybutanaote, ethyl 3-methylbutanoate, hexanoic acid, butanoic acid, and 3-methylbutanoic acid are responsible for fruity fermented (FF) off-flavor; however, these compounds were identified in samples that were artificially created by curing immature peanuts at a constant high temperature. The objective of this study was to characterize the volatile compounds contributing to naturally occurring FF off-flavor. Volatile compounds of naturally occurring FF and no-FF samples were characterized using solvent-assisted flavor evaporation (SAFE), solid phase microextraction (SPME), gas chromatography-olfactometry (GC-O), and gas chromatography-mass spectrometry (GC-MS). Aroma extract dilution analysis (AEDA) identified 12 potent aroma active compounds, none of which were the previously identified esters, with no consistent differences among the aroma active compounds in no-FF and FF samples. Hexanoic acid alone was identified in the naturally occurring FF sample using the SAFE GC-MS methodology, whereas two of the three previously identified esters were identified in natural and artificially created samples. The same two esters were confirmed by SPME GC-MS in natural and artificially created samples. This study demonstrated the need for caution in the direct application of data from artificially created samples until those compounds are verified in natural samples. However, these results suggest that a laboratory method using SPME-GC techniques could be developed and correlated on an ester concentration versus FF intensity basis to provide an alternative to sensory analysis for detection of FF off-flavor in peanut lots.     

杀菌方式对即食胡萝卜片挥发性风味物质的影响

为研究不同杀菌方式对即食胡萝卜片挥发性风味物质的影响,运用固相微萃取和气相色谱-质谱联用技术,分别对新鲜胡萝卜片和经巴氏杀菌、超高压杀菌、热辅助超高压杀菌处理的即食胡萝卜片及其贮藏期间(4℃,60 d)的挥发性组分进行对比分析。试验结果表明:新鲜胡萝卜片的主要芳香成分为萜烯类物质。与未杀菌组相比,经不同杀菌处理后,即食胡萝卜片的萜烯类物质含量均有所降低,其中巴氏杀菌组降低的最多。在贮藏前期(20~30 d),超高压处理即食胡萝卜片的萜烯类物质的含量最高,超高压杀菌在短期内较好地保持了胡萝卜特有的香气,即食胡萝卜片品质较好;其次是热辅助压力杀菌组,热辅助压力杀菌组即食胡萝卜片的β-蒎烯、β-石竹烯的含量较其他处理组较高,较好地保持了胡萝卜的松树树脂香气以及辛香气味;而巴氏杀菌组即食胡萝卜片的萜烯类物质含量最低,即食胡萝卜片的品质相对较差。研究结果可为新型杀菌技术在即食产品领域的应用提供参考。     

Dynamic headspace gas chromatography/mass spectrometry characterization of volatiles produced in fish oil enriched mayonnaise during storage

Protection against lipid oxidation and formation of unpleasant fishy and rancid off-flavors in oil-in-water food emulsions, such as fish oil enriched mayonnaise, is difficult to achieve. Volatile profiles from stored mayonnaises with different oil phase compositions were collected using a developed dynamic headspace sampling technique, in which interfering acetic acid was removed in situ with potassium hydroxide, and subsequently 148 volatiles were characterized and monitored by gas chromatography/mass spectrometry. Multivariate statistics showed correlation between the concentration of 62 volatiles and the fish oil and storage parameters, indicating the formation of lipid oxidation products, which impose fishy off-flavors. Further verification was obtained by gas chromatography/olfactometry, by which, among 78 odors, cis-4-heptenal and trans,cis-2,4-heptadienal were detected as distinct fishy notes. In total, 27 volatiles, including 1-penten-3-one, cis-2-penten-1-ol, cis-3-hexenal, cis-4-heptenal, 1-octen-3-one, 1,cis-5-octadien-3-one, 1-octen-3-ol, trans,cis-2, 4-heptadienal, and trans,cis-2,6-nonadienal, were suggested to contribute to the developed unpleasant fishy and rancid off-flavors.     

Tyrosinase inhibitory activity of the olive oil flavor compounds.

A series of alpha,beta-unsaturated aldehydes, otherwise known as (2E)-alkenals, characterized from the olive Olea europaea L. (Oleaceae) oil flavor was found to inhibit the oxidation of L-3, 4-dihydroxyphenylalanine (L-DOPA) catalyzed by mushroom tyrosinase, and the inhibition kinetics analyzed by a Lineweaver-Burk plot found that they are noncompetitive inhibitors. The inhibition mechanism presumably comes from their ability to form a Schiff base with a primary amino group in the enzyme. In addition, the hydrophobic alkyl chain length from the hydrophilic enal group seems to relate to their affinity to the enzyme, and this results in their inhibitory potency.     

基于判别分析法的金华火腿挥发性风味物质的形成过程分析

为了弄清金华火腿风味物质的形成过程,以60只杂交猪后腿为原料,按照传统工艺加工金华火腿,用气质联用仪(GC-MS)分析了6个工艺点的肌肉中挥发性风味物质的出峰面积,并用判别分析法分别研究了用挥发性风味物质的出峰面积和出峰面积占总出峰面积的百分率建立的判别函数判断金华火腿加工程度的可能性.研究结果表明,用金华火腿挥发性风味化合物的峰面积进行逐步判别分析,有20种挥发性化合物进入判别函数,而用峰面积占总出峰面积的百分率进行逐步判别分析,有17种挥发性化合物进入判别函数,建立的两套判别函数都能准确判别火腿的加工程度.结果提示:金华火腿风味化合物是在加工过程中逐步形成的,在不同加工阶段,火腿特征风味化合物的含量及其比例各具特征,可以用以辨别火腿的加工时间.     

真空冷冻干燥对柠檬挥发性风味化合物保留的影响

为探索真空冷冻干燥方法对柠檬中挥发性风味化合物保留特性的影响,该研究采用一体化冻干、传统冷冻干燥2种不同工艺方法进行对比干燥试验。结果表明,柠檬一体化冻干法在真空冻结阶段预先脱除了近1/3的初始水分,在预冻和升华干燥环节分别与比传统冻干法节省2.5、2h,冻干后形成相对致密的多孔网络结构,细胞壁孔室较为完整。新鲜柠檬原料挥发性风味化合物中单萜烯类化合物占绝对主导地位,主要为D-柠檬烯、萜品烯、左旋-β-蒎烯、β-蒎烯,主要倍半萜烯风味化合物为1-石竹烯、巴伦西亚橘烯、β-防风根烯,主要醛类化合物为柠檬醛、二甲基-辛二烯醛、壬醛、癸醛、己醛,主要醇类化合物为α-松油醇、橙花醇、4-萜烯醇、芳樟醇、香叶醇,主要酯类化合物为橙花乙酸酯、5-甲基-2-4-己烯-1-醇乙酸酯;各类主要挥发性风味化合物在2种方法冻干柠檬中保留率均较低,绝大部分迁移出被冷阱凝霜捕集或真空泵抽排机外损失;一体化冻干柠檬中各类风味化合物含量显著高于传统冻干柠檬(P0.05),对挥发性风味化合物的保留具有显著优势;主要单萜烯类风味化合物在传统冻干冷阱凝霜中含量显著高于一体化冻干冷阱凝霜(P0.05),而主要倍半萜烯化合物、醛类化合物、醇类化合物、脂类化合物在一体化冷阱凝霜中含量均显著高于传统冻干冷阱凝霜(P0.05)。2种冻干柠檬挥发性风味化合物保留特性的差异可能与冻干工艺时间、微观组织形态有关。该研究结果为柠檬等果蔬冷冻干燥加工制品的保香提质提供参考。     

Effect of a hay-based diet or different upland grazing systems on milk volatile compounds

The effect of animal feeding on milk volatile organic compounds (VOCs) of metabolic origin was tested on a hay-based diet (H), a highly diversified pasture under continuous grazing (CG), or a less diversified pasture under rotational grazing (RG). Individual milk of 24 Montbe?liarde cows (8 per treatment) were sampled after 2 weeks. Pasture-derived milk was richer (p < 0.05) in camphene, sabinene, β-caryophyllene, and skatole than H milk. Neither milk yield nor fat content affected the majority of VOCs measured. Skatole increased slightly with milk yield, while indole and cineole decreased slightly with milk fat content but with poor regression (R(2) < 0.54). Multivariate analysis showed that, on the basis of those VOCs of metabolic origin whose concentration differed between treatment (dimethyl-sulfone, skatole, toluene, undecanoic acid, 1-octadecene, benzeneacetaldehyde, octanoic acid, and 2-pentanone-4-hydroxy-4-methyl), it was possible to obtain good discriminations among feeding systems. This study is promising for a future use of VOCs of metabolic origin to trace animal feeding systems.     

Determination of trace volatile organic compounds in fish tissues by gas chromatography

Several volatile organic compounds associated with petroleum fuels (mainly alkylated benzenes) were extracted from spiked fish tissue samples with a stream of air, trapped on charcoal, eluted with a solvent, and analyzed by gas chromatography. These volatile compounds are among the most water-soluble components of crude oils and petroleum products, and they have been associated with tainting in fish tissues. Recoveries for these compounds were about 90% when spiked directly either onto traps or into fish tissues although naphthalene desorbed poorly from the charcoal; recoveries of this compound were about 50%. Relative standard deviations (RSD) for most recoveries of spiked samples were in the 2-10% range based on 6 samples analyzed in duplicate. However, when live fish were contaminated experimentally by adding the aromatic compounds to the aquarium water, the RSDs were higher (10-30%).