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Rice flour is one of the most valuable cereal flours from a nutritional viewpoint. However, its use is limited to unfermented baked products since rice proteins are unable to hold gas produced during fermentation. Protein functionality can be modified by cross-linking. Rice flour was treated with different concentrations of a microbial transglutaminase (TG). The extent of the modification was evaluated by quantifying amino and thiol groups. The addition of TG improved the dynamic rheological properties of rice flour doughs, resulting in a progressive increase of the viscous (G″) and elastic (G′) moduli with increase in TG concentration. The improvement in rice protein functionality became evident in breadmaking, since it was possible to obtain rice bread with an increased specific volume and softer crumb at 1% TG level in the presence of 2% hydroxypropylmethylcellulose. Analyses showed that rice proteins are polymerised through the TG reaction, providing a protein network necessary for holding the gas produced in fermentation. [Copyright &y& Elsevier]

The influence of N-stress on the transport of amino acids in the xylem sap was studied for nodulated and non-nodulated soybean plants. The transfer of non-nodulated plants cultivated with nitrate or of nodulated plants dependent exclusively on N2 fixation to hydroponics with N-free nutrient solution (N-stress), led to a pronounced increase in aspartate and fall in asparagine (Asn) in the xylem sap. Such a change was also observed during the ‘N-hunger’ phase of the growth cycle of nodulated plants, characterized by the transient yellowing of leaves and coinciding with the initial stages of nodule development. In this case, aspartate increased to around 68% of the xylem amino acids while Asn, normally the most abundant amino acid, fell to 10%. The changes were reversible on recovery of plants from N-stress. In the case of nodulated plants, the fall in xylem Asn during N-stress and its subsequent rise during recovery closely followed Asn synthetase activity in the nodule, while aspartate produced an inverse relationship. Aspartate was prominent in the phloem, independent of the treatment. The possibility that the phenomenon is related to the metabolism of aspartate recycled through the root system is discussed. [Copyright &y& Elsevier]

An assay of γ-glutamylcysteine synthetase (γ-GCS) and glutathione synthetase (GS) in crude extracts of cultured cells and tissues is described. It represents a novel combination of known methods, and is based on the formation of glutathione (GSH) from cysteine, glutamate and glycine in the presence of rat kidney GS for the assay of γ-GCS, or from γ-glutamylcysteine and glycine for the assay of GS. GSH is then quantified by the Tietze recycling method. Assay mixtures contain the γ-glutamyl transpeptidase (GGT) inhibitor acivicin in order to prevent the degradation of γ-glutamylcysteine and of the accumulating GSH, and dithiothreitol in order to prevent the oxidation of cysteine and γ-glutamylcysteine. γ-GCS and GS levels determined by this method are comparable to those determined by others. The method is suitable for the rapid determination of γ-GCS GS in GGT-containing tissues and for the studies of induction of γ-GCS and GS in tissue cultures. [Copyright &y& Elsevier]