Vitamin content and amino acid composition of pickled garlic processed with and without fermentation

The effect of processing, with and without fermentation, upon the nutritional composition of pickled garlic was evaluated. On a dry basis, the fermented product had a higher content of riboflavin, alpha-tocopherol, and most individual amino acids but a lower thiamin level than the unfermented product. Ascorbic acid was totally lost during processing. The chemical scores for the unfermented and fermented product were 88 and 108%, respectively, with the limiting amino acid being leucine. Water blanching (90 degrees C for 4 min) affected only the ascorbic acid content, whereas fermentation significantly affected the contents of thiamin, ascorbic acid, and alpha-tocopherol, as well as glutamic acid and arginine. For each processing type, the effect of the preservation method and storage time on vitamins and amino acid composition was also analyzed. In the case of the fermented product, usage of the corresponding fermentation brine plus refrigerated storage was also assayed as the packing/preservation method and was found to give the best result from a nutritional standpoint.     

Interaction between fenhexamid and yeasts during the alcoholic fermentation of Saccharomyces cerevisiae

The behavior of the fungicide fenhexamid, N-(2,3-dichloro-4-hydroxyphenyl)-1-methyl-cyclohexanecarboxamide, has been studied at concentrations corresponding to the limits fixed for grapes (3 mg kg(-1)), or higher, during the alcoholic fermentation. The presence of the fungicide did not affect the amount of alcohol produced. The amount of fenhexamid in the liquid phase decreased by ca. 15%, but the missing fenhexamid was recovered unchanged from yeasts. This suggests that the fungicide is not degraded during the fermentation process, but adsorbed by yeasts. Two constituents of Saccharomyces cerevisiae cell wall, chitin and glucan, tested as potential adsorbents, exhibited affinity for fenhexamid.     

Behavior of a fenhexamid photoproduct during the alcoholic fermentation of Saccharomyces cerevisiae

The fungicide fenhexamid [N-(2,3-dichloro-4-hydroxyphenyl)-1-methylcyclohexanecarboxamide] degraded rapidly by UV or sunlight irradiation, yielding 7-chloro-6-hydroxy-2-(1-methylcyclohexyl)-1,3-benzoxazole (CHB) as a main photoproduct. CHB was isolated, and its effect on alcoholic fermentation of Saccharomyces cerevisiae was studied. The results indicate that the presence of CHB does not affect the extent of alcohol production. After 12 days, the amount of CHB in the fermentation medium decreased by ca. 65%. Only 25% of the missing CHB was recovered unchanged from yeasts, most likely because it was adsorbed on the yeast wall cell. The remaining part degraded during the fermentation process. Glucan and chitin, two potential adsorbents, which constitute yeast cell walls, exhibited affinity for CHB.     

温度对固定化酵母酒精分批发酵的影响及动力学模型

该文以甜高粱茎秆汁液为原料,探讨了温度（25～37 ℃）对甜高粱汁固定化酵母酒精分批发酵的影响,并对不同温度下固定化酵母乙醇发酵的动力学模型进行了研究。结果表明：温度的升高可以提高细胞生长速率,但过高的温度却阻碍了细胞的生长,从而影响了酒精的产量。应用Hinshelwood模型,分别对酒精发酵过程中细胞生长动力学和酒精合成动力学进行了模拟,得到25～34℃范围内不同温度下各种动力学参数。在此基础上,进一步研究了温度同细胞生长动力学参数之间的内在联系,得到酒精分批发酵过程中酵母细胞质量浓度的变化同温度以及底物质量浓度之间的一般关系式,验证试验结果表明,该模型具有很好的适用性。     

Improved organoleptic and nutritive properties of bakery products supplemented with amino acid overproducing Saccharomyces cerevisiae yeasts

Spontaneous yeast mutants isolated in continuous culture as resistant to toxic amino acid analogues, able to increase up to 40 times their free amino acid pool of Thr, up to 160 times their pool of Met, or up to 20 times their pool of Lys, were characterized with regard to properties of industrial interest. Growth rate, mu (h(-1)), and biomass yield, Y (g/L), of the amino acid overproducing mutants (AA(S)) were in many cases similar to those of the wild type, whereas their free amino acid content was substantially increased in laboratory and industrial media (molasses). Doughs fermented with 3% baker's yeast and 0.5% AA(S) mutants produced bakery products that displayed texture similar to those fermented with 3.5% baker's yeast, but the former had a considerable improvement of their taste and aroma. On the other hand, bread content of the essential amino acids Lys, Met, and Thr provided by yeast was also increased.     

Ferulic acid release and 4-vinylguaiacol formation during brewing and fermentation: indications for feruloyl esterase activity in Saccharomyces cerevisiae

The release of ferulic acid and the subsequent thermal or enzymatic decarboxylation to 4-vinylguaiacol are inherent to the beer production process. Phenolic, medicinal, or clove-like flavors originating from 4-vinylguaiacol frequently occur in beer made with wheat or wheat malt. To evaluate the release of ferulic acid and the transformation to 4-vinylguaiacol, beer was brewed with different proportions of barley malt, wheat, and wheat malt. Ferulic acid as well as 4-vinylguaiacol levels were determined by HPLC at several stages of the beer production process. During brewing, ferulic acid was released at the initial mashing phase, whereas moderate levels of 4-vinylguaiacol were formed by wort boiling. Higher levels of the phenolic flavor compound were produced during fermentations with brewery yeast strains of the Pof(+) phenotype. In beer made with barley malt, ferulic acid was mainly released during the brewing process. Conversely, 60-90% of ferulic acid in wheat or wheat malt beer was hydrolyzed during fermentation, causing higher 4-vinylguaiacol levels in these beers. As cereal enzymes are most likely inactivated during wort boiling, the additional release of ferulic acid during fermentation suggests the activity of feruloyl esterases produced by brewer's yeast.     

Positional distribution of conjugated linoleic acid in triacylglycerol of Saccharomyces cerevisiae

Saccharomyces cerevisiae was cultivated in the presence of cis-9,trans-11 or trans-10,cis-12 isomers of free conjugated linoleic acid (CLA), and the effects of the isomers on the regioisomerisms of triacylglycerol (TAG) of the yeast were elucidated. Both isomers constituted about 34% of all fatty acids and increased drastically the number of different TAG species. Nearly all of the species contained CLA in at least one sn-position. In the most abundant species analyzed (20% of total species), the cis-9,trans-11 isomer appeared in combination with monounsaturated fatty acids (C16:1, C:18:1) whereas trans-10,cis-12 isomer was most frequently present with a medium chain fatty acid (C10:0 or C12:0) in the sn-2 position and C16:0 in one of the end positions (14% of total species). With either isomer, the amount of TAG species in which CLA encompassed all sn-positions was ca. 4%. Thus, S. cerevisiae can be used to produce edible single cell oil characterized by very heterogeneous distribution of CLA among the different TAG species.     

瘤胃真菌与酿酒酵母仿生共培养提升秸秆发酵产乙醇量

玉米秸秆中具有较高的纤维素、半纤维素含量,是一种具有稳定产率、可集中处理、可代替木材作制浆原料的生物质材料。为了研究厌氧微生物与酵母共培养预处理玉米秸秆的产物,该研究模拟反刍动物消化玉米秸秆的过程,从羊瘤胃液中分离出厌氧真菌（Pecoramyces sp.）。以玉米秸秆茎皮碎为底物,与厌氧真菌、酿酒酵母菌S1145在39℃进行共培养72 h,分析发酵对秸秆茎皮降解及其代谢产物的影响。结果表明,在瘤胃真菌作用下,添加不同量的酿酒酵母可对代谢产物中乙醇含量产生影响,其中添加5 mL酿酒酵母时产生的乙醇含量最高,占总代谢产物比例为32.09%,相对于未添加酿酒酵母的对照组,乙醇含量提高了23.04百分点。研究表明,在厌氧真菌与酿酒酵母共培养预处理玉米秸秆茎皮的过程中,添加酿酒酵母可提高乙醇产量,为玉米秸秆高效资源化处理和生物质燃料生产提供了一种可靠的方法。     

Biocatalytic production of dihydrocoumarin from coumarin by Saccharomyces cerevisiae

Natural dihydrocoumarin, which is of great interest in the flavor industry, was biotechnologically produced from pure coumarin or tonka bean meal with Pseudomonas orientalis, Bacillus cereus, and various Saccharomyces cerevisiae strains. Coumarin was shown to be converted to melilotic acid, which yielded dihydrocoumarin upon distillation during purification. About 1.0 g/L product was obtained from 25 g/L tonka beans with S. cerevisiae within 147 h. This dihydrocoumarin thus fulfills all of the criteria of a natural raw material and can be used as a natural flavoring in accordance with U.S. and European Union regulations.     

Influence of glyphosate on amino acid composition of Egyptian broomrape

The parasitic plant broomrape is entirely dependent on its host for reduced carbon and nitrogen and is also susceptible to inhibition by glyphosate that is translocated to the parasite through a host. Studies were conducted to examine the effect of broomrape parasitism on amino acid concentrations of two hosts: common vetch that is tolerant of low levels of glyphosate and oilseed rape that has been genetically engineered for glyphosate resistance. The influence of glyphosate on the amino acid content of broomrape and the two hosts was also examined. Amino acid concentrations in leaves and roots of parasitized common vetch plants were generally similar to those of the corresponding tissues of nonparasitized plants. Amino acid concentrations in broomrape were lower than those of the parasitized common vetch root. For common vetch, glyphosate applied at rates that selectively inhibited broomrape growth did not alter individual amino acid concentrations in the leaves, but generally increased amino acid levels at 0.18 kg ha-1. Glyphosate application also increased the amino acid concentrations, with the exception of arginine, of broomrape growing on common vetch and did not generally influence concentrations in leaves or roots of common vetch. In oilseed rape, parasitization by broomrape generally led to higher amino acid concentrations in leaves but lower concentrations in roots of parasitized plants. Broomrape had higher amino acid concentrations than roots of the parasitized oilseed rape. Glyphosate applied at 0.25 and 0.5 kg ha-1 generally increased the amino acid concentrations in oilseed rape leaves, but the 0.75 kg ha-1 application caused the amino acid concentrations to decrease compared to those of untreated plants. In oilseed rape root the general trend was an increase in the concentration of amino acids at the two highest rates of glyphosate. Individual amino acid concentrations in broomrape attachments growing on oilseed rape were generally increased following glyphosate application of 0.25 kg ha-1. These results indicate that low rates of glyphosate alter amino acid profiles in both host and broomrape and raise questions about the regulation of amino acid metabolism in the parasite.     

Enhancing volatile phenol concentrations in wine by expressing various phenolic acid decarboxylase genes in Saccharomyces cerevisiae

Phenolic acids, which are generally esterified with tartaric acid, are natural constituents of grape must and wine and can be released as free acids (principally p-coumaric, caffeic, and ferulic acids) by certain cinnamoyl esterase activities during the wine-making process. Some of the microorganisms present in grape can metabolize the free phenolic acids into 4-vinyl and 4-ethyl derivatives. These volatile phenols contribute to the aroma of wine. The Saccharomyces cerevisiae phenyl acrylic acid decarboxylase gene (PAD1) is steadily transcribed, but its encoded product, Pad1p, shows low activity. In contrast, the phenolic acid decarboxylase (PADC) from Bacillus subtilis and the p-coumaric acid decarboxylase (PDC) from Lactobacillus plantarum display substrate-inducible decarboxylating activity in the presence of phenolic acids. In an attempt to develop wine yeasts with optimized decarboxylation activity on phenolic acids, the padc, pdc, and PAD1 genes were cloned under the control of S. cerevisiae's constitutive phosphoglyceratekinase I gene promoter (PGK1(P)()) and terminator (PGK1(T)()) sequences. These gene constructs were integrated into the URA3 locus of a laboratory strain of S. cerevisiae, Sigma1278b. The overexpression of the two bacterial genes, padc and pdc, in S. cerevisiae showed high enzyme activity. However, this was not the case for PAD1. The padc and pdc genes were also integrated into an industrial wine yeast strain, S. cerevisiae VIN13. As an additional control, both alleles of PAD1 were disrupted in the VIN13 strain. In microvinification trials, all of the laboratory and industrial yeast transformants carrying the padc and pdc gene constructs showed an increase in volatile phenol formation as compared to the untransformed host strains (Sigma1278b and VIN13). This study offers prospects for the development of wine yeast starter strains with optimized decarboxylation activity on phenolic acids and the improvement of wine aroma in the future.     

Antioxidative activity of amino phospholipids and phospholipid/amino Acid mixtures in edible oils as determined by the Rancimat method

Phosphatidylethanolamine (PE), phosphatidylcholine (PC), lysine (Lys), and mixtures of them were tested for antioxidative activity in refined olive oil by the Rancimat method to investigate the role of the chemical reactions produced in the Rancimat vessel on the induction periods (IPs) obtained. PE and Lys, but not PC, increased the IPs of the oil when tested alone. In addition, PE/Lys and PC/Lys mixtures, but not PC/PE mixtures, exhibited a synergistic effect. All these results can be understood considering the in situ formation of oxidized lipid/amino compound reaction products with antioxidative activities. Thus, the formation of pyrroles could be detected after derivatization with p-(dimethylamino)benzaldehyde, and some of these compounds could be unambiguously identified by GC-MS after their conversion into volatile derivatives. In addition, the formed products contributed to the color developed, and a correlation was observed between the Rancimat IPs obtained and the yellowness index of the oxidized oils recovered from the Rancimat. Furthermore, the differences observed in the antioxidative activities of PE, PC, Lys, and their mixtures could be explained according to the lipophility and hydrophility of the oxidized lipid/amino compound reaction products formed. All these results suggest that chemical reactions are being produced in the Rancimat vessel and the Rancimat IPs obtained are a consequence of the antioxidative activities of the products formed in these reactions. Furthermore, Rancimat may be a valuable tool for testing antioxidative activities of antioxidants produced during food processing if favorable conditions for antioxidant formation are employed.     

Distribution of protein oxidation products in the proteome of thermally processed milk

During thermal milk processing, severe oxidation can occur, which alters the technological and physiological properties of the milk proteins. Due to differences in composition and physicochemical properties, it can be expected that the particular milk proteins are differently affected by oxidative damage. Therefore, the protein-specific distribution of oxidation products in the heated milk proteome was investigated. Raw and heated milk samples were separated by one-dimensional gel electrophoresis. Protein oxidation was visualized by Western blot after derivatization of protein carbonyls with 2,4-dinitrophenylhydrazine. Thus, α-lactalbumin displayed enhanced oxidation compared to β-lactoglobulin, despite its lower concentration in milk. Highly selective oxidation was detected for a previously unassigned minor milk protein. The protein was identified by its peptide mass fingerprint as a variant of α(S1)-casein (α(S1)-casein*). Similar oxidation patterns were observed in several commercial milk products.     

Effect of carbohydrate substrate on fermentation by kefir yeast supported on delignified cellulosic materials

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.     

Genetic determinants of the release of mannoproteins of enological interest by Saccharomyces cerevisiae

Cell wall mannoproteins released by Saccharomyces cerevisiae during wine fermentation and aging have recently attracted the attention of enologists and researchers in enology due to their positive effect over a number of technological and quality properties of the wines, including protein and tartaric stability, aroma and color stability, astringency, mouthfeel, malolactic fermentation, or foam properties of sparkling wines. This work has investigated the effect of deletions involving genes related to cell wall biogenesis on the release of mannoproteins, as well as the effect of the released mannoproteins on wine protein stability. When available, the phenotypes have been studied in different genetic backgrounds, in haploid or diploid strains, and in homo- or heterozygosis. Strains deleted for GAS1, GPI7, or KNR4 release higher amounts of mannoproteins and polysaccharides to the medium. These increased amounts of mannoproteins and polysaccharides lead to a stronger stability of Sauvignon Blanc wines against protein haze.     

Evaluation of the antimicrobial activity of citrus essences on Saccharomyces cerevisiae

The aim of this research was to assess the antimicrobial activity of nine different industrial essences used in a soft drink factory in relation to their composition, as well as to verify the role of vapor pressure on their bioactivity. The essences were tested against a Saccharomyces cerevisiae strain isolated from spoiled soft drinks. The tests were carried out by adding the essences directly to a liquid medium or into the headspace of closed systems inoculated with the yeast. The headspace composition was evaluated through a solid phase microextraction-gas chromatography technique. The use of a mass spectrometer allowed the identification of the peaks detected. The microbial growth was indirectly monitored by measuring the metabolic CO2 released by the yeast. The results obtained indicated that the most effective essences were characterized by the highest concentration of some terpenes, such as citral, beta-pinene, and p-cymene. Moreover, all of the essences were more bioactive when added directly to the liquid medium.     

L-(-)-malic acid production by Saccharomyces spp. during the alcoholic fermentation of wine (1)

In an attempt to increase the acidity of wine by biological means, malate-producing yeasts were selected from a collection of 282 strains isolated in different parts of Spain. Only 4% of these strains (all of which belonged to Saccharomyces cerevisiae) produced l-(-)-malic acid in the range of 0.5-1 g/L. This was formed between days 2 and 6 of alcoholic fermentation, reaching a maximum on days 3 and 4; the concentration remained stable from day 7. Malic acid production was favored by temperatures in the 18-25 degrees C range and by musts with a high pH and low concentrations of sugar, initial malic acid, and yeast-assimilable nitrogen. Oxaloacetic acid, a precursor of malic acid, had no influence on malate production. The precursors pyruvic and fumaric acid did, however, have a significant effect on the production of this acid in some strains. No direct relation between pyruvate and malate metabolism was observed.     

Evidence for an extracellular acid proteolytic activity secreted by living cells of Saccharomyces cerevisiae PlR1: impact on grape proteins

In this work, Saccharomyces cerevisiae PlR1, a strain isolated from Pinot noir grapes in the Champagne area, was shown to secrete an acid proteolytic activity against bovine serum albumin. This proteolytic activity was detectable in cell-free culture supernatants at the beginning of the exponential growth phase and increased with yeast growth. Using a zymography method, only one protease band with a molecular mass of 72 kDa was observed. This extracellular proteolytic activity was detected in the pH range from 2 to 4 with a maximal value at pH 2.5 and 38 °C and was completely inhibited by pepstatin A. The secretion of this protease did not need any protein inducer and seemed to be insensitive to nitrogen catabolic repression. S. cerevisiae PlR1 was also able to secrete this proteolytic activity during alcoholic fermentation, and it was found to be active against grape proteins, with a molecular mass around 25 kDa, at optimal conditions of 38 °C, pH 3.5.     

高压脉冲电场对酿酒酵母钝化机理研究

为探究高压脉冲电场（PEF）对微生物的钝化机理,该试验主要采用Lowry法、SDS-PAGE电泳、APIZYM试剂盒、流式细胞仪等方法测定PEF处理对酿酒酵母蛋白质含量、胞内酶活性和DNA等的影响。结果显示：PEF处理后,酿酒酵母胞内蛋白质含量显著降低（p<0.05）,SDS-PAGE 电泳图分析发现酿酒酵母胞内蛋白谱图不清晰,且有小分子和 60 KDa 以上大分子蛋白谱带缺失,酿酒酵母细胞内13种酶的活性均有不同程度的下降,细胞DNA含量降低,部分DNA变性。PEF钝化微生物与其胞内酶失活、蛋白质和DNA发生外泄或变性有关。