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1.
Dornez E Joye IJ Gebruers K Delcour JA Courtin CM 《Journal of agricultural and food chemistry》2006,54(11):4028-4034
The endoxylanases associated with wheat kernels consist of wheat endogenous endoxylanases on one hand and kernel-associated microbial endoxylanases on the other hand. Assessment of their presence, based on analysis of their enzymic activity, can be expected to be hampered by the presence in wheat of high levels of endogenous endoxylanase inhibitors, which are able to inhibit the wheat-kernel-associated microbial endoxylanases. On the basis of preliminary experiments aimed at clarifying the distribution of the wheat-associated endoxylanases, a method to estimate total endoxylanase activities in wheat kernels was developed. Extensive washing of wheat kernels with universal buffer of pH 8.0 provided near-quantitative separation of the microbial endoxylanases located on the surface of wheat kernels from the endogenous endoxylanases and endoxylanase inhibitors located in such kernels. The microbial or endogenous nature of the endoxylanases was confirmed by making use of the inhibition specificity of endoxylanase inhibitors. Determination of the endoxylanase activity in the washing liquid, corresponding to the microbial endoxylanase population, and the washed kernels, corresponding to the endogenous endoxylanase population, allowed estimation of the total endoxylanase activities associated with the wheat kernel. Results showed that microbial endoxylanases can account for over 90% of the total wheat-associated endoxylanase activity and that the latter can be at least 5 times higher than the apparent endoxylanase activity. 相似文献
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Dornez E Gebruers K Wiame S Delcour JA Courtin CM 《Journal of agricultural and food chemistry》2006,54(22):8521-8529
To gain insight into the distribution of arabinoxylans (AX), endoxylanases, and endoxylanase inhibitors in industrial wheat roller milling, all streams, that is, 54 flour fractions, 4 bran fractions, and the germ, were analyzed for ash, starch, and protein contents, alpha-amylase activity levels, total (TOT-AX) and water-extractable arabinoxylan (WE-AX) contents, endoxylanase activity levels, and endoxylanase inhibitor (TAXI and XIP) contents. In general, bran fractions were significantly richer in TOT-AX and WE-AX contents, endoxylanase activity levels, and endoxylanase inhibitor contents than germ and, even more so, than flour fractions. In the 54 different flour fractions, minimal and maximal values for TOT-AX and WE-AX contents differed by ca. 2-fold, whereas they differed by ca. 15-fold for endoxylanase activity levels. The latter were positively correlated with ash and negatively correlated with starch content, suggesting that the endoxylanase activity in flour is strongly influenced by the level of bran contamination. TAXI contents in the flour fractions varied ca. 4-fold and were strongly correlated with bran-related parameters such as ash content and enzyme activity levels, whereas XIP contents varied ca. 3-fold and were not correlated with any of the parameters measured in this study. The results can be valuable in blending and optimizing wheat flour fractions to obtain flours with specific technological and nutritional benefits. 相似文献
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Valerie Van Craeyveld Emmie Dornez Ulla Holopainen Emilia Selinheimo Kaisa Poutanen Jan A. Delcour Christophe M. Courtin 《Cereal Chemistry》2010,87(4):283-291
Wheat bran‐derived arabinoxylan‐oligosaccharides (AXOS) recently have been shown to potentially exert prebiotic effects. In this study, 15 bran samples obtained by milling different wheat cultivars were treated with xylanases from Hypocrea jecorina (XHJ), Aspergillus aculeatus (XAA), and Pseudoalteromonas haloplanktis (XPH) to assess the effect of bran source and xylanase properties on the AXOS yield and structure. The total arabinoxylan (AX) extraction yield was higher with XHJ (8.2–10.7%) and XAA (8.2–10.8%) than with XPH (6.9–9.5%). Irrespective of the enzyme, a significant negative correlation was observed between extraction yield and arabinose to xylose (A/X) ratio of bran AX (r = –0.7), but not between yield and bran AX level. The A/X ratio of the extracted material was 0.27–0.34 for all bran samples and all enzymes, which combined with yield data and microscopic analysis, indicated primary hydrolysis of aleurone and nucellar epidermis AX. The average degree of polymerization (avDP) of the extracted AX was very low for all enzymes (2–3), owing to the release of high levels of monomeric arabinose and xylose. The release of these monosaccharides could be ascribed to 1) the activity of wheat bran‐associated enzymes (arabinofuranosidases and xylosidases); 2) the hydrolytic properties of the xylanases themselves; and 3) the presence of xylosidases as contaminations in enzyme preparation, in that order of importance. Heat treatment of bran before xylanase treatment significantly decreased the levels of monomeric arabinose and xylose in the extract, without affecting the extraction yield, resulting in a higher avDP of 3–7, thus yielding true AXOS. Overall, for AXOS production, wheat cultivars with a low bran A/X ratio of the AX are preferable as starting materials, and inactivation of bran‐associated enzymes before incubation is desirable. The XHJ xylanase was the best enzyme for wheat bran‐derived AXOS production. 相似文献
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Dornez E Gebruers K Cuyvers S Delcour JA Courtin CM 《Journal of agricultural and food chemistry》2007,55(17):7149-7155
The impact of varying levels of endoxylanase activity in wheat flour on arabinoxylan (AX) in mixed and rested dough was studied using eight industrially milled wheat flour fractions with varying endoxylanase activity levels. Analysis of the levels of reducing end xylose (RX) and solubilized AX (S-AX) formed during mixing and resting and their correlation with the endoxylanase activity in the flour milling fractions showed that solubilization of AX during the mixing phase is mainly due to mechanical forces, while solubilization of AX during resting is caused by endoxylanase activity. Moreover, solubilization of AX during the dough resting phase is more outspoken than that during the mixing phase. Besides endoxylanase activity, there were significant xylosidase and arabinofuranosidase activities during the dough resting phase. The results indicate that wheat flour-associated endoxylanases can alter part of the AX in dough, thereby changing their functionality in bread making and potentially affecting dough and end product properties. 相似文献
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Quantification of Wheat TAXI and XIP Type Xylanase Inhibitors: A Comparison of Analytical Techniques
Kurt Gebruers Johnny Beaugrand Evi Croes Emmie Dornez Christophe M. Courtin Jan A. Delcour 《Cereal Chemistry》2008,85(5):586-590
To date, three different techniques are available for the quantification of TAXI and XIP type proteinaceous xylanase inhibitors in cereals. A first approach is based on the determination of the residual activities of xylanases (also referred to as endo‐1,4‐β‐d ‐xylanases, EC 3.2.1.8), which are specifically inhibited by these inhibitors, after incubation with sample containing the inhibitors. The other two techniques are immunoblotting and ELISA which are based on recognition of TAXI and XIP proteins by specific antibodies. TAXI, as well as XIP, are easily extracted by aqueous buffers. Hence, the large difference in their concentrations (2–10 fold higher for XIP than for TAXI in whole meal) is not caused by differences in extractability. The repeatabilities of the three techniques are comparable. The intra‐assay and inter‐assay coefficients of variation were 6–7 and 10–14%, respectively, which is in the range of values described for methods to quantify other compounds in plant and animal tissues. The three methods give comparable results, suggesting they have similar accuracies. The choice of the technique to be used will depend not only on the sensitivity and dynamic range needed, but also on its technical simplicity and the need for high‐throughput analysis. 相似文献
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Emmie Dornez Priscilla Verjans Willem F. Broekaert Astrid M. Cappuyns Jan F. Van Impe Filip Arnaut Jan A. Delcour Christophe M. Courtin 《Cereal Chemistry》2011,88(2):124-129
In situ enrichment of bread with arabinoxylan‐oligosaccharides (AXOS) through enzymic degradation of wheat flour arabinoxylan (AX) by the hyperthermophilic xylanase B from Thermotoga maritima (rXTMB) was studied. The xylanolytic activity of rXTMB during breadmaking was essentially restricted to the baking phase. This prevented problems with dough processability and bread quality that generally are associated with thorough hydrolysis of the flour AX during dough mixing and fermentation. rXTMB action did not affect loaf volume. Bread with a dry matter AXOS content of 1.5% was obtained. Further increase in bread AXOS levels was achieved by combining rXTMB with xylanases from Pseudoalteromonas haloplanktis or Bacillus subtilis. Remarkably, such a combination synergistically increased the specific bread loaf volume. Assuming an average daily consumption of 180 g of fresh bread, the bread AXOS levels suffice to provide a substantial part of the AXOS intake leading to desired physiological effects in humans. 相似文献
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Study of grain cell wall structures by microscopic analysis with four different staining techniques 总被引：1，自引：0，他引：1
Emmie Dornez Ulla HolopainenSven Cuyvers Kaisa PoutanenJan A. Delcour Christophe M. CourtinEmilia Nordlund 《Journal of Cereal Science》2011,54(3):363-373
Four different grain cell wall staining techniques were compared. Two techniques specifically detected arabinoxylan (AX). The first technique used a xylanase probe, while the other one was based on immunolabeling of AX using monoclonal antibodies. The two other staining techniques, one based on Calcofluor and the other on immunolabeling using monoclonal antibodies, stained mixed-linkage β-glucan. Cell walls of wheat, barley, oat and rye grains, differing both in content and location of AX and β-glucan, were examined. The staining methods were complementary to each other in revealing the location and distribution of the major cereal dietary fiber components AX and β-glucan in the different grains. AX was mostly concentrated in nucellar epidermis and aleurone cells, whereas β-glucan was concentrated more in subaleurone cells. Furthermore, in the case of barley and rye, the endosperm cell walls also contained high amounts of β-glucan. Interestingly, β-glucan in rye and barley endosperm cell walls was located adjacent to the cell contents, suggesting that it is not evenly distributed in the endosperm cell walls. The results give new insight into the structure of the cereal dietary fiber complex. Further development of microscopic techniques will help in elucidating the cereal cell wall structure even in more detail. 相似文献
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Dornez E Cuyvers S Gebruers K Delcour JA Courtin CM 《Journal of agricultural and food chemistry》2008,56(6):2246-2253
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. 相似文献