Effects of native and enzymatically hydrolysed soya and oat lecithins in starch phase transitions and bread baking

The effects of oat and soya lecithins and their hydrolysates on crystallisation of wheat starch gel and on bread structure were studied. In baking studies the lecithins were compared with commonly used commercial emulsifiers. Soya lecithin hydrolysate retarded starch gel crystallisation and bread staling as effectively as the best commercial emulsifiers. The oat lecithins were interesting. They did not affect significantly the starch gel crystallisation but both of them retarded bread staling much more effectively than the soya lecithin. Oat lecithins were as good as the commercial Amidan indicating that glycolipids in oat lecithins slowed bread staling. © 1998 SCI.     

Effects of enzymes in fibre-enriched baking

The aim of the present study was to improve the quality of fibre-enriched wheat breads by enzymic treatment of the fibre fraction. The suitability of different enzymes in fibre-enriched baking and their effects on the dietary fibre content and the ratio of insoluble: soluble fibre content of the breads were studied. The enzyme preparations used were a hemicellulolytic culture filtrate of Trichoderma reesei, a specific (pI 9) xylanase of T reesei and Fermizyme, an α-amylase preparation containing a standardised level of hemicellulase activity. Rye bran was extracted in water (10% (w/w) suspension) to determine the solubilities of the β-glucans and pentosans. Addition of T reesei culture filtrate significantly increased the amount of extractable pentosan obtained from nonautoclaved rye bran. Rye bran supplementation (5%) of wheat flour increased the farinograph absorption and dough development time, but had little or no effect on stability and softening of the dough. The added enzymes decreased dough stability and increased softening. Addition of enzymes caused significant differences in the stickiness of the wheat doughs both with (P<0·003) and without (P<0·001) rye bran. Fermizyme significantly increased the stickiness of wheat doughs both with and without rye bran. The baking results of the fibre-enriched breads were improved by the added enzymes. Addition of T reesei culture filtrate increased the specific volume of the wheat breads both with and without rye bran by almost 20%. Enzyme mixtures were more efficient than individual xylanase in softening the bread crumb and reducing the staling rate of wheat breads both with and without rye bran. Incorporation of enzymes reduced the total dietary fibre content of the breads, but at least doubled the amount of soluble pentosan. The proportions of fluorescent cell walls in the breads were detected by microscopical image analysis. Enzyme addition caused the surface area of insoluble cell walls originating from wheat flours to decrease, suggesting that the enzymes exert more effects on wheat endorsperm cell walls than on bran particles. © 1998 SCI.     

The Rieske Oxygenase SnoT Catalyzes 2′′-Hydroxylation of l-Rhodosamine in Nogalamycin Biosynthesis

Nogalamycin is an anthracycline anti-cancer agent that intercalates into the DNA double helix. The binding is facilitated by two carbohydrate units, l -nogalose and l -nogalamine, that interact with the minor and major grooves of DNA, respectively. However, recent investigations have shown that nogalamycin biosynthesis proceeds through the attachment of l -rhodosamine (2′′-deoxy-4′′-epi-l -nogalamine) to the aglycone. Herein, we demonstrate that the Rieske enzyme SnoT catalyzes 2′′-hydroxylation of l -rhodosamine as an initial post-glycosylation step. Furthermore, we establish that the reaction order continues with 2–5′′ carbocyclization and 4′′ epimerization by the non-heme iron and 2-oxoglutarate-dependent enzymes SnoK and SnoN, respectively. These late-stage tailoring steps are important for the bioactivity of nogalamycin due to involvement of the 2′′- and 4′′-hydroxy groups of l -nogalamine in hydrogen bonding interactions with DNA.     

Use of enzymes to elucidate the factors contributing to bitterness in rye flavour

In spite of the health-beneficial character of whole grain rye its use may be limited because of bitter taste. The impact of non-volatile chemical compounds on the bitter taste of rye was analysed by the aid of enzymatic hydrolysis, releasing potentially flavour-active compounds from the rye matrix. Whole grain rye flour–water suspension was treated with hydrolytic enzymes, whereafter portions of the rye suspensions were baked into crackers, assessed for their sensory profile as well as solubilised hydrolysis products. Heat treatment reduced the perceived bitterness. The treatment with enzyme preparation with high protease activity increased the bitterness of rye and also wheat flour both as suspension and as crackers. Other enzymes tested (with high polygalacturonase, endo-glucanase, xylanase or amyloglucosidase activity) had no significant impact on the perceived bitterness. Thus, small molecular weight peptides were considered to be a significant contributor to the bitter note of rye.     

Effect of enzymatic cross-linking of β-casein on proteolysis by pepsin

Food texture has a significant influence on the sensation of satiety. The digestibility of a protein matrix can be decreased by e.g. disulfide cross-links during heating, but the structure and properties of a single protein molecule can also be modified by cross-linking enzymes. In this study the effects of cross-linking of β-casein by fungal Trichoderma reesei tyrosinase (TrTyr) and bacterial Streptoverticillium mobaraense transglutaminase (Tgase) on digestibility by proteolytic pepsin were investigated by different methods. The enzymatic reaction conditions were selected in such a way that high and low molecular mass cross-linked β-casein polymers were formed. SDS-PAGE (sodium dodecyl sulphate-polyacrylamide gel electrophoresis) was used to analyze the pH stability of the cross-linked β-casein in acidic solution mimicking gastric conditions typically present during proteolytic digestion. In order to monitor the extent of pepsin digestion, the proteolytic process was halted at specific time points and aliquots of the reaction mixtures were subjected to SDS-PAGE, size-exclusion chromatography (SEC) and matrix-assisted laser desorption ionization-time of flight mass spectrometric (MALDI-TOF MS) analyses in order to evaluate sizes and quantities of the digested protein fragments. A pH-stat method was used to determine the degree of hydrolysis (DH) of the enzymatically cross-linked β-casein. The results demonstrated that enzymatically cross-linked β-casein was stable under acidic conditions and was more resistant to pepsin digestion when compared to non cross-linked β-casein. The research results will have high impact on the development of novel food structures with improved properties such as good satiety, controlled energy intake and digestibility.     

Effects of wheat sourdough process on the quality of mixed oat-wheat bread

The aim of this work was to study the effects of sourdough fermentation of wheat flour with Lactobacillus plantarum, on the quality attributes of mixed oat-wheat bread (51 g whole grain oat flour and 49 g/100 g white wheat flour). Emphasis was laid both on β-glucan stability as well as bread structure and sensory quality. The variables of the sourdough process were: dough yield (DY), fermentation time, fermentation temperature, and amount of sourdough added to the bread dough. The sourdough process was shown to be a feasible method for mixed oat-wheat bread, and, when optimized, provided bread quality equal to straight dough baking. A small amount (10g/100 g dough) of slack sourdough fermented at high temperature for a long time resulted in the most optimal sourdough bread with the highest specific volume (3.5 cm³/g), the lowest firmness after 3 days storage (0.31 kg), and low sensory sourness with high intensity of the crumb flavour. Wheat sourdough parameters did not affect the content of oat β-glucan in the bread. Additionally, both straight dough and sourdough bread contained 1.4-1.6 g β-glucan/100 g fresh bread. The average molecular weight of β-glucan was 5.5 × 10⁵ in both types of bread, while that of oat flour was 10 × 10⁵. This indicates that a slight degradation of β-glucan occurred during proofing and baking, and it was not affected by variation in the acidity of the bread between pH 4.9-5.8.     

Investigation of limiting metabolic steps in the utilization of xylose by recombinant Saccharomyces cerevisiae using metabolic engineering

A Saccharomyces cerevisiae screening strain was designed by combining multiple genetic modifications known to improve xylose utilization with the primary objective of enhancing xylose growth and fermentation in xylose isomerase (XI)-expressing strains. Strain TMB 3045 was obtained by expressing the XI gene from Thermus thermophilus in a strain in which the GRE3 gene coding for aldose reductase was deleted, and the genes encoding xylulokinase (XK) and the enzymes of the non-oxidative pentose phosphate pathway (PPP) [transaldolase (TAL), transketolase (TKL), ribose 5-phosphate ketol-isomerase (RKI) and ribulose 5-phosphate epimerase (RPE)] were overexpressed. A xylose-growing and fermenting strain (TMB 3050) was derived from TMB 3045 by repeated cultivation on xylose medium. Despite its low XI activity, TMB 3050 was capable of aerobic xylose growth and anaerobic ethanol production at 30 degrees C. The aerobic xylose growth rate reached 0.17 l/h when XI was replaced with xylose reductase (XR) and xylitol dehydrogenase (XDH) genes expressed from a multicopy plasmid, demonstrating that the screening system was functional. Xylose growth had not previously been detected in strains in which the PPP genes were not overexpressed or when overexpressing the PPP genes but having XR and XDH genes chromosomally integrated. This demonstrates the necessity to simultaneously increase the conversion of xylose to xylulose and the metabolic steps downstream of xylulose for efficient xylose utilization in S. cerevisiae.     

Barriers and drivers for sustainable building

What are the actual barriers and drivers for sustainable building? A literature review, interviews and case studies are presented to address this question. Sustainable building is not hindered by a lack of technologies and assessment methods, but is instead beset with organizational and procedural difficulties entailed by the adoption of new methods. New technologies are resisted because they require process changes entailing risks and unforeseen costs. These hindrances can be reduced by learning what kind of decision-making phases, new tasks, actors, roles and ways of networking are needed. The barriers are outlined as steering mechanisms, economics, a lack of client understanding, process (procurement and tendering, timing, cooperation and networking), and underpinning knowledge (knowledge and common language, the availability of methods and tools, innovation). The most important actions to promote sustainable building are the development of the awareness of clients about the benefits of sustainable building, the development and adoption of methods for sustainable building requirement management, the mobilization of sustainable building tools, the development of designers' competence and team working, and the development of new concepts and services. The interviews and case studies were carried out in Finland, but the results may be applicable or interesting to other countries as well.

Quels sont les obstacles et les vecteurs actuels en matière de construction de bâtiments durables ? Il est présenté une analyse bibliographique, des entretiens et des études de cas afin d'examiner cette question. La construction de bâtiments durables n'est pas entravée par un manque de technologies et de méthodes d'évaluation, mais est plutôt en butte à de multiples difficultés organisationnelles et procédurales occasionnées par l'adoption de méthodes nouvelles. Il y a une résistance aux nouvelles technologies parce qu'elles nécessitent des modifications des processus entraînant des risques et des coûts imprévus. Il est possible de réduire ces entraves en faisant l'apprentissage de ce qui est nécessaire, s'agissant des phases de prise de décision, des nouvelles tâches, des nouveaux acteurs, des nouvelles fonctions et des nouveaux modes de mise en réseau. Les obstacles passés en revue concernent les mécanismes de pilotage, l'économie, un manque de compréhension des clients, les processus (achats et appels d'offres, timing, coopération et mise en réseau) et les connaissances de base (connaissances et langage commun, disponibilité des méthodes et des outils, innovation). Les mesures les plus importantes pour promouvoir la construction de bâtiments durables sont le développement de la sensibilisation des clients aux avantages d'un bâtiment durable, le développement et l'adoption de méthodes de gestion des exigences propres aux bâtiments durables, la mobilisation des outils de construction durable, le développement des compétences des concepteurs et du travail d'équipe, et le développement de concepts et de services nouveaux. Les entretiens et les études de cas ont été réalisés en Finlande, mais les résultats peuvent également s'appliquer à d'autres pays ou présenter un intérêt pour d'autres pays.

Mots clés: obstacles, industrie du bâtiment, vecteurs, gestion, changement organisationnel, professionnalisme, processus de construction durable, bâtiment durable