CHEMICAL AND SENSORY CHARACTERIZATION OF COMMERCIAL SAUERKRAUT1

Canned sauerkraut from eight U.S. companies was analyzed for salt, titra-table acidity (TA), fermentation substrates and end products, volatile sulfur compounds and sensory characteristics. The TA ranged from 0.9–1.5%, while salt content ranged from 1.4–2.0%, which was lower than in previous surveys. High performance liquid chromatography (HPLC) was used to monitor lactic, acetic, malic, succinic, propionic and butyric acids; mannitol, ethanol, propanol, glycerol, glucose, fructose and sucrose. Low concentrations of propionic acid, propanol and glycerol were found. These three compounds are not characteristic of lactic acid fermentations. No butyric acid was detected. GC analysis revealed seven main sulfur compounds (hydrogen sulfide, methanethiol, dimethyl sulfide, carbon disulfide, dimethyl disulfide, allyl isothiocyanate (AITC) and dimethyl trisulfide) and six other organic compounds (methanol, ethanol, n-propanol, 2propanol, acetaldehyde and ethyl acetate) in the headspace of sauerkraut juice. A profile panel characterized aroma, flavor and after-taste of sauerkraut with ten distinct notes. The sour, sulfur and salt notes had the greatest impact on sauerkraut flavor.     

Involvement of Volatile Sulfur Compounds in Ionizing Radiation-induced Off-odor of Fresh Orange Juice

ABSTRACT: The influences of ionizing radiation on volatile sulfur compounds in fresh Valencia orange juice were analyzed using gas chromatography (GC)-pulsed flame photometric detection and sensory evaluation. Methyl sulfide (MS) and methanethiol (MT) were induced most, followed by dimethyl disulfide and dimethyl trisulfide. Carbon disulfide was reduced by irradiation, while hydrogen sulfide was not consistently affected. Sensory evaluation indicated that the odor of irradiated juice differed from the nonirradiated samples at 0.5, 1, 2, or 3 kGy. Addition of the 2 major irradiation-induced sulfur compounds (MS and MT) into fresh juice changed the juice odor, indicating that those 2 compounds were probably involved in the development of irradiation-induced off-odor.     

Changes in Volatile Sulfur Compounds of Whisky During Aging

Volatile sulfur compounds of malt whiskies were analyzed using a gas chromatograph equipped with a flame photometric detector by direct injection and solvent extraction methods. Sulfur compounds identified by coupled gas chromatography-mass spectrometry and by matching GC retention times were dimethyl sulfide, dimethyl disulfide, dimethyl trisulfide, 3-(methylthio)propanal, 3-(methylthio)propanol, 3-(methylthio)propyl acetate, ethyl 3-(methylthio)-propanoate, dihydro-2-methyl-3(2H)-thiophenone, 2-thiophene-carboxyaldehyde, 5-methyl-2-thiophenecarboxaldehyde, benzothiophene and benzothiazole. Quantitative changes in these volatile sulfur compounds were studied by analyzing 48 aged and unaged malt whiskies by these methods. Dimethyl sulfide, 3-(methylthio)propyl acetate, dihydro-2-methyl-3(2H)-thiophenone and ethyl 3-(methylthio)propanoate decreased rapidly during aging and disappeared within three years. Dimethyl disulfide decreased gradually during aging. Dimethyl disulfide proved to be formed during distillation by the action of copper.     

Volatile Composition and Aroma Activity of Guava Puree Before and After Thermal and Dense Phase Carbon Dioxide Treatments

Volatiles from initially frozen, dense phase carbon dioxide (DPCD)‐ and thermally treated guava purees were isolated by solid phase microextraction (SPME), chromatographically separated and identified using a combination of gas chromatography‐mass spectrometry (GC‐MS), GC‐olfactometry (GC‐O), and GC‐pulsed flame photometric detector (GC‐PFPD, sulfur mode). Fifty‐eight volatiles were identified using GC‐MS consisting of: 6 aldehydes, 2 acids, 15 alcohols, 6 ketones, 21 esters, and 8 terpenes. Eleven volatiles were newly identified in guava puree. Hexanal was the most abundant volatile in all 3 types of guava puree. Ten sulfur compounds were identified using GC‐PFPD of which 3 possessed aroma activity and 3 were not previously reported in guava puree. Both treatments profoundly reduced total sulfur peak areas and produced different peak patterns compared to control. Thermal treatment reduced total sulfur peak area 47.9% compared to a loss of 34.7% with DPCD treatment. Twenty‐six volatiles possessed aroma activity. (Z)‐3‐Hexenyl hexanoate was the major contributor to the aroma of the freshly thawed and DPCD‐treated guava puree. DPCD treatment reduced total MS ion chromatogram (MS TIC) peak area 35% but produced a GC‐O aroma profile very similar to control. Whereas thermal treatment reduced total TIC peak area only 8.7% compared to control but produced a 35% loss in total GC‐O peak intensities.     

Characterization of volatile compounds in different dried sea cucumber cultivars

Sea cucumber is one of the most well-known and precious seafood in Asian countries. To better understand the sensory properties of dried sea cucumber products, volatile compounds of 8 dried sea cucumber cultivars were analyzed by using solid-phase microextraction (SPME) combined with gas chromatography-mass spectrometry. Forty-two volatile compounds comprising aldehydes (13), alcohols (13), aromatic compounds (9), furans (3), and others (4) were identified. Quantitative results revealed that volatile composition in all tested sea cucumbers were similar, but the variation existed in both the composition and the concentrations of some compounds. The concentration of hexanal, heptanal, 1-heptanol and benzaldehyde varied the most among different sea cucumber cultivars. Besides, 2-methyl-butanal, acetophenone, 2-methyl-furan, benzoic acid methyl ester and dimethyl sulfide were only detected in S. japonicus, a Chinese domestic sea cucumber cultivar, which was the main difference in volatile compounds compared with the other cultivars. There were 17 identified compounds which were considered to be odor-active compounds as their concentrations exceeded their odor detection thresholds in water.     

Quantification of trace volatile sulfur compounds in milk by solid-phase microextraction and gas chromatography-pulsed flame photometric detection

Volatile sulfur compounds have been reported to be responsible for the sulfurous off-flavors generated during the thermal processing of milk; however, their analysis has been a challenge due to their high reactivity, high volatility, and low sensory threshold. In this study, reactive thiols were stabilized and the volatile sulfur compounds in milk were extracted by headspace solid-phase microextraction, and analyzed by gas chromatography and pulsed-flame photometric detection. Calibration curves for 7 sulfur-containing compounds were constructed in milk by the standard addition technique. Raw, pasteurized, and UHT milk samples with various fat contents were analyzed. Compared with raw and pasteurized samples, UHT milk contained substantially higher concentrations of hydrogen sulfide, methanethiol, carbon disulfide, dimethyl trisulfide, and di-methyl sulfoxide. The high odor activity values calculated for methanethiol and dimethyl trisulfide suggested that these 2 compounds, in addition to di-methyl sulfide reported in a previous study, could be the most important contributors to the sulfurous note in UHT milk.     

Volatile Sulfur Compounds Formed in Disrupted Tissues of Different Cabbage Cultivars

Thirty-eight cultivars of cabbage (Brassica oleracea var capitata) were analyzed for production of volatile sulfur compounds after samples were homogenized and held at 30 °C from 10 to 100 min. Allyl iso-thiocyanate was detected in most cultivars, and it was formed rapidly compared to methanethiol-related compounds. Patterns of methane-thiol production varied among cultivars. Hydrogen sulfide formed rapidly compared to methanethiol-related compounds, but it was completely depleted after 40 min. Dimethyl disulfide and dimethyl trisulfide concentrations initally low (< 0.78 ppm), increased linearly through 100 min (to 3.3 ppm). Wide variations in abilities to produce volatile sulfur compounds were observed for the different cultivars.     

Bacteria and Volatile Compounds Associated with Ground Beef Spoilage

Ground beef (GB) samples were maintained in atmospheres of 2 or 18% oxygen. Similar putrid spoilage occurred at both concentrations, although the microflora differed. Two of 10 isolates from fresh and spoiled GB, nonfluorescent pseudomonads, produced putrid aromas but only 4 volatile compounds in common when inoculated into sterile GB. A Moraxella isolate produced a pronounced estery, decayed vegetable odor while others produced a decayed straw, ammoniacal or sour aroma. Differences in spoilage aromas apparently were not characterized by individual compounds but rather by the concentration of sulfur compounds and their ratio to other compound classes. Acetone, methyl ethyl ketone, dimethyl sulfide and dimethyl disulfide were indexes of microbial spoilage.     

Low temperature catalytic oxidation of hydrogen sulfide and methanethiol using wood and coal fly ash

The feasibility of reusing waste material as an inexpensive catalyst to remove sulfur compounds from gaseous waste streams has been demonstrated. Wood and coal fly ash were demonstrated to catalytically oxidize H2S and methanethiol (CH3SH) at low temperatures (23-25 degrees C). Wood ash had a significantly higher surface area compared to coal ash (44.9 vs 7.7 m2/g), resulting in a higher initial H2S removal rate (0.16 vs 0.018 mg/g/min) under similar conditions. Elemental sulfur was determined to be the end product of H2S oxidation, since X-ray diffraction analysis indicated the presence of crystalline sulfur. Catalytic decay occurred apparently due to surface deposition of sulfur and a subsequent decline in surface area (44.9-1.4 m2/g) during the reaction of H2S with the ash. Methanethiol was stoichiometrically converted to dimethyl disulfide ((CH3)2S2) without significant catalytic decay. Catalytic decay was reduced and H2S conversion increased (10% at 1.8 days vs 94% at 4.2 days) when H2S loading was decreased to levels typical of many environmental applications (500 ppmv inlet and 1.43 mg/min vs 60 ppmv, 0.09 mg/ min). Catalyst regeneration using hot water (85 degrees C) washing was possible, but only increased fractional conversion from 0.2 to 0.6 and the initial reaction rate to 50% of the original H2S oxidation activity.     

Catalytic ozonation of gaseous reduced sulfur compounds using wood fly ash

The feasibility of reusing wood ash as an inexpensive catalyst in a catalytic ozonation process has been demonstrated. Catalytic ozonation was demonstrated to oxidize H2S, methanethiol (MT), dimethyl sulfide (DMS), and dimethyl disulfide (DMDS) at low temperatures (23-25 degrees C). The process oxidized 25-50% of an inlet MT stream at 70 ppmv without the formation of DMDS (contrary to ash plus oxygen in air), oxidized 90-95% of an 85 ppmv stream of DMS, and oxidized 50% of a 100 ppmv DMDS stream using 2 g of wood ash at a space velocity of 720 h(-1) using ozone concentrations ranging from 100 to 300 ppmv. Similarly, 60-70% conversion of a 70 ppmv H2S stream was achieved with 2 g of ash in 1.1 s without catalytic deactivation (approximately 44 h). The overall oxidation rate of H2S, DMS, and DMDS increased with increasing ozone concentration contrary to the oxidation rate of MT, which was independent of ozone concentration. Dimethyl sulfoxide and dimethyl sulfone were identified as the primary end products of DMS oxidation, and SO2 was the end product of H2S and MT oxidation.     

Gas chromatographic analysis of volatile sulfur compounds from heated milk using static headspace sampling.

An investigation was conducted to test the feasibility of using gas chromatography with static headspace sampling as an objective tool to measure milk flavor quality. Heated milk off-flavor was chosen for study. Different strategies were tried for increasing the sensitivity of a commercially available headspace method, including salting out with sodium sulfate, cryofocusing during injection, and applying backpressure to the sampling loop. With the aid of a sulfur-specific detector, the resulting system was sufficiently sensitive to detect the sulfur volatiles, H2S and dimethyl sulfide, at the concentrations found in pasteurized skim milk. Milk that was heated to varying degrees was analyzed, and the analytical results were compared with the intensity of heated flavor as determined by a sensory panel. For skim milk, correlations were moderately strong: Spearman's correlation coefficients for H2S and dimethyl sulfide were .75 and .60, respectively. Correlations were weak for whole milk.     

Effect of various dairy packaging materials on the headspace analysis of ultrapasteurized milk

Milk from three different dairies (each a separate trial: 1, 2, and 3) was standardized to 2% fat and processed at 140.6, 129.4, 118.3, and 107.2 degrees C (temperatures 1, 2, 3, and 4, respectively) for 2 s and packaged into six different packaging boards [standard (A) milk boards with standard seam, juice boards with standard (B) and J- bottom (D) seams, barrier boards with standard (C) and J-bottom (E) seams, and foil (F) boards with J-bottom seam] resulting in 24 different treatments. A Shimadzu 15A series chromatograph equipped with a Porapak-P column was used to measure the headspace of the milk stored at 6.7 degrees C for 1, 2, 3, 5, 10, and 15 wk of storage. Gas chromatographic headspace analysis for sulfur compounds showed that hydrogen sulfide, methanethiol, and dimethyl sulfide were detected in milk processed at 140.6, 129.4, 118.3, and 107.2 degrees C. In addition, dimethyl disulfide was detected in milk processed at 140.6 and 129.4 degrees C, and dimethyl trisulfide was detected at 140.6 degrees C. Milk processed at 140.6 degrees C contained the most sulfur compounds. Samples C1, E1, and F1 retained the most hydrogen sulfide and methanethiol at 6 d of storage. Methanethiol appeared to be heat-induced. At wk 6, a slightly hammy or cardboardy flavor was detected for milk packaged in boards with standard seams (A, B, and C), and a slightly cooked flavor was detected for milk packaged in barrier and foil boards with J-bottom (E and F) seams. The hammy or cardboardy flavor intensified with storage time, and all of the cooked flavor dissipated at wk 10.     

基于电子鼻和气相色谱-质谱法结合相对气味活度值分析植物油对红油辣椒气味的影响

目的 为探究植物油对红油辣椒气味的影响。方法 采用电子鼻、气质联用技术(gas chromatography-mass spectrometry,GC-MS)结合正交偏最小二乘判别分析(orthogonal partial least squares discriminant analysis,OPLS-DA)和相对气味活度值(Relative Odor Activity Value,ROAV)等分析方法探究不同品种的植物油对红油辣椒气味物质的影响。结果 电子鼻检测结果结合OPLS-DA分析表明不同品种的植物油制备的红油辣椒其整体气味轮廓差异明显。GC-MS检测结果表明5种植物油制备的红油辣椒共检测到101种挥发性物质,其中醇类29种、醛类30种、烃类12种、硫醚类3种、酯类6种、酸类2种以及其他化合物19种；醇类、醛类、硫醚类是红油辣椒的主要挥发性物质。ROAV分析表明A样品(精炼菜籽油)的关键性化合物是：苯乙醛、反-2-壬醛、二甲基硫醚；B样品(大豆油)的关键性化合物是：1-庚烯-3-酮、二甲基硫醚；C(花生油)、E(菜籽油)样品的关键性化合物是：二甲基硫醚; D(玉米油)样品的关键性化合物是：二甲基硫醚、(Z)-2-壬烯醛、1-辛烯-3-酮。结论 不同品种的植物油制备的红油辣椒的主要挥发性物质有一定差,二甲基硫醚是红油辣椒的共有关键性化合物。     

Hydrogen sulfide oxidation by a microbial consortium in a recirculation reactor system: sulfur formation under oxygen limitation and removal of phenols

Wastewater from petroleum refining may contain a number of undesirable contaminants including sulfides, phenolic compounds, and ammonia. The concentrations of these compounds must be reduced to acceptable levels before discharge. Sulfur formation and the effect of selected phenolic compounds on the sulfide oxidation were studied in autotrophic aerobic cultures. A recirculation reactor system was implemented to improve the elemental sulfur recovery. The relation between oxygen and sulfide was determined calculating the O2/S2- loading rates (Q(O2)/Q(S)2- = Rmt), which adequately defined the operation conditions to control the sulfide oxidation. Sulfur-producing steady states were achieved at Rmt ranging from 0.5 to 1.5. The maximum sulfur formation occurred at Rmt of 0.5 where 85% of the total sulfur added to the reactor as sulfide was transformed to elemental sulfur and 90% of it was recovered from the bottom of the reactor. Sulfide was completely oxidized to sulfate (Rmt of 2) in a stirred tank reactor, even when a mixture of phenolic compounds was present in the medium. Microcosm experiments showed that carbon dioxide production increased in the presence of the phenols, suggesting that these compounds were oxidized and that they may have been used as carbon and energy source by heterotrophic microorganisms present in the consortium.     

Oxidative degradation of dimethyl sulfoxide by Cryptococcus humicolus WU-2, a newly isolated yeast

A dimethyl sulfoxide (DMSO)-degrading yeast strain Cryptococcus humicolus WU-2 was isolated and characterized. When 0.64 mM (50 mg/l) DMSO was added as the sole source of sulfur, DMSO was completely consumed by WU-2 in 48 h and oxidized to dimethyl sulfone with a molar conversion ratio of 83%. WU-2 also oxidized alkyl sulfides such as dimethyl sulfide, ethyl methyl sulfide and diethyl sulfide into the corresponding sulfones, which are odorless compounds.     

Assessment of rumen processes by selected-ion-flow-tube mass spectrometric analysis of rumen gases.

This work investigated the potential to use measurement of the concentration of certain gases in the rumen headspace to gain information about rumen processes and as a potential diagnostic tool. We used new equipment (selected-ion-flow-tube mass spectrometer) that allows rapid and precise analysis of many of the gases present in a sample. Samples of rumen headspace gas and corresponding samples of rumen liquor were taken from three lactating cows, prepared with rumen fistulae, at intervals after receiving their morning feed allocation (grass silage and concentrates). Hydrogen sulfide, methyl sulfide, and dimethyl sulfide, were the predominant gases that were measured in the rumen headspace by this technique. The concentrations of these sulfur compounds declined over the interval after feeding, mirroring ammonia concentrations measured in rumen liquor, reflecting their common dependence on the fermentation of sulfur amino acids. Ammonia concentrations in rumen headspace gas varied in the opposite direction to the concentration of ammonia in rumen liquor and likely depend more on the pH of rumen liquor. Consideration of the pKa of ammonia suggests that ammonia concentrations in rumen gas will be very low below pH 6, representing a useful diagnostic for subacute ruminal acidosis. Low concentrations of volatile fatty acids were detected in rumen gas. The molar proportions of volatile fatty acids were similar in gas and liquor samples, with rumen gas containing slightly less acetic acid and disproportionately more valeric and caproic acids.     

Analysis of grapefruit sulphur volatiles using SPME and pulsed flame photometric detection

Sulphur volatiles are major factors in the perceived aroma of grapefruit juice, GFJ. The objective of this study was to develop a procedure to concentrate, separate, identify and quantify the major volatile sulphur compounds, VSC’s, in grapefruit juices. SPME parameters such as headspace atmosphere, fibre coating, extraction time and temperature were evaluated. High resolution capillary GC using ZB-5, DB-Wax and PLOT columns coupled with pulsed flame photometric detection, PFPD, were employed for separation and detection. Thirteen sulphur volatiles were identified including; hydrogen sulphide, sulphur dioxide, methanethiol, dimethyl sulphide, carbon disulphide, dimethyl disulphide, 2-methyl thiophene, 3-methyl thiophene, methional, dimethyl trisulphide, 3-mercaptohexylacetate, 2,8-epithio-cis-p-menthane and 1-p-menthene-8-thiol. Five additional VSC’s were tentatively identified. Canned reconstituted GFJ had more total sulphur volatiles and a greater number than fresh GFJ. Hydrogen sulphide comprised over 80% of total sulphur volatiles in fresh GFJ but only 5% in canned GFJ.     

Changes in Volatile Sulfur Compounds in Strawberry Puree during Heating

ABSTRACT: Solid-phase microextraction coupled with gas chromatography/pulsed flame photometric detection was used to monitor methane thiol, hydrogen sulfide, sulfur dioxide, dimethyl sulfide, carbon disulfide, methyl thioacetate, dimethyl sulfide, methyl thiobutyrate, and dimethyl trisulfide after heating strawberry puree at 95°C for 0, 0.5, 1.0, 1.5, 2.5, 4, and 10 min. After heating 10 min, dimethyl trisulfide increased from 0.11 to 0.41 ng/mL, and dimethyl disulfide decreased from 1.3 to 0.3 ng/mL. Concentrations of methyl thiobutyrate and methyl thioacetate were approximately 6 and 60 ng/mL, respectively, and essentially unaffected by heating. Dimethyl sulfide (cabbage aroma) was not detected in fresh puree but increased exponentially during heating, reaching a value of 500 ng/mL (100 × its odor threshold) at 10 min. Dimethyl sulfide was the major sulfur aroma impact compound in heated strawberry puree and a major contributor to the flavor change associated with heated strawberry puree.     

The effect of pH on thiosulfate formation in a biotechnological process for the removal of hydrogen sulfide from gas streams

In a biotechnological process for hydrogen sulfide (H2S) removal from gas streams, operating at natronophilic conditions, formation of thiosulfate (S2O3(2-)) is unfavorable, as it leads to a reduced sulfur production. Thiosulfate formation was studied in gas-lift bioreactors, using natronophilic biomass at [Na+] + [K+] = 2 mol L(-1). The results show that at sulfur producing conditions, selectivity for S2O3(2-) formation mainly depends on the equilibrium between free sulfide (HS(-)) and polysulfide (Sx(2-)), which can be controlled via the pH. At pH 8.6, 21% of the total dissolved sulfide is present as Sx(2-) and selectivity for S2O3(2-) formation is 3.9-5.5%. At pH 10, 87% of the total dissolved sulfide is present as Sx(2-) and 20-22% of the supplied H2S is converted to S2O3(2-), independent of the H2S loading rate. Based on results of bioreactor experiments and biomass activity tests, a mechanistic model is proposed to describe the relation between S2O3(2-) formation and pH.