Cereal Starches Research Articles

Lytic polysaccharide monooxygenases and other oxidative enzymes are abundantly secreted by Aspergillus nidulans grown on different starches

BackgroundStarch is the second most abundant plant-derived biomass and a major feedstock in non-food industrial applications and first generation biofuel production. In contrast to lignocellulose, detailed insight into fungal degradation of starch is currently lacking. This study explores the secretomes of Aspergillus nidulans grown on cereal starches from wheat and high-amylose (HA) maize, as well as legume starch from pea for 5 days.ResultsAspergillus nidulans grew efficiently on cereal starches, whereas growth on pea starch was poor. The secretomes at days 3–5 were starch-type dependent as also reflected by amylolytic activity measurements. Nearly half of the 312 proteins in the secretomes were carbohydrate-active enzymes (CAZymes), mostly glycoside hydrolases (GHs) and oxidative auxiliary activities (AAs). The abundance of the GH13 α-amylase (AmyB) decreased with time, as opposed to other starch-degrading enzymes, e.g., the GH13 AmyF, GH15 glucoamylases (GlaA and GlaB), and the GH31 α-glucosidase (AgdE). Two AA13 LPMOs displayed similar secretion patterns as amylolytic hydrolases and were among the most abundant CAZymes. The starch-active AnLPMO13A that possesses a CBM20 carbohydrate-binding module dominated the starch-binding secretome fraction. A striking observation is the co-secretion of several redox-active enzymes with the starch-active AA13 LPMOs and GHs, some at high abundance. Notably nine AA9 LPMOs, six AA3 sub-family 2 (AA_2) oxidoreductases, and ten AA7 glyco-oligosaccharide oxidases were identified in the secretomes in addition to other non-CAZyme oxidoreductases.ConclusionsThe co-secretion and high abundance of AA13 LPMOs are indicative of a key role in starch granule deconstruction. The increase in AA13 LPMO abundance with culture time may reflect accumulation of a more resistant starch fraction towards the later stages of the culture. The identification of AmyR sites upstream AA13 LPMOs unveils co-regulation of LPMOs featuring in starch utilization. Differential deployment of amylolytic hydrolases and LPMOs over time suggests additional regulatory mechanisms. The abundant co-secretion of distinct AA3 and AA7 oxidoreductases merits further studies into their roles and possible interplay with LPMOs and other enzymes in the deconstruction of starchy substrates. The study reports for the first time the biological significance of LPMOs in starch degradation and the temporal interplay between these and amylolytic hydrolases.Electronic supplementary materialThe online version of this article (doi:10.1186/s13068-016-0604-0) contains supplementary material, which is available to authorized users.

Pichia pastoris에서 생산된 인체 췌장 α-아밀레이스 동질효소의 촉매활성에 대한 염소이온의 영향

HPA는 식품으로 섭취되는 녹말을 분해하는데 있어서 매우 중요한 역할을 수행하는 효소이기 때문에 HPA 효소 활성의 억제는 당뇨와 비만과 같은 질환의 예방과 치료에 있어서 의미를 가진다. 따라서 HPA는 당뇨병 치료와 비만 예방을 위한 새로운 식 의약품 소재 개발을 위한 주요 타깃 효소 중 하나이며, 새로운 소재의 개발을 위해서는 HPA의 반응 메커니즘을 비롯하여 천연 기질 분해 특성에 대한 이해가 반드시 필요하다. 본 연구에서는 HPA의 동질효소 중 연구가 거의 진행되지 않은 HPA II에 대한 효소 특성화를 진행하고자 P. pastoris 시스템을 이용하여 재조합 HPA II를 생산하였으며, 녹말 분해와 관련된 효소적 특성을 분석하였다. HPA II는 10 mM NaCl까지 농도 의존적으로 효소활성이 증가하였으며, 최적 활성을 위한 pH는 0 mM NaCl 조건에서 pH 6.5이었으나 10 mM NaCl조건에서 pH 7.5로 이동하는 특성을 보였으며, 이는 HPA I을 포함하는 염소이온 의존형 아밀레이스가 나타내는 전형적인 특징이다. 염소이온 존재 시 최적 pH가 염기성 pH 영역으로 이동하는 것은 염소 이온과 효소의 결합에 의해 HPA II의 산/염기 촉매 잔기의 <TEX>$pK_a$</TEX>값이 커진다는 것을 의미하며, 염소이온을 첨가하였을 때 녹말에 대한 가수분해 활성의 증대 정도가 산성 pH 영역보다 염기성 pH 영역에서 두드러지게 나타났다는 점이 이를 뒷받침하였다. 반응속도론적 분석 결과에 따르면 염소이온 존재 시 효소활성의 증대는 대부분 전환수(turnover number)의 증대에 의한 것으로 나타났으며, 가용성 녹말 보다 곡류 녹말에 대한 전환수의 증대가 크게 나타났다. 염소이온은 활성의 증대뿐만 아니라 고농도의 기질 조건에서 기질에 의한 효소 활성 억제 양상을 심화시키는 것으로 나타났다. 결론적으로 HPA II의 특징은 HPA I과 거의 유사한 경향을 나타내었으며, 염소이온 첨가여부에 따른 HPA II의 가수분해활성 결과를 바탕으로 향 후 HPA에 대한 곡류 녹말 가수분해 활성 억제제 개발을 위한 연구를 추진할 계획이다. The AMY2B gene, encoding human pancreatic <TEX>${\alpha}$</TEX>-amylase isozyme (HPA II), was expressed in Pichia pastoris, and the effects of chloride ions on HPA II activity toward starch substrates were investigated. As seen with chloride ion-dependent <TEX>${\alpha}$</TEX>-amylases-including HPA I, the isozyme of HPA II-chloride ions increased enzyme activity and shifted the optimal pH to an alkaline pH. The activity enhancement by chloride was more significant at pH 8 than that at pH 6, suggesting that the protonation state of the general acid/base catalyst of HPA II was important for the hydrolysis of starches at an alkaline pH because of the increase in its <TEX>$pK_a$</TEX> by chloride ions. The turnover values for cereal starches as the substrates markedly increased in the presence of chloride by up to 7.2-fold, whereas that for soluble starch increased by only 1.7-fold. Chloride inhibited substrate hydrolysis at high substrate concentrations, with <TEX>$K_i$</TEX> values ranging from 6 to 15 mg/mL.

Designer Plants for Biofuels: A Review

Injudicious over-consumption of fossil fuels over the last century has generated an imbalance in the carbon cycle, dramatically increasing atmospheric carbon dioxide and contributing to climate change. Much of the released carbon is ancient, accumulating in the earth’s crust in the form of oil, coal or methane gas over millions of years. In contrast, the carbon in biofuels has only recently been sequestered from the atmosphere as a result of photosynthesis. From this perspective, the release of carbon dioxide from biofuels can be viewed as carbon neutral making biofuels particularly attractive as an energy source. First generation biofuels relied primarily on cereal starch as a source of glucose for biofuel production, a practice that faced scrutiny due to its competition for human food, its impact on biodiversity and reliance on chemical fertilizers and fossil fuels for harvest. Second generation biofuels focused on lignocellulosic waste as a carbon resource for bioenergy production. Cellulosic biomass is the most abundant of the renewable resources and represents an enormous storehouse of sugars. However, plant cell walls are chemically complex, heterogeneous structures that have evolved to counter the process of enzymatic digestion. The layered structure with cross-linkages among cellulose, xylan and lignin are examples of the recalcitrant moieties that resist enzymatic breakdown. The use of exogenous enzymes or chemical treatment to weaken these barriers is expensive and typically achieves only partial hydrolysis. Recent advancements in plant genetic engineering have demonstrated the potential to design plants for improved cell wall deconstruction as well as to produce cell wall carbohydrases within the plant biomass. These technologies offer significant promise to lower the cost of production of biofuels from lignocellulosic biomass. In this review, we provide summary of recent research efforts focused on improving the biomass characteristics of plants for biofuel production through alteration of the major cell wall biosynthesis genes or pathways. Keywords: Biofuel, biomass, cell wall, genetic engineering, lignin, lignocellulose, transcription factor.

Alterations of starch structure lead to increased resistant starch of steamed rice: Identification of high resistant starch rice lines

The development of low calorie foods to aid obesity control is a growing area of research. Among these, resistant starch (RS) in cereals has beneficial effects on reducing colon cancer rate and better fatty acid composition as well as lowering calories. Rice contains digestible starch and indigestible RS, the proportions of which are affected by starch biosynthetic enzymes. Rice lines that carry mutations in starch biosynthesis genes may have high levels of RS. In this study, percentage RS and non-digested component values were determined in steamed rice from several rice lines. These include several high-amylose indica rice cultivars, and lines carrying mutations in the starch synthase (SS) IIIa and/or branching enzyme (BE) IIb genes. High RS rice lines contained high levels of non-digested component. RS values ≤ 4% correlated with apparent amylose content. RS values of BEIIb-deficient mutant lines were particularly high (15 ≤ RS ≤ 35%), and were correlated with the amount of amylopectin long chains. Among rice lines used in this study, be2b mutant lines having large portions of amylopectin long chains were the best candidates for high RS rice foods.

The development of plant food processing in the Levant: insights from use-wear analysis of Early Epipalaeolithic ground stone tools.

In recent years, the study of percussive, pounding and grinding tools has provided new insights into human evolution, more particularly regarding the development of technology enabling the processing and exploitation of plant resources. Some of these studies focus on early evidence for flour production, an activity frequently perceived as an important step in the evolution of plant exploitation. The present paper investigates plant food preparation in mobile hunter-gatherer societies from the Southern Levant. The analysis consists of a use-wear study of 18 tools recovered from Ohalo II, a 23 000-year-old site in Israel showing an exceptional level of preservation. Our sample includes a slab previously interpreted as a lower implement used for producing flour, based on the presence of cereal starch residues. The use-wear data we have obtained provide crucial information about the function of this and other percussive tools at Ohalo II, as well as on investment in tool manufacture, discard strategies and evidence for plant processing in the Late Pleistocene. The use-wear analysis indicates that the production of flour was a sporadic activity at Ohalo II, predating by thousands of years the onset of routine processing of plant foods.

What the pig ate: A microbotanical study of pig dental calculus from 10th–3rd millennium BC northern Mesopotamia

One of the main questions that zooarcheologists have attempted to answer in their studies of ancient agropastoral economies relates to animal diet. Starch granules and phytoliths, which derive from the plant foods consumed over the course of an animal's life, become imbedded in dental calculus and thus offer direct clues about diet. In this paper, we investigate pig diet with an eye toward understanding husbandry strategies in northern Mesopotamia, the region in which pigs were first domesticated, from the Epipaleolithic though the Early Bronze Age. Our data reveal that pigs consumed an assortment of plant foods, including grasses, wild tubers, acorns, and domestic cereals. Although poor preservation plagued the identification of plant microremains at Epipaleolithic (10th millennium cal. BC) Hallan Çemi, the identification of a diet based on tubers and grasses matches models of wild boar diet. Pigs at 6th millennium Domuztepe, 5th millennium Ziyadeh, and 4th millennium Hacinebi consumed cereals, particularly oats (Avena sp.) and barley (Hordeum sp.), as well as wild plant food resources. Several of the cereal starch granules showed evidence of cooking, indicating that pigs had access to household refuse beginning at least in the late Neolithic. Moreover, calculus from morphologically wild specimens also contained cooked cereal grains. This points to a close relationship between wild boar populations and human settlements in the Neolithic and beyond. Preservation was poor for 3rd millennium sites in the study, including Atij, Raqa'i, Ziyadeh, and Leilan, but the available data suggest that pigs ate oats, barley and other Triticeae (the tribe that includes wheat, barley, and goatgrass), and other grasses. This may represent foddering practices in the Early Bronze Age.

Identification of carbohydrate parameters in commercial unripe banana flour

Summary Unripe banana flour (UBF), which is rich in resistant starch (RS), has shown several positive physiological effects in clinical trials. Although such observations encourage the emergence of UBF in the food market, specific identity or quality standards for the product are still lacking. This work aimed to assess and propose characterization parameters for commercially available UBF. The results showed that three of the brands examined presented a RS content higher than 40%, whereas nine showed a lower content, with two having less than 10% RS and over 80% total starch, which was fully identified as cereal starch by light microscopy (LM). The presence of banana peel in the flour was correlated with the lipid (r = 0.870), ash (r = 0.812), protein (r = 0.704) and total starch (r = − 0.761) contents. According to principal components analysis (PCA) and LM identification, the main parameters for the characterization of commercial UBFs are the contents of RS, dietary fiber, lipid and ash. The large variability in RS content (4 to 62%) found in commercial UBFs is one reason why consumers would benefit from additional labeling information, such as the inclusion of the RS and soluble sugar (SS) contents, the unripe banana cultivar used, and indications about use of the peel. Moreover, adulterations could be verified by food inspection agencies via LM, which can be used as a tool to identify the type and state of the starch present.

Preliminary structural optimization of some fumonisin metabolites by density functional theory calculation

Maize (Zea mays L.) is often contaminated with Fusarium verticillioides. This harmful fungus produces fumonisins as secondary metabolites. These fumonisins can appear both free and hidden form in planta. The hidden form is usually bound covalently to cereal starch. From the hidden fumonisins, during enzymatic degradation, glycosides are formed, and the fumonisin is further decomposed during a de-esterification step. In this short communication some preliminary DFT calculated structural results which could be useful in the future to help to understand the van der Waals force controlled molecular interactions between these kinds of mycotoxin molecules and enzymes are demonstrated.

Effect of decortication and protease treatment on physicochemical and functional characteristics of red sorghum (Sorghum bicolor) and yellow maize (Zea maiz) starches

Sorghum is a cereal from which starch is not commonly isolated; however, its functional characteristics are similar to other cereal starches such as maize. Red sorghum kernels were processed with and without mechanical decortication followed by steeping in a sodium bisulfite solution to 50% solids, with and without a commercial protease following by wet milling. For comparison purposes, yellow maize kernels were also protease treated and wet milled. Results indicate a significant increase on starch yield in both cereals when the decorticated sorghum or maize flours were treated with the protease from 59.11 to 63.21% and 43.59 to 58.89%, as well as purity from 96.52 to 98.45 and 95.95 to 98.75% for maize and sorghum, respectively. The combination of mechanical decortication and protease treatments increase starch gelatinization temperature from 77.5 to 81.5°C, as well as a decrease on the final viscosity, indicating that the protein associated to the starch granules restricted swelling and amylose leaching during pasting. Isolated starch from decorticated sorghum kernels was lighter in color due to the removal of pericarp rich in phenolics. The mechanical decortication prior to wet milling presented the advantage of the removal of stable sorghum bran that contains an array of nutraceutical and antioxidant compounds, whereas the use of the proposed decortication followed by enzyme treatment promote higher yields of refined starch.

Functionality of maize, wheat, teff and cassava starches with stearic acid and xanthan gum

Consumer concerns to synthetic chemicals have led to strong preference for ‘clean’ label starches. Lipid and hydrocolloids are food friendly chemicals. This study determines the effects of stearic acid and xanthan gum alone and in combination on the functionality of maize, wheat, teff and cassava starches. An increase in viscosity was observed for all starches with stearic acid and xanthan gum compared to the controls with cassava having the least increase. A further increase in viscosity was observed for the cereal starches with combination of stearic acid and xanthan gum. Stearic acid reduced retrogradation, resulting in soft textured pastes. Combination of stearic acid and xanthan gum reduced the formation of type IIb amylose–lipid complexes, syneresis, and hysteresis in cereal starches compared to stearic acid alone. A combination of stearic acid and xanthan gum produce higher viscosity non-gelling starches and xanthan gum addition increases physical stability to freezing and better structural recovery after shear.

Uniqueness of Ethiopian traditional alcoholic beverage of plant origin, tella

There are many kinds of traditional fermented beverages in Ethiopia, not only of animal origin, but also of plant origin. In everyday life people enjoy fermented beverages and particularly when having guests, they like to treat them to traditional alcoholic beverages. Tella, tej, areki, borde, and shamita are drinks that each household brews to treat guests. Substrates for their production are from locally available raw materials. Therefore, the basic production method is the same, but the tastes may vary. One of the most consumed fermented alcoholic beverages is tella, which is made mostly with barley but wheat, maize, sorghum, and teff are utilized depending on the region. Its production process shows the similarity to beer: addition of malt and gesho which has the same function as hops in beer. The main fermentation yeast is Saccharomyces cerevisiae and saccharification of cereal starch seems to depend on malt. However, the degree of alcoholic fermentation is low and alcohol content varies between 2 and 6%. Lactic acid bacteria are very active in tella so pH ranges 4–5 give typical tastes such as sourness, sweetness, and bitterness. As the Ethiopian economy improves, more people drink western style beers. Tella has not been commercialized yet, so the process has not been standardized and modernized. Considering the case of Korean makgeolli and the Ethiopian creativity of utilizing gesho in tella, Ethiopia should pay more attention to tella for globalization.

Modification of starch metabolism in transgenic Arabidopsis thaliana increases plant biomass and triples oilseed production.

We have identified a novel means to achieve substantially increased vegetative biomass and oilseed production in the model plant Arabidopsis thaliana. Endogenous isoforms of starch branching enzyme (SBE) were substituted by either one of the endosperm-expressed maize (Zea mays L.) branching isozymes, ZmSBEI or ZmSBEIIb. Transformants were compared with the starch-free background and with the wild-type plants. Each of the maize-derived SBEs restored starch biosynthesis but both morphology and structure of starch particles were altered. Altered starch metabolism in the transformants is associated with enhanced biomass formation and more-than-trebled oilseed production while maintaining seed oil quality. Enhanced oilseed production is primarily due to an increased number of siliques per plant whereas oil content and seed number per silique are essentially unchanged or even modestly decreased. Introduction of cereal starch branching isozymes into oilseed plants represents a potentially useful strategy to increase biomass and oilseed production in related crops and manipulate the structure and properties of leaf starch.

Effect of the particle size of maize, rice, and sorghum in extruded diets for dogs on starch gelatinization, digestibility, and the fecal concentration of fermentation products.

The influence of rice, maize, and sorghum raw material particle size in extruded dry dog food on the digestibility of nutrients and energy and the fecal concentration of fermentation products was investigated. Three diets with similar nutrient compositions were formulated, each with 1 starch source. Before incorporation into diets, the cereals were ground into 3 different particle sizes (approximately 300, 450, and 600 µm); therefore, a total of 9 diets were in a 3 × 3 factorial arrangement (3 cereals and 3 particle sizes). Fifty-four beagle dogs (12.0 ± 0.1 kg BW) were randomly assigned to the diets, with 6 dogs per diet. The digestibility was measured with the chromium oxide method. The data were evaluated with ANOVA considering the carbohydrate source, grinding effect, and interactions. The means were compared with the Tukey test and polynomial contrasts (P < 0.05). With the same grinding procedure, rice was reduced to smaller particles than other cereals. The cereal mean geometric diameter (MGD) was directly related to starch gelatinization (SG) during extrusion. For rice diets, the MGD and SG did not change nutrient digestibility (P > 0.05); only GE digestibility was reduced at the largest MGD (P < 0.01). For maize and sorghum diets, the total tract apparent nutrient digestibility was reduced for foods with greater MGD and less SG (P < 0.01). A linear reduction in nutrient digestibility according to cereal particle size was observed for sorghum (r2 < 0.72; P < 0.01). Higher concentrations of fecal total short-chain fatty acids (SCFA) were observed for sorghum diets (P < 0.05) than for other diets. The rice diets led to the production of feces with less lactate (P < 0.05). The increase in raw material MGD did not influence fecal SCFA for rice diets, but for the dogs fed maize and sorghum foods, an increase in propionate and butyrate concentrations were observed as MGD increased (P < 0.05). In conclusion, for dogs fed different particle sizes of the cereal starches in the extruded diets, the digestibility and fecal characteristics were affected, and this effect was ingredient dependent.

Effects of granule size of cross-linked and hydroxypropylated sweet potato starches on their physicochemical properties.

Sweet potato starch was modified by cross-linking, hydroxypropylation, and combined cross-linking and hydroxypropylation, and the starches were subsequently sieved to obtain differently sized granule fractions. The effects of granule size of native and modified sweet potato starch fractions and all fractions were investigated with respect to their physicochemical properties. The large-size granule fraction (27-30 μm) showed a 16-20% higher chemical phosphorylation and a 4-7% higher hydroxypropylation than the small-size granule fraction (14-16 μm). The large-size granule fractions of native and modified sweet potato starches showed lower transition temperatures (0.7-3.1 °C for peak temperature of gelatinization) and lower enthalpy changes (0.6-1.9 J/g) during gelatinization than the small-size granule fractions, making the sweet potato starch different from cereal starches. The large-size granule fraction of native starch showed a higher paste viscosity (78-244 cP) than the corresponding small-size granule fraction. In addition, cross-linking and hydroxypropylation affected the paste viscosity of the large-size granule fraction significantly more than that of the small-size granule fraction when compared to the corresponding parental starch fractions. The large-size granule fraction of native and dual-modified starches showed a lower syneresis after freeze-thaw treatments than the small-size granule fractions. The difference in swelling power between large- and small-size granule fractions was not significant. In general, the large-size granule fraction of sweet potato starch was more susceptible for cross-linking and hydroxypropylation and the physicochemical properties were changed to a higher extent compared to the corresponding small-size granule fraction.

Effect of surfactant treatment on swelling behaviour of normal and waxy cereal starches

Starch swelling behaviour greatly affects its functionality in a food matrix. For some granular starches pre-treatment with the surfactant, sodium dodecyl sulphate, is known to dramatically affect swelling behaviour. The purpose of this study was to assess the effect of this surfactant treatment on the swelling behaviour of a variety of waxy and normal cereal starches. A concurrent mid-infrared spectroscopy study was carried out to investigate the chemical nature of variations in swelling behaviour. The native normal starches (amylose content 23–28%) showed significant variation in their pasting properties, which was largely eliminated by surfactant treatment. Surfactant treatment had less effect on the behaviour of the waxy starches (amylose contents 1–8%), which still exhibited some residual variation. Waxy durum appeared to be unique within the waxy starches, behaving more similarly to the normal starches. The spectroscopic data highlighted the carbohydrate fingerprint region as the main source of variation between samples.

A genetic strategy generating wheat with very high amylose content.

Resistant starch (RS), a type of dietary fibre, plays an important role in human health; however, the content of RS in most modern processed starchy foods is low. Cereal starch, when structurally manipulated through a modified starch biosynthetic pathway to greatly increase the amylose content, could be an important food source of RS. Transgenic studies have previously revealed the requirement of simultaneous down-regulation of two starch branching enzyme (SBE) II isoforms both located on the long arm of chromosome 2, namely SBEIIa and SBEIIb, to elevate the amylose content in wheat from ~25% to ~75%. The current study revealed close proximity of genes encoding SBEIIa and SBEIIb isoforms in wheat with a genetic distance of 0.5 cM on chromosome 2B. A series of deletion and single nucleotide polymorphism (SNP) loss of function alleles in SBEIIa, SBEIIb or both was isolated from two different wheat populations. A breeding strategy to combine deletions and SNPs generated wheat genotypes with altered expression levels of SBEIIa and SBEIIb, elevating the amylose content to an unprecedented ~85%, with a marked concomitant increase in RS content. Biochemical assays were used to confirm the complete absence in the grain of expression of SBEIIa from all three genomes in combination with the absence of SBEIIb from one of the genomes.

Functional properties of arrowroot starch in cassava and sweet potato composite starches

Root and tuber composite flours and/or starches can meet industrial requirements of carbohydrate-based food products since they gelatinize at relative low temperatures with rapid and uniform swelling of granules, and they exhibit a high viscosity profile compared to cereal starches. Arrowroot starch (10, 20, 30, and 40%, respectively) was mixed in cassava and sweet potato starches and their resulting composite gels were investigated for their gelatinization enthalpies, pasting, and freeze-thaw properties. Peak viscosities of composite starches significantly increased (P < 0.05) from 224.45 to 360.25 RVU in cassava mix, to 306.65–580.25 RVU in sweet potato mix. The gelatinization enthalpies of sweet potato and cassava composite starches were significantly affected, which suggested that the thermal energy during gelatinization to break the structural element in starch granular packing was substantially altered with increasing increments of AS. This meant that granular intermolecular bond increased, whereas granule swelling decreased. The addition of AS minimized freeze-thaw damage by reducing the available water to form ice crystals in cassava and sweet potato gel pastes after the first freeze-thaw cycle. This confirmed that partial substitution of cassava and sweet potato starches with AS formed a paste with improved freeze-thaw stability. Addition of arrowroot starch to cassava and sweet potato starches apparently improved gel stability and may find use in modulating gelling properties of these starches in commercial products.

Dry or Steam Rolling of Soft Grains: Dairy and Beef Bioprocessing Perspectives

This article yields pragmatic perspectives on dry-rolling vs. steam-rolling of barley and wheat grains for modern dairy and beef industries. Dry-rolling could suffice exposing soft cereal starch and protein to adequate (but not excess) ruminal microbial fermentation without compromising rumen health when dietary space for sufficient physically effective fibre is designed. In high-producing dairy and finishing beef diets, however, due to the highly concentrated cereal starch, steam-rolling could provide healthier rumen conditions over dry-rolling.

Comparison of molecular structures and functional properties of high-amylose starches from rice transgenic line and commercial maize

High-amylose cereal starches are attracting considerable attention because of their potential health benefits. In this study, the molecular structures and functional properties of high-amylose starches from a rice transgenic line and commercial maize were investigated and compared. High-amylose rice and maize starches had apparent amylose contents of 65.6 and 49.4%, respectively. Compared with high-amylose maize starch, high-amylose rice starch had amylopectin with a higher long branch-chain content and average chain length and with a lower short branch-chain content and degree of branching. High-amylose rice and maize starches exhibited C-type and CA-type crystallinity, respectively. The high-amylose rice starch had a significantly higher gelatinization temperature and lower gelatinization enthalpy, swelling power and pasting viscosity than high-amylose maize starch. High-amylose rice starch had a significantly higher resistance to acid hydrolysis and slightly higher resistance to amylase hydrolysis than high-amylose maize starch. Gelatinized and retrograded starches from high-amylose rice had significantly lower rapidly digestible starch and higher resistant starch contents than high-amylose maize starch. These results were also compared with those obtained from normal rice and maize starches. The significantly different molecular structures of rice and maize starches resulted in their different functional properties.

Preparation of linear maltodextrins using a hyperthermophilic amylopullulanase with cyclodextrin- and starch-hydrolysing activities

A novel method for the preparation of linear maltodextrins from cyclodextrins and starch was proposed. To accomplish this process, an amylopullulanase from hyperthermophilic archaeon Caldivirga maquilingensis (CMApu) was characterized and used. CMApu with an estimated molecular mass of 62.7 kDa by SDS-PAGE had a maximal pullulan-hydrolysing activity at 100°C and pH 5.0. It could also hydrolyse amylopectin (AP), starch, β-CD and amylose (AM), in a decreasing order of relative activities from 88.96% to 57.17%. TLC and HPAEC analysis revealed that CMApu catalyzed the debranching and degrading reactions to produce linear malto-oligosaccharides (≤ G8-G1) from G8-β-CD and/or normal CDs, amylodextrins (DP6-96) from AM, and amylodextrins (DP1-76) from AP and potato starch. Our results showed that CMApu had a great potential for the industrial preparation of linear maltodextrins from normal starch instead of waxy starch, malto-oligosaccharides or sucrose. And the high optimal temperature of CMApu facilitated the simultaneous gelatinization and hydrolysis of cereal starch.