Analytical Characterization of the Hydrolysis of Barley Malt Macromolecules During Enzymatic Degradation Over Time Using AF4/MALS/RI

The changes on the molecular weight distribution (MWD) and particle size distribution (PSD) during hydrolysis of barley malt in isothermal mashing procedures were determined using asymmetrical flow field flow fractionation coupled to multiangle laser light scattering and refractive index (AF4/MALS/RI). Mash/trials were focused on amylolytic starch degradation. Therefore, temperatures (65, 70, and 75 °C) were selected according to α‐ and β‐amylases range of activity. Samples were produced by triplicate, tracking amylolytic processes over time periods from 10 to 90 min in each mash/trial. AF4/MALS/RI analysis demonstrated significant differences on the values of the MWD and PSD according to the temperature/time profile used. At mashing times over 30 min at a temperature of 65 °C, when α‐ and β‐amylase are both active, the decrease over time of the MWD and PSD was significantly higher (P < 0.005) than at 70 °C when mainly α‐amylase is active. At 75 °C, also the activity of α‐amylase decreased and the MWD and PSD were significantly lower (P < 0.005) than at 70 or 65 °C at any time of the procedure. The MWD and PSD of beer components influence beer palate fullness, thus AF4/ MALS/RI would be a powerful tool for breweries to adapt their technological processes to obtain beers with particular sensorial attributes.     

Assessing the Potential Content of Ethyl Carbamate in White,Red, and Rosé Wines as a Key Factor for Pursuing Urea Degradation by Purified Acid Urease

The ethyl carbamate (EC) content of a wine after a given temperature‐time storage was theoretically predicted from the potential concentration of ethyl carbamate (PEC), as determined via an accelerated EC formation test. Such information was used to decide whether an enzymatic treatment was needed to reduce the wine urea level before bottling/aging. To this end, 6 white, red, and rosé wines, manufactured in Italy as such or enriched with urea, were tested for their PEC content either before or after enzymatic treatment using a purified acid urease preparation derived from Lactobacillus fermentum. The treatment was severely affected by the total phenolic content (TP) of the wine, the estimated pseudo‐first‐order kinetic rate constant for NH₃ formation reducing by a factor of approximately 2000 as the TP increased from 0 to 1.64 g L^‐1. Such a sensitivity to TP was by far greater than that pertaining to a killed cell‐based enzyme preparation used previously. Urea hydrolysis was successful at reducing EC concentration in wines with low levels of TP and other EC precursors.     

Residual stress of as-deposited and rolled wire+arc additive manufacturing Ti–6Al–4V components

Wire + arc additive manufacturing components contain significant residual stresses, which manifest in distortion. High-pressure rolling was applied to each layer of a linear Ti–6Al–4V wire + arc additive manufacturing component in between deposition passes. In rolled specimens, out-of-plane distortion was more than halved; a change in the deposits' geometry due to plastic deformation was observed and process repeatability was increased. The Contour method of residual stresses measurements showed that although the specimens still exhibited tensile stresses (up to 500?MPa), their magnitude was reduced by 60%, particularly at the interface between deposit and substrate. The results were validated with neutron diffraction measurements, which were in good agreement away from the baseplate.

This paper is part of a Themed Issue on Measurement, modelling and mitigation of residual stress.     

Rational protein design of ThDP-dependent enzymes-engineering stereoselectivity

Benzoylformate decarboxylase (BFD) from Pseudomonas putida is an exceptional thiamin diphosphate-dependent enzyme, as it catalyzes the formation of (S)-2-hydroxy-1-phenylpropan-1-one from benzaldehyde and acetaldehyde. This is the only currently known S-selective reaction (92 % ee) catalyzed by this otherwise R-selective class of enzymes. Here we describe the molecular basis of the introduction of S selectivity into ThDP-dependent decarboxylases. By shaping the active site of BFD through the use of rational protein design, structural analysis, and molecular modeling, optimal steric stabilization of the acceptor aldehyde in a structural element called the S pocket was identified as the predominant interaction for adjusting stereoselectivity. Our studies revealed Leu461 as a hot spot for stereoselectivity in BFD. Exchange to alanine and glycine resulted in variants that catalyze the S-stereoselective addition of larger acceptor aldehydes, such as propanal with benzaldehyde and its derivatives-a reaction not catalyzed by the wild-type enzyme. Crystal structure analysis of the variant BFDL461A supports the modeling studies.     

Horizontal nutrient flows and balances in irrigated urban gardens of Khartoum, Sudan

The role of urban agriculture (UA) for the supply of fresh vegetables, fruits and meat for local markets is well known. The periodically flooded Gerif soils on the River Nile banks in the core of Khartoum city harbour vegetable gardens that supply perishable leafy vegetables with a short life cycle. In an effort to assess their sustainability and possible negative environmental impact we used a horizontal balance approach to determine the nutrient use efficiency of four intensively cropped UA gardens. Two of the gardens were located in downstream lowlands (L1 and L2) and the other two belonged to the upstream highlands (H1 and H2). The river sediments contributed on average 873 kg nitrogen (N), 6.5 kg phosphorus (P), 6.8 kg potassium (K) and 8,317 kg carbon (C) per hectare in lowland gardens, while only 289, 1.6, 2.5 and 1,938 kg N, P, K and C ha⁻¹ reached the highlands. The farmers’ management in all four gardens resulted in horizontal N and C surpluses of 75–342 kg N ha⁻¹ year⁻¹ and 798–6,412 kg C ha⁻¹ year⁻¹, in contrast to P and K for which negative balances up to −45 kg P ha⁻¹ year⁻¹ and −583 kg K ha⁻¹ year⁻¹ were recorded. While the River Nile floods as important N and C source contribute significantly to soil fertility maintenance, the negative P and K balances call for a better integration of UA gardening with livestock husbandry and the regular addition of animal manure in these cropping systems.     

Study on the applicability of high-pressure homogenization for the production of banana juices

The aim of this preliminary study was to evaluate the potential applicability of high-pressure homogenization (HPH) for the production of banana juices. To this purpose, a prototype equipment working up to 400 MPa and a lab-scale homogenizer working up to 150 MPa were used. Temperature, microbial load, pectate lyase activity, colour and viscosity of the samples homogenized at increasing pressure were evaluated. Pressures higher than 200 MPa were needed to obtain 4 log unit reduction of total mesophilic bacteria and pectate lyase inactivation. Following HPH, banana juice resulted brighter and less viscous than the untreated one. Data suggest that HPH treatments could be a reliable technological alternative to conventional heat treatments for the production of added-value fruit juices. However, the homogenization design could play a critical role in affecting the product quality attributes. In fact, homogenization performed at the same operative pressure by using different equipment leads to different effects on product quality.     

Rapid detection of genus Cronobacter in powdered infant formula milk

Rapid and specific detection of Cronobacter spp. in powdered infant formula milk (IFM) is of great importance for health and safety reasons. In the present study, two rapid and specific methods, the immunochromatographic strip (ICT) and the matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS), were tested for the detection of Cronobacter spp. in IFM. IFM samples spiked by Cronobacter spp. were correctly detected as positive by both methods. These results were verified by the classical cultivation microbiological method (ISO/TS 22964:2006). All three methods were used for the analyses of 13 IMF samples from a local market with identical results. Only one IFM sample was found to be positive. Both tested methods considerably reduced the total detection time, to 24?h (ICT) and 46?h (MALDI-TOF MS), whereas the reference ISO/TS 22964:2006 method needs 140?h.     

Common wheat (Triticum aestivum L.) and its use as a brewing cereal – a review

Wheat (Triticum aestivum L.) has a long tradition as a raw material for the production of malt and beer. Nevertheless, it has been studied to a much lesser extent than barley, which is the number one brewing cereal. The protein content of wheat ranges from about 6 to 20%, depending on the variety and baking characteristics, as well as on environmental conditions during growth. Since wheat is the most used cereal in the baking industry, the focus of wheat breeding and research has been about optimization for baking purposes (i.e. high protein content, stable falling numbers, constant baking qualities). It is well known that wheat varieties with a high protein content lead to problems in the brewing process. Therefore, varieties with a low protein content and with low viscosity values are favoured for malting and brewing. Since wheat beer yield has nearly doubled from 1990 to 2009, and is still increasing, more focus has been placed on conducting research on wheat for the malting and brewing industry. Currently, every tenth beer sold in Germany is a wheat beer. Therefore, it is of major interest to screen wheat varieties for brewing processability and to give more focus to wheat as a brewing cereal. In this review, a detailed characterization of wheat is given, particularly in regard to carbohydrates, pentosans, protein fractions and enzymes. The impact of wheat and its quality on the malting and brewing process is reviewed. Copyright © 2014 The Institute of Brewing & Distilling