Review: Amylopectin synthesis and hydrolysis – Understanding isoamylase and limit dextrinase and their impact on starch structure on barley ( Hordeum vulgare ) quality

Barley fermentation on nutritional constituents: structural changes and structure-function correlations

Over the past few years, the demand for healthy grains has become increasingly important. Barley is a basic material for food and animal feed, which is considered an excellent source of multiple nutrients. However, due to limitations in processing techniques, the nutritional attributes of barley have not been completely realized. The functional profile of barley nutrients can be effectively improved by fermentation, due in large to the structural alteration of barley nutrients. The current review outlines the structural changes of barley nutrients during fermentation and summarizes the potential mechanisms by which structural alteration occurs. Correlations between the nutrient structures and their nutritional properties are also discussed. In general, fermentation leads to decreased particle size and modified internal structures of macromolecular nutrients. Enzyme action, pH alterations and interactions between nutrient matrices may contribute to these structural alterations. Barley nutrients with modified structure exhibit enhanced health promoting functions and digestive characteristics, which will further contribute to the utilization of barley resources in the food industry.

Study on the anti-retrogradation of wheat amylopectin by addition of alkali-soluble glutenin

The retrogradation of wheat amylopectin during cold storage is the main reason for the increasing hardness of flour products such as steamed bread, bread and pastries, etc. Addition of gluten protein components is a green, safe, cheap and efficient method to inhibit the retrogradation of wheat amylopectin. In this paper, as being stored at 4 °C for 7 d, retrogradation rate of wheat amylopectin decreased from 55.02 % to 14.37 % after it was mixed with 20 % alkali-soluble glutenin (ASG) at 30 °C for 90 min, a 73.8 % reduction. The infrared results showed that the intensity of bending vibration of water molecules and intra-molecular β-sheet content of ASG decreased during the interaction between amylopectin and ASG. Meanwhile, intermolecular β-sheet and random coil contents of ASG increased. The results of 13C Solid-state NMR indicated that Qβ, Pγ and Lγ of ASG involved in interaction of wheat amylopectin, ASG and molecule of water. Under the optimal conditions, the interaction of wheat amylopectin and ASG began to form spheres containing disulfide bonds, resulting in the attenuation or disappearance of the diffraction peak at 2θ 19.7°, which may be marked as the criterion for the best mixing time of wheat amylopectin and ASG. The retrogradation kinetic index (n) of wheat amylopectin decreased significantly with the addition of ASG and formation of disulfide bond was the key factor. ASG could be potentially used as an anti-retrogradation agent for amylopectin.

Structure of a highly branched galacturonoglucan from fruits of Schisandra chinensis (Turcz.) Baill

A novel galacturonoglucan, named SCP-1, is isolated and purified from Schisandra chinensis fruits. The structure of SCP-1 is systematically investigated by a combination of monosaccharide compositions, absolute M_w, methylation analysis, partial acid hydrolysis, isoamylase degradations, and nuclear magnetic resonance spectroscopy. The structure of SCP-1 is theoretically described as follows: (i) Glc and GalA in a molar ratio of 17:3; (ii) → 4)-α-Glcp-(1→, →4,6)-α-Glcp-(1→, →3,4,6)-α-Glcp-(1→, α-Glcp-(1→, →4)-α-GalAp-6-OMe-(1→, α-GalAp-6-OMe-(1→, β-Glcp-(1→, →6-)-β-Glcp-(1 → and →3,4)-β-Glcp-(1 → in a molar ratio of 48:5:3:3:10:5:12:5:9; (iii) a repeating unit of →4)-α-Glcp-(1 → as a backbone with branched points at C-3 and C-6, substituted by different types of acidic and neutral side chains to form multiple branches; and (iv) a rigid rod configuration deduced from α value of 1.26 in Mark-Houwink equation ([η] = kM^α). Anti-tumor assay investigated the effects of SCP-1 on human HepG2 cancer cell lines in vitro. This is for the first time to report a galacturonoglucan in S. chinensis fruits.

Interfacial Catalysis during Amylolytic Degradation of Starch Granules: Current Understanding and Kinetic Approaches

Enzymatic hydrolysis of starch granules forms the fundamental basis of how nature degrades starch in plant cells, how starch is utilized as an energy resource in foods, and develops efficient, low-cost saccharification of starch, such as bioethanol and sweeteners. However, most investigations on starch hydrolysis have focused on its rates of degradation, either in its gelatinized or soluble state. These systems are inherently more well-defined, and kinetic parameters can be readily derived for different hydrolytic enzymes and starch molecular structures. Conversely, hydrolysis is notably slower for solid substrates, such as starch granules, and the kinetics are more complex. The main problems include that the surface of the substrate is multifaceted, its chemical and physical properties are ill-defined, and it also continuously changes as the hydrolysis proceeds. Hence, methods need to be developed for analyzing such heterogeneous catalytic systems. Most data on starch granule degradation are obtained on a long-term enzyme-action basis from which initial rates cannot be derived. In this review, we discuss these various aspects and future possibilities for developing experimental procedures to describe and understand interfacial enzyme hydrolysis of native starch granules more accurately.

Cluster Size of Amylopectin and Nanosized Amylopectin Fragments Characterized by Pyrene Excimer Formation

Amylopectin from waxy corn and the three nanosized amylopectin fragments (NAFs)—NAF(56), NAF(20), and NAF(8)—from waxy corn starch with a hydrodynamic diameter of 227, 56, 20, and 8 nm, respectively, were randomly labeled with 1-pyrenebutyric acid. The efficiency of these pyrene-labeled amylopectin-based polysaccharides (Py-AbPS) for pyrene excimer formation (PEF) upon diffusive encounter between an excited and a ground-state pyrene increased with increasing concentration of unlabeled NAF(56) in Py-AbPS dispersions in DMSO. Fluorescence decay analysis of the Py-AbPS dispersions in DMSO prepared with increasing [NAF(56)] yielded the maximum number (N_blob^exp) of anhydroglucose units (AGUs) separating two pyrene-labeled AGUs while still allowing PEF. Comparison of N_blob^exp with N_blob^theo, obtained by conducting molecular mechanics optimizations on helical oligosaccharide constructs with HyperChem, led to a relationship between the interhelical distance (d_h-h) in a cluster of oligosaccharide helices, [NAF(56)], and the number of helices in a cluster. It was found that the AbPSs were composed of building blocks made of 3.5 (±0.9) helices that self-assembled into increasingly larger clusters with increasing [NAF(56)]. The ability of PEF-based experiments to yield the cluster size of AbPSs provides a new experimental means to probe the interior of AbPSs at the molecular level.

Fermentation Characteristics of Rye and Sorghum Depending on Water:Feed Ratio

This study was conducted to determine the fermentation characteristics of rye or sorghum mixed with different ratios of water (25%, 37.5%, 50%, 62.5%, and 75% in dry matter (DM)), incubated up to 48 h. The pH of the fermented rye at a DM content of 25% after 24 h had the lowest values (3.57) compared to that at a DM content of 75% (6.42). In fermented sorghum, pH values were lower than 4 already after incubation at 25% DM for 12 h (3.93) in comparison to that at DM content 75% (6.51). The L-lactic acid concentration in the fermented rye with 25% DM content after 24 h was significantly the highest (18.7 g/kg DM), as was that of sorghum with 25% DM content after 24 h (22.2 g/kg DM). Moreover, the acetic acid level in the fermented rye with 25% DM content after 24 h was significantly the highest (3.02 g/kg DM) compared to the other DM contents of fermented rye. Also, in fermented sorghum (25% DM), the acetic acid content was significantly the greatest (1.49 g/kg DM) in comparison to the other DM contents of fermented sorghum. Overall, fermented rye and sorghum containing 25 or 37.5% DM for 24 h and 12 h for rye and sorghum, respectively are sufficient for fermentation to be optimized based on the values of pH and lactic acid content, except for acetic acid content, which may negatively affect the palatability in animals.

Interplay of starch debranching enzyme and its inhibitor is mediated by Redox-Activated SPL transcription factor

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We have first time described that pullulanase inhibitor is under control of SPL transcriptional factor in barley.

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SPL3 mediated transcriptional regulation of pullulanase inhibitor is redox-dependent.

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Antagonistic relationship between pullulanase and its inhibitors is epigenetically guided via miR156 targeted SPL3.

The germination process is of central importance across the cultivated species involving several key enzymes for mobilization of stored food reserves. Pullulanase (PUL), a starch-debranching enzyme, plays an important role in mobilizing stored endosperm food reserves during germination. Pullulanase inhibitor (PULI) hinders PUL’s activity through an unknown mechanism. Barley has one PUL and two PULI genes. During the time-dependent processes of seed germination, only PULI-1 expression shows an antagonistic relationship with that of PUL. Our data have indicated that the expression of PULI-1 is modulated by SPL (Squamosa-promoter-binding Protein Like) transcription factors, known to be targeted by miR156. We show that the binding of recombinant HvSPL3 protein to the PULI-1 promoter occurs under reducing, but not under oxidizing conditions. Replacement of Cys residues with threonine in HvSPL3 abolishes the binding, indicating an essential role of the redox state in the expression of PULI. Our findings may have important implications for the industrial use of starch.

Exploring the factors that affect the themostability of barley limit dextrinase - Inhibitor complex

Barley Limit dextrinase (Hordeum vulgare HvLD) is the unique endogenous starch-debranching enzyme, determining the production of a high degree of fermentation. The activity of HvLD is regulated by an endogenous LD inhibitor protein (LDI). In beer production, free LD is easy to inactivate in mashing process under the condition of high temperature. The binding of LD with LDI protects it against heat inactivation. Exploring the factors affecting the themostability of HvLD-LDI complex is important for beer production. In this work, the themostability of HvLD-LDI complex at different NaCl concentrations and temperatures were explored by molecular dynamics simulation and binding free energy calculation. In NaCl solution, the complex exhibits higher conformational stability at 343 K and 363 K than those in pure water. Root mean square fluctuation (RMSF) analysis identified the thermal sensitive regions of HvLD and LDI. The binding free energy results suggest that the LD-LDI complex is more stable in NaCl solution than those in pure water at high temperature. The residues with high contribution to the complex were identified. The structural and dynamic details will help us to understand the driving forces that lead to the themostability of HvLD-LDI complex at different temperatures and different salt concentrations, which will facilitate the optimization conditions of beer production for maintaining the thermal stability and activity of HvLD.

Application of Mass Spectrometry-Based Proteomics to Barley Research

Barley (Hordeum vulgare) is the fourth most cultivated crop in the world in terms of production volume, and it is also the most important raw material of the malting and brewing industries. Barley belongs to the grass (Poaceae) family and plays an important role in food security and food safety for both humans and livestock. With the global population set to reach 9.7 billion by 2050, but with less available and/or suitable land for agriculture, the use of biotechnology tools in breeding programs are of considerable importance in the quest to meet the growing food gap. Proteomics as a member of the "omics" technologies has become popular for the investigation of proteins in cereal crops and particularly barley and its related products such as malt and beer. This technology has been applied to study how proteins in barley respond to adverse environmental conditions including abiotic and/or biotic stresses, how they are impacted during food processing including malting and brewing, and the presence of proteins implicated in celiac disease. Moreover, proteomics can be used in the future to inform breeding programs that aim to enhance the nutritional value and broaden the application of this crop in new food and beverage products. Mass spectrometry analysis is a valuable tool that, along with genomics and transcriptomics, can inform plant breeding strategies that aim to produce superior barley varieties. In this review, recent studies employing both qualitative and quantitative mass spectrometry approaches are explored with a focus on their application in cultivation, manufacturing, processing, quality, and the safety of barley and its related products.

Brewing with Starchy Adjuncts: Its Influence on the Sensory and Nutritional Properties of Beer

In brewing, the use of cereals (wheat, barley, maize, rice, sorghum, oats, rye or millet), pseudo-cereals (buckwheat, quinoa or amaranth) and tubers (sweet potato), as starch adjuncts, is being promoted for the production of a variety of high-quality beers, from sensory and nutritional points of view. The sensory properties of the obtained beer depend on the characteristics of each adjunct but also on the forms in which the adjunct is added: whole cereal, grits, malted, extruded grains, torrefied and syrup. Among these common forms, the extruded grains (maize or rice) produce a higher content of aroma compounds in beer. From a nutritional point of view, the use of non-conventional starch adjuncts, such as black rice, buckwheat or sweet potato, leads to an increase in the polyphenol content of the beer, and thus, its antioxidant capacity. Cereals such as maize, rice, sorghum or millet are the most promising for the production of gluten-free beers. A close relationship can be developed between the use of adjuncts in the beer industry and the use of commercial enzymes. Advances made by biotechnology to design new enzymes with different functionalities could be associated to a future increase in adjunct usage in brewing.

A comprehensive review of the factors influencing the formation of retrograded starch

The retrogradation of starch is an inevitable change that occurs in starchy food during processing and storage, in which gelatinized starch rearranges into an ordered state. The chain length, proportion and structure of amylose and amylopectin vary in different types of starch granules, and the process is affected by the genes and growth environment of plants. The internal factors play a significant role in the formation of retrograded starch, while the external factors have a direct impact on its structural rearrangement, and the creation of suitable conditions enables food components to affect the rearrangement of starch. Interestingly, water not only directly affects the gelatinization and retrogradation of starch, but also serves as a bridge to deliver the influence of other components that influence retrogradation. Moreover, there are three mechanisms responsible for forming retrograded starch: the migration of starch molecular chains in the starch-water mixed system, the redistribution of water molecules, and the recrystallization kinetics of gelatinized starch. In this paper, the effects of internal factors (amylose, amylopectin, food ingredients) and external factors (processing conditions) on the formation of retrograded starch and the mechanism controlling these effects are reviewed.

Microbial starch debranching enzymes: Developments and applications

Starch debranching enzymes (SDBEs) hydrolyze the α-1,6 glycosidic bonds in polysaccharides such as starch, amylopectin, pullulan and glycogen. SDBEs are also important enzymes for the preparation of sugar syrup, resistant starch and cyclodextrin. As the synergistic catalysis of SDBEs and other starch-acting hydrolases can effectively improve the raw material utilization and production efficiency during starch processing steps such as saccharification and modification, they have attracted substantial research interest in the past decades. The substrate specificities of the two major members of SDBEs, pullulanases and isoamylases, are quite different. Pullulanases generally require at least two α-1,4 linked glucose units existing on both sugar chains linked by the α-1,6 bond, while isoamylases require at least three units of α-1,4 linked glucose. SDBEs mainly belong to glycoside hydrolase (GH) family 13 and 57. Except for GH57 type II pullulanse, GH13 pullulanases and isoamylases share plenty of similarities in sequence and structure of the core catalytic domains. However, the N-terminal domains, which might be one of the determinants contributing to the substrate binding of SDBEs, are distinct in different enzymes. In order to overcome the current defects of SDBEs in catalytic efficiency, thermostability and expression level, great efforts have been made to develop effective enzyme engineering and fermentation strategies. Herein, the diverse biochemical properties and distinct features in the sequence and structure of pullulanase and isoamylase from different sources are summarized. Up-to-date developments in the enzyme engineering, heterologous production and industrial applications of SDBEs is also reviewed. Finally, research perspective which could help understanding and broadening the applications of SDBEs are provided.

The Brewing Industry and the Opportunities for Real-Time Quality Analysis Using Infrared Spectroscopy

Brewing is an ancient process which started in the middle east over 10,000 years ago. The style of beer varies across the globe but modern brewing is very much the same regardless of the style. While there are thousands of compounds in beer, current methods of analysis rely mostly on the content of only several important processing parameters such as gravity, bitterness, or alcohol. Near infrared and mid infrared spectroscopy offer opportunities to predict dozens to hundreds of compounds simultaneously at different stages of the brewing process. Importantly, this is an opportunity to move deeper into quality through measuring wort and beer composition, rather than just content. This includes measuring individual sugars and amino acids prior to fermentation, rather than total °Plato or free amino acids content. Portable devices and in-line probes, coupled with more complex algorithms can provide real time measurements, allowing brewers more control of the process, resulting in more consistent quality, reduced production costs and greater confidence for the future.

Beer Molecules and Its Sensory and Biological Properties: A Review

The production and consumption of beer plays a significant role in the social, political, and economic activities of many societies. During brewing fermentation step, many volatile and phenolic compounds are produced. They bring several organoleptic characteristics to beer and also provide an identity for regional producers. In this review, the beer compounds synthesis, and their role in the chemical and sensory properties of craft beers, and potential health benefits are described. This review also describes the importance of fermentation for the brewing process, since alcohol and many volatile esters are produced and metabolized in this step, thus requiring strict control. Phenolic compounds are also present in beer and are important for human health since it was proved that many of them have antitumor and antioxidant activities, which provides valuable data for moderate dietary beer inclusion studies.

Effects of the Starch Molecular Structures in Barley Malts and Rice Adjuncts on Brewing Performance

Background: Achieving optimal fermentation is challenging when the variation within malt starch structure and enzyme activities are not part of the standard malting specifications. This study explores how the variation of starch and starch amylolytic enzymes in both malts and rice adjuncts affect the mashing and the subsequent yeast fermentation in the laboratory-scale production of beer. Results: The addition of rice adjuncts significantly increased the maltose content whilst reducing the glucose content during mashing. The maltotriose content, released during mashing, was significantly negatively correlated with the total amylose content (r = −0.64, p < 0.05), and significantly negatively correlated with the number of amylopectin longer chains (degree of polymerization 37–100) (r = −0.75, p < 0.01). During fermentation, while the content of maltotriose significantly and positively correlated with both the rate and amount of ethanol production (r = 0.70, p < 0.05; r = 0.70, p < 0.05, respectively), the content of soluble nitrogen in the wort was significantly and positively correlated with both the rate and the amount of ethanol production (r = 0.63, p< 0.05; r = 0.62, p < 0.05, respectively). The amount of amylopectin with longer chains was; however, significantly negatively correlated with the ethanol production (r = −0.06, p < 0.05). Small variations among the ethanol concentration and the rate of ethanol production during fermentation were found with the addition of different rice varieties. Conclusions: The effects of the rice adjuncts on the performance of fermentation depends on the properties of the malt, including the protein modification and malt enzyme activities. This study provides data to improve standard malt specifications in order for brewers to acquire more efficient fermentation, and includes useful molecular structural characterisation.