The effects of soil nutrient status on the performance of four South African wheat genotypes were investigated in a long-term fertilization experiment. The objective was to quantify the effects of soil fertility on yield, yield components, grain nitrogen content, grain protein yield, grain protein content, flour yield and bread-making quality. The relative contribution of main stems and tillers, as well as the contribution of first, second and third kernels in the spikelets to grain yield and grain protein content were determined. The interactive effects between photoperiod, temperature and vernalization on grain yield, yield components and grain protein content were also quantified. Increasing soil fertility increased grain yield and most components of yield, grain nitrogen content, grain protein yield, aboveground biomass and harvest index, but depressed mean kernel mass. Significant interactions between cultivar and soil fertility were observed for grain yield, grain number, kernel mass, protein yield, biomass and harvest index, indicating differences in cultivar ability to produce yield and quality. Within a cultivar, the main stem, first tiller and second tiller did not differ in mean grain protein content, indicating that late-maturing tillers do not affect the grain protein content of wheat. Grain protein content, flour yield, loaf volume, water absorption and mixograph peak mixing time varied with soil fertility. The interaction between cultivar and soil fertility was significant for the above mentioned parameters with the exception of mixograph peak mixing time, indicating wheat genotypes differences in bread-making quality potential. The potential ability of wheat cultivar Kariega to produce higher grain yield, protein yield and loaf volume in the K and P limiting soil fertility situations deserve further investigation. In a growth chamber study, the low temperature regimes and long photoperiod conditions resulted in the highest grain yield, number of grains, largest mean kernel size and highest grain protein content. / Dissertation (PhD)--University of Pretoria, 2003. / Plant Production and Soil Science / unrestricted

<p>Vreme (rok) setve jedan je od najvažnijih faktora u proizvodnji strnih žita i praktično određuje intenzitet delovanja svih ostalih činilaca proizvodnje p&scaron;enice. Među brojnim faktorima koji određuju visinu prinosa, najče&scaron;ći uzrok malih prinosa ozime p&scaron;enice vezan je za vreme setve izvan optimalnog roka, upotreba neadekvatnih količina semena i izbor sorti nedovoljno prilagođenih datim agroekolo&scaron;kim uslovima. Osim toga, vreme setve predstavlja ekonomski najjeftiniju agrotehničku meru i najisplativiji način za povećanje prinosa zrna ozime p&scaron;enice, međutim eventualno ka&scaron;njenje u setvi ne može se na adekvatan način nadoknaditi ni jednom drugom agrotehničkom merom. Ekstremne vremenske prilike već predstavljaju izazov za proizvođače, a mnogobrojni klimatski scenariji predviđaju dalje povećanje njihove učestalosti u budućnosti. Upravo će u ovakvim promenljivim vremenskim uslovima optimalno vreme steve uz adekvatnu gustinu useva i izbor odgovarajućih genotipova biti od velike važnosti u cilju ublažavanja negativnog delovanja vremenskih činioca na visinu i stabilnost prinosa, kao i na tehnolo&scaron;ki kvalitet zrna ozime p&scaron;enice.<br />Prevashodni cilj istraživanja u disertaciji bio je proučavanje uticaja različitog vremena, gustina setve i njihove interakcije na prinos, komponente prinosa i kvalitet zrna različitih sorti p&scaron;enice. Istraživanje interakcije vremena, gustina setve i sorti ozime p&scaron;enice izvedeno je na oglednim poljima Instituta za ratarstvo i povrtarstvo na Rimskim &scaron;ančevima, u periodu od proizvodne 1981/82. do 2012/13. godine, na ogledu pod nazivom &bdquo;Rokovi setve&ldquo;. Ogled se postavlja svake godine, na zemlji&scaron;tu tipa karbonatni černozem, a izvodi se kao trofaktorijalni (Split-split-plot dizajn), u četiri ponavljanja, sa rasporedom varijanti po slučajnom blok sistemu.<br />Tokom 32-godi&scaron;njeg ispitivanog perioda, prinos zrna je znatno varirao u zavisnosti od vremenskih uslova i kretao se u proseku za sve tretmane od 4,35 t ha-1 u 2003., do 8,70 t ha-1 u 2013. godini. Na osnovu jednačine trenda prinosa, uočeno je da je godi&scaron;nje povećanje prinosa, u proseku za sve tretmane iznosilo 10,7 kg ha-1. Iz 32 analizirane godine izdvojeno je 5 godina sa najvećim prinosima, 12 godina sa malim prinosima p&scaron;enice, dok se preostalih 15 godina moglo označiti kao srednje rodne godine. U pogledu temperaturnih uslova i uslova vlažnosti u rodnim, srednje rodnim i nerodnim godinama postojale su značajne razlike između ovih grupa. U rodnim godinama, variranje prinosa u zavisnosti od rokova setve bilo je najmanje. Najveći prinos zrna, tokom posmatranog perioda, u proseku za sve ispitivane sorte i gustine setve ostvaren je setvom u II roku (11-20. X), i bio je značajno veći u odnosu na sve ostale rokove izuzev I roka. Između I i III roka, nije ostvarena statistički značajna razlika u visini prinosa, ali su prinosi u oba ova roka bili značajno veći u odnosu na novembarske i decembarski rok setve. Drugi rok odlikovao se najmanjim variranjem prinosa tokom istraživanog perioda. Novembarska setva smanjivala je prinos u proseku za 11%, a decembarska za 27%, u odnosu na prinose iz optimalnih agrotehničkih rokova. Prosečno dnevno smanjenje prinosa zrna iznosilo je 38 kg dan-1. Najmanje smanjenje prinosa prilikom ka&scaron;njenja u setvi bilo je u rodnim, zatim u srednjerodnim, a najveće u nerodnim godinama. U optimalnim rokovima setve (I i II rok) gustina od 500 kl. zrna m-2 bila je optimalna, dok je u kasnim rokovima (novembarskim i decembarskom), povećanje količine semena (do najvi&scaron;e 700 kl. zrna m-2),<br />imalo opravdanja. Odlaganje setve od I do V roka, uticalo je na povećanje sadržaja proteina, vlažnog glutena, moći upijanja vode, sedimentacionu vrednost, zapreminu i vrednosnog broja sredine hleba, kod obe sorte. Na osnovu prosečnih vrednosti za sve rokove setve, sorta Zvezdana ostvarila je bolje parametre kvaliteta u odnosu na NS 40S.</p> / <p>Sowing date is one of the most important field crop management measures in the production of small grains and it practically determines the intensity of all other factors in wheat production. Among many factors which determine yield, sowing outside the optimum period, use of inappropriate seed rates and selection of cultivars insufficiently adapted to a given agro-ecological conditions, are recognized as the most common causes of low yields of winter wheat. Moreover, sowing date is economically cheapest field crop management measure and a cost-effective way to increase grain yield. However, eventual delay in sowing cannot be adequately compensated by any other field crop management measure. Extreme weather events are already a significant challenge for grain producers and are predicted to increase under numerous future climate scenarios. In these altered weather conditions, optimal sowing date with an adequate sowing density and choice of appropriate genotypes will be of great importance in order to mitigate the negative effects of climate factors on yield stability, as well as on the bread making quality of winter wheat.<br />The aim of this research was to investigate the effects of different sowing dates, sowing densities and their interactions on yield, yield components and grain quality of different wheat cultivars. The study of interaction of sowing dates, sowing densities and cultivars of winter wheat was carried out on experimental fields of the Institute of Field and Vegetable Crops, in the 1981/82. &ndash; 2012/13. period. The experiment was set each year, on the calcareous chernozem soil, as a three factor trial (split-split-plot design), in four replications, with variants in the randomized block design.<br />During the 32-year studied period, grain yield has varied considerably depending on weather conditions and ranged from 4.35 t ha-1 in 2003., to 8.70 t ha-1 in 2013., on average for all treatments. It was observed that the annual increase in yields during the investigated period was 10.7 kg ha-1. From the 32 years analyzed there were 5 years with high yields, 12 years with low grain yields, while the remaining 15 years could be identified as a medium yielding years. There were significant differences in temperature regimes and moisture conditions between these three types of years. Yield variation caused by the different sowing date was much lower in high yielding in comparison to low yielding years. For the entire examined period, on average of all tested cultivars and planting densities, the highest grain yields were obtained in the II sowing date (11-20. X), and were significantly higher in comparison to all other sowing dates, except the earliest (I sowing date). There were no statistically significant differences in yields between I and III sowing date, but they were significantly higher in comparison to sowing in November and December. Second sowing date had the lowest yield variation during the studied period. Sowing in November reduced yield by 11% and December sowing by 27% on average, compared to optimal (October) sowing dates. During the investigated period, average daily reduction of grain yield was 38 kg day-1. The smallest decline in yields caused by the delay in sowing was in high yielding years, followed by medium yielding, and the largest yield decline was found in low yielding years. In the optimal sowing dates (I and II), a density of 500 viable kernels m-2 proved to be optimal, while in the later sowing dates (November and December), increasing the sowing density up to 700 viable kernels m-<br />2, was justified. Delay in sowing from I to V sowing date caused an increase in the bread-making quality parameters such as protein content, wet gluten content, water absorption capacity, Zeleny sedimentation value, bread loaf volume and value number of bread, for both cultivars examined. On average for all sowing dates and densities, cultivar Zvezdana achieved higher values for almost all bread-making quality parameters tested in comparison to NS 40S.</p>

Thesis (M.Sc. (Agronomy)) --University of Limpopo, 2013 / In South Africa, wheat ranks first among the winter cereal crops produced and plays an important role in the country’s economy. The study was conducted to evaluate different South African wheat cultivars under irrigation for quality and yield parameters in Limpopo province. A field experiment was conducted during 2011 winter growing season under irrigation at the University of Limpopo experimental farm (Syferkuil). Eight wheat cultivars namely: Olifants, CNR 826, SST 347, Baviaans, Duzi, Steenbrass, SST 356 and Krokodil were laid out in a randomized complete block design with four replications for evaluation of yield and quality. The results showed that the highest grain yield obtained was 2372 kg/ha by CNR 826, and the lowest 311 kg/ha by SST 347. Flour yield, break flour yield, flour protein and mixogram development time and water absorption were not significantly different among cultivars. The highest hectolitre mass was 75.13 kghl-1for CNR 826 and the lowest 72.20 kghl-1 for Olifants. The highest falling number obtained was 187.00 sec for SST 347 and the lowest was 81.50 sec for Steenbrass. Cultivars CNR 826, SST 347, Steenbrass and SST 356 showed a good potential on protein content but Krokodil, Olifants and Baviaans had poor protein contents at 9.63%, 9.73% and 10.24% respectively. These results showed that wheat cultivars evaluated were within the requirements of the grading systems of South Africa as regards hectolitre mass and protein content. All these cultivars did not reach the required grade of 220 seconds in falling numbers with Olifants (97.50 sec), CNR 826 (103.50 sec), SST 347 (187.00 sec), Baviaans (146.75 sec), Krokodil (139.50 sec), Steenbrass (81.50 sec) and Duzi (50.25 sec), but only SST 356 met the requirement for utility grade with164.50 seconds. Olifants, CNR 826, Krokodil and Steenbrass yielded above 1500 kgha-1thus showing good potential under Limpopo conditions. These cultivars could be included in future performance evaluations in Limpopo.

Les résultats de cette étude de la composition du fruit à pain récolté sur un territoire contrasté du point de vue agropédoclimatique, et de son amidon, montrent que la teneur en amidon du fruit à pain apparaît comme étant influencée par la saison, mais pas par la zone de récolte. La teneur en amidon beaucoup plus élevée pour les fruits à pain développés durant la saison la plus sèche est un résultat très original. La connaissance du cycle de développement des fruits à pain à la Martinique a été décrite pour une première fois, permettant de déterminer une période de récolte optimisée par rapport à la floraison : la 16ème semaine pour une croissance maximale, ou la 17ème semaine pour une plus haute teneur en amidon. L’étude de Worrell et al., (1998), la seule publiée actuellement, menée à la Barbade, a montré un cycle plus long de 2 semaines environ.Du point de vue de la diversité génétique, les fruits à pain récoltés en Martinique constituent un seul groupe, à l’opposé de ceux récoltés en Guadeloupe qui constituent 2 sous-groupes proches.En ce qui concerne l’amidon, nos résultats montrent que les dimensions des grains d’amidon de fruits matures sont comprises entre 9 et 12 µm. Leur taille augmente avec la croissance du fruit puisque dans un fruit immature leur diamètre moyen était de 7,5 µm. Il s’agit d’amidons de type B à très haute cristallinité, dont les températures d'empesage sont autour de 75 °C. Parmi les facteurs agropédoclimatiques, l’humidité a eu un rôle actif sur la qualité de l’amidon puisque à la fois la quantité d’amylose et la masse molaire de l’amylopectine diminuent. L’amidon a une solubilité et un gonflement faible du même ordre de grandeur que les amidons classiques et une forte viscosité à la gélatinisation et à la rétrogradation, lui conférant une aptitude à l’utilisation comme gélifiant.Des essais d’applications alimentaires ont été effectués en panification et en extrusion. Des transformations en produits de type crackers ont donné des résultats moyennement satisfaisant avec 100 % de farine de fruit à pain. En panification l’incorporation de farine de fruit à pain a des actions délétères sur la valeur boulangère. L’acceptabilité d’un goût « nature, vert » conféré par la farine de fruit à pain devra notamment être évaluée lors de travaux ultérieurs.Le développement de produits à base de fruit à pain permettra / The results of this study the composition of breadfruit harvested in an area of agro climatic soil contrasting views, and its starch, show that the starch content of breadfruit appears to be influenced by season, but not by collection area. The starch content is much higher for breadfruit developed during the driest season is a very original result. Knowledge of the development cycle of breadfruit in Martinique has been described for the first time, to determine an optimal harvest period compared to flower: the 16th week for maximum growth, or the 17th week for a higher starch content. The study by Worrell et al., (1998), the only currently published, conducted in Barbados, showed a longer cycle of about 2 weeks.From the perspective of genetic diversity, breadfruit harvested in Martinique as a single group, in contrast to those collected in Guadeloupe that are close to two subgroups.With regard to starch, our results show that the size of starch granules of mature fruits are between 9 and 12 microns. Their size increases with the growth of the fruit as an immature fruit in their mean diameter was 7.5 microns. This is B-type starches with very high crystallinity, with temperatures of gelatinization are around 75 °C. Agro climatic soil factors, humidity took an active role on the quality of starch, since both the amount of amylose and amylopectin molecular weight of the decline. The starch has a solubility and low swelling of the same order of magnitude as the conventional starches and high viscosity to gelatinization and retrogradation, giving it a suitability for use as a gelling agent.Testing of food applications were made in bakery and extrusion. Changes in products like crackers gave moderately satisfactory results with 100 % breadfruit flour. Incorporation into bread flour breadfruit has deleterious actions on the baking. The acceptability of a taste "nature green" conferred by the breadfruit flour will be particularly assessed in future work.Product development based breadfruit allow several things, which meet the growing demand for food diversification.

[ES] La inspección visual es un parámetro de calidad que describe tanto el aspecto externo como la estructura interna en los productos derivados de cereales. El análisis digital de imagen (ADI) es una herramienta ampliamente utilizada en diversos campos para procesar y analizar los objetos que observamos visualmente. Sin embargo, a pesar de su potencial, ha sido escasamente explotado en el ámbito de alimentos. La estructura de la miga de los productos derivados de cereales es uno de los parámetros característicos del pan y en este contexto es fundamental realizar el seguimiento de los cambios estructurales que se producen durante el proceso o debido a las modificaciones en la formulación. Por ello, el objetivo principal de la presente tesis doctoral fue definir la interrelación entre la estructura y parámetros de calidad de masas y productos horneados, así como extender la utilidad del ADI y su uso para optimizar los procesos y las formulaciones en productos horneados. Para ello, en primer lugar, se establecieron las condiciones óptimas de captura y se estudió la forma de mejorar la detección de bordes. Posteriormente se evaluó el potencial del análisis de imagen para cuantificar los cambios estructurales ocurridos en la formación de geles de almidón en un analizador rápido de fuerza. Seguidamente, se estudió el impacto en la estructura de la adición o sustitución de distintos ingredientes o aditivos en panes con y sin gluten. Y finalmente se investigaron las posibles correlaciones entre los resultados obtenidos de la caracterización tecnológica (perfil de textura, estructura de la miga, humedad) frente a la percepción sensorial (propiedades del bolo, masticación y deglución). El ADI permitió cuantificar las diferentes estructuras obtenidas con los distintos almidones. Además, el estudio reveló las diferencias en el tiempo necesario para formar una estructura homogénea y bien distribuida, que fue dependiente del origen del almidón. La modificación de la formulación de panes con o sin gluten requirió de la adaptación del proceso y permitió obtener diferentes estructuras atendiendo a los ingredientes /aditivos estudiados. El ADI resultó ser una herramienta eficaz para detectar y cuantificar los cambios originados a nivel estructural, en masa y producto final. Además, los cambios cuantificados mediante ADI obtuvieron correlaciones estadísticamente significativas con varios de los parámetros estudiados de percepción sensorial, como son la adhesividad del bolo y el tiempo total para masticar y deglutir una muestra. Por lo tanto, el ADI resultó una herramienta suficientemente específica y no destructiva, que permitió caracterizar el impacto del cambio de la formulación en la distribución alveolar de panes con y sin gluten. Existiendo relación entre este y los parámetros utilizados habitualmente en la caracterización de productos derivados de cereales, así como con la percepción sensorial. / [CA] La inspecció visual és un paràmetre de qualitat que descriu tant l'aspecte extern com l'estructura interna en els productes derivats de cereals. L'anàlisi digital d'imatge (ADI) és una eina àmpliament utilitzada en diversos camps per a processar i analitzar els objectes que observem visualment. No obstant això, malgrat el seu potencial, ha sigut escassament explotat en l'àmbit d'aliments. L'estructura de la molla dels productes derivats de cereals és un dels paràmetres característics del pa i en aquest context és fonamental realitzar el seguiment dels canvis estructurals que es produeixen durant el procés o a causa de les modificacions en la formulació. Per això, l'objectiu principal de la present tesi doctoral va ser definir la interrelació entre l'estructura i paràmetres de qualitat dels diferents tipus de masses i productes enfornats, així com estendre la utilitat de l'ADI i el seu ús per a optimitzar els processos i les formulacions en productes enfornats. Per a això, en primer lloc, es van establir les condicions òptimes de captura i es va estudiar la manera de millorar la detecció de les vores. Posteriorment es va avaluar el potencial de l'anàlisi d'imatge per a quantificar els canvis estructurals ocorreguts en la formació de gels de midó en un analitzador ràpid de força. Seguidament, es va estudiar l'impacte en l'estructura de l'addició o substitució de diferents ingredients o additius en pans amb glútens i sense glútens. I finalment es van investigar les possibles correlacions entre els resultats obtinguts de la caracterització tecnològica (perfil de textura, estructura de la molla, humitat) enfront de la percepció sensorial (propietats del bol, masticació i deglució). L'ADI va permetre quantificar les diferents estructures obtingudes amb els diferents midons. A més, l'estudi va revelar les diferències en el temps necessari per a formar una estructura homogènia i ben distribuïda, que fou dependent de l'origen del midó. La modificació de la formulació de pans amb gluten o sense va requerir de l'adaptació del procés i va permetre obtindre diferents estructures atesos els ingredients /additius estudiats. L'ADI va resultar ser una eina eficaç per a detectar i quantificar els canvis originats a l'entorn estructural, en massa i producte final. A més, els canvis quantificats mitjançant ADI van obtindre correlacions estadísticament significatives amb els diversos paràmetres estudiats de percepció sensorial, com són l'adhesivitat del bol i el temps total per a mastegar i deglutir una mostra. Per tant, l'ADI va resultar una eina prou específica i no destructiva, que va permetre caracteritzar l'impacte del canvi de la formulació en la distribució alveolar de pans amb glutens i sense. Tot i existint relació entre aquest i els paràmetres utilitzats habitualment en la caracterització de productes derivats de cereals, així com amb la percepció sensorial. / [EN] Visual inspection is a quality parameter that describes both the external appearance as the internal structure in cereal-based products. Digital image analysis (DIA) is a tool widely used in several fields to process and analyse objects visually observed by the human eye. However, despite of its potential, it has been barely explored for food analysis purposes. Crumb structure in cereal-derived products is one of the most characteristic parameters in bread. Due to this, following up the structural changes caused by the process or by the formulation changes, is of fundamental importance. For that reason, the main target of this thesis was the definition of the relationship between the structure and the quality parameters of dough and baked products. Moreover, extending the DIA utility and its use to improve process and mixes in baked products represented other main objective of this work. To do that, first, the optimal capture conditions were established and the way to improve the edge detection was studied. Afterwards, image analysis was evaluated to quantify the structural changes that happened during the starch gels formation in a fast force analyser. Then, the impact on the structure by adding or replacing different ingredients or additives in gluten-free breads was studied. Finally, the possible correlations between the results obtained from technological characterization (texture profile, crumb structure, moisture content) versus sensory perception (bolus properties, chewing and swallowing) were also investigated. DIA allowed the quantification of the different structures obtained from different starches. In addition, the study revealed the differences in time needed to form a homogeneous and well-distributed structure, which was dependent on the origin of the starch. Formulation modification in bread with or without gluten required a process adjustment that allowed to obtain different structures depending on the ingredients / additives studied. DIA has been proved to be an effective tool for detecting and quantify changes originated at the structural, dough and final product levels. In addition, the changes quantified by DIA obtained statistically significant correlations with several parameters studied for the sensory perception, such as bolus adhesion and total time to chew and swallow the sample. Therefore, DIA was a sufficiently specific and non-destructive tool, which allowed to characterize the impact of the formulation change on the bread cell distribution with and without gluten. There being a relationship between this, and the parameters usually used in cereal products characterization, as well as sensory perception. / Authors acknowledge the financial support of the Spanish Ministry of Economy and Competitiveness (Projects AGL2011-23802 and AGL2014-52928-C2-1-R), the European Regional Development Fund (FEDER) and Generalitat Valenciana (Projects Prometeo 2012/064 and Prometeo 2017/189), the Spanish Ministry of Science, Innovation and Universities (RTI2018-095919-B-C21), and the European Regional Development Fund. This work is based upon the work from COST Action 18101 SOURDOMICS – Sourdough biotechnology network towards novel, healthier and sustainable food and bioprocesses, the European Regional Development Fund and the joint project between research group from IATA-CSIC and the research groups of Nutriomics and CIDPRO from Tecnologico de Monterrey, Mexico. / Garzón Lloría, R. (2021). Análisis estructural de los productos derivados de cereales y su aplicación en la optimización de procesos y productos [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/166856

Doctor of Philosophy / Department of Grain Science and Industry / Finlay I. MacRitchie / Expansion of dough and hence breadmaking performance is postulated to depend on a dual mechanism for stabilization of inflating gas bubbles. Two flours were used in this study, one from the wheat variety Jagger (Jagger) and the other from a composite of soft wheat varieties (soft). The primary stabilizing mechanism is due to the gluten-starch matrix surrounding the bubble. The secondary mechanism operates when gas bubbles come into close contact during later proofing and early baking. When discontinuities occur in the gluten-starch matrix surrounding gas bubbles, thin liquid lamellae stabilized by adsorbed surface active compounds, provide a secondary stabilization. A key parameter in the primary stabilizing dough film is thought to be the property of strain hardening. Jagger flour gave higher test-bake loaf volume than soft wheat flour and higher strain hardening index for dough. Rheological properties of doughs were varied by addition of protein fractions prepared by pH fractionation. Fractions were characterized by SE-HPLC and MALLS. The molecular weight distribution (MWD) of fractions progressively shifted to higher values as the pH of fractionations decreased. Mixograph peak development time paralleled the MWD. However, the strain hardening index and the test-bake loaf volume increased with increasing MWD up to a point (optimum), after which they declined. At a given strain rate the behavior at the optimum appeared to result from slippage of the maximum number of statistical segments between entanglements, without disrupting the entangled network of polymeric proteins. Shift of MWD to MW higher than the optimum results in a stronger network with reduced slippage through entanglement nodes, whereas a shift to lower MWs will decrease the strength of the network due to less number of entanglements per chain. In order to study the secondary stabilizing mechanism, different lipid fractions were added incrementally to the defatted flours. No effects were observed on the rheological properties of the dough. However, large effects on the loaf volume were measured. The additives used were the total flour lipid and its polar and non polar fractions and the fatty acids palmitic, linoleic and myristic. Polar lipids and palmitic acid had positive or little effect on loaf volume respectively. Non polar lipid, linoleic and myristic acids had negative effects on loaf volume. 1 The different effects of the lipid fractions are thought to be related to the type of monolayer that is formed. Polar lipid and palmitic acid form condensed monolayers at the air/water interface whereas non polar lipid, linoleic and myristic acids form expanded monolayers.

Les microorganismes sont essentiels au maintien et au fonctionnement des écosystèmes. Dans certains produits alimentaires, la communauté microbienne, composée principalement de levures et de bactéries lactiques, fermente les sucres, affecte positivement les qualités organoleptiques du produit et augmente sa durée de conservation. C’est le cas du levain de panification. Cette thèse visait principalement à décrire les patterns de diversité des levures de levains français produits à partir de farine issue de l’agriculture biologique et à conserver une partie de cette diversité. Grâce à des méthodes d’analyses culturales et non culturales de la diversité des levures, nous avons mis en évidence une diversité spécifique caractéristique de chaque levain étudié. Nous avons aussi montré la dominance du genre Kazachstania et la convergence des souches isolées de levain pour la capacité à consommer du raffinose et du saccharose. Bien que la densité et la composition en espèces varient entre deux levains, aucune structuration spatiale de la diversité n’a été mise en évidence. Les pratiques de panification et leurs effets sur la diversité des communautés microbiennes ont également été analysés. Deux typologies de pratiques de panification (plutôt « intensives » et plutôt « extensives »), affectant l’espèce dominante des populations de levures, ont été révélées. / Microorganisms are essential for the maintenance and functioning of the ecosystems. In some food products, microbial community, mainly composed by yeasts and lacid actic bacteria which ferment sugars, positively affects organoleptic qualities and shelf life of the product. It is the case of bread sourdough. This PhD aimed at describing yeast diversity patterns of organic French bread sourdoughs and conserving a part of this diversity. Using cultural-Based and non-Cultural based analyses of yeast diversity, we highlighted a unique specific diversity of each sourdough. We also shown the predominance of Kazachstania genus and a convergence of sourdoughs’ yeasts isolates for the ability to consume raffinose and sucrose. Although density and species composition varied between sourdoughs, no spatial pattern was highlighted. Bread-Making practices and their effects on microbial communities’ diversity were also analyzed. Two bread-Making practice typologies (quite « intensive » and quite « extensive »), affecting dominant yeast species were also revealed.