مخمر به فرانسه لوور به انگلیسی ییست

معنی کلمه مخمر به فرانسه لوور به انگلیسی ییست

معنی واژه مخمر به فرانسه لوور به انگلیسی ییست

معنیمُخَمِّرها ( به انگلیسی : Yeast، به فرانسه Levure، به آلمانی Hefen و به عربی خمیرة) دسته‌ای از یوکاریوت‌های تک‌سلولی هستند که در فرمانرو قارچ‌ها و شاخه آسکومیست‌ها دسته بندی می‌شوند. معروف‌ترین آنها ساکارومایسس سرویزیه نام دارد که به مخمر نان نیز معروف است و در تخمیر خمیر نان نقش دارد. مخمرها اغلب به روش تقسیم سلولی (جوانه زدن) تکثیر می‌شوند ولی ممکن است تکثیر جنسی (حاصل ادغام دو سلول) نیز داشته باشند.
ساکارومایسس بایانوس در ساخت شراب کاربرد دارد و ساکارومایسس بولاردی در پزشکی کاربرد دارد.
کاندیدا آلبیکنس از مخمرهای بیماریزا است که ایجاد کاندیدیازیس می‌کند. از دیگر مخمرها می‌توان به پیچیا و شیزومایسس پومبه اشاره کرد.



منابع

در ویکی‌انبار پرونده‌هایی دربارهٔ مخمر موجود است.
ویکی‌پدیای انگلیسی
رده‌های صفحه: افزودنی‌های خوراکی قارچ‌ها

قس عربی

؟الخمیرة

Yeast of the species Saccharomyces cerevisiae.


التصنیف العلمی
النطاق: حقیقیات النوى
مملکة: الفطریات
Typical divisions
النظام البکتیری نظام الفطریات
الخمیرة میکروبات أحادیة الخلیة یمکنها التواجد فی وسط به أکسجین أی تتنفس الأکسجین کما یمکن لبعضها العیش بدون هواء وهی من مملکة الفطریات.
یستعمل الإنسان الخمیرة فی صناعة الخبز والمعجنات وکذلک تصنیع المشروبات الکحولیة.
ثمة 39 نوع من الخمائر معروفة یتفرع من هذه الأنواع مئات الأنواع الفرعیة حیث ان معظم خلایا الخمیرة تتبع الفطریات الزقیة لکن اجزاء أخرى تتبع BASIDIMYCOTA.
تستمد الخمائر طقتها من تحلیل السکر الموجود فی بیئتها وتتکاثر بالتکاثر الجنسی واللاجنسی والانقسام.
محتویات
تعریف

هی کائنات حقیقیة النواه وحیدة الخلیة تصنف ضمن الکائنات الحیة الدقیقة فی مملکة الفطریات. تنقسم إلى 700 نوع تقسم مجدداً إلى 5000 فرع. وهی لاهوائیة اختیاریة. • صفاتها :
تهیمن على التنوع الفطری فی المحیطات
معظمها یتکاثر لا جنسیا بالتبوغ رغم أن عدد قلیل منها یتکاثر لاجنسیا بالانشطار الثنائی
الاشکال متعددة الخلایا منها تکون عبارة عن خلایا متکاثرة لا جنسیا بقیت متصلة بعد عملیة التبرعم أو خیوط کاذبة.
تختلف أحجامها بحسب أنواعها وهی تتراوح بین (3–4) µm على الرغم أن بعضها قد یصل إلى 40.
الخمائر بالغة الأهمیة اقتصادیا: مسؤولة عن التخمّر فی معظم الصناعات الغذائیة من إنتاج منتجات الحلیب (أجبان) وصناعة الخبز إلى صناعة الخمور أو المشروبات الکحولیة. بعض أنواع الخمائر بدأ باستخدامه فی بدایات القرن الماضی کمصدر أساسی للمضادات الحیویة مثل البینیسیلین. منها ما یسبب الامراض الانتهازیة للإنسان کداء المبیضات.
أنواع الخمائر (Schizosaccharomyces: pombe) (Penicillium: bilaiae, camemberti, candida) (Saccharomyces: cerevisiae, boulardii, carlsbergensis, uvarum) (Candida: albicans, utilis) (Brettanomyces: bruxellensis) (Pichia: pastoris) ماهی اهمیة وجود الزیت والنشأ فی الخمیرة؟؟؟
فوائد الخمائر

1. تعتبر الخمیرة من أغنى المصادر بالحدید العضوی (وهو الشکل الطبیعی للحدید العضوی) غنی بالزنک.
2. مصدر واسع للفیتامینات العضویة الطبیعیة ما عدا فیتامین B12
3. منجم طبیعی للمعادن النادرة بالجسم، وهی مصدر مهم للبروتین
4. تخفض مستوى الکولیسترول بالدم عند مزجه مع اللستین کما أنها تخفف حدة أوجاع وآلام التهاب الاعصاب
5. تعتبر الخمیرة طعاماً کاملاً حیث إن الخمیره غنیة بالفوسفور، فالأفضل زیادة تناول الکالسیوم کشرب الحلیب معها، حیث إن الفوسفور یساعد على إخراج الکالسیوم من الجسم، والاستعمال الجید هو بزیادة الفیتامین بی مرکب والکالسیوم عند تناول الخمیرة مما یؤدی إلى تحسین أداء الخمیره.
6. تناول الخمیره مع الماء یعید الحیویة والنشاط إلى الجسم المنهک خلال دقائق. هذا المفعول یدوم ساعات.
7. جرعات عالیة تهدئ الاعصاب، تعدل المزاج، تحسن النوم، تستعمل فی علاج المصران الاعور، والشقیقة
8. الخمائر مصدر غنی بعنصر الکرومیوم الذی یعالج مرض السکری (النوع الثانی).
9. تستعمل الخمیرة فی علاج حساسیة الجلد، وفی صناعة ماسکات الوجه وفی التجمیل، وفی علاج حب الشباب
10. تعتبر منشطاً للمناعة بالجسم وتزیل تأثیر الأشعة فوق البنفسجیة الشمسیة التی تؤدی إلى ضعف المناعة فی الجسم أمام الالتهابات والسرطانات.
المعلومات الغذائیة

تحتوی کل 100غ من الخمیرة، بحسب وزارة الزراعة الأمیرکیة على المعلومات الغذائیة التالیة :
السعرات الحراریة: 158
الدهون: 0
الکاربوهیدرات: 11.80
الألیاف: 3
البروتینات: 27.80
الکولسترول: 0
تاریخ الخمیرة

تعتبر خمیرة الخبز کائنات وحیدة الخلیة نباتیة لا تحتوی على مادة الیخضور (الکلوروفیل)، وهی تحتاج إلى أغذیة معینة کی تؤمن حاجتها من الطاقة اللازمة لعملیاتها الحیویة المختلفة ولتکاثرها الذی هو ضروری لزیادة حصیلتها وحیث أن جمیع الکائنات الدقیقة التی تخلو خلایاها من الیخضور أو ما یماثله من أصباغ لزاماً علیها أن تحصل على طاقتها وعلى العناصر اللازمة لنموها عن طریق تناولها الغذاء الخارجی. یعود تاریخ الحصول على الخمیرة الطریة واستخدامها فی صناعة الخبز لأول مرة إلى معامل الکحول (المشروبات الروحیة) حیث کانت الخمیرة فی ذلک العصر هی عبارة عن منتج ثانوی (رواسب) فی المخمر الکحولی. ونظراً لزیادة الحاجة إلى استهلاک الخمیرة تم تطویر تقنیة صناعتها وإنشاء مصانع لإنتاجها وذلک منذ عام 1880 وأصبحت مستقلة عن معامل الکحول ونتیجة لذلک أصبح منتجها الرئیسی هو الخمیرة الطریة والمنتج الثانوی هو الکحول ثم نتیجة لزیادة التقنیة فی هذه الصناعة إقتصر إنتاج هذه المصانع على الخمیرة فقط. وبدأت الدراسات والأبحاث لتطویر صناعة الخمیرة حیث أن تکاثر خلایا الخمیرة تدریجیاً بدءاً من الزرع فی المختبر الحیوی وحتى الحصول على الزرعة الأولى أصبح عملاً فی منتهى الدقة.
مصادر

المعلومات الغذائیة عن الخمیرة
انظر أیضاً

میکروبیولوجیا الغذاء
تصنیف: مواد مضافة غذائیة

قس ترکی استانبولی

Maya, çok hücreli ökaryot yapılı mantarlar.
Bazı türleri ekmek kabartmak, alkollü içki fermantasyonu ve hatta yakıt pillerinin çalışmasında kullanılır. Çoğu maya Ascomycota bölümüne ait olmakla beraber bazıları Basidiomycotaya aittirler. Bazı mayalar, örneğin Candida albicans insanlarda enfeksiyona yol açar (kandidiyaz). Pembe mayalar (Rhodotorula), duş perdelerinde ve evdeki nemli yüzeyde yaşar, yüzeyler üzerinde lekeli bir görünüm oluşturur. Binden fazla maya türü tanımlıdır. En yaygın kullanılan maya olan Saccharomyces cerevisiae, binlerce yıl önce şarap, bira ve ekmek yapımı için evcilleştirilmiştir. Maya sözcüğü Türkçeye Farsçadan girmiştir.
Konu başlıkları
Fizyoloji

Maya türleri zorunlu aerobik veya istemli anaerobik (fakültatif anaerobik) fizyolojiye sahip olabilirler. Zorunlu anaerobik maya türü bilinmemektedir. Oksijen yokluğunda fermantatif mayalar enerji elde etmek için karbonhidratları karbon dioksit ve etanol (alkol) veya laktik asite dönüştürürler. Biracılık ve şarapçılıkta ortaya çıkan etanol şişelenir, ekmek yapımında ise etanol buharlaşır, açığa çıkan karbondioksit ekmeği kabartır.
Örneğin, glukoz fermantasyon reaksiyonu özetle şöyledir:
C6H12O6 (glikoz) → 2 C2H5OH + 2 CO2
Biyoteknolojide kullanımı
Mayanın faydalı fizyolojik özellikleri onun biyoteknoloji alanında kullanılmasına yol açmıştır. Şekerlerin maya tarafında fermantasyonu bu teknolojinin en eski uygulamasıdır. Ekmek mayası ekmek imalatında, bira mayası bira fermantasyonunda kullanılır. Maya şarap yapımında da kullanılır.
Modern biyoteknolojide maya başka canlılara ait proteinlerin ucuz yolla üretiminde kullanılmaktadır. Örneğin, insülin, interferon gibi insan proteinleri, hepatit B virüsünün kabuk proteinleri (aşı üretimi için) maya tarafından üretilebilmektedir.
Üremesi

Maya tomurcuklanma yoluyla eşeysiz olarak, veya askospor oluşumu yoluyla eşeyli olarak ürer. Eşeysiz üremesinde ana hücreden bir tomurcuk büyür ve yetişkin boyuta ulaştığında şartlar uygunsa ana hücreden ayrılır. Az besinli ortamda eşeyli üreyebilen mayalar askospor oluştururlar. Tam bir üreme döngüsüne sahip olmayan mayalar Candida türünde sınıflandırılırlar.
Büyüme ortamı

Çoğu maya, yüksek şekerli çevresel nümunelerden izole edilebilir. Meyvelerde, örneğin üzüm, elma veya şeftaliden, bitki özsuyu sızmalarında bulunur. Bazı mayalar toprak ve böceklerde bulunurlar.
Maya üretmek için kullanılan yaygın bir büyüme ortamı patates dekstroz agar (PDA) veya patates dekstroz ortamıdır. 200 dilimlenmiş patates 5-10 dakika suda haşlanır, sıvı kısım başka bir kaba aktarılır. Daha sonra üzerine saf su eklenerek 1 lye tamamlanır. Dekstroz (glikoz) eklenir (20 g/l) veya PDA için ilaveten 20 g agar eklenir, ortam otoklavlanarak sterilize e mantardır
Kaynak

İngilizce Wikipedianın Yeast maddesinin 7.08.2006 tarihli sürümü
Kategori: Mayalar (mikoloji)

قس انگلیسی

Yeasts are eukaryotic microorganisms classified in the kingdom Fungi, with 1,500 species currently described (estimated to be only 1% of all fungal species). Yeasts are unicellular, although some species with yeast forms may become multicellular through the formation of a string of connected budding cells known as pseudohyphae, or false hyphae, as seen in most molds. Yeast size can vary greatly depending on the species, typically measuring 3–4 µm in diameter, although some yeasts can reach over 40 µm. Most yeasts reproduce asexually by mitosis, and many do so by an asymmetric division process called budding.
By fermentation, the yeast species Saccharomyces cerevisiae converts carbohydrates to carbon dioxide and alcohols – for thousands of years the carbon dioxide has been used in baking and the alcohol in alcoholic beverages. It is also extremely important as a model organism in modern cell biology research, and is one of the most thoroughly researched eukaryotic microorganisms. Researchers have used it to gather information about the biology of the eukaryotic cell and ultimately human biology. Other species of yeast, such as Candida albicans, are opportunistic pathogens and can cause infections in humans. Yeasts have recently been used to generate electricity in microbial fuel cells, and produce ethanol for the biofuel industry.
Yeasts do not form a single taxonomic or phylogenetic grouping. The term yeast is often taken as a synonym for Saccharomyces cerevisiae, but the phylogenetic diversity of yeasts is shown by their placement in two separate phyla: the Ascomycota and the Basidiomycota. The budding yeasts ("true yeasts") are classified in the order Saccharomycetales.
Contents
History

See also: History of wine and History of beer
The word "yeast" comes to us from Old English gist, gyst, and from the Indo-European root yes-, meaning boil, foam, or bubble. Yeast microbes are probably one of the earliest domesticated organisms. People have used yeast for fermentation and baking throughout history. Archaeologists digging in Egyptian ruins found early grinding stones and baking chambers for yeasted bread, as well as drawings of 4,000-year-old bakeries and breweries. In 1680, the Dutch naturalist Anton van Leeuwenhoek first microscopically observed yeast, but at the time did not consider them to be living organisms but rather globular structures. In 1857, French microbiologist Louis Pasteur proved in the paper "Mémoire sur la fermentation alcoolique" that alcoholic fermentation was conducted by living yeasts and not by a chemical catalyst. Pasteur showed that by bubbling oxygen into the yeast broth, cell growth could be increased, but fermentation was inhibited – an observation later called the "Pasteur effect".
By the late 18th century, two yeast strains used in brewing had been identified: Saccharomyces cerevisiae, so-called top-fermenting yeast, and S. carlsbergensis, bottom-fermenting yeast. S. cerevisiae has been sold commercially by the Dutch for bread making since 1780; while, around 1800, the Germans started producing S. cerevisiae in the form of cream. In 1825, a method was developed to remove the liquid so the yeast could be prepared as solid blocks. The industrial production of yeast blocks was enhanced by the introduction of the filter press in 1867. In 1872, Baron Max de Springer developed a manufacturing process to create granulated yeast, a technique that was used until the first World War. In the United States, naturally occurring airborne yeasts were used almost exclusively until commercial yeast was marketed at the Centennial Exposition in 1876 in Philadelphia, where Charles L. Fleischmann exhibited the product and a process to use it, as well as serving the resultant baked bread.
Nutrition and growth

Yeasts are chemoorganotrophs, as they use organic compounds as a source of energy and do not require sunlight to grow. Carbon is obtained mostly from hexose sugars, such as glucose and fructose, or disaccharides such as sucrose and maltose. Some species can metabolize pentose sugars like ribose, alcohols, and organic acids. Yeast species either require oxygen for aerobic cellular respiration (obligate aerobes) or are anaerobic, but also have aerobic methods of energy production (facultative anaerobes). Unlike bacteria, there are no known yeast species that grow only anaerobically (obligate anaerobes). Yeasts grow best in a neutral or slightly acidic pH environment.
Yeasts vary in what temperature range they grow best. For example, Leucosporidium frigidum grows at -2 to 20 °C (28 to 68 °F), Saccharomyces telluris at 5 to 35 °C (41 to 95 °F), and Candida slooffi at 28 to 45 °C (82 to 113 °F). The cells can survive freezing under certain conditions, with viability decreasing over time.
In general, yeasts are grown in the laboratory on solid growth media or in liquid broths. Common media used for the cultivation of yeasts include potato dextrose agar (PDA) or potato dextrose broth, Wallerstein Laboratories nutrient (WLN) agar, yeast peptone dextrose agar (YPD), and yeast mould agar or broth (YM). Home brewers who cultivate yeast frequently use dried malt extract (DME) and agar as a solid growth medium. The antibiotic cycloheximide is sometimes added to yeast growth media to inhibit the growth of Saccharomyces yeasts and select for wild/indigenous yeast species. This will change the yeast process.
The appearance of a white, thready yeast, commonly known as kahm yeast, is often a byproduct of the lactofermentation (or pickling) of certain vegetables, usually the result of exposure to air. Although harmless, it can give pickled vegetables a bad flavor and must be removed regularly during fermentation.
Ecology

Yeasts are very common in the environment, and are often isolated from sugar-rich material. Examples include naturally occurring yeasts on the skins of fruits and berries (such as grapes, apples or peaches), and exudates from plants (such as plant saps or cacti). Some yeasts are found in association with soil and insects. The ecological function and biodiversity of yeasts are relatively unknown compared to those of other microorganisms. Yeasts, including Candida albicans, Rhodotorula rubra, Torulopsis and Trichosporon cutaneum, have been found living in between peoples toes as part of their skin flora. Yeasts are also present in the gut flora of mammals and some insects and even deep-sea environments host an array of yeasts.
An Indian study of seven bee species and 9 plant species found 45 species from 16 genera colonise the nectaries of flowers and honey stomachs of bees. Most were members of the Candida genus; the most common species in honey stomachs was Dekkera intermedia and in flower nectaries, Candida blankii. Yeast colonising nectaries of the stinking hellebore have been found to raise the temperature of the flower, which may aid in attracting pollinators by increasing the evaporation of volatile organic compounds. A black yeast has been recorded as a partner in a complex relationship between ants, their mutualistic fungus, a fungal parasite of the fungus and a bacterium that kills the parasite. The yeast have a negative effect on the bacteria that normally produce antibiotics to kill the parasite and so may affect the ants health by allowing the parasite to spread.
Reproduction



The yeast cells life cycle:
1. Budding
2. Conjugation
3. Spore
See also: Mating of yeast
Yeasts, like all fungi, may have asexual and sexual reproductive cycles. The most common mode of vegetative growth in yeast is asexual reproduction by budding. Here, a small bud (also known as a bleb), or daughter cell, is formed on the parent cell. The nucleus of the parent cell splits into a daughter nucleus and migrates into the daughter cell. The bud continues to grow until it separates from the parent cell, forming a new cell. The daughter cell produced during the budding process is generally smaller than the mother cell. Some yeasts, including Schizosaccharomyces pombe, reproduce by fission instead of budding, thereby creating two identically sized daughter cells.
In general, under high stress conditions like nutrient starvation, haploid cells will die; under the same conditions, however, diploid cells can undergo sporulation, entering sexual reproduction (meiosis) and producing a variety of haploid spores, which can go on to mate (conjugate), reforming the diploid.
Some pucciniomycete yeasts, in particular species of Sporidiobolus and Sporobolomyces produce aerially dispersed, asexual ballistoconidia.
Uses

The useful physiological properties of yeast have led to their use in the field of biotechnology. Fermentation of sugars by yeast is the oldest and largest application of this technology. Many types of yeasts are used for making many foods: bakers yeast in bread production; brewers yeast in beer fermentation; yeast in wine fermentation and for xylitol production. So-called red rice yeast is actually a mold, Monascus purpureus. Yeasts include some of the most widely used model organisms for genetics and cell biology.
Alcoholic beverages
Alcoholic beverages are defined as beverages that contain ethanol (C2H5OH). This ethanol is almost always produced by fermentation – the metabolism of carbohydrates by certain species of yeast under anaerobic or low-oxygen conditions. Beverages such as mead, wine, beer, or distilled spirits all use yeast at some stage of their production. A distilled beverage is a beverage containing ethanol that has been purified by distillation. Carbohydrate-containing plant material is fermented by yeast, producing a dilute solution of ethanol in the process. Spirits such as whiskey and rum are prepared by distilling these dilute solutions of ethanol. Components other than ethanol are collected in the condensate, including water, esters, and other alcohols, which (in addition to that provided by the oak it is aged in) account for the flavour of the beverage.
Beer


Beer being fermented by brewers yeast
Brewing yeasts may be classed as "top cropping" (or "top-fermenting") and "bottom-cropping" (or "bottom-fermenting"). Top cropping yeasts are so called because they form a foam at the top of the wort during fermentation. An example of a top-cropping yeast is Saccharomyces cerevisiae, sometimes called an "ale yeast". Bottom-cropping yeasts are typically used to produce lager-type beers, though they can also produce ale-type beers. These yeasts ferment well at low temperatures. An example of bottom-cropping yeast is Saccharomyces pastorianus, formerly known as S. carlsbergensis.
Decades ago, taxonomists reclassified S. carlsbergensis (uvarum) as a member of S. cerevisae, noting that the only distinct difference between the two is metabolic. Lager strains of S. cerevisae secrete an enzyme called melibiase, allowing it to hydrolyse melibiose, a disaccharide, into more fermentable monosaccharides. Top-cropping and bottom-cropping, cold-fermenting and warm-fermenting distinctions are largely generalizations used by the laypersons to communicate to the general public.
The most common top cropping brewers yeast, S. cerevisiae, is the same species as the common baking yeast. Brewers yeast is also very rich in essential minerals and the B vitamins (except B12). However, baking and brewing yeasts typically belong to different strains, cultivated to favour different characteristics: baking yeast strains are more aggressive, to carbonate dough in the shortest amount of time possible; brewing yeast strains act slower, but tend to produce fewer off-flavours and tolerate higher alcohol concentrations (with some strains, up to 22%).
Dekkera/Brettanomyces is a genus of yeast known for their important role in the production of Lambic and specialty sour ales, along with the secondary conditioning of a particular Belgian Trappist beer. The taxonomy of the genus Brettanomyces has been debated since its early discovery and has seen many re-classifications over the years. Early classification was based on a few species that reproduced asexually (anamorph form) through multipolar budding. Shortly after, the formation of ascospores was observed and the genus Dekkera, which reproduces sexually (teleomorph form), was introduced as part of the taxonomy. The current taxonomy includes five species within the genera of Dekkera/Brettanomyces. Those are the anamorphs Brettanomyces bruxellensis, Brettanomyces anomalus, Brettanomyces custersianus, Brettanomyces naardenensis, and Brettanomyces nanus, with teleomorphs existing for the first two species, Dekkera bruxellensis and Dekkera anomala. The distinction between Dekkera and Brettanomyces is arguable with Oelofse et al. (2008) citing Loureiro and Malfeito-Ferreira from 2006 when they affirmed that current molecular DNA detection techniques have uncovered no variance between the anamorph and teleomorph states. Over the past decade, Brettanomyces spp. have seen an increasing use in the craft-brewing sector of the industry with a handful of breweries having produced beers that were primary fermented with pure cultures of Brettanomyces spp. This has occurred out of experimentation as very little information exists regarding pure culture fermentative capabilities and the aromatic compounds produced by various strains. Dekkera/Brettanomyces spp. have been the subjects of numerous studies conducted over the past century, although a majority of the recent research has focused on enhancing the knowledge of the wine industry. Recent research on 8 Brettanomyces strains available in the brewing industry focused on strain specific fermentations and identified the major compounds produced during pure culture anaerobic fermentation in wort.
Wine
Main article: Yeast in winemaking
Yeast is used in winemaking, where it converts the sugars present in grape juice (must) into ethanol. Yeast is normally already present on grape skins. Fermentation can be done with this endogenous "wild yeast," but this procedure gives unpredictable results, which depend upon the exact types of yeast species present. For this reason, a pure yeast culture is usually added to the must; this yeast quickly dominates the fermentation. The wild yeasts are repressed, which ensures a reliable and predictable fermentation.
Most added wine yeasts are strains of S. cerevisiae, though not all strains of the species are suitable. Different S. cerevisiae yeast strains have differing physiological and fermentative properties, therefore the actual strain of yeast selected can have a direct impact on the finished wine. Significant research has been undertaken into the development of novel wine yeast strains that produce atypical flavour profiles or increased complexity in wines.
The growth of some yeasts, such as Zygosaccharomyces and Brettanomyces, in wine can result in wine faults and subsequent spoilage. Brettanomyces produces an array of metabolites when growing in wine, some of which being volatile phenolic compounds. Together, these compounds are often referred to as "Brettanomyces character", and are often described as "antiseptic" or "barnyard" type aromas. Brettanomyces is a significant contributor to wine faults within the wine industry.
Researchers from University of British Columbia, Canada, have found a new strain of yeast that has reduced amines. The amines in red wine and Chardonnay produce off-flavors and cause headaches and hypertension in some people. About 30 percent of people are sensitive to biogenic amines, such as histamines.
Baking
Main article: Bakers yeast
Yeast, the most common one being S. cerevisiae, is used in baking as a leavening agent, where it converts the fermentable sugars present in dough into the gas carbon dioxide. This causes the dough to expand or rise as gas forms pockets or bubbles. When the dough is baked, the yeast dies and the air pockets "set", giving the baked product a soft and spongy texture. The use of potatoes, water from potato boiling, eggs, or sugar in a bread dough accelerates the growth of yeasts. Most yeasts used in baking are of the same species common in alcoholic fermentation. In addition, Saccharomyces exiguus (also known as S. minor), a wild yeast found on plants, fruits, and grains, is occasionally used for baking. In bread making, the yeast initially respires aerobically, producing carbon dioxide and water. When the oxygen is depleted, fermentation begins, producing ethanol as a waste product; however, this evaporates during baking.


A block of fresh yeast
It is not known when yeast was first used to bake bread. The first records that show this use came from Ancient Egypt. Researchers speculate a mixture of flour meal and water was left longer than usual on a warm day and the yeasts that occur in natural contaminants of the flour caused it to ferment before baking. The resulting bread would have been lighter and tastier than the normal flat, hard cake.


Active dried yeast, a granulated form in which yeast is commercially sold
Today, there are several retailers of bakers yeast; one of the best-known in North America is Fleischmann’s Yeast, which was developed in 1868. During World War II, Fleischmanns developed a granulated active dry yeast, which did not require refrigeration, had a longer shelf life than fresh yeast and that rose twice as fast. Bakers yeast is also sold as a fresh yeast compressed into a square "cake". This form perishes quickly, and must, therefore, be used soon after production. A weak solution of water and sugar can be used to determine whether yeast is expired. In the solution, active yeast will foam and bubble as it ferments the sugar into ethanol and carbon dioxide. Some recipes refer to this as proofing the yeast as it "proves" (tests) the viability of the yeast before the other ingredients are added. When using a sourdough starter, flour and water are added instead of sugar; this is referred to as proofing the sponge.
When yeast is used for making bread, it is mixed with flour, salt, and warm water or milk. The dough is kneaded until it is smooth, and then left to rise, sometimes until it has doubled in size. Some bread doughs are knocked back after one rising and left to rise again. A longer rising time gives a better flavour, but the yeast can fail to raise the bread in the final stages if it is left for too long initially. The dough is then shaped into loaves, left to rise until it is the correct size, and then baked. Bread machine recipes usually call for dried yeast; however, a (wet) sourdough starter can also work.
Bioremediation
Some yeasts can find potential application in the field of bioremediation. One such yeast, Yarrowia lipolytica, is known to degrade palm oil mill effluent, TNT (an explosive material), and other hydrocarbons, such as alkanes, fatty acids, fats and oils. It can also tolerate high concentrations of salt and heavy metals, and is being investigated for its potential as a heavy metal biosorbent.
Industrial ethanol production
See also: Bioethanol
The ability of yeast to convert sugar into ethanol has been harnessed by the biotechnology industry to produce ethanol fuel. The process starts by milling a feedstock, such as sugar cane, field corn, or other cereal grains, and then adding dilute sulfuric acid, or fungal alpha amylase enzymes, to break down the starches into complex sugars. A glucoamylase is then added to break the complex sugars down into simple sugars. After this, yeasts are added to convert the simple sugars to ethanol, which is then distilled off to obtain ethanol up to 96% in concentration.
Saccharomyces yeasts have been genetically engineered to ferment xylose, one of the major fermentable sugars present in cellulosic biomasses, such as agriculture residues, paper wastes, and wood chips. Such a development means ethanol can be efficiently produced from more inexpensive feedstocks, making cellulosic ethanol fuel a more competitively priced alternative to gasoline fuels.
Nonalcoholic beverages


A Kombucha culture fermenting in a jar
Root beer and other sweet carbonated beverages can be produced using the same methods as beer, except the fermentation is stopped sooner, producing carbon dioxide, but only trace amounts of alcohol, and a significant amount of sugar is left in the drink. Kvass, a fermented drink made from rye, is popular in Eastern Europe; it has a recognizable, but low alcoholic content. Yeast in symbiosis with acetic acid bacteria is used in the preparation of kombucha, a fermented sweetened tea. Species of yeast found in the tea can vary, and may include: Brettanomyces bruxellensis, Candida stellata, Schizosaccharomyces pombe, Torulaspora delbrueckii and Zygosaccharomyces bailii. Kombucha is a popular beverage in Eastern Europe and some former Soviet republics under the name chajnyj grib (Чайный гриб), which means "tea mushroom". Kefir and kumis are made by fermenting milk with yeast and bacteria.
Nutritional supplements
See also: Tibicos
Yeast is used in nutritional supplements popular with vegans and the health conscious, where it is often referred to as "nutritional yeast". It is a deactivated yeast, usually S. cerevisiae. It is an excellent source of protein and vitaminsneeded, especially the B-complex vitamins, whose functions are related to metabolism, as well as other minerals and cofactors required for growth. It is also naturally low in fat and sodium. Some brands of nutritional yeast, though not all, are fortified with vitamin B12, which is produced separately by bacteria. Nutritional yeast, though it has a similar appearance to brewers yeast, is very different and has a very different taste. Brewers yeast is a good source of B-complex vitamins but, contrary to some claims, it contains little or no vitamin B12.
Nutritional yeast has a nutty, cheesy flavor that makes it popular as an ingredient in cheese substitutes. It is often used by vegans in place of Parmesan cheese. Another popular use is as a topping for popcorn. It can also be used in mashed and fried potatoes, as well as in scrambled eggs. It comes in the form of flakes, or as a yellow powder similar in texture to cornmeal, and can be found in the bulk aisle of most natural food stores. In Australia, it is sometimes sold as "savory yeast flakes". Though "nutritional yeast" usually refers to commercial products, inadequately fed prisoners have used "home-grown" yeast to prevent vitamin deficiency.
Probiotics
Some probiotic supplements use the yeast S. boulardii to maintain and restore the natural flora in the gastrointestinal tract. S. boulardii has been shown to reduce the symptoms of acute diarrhea in children, prevent reinfection of Clostridium difficile, reduce bowel movements in diarrhea-predominant IBS patients, and reduce the incidence of antibiotic, travelers, and HIV/AIDS associated diarrheas.
Aquarium hobby
Yeast is often used by aquarium hobbyists to generate carbon dioxide (CO2) to nourish plants in planted aquariums. A homemade setup is widely used as a cheap and simple alternative to pressurized CO2 systems. While not as effective as these, the homemade setup is considerably cheaper for less-demanding hobbyists.
There are several recipes for homemade CO2, but they are variations of the basic recipe: Bakers yeast, with sugar, baking soda, and water, are added to a plastic bottle. A few drops of vegetable oil at the start reduces surface tension and speeds the release of CO2. This will produce CO2 for about 2 or 3 weeks; the use of a bubble counter determines production. The CO2 is injected in the aquarium through a narrow hose and released through a diffuser that helps dissolve the gas in the water. The CO2 is used by plants in the photosynthesis process.
Science


Diagram showing a yeast cell
Several yeasts, in particular S. cerevisiae, have been widely used in genetics and cell biology. This is largely because S. cerevisiae is a simple eukaryotic cell, serving as a model for all eukaryotes, including humans for the study of fundamental cellular processes such as the cell cycle, DNA replication, recombination, cell division, and metabolism. Also, yeasts are easily manipulated and cultured in the laboratory, which has allowed for the development of powerful standard techniques, such as yeast two-hybrid, synthetic genetic array analysis, and tetrad analysis. Many proteins important in human biology were first discovered by studying their homologues in yeast; these proteins include cell cycle proteins, signaling proteins, and protein-processing enzymes.
On 24 April 1996, S. cerevisiae was announced to be the first eukaryote to have its genome, consisting of 12 million base pairs, fully sequenced as part of the Genome project. At the time, it was the most complex organism to have its full genome sequenced, and took seven years and the involvement of more than 100 laboratories to accomplish. The second yeast species to have its genome sequenced was Schizosaccharomyces pombe, which was completed in 2002. It was the sixth eukaryotic genome sequenced and consists of 13.8 million base pairs. As of 2012, over 30 yeast species have had their genomes sequenced and published.
Yeast extract
Main article: Yeast extract

Marmite and Vegemite, products made from yeast extract

Marmite and Vegemite have a distinctive dark colour
Yeast extract is the common name for various forms of processed yeast products that are used as food additives or flavours. They are often used in the same way that monosodium glutamate (MSG) is used and, like MSG, often contain free glutamic acid. The general method for making yeast extract for food products such as Vegemite and Marmite on a commercial scale is to add salt to a suspension of yeast, making the solution hypertonic, which leads to the cells shrivelling up. This triggers autolysis, wherein the yeasts digestive enzymes break their own proteins down into simpler compounds, a process of self-destruction. The dying yeast cells are then heated to complete their breakdown, after which the husks (yeast with thick cell walls that would give poor texture) are separated. Yeast autolysates are used in Vegemite and Promite (Australia); Marmite, Bovril and Oxo (the United Kingdom, Republic of Ireland and South Africa); and Cenovis (Switzerland).
Pathogenic yeasts



A photomicrograph of Candida albicans showing hyphal outgrowth and other morphological characteristics.
Some species of yeast are opportunistic pathogens that can cause infection in people with compromised immune systems.
Cryptococcus neoformans is a significant pathogen of immunocompromised people causing the disease termed cryptococcosis. This disease occurs in about 7–9% of AIDS patients in the USA, and a slightly smaller percentage (3–6%) in western Europe. The cells of the yeast are surrounded by a rigid polysaccharide capsule, which helps to prevent them from being recognised and engulfed by white blood cells in the human body.
Yeasts of the Candida genus are another group of opportunistic pathogens that causes oral and vaginal infections in humans, known as candidiasis. Candida is commonly found as a commensal yeast in the mucus membranes of humans and other warm-blooded animals. However, sometimes these same strains can become pathogenic. Here the yeast cells sprout a hyphal outgrowth, which locally penetrates the mucosal membrane, causing irritation and shedding of the tissues. The pathogenic yeasts of candidiasis in probable descending order of virulence for humans are: C. albicans, C. tropicalis, C. stellatoidea, C. glabrata, C. krusei, C. parapsilosis, C. guilliermondii, C. viswanathii, C. lusitaniae, and Rhodotorula mucilaginosa. Candida glabrata is the second most common Candida pathogen after C. albicans, causing infections of the urogenital tract, and of the bloodstream (candidemia).
Food spoilage

Yeasts are able to grow in foods with a low pH, (5.0 or lower) and in the presence of sugars, organic acids and other easily metabolized carbon sources. During their growth, yeasts metabolize some food components and produce metabolic end products. This causes the physical, chemical, and sensible properties of a food to change, and the food is spoiled. The growth of yeast within food products is often seen on their surface, as in cheeses or meats, or by the fermentation of sugars in beverages, such as juices, and semi-liquid products, such as syrups and jams. The yeast of the Zygosaccharomyces genus have had a long history as a spoilage yeast within the food industry. This is due mainly to the fact that these species can grow in the presence of high sucrose, ethanol, acetic acid, sorbic acid, benzoic acid, and sulphur dioxide concentrations, representing some of the commonly used food preservation methods. Methylene blue is used to test for the presence of live yeast cells.
See also

Fungi portal
Mycosis (Fungal infection in animals)
Bioaerosol
Ethanol fermentation
Start point (yeast)
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^ Fleet GH, Praphailong W. (2001). "Yeasts". In Moir CJ. Spoilage of Processed Foods: Causes and Diagnosis. Food Microbiology Group of the Australian Institute of Food Science and Technology (AIFST). pp. 383–397. ISBN 0-9578907-0-2.
^ Downes FP, Ito K. (2001). Compendium of Methods for the Microbiological Examination of Foods. Washington, DC: American Public Health Association. p. 211. ISBN 978-0-87553-175-5.
Cited texts
Alexopoulos CJ, Mims CW, Blackwell M. (1996). Introductory Mycology. New York, New York: Wiley. ISBN 0-471-52229-5.
Kirk PM, Cannon PF, Minter DW, Stalpers JA. (2008). Dictionary of the Fungi (10th ed.). Wallingford, UK: CAB International. ISBN 0-85199-826-7.
Moore-Landecker E. (1996). Fundamentals of the Fungi. Englewood Cliffs, New Jersey: Prentice Hall. ISBN 0-13-376864-3.
External links

Look up yeast in Wiktionary, the free dictionary.
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Cell cycle and metabolic cycle regulated transcription in yeast
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Current research on Yeasts at the Norwich Research Park
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Categories: Brewing ingredientsFood additivesLeavening agentsMedicinal fungiVegan cuisineYeastsYeast extract spreadsFermentation (food)

قس فرانسه
Une levure est un champignon unicellulaire1 apte à provoquer la fermentation des matières organiques animales ou végétales. Les levures sont employées pour la fabrication du vin, de la bière, des alcools industriels, des pâtes levées et dantibiotiques.
Lorsquon parle de « levure » sans précision, on désigne en général la levure de boulanger (ou de bière), Saccharomyces cerevisiae. Il ne faut pas la confondre avec le levain ou la levure chimique, ne serait-ce que pour éviter les déboires culinaires.
La dénomination levure découle de lobservation des fermentations et tout particulièrement celle qui a lieu durant la fabrication du pain : on dit communément et depuis longtemps que le pain lève. Ce nest pas, à proprement parler, une dénomination scientifique actuelle. Mais limportance des levures dans le domaine des fermentations conduit à conserver ce terme générique qui continue à être correctement perçu.
Sommaire
Histoire

Si les Egyptiens utilisaient déjà la levure pour faire lever leur pain, il a fallu attendre 1857 pour que Louis Pasteur prouve et explique dans "Mémoire sur la fermentation alcoolique" que les levures étaient des organismes vivants (Effet Pasteur).
Types de levure

Le terme courant de levure désigne généralement le genre Saccharomyces (levure de bière ou levure de boulangerie). Il existe beaucoup dautres genres de levures ; parmi les plus connues, le genre Candida possède un pouvoir pathogène chez lhomme, responsable des mycoses de type candidoses.
La plupart s’apparente aux Ascomycètes (type truffe, pézize), quelques-unes à l’autre grand groupe de champignons supérieurs, les Basidiomycètes (type amanites, bolets) et d’autres enfin sont des formes imparfaites non rattachables clairement à aucun groupe défini. La levure de raisin mesure environ 2 à 9 µm.
Ces micro-organismes, de forme variable selon l’espèce (sphérique, ovoïde, en bouteille, triangulaire ou apiculée, cest-à-dire renflée à chaque bout comme un citron) mais généralement ovales, denviron 6 à 10 microns et jusqu’à 50 microns, se multiplient par bourgeonnement ou par fission (scissiparité). Ils sont souvent capables daccomplir une sporulation soit dans un but de dormance en milieu défavorable, soit dans un but de dispersion.
Modes de multiplication

Pour la plupart des levures la multiplicatio
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