Effect of reducing and oxidizing agents and pH on malt endoproteolytic activities and brewing mashes

The activities of the four endoproteinase classes of malted barley are known to vary with pH, and it seemed likely that the cysteine enzyme activities could be altered by redox agents. This study determined how altering the pH and adding redox agents to mashes influenced the worts that were produced during the brewing process. The reducing agents cysteine.HCl, dithiothreitol, and beta-mercaptoethanol increased the proteolysis that occurred in malt extracts and mashes. This increased proteolysis was negated by the addition of the oxidizing agents diamide or hydrogen peroxide. The addition of reducing agents to mashes increased the soluble protein, free amino nitrogen (FAN), and extract values of their resultant worts, and this effect was abolished by the concomitant addition of oxidizing agents. Raising the pH values of the mashes strongly reduced their proteolytic activities, soluble protein, FAN, and extract values, but not their beta-glucan levels. These results show that several of the major aspects of malting and brewing quality can be adjusted by varying the pH and redox qualitites of mashes, which could be helpful to brewers. These results also strengthen the previous proposal made by Buchanan et al. that the redox status of plants may play a significant part in controlling their physiology.     

Medium-term transformations of organic N in a cultivated soil

We followed in situ the evolution of nitrogen recently incorporated into a soil under maize culture for 4 years. Each year, a different pair of plots treated by removal or return of maize crop residues received a single pulse of ¹⁵N-labelled fertilizer. Unlabelled fertilizer was otherwise supplied. In parallel, plots supplied with unlabelled fertilizer received a single pulse of ¹⁵N-labelled maize crop residues. Varying weather affected total and fertilizer-derived N in the crop and residual inorganic N in the topsoil, but it did not affect fertilizer-N immobilization and remineralization. There was no consistent effect of crop residue return on total soil N, immobilization of fertilizer N, or the decay kinetics of recently immobilized N. Recently incorporated organic N from crop residues and microbial immobilization of inorganic N displayed similar mid-term decay kinetics. Crop residue N and immobilized N enter a labile compartment with an average residence time of a few months. A proportion, estimated at 28%, enters a more stable compartment from which the mineralization was imperceptible in 4 years. Particle-size fractions >50 um, which receive most of the crop residue N, retained it for only a short time. The mid-term stabilization of N was mainly in soil fractions <50 um.     

A comparison of color formation and maillard reaction products of a lactose-lysine and lactose-N(alpha)-acetyllysine model system

The formation of color and Maillard reaction products in two model systems consisting of lactose and lysine or N(alpha)-acetyllysine has been investigated. During heating, the blockage of the N(alpha) group of lysine determined a faster color and antioxidative ability development compared to the system with free lysine. This is combined to a greater amount of melanoidin formation in the acetylated lysine system, while in the free lysine system a higher amount of pyrraline and hydroxymethyl furfural were detected. The pattern of low molecular weight products suggests that 3-deoxyglucosone and 1-deoxyglucosone degradation pathways are favored for free lysine and N(alpha)-acetyllysine, respectively. Whole data allow us to hypothesize that in a lactose-N(alpha)-acetyllysine model system the formation of colored high molecular weight polymer proceeds faster because less material is dispersed in reaction pathways, mainly the Strecker degradation, which leads to small and intermediate molecular weight products.     

DDE in eggs of two crocodile species from Belize

Organochlorine (OC) residues were recently detected in nonviable Morelet's crocodile (Crocodylus moreletii) eggs from northern Belize. To further the assessment of contaminant exposure in Belizean crocodiles, nonviable Morelet's crocodile eggs (n = 11) from southern Belize and American crocodile (Crocodylus acutus) eggs (n = 12) from the coastal zones of Belize were screened for 20 OCs. Results indicated p,p-DDE to be the most prevalent OC (96% occurrence) in eggs examined, with concentrations ranging from 5 to 372 ng/g. These concentrations are similar to those observed in crocodile eggs (10-180 ng/g) from northern Belize. A general trend toward higher DDE concentrations in Morelet's crocodile eggs (mean = 103 ppb) compared with American crocodile eggs (mean = 31 ppb) was observed. However, this trend may be due to site-specific contamination rather than differences in interspecific susceptibility to chemical exposure. Other OCs detected in crocodile eggs included the parent compound, p,p-DDT, and its metabolite, p, p-DDD.     

Formaldehyde quantitation in air samples by thiazolidine derivatization: factors affecting analysis

A new method for the determination of trace levels of formaldehyde in air was developed and validated. The method is based on the reaction of formaldehyde with cysteamine to form thiazolidine. Air samples containing trace levels of formaldehyde were prepared from paraformaldehyde. The percent yield of formaldehyde from paraformaldehyde was 85.1 +/- 1.14%. Air samples were bubbled into an aqueous cysteamine trap. Thiazolidine formed from formaldehyde and cysteamine in the trap was determined by gas chromatography with a fused silica capillary column and a nitrogen-phosphorus detector (NPD). The lowest detection level for thiazolidine was 17.2 pg, equivalent to 5.80 pg formaldehyde. The recovery efficiency of trace gas phase formaldehyde in air was greater than 90%. Formaldehyde levels in ambient laboratory air were 48.9-56.2 ppb (v/v).