Xylan-degrading enzymes and arabinoxylan solubilisation in barley cultivars of differing malting quality

The occurrence and structural heterogeneity of arabinoxylan in commercial pilsner beers and their non-alcoholic counterparts

The impact of arabinoxylan (AX) on the brewing process and beer characteristics depends on its content and structure and is often overlooked in research and industry. This paper reports on the occurrence and structural heterogeneity of AX in a set of commercial pilsner beers and their non-alcoholic counterparts. Fractionation by graded ethanol precipitation allowed us to isolate AX-rich fractions from beer with a number-average degree of polymerisation of 4 to 308 and an average degree of substitution in the range of 0.43 to 0.88. Pilsner beers had a higher content of high-molecular-weight AX than their non-alcoholic counterparts. The structural heterogeneity among the various commercial beers differed. By comparing the chemical composition of the beers, differences in beer production methods and ingredient selection were deduced and used to tentatively explain the differences in AX content and structural heterogeneity.

The Role of Endogenous Enzymes during Malting of Barley and Wheat Varieties in the Mitigation of Styrene in Wheat Beer

Knowledge of the biochemical processes responsible for the release of phenolic acids (precursors of vinyl aromatics) during malting is important to find mitigation strategies for the toxicologically relevant styrene (formed from cinnamic acid) in wheat beer. Therefore, grain and malts of four barley and three wheat varieties were screened for the activities of various enzymes and the amounts of nonstarch polysaccharides (to which the phenolic acids are bound to a certain extent). During malting, a very strong degradation of β-glucan, synonymous to a depletion of the cell walls, was found, suggesting that a partial degradation of cell walls cannot have an effect on the release of phenolic acids. In barley malts, water-extractable arabinoxylan contents were between 0.59 and 0.79 g/100 g dm and in wheat malts between 0.93 and 1.51 g/100 g dm. Additionally, higher soluble ferulic acid contents in wheat wort compared to barley wort indicated that the degradation of nonstarch polysaccharides has an impact on the release of phenolic acids. For the feruloyl esterase, higher activities were found in malts of the barley varieties. However, this fact was not reflected by the free phenolic acid contents in those malts. Correlation coefficients between the protease activity and the feruloyl esterase, α- and β-amylase, and β-glucanase activities were proven to be insignificant, highlighting that the protease activity had no effect on the activities of these other enzymes.

β-Glucan Degradation During Malting of Different Purpose Barley Varieties

The aim of this study was to investigate the possibility of predicting the concentration of β-glucan from starting barley and malt, as well as malt and wort for different types and purpose of barley groups. The strength of the correlation between types and purpose of barley groups was determined between the values of β-glucans and other indicators of cytolytic degradation. Statistically significant correlations were obtained for β-glucans in barley-malt (r = 0.9717) and barley-wort (r = 0.9998) for brewing (B w-tr) and brewing/feed winter two-row (B/Fe w-tr) varieties, and for brewing/brewing feed/feed spring varieties (B/B-Fe/Fe w-tr) between barley and Δm (Δm = β-glucan difference between barley and malt) (r = 0.8779). For the dual-purpose varieties (B/Fe w-tr), a strong correlation for β-glucans was found between malt and wort (r = 0.8188), malt and Δm* (Δm* = % of degraded β-glucan in malt in regard to the starting β-glucan in barley) (r = −0.9099), as well as Δm and Δm* (r = 0.9951). The results indicate that the starting concentration of β-glucan in barley and malt can be used as predictors of their concentration in wort only in brewing and dual-purpose (brewing-feed) varieties.

Genetic variation of HvXYN1 associated with endoxylanase activity and TAX content in barley (Hordeum vulgare L.)

BACKGROUND

Endo-β-1,4-xylanase1 (EA), the key endoxylanase in plants, is involved in the degradation of arabinoxylan during grain germination. In barley (Hordeum vulgare L.), one gene (HvXYN-1) that encode a endo-beta-1,4-xylanase, has been cloned. However, the single nucleotide polymorphisms (SNPs) that affect the endoxylanase activity and total arabinoxylan (TAX) content have yet to be characterized. The investigation of genetic variation in HvXYN1 may facilitate a better understanding of the relationship between TAX content and EA activity in barley.

RESULTS

In the current study, 56 polymorphisms were detected in HvXYN1 among 210 barley accessions collected from 34 countries, with 10 distinct haplotypes identified. The SNPs at positions 110, 305, 1045, 1417, 1504, 1597, 1880 bp in the genomic region of HvXYN1 were significantly associated with EA activity (P < 0.0001), and the sites 110, 305, and 1045 were highly significantly associated with TAX content. The amount of phenotypic variation in a given trait explained by each associated polymorphism ranged from 6.96 to 9.85%. Most notably, we found two variants at positions 1504 bp and 1880 bp in the second exon that significantly (P < 0.0001) affected EA activity; this result could be used in breeding programs to improve beer quality. In addition, African accessions had the highest EA activity and TAX content, and the richest germplasm resources were from Asia, indicating the high potential value of Asian barley.

CONCLUSION

This study provided insight into understanding the relationship, EA activity, TAX content with the SNPs of HvXYN1 in barley. These SNPs can be applied as DNA markers in breeding programs to improve the quality of barley for beer brewing after further validation.

Impact of Cereal Seed Sprouting on Its Nutritional and Technological Properties: A Critical Review

Sprouting induces activation and de novo synthesis of hydrolytic enzymes that make nutrients available for plant growth and development. Consumption of sprouted grains is suggested to be beneficial for human health. Positive consumer perceptions about sprouted cereals have resulted in new food and beverage product launches. However, because there is no generally accepted definition of "sprouting," it is unclear when grains are to be called sprouted. Moreover, guidelines about how much sprouted grain material food products should contain to exert health benefits are currently lacking. Accordingly, there is no regulatory base to develop appropriate food labeling for "sprouted foods." This review describes the nutritional and technological properties of sprouted grains in relation to processing conditions and provides guidelines to optimize sprouting practices in order to maximize nutritive value. Relatively long sprouting times (3 to 5 days) and/or high processing temperatures (25 to 35 °C) are needed to maximize the de novo synthesis and/or release of plant bioactive compounds. Nutrient compositional changes resulting from sprouting are often associated with health benefits. However, supportive data from clinical studies are very scarce, and at present it is impossible to draw any conclusion on health benefits of sprouted cereals. Finally, grains sprouted under the above-mentioned conditions are generally unfit for use in traditional food processing and it is challenging to use sprouted grains as ingredients without compromising their nutrient content. The present review provides a basis for better defining what "sprouting" is, and to help further research and development efforts in this field as well as future food regulations development.

Impact of Preharvest Sprouting on Endogenous Hydrolases and Technological Quality of Wheat and Bread: A Review

The cereal-based food industry faces the challenge to produce food of high and uniform quality to meet consumer demands. However, adverse weather conditions, including prolonged and repeated rainfall, before harvest time evoke germination of the kernels in the ear of the parent plant, which is known as preharvest sprouting (PHS). PHS results in the production of several hydrolytic enzymes in the kernel, which decreases the technological quality of wheat and causes problems during processing of the flour into cereal-based products. Therefore, wheat that is severely sprouted in the field is less suitable for products for human consumption, and is often discounted to animal feed. Up till now, most knowledge on PHS is obtained by research on laboratory-sprouted wheat as a proxy for field-sprouted wheat. Knowledge on PHS in the field itself is more scarce. This review gives a comprehensive overview of the recent findings on PHS of wheat in the field, compared to knowledge on controlled sprouting. The physiological and functional changes occurring in wheat during PHS and their impact on wheat and bread quality are discussed. This review provides a useful background for further research concerning the potential of field-sprouted wheat to be used as raw material in the food industry.

Morphology, Carbohydrate Distribution, Gene Expression, and Enzymatic Activities Related to Cell Wall Hydrolysis in Four Barley Varieties during Simulated Malting

Many biological processes, such as cell wall hydrolysis and the mobilisation of nutrient reserves from the starchy endosperm, require stringent regulation to successfully malt barley (Hordeum vulgare) grain in an industrial context. Much of the accumulated knowledge defining these events has been collected from individual, unrelated experiments, and data have often been extrapolated from Petri dish germination, rather than malting, experiments. Here, we present comprehensive morphological, biochemical, and transcript data from a simulated malt batch of the three elite malting cultivars Admiral, Navigator, and Flagship, and the feed cultivar Keel. Activities of lytic enzymes implicated in cell wall and starch depolymerisation in germinated grain have been measured, and transcript data for published cell wall hydrolytic genes have been provided. It was notable that Flagship and Keel exhibited generally similar patterns of enzyme and transcript expression, but exhibited a few key differences that may partially explain Flagship's superior malting qualities. Admiral and Navigator also showed matching expression patterns for these genes and enzymes, but the patterns differed from those of Flagship and Keel, despite Admiral and Navigator having Keel as a common ancestor. Overall (1,3;1,4)-β-glucanase activity differed between cultivars, with lower enzyme levels and concomitantly higher amounts of (1,3;1,4)-β-glucan in the feed variety, Keel, at the end of malting. Transcript levels of the gene encoding (1,3;1,4)-β-glucanase isoenzyme EI were almost three times higher than those encoding isoenzyme EII, suggesting a previously unrecognised importance for isoenzyme EI during malting. Careful morphological examination showed that scutellum epithelial cells in mature dry grain are elongated but expand no further as malting progresses, in contrast to equivalent cells in other cereals, perhaps demonstrating a morphological change in this critical organ over generations of breeding selection. Fluorescent immuno-histochemical labelling revealed the presence of pectin in the nucellus and, for the first time, significant amounts of callose throughout the starchy endosperm of mature grain.

Effects of variety and steeping conditions on some barley components associated with colonic health

BACKGROUND

Butyric acid is produced by degradation of dietary fibre by microbiota and is crucial for maintaining a healthy colon. The physicochemical properties are important for butyric acid formation, and this study aimed to evaluate the use of malting to tailor the functional characteristics of barley dietary fibre. The effect of different steeping conditions was evaluated in laboratory-scale malting experiments with three different barley varieties.

RESULTS

Steeping at 35°C and with 0.4 % (v/v) lactic acid resulted in a higher content of β-glucan and soluble fibre in malts than in those steeped at lower temperature and lower lactic acid concentration. Resistant starch increased, whereas the content of soluble arabinoxylan was lower. Dietary fibre components in Tipple were more affected by steeping conditions than the other varieties. The total contents of iron, phytate and amylose were little influenced by steeping conditions.

CONCLUSION

The selection of steeping conditions during malting influences composition and the characteristics of dietary fibre in barley. However, the choice of barley variety is also important for tailoring of functional ingredients beneficial for colonic health. © 2016 The Authors. Journal of the Science of Food and Agriculture published by JohnWiley & Sons Ltd on behalf of Society of Chemical Industry.

Purification and characterisation of arabinoxylan arabinofuranohydrolase I responsible for the filterability of barley malt

Dan'er is a widely grown malt barley cultivar in China, but its filterability defects have severely impeded its application in beer brewing. Previous investigations have suggested that we should identify the malt filterability correlated proteins, one of which was postulated to be arabinoxylan arabinofuranohydrolase I (AXAH-I). To verify this hypothesis, we purified AXAH-I from Dan'er malt, characterised its enzyme performance, and investigated its influence on filterability by adding different amounts of purified enzyme to the mash. With 6 mU g(-1) malt AXAH-I supplemented, the wort separation rate increased by 31.8%, viscosity decreased by 3.6%, and the endosperm reserve contents declined concomitantly. Unexpectedly, the wort turbidity increased with increasing AXAH-I. We also tried to optimise the use of currently available commercial enzyme products for filterability improvement in beer brewing, by supplementing them with purified AXAH-I and β-amylase. AXAH-I could be a functional component for novel commercial enzyme products in the beer industry.

Content and molecular weight of water-extractable arabinoxylans in wheat malt and wheat malt-based wort with different Kolbach indices

BACKGROUND

Arabinoxylans (AXs) are partially water-extractable polymers that cause problems of viscosity and filterability during beer brewing. This study investigated the effects of Kolbach index (KI) on water-extractable AXs (WEAXs).

RESULTS

KI had positive correlations with extract (r = 0.845) and free amino nitrogen (FAN) (r = 0.958). The contents of malt WEAXs (WEAXsm), total AXs and wort AXs (WAXs) were 10.8-11.6 g kg⁻¹, 57.5-60.8 g kg⁻¹ and 137.5-140.5 mg per 100 mL respectively and the corresponding arabinose/xylose (A/X) ratios were 0.52-0.56, 0.55-0.62 and 0.48-0.50. The molecular weight (Mw) ranged from 4.92 × 10⁴ to 6.93 × 10⁴ Da for WEAXsm and from 1.24 × 10⁴ to 2.90 × 10⁴ Da for WAXs. KI had negative correlations with the average degree of polymerization (avDP) of malt (r = -0.877) and wort (r = -0.978). Wort viscosity showed a positive correlation with the Mw of WEAXsm (Mwm) (r = 0.821).

CONCLUSION

Increasing KI can promote the degradation of the xylan backbone, while it cannot affect the branching of the polymer chain and the content and Mw of WEAXs.

Proteomic analysis of differences in barley (Hordeum vulgare) malts with distinct filterability by DIGE

Filterability is an essential quality parameter of barley malt and significantly impacts productive efficiency and quality of beer. In the study, differences of metabolic capability, rather than of initial contents of macromolecules in barleys, were found to be the main reason for malt filterability gap between the widely used cultivars Dan'er and Metcalfe in China. Comparative proteomics based on fluorescent difference gel electrophoresis (DIGE) was employed to quantitatively analyze proteins of four commercial malts belonging to the two cultivars, and 51 cultivar-differential spots were identified to 40 metabolic proteins by MALDI-TOF/TOF mass spectrometry, mainly including hydrolases and pathogen-related proteins. According to their function analysis and abundance comparison between cultivars, filterability-beneficial and -adverse proteins were putatively proposed. Two most remarkable differential proteins, β-amylase and serpin Z7, were further investigated to verify their effects on Dan'er malt filterability. These results provide biological markers for barley breeders and maltsters to improve malt filterability.

BIOLOGICAL SIGNIFICANCE

To the best of our knowledge, this is the first report of comprehensive investigation of metabolic proteins related to wort filterability of barley malts, and sheds light on clues for filterability improvement. Visible differences in the expression level of metabolic proteins between Dan'er and Metcalfe malts using 2D-DIGE signify a valuable tool for cultivar comparison, illustration of key proteins responsible for filterability and even other qualities of barley malts. And with these explorations on biomarkers of malt filterability and other aspects, there will be higher efficiency and quality of beer brewing, less application of exogenous hydrolases and more expending market for Chinese malting barleys. This article is part of a Special Issue entitled: Translational Plant Proteomics.

Impact of low hydration of barley grain on β-glucan degradation and lipid transfer protein (LTP1) modifications during the malting process

One of the objectives of the malting industry is to reduce the energy cost during kilning without major effect on malt quality. In this study, the impact of a low hydration steeping process on lipid transfer protein (LTP1) modifications and β-glucan breakdown was evaluated in low (LH) and high (HH) hydrated malts. LTP1 modifications analyzed by MS/MS revealed acylation, glycation, and disulfide bond breakage in both LH and HH malts. LTP1 free amine content measurement and fluorescence of Maillard protein adducts revealed no significant difference between LH and HH malts. Immunolabeling of LTP1 during malting highlighted the diffusion of the protein from the aleurone layer to the endosperm at the end of steeping in both LH and HH malts. By contrast, a significant higher amount of β-glucans was measured in LH malts after five days of germination, whereas no significant difference between LH and HH malts was revealed through immunostaining of β-glucans or evaluation of the endosperm integrity after seven days of germination. The possibility to reduce the effects of a low hydration steeping process on β-glucan hydrolysis by increasing germination time was discussed.

Post-translational processing of beta-d-xylanases and changes in extractability of arabinoxylans during wheat germination

Endo-1,4-beta-d-xylanase (EC 3.2.1.8, beta-d-xylanase) activity, and arabinoxylan (AX) level and extractability were monitored for the first time simultaneously in wheat kernels (Triticum aestivum cv. Glasgow) up to 24 days post-imbibition (DPI), both in the absence and presence of added gibberellic acid (GA). Roughly three different stages (early, intermediate and late) can be discriminated. Addition of GA resulted in a faster increase of water extractable arabinoxylan (WEAX) level in the early stage (up to 3-4 DPI). This increase was not accompanied by the discernible presence of homologues of the barley X-I beta-d-xylanase as established by immunodetection. This suggests that other, yet unidentified beta-d-xylanases operate in this early time window. The intermediate stage (up to 13 DPI) was characterized by the presence of unprocessed 67 kDa X-I like beta-d-xylanase, which was much more abundant in the presence of GA. The occurrence of higher levels of the unprocessed enzyme was related with higher beta-d-xylanase activities and a further increase in WEAX level, pointing to in vivo activity of the unprocessed 67 kDa beta-d-xylanase. During the late stage (up to 24 DPI) gradual processing of the 67 kDa beta-d-xylanase occurred and was associated with a drastic increase in beta-d-xylanase activity. Up to 120-fold higher activity was recorded at 24 DPI, with approx. 85% thereof originating from the kernel remnants. The WEAX level decreased during the late stage, suggesting that the beta-d-xylanase is processed into more active forms to achieve extensive AX breakdown.

Hagberg falling number and the nutritional value of wheat in broiler chicken diets

1. Three experiments were performed to study the effect of Hagberg falling number in wheat on performance, nutrient digestibility and AMEN in broilers. In two experiments, one hard and one soft wheat variety were used to study the interaction between falling number and hardness of wheat with regard to nutritional value. In these experiments, wheat batches with high falling number when harvested under dry conditions were used in broiler diets. 2. Wheat with reduced falling numbers (high, medium and low) was obtained by controlled germination. In the third experiment, wheat with reduced falling numbers were obtained by delayed harvesting times. 3. In each experiment, a total of 4 cereal batches with different falling numbers from each wheat variety were used to produce corresponding experimental diets with wheat as the major ingredient. Each diet was fed to broiler chickens ad libitum from d 1 to d 17 of age. 4. There was no consistent effect of falling number on performance. Low falling number did not improve feed utilisation or AMEN compared to the original wheat, despite a higher AMEN associated with higher starch digestibility. This phenomenon was not observed after reduction of falling number by delayed harvesting. Apparently, natural reduction of falling number resulted in enhanced degradation of arabinoxylans compared to controlled germination.