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1.
Application of aroma extract dilution analysis on the volatiles formed by reacting glucose and L-phenylalanine (30 min, 100 degrees C) revealed the Strecker aldehyde, phenylacetaldehyde (PA), and, in addition, phenylacetic acid (PAA) as the two key odorants among the volatiles formed. Quantitative measurements on alpha-dicarbonyl formation revealed that the 3-deoxyosone and glyoxal were formed as the first prominent sugar degradation products, whereas 2-oxopropanal became predominant after approximately 4 h at 100 degrees C. Among the four alpha-dicarbonyls analyzed, 2-oxopropanal proved to be the most effective in generating PA as well as PAA from phenylalanine, but the reaction parameters significantly influenced the ratio of both odorants; for example, at pH 3.0 the ratio of PA to PAA was 3:1, whereas at pH 9.0 the ratio was 1:5. Furthermore, in the presence of oxygen and copper ions the formation of the acid was further increased. 3-Deoxyosone and glucosone were found to be effective precursors of phenylacetaldehyde, but neither was very effective in acid generation. On the basis of the results, a new oxygen-dependent formation pathway of the Strecker reaction is proposed.  相似文献   

2.
A biocatalyst was prepared by immobilization of Saccharomyces cerevisiae cells on grape skins. Repeated batch fermentations were conducted using this biocatalyst as well as free cells, at 25, 20, 15, and 10 degrees C. Solid phase microextraction (SPME) was used in monitoring the evolution of volatile byproducts. The effect of immobilization and temperature on evolution patterns of volatiles was obvious. The major part of esters was formed after consumption of 40-50% of the sugars. Similar processes were observed for amyl alcohols and 2-phenylethanol, whereas 1-propanol and 2-methyl-1-propanol were formed during the whole alcoholic fermentation period at an almost constant formation rate. Acetaldehyde and acetoin were synthesized in the early stages of fermentation. Afterward, their amount decreased. In most cases, immobilized cells exhibited higher formation rates of volatiles than free cells. The final concentration of esters was higher in wines produced by immobilized biocatalyst. Their amount increased with temperature decrease. The opposite was observed for higher alcohols.  相似文献   

3.
Mixtures of glycine, glucose, and starch were extrusion cooked using sodium hydroxide at 0, 3, and 6 g/L of extruder water feed, 18% moisture, and 120, 150, and 180 degrees C target die temperatures, giving extrudates with pH values of 5.6, 6.8, and 7.4. Freeze-dried equimolar solutions of glucose and glycine were heated either dry or after equilibration to approximately 13% moisture at 180 degrees C in a reaction-tube system designed to mimic the heating profile in an extruder. Volatile compounds were isolated onto Tenax and analyzed by gas chromatography-mass spectrometry. For the extrudates, total yields of volatiles increased with decreasing pH at 180 degrees C, reached a maximum at pH 6.8 at 150 degrees C, and increased with increasing pH at 120 degrees C. Amounts increased with temperature at all pH values. Pyrazines were the most abundant class for all sets of conditions (54-79% of total volatiles). Pyrroles, ketones, furans, oxazoles, and pyridines were also identified. Yields of volatiles from the reaction-tube samples increased by >60% in the moist system. Levels of individual classes also increased in the presence of moisture, except pyrazines, which decreased approximately 3.5-fold. Twenty-one of the compounds were common to the reaction-tube samples and the extrudates.  相似文献   

4.
Camellia oil is widely used in some parts of the world partly because of its high oxidative stability. The effect of heating a refined camellia oil for 1 h at 120 degrees C or 2 h at 170 degrees C with exogenous antioxidant, namely, caffeic acid and tyrosol, was studied. Parameters used to assess the effect of heating were peroxide and K values, volatile formation, and fatty acid profile. Of these, volatile formation was the most sensitive index of change as seen in the number of volatiles and the total area count of volatiles in gas chromatograms. Hexanal was generally the dominant volatile in treated and untreated samples with a concentration of 2.13 and 5.34 mg kg(-1) in untreated oils heated at 120 and 170 degrees C, respectively. The hexanal content was significantly reduced in heated oils to which tyrosol and/or caffeic acid had been added. Using volatile formation as an index of oxidation, tyrosol was the more effective antioxidant of these compounds. This is contradictory to generally accepted antioxidant structure-activity relationships. Changes in fatty acid profiles after heating for up to 24 h at 180 degrees C were not significant.  相似文献   

5.
不同调控措施对葡萄冬剪枝条堆肥效果的影响   总被引：1，自引：0，他引：1  
王震  胡强  朱计谋  赵师成 《土壤通报》2021,52(3):629-634
以葡萄冬剪枝条为原料,以饼肥、尿素、碳酸氢铵为氮源,EM菌、生物菌肥发酵剂、秸秆发酵剂为接种外源微生物,设置9个处理,进行为期60天的堆肥,研究了不同调控措施堆体温度、堆肥基质物理性质、pH值、堆体腐熟程度和养分含量的变化。研究结果表明:葡萄枝屑添加不同氮源对堆温影响较大,添加饼肥的处理增加了堆体50 ℃以上高温的持续时间,且处理1（添加饼肥、C/N 20∶1、接种EM菌发酵剂）高温维持时间最长,为10天。堆肥结束时,各处理容重、总孔隙度、通气孔隙度和持水孔隙度都有所增加,且都在理想基质范围内,各处理pH值变化基本一致,均是先升高后降低;除处理6（添加碳酸氢铵、C/N 30∶1、接种生物菌肥发酵剂）外,其他处理种子发芽指数均在1以上,各处理种子发芽指数都可满足植物的生长;处理1全量氮、磷和钾含量相对较高,分别为3.160%、0.959%和1.880%,实际应用价值更大。综合考虑,添加饼肥、调整碳氮比为20∶1、接种EM菌发酵剂,为最佳葡萄枝屑基质化发酵配比。  相似文献   

6.
The sulfhydryl (SH) content of egg white proteins (10% v/v or 9.64 mg of protein/mL) after heat (50-85 degrees C) and combined heat- and high-pressure treatments (100-700 MPa, 10-60 degrees C) was determined using 5',5-dithiobis (2-nitrobenzoic acid) (DTNB), both for the soluble fraction and the total protein fraction. Only irreversible changes were taken into account. Both physical treatments were performed at two pH levels: pH 7.6, corresponding to the pH of fresh egg white, and pH 8.8, corresponding to that of aged egg white. Both heat and combined heat- and high-pressure treatment resulted in an exposure of buried SH groups. These exposed SH groups were involved in the formation of disulfide bond stabilized protein aggregates, as shown by gel electrophoresis. Under severe processing conditions (above 70 degrees C at atmospheric pressure or above 500-600 MPa, depending on the temperature applied), a decrease in total SH content could be observed, probably due to the formation of disulfide bonds by oxidation, especially at alkaline pH when the thiolate anion was more reactive. The high degree of exposure of sulfhydryl groups, and subsequent oxidation and sulfhydryl-disulfide bond exchange reactions resulting in soluble aggregates, can explain why pressure-induced egg white gels are softer and more elastic than heat-induced ones. When pressure treatment was performed at low temperatures (e.g., 10 degrees C), a lower pressure was required to induce similar changes in the sulfhydryl content, as compared to higher temperatures (e.g., 25 degrees C), indicating an antagonistic effect between pressure and temperature in the domain studied (10-60 degrees C, 100-700 MPa). Treatment conditions resulting in extensive protein insolubilization were accompanied by a transfer of free sulfhydryl groups from the soluble to the insoluble protein fraction. These SH groups were mainly accessible to DTNB.  相似文献   

7.
The suitability of delignified cellulosic (DC) material supported kefir yeast to ferment raw materials that contain various single carbohydrates, for the production of potable alcohol and alcoholic drinks, is examined in this investigation. Results are reported of fermentations carried out with sucrose, fructose, and glucose in synthetic media. Repeated batch fermentations at various initial sugar concentrations of sucrose, fructose, and glucose were performed at 30 degrees C in the presence of the aforementioned biocatalyst. The results clearly show feasible yields in the range of 0.38-0.41 g/g, alcohol concentrations of 7.6-8.2% v/v, fermentation time of 90-115 h, and conversion of 92-96%. DC material supported kefir fermented 11-fold more rapidly than free cells and 9-fold more rapidly in comparison to kissiris supported kefir. The main volatile byproducts such as amyl alcohols (mixture of 2-methyl-1-butanol and 3-methyl-1-butanol), ethanal, and ethyl acetate were formed in all sugar fermentation products. The formation of 65-110 ppm of ethyl acetate is as high and even higher than that obtained with traditional wine yeasts. The increase of the initial concentration of sugar in the fermentation media resulted in an increase in contents of volatiles. The fine aroma that was obtained in the product of fructose could be attributed to the high percentage of ethyl acetate on total volatiles. The efficiency of DC material supported kefir was the same for the fermentations of individual sugars or a mixture of fructose, sucrose, and glucose. When whey with raisin extracts was fermented, lower yields were obtained but the aroma of the product was even better.  相似文献   

8.
The effects of extrusion temperature, 150-190 degrees C, and torque, 50-70%, on the content and configuration of conjugated linoleic acids (CLA) in corn extrudates were analyzed by GC and HPLC. At a temperature of 150 degrees C, CLA content increased from 1.2 mg/g of oil in feed to 7.8 mg/g of oil in corn extrudates. A decrease in total CLA (P < 0.05) was obtained when the product temperature was further increased to 190 degrees C. Alteration of CLA geometrical configuration was observed at higher extrusion temperatures. trans,trans-CLA significantly increased (P < 0.05) from 10.2% in feed to 11.9% of CLA at the extrusion condition of 190 degrees C and 70% torque. The highest expansion of extrudates was found at the product temperature of 150 degrees C and 70% torque. This extrusion condition also gave the maximum total CLA content and minimum trans,trans-CLA formation.  相似文献   

9.
Headspace solid-phase microextraction (HS-SPME) was used to isolate the volatile compounds, which are formed during peroxidation of fatty acids in vegetable oils. Isolated compounds were characterized by GC-MS and quantified using GC with FID detection. Four fibers for HS-SPME method development were tested, and the divinylbenzene/carboxene/PDMS fiber was selected as providing the best detection of analyzed compounds. Extraction curves, limits of detection, repeatability, and linearity were investigated for 14 aldehydes, ketones, hydrocarbons, and alcohols being products of fatty acids autoxidation. Limits of detection for 11 of these were below 1 microg/L. For quantitative purposes, to minimize the influence of temperature on hydroperoxide formation and the changes in the volatiles profile of the extracts, sampling was performed at 20 degrees C. For compound characterization by GC-MS, sampling temperature of 50 degrees C was applied. The developed method was applied to the analysis of refined and cold-pressed rapeseed oil stored at 60 degrees C for 10 days, and for 10 different vegetable oils of various degree of peroxidation. All samples were subjected to sensory analysis. The results of PCA sensory analysis were related to the amount of volatile compounds isolated by SPME method. In cases where the amount of compounds was highest, the samples were perceived as the worst, whereas those with low levels of volatile compounds were the most desired ones according to sensory evaluation. The relation was observed for both total volatiles, quantified C5-C9 aldehydes, and 14 compounds selected in method development. SPME revealed to be a rapid and sensitive method for the extraction and quantitation of trace volatile compounds from plant oils even at ambient temperature.  相似文献   

10.
This study was conducted to compare the transformation of both isoflavone derivatives (aglycones, beta-glucosides, and acetyl and malonyl gluclucosides) and beta-glucosidase activity in kojis fermented with various generally recognized as safe filamentous fungi including Aspergillus awamori, Aspergillus oryzae, Aspergillus sojae, Rhizopus azygosporus, and Rhizopus sp. no. 2. Solid fermentation was performed to prepare the kojis by inoculating the steamed black beans with starter organism and culturing at 30 degrees C for 3 days. Results revealed that fermentation caused a marked increase in the content of aglycone (daidzein, glycitein, and genistein), the bioactive isoflavone, and a significant reduction in the content of beta-glucoside isoflavone (daidzin, glycitin, and genistin), compared with the unfermented steamed black bean. The extent of increased aglycone and reduced beta-glucoside isoflavone content varied with the starter organism used. Among the various black bean kojis prepared, the Rhizopus sp. no. 2 koji showed the highest level of enhancement in aglycone content. In the Rhizopus sp. no. 2 koji, the percentage of aglycone to total isoflavone increased from an initial approximately 2.9 to approximately 58.9% after fermentation. In comparison, the percentages found in kojis prepared with other starter organisms ranged from 18.9 to 38.9% after fermentation. Further preparations of black bean kojis with A. awamori at different cultivation temperatures (25, 30, and 35 degrees C) and various fermentation periods (1-5 days) revealed that koji prepared at 30 degrees C for 4 days showed the highest content of aglycones, with 7.7-, 5.7-, and 4.8-fold increases in the content of daidzein, genistein, and glycitein, respectively. In addition, the increase of aglycone content and the increase of beta-glucosidase activity during the fermentation of this koji showed a similar trend.  相似文献   

11.
Fermentation of pure teff (Eragrostis teff), pure grass-pea (Lathyrus sativus), and their mixtures, 9:1 and 8:2 (teff/grass-pea) has been done at two temperatures (room temperature and 35 degrees C) in duplicate using the strains of Lactobacillus plantarum, for bacterial fermentation, and Aspergillus oryzae and Rhizopus oligosporus in succession for solid-state fungal fermentation as inocula. In addition, the natural or spontaneous and back-slopping methods of bacterial fermentation have been done on the above four substrate groups. The pH and essential amino acid profiles of the different fermentation processes were compared. The back-slopping in teff at a temperature of 35 degrees C gave the sharpest pH drop. All fermentations done at 35 degrees C showed a steeper slope in their pH versus time plot compared to their room temperature counterpart. Fungal fermentation gave an improved amino acid profile for the essential ones in all of the substrate groups, except in pure grass-pea. Fermented teff/grass-pea (8:2) in this fungal fermentation has been found to be quite comparable in essential amino acid profile to an ideal reference protein recommended for children of 2-5 years of age. None of the bacterial fermentations produced a net change in their essential amino acid profile in any of the substrate groups investigated. Solid state fungal fermentation on pure grass-pea using the fungal strains R. oligosporous and A. oryzae in succession has shown that the neurotoxin beta-N-oxalyl-alpha,beta-diaminopropionic acid (beta-ODAP) in grass-pea has been removed by 80% on average for the high-toxin variety and by up to 97% for the low-toxin variety as determined by an improved chromatographic method with bioelectrochemical detection coupled on-line with refractive index detection.  相似文献   

12.
This investigation announces the use of potato pieces as a suitable support for cell immobilization resulting in extremely low temperature wine making. The results showed an increase of the total esters by immobilized cells and reduction of higher alcohols. Likewise, percentages of total esters on total volatiles were increased by the drop in temperature, while percentages of higher alcohols were reduced in wines. Kinetics experiments at different temperatures allowed the calculation of activation energy (Ea) and showed reduction in the case of immobilized cells as compared with free cells. These results may lead to the conclusion that the increased productivities that are obtained by immobilized cells, can be attributed to the catalytic activity by the support to enzymes, which are involved in the process. Biocatalysts were prepared by immobilization of Saccharomyces cerevisiae, strain AXAZ-1, on whole potatoes and potato pieces, and their efficiency for alcoholic repeated batch fermentations of glucose and grape must in the range 2-30 degrees C was examined. To study the operational stability of biocatalyst, 35 repeated batch fermentations of grape must were performed without any significant reduction of the fermentation activity. Wines were analyzed for volatile byproducts determination by GC and GC-MS.  相似文献   

13.
The volatiles formed from [1-(13)C]-ribose and cysteine during 4 h at 95 degrees C in aqueous phosphate buffer (pH 5) were analyzed by headspace SPME in combination with GC-MS. The extent and position of the labeling were determined using MS data. The identified volatiles comprised sulfur compounds such as 2-[(13)C]methyl-3-furanthiol, 2-[(13)CH(2)]furfurylthiol, [1-(13)C]-3-mercaptopentan-2-one, [1-(13)C]-3-mercaptobutan-2-one, [4-(13)C]-3-mercaptobutan-2-one, and 3-mercaptobutan-2-one. The results confirm furan-2-carbaldehyde as an intermediate of 2-furfurylthiol, as well as 1,4-dideoxypento-2,3-diulose as an intermediate of 2-methyl-3-furanthiol and 3-mercaptopentan-2-one. Loss of the C-1 and C-5 carbon moieties during the formation of 3-mercaptobutan-2-one suggests two different mechanisms leading to the key intermediate butane-2,3-dione.  相似文献   

14.
Postharvest diseases of mango fruit (Mangifera indica L.) cause economic losses during storage and can be controlled by chemical, physical, or biological methods. This study investigated the effects of different physical and/or chemical disease control methods on production of volatiles, color development and other quality parameters in ripe 'Kensington Pride' mango fruit. Hard mature green mango fruit were harvested from an orchard located at Carnavon, Western Australia. The fruit were heat-conditioned (8 h at 40 +/- 0.5 degrees C and 83.5 +/- 0.5% RH), dipped in hot water (52 degrees C/10 min), dipped in prochloraz (Sportak 0.55 mL x L(-1)/5 min), dipped in hot prochloraz (Sportak 0.55 mL x L(-1) at 52 degrees C/5 min), dipped in carbendazim (Spin Flo 2 mL x L(-1)/5 min), and dipped in hot carbendazim (Spin Flo 2 mL x L(-1) at 52 degrees C/5 min). Nontreated fruit served as control. Following the treatments, the fruit were air-dried and kept in cold storage (13 +/- 0.5 degrees C) for three weeks before being ripened at 21 +/- 1 degrees C. The ripe pulp of the fruit that was treated with hot prochloraz or carbendazim at ambient and high temperatures showed enhanced concentrations of volatiles, while heat conditioning and hot water dipping did not significantly affect the volatile development. Ripening time, and color development were measured daily while disease incidence and severity, weight loss, firmness, and concentrations of soluble solids, titratable acidity, ascorbic acid, total carotenoids, and volatiles were determined at the eating soft ripe stage. Hot water dipping or fungicide treatments (at ambient or at a high temperature) reduced postharvest diseases incidence and severity. Fruit quality (soluble solids concentration, titratable acidity, ascorbic acid and total caretonoids) was not substantially affected by any of the treatments.  相似文献   

15.
Evening primrose meal (EPM: 1% and 2%, w/w) reduced (p 相似文献   

16.
Kinetics of maneb degradation during thermal treatment of tomatoes   总被引：1，自引：0，他引：1  
The kinetics of maneb degradation in tomato homogenates at high temperatures and at two pH values (4 and 9) and the rate of formation of the toxic metabolite, ethylenethiourea (ETU), were studied. Maneb was measured as carbon disulfide by headspace gas-chromatography and ETU by high-performance liquid chromatography with photodiode array detection. First-order kinetics adequately described the degradation of maneb in tomato homogenates. The degradation rate constants exhibited an Arrhenius temperature dependence in the range from 50 to 90 degrees C and the apparent activation energy (E(a)) was calculated to be 36 KJ mol(-1) in homogenates with natural pH (4). Raising temperature from 60 to 75 and to 90 degrees C, ETU formation was significantly increased. Interestingly, the selectivity toward ETU showed a downward trend when the total conversion increased at longer heating times. When the pH of the tomato homogenates was adjusted to 9, the degradation of maneb proceeded faster at both 60 and 90 degrees C. The combination of alkaline pH and the highest temperature (90 degrees C) resulted in the maximum ETU conversion rates. The results of the present study on the fate of maneb and ETU residues during tomato processing, may prove valuable in estimating potential risk from dietary exposure.  相似文献   

17.
The effect of pH on acrylamide formation and elimination kinetics was studied in an equimolar (0.1 M) asparagine-glucose model system in phosphate or citrate buffer, heated at temperatures between 120 and 200 degrees C. To describe the experimental data, a simplified kinetic model was proposed and kinetic parameters were estimated by combined nonlinear regression and numerical integration on the data obtained under nonisothermal conditions. The model was subsequently validated in a more realistic potato-based matrix with varying pH. By increasing acidity, the reaction rate constants at T(ref) (160 degrees C) for both acrylamide formation and elimination can significantly be reduced, whereas the temperature dependence of both reaction rate constants increases. The introduction of a lyophilized potato matrix (20%) did not affect the acrylamide formation reaction rate constant at reference temperature (160 degrees C) as compared to the asparagine-glucose model system; the elimination rate constant at T(ref), on the contrary, was almost doubled.  相似文献   

18.
Lentil flour was extruded at die temperatures of 135, 160, and 175 degrees C. The soluble protein content in the extrudates decreased by 40.1% in the extracting buffer (1% sodium dodecyl sulfate in 50 mM sodium phosphate buffer, pH 6.9) as the extrusion die temperature was increased to 175 degrees C. The most insoluble proteins in the extrudates extruded at die temperatures of up to 175 degrees C could be resolubilized by using sonication. The total disulfide content and sulfhydryl content in the extrudates decreased. The SDS-PAGEs showed that the molecular weight distribution of proteins in the lentil flour changed little before and after extrusion as well as during reduction. The results from this study show that the extrusion temperature had less effect on the solubility and molecular weight of the lentil proteins, which contain a lower level of cysteine residues than wheat proteins.  相似文献   

19.
Urea occurs naturally in many food products, and its presence affects food quality. However, little is known about its impact on flavor generation in food production. In this study, the urea contents in beef, pork, and chicken were determined. The effects of urea and pH on thermal flavor generation were investigated using the model system of cysteine with ribose, which was heated to the roasting temperature of 180 degrees C for 2 h at pH 5 and pH 8.5. The results revealed relatively large amounts of urea in these meats and demonstrated that pH affects aroma generation. Volatiles identified from the reaction system of ribose and cysteine showed that sulfur-containing compounds such as thiophenes, thiazoles, and thiophenethiols were the most abundant compounds. The addition of urea into the reaction mixture caused the disappearance or reduction in content of some sulfur-containing compounds but resulted in the generation of several important nitrogen-containing volatiles, like pyrazine, methylpyrazine, 2,5- (and 2,6-)dimethylpyrazine and other alkylpyrazines, which are known to elicit roasty, nutty flavor notes. A plausible explanation for this phenomenon is that ammonia can be released from urea upon heating and the formed ammonia competes with hydrogen sulfide to react with Maillard reaction precursors to produce nitrogen-containing compounds such as alkylpyrazines.  相似文献   

20.
前期工作构建了苹果酸转运蛋白基因过表达的卷枝毛霉重组菌株Mc-MT-2,该菌株的脂质含量大幅度提高。该研究从培养基成分筛选、微生物生长控制以及发酵模式等方面深入探讨Mc-MT-2菌株发酵产油脂的调控策略。结果表明,Mc-MT-2菌株最佳生长及产孢培养条件是以葡萄糖与苹果酸为复合碳源且复合配比为9∶1,氮源为胰蛋白胨,其他成分同Kendrick培养基,初始pH值为5。经分批培养获得生物量、脂质含量和脂质产量分别为11.2 g/L,24%和2.6 g/L。在3 L发酵罐扩大培养中,补料培养Mc-MT-2菌株获得生物量、脂质含量和脂质产量最大值为15.4 g/L、28.6%和4.4 g/L,比分批培养分别提高1.38、1.19和1.69倍。该研究为卷枝毛霉重组菌株Mc-MT-2在脂质生产中的进一步应用奠定理论基础。  相似文献   

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