Subunit and cofactor binding of Saccharomyces cerevisiae sulfite reductase - towards developing wine yeast with lowered ability to produce hydrogen sulfide

Wine yeast, in common with other industrial Saccharomyces cerevisiae yeast, can produce hydrogen sulfide during alcoholic fermentation. The aim of this work was to evaluate a genetic strategy for reducing hydrogen sulfide production by lowering the activity of NADPH-dependent sulfite reductase, a key enzyme in the biosynthesis of the sulfur-containing amino acids. The role of amino acids predicted to be necessary for cofactor binding was investigated by comparisons with other proteins in the ferredoxin family. Substitutions in the glycine-rich loop domain (glycines 891 and 893) and at serine 953 of the alpha subunit, Met10p, appear to strongly affect NADPH binding. However, mutations in two amino acids that are completely conserved within the NADPH binding domain of the ferredoxin reductase family, lysine 959 and cysteine 987, have minimal effect on enzyme activity. Serine 820 is indicated to be essential for efficient FAD binding. The two-hybrid system was used to confirm that Met 1 0p interacts with Met5p, the predicted beta subunit of sulfite reductase. Binding of the subunits could only be demonstrated in the absence of methionine, indicating that an additional factor, possibly siroheme, is required to mediate this interaction. Strategies to decrease, but not eliminate, sulfite reductase activity in the cell using identified mutants were tested, and the findings are discussed with the a view to producing improved wine strains.     

The physicochemical characteristics of nonfat set yoghurt containing some hydrocolloids

The effect of incorporating the hydrocolloids carrageenan (0.10%, 0.30%), xanthan gum (0.15%, 0.35%) and alginate (0.05%, 0.15%) in nonfat set yoghurt was examined in respect of instrumental texture profile and water‐holding capacity (WHC) of the yoghurt. The yoghurts which exhibited the similar behaviour of commercial yoghurts in terms of WHC, firmness and consistency, low adhesiveness and gumminess were analysed by difference‐from‐control sensory test. Carrageenan increased firmness, adhesiveness, gumminess and WHC at the highest concentration tested. The sensory tests did not show any significant difference between the formulations tested.     

A linear dynamic system approach for cattle herd optimal shaping

The time evolution of a herd of cattle is modelled as a linear dynamic system with slow time variation in model parameters. From this model, the optimal policy for the herd shaping is established, allowing the minimal initial cost with cattle acquisition and the maximal farm resources utilization in the steady state. The same methodology can be employed in several different production schemes, with different constraints and different objective functions. The optimization problem is formulated as a convex programming one, being solved with efficient algorithms, while keeping guaranteed convergence to the global optimum. This methodology is simpler than the dynamic programming optimization method.     

An assessment of factors characterising the microbiology of Grana Trentino cheese,a Grana‐type cheese

In this study, microbiological aspects of Grana Trentino, a variant of Grana Padano cheese, were defined by plate counts, random amplified polymorphic DNA (RAPD) PCR genotying, 16S rRNA gene sequencing of bacterial isolates and PCR–denaturing gradient gel electrophoresis (PCR–DGGE). Results showed variability in monthly fluctuations of whey culture counts, differences in the diffusion of bacterial genotypes among producers and dairy plant‐specific microbial associations. Moreover, the presence of bacteria not previously reported in this cheese type was highlighted, including coagulase‐negative staphylococci and Lactobacillus sanfranciscensis‐like micro‐organisms.     

MACRODONTIN, A NEW PROTEASE ISOLATED FROM FRUITS OF PSEUDANANAS MACRODONTES (MORR.) HARMS (BROMELIACEAE)

A cysteine proteinase was isolated from immature fruits of Pseudananas macrodontes (Morr.) Harms, a species taxonomically close to pineapple grown in the northeast of Argentina. The protease is active at pH 7.0 to 10.5, and rather unstable at temperatures over 45C. Crude extracts were purified by acetone fractionation followed by chromatofocusing at the pH range 4.5 to 6.5. Two main proteolytic fractions were obtained: fraction I (M_r= 20.6 kDa, pI = 5.9) and fraction II (M_r= 19.3 kDa, pI = 5.3), both homogeneous by gel-filtration and SDS-PAGE criteria. This new plant protease (“macrodontin”) could be valuable in processes carried out in neutral-weak alkaline media. The thermal behavior of the crude enzyme is also a useful property, since it could be easily inactivated in foodstuffs by heating 10 min at 75C. Comparison of macrodontin and alcalase proteolytic behavior on soy concentrates is presented.     

Optimization of Extrusion Cooking Process for Chickpea (Cicer arietinum, L.) Defatted Flour by Response Surface Methodology

Response surface methodology was employed to optimize the production of a snack food from chickpea. The independent variables, process temperature (123–137°C) and feed moisture (13–27% d.s.b.) were selected at five levels (rotatable five level composite design: ?√2, ?1, 0, 1, +√2) in the extrusion of defatted chickpea flour. Response variables were expansion ratio, shear strength of the extra-date and sensory preference assessed by an untrained panel. Expansion ratio increased steadily with decrease in feed moisture similar to cereal extrusion. Regions of maxima were observed for sensory preference and shear strength, and these two product attributes were linearly related. The most acceptable chickpea snack was rated higher than a commercial corn snack.     

DETERMINATION OF DIFFERENT VOLATILE BASE COMPONENTS AS QUALITY CONTROL INDICES IN FISH BY OFFICIAL METHODS AND FLOW INJECTION ANALYSIS

Flesh concentration of Trimethylamine Oxide‐Nitrogen (TMAO‐N), Trimethylamine‐Nitrogen (TMA‐N) and Total Volatile Base Nitrogen (TVB‐N) are the most studied parameters used as indices of spoilage in fish and fishery products. In the present work, the official methods to determine TVB‐N, TMA‐N and TMAO‐N were compared with the Flow Injection Analysis (FIA) technique using three different fish species over their storage in melting ice for a period of 16 days. There was a good correlation between determinations made using official and FIA methods with no apparent significant differences. FIA thus appears to be a suitable method for TMAO‐N, TMA‐N and TVB‐N in fish extract and the use of this system is much faster and simpler than the official methods for determination of these parameters. On the other hand, the individual concentrations of TMAO‐N, TMA‐N and TVB‐N were not found to represent reliable indices of spoilage in fish, which had been frozen and thawed and then presented in chilled format.