Impact of Starch Gelatinization and Kernel Fissuring on the Milling Breakage Susceptibility of Parboiled Brown Rice

Parboiling, a hydrothermal treatment of paddy or brown rice, improves the texture and nutritional characteristics of cooked rice. We investigated milling breakage susceptibility of brown rice parboiled under different soaking and steaming conditions, resulting in samples with different degrees of starch gelatinization and levels of fissured grains and white bellies, that is, parboiled grains with translucent outer layers and an undesirable opaque center. The milling breakage susceptibility was 2.1% for raw rice and ranged from less than 1% up to 11.3% for parboiled rice. Parboiled samples with increased milling breakage susceptibility contained higher levels of white bellies and fissured grains. In white bellies, starch gelatinization is incomplete. Scanning electron microscopy revealed inhomogeneities in individual white bellies and fissured rice grains, indicating moisture gradients inside the grains during parboiling. Starch needs to be completely gelatinized to ensure the absence of white bellies and minimal fissured grain levels in the parboiled end product and, as a consequence, a decreased milling breakage.     

Phytochemicals and dietary fiber components in rye varieties in the HEALTHGRAIN Diversity Screen

Ten rye varieties grown in one location were analyzed for their contents of dietary fiber (arabinoxylan and beta-glucan) and phytochemicals (folate, tocols, phenolic acids, alkylresorcinols, and sterols). The varieties included old and modern varieties from five European countries. Significant differences were observed in the contents of all phytochemicals in whole grains and in the fiber contents in the flour and bran. The old French varieties Haute Loire and Queyras had high contents of most phytochemicals, whereas the Polish varieties Dankowskie-Zlote and Warko were relatively poor in phytochemicals. The varieties with a high content of folate tended to have low alkylresorcinol contents and vice versa. Furthermore, high contents of arabinoxylans were associated with high contents in tocols and sterols. The 10 selected rye samples comprising old populations and old and modern varieties from different ecological regions of Europe demonstrate high natural variation in their composition and show that landraces and old populations are useful genetic resources for plant breeding. The contents of single phytochemicals can likely be affected by breeding, and they may be adjusted by the right selection of genotype.     

The primary structure of wheat glutenin subunit 1Dx2 revealed by electrospray ionization mass spectrometry

The high molecular weight glutenin subunits (HMW-GS) play a key role in end-use quality of wheat. Their particular primary structure is mostly derived from DNA sequencing, which gives no information on potential post-translational modifications. This paper reveals the primary structure of HMW-GS 1Dx2 by proteomic analysis. For this purpose, HMW-GS were first isolated from wheat flour (cv. Contra). The relative molecular mass (M_r) of subunit 1Dx2 present in the HMW-GS mixture was then very accurately determined with high-performance liquid chromatography–electrospray ionization-mass spectrometry using a quadrupole-time-of-flight mass analyzer (HPLC–ESI-QTOF-MS). The obtained M_r value (87,105) differed from the value derived from its protein sequence in the NCBI database (87,007). The subunit was further purified by preparative reversed-phase HPLC and partially hydrolyzed with chymotrypsin. The resulting 1Dx2 peptides were then analyzed by HPLC–ESI-MS/MS and the MS data were compared to amino acid sequences in protein databases. The discrepancy between the calculated and the measured M_r of 1Dx2 was explained by a missing proline in the 1Dx2 amino acid sequence from the database and not by any post-translational glycosylation.     

Amylases and bread firming – an integrated view

Despite much research, bread crumb firming during storage and amylase anti-staling properties are still ill understood. We present a coherent view on the topic based on literature, experimental data, and food polymer science-related concepts. During bread storage, the gelatinised starch (amylopectin) network, present in soft, fresh bread, is gradually transformed into an extensive, partially crystalline, permanent amylopectin network, with amylopectin crystallites acting as junction zones. This network increasingly accounts for the bulk rheological behaviour of aging bread crumb. Furthermore, as amylopectin retrogradation proceeds, moisture migration within the crumb structure occurs, and more and more water is immobilised within amylopectin crystallites. The crystalline hydrate water can no longer plasticise the different networks, which goes hand in hand with increased crumb firmness and decreased crumb resilience, due to a less flexible gluten network. The efficiency of anti-staling amylases can be related to the extent they limit the formation and the strength of the permanent amylopectin network, and the water immobilisation. Conventional alpha-amylases weaken the amylopectin network by cutting the long polymer chains connecting the crystalline regions, but have little effect on amylopectin recrystallisation. In contrast, maltogenic alpha-amylase primarily shortens the amylopectin side chains, thus hindering amylopectin recrystallisation, and the concomitant network formation and water immobilisation.     

Evidence for the Non-Glycoprotein Nature of High Molecular Weight Glutenin Subunits of Wheat

An isolation and purification procedure for wheat high molecular weight glutenin subunits (HMW-GS) involving no steps expected to cause deglycosylation of glycoproteins was developed to allow removal of the maximum amount of carbohydrates not covalently linked to HMW-GS. Flour was defatted and then extracted with 50%n-propanol (50%n-PrOH) to remove arabinogalactans and glucose-containing material. HMW-GS were extracted with 50%n-PrOH containing 5% β-mercaptoethanol, precipitated in 60%n-PrOH, alkylated and recovered by precipitation. The partially purified HMW-GS were separated by cation exchange chromatography and resulting fractions purified by RP–HPLC. The purified HMW-GS contained only 0·1% of glucose (corresponding to 51–59 monosaccharide residues per 100 HMW-GS molecules) and no other amino or neutral sugars. The HMW-GS gave a positive reaction in a periodate–digoxigenin glycan detection assay when labelled in solution (with or without periodate oxidation) but not when labelled directly on-the-blot. HMW-GS expressed inEscherichia coli, a micro-organism without glycosylation capabilities, reacted in an identical way. Possible reasons are given for the difference in results obtained after labelling in solution or on-the-blot. No positive reaction between the purified HMW-GS and mannose-specificGalanthus nivalisagglutinin was observed. The presence of N-acetylglucosamine in HMW-GS has been previously reported²⁰. Since neither mannose nor N-acetylgalactosamine were found in the HMW-GS, and these proteins lack the sequon necessary for N-glycosylation, only O-linked GlcNAc moieties are possible. This modification could not be detected using a galactosyltransferase labelling assay. Taken together these results suggest that HMW-GS are not glycosylated.     

Spontaneous Pancreatic beta cell tumor in the rat. A light and electron microscopic study.

Fine structural study of a pancreatic neoplasm found at autopsy of a 27-month-old female Long-Evans rat showed that the tumor consisted of, and derived from beta cells of the islets of Langerhans.     

Contribution of wheat endogenous and wheat kernel associated microbial endoxylanases to changes in the arabinoxylan population during breadmaking

Wheat kernel associated endoxylanases consist of a majority of microbial endoxylanases and a minority of endogenous endoxylanases. At least part of these enzymes can be expected to end up in wheat flour upon milling. In this study, the contribution of both types of these endoxylanases to changes in the arabinoxylan (AX) population during wheat flour breadmaking was assessed. To this end, wheat flour produced from two wheat varieties with different endoxylanase activity levels, both before and after sodium hypochlorite surface treatment of the wheat kernels, was used in a straight dough breadmaking procedure. Monitoring of the AX population during the breadmaking process showed that changes in AX are to a large extent caused by endogenous endoxylanases, whereas the contribution of microbial endoxylanases to these changes was generally very low. The latter points to a limited contamination of wheat flour with microbial enzymes during milling or to an extensive inactivation of these wheat flour associated microbial endoxylanases by endoxylanase inhibitors, present in wheat flour. When all wheat kernel associated microbial endoxylanases were first washed from the kernels and then added to the bread recipe, they drastically affected the AX population, suggesting that they can have a large impact on whole meal breadmaking.     

A simple and accurate method for determining wheat grain fructan content and average degree of polymerization

An improved method for the measurement of fructans in wheat grains is presented. A mild acid treatment is used for fructan hydrolysis, followed by analysis of the released glucose and fructose with high performance anion exchange chromatography with pulsed amperometric detection (HPAEC-PAD). Not only the amount of fructose set free from fructans but also the released glucose can be quantified accurately, allowing determination of the average degree of polymerization of fructans (DP(av)). Application of the mild acid treatment to different grain samples demonstrated that a correction should be made for the presence of sucrose and raffinose, but not for stachyose or higher raffinose oligosaccharides. The fructan content and DP(av) of spelt flour, wheat flour, and whole wheat flour were 0.6%, 1.2%, and 1.8% of the total weight and 4, 5, and 6, respectively. Validation experiments demonstrate that the proposed quantification method is accurate and repeatable and that also the DP(av) determination is precise.