Effect of a Cell‐Wall‐Degrading Enzyme Complex on Starch Recovery and Steeping Requirements of Sorghum and Maize

The effect of a commercial cell‐wall‐degrading enzyme (CWDE) complex on the steeping time and starch yields of white regular sorghum (RSOR) compared with yellow maize (YMZ) was determined. An in vitro wet‐milling method standardized to test dosages of 0–120 fungal β‐glucanase units (FBG)/100 mL indicated that starch yields were significantly higher for YMZ than RSOR and increased proportionally as enzyme dosage increased. A factorial experiment with a level of confidence of P < 0.05 was performed to study the effect of CWDE addition to coarsely ground grains for 4 hr after 20 or 44 hr of SO₂ steeping of whole grains. At both regular steep times, YMZ yielded significantly higher amounts of starch than RSOR. When steep times were compared, grains soaked for 48 hr produced 1.7% higher starch yields than counterparts treated for 24 hr. CWDE significantly increased starch yields and recoveries. Enzyme‐treated grains yielded 2.5% more starch than counterparts steeped regularly. For both grains, the best wet‐milling conditions to obtain the highest amount of starch were 48 hr of steeping and CWDE addition. Under these conditions, YMZ and RSOR yielded 66.9 and 66.6% starch, respectively. Starches obtained after the enzyme treatment at both steep times contained higher amounts of residual protein and ash compared with the untreated counterparts. Rapid viscoamylograph properties of YMZ and RSOR starches were not affected by the use of the CWDE nor the steep time. In comparison with RSOR starch, the YMZ starch initiated gelatinization at lower temperature, had less shear thinning and higher viscosity or setback at the end of cooling.     

Laboratory Yields and Process Stream Compositions from E‐Mill and Dry‐Grind Corn Processes Using a Granular Starch Hydrolyzing Enzyme

In dry‐grind corn processing, the whole kernel is fermented to produce ethanol and distillers dried grains with solubles (DDGS); the E‐Mill process was developed to generate coproducts in addition to DDGS. Compositions of thin stillage and wet grains obtained from the E‐Mill process will be different from the dry‐grind process. Knowledge of thin stillage compositions will provide information to improve coproducts from both processes. Laboratory dry‐grind and E‐Mill processes that used granular starch hydrolyzing enzymes (GSHE) were compared and process yields determined. Two methods, centrifugation and screening, were used to produce thin stillage and wet grains from the laboratory processes. Compositions of process streams were determined. In the dry‐grind process using GSHE, solids contents of beer, whole stillage, and wet grains were higher compared to the same fractions from the E‐Mill process using GSHE. Solids contents of mash for both processes were similar. Total solids, soluble solids, and ash contents of thin stillage were similar for the two processes. Fat content of thin stillage from E‐Mill was lower than that from the dry‐grind process; protein content of E‐Mill thin stillage was higher than that from dry‐grind thin stillage. Removal of germ and fiber before fermentation changed composition of thin stillage from the E‐Mill process. The screening method produced higher thin stillage and lower wet grains yields than using a centrifugation method. The screening method was less time consuming but resulted in limited wet grains material for additional analyses or processing. The centrifugation method of thin stillage separation removed more solids from thin stillage than the screening method.     

Effect of Enzymatic Tempering of Wheat Kernels on Milling and Baking Performance

This study examined the effect of cell‐wall‐degrading enzymes added to temper water on wheat milling performance and flour quality. An enzyme cocktail consisting of cellulase, xylanase, and pectinase and five independent variables (enzyme concentration, incubation time, incubation temperature, tempered wheat moisture content, and tempering water pH) were manipulated in a response surface methodology (RSM) central composite design. A single pure cultivar of hard red winter wheat was tempered under defined conditions and milled on a Ross experimental laboratory mill. Some treatment combinations affected flour yield from the break rolls more than that from the reduction rolls. However, a maximum for flour yield was not found in the range of parameters studied. Though treatments did not affect the optimum water absorption for breadmaking, enzyme‐treated flours produced dough exhibiting shorter mixing times and slack and sticky textures compared with the control. Regardless of differences in mixing times, specific loaf volumes were not significantly different among treatments. Crumb firmness of bread baked with flour milled from enzyme‐treated wheat was comparable to the control after 1 day but became firmer during storage up to 5 days.     

Use of Proteases to Reduce Steep Time and SO2 Requirements in a Corn Wet‐Milling Process

To eliminate the diffusion barriers associated with enzyme addition during conventional steeping, we have developed a two‐stage milling procedure to evaluate the effects of enzyme addition on corn wet milling. The current study compares the effects of the addition of commercially available enzyme preparations during conventional steeping to their comparable addition in the two‐stage procedure. Results are presented in terms of yields of fiber, starch, germ, and gluten. The results demonstrate that the application of enzymes to the normal steeping step of wet milling is not an effective means of decreasing the steeping time or sulfur dioxide usage. Only when specific enzymes are added to the hydrated ground corn, using the modified two‐stage procedure, are enzymes effective in decreasing the steeping time and sulfur dioxide requirements. The overall steeping time with the two‐stage modified procedure ranges from 6 to 8 hr, representing a 67–83% reduction over the conventional process. The modified process greatly decreases, and possibly eliminates, the need for sulfur dioxide addition, while producing starch yields and quality equivalent to that from the conventional process.     

Pretreatment of Wet‐Milled Corn Fiber to Improve Recovery of Corn Fiber Oil and Phytosterols

The phytosterol‐containing oil in the corn fiber (corn fiber oil) has potential use as a natural low‐density lipoprotein (LDL) lowering nutraceutical but its low concentration (1–3%) makes it difficult and expensive to extract. Pretreatment of corn fiber with dilute acid or glucosidases removed nonlipid components of fiber, producing oil‐enriched fractions that should be more amenable to efficient and inexpensive oil extraction. Acid, as well as enzymes, significantly increased the content of corn fiber oil and its phytosterol compounds by hydrolyzing (and removing) the starch and nonstarch (cell wall) polysaccharides from the wet‐milled corn fiber. Dual treatment of the fiber with acid and enzyme greatly increased the concentrations of corn fiber oil and its phytosterol components, compared with acid or enzyme treatments alone. Depending on the treatment, the oil concentration in the residual solids increased from 0.3 to 10.8% (21–771% increase in conc.) and the total phytosterol concentration increased from 19.8 to 1256.2 mg/g of fiber (11–710% increase in conc.) compared with untreated fiber.     

Treating Thin Stillage and Condensed Distillers Solubles with Phytase for Production of Low‐Phytate Coproducts

Fuel ethanol production from grains is mainly based on dry‐grind processing, during which phytate is concentrated about threefold in distillers dried grains with solubles (DDGS), a major coproduct. To reduce phytate in DDGS, Natuphos and Ronozyme industrial phytase preparations were used to treat commercially made thin stillage (TS). Changes in phosphorous (P) profile were monitored, and effects of reaction temperature, time, and enzyme concentration were investigated. Results showed that at a temperature ≤60°C for Natuphos phytase (≤70°C for Ronozyme phytase) and a concentration ≤4.8 FTU/mL of TS for Natuphos phytase (≤48 FYT/mL for Ronozyme phytase), a complete phytate hydrolysis (phytate P decreased to 0) could be achieved within 5–60 min of enzymatic treatment. Reduction in phytate P was generally accompanied by increase in inorganic P, whereas total P remained relatively unchanged. When condensed distillers solubles (CDS), the concentrated form of TS, was used as the substrate, phytate hydrolysis by each of the two enzyme preparations was as effective as on TS. Because a previous study from the author's laboratory showed that all types of P are mostly concentrated in TS and CDS but much less in distillers wet grains, phytase treatments of TS and CDS described in the present study can be an effective means in producing low‐phytate DDGS.     

Protein Extraction from Triticale Distillers Grains

Triticale is being actively explored as a feedstock for bioethanol production in Western Canada. Triticale distillers grains, an important coproduct of the bioethanol industry, are used mainly as animal feed. This study aims to develop methods of protein extraction from triticale distillers wet grains and distillers dried grains with solubles. Osborne fractionation showed low protein extractability because excessive protein denaturation occurred during sample preparation. Five methods were used to extract proteins: pH shifting, 60% ethanol, alkaline‐ethanol solution, glacial acetic acid, and enzyme‐aided extraction. Extracts obtained with the alkaline‐ethanol and glacial acetic acid methods showed comparatively higher protein contents (≈61–65%) when compared with the other extraction methods (≈35–57%). Enzyme‐aided extraction with Protex 6L yielded 75–82% protein at a content of 43–57%, depending on the types of raw materials. Establishing methods of protein extraction from triticale distillers grains would facilitate further studies on new uses of triticale proteins.     

Effect of Digestive Enzyme Treatment on Antioxidant Properties of Germinated Green Gram Fortified with Minerals

The antioxidant activity (AA) of green gram germinated in mineral‐fortified water (with iron at 100 or 200 mg/100 mL or zinc at 50 or 100 mg/100 mL), cooked under pressure (PC), or microwaved and subjected to digestive enzyme treatment was determined by using three assay methods. Total AA showed that dehulled grains (DG) had higher AA than whole grains (WG). Cooking reduced the AA in both methods compared with raw grains with a lower percent retention of AA, although significant variations were not found between methods. The percent retention of AA in postdigestion samples was 22.68–51.39 (DG) and 15.67–44.0 (WG). Free radical scavenging activity indicated a different pattern, in which WG exhibited higher AA than DG and, among cooking methods, PC grains had higher activity. A reducing‐power assay showed similar results: DG had lower and PC samples had higher AA. Postdigestion AA of WG was higher for cooked than raw samples, although DG showed the opposite trend. In all cases, samples fortified with iron showed less AA because of prooxidant action of iron. In all assays, postdigestion samples had less activity than predigested extracts. In conclusion, germinated grains showed high AA, influenced by the presence of minerals, dehulling process, and cooking.     

钙处理对葡萄柚果实细胞壁物质代谢及其相关基因表达的影响

【目的】研究采前、 采后钙处理对葡萄柚果实细胞壁组分、 细胞壁降解酶活性变化及其相关基因表达的影响,可为了解钙与果实细胞壁物质代谢之间的关系,揭示钙对果实软化的作用机理,为调控葡萄柚果实膳食纤维含量,提高果实质地品质提供理论依据。【方法】试验于2011年2月至11月在云南省玉溪市葡萄柚果园进行,供试品种为‘里约红’葡萄柚,该品种于2005年嫁接于当地砧木,株行距为3 m×3 m。试验由采前和采后钙处理两部分组成。采前钙处理在幼果初期、 幼果末期、 膨大初期、 膨大末期、 转色期,叶面喷施2% CaCl2; 采后钙处理在果实成熟采后浸于2% CaCl2溶液5 min, 室温贮藏。之后每15天取样一次,每次取10个果实,测定葡萄柚果肉细胞壁组分、 细胞壁降解酶活性及其基因表达量。【结果】随葡萄柚果实后熟软化,紧密结合型果胶(共价结合型果胶)解聚为松散结合型果胶(水溶性果胶、 离子结合型果胶),紧密结合型半纤维素(24% KOH可溶性半纤维素)解聚使其含量下降,而松散结合型半纤维素含量增加(4%KOH可溶性半纤维素)。果实PG、 PME、 Cx、 α-L-Af和β-Gal酶活性及其基因表达量均随果实软化呈不同程度增加。PME活性在果实采收后表现出较高含量,而PG活性在果实贮藏前期急剧增加,其酶基因的表达量与酶活性变化趋势基本一致。Cx、 α-L-Af和β-Gal活性在贮藏中、 后期上升较快,相关酶基因的表达量亦明显增加。钙处理显著地降低果实细胞壁降解酶活性和基因表达水平,其中采后钙处理对α-L-Af和β-Gal活性和基因表达在贮藏中、 后期的调控作用较显著,酶活性和基因表达均维持在较低水平。【结论】外源钙处理降低细胞壁降解酶活性及其基因表达,抑制了细胞壁物质的解聚,采后钙处理对细胞壁物质代谢的调控效果优于采前钙处理。外源钙处理抑制了细胞壁降解酶基因表达水平,降低了细胞壁降解酶活性,减缓了果胶、 半纤维素的解聚,从而达到调控果实膳食纤维含量、 维持果实质地品质、 延长果实货架期寿命的目的。     

Regulation of bacterial and fungal MCPA degradation at the soil-litter interface

Much is known about mechanisms and regulation of phenoxy acid herbicide degradation at the organism level, whereas the effects of environmental factors on the performance of the phenoxy acid degrading communities in soils are much less clear. In a microcosm experiment we investigated the small-scale effect of litter addition on the functioning of the MCPA degrading communities. ¹⁴C labelled MCPA was applied and the functional genes tfdA and tfdAα were quantified to characterise bacterial MCPA degradation. We identify the transport of litter compounds as an important process that probably regulates the activity of the MCPA degrading community at the soil-litter interface. Two possible mechanisms can explain the increased tfdA abundance and MCPA degradation below the litter layer: 1) transport of α-ketoglutarate or its metabolic precursors reduces the costs for regenerating this co-substrate and thereby improves growth conditions for the MCPA degrading community; 2) external supply of energy and nutrients changes the internal resource allocation towards enzyme production and/or improves the activity of bacterial consortia involved in MCPA degradation. In addition, the presence of litter compounds might have induced fungal production of litter-decaying enzymes that are able to degrade MCPA as well.     

不同土壤改良剂对土壤生化性质与烤烟产量的影响

通过田间试验,探讨以石灰、粉煤灰、白云石、废菌棒和化肥构成的不同组合改良剂对土壤微生物数量、酶活性和烤烟产量的影响。结果表明施用不同组合改良剂后,耕层土壤细菌、放线菌、磷细菌、钾细菌和纤维素分解菌的数量、土壤过氧化氢酶、脲酶、磷酸酶和纤维素酶的活性及烤烟产量均比对照有不同程度提高,其中添加废菌棒处理的微生物数量、酶活性和烤烟产量变化明显高于无添加废菌棒处理,且均以“石灰+菌棒+常规化肥”改良剂组合变化最明显,差异显著性检验表明该组合处理的5种微生物数量、4种酶活性及烤烟生物和经济产量与对照相比差异均达极显著水平。相关分析表明耕层土壤5种微生物数量和4种酶活性与烤烟生物及经济产量均呈极显著的正相关。表明施用不同组合改良剂能促进土壤细菌、放线菌、磷细菌、钾细菌及纤维素分解菌的繁殖,增强过氧化氢酶、脲酶、磷酸酶及纤维素酶的活性,促进烤烟产量的提高,其中以“石灰+菌棒+常规化肥”组合改良剂的效果最好。     

猪毛角蛋白降解菌的分离筛选及其降解特性研究

为了筛选能高效降解猪毛角蛋白的微生物,该研究利用猪毛角蛋白为唯一碳氮源的培养基从土壤中分离角蛋白降解菌,并对其菌种分类及降解角蛋白的特性进行了研究。通过驯化共筛选到6株能够降解猪毛角蛋白的菌株,经过7 d发酵培养,菌株X-3对猪毛角蛋白的降解率达77.3%,降解效果最佳。结合菌株形态特征、生理生化特征及16S rDNA发育进化树分析,初步鉴定该菌株为凝结芽孢杆菌(Bacillus coagulans)。菌株X-3是一株广谱的角蛋白降解菌,对猪毛、羊毛、鸡毛、鹅毛、鸭毛的降解率均大于60%。该菌株在角蛋白底物作用下可产生角蛋白酶和二硫键还原酶,且酶活与猪毛角蛋白降解率变化存在显著的正相关性,表明菌株X-3产生的角蛋白酶和二硫键还原酶在角蛋白降解中起到非常关键的作用。在降解过程中,产生了大量的可溶性蛋白,二硫键中的硫也随之转化为硫酸盐、亚硫酸盐和巯基化合物,其中硫酸盐是主要的转化形式。该菌株的分离筛选丰富了猪毛角蛋白降解菌的微生物资源库,在氨基酸饲料生产中具有潜在的应用价值。     

Starch and By‐Products from a Laboratory‐Scale Barley Starch Isolation Procedure

Starch was isolated from three different barleys with normal, highamylose, or high‐amylopectin (waxy) starch. The laboratory‐scale starch isolation procedure included crushing of grains, steeping, wet milling, and sequential filtration and washing with water and alkali, respectively. Yield and content of starch, protein, and dietary fiber, including β‐glucan, were analyzed in isolated starch and in the by‐products obtained. Starch yield was 25–34%, and this fraction contained 96% starch, 0.2–0.3% protein, and 0.1% ash. Most of the remaining starch was found in the coarse material removed by filtration after wet milling, especially for the high‐amylose barley, and in the starch tailings. Microscopy studies showed that isolated starch contained mostly A‐granules and the starch tailings contained mostly B‐granules. Protein concentration was highest in the alkali‐soluble fraction (54%), whereas dietary fiber concentration was highest in the material removed by filtration after alkali treatment for the normal and waxy barleys (55%). The β‐glucan content was especially high for the waxy barley in this fraction (26%). The study thus showed that it was possible to enrich chemical constituents in the by‐products but that there were large differences between barleys. This result indicates a need for modifications in the isolation procedures for different barleys to obtain high yields of starch and different by‐products. Valuable by‐products enriched in β‐glucan or protein, for example, may render starch production more profitable.     

Extraction of β‐Glucan from Oats for Soluble Dietary Fiber Quality Analysis

Extraction protocols for β‐glucan from oat flour were tested to determine optimal conditions for β‐glucan quality testing, which included extractability and molecular weight. We found mass yields of β‐glucan were constant at all temperatures, pH values, and flour‐to‐water ratios, as long as sufficient time and enough repeat extractions were performed and no hydrolytic enzymes were present. Extracts contained about 30–60% β‐glucan, with lower proportions associated with higher extraction temperatures in which more starch and protein were extracted. All commercial starch hydrolytic enzymes tested, even those that are considered homogenous, degraded β‐glucan apparent molecular weight as evaluated by size‐exclusion chromatography. Higher concentration β‐glucan solutions could be prepared by controlling the flour‐to‐water ratio in extractions. Eight grams of flour per 50 mL of water generated the highest native β‐glucan concentrations. Routine extractions contained 2 g of enzyme‐inactivated flour in 50 mL of water with 5mM sodium azide (as an antimicrobial), which were stirred overnight, centrifuged, and the supernatant boiled for 10 min. The polymer extracted had a molecular weight of about 2 million and was stable at room temperature for at least a month.     

Pasting Properties and Surface Characteristics of Starch Obtained from an Enzymatic Corn Wet‐Milling Process

Recently, we reported the development of an enzymatic corn wet‐milling process that reduces or eliminates sulfur dioxide requirements during steeping, considerably reduces steep time, and produces starch yields comparable to that of conventional corn wet‐milling. The best results so far, using the enzymatic corn wet‐milling procedure, were achieved when a particular protease enzyme (bromelain) was used. In this study, pasting properties and surface characteristics of starch obtained from six different enzyme treatments (three glycosidases [β‐glucanase, cellulase, and xylanase] and three proteases [pepsin, acid protease, and bromelain]) using the enzymatic corn wet‐milling procedure were evaluated and compared with those from starch obtained using the conventional corn wet‐milling procedure. Significant effects from enzymatic milling were observed on all the three starch pasting properties (peak, shear thinning, and setback). The setback viscosities of starch from all enzyme treatments were significantly lower compared with those of the control sample, indicating that starch polymers from enzymatic corn wet‐milling do not reassociate to the same extent as with the control. Comparison between bromelain treatment and the control sample showed that starch samples obtained from bromelain treatment are very similar to control starch in water‐binding capacity, molecular breakdown, and time to swell when cooked in water. Significant effects from enzymatic milling were observed on the surface characteristics of starch granules. The glycosidase treatments, especially the β‐glucanase samples, showed holes in the starch granules. No visual differences were observed in starch granules between bromelain and control samples.     

Endogenous Action of Cysteine Endopeptidase and Three Carboxypeptidases on Triticale Prolamins

Quantitative and qualitative changes occurring in the prolamin fraction in the starchy endosperm of triticale grains were analyzed by SDS‐PAGE on consecutive days of germination. The most intensive hydrolysis of prolamins was observed after the second day of the process. The high molecular weight fractions of prolamins were degraded with the highest rate. Endopeptidase EP8 was capable of hydrolyzing all fractions of prolamins isolated from dry triticale grains, but the high molecular weight fractions were the most rapidly degraded by the enzyme. Carboxypeptidases I, II, and III isolated from triticale grains hydrolyzed prolamins proteolytically modified by endopeptidase EP8, whereas intact prolamins were degraded slightly. Differences in the activity of the studied carboxypeptidases against crude prolamins indicate that carboxypeptidase II may be involved in the initiation of the hydrolysis process and, together with carboxypeptidases I and III, participates in the later stages of degradation of prolamins to amino acids. Experiments with exogenous GA₃ demonstrated that the synthesis of EP8 is induced by this hormone and takes place in the aleurone layer. Mass spectrometry analysis showed the enzyme to be a homologue of barley endopeptidase EP‐A. Both enzymes belong to the cysteine class endopeptidases.     

Ethanol Production from Modified and Conventional Dry‐Grind Processes Using Different Corn Types

Different corn types were used to compare ethanol production from the conventional dry‐grind process to wet or dry fractionation processes. High oil, dent corn with high starch extractability, dent corn with low starch extractability and waxy corn were selected. In the conventional process, corn was ground using a hammer mill; water was added to produce slurry which was fermented. In the wet fractionation process, corn was soaked in water; germ and pericarp fiber were removed before fermentation. In the dry fractionation process, corn was tempered, degerminated, and passed through a roller mill. Germ and pericarp fiber were separated from the endosperm. Due to removal of germ and pericarp fiber in the fractionation methods, more corn was used in the wet (10%) and dry (15%) fractionation processes than in the conventional process. Water was added to endosperm and the resulting slurry was fermented. Oil, protein, and residual starch in germ were analyzed. Pericarp fiber was analyzed for residual starch and neutral detergent fiber (NDF) content. Analysis of variance and Fisher's least significant difference test were used to compare means of final ethanol concentrations as well as germ and pericarp fiber yields. The wet fractionation process had the highest final ethanol concentrations (15.7% v/v) compared with dry fractionation (15.0% v/v) and conventional process (14.1% v/v). Higher ethanol concentrations were observed in fractionation processes compared to the conventional process due to higher fermentable substrate per batch available as a result of germ and pericarp fiber removal. Germ and pericarp yields were 7.47 and 6.03% for the wet fractionation process and 7.19 and 6.22% for the dry fractionation process, respectively. Germ obtained from the wet fractionation process had higher oil content (34% db) compared with the dry fractionation method (11% db). Residual starch content in the germ fraction was 16% for wet fractionation and 44% for dry fractionation. Residual starch in the pericarp fiber fraction was lower for the wet fractionation process (19.9%) compared with dry fractionation (23.7%).     

装配加温除湿系统的轻简装配式日光温室设计及性能试验

针对中国传统日光温室土地利用率低、建设成本高、墙体构造各异及温度和湿度环境难以调控等突出问题,该研究设计出一种轻简装配式日光温室,并配套了基于温室主动蓄放热原理的冬季夜晚加温和除湿系统,其温室骨架可与主动蓄放热系统结合为一体。研究结果表明:相比于传统砖墙日光温室,轻简装配式温室冬季夜晚温度提高4.5℃以上;采用基于主动蓄放热系统热能的除湿系统,可将温室夜间相对湿度降低14%,相对湿度控制在80%以下;该温室可实现整体式装配安装,大大减少了施工时间和安装成本,温室后墙厚度为166 mm,与后墙为600 mm厚的砖墙温室相比,墙体占地面积减少72%,显著提高了土地利用率。     

Precipitation of enzymes and organic matter by aluminum—Impacts on carbon mineralization

The precipitation of dissolved organic matter (DOM) by aluminum (Al) results in a stable soil organic matter (OM) fraction. Extracellular enzymes can also be removed from soil solution by sorption or precipitation, but whether this affects their activity and their importance for carbon (C) mineralization is largely unknown. We studied the activity of eight extracellular enzymes, precipitated by Al together with DOM, in relation to C mineralization of the precipitated OM. Dissolved OM was obtained from the Oi and Oa horizon of two forest soils and precipitated at different Al : C ratios and pH values to achieve a large variation in composition and C mineralization of precipitated OM. All eight enzymes were present in a functional state in precipitated OM. On average 53% of DOM was precipitated, containing on average 17%–41% of the enzyme activity (EA) involved in C degradation (chitinase, cellobiohydrolase, β‐glucosidase, glucuronidase, lacasse, and xylosidase) previously present in soil solution. In contrast, on average only 4%–7% of leucine‐aminopeptidase and acid‐phosphatase activity was found in precipitated OM. The EA found in precipitates significantly increased the percentage of C mineralized of precipitated OM, with a stronger influence of C‐degrading enzymes than enzymes involved in N and P cycling. However, after 8 weeks of incubation the correlations between EA and C mineralization disappeared, despite substantial EA being still present and only 0.5%–7.7% of C mineralized. Thus, degradation of precipitated OM seems to be governed by EA during the first degradation phase, but the long‐term stability of precipitated OM is probably related to its chemical properties.     

Effect of Steeping Treatment on Pasting and Thermal Properties of Sorghum Starches

Chemical treatments in wet milling could improve the physico‐chemical properties of starch isolated from high‐tannin sorghums. Sorghums Chirimaugute (medium‐tannin), DC‐75 (high‐tannin), and SV2 (tannin‐free) were steeped in water, dilute HCl (0.9%, v/v), formaldehyde (0.05%, v/v), and NaOH (0.3%, w/v) solutions before wet milling and starch separation. Pasting, textural, and thermal properties of starch were determined. Steeping in NaOH resulted in starches with higher peak viscosity (PV), cool paste viscosity (CPV), and setback than when water, HCl, and formaldehyde were used. The time to PV (P_time) and PV temperature (P_temp) were markedly reduced by treatment with NaOH. NaOH could have caused a degree of pregelatinization. HCl treatment gave starches with higher P_temp and P _time, presumably due to delayed granule swelling. Gel hardness was largely determined by the starch amylase content. The low hardness of DC‐75 starch gels was slightly improved in NaOH‐treated grains. Gelatinization temperatures of sorghum starches were generally low, regardless of steeping treatment. Starch from NaOH‐treated grain generally had slightly higher gelatinization temperatures than when water, HCl, or HCHO was used. Chemical treatments during steeping of sorghum grains greatly affected starch properties. Dilute alkali steeping during wet milling could be used to improve properties of starch isolated from tannin‐containing sorghums.