Measurement of total starch in cereal products by amyloglucosidase-alpha-amylase method: collaborative study.
McCleary, B. V., Gibson, T. S. & Mugford, D. C. (1997). Journal of AOAC International, 80, 571-579.
An American Association of Cereal Chemists/AOAC collaborative study was conducted to evaluate the accuracy and reliability of an enzyme assay kit procedure for measurement of total starch in a range of cereal grains and products. The flour sample is incubated at 95 degrees C with thermostable alpha-amylase to catalyze the hydrolysis of starch to maltodextrins, the pH of the slurry is adjusted, and the slurry is treated with a highly purified amyloglucosidase to quantitatively hydrolyze the dextrins to glucose. Glucose is measured with glucose oxidase-peroxidase reagent. Thirty-two collaborators were sent 16 homogeneous test samples as 8 blind duplicates. These samples included chicken feed pellets, white bread, green peas, high-amylose maize starch, white wheat flour, wheat starch, oat bran, and spaghetti. All samples were analyzed by the standard procedure as detailed above; 4 samples (high-amylose maize starch and wheat starch) were also analyzed by a method that requires the samples to be cooked first in dimethyl sulfoxide (DMSO). Relative standard deviations for repeatability (RSD(r)) ranged from 2.1 to 3.9%, and relative standard deviations for reproducibility (RSD(R)) ranged from 2.9 to 5.7%. The RSD(R) value for high amylose maize starch analyzed by the standard (non-DMSO) procedure was 5.7%; the value was reduced to 2.9% when the DMSO procedure was used, and the determined starch values increased from 86.9 to 97.2%.
A procedure to measure amylose in cereal starches and flours with concanavalin A.
Gibson, T. S., Solah, V. A. & McCleary, B. V. (1997). Journal of Cereal Science, 25(2), 111-119.
A modified procedure for the determination of amylose in cereal starches and flours based on complex formation between the lectin concanavalin A (Con A) and amylopectin has been developed and characterised. The assay format is suitable for multi-sample analysis, allowing the analysis of up to 20 samples per day. In the procedure, the amylopectin in a solubilised, lipid-free starch sample is precipitated by reaction with Con A and removed by centrifugation. The amylose remaining in the supernatant is then determined after amylolytic hydrolysis to glucose and expressed as a proportion (%) of the glucose derived from amylolytic hydrolysis of the total starch in a separate aliquot of the solubilised sample (i.e. prior to Con A treatment). The Con A procedure correlates well (r>0•993) with existing Con A-based and iodine-based procedures and yields a linear standard curve for starch samples containing from ∼0 to ∼100% amylose. Advantages of this modified Con A procedure for amylose determination include its applicability to flour samples without the need for prior starch purification; it allows the simultaneous estimation of total starch and does not require a calibration curve. Repeated analyses of a set of samples yielded repeatability (within laboratory) relative standard deviations of <5% for pure starches and ∼10% for flours. A commercially available assay kit has been developed to facilitate the use of the Con A procedure in routine amylose determinations.
Measurement of carbohydrates in grain, feed and food.
McCleary, B. V., Charnock, S. J., Rossiter, P. C., O’Shea, M. F., Power, A. M. & Lloyd, R. M. (2006). Journal of the Science of Food and Agriculture, 86(11), 1648-1661.
Procedures for the measurement of starch, starch damage (gelatinised starch), resistant starch and the amylose/amylopectin content of starch, β-glucan, fructan, glucomannan and galactosyl-sucrose oligosaccharides (raffinose, stachyose and verbascose) in plant material, animal feeds and foods are described. Most of these methods have been successfully subjected to interlaboratory evaluation. All methods are based on the use of enzymes either purified by conventional chromatography or produced using molecular biology techniques. Such methods allow specific, accurate and reliable quantification of a particular component. Problems in calculating the actual weight of galactosyl-sucrose oligosaccharides in test samples are discussed in detail.
High hydrostatic pressure influences antinutritional factors and in vitro protein digestibility of split peas and whole white beans.
Linsberger-Martin, G., Weiglhofer, K., Thi Phuong, T. P. & Berghofer, E. (2013). LWT-Food Science and Technology, 51(1), 331-336.
Legumes are of high nutritional value but consumption is low in Western countries due to long processing and antinutritional factors. The development of convenience products can help to overcome these constraints. The present study investigated the effect of high hydrostatic pressure on oligosaccharides, phytic acid and total phenolic acid content, trypsin inhibitor activity and protein digestibility in peas and beans. Oligosaccharides were significantly reduced through pressurisation by up to 68% in peas and 48% in beans but reduction was lower than in cooked samples (max. 82% in peas and 80% in beans). Phytic acid was reduced by high pressure by up to 36% in peas and 11% in beans. Total phenolic acid content was reduced only in some pressurised peas and beans as compared to untreated peas and beans. Reduction of phytic acid (max. 48%) and total phenolic acids (max. 78%) through cooking was greater than through pressurisation. Trypsin inhibitor activity decreased by up to 100% in peas and 84% in beans during pressurisation. Protein digestibility increased by up to 4.3% in peas when treated at 600 MPa and 60°C regardless of time and by 8.7% in beans treated at 600 MPa at 60°C for 60 min.
New determination method of amylose content in potato starch.
Stawski, D. (2008). Food Chemistry, 110(3), 777-781.
Thermal stability of potato starch depends on amylose content. Temperature at 50% mass loss from thermogravimetric analysis was used to determine the starch components. The same analysis was carried out to analyse the samples from potato, rice, wheat and high amylose. The results (26.9% of amylose content for potato, 29.1% for rice and 20.9% for wheat) were compared with results obtained from the blue value method and enzymatic method. Satisfactory compatibility for potato and rice was obtained. For such kind of samples thermogravimetric analysis can be used for amylose determination.
High pressure phase transition kinetics of maize starch.
Buckow, R., Heinz, V. & Knorr, D. (2007). Journal of Food Engineering, 81(2), 469-475.
In this paper, the impact of high hydrostatic pressure, temperature and time on the gelatinization of maize starch is reported. Starch transition has been assessed by microscopic inspections of the granule’s loss in birefringence which occurs during the first stage of gelatinization in consequence of the water uptake. Experiments have been carried out under combined pressure–temperature treatments in the range of 0.1–650 MPa and 30–75°C. The rate of gelatinization has been determined by an interpolating model and isokineticity lines were plotted in pressure–temperature diagrams. Pressure higher than 300 MPa is necessary to reduce significantly the onset temperature of gelatinization. At those pressures, the isokineticity lines are bended to the left, indicating that the phase transition in birefringence is occurring at lower temperatures. At 30°C, maize starch was gelatinized completely after 30 min at 650 MPa.
Characterization of starch from tubers of yam bean (Pachyrhizus ahipa).
Forsyth, J. L., Ring, S. G., Noel, T. R., Parker, R., Cairns, P., Findlay, K. & Shewry, P. R. (2002). Journal of Agricultural and Food Chemistry, 50(2), 361-367.
Detailed studies of the starch present in tubers of six accessions of Pachyrhizus ahipa (ahipa) have been carried out using starches from tubers of P. erosus (Mexican yam bean) and seeds of ahipa and wheat for comparison. Starch accounted for 56−58% of the tuber dry weight with granules occurring in a range of geometric forms and in sizes from below 5 μm to about 35 μm (mean about 10 μm in all accessions except two). The amylose content ranged from 11.6 to 16.8% compared with 16.9% in P. erosus tubers and over 23% in the seed starches. X-ray diffraction analysis showed A-type or CA-type diffraction patterns. The chain-length distribution of the amylopectin after enzyme debranching showed a peak at DP11 similar to that of wheat starch, but had a less marked shoulder at DP 21−22 and contained a higher proportion of longer chains. Differential scanning calorimitry showed an endothermic peak corresponding to gelatinization with Tmax ranging from 59 to 63°C, which was similar to the Tmax of wheat (about 64°C). The composition of the ahipa starch may mean that it is suitable for food applications that require low amylose content and low retrogradation after processing.
Effects of wheat inclusion and xylanase supplementation of the diet on productive performance, nutrient retention, and endogenous intestinal enzyme activity of laying hens.
Mirzaie, S., Zaghari, M., Aminzadeh, S., Shivazad, M. & Mateos, G. G. (2012). Poultry Science, 91(2), 413-425.
An experiment was conducted to study the effects of inclusion of a wheat cultivar (high in nonstarch polysaccharides) and xylanase supplementation of the diet on productive performance, pH of the gastrointestinal tract, nutrient retention, and intestinal enzyme activity of Hy-Line W-36 laying hens from 25 to 47 wk of age. The experiment was completely randomized with 8 treatments arranged factorially with 4 levels of wheat (0, 23, 46, and 69%) that corresponded to a dietary arabinoxylan content of 3.0, 3.3, 3.6, and 3.9%, with or without xylanase supplementation. Each treatment was replicated 5 times. For the entire experimental period, egg weight (P< 0.05) and egg mass (P< 0.01) were reduced and the feed conversion ratio was hindered (P< 0.05) with increased levels of wheat in the diet, but ADFI and egg production were not affected. Xylanase supplementation improved egg production (P< 0.05), egg mass (P< 0.01), and the feed conversion ratio (P< 0.01). Diet did not affect egg quality at any age, except for shell thickness at 47 wk that was improved with xylanase supplementation (P< 0.05). Digesta pH of the different organs of the gastrointestinal tract was not affected by wheat inclusion or xylanase supplementation. Ileal viscosity increased (P< 0.001) with wheat inclusion and decreased (P< 0.001) with xylanase supplementation at all ages. Fat digestibility (P< 0.001) decreased with increased levels of wheat but AMEn content of the diets (P< 0.05) and nitrogen retention were not affected. Wheat inclusion increased (P< 0.001) amylase (33 wk), lipase (33 wk), and aminopeptidase (47 wk) activity in the duodenum as well as lipase activity in the jejunum at 47 wk of age. However, xylanase supplementation did not affect the activity of any of the enzymes studied. It is concluded that most of the negative effects of wheat inclusion in the diet were reduced or even disappeared with xylanase supplementation. Wheat with a high nonstarch polysaccharide content (Pishtaz cultivar) can be used at levels of up to 69% in laying-hen diets without negatively affecting bird performance, provided that feeds are supplemented with xylanase.
Effect of cultivar, location and year on total starch, amylose, phosphorus content and starch grain size of high starch potato cultivars for food and industrial processing.
Šimková, D., Lachman, J., Hamouz, K. & Vokál, B. (2013). Food Chemistry, 141(4), 3872-3880.
In recent time the interest of industry increases particularly in processing and use of potato high amylopectin (AMP) starches. Therefore the plant breeders effort to obtain “waxy” potato cultivars with low amylose (AMS) content. In this four-year study sixteen potato cultivars grown on five experimental locations were evaluated on the percentage of AMS/AMP by enzymatic method, starch content by the underwater weight method, phosphorus (P) content in starch digests spectrophotometrically, and starch granule size determined by laser diffraction method. Between enzymatic and iodine–potassium iodide method good correlation has been revealed (r= 0.71). The correlation analysis between AMS and P levels showed a clear negative correlation. For all measured parameters (starch, AMS, P, starch granule size) significant impact of cultivar has been determined. Location and year have lower, but significant impact. No statistically significant effect of year on AMS has been found. The cultivar Amado distinguished with the highest AMP and P contents and the cultivar Westamyl showed all positive values interesting for growers and processors.
Structure and digestibility of debranched and hydrothermally treated water yam starch.
Trinh, K. S., Choi, S. J. & Moon, T. W. (2013). Starch‐Stärke, 65(7‐8), 679-685.
Debranched water yam starch was subjected to repeated hydrothermal treatment (HTT), and its physicochemical and structural properties and digestion pattern were investigated. The B-type crystalline pattern of raw starch was recrystallized to B- and CA-type patterns by debranching and repeated HTT. The degree of relative crystallinity of debranched starch gradually increased and reached its maximum (43.3%) after five repetitions of HTT. The thermal transition temperatures and melting enthalpy of recrystallized starches increased progressively, reflecting the perfection of their crystalline structure, leading to the accumulation of boiling-stable crystalline structure under repeated HTT conditions. As a result, RS of HTT starches reached a very high level (> 92.2%). The boiling-stable RS content depended on the repetition of this treatment and was maximized (81.0%) after five repetitions.
Elimination of resistant starch type II within the framework of total starch and dietary fibre analysis by microwave irradiation.
Themeier, H., Hollmann, J., Neese, U. & Lindhauer, M. G. (2010). Quality Assurance and Safety of Crops & Foods, 2(1), 46-51.
Introduction The presence of resistant starch in samples containing non-starch polysaccharides has always been a challenge to enzymatic total starch and total fibre analysis. Objective and methods Based on microwave-induced pressure disintegration technique the Association of Official Analytical Chemists methods for the determination of total starch (AOAC 996.11) and total dietary fibre (AOAC 991.43) have been modified to completely eliminate undesirable resistant starch fractions with respect to digestion procedures using thermostable α-amylase and amyloglucosidase. Results Microwave treatment of high-amylose starch samples resulted in excellent total starch recovery in the Association of Official Analytical Chemists standard method no. 996.11. After integration of microwave disintegration technique into the total dietary fibre method AOAC 911.43 irradiation experiments with different model mixtures consisting of non-starch polysaccharides components and high-amylose starch fractions resulted in the complete elimination of undesirable resistant starch fractions. Conclusion Therefore the microwave technique can be a very efficient means for the elimination of resistant starch and provides more realistic values in analytical total dietary fibre procedures with respect to samples containing critical enzyme resistant starches.
Processing properties of Korean rice varieties in relation to rice noodle quality.
Han, H. M., Cho, J. H. & Koh, B. K. (2011). Food Science and Biotechnology, 20(5), 1277-1282.
The purpose of this study was to investigate the physicochemical and pasting properties of rice developed in Korea in relation to noodle quality. Two Indica lines (Hanareumbyeo and Chenmaai) and 7 japonica lines (Jinsumi, Goamibyeo, Manmibyeo, Milyang261, Seolgaeng, Suweon517, and YR24088 Acp9) were wet milled followed by lyophilized and passed through a 115 mesh sieve. The amylose contents were varied from 10.1 to 32.1%. Among them, Milyang261 showed unique paste viscosity although its amylose content was very high as 32.1% with poor cooking properties. Except Milyang261 and Suweon517, the high amylose content lines of Chenmaai, Goamibyeo, and YR24088 Acp9 showed desirable cooking properties in cooking loss, tensile strength, and texture profile. No item was selected as a key factor for rice noodles. However, amylose content, paste viscosity, and damaged starch could be positive components for improvement of rice noodle quality. The high amylose line of Chenmaai, YR24088 Acp9, and Goamibyeo showed the most appropriate properties for making extruded rice noodles with good cooking and textural properties. The paste properties, damaged starch, and high amylose content of the flour can be used as indicators of the rice noodle quality.
Molecular diversity and differential expression of starch-synthesis genes in developing kernels of three maize inbreds.
Ding, X. Z., Wang, B. G., Gao, Q. H., Zhang, Q., Yan, G. Q., Duan, K. & Huang, J. H. (2009). Plant Cell Reports, 28(10), 1487-1495.
The maize genome remains abundant in molecular diversity, and the rich genetic diversity of maize starch-synthesis genes is crucial for controlling various grain traits. To explore the unique mechanism controlling the advantageous waxy trait and characterize the molecular feature of genes relevant to starch composition in two elite waxy inbreds, expression profiling combined with gene organization analysis was performed in them as compared to one normal inbred. Genotype-specific expression patterns were observed for most genes studied. The waxy inbreds were shown to contain mutations in multiple starch-synthesis genes, namely gbssI (wx), gbssIIb and isa2 (potentially isa3 too). The mis-splicing events directly accounted for wx loss of function. Contrarily, disruption of 5′ and 3′ transcript sequence may contribute to the absence of GbssIIb and Isa2 transcripts in waxy inbreds, respectively. Besides, the splicing of Sugary1 transcript was developmentally regulated in the normal inbred, and DNA polymorphisms were detected within SSIIIb-1 gene in waxy inbreds.
Value Added of Resistant Starch Maize-Based Matrices in Breadmaking: Nutritional and Functional Assessment.
Collar, C., Balestra, F. & Ancarani, D. (2014). Food and Bioprocess Technology, 7(12), 3579-3590.
The ability of white (W) and yellow (Y) maize flour as basic ingredients to make nutritious and healthy breads meeting functional and sensory standards is investigated. Resistant starch (R) and common wheat flour (WF) were incorporated into formulations as single and associated extra ingredients, and dough machinability, bread nutritional and functional profiles, starch hydrolysis kinetics and keeping behaviour were assessed in blended maize matrices and compared with the maize and wheat flour counterparts. Simultaneous replacement of maize flour samples by R and WF at 40 % significantly modified textural profile, crumb grain features and firming kinetics, and free polyphenol pattern of breads thereof compared to the respective Y or W maize counterparts. Bigger specific volume (+28 % Y-R-WF, +36 % W-R-WF), softer crumb bread (−64 % Y-R-WF, W-R-WF), more aerated structure and homogeneous crumb grain, and lower and slower staling kinetics are observed in composite Y and W maize-based breads, respectively. Nutritional information on maize-based blended breads showed most appealing nutritional quality than WF breads, in terms of lower digestible starch (up to −21 % in Y-R-WF, W-R-WF, WR) and rapidly digestible starch (up to −37 % in W-R-WF), higher slowly digestible starch (up to three times in WR) and resistant starch contents (from five to six times in Y-R-WF, W-R-WF, W-R, Y-R) of medium-high sensorially rated bread matrices. All single and blended maize-based breads can be labelled as high-fibre breads (6 g dietary fibre (DF)/100 g food). According to health-related benefits and prebiotic dosage of resistant starch a daily intake of 100 g of single Y-R, W-R, W-R-WF and W-R-WF provides enough resistant starch to positively affect postprandial glucose and insulin levels, while 170 g covers the amount necessary to enhance health.
Registration of Common Wheat Germplasm with Mutations in Genes Conferring Increased Grain Amylose and Resistant Starch Content.
Schönhofen, A., Hazard, B., Zhang, X. & Dubcovsky, J. (2016). Journal of Plant Registrations, 10(2), 200-205.
Starch present in the endosperm of common wheat (Triticum aestivum L.) grains is an important source of carbohydrates worldwide. Starches with a greater proportion of amylose have increased levels of resistant starch, a dietary fiber that can provide human health benefits. Induced mutations in STARCH BRANCHING ENZYME II (SBEII) genes in wheat are associated with increased amylose and resistant starch. Ethyl methane sulfonate mutations in SBEIIa and SBEIIb paralogs were combined in the hexaploid wheat cultivar Lassik. Four mutant combinations were generated: SBEIIa/b-AB (Reg. No. GP-997, PI 675644); SBEIIa/b-A, SBEIIa-D (Reg. No. GP-998, PI 675645); SBEIIa/b-B, SBEIIa-D (Reg. No. GP-999, PI 675646); and SBEIIa/b-AB, SBEIIa-D (Reg. No. GP-1000, PI 675647). The SBEII mutant lines were compared with a wild-type control in a greenhouse and field experiment. The quintuple mutant line (SBEIIa/b-AB, SBEIIa-D) presented significant increases in both amylose (51% greenhouse; 63% field) and resistant starch (947% greenhouse; 1057% field) relative to the control. A decrease in total starch content (7.8%) was observed in the field experiment. The quintuple mutant also differed in starch viscosity parameters. Registration of the hexaploid wheat SBEII-mutant lines by University of California, Davis can help expedite the development of common wheat cultivars with increased amylose and resistant starch content.
Effects of timing and severity of salinity stress on rice (Oryza sativa L.) yield, grain composition, and starch functionality.
Thitisaksakul, M., Tananuwong, K., Shoemaker, C. F., Chun, A., Tanadul, O. U. M., Labavitch, J. M. & Beckles, D. M. (2015). Journal of Agricultural and Food Chemistry, 63(8), 2296-2304.
The aim of this work was to examine agronomic, compositional, and functional changes in rice (Oryza sativa L. cv. Nipponbare) grains from plants grown under low-to-moderate salinity stress in the greenhouse. Plants were grown in sodium chloride-containing soil (2 or 4 dS/m2 electrical conductivity), which was imposed 4-weeks after transplant (called Seedling EC2 and EC4) or after the appearance of the anthers (called Anthesis EC2 and EC4). The former simulates field conditions while the latter permits observation of the isolated effect of salt on grain filling processes. Key findings of this study are the following: (i) Plants showed adaptive responses to prolonged salt treatment with no negative effects on grain weight or fertility. Seedling EC2 plants had more panicles and enhanced caryopsis dimensions, while surprisingly, Seedling EC4 plants did not differ from the control group in the agronomic parameters measured. (ii) Grain starch increased in Seedling EC4 (32.6%) and Anthesis EC2 (39%), respectively, suggesting a stimulatory effect of salt on starch accumulation. (iii) The salinity treatment of 2 dS/m2 was better tolerated at anthesis than the 4 dS/m2 treatment as the latter led to reduced grain weight (28.8%) and seed fertility (19.4%) and compensatory increases in protein (20.1%) and nitrogen (19.8%) contents. (iv) Although some salinity treatments led to changes in starch content, these did not alter starch fine structure, morphology, or composition. We observed no differences in reducing sugar and amylose content or starch granule size distribution among any of the treatments. The only alterations in starch were limited to small changes in thermal properties and glucan chain distribution, which were only seen in the Anthesis EC4 treatment. This similarity of compositional and functional features was supported by multivariate analysis of all variables measured, which suggested that differences due to treatments were minimal. Overall, this study documents the specific response of rice under defined conditions, and illustrates that the plasticity of plant response to mild stress is complex and highly context-dependent, even under greenhouse conditions in which other potential environmental stress impacts are minimized.
Glycemic potency of muffins made with wheat, rice, corn, oat and barley flours: a comparative study between in vivo and in vitro.
Soong, Y. Y., Quek, R. Y. C. & Henry, C. J. (2015). European Journal of Nutrition, 54(8), 1281-1285.
Purpose: Muffins made with wheat flour are a popular snack consumed in western and emerging countries. This study aimed to examine the content of amylose, glycemic response (GR) and glycemic index (GI) of muffins baked with refined wheat and rice flours, as well as wholegrain corn, oat and barley flours. Methods: This study adopted a randomized, controlled, crossover, non-blind design. Twelve healthy participants consumed wheat, rice, corn, oat and barley muffins once and the reference glucose solution three times in a random order on non-consecutive day. Capillary blood samples were taken every 15 min in the first 60 min and every 30 min for the remaining 60 min for blood glucose analysis. The Megazyme amylose/amylopectin assay procedure was employed to measure amylose content. Results: The GR elicited from the consumption of wheat, rice and corn muffins was comparable between these samples but significantly greater when compared with oat and barley muffins. Consumption of wholegrain muffins, apart from corn muffin, blunted postprandial GR when compared with muffins baked with refined cereal flours. Muffins baked with wheat, rice, corn, oat and barley flours gave rise to GI values of 74, 79, 74, 53 and 55, respectively. The content of amylose was significantly higher in corn, oat and barley muffins than wheat and rice muffins. Conclusions: The greater content of amylose and fibre may play a part in the reduced glycemic potency of oat and barley muffins. Wheat flour can be substituted with oat and barley flours for healthier muffins and other bakery products.
Effect of surfactant treatment on swelling behaviour of normal and waxy cereal starches.
Blake, L. H., Jenner, C. F., Gidley, M. J. & Cozzolino, D. (2015). Carbohydrate Polymers, 125, 265-271.
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.
Effects of ripening temperature on starch structure and gelatinization, pasting, and cooking properties in rice (Oryza sativa).
Chun, A., Lee, H. J., Hamaker, B. R. & Janaswamy, S. (2015). Journal of Agricultural and Food Chemistry, 63(12), 3085-3093.
The effect of ripening temperature on rice (Oryza sativa) grain quality was evaluated by assessing starch structure and gelatinization, pasting, and cooking properties. As the ripening temperature increased, the amylose content and number of short amylopectin chains decreased, whereas intermediate amylopectin chains increased, resulting in higher gelatinization temperatures and enthalpy in the starch. These results suggested that an increase in cooking temperature and time would be required for rice grown at higher temperatures. A high ripening temperature increased the peak, trough, and final viscosities and decreased the setback due to the reduction in amylose and the increase in long amylopectin chains. With regard to starch crystallinity and amylopectin molecular structure, the highest branches and compactness were observed at 28/20°C. Rice that was grown at temperatures above 28/20°C showed a deterioration of cooking quality and a tendency toward decreased palatability in sensory tests.
Incorporation of flavonoid derivatives or pentagalloyl glucose into lignin enhances cell wall saccharification following mild alkaline or acidic pretreatments.
Grabber, J. H., Santoro, N., Foster, C. E., Elumalai, S., Ralph, J. & Pan, X. (2015). BioEnergy Research, 8(3), 1391-1400.
Partial substitution of normal monolignols with phenolic precursors from other metabolic pathways may improve the susceptibility of lignified biomass to chemical pretreatment and enzymatic saccharification for biofuel production. Flavonoids and gallate esters readily undergo oxidative coupling reactions, suggesting they could serve as alternate monomers for forming lignin in plants. To test this premise, primary cell walls of Zea mays (L.) were artificially lignified with normal monolignols plus various flavan-3-ol/phenolic ester derivatives, flavonol glycoside/gallate ester derivatives, or pentagalloyl glucose added as 0 or 45 % of the precursor mixture. Most alternate monomers readily copolymerized with normal monolignols, but wall-bound lignin was most efficiently formed with epicatechin, epicatechin gallate, epigallocatechin gallate, or hyperoside. Yields of glucose from a high-throughput digestibility platform were used to examine how lignin modifications affected the susceptibility of cell walls to enzymatic hydrolysis following alkaline or acidic pretreatments of different severities. With the exception of hyperoside, incorporation of alternate monomers into lignin improved yields of enzymatically released glucose by 18-60 % after mild alkaline pretreatment and by 6-34 % after mild acid pretreatment. Responses due to lignin modification diminished as pretreatment severity increased. Overall, our results suggest that apoplastic deposition of pentagalloyl glucose or gallated flavan-3-ols such as epicatechin gallate or epigallocatechin gallate for incorporation into lignin could be promising plant genetic engineering targets for improving sugar yields from grass biomass crops that are subjected to low-temperature alkaline pretreatments.