Changes in Nixtamalized Corn Flour Dependent on Postcooking Steeping Time

We studied the effect of steeping time on various physical and chemical properties of maize flour prepared by the traditional nixtamalization process as well as in oversaturated calcium ion conditions. The calcium content of the corn flour was measured by atomic absorption spectroscopy and was correlated with X‐ray diffraction, viscosity, and pH measurements. Calcium content of the flour showed a nonlinear dependence on steeping time, with a local calcium maximum occurring at ≈7 hr. The pH level of the corn flour increased with steeping time, thus roughly following the time trend shown by the steeping time dependence of the calcium content. Flour crystallinity and peak viscosity of water suspensions of the flour reached maximal values at ≈7–9 hr of steeping, in agreement with manufacturing experience showing that these are appropriate steeping times to prepare tortillas with the desirable rheological and organoleptic properties.     

Effect of Temperature and Steeping Time on Calcium and Phosphorus Content in Nixtamalized Corn Flours Obtained by Traditional Nixtamalization Process

This report shows the effect of temperature (72, 82, and 92°C) during the cooking stage and steeping time (0, 1, 3, 5, 7, 9, 11, 13, and 15 hr) on calcium and phosphorus contents in nixtamalized corn flours obtained by the traditional nixtamalization process (NCF). In addition, calcium and phosphorus contents in industrial nixtamalized corn flours were analyzed for comparative purposes. Atomic absorption spectroscopy and UV‐vis spectroscopy methods were used to study the calcium and phosphorus contents as well as the Ca²⁺/P ratio in NCF and industrial nixtamalized corn flours. Additionally, deposition and identification of calcium compounds in the nixtamalized corn pericarp were analyzed by low‐vacuum scanning electron microscopy, energy dispersive spectrometry, and X‐ray diffraction techniques. Dry matter loss in NCF is also reported. As the temperature increased, Ca²⁺ content was enhanced, while the phosphorus content decreased with statistical differences (P ≤ 0.05) between thermal treatments. Ca²⁺ content in industrial nixtamalized corn flours was significantly lower (P ≤ 0.05) than that of NCF. On the other hand, no statistical differences (P ≤ 0.05) were found between phosphorus content in commercial nixtamalized corn flours and NCF. Calcium compounds, identified as calcite, were detected in corn pericarp. Statistical differences (P ≤ 0.05) were observed in phosphorous content in NCF obtained at different cooking temperatures. In addition, a decrease in phosphorus levels significantly correlated with the steeping time at 92°C (r = –0.91). At 72, 82, and 92°C, the average Ca²⁺/P ratio in NCF was 0.45 ± 0.03, 0.61 ± 0.05, and 0.82 ± 0.05, respectively, indicating a correlation between this parameter and the cooking temperature. However, no correlation was found between the Ca²⁺/P ratio and the steeping time. This behavior is attributed to calcium attached to corn kernel. In commercial nixtamalized corn flours, the Ca²⁺/P ratio was significantly lower (P ≤ 0.05) than that of NCF. There was a significant correlation (P ≤ 0.01) between dry matter loss and steeping time (r = 0.99) in NCF, this fact influenced the Ca²⁺/P ratio due to the calcium attached to pericarp. At 82 and 92°C, maximum values of Ca²⁺/P ratio were detected in NCF at 7 hr of steeping time and at 9 hr at 72°C. These results can be used with industrial purposes to assess a maximum calcium‐to‐phosphorus ratio, and at the same time, to avoid the loss of pericarp to increase the functional properties of NCF.     

Study of Calcium Ion Diffusion in Nixtamalized Quality Protein Maize as a Function of Cooking Temperature

In this report, the effect of temperature on the calcium content of Quality Protein Maize (QPM H-368C) during the nixtamalization process as a function of the steeping time for three cooking temperatures (72, 82, and 92°C) is presented. Also, for the first time, we report in physico-chemical terms the end of the cooking stage during the nixtamalization process that was established when the moisture content in corn kernels reached a value of 36% (w/w) with a lime concentration of 1% (w/v), independent of the cooking temperature. Atomic absorption spectroscopy was used to determine the calcium concentration in the whole kernel and in its different anatomical components (pericarp, endosperm, and germ) as well as in 10% of the outermost layers, the next 10%, and the remaining 80% of the endosperm as a function of the steeping time. It was found that if the cooking temperature increases, the calcium content increases also. For steeping times in the range of 5–7 hr, a relative maximum was found in the calcium contents of 0.24, 0.21, and 0.18% (w/w) in QPM H-368 flours at 92, 82, and 72°C, respectively. Calcium was found in the most external layers in the endosperm and minimum diffusion occurs in the internal 80%. Phosphorous was measured by using UV spectroscopy and the results showed that it remains constant at 0.24% throughout the process. Scanning electron microscopy analysis was used to explain the calcium ion diffusion in the kernel. The physical changes in the pericarp govern the calcium diffusion process.     

Technological and Nutritional Properties of Flours and Tortillas from Nixtamalized and Extruded Quality Protein Maize (Zea mays L.)

Nixtamalized and extruded flours from quality protein maize (QPM, V‐537C) and tortillas made from them were evaluated for some technological and nutritional properties and compared with the commercial brand MASECA. Both QPM flours showed higher (P < 0.05) protein content, total color difference, pH, available lysine, and lower (P < 0.05) total starch content, Hunter L value, water absorption index, gelatinization enthalpy, resistant starch, and retrograded resistant starch than nixtamalized MASECA flour. Tortillas from nixtamalized and extruded QPM flours had higher contents of essential amino acids than tortillas from MASECA flour, except for leucine. Tortillas from processed QPM flours also showed higher (P < 0.05) values of the nutritional indicators calculated protein efficiency ratio (C‐PER 1.80–1.85 vs. 1.04), apparent and true in vivo protein digestibility (78.4‐79.1 vs. 75.6% and 76.4–77.4 vs. 74.2%, respectively), PER (2.30–2.43 vs. 1.31), net protein retention (NPR; 2.88–2.89 vs. 2.11), and protein digestibility corrected amino acid score (PDCAAS; 54–55 vs. 29% based on preschool children and 100 vs. 85% based on adults) than MASECA flour. The use of QPM for flour and tortilla preparation may have a positive effect on the nutritional status of people from countries where these products are widely consumed.     

Levels of Protein and Protein Composition in Hard Winter Wheat Flours and the Relationship to Breadmaking

Protein and protein fractions were measured in 49 hard winter wheat flours to investigate their relationship to breadmaking properties, particularly loaf volume, which varied from 760 to 1,055 cm³ and crumb grain score of 1.0–5.0 from 100 g of flour straight‐dough bread. Protein composition varied with flour protein content because total soluble protein (SP) and gliadin levels increased proportionally to increased protein content, but albumins and globulins (AG), soluble polymeric proteins (SPP), and insoluble polymeric protein (IPP) levels did not. Flour protein content was positively correlated with loaf volume and bake water absorption (r = 0.80, P < 0.0001 and r = 0.45, P < 0.01, respectively). The percent SP based on flour showed the highest correlation with loaf volume (r = 0.85) and low but significant correlation with crumb grain score (r = 0.35, P < 0.05). Percent gliadins based on flour and on protein content were positively correlated to loaf volume (r = 0.73, P < 0.0001 and r = 0.46, P < 0.001, respectively). The percent IPP based on flour was the only protein fraction that was highly correlated (r = 0.62, P < 0.0001) with bake water absorption followed by AG in flour (r = 0.30, P < 0.05). Bake mix time was correlated positively with percent IPP based on protein (r = 0.86) but negatively with percent SPP based on protein (r = ‐0.56, P < 0.0001).     

Correlation of Quality Parameters with the Baking Performance of Wheat Flours

The baking performance of a set of flours from 13 wheat cultivars was determined by means of two different microscale baking tests (10 g of flour each). In the micro‐rapid‐mix test the dough was mixed for a fixed time at a high speed, whereas the microbaking test used mixing to optimum dough consistency in a microfarinograph. Quality parameters such as sedimentation value, crude protein content, dough and gluten extension data, and microfarinograph data were also determined. Finally, quality‐related protein fractions (gliadins, glutenins, SDS‐soluble proteins, and glutenin macropolymer) were quantitated by extraction/HPLC methods with reversed‐phase and gel‐permeation columns. All quality parameters were correlated with the bread volumes of both baking tests. The results demonstrated that the microbaking test (adapted mixing time) was much more closely related to the quality parameters than the micro‐rapid‐mix test (fixed mixing time), which hardly showed any correlation. Among the standard quality parameters, only the crude protein content showed a medium correlation with the bread volume of the microbaking test (r = 0.71), whereas the contents of gliadins (r = 0.80), glutenins (r = 0.76), and glutenin macropolymer (r = 0.80) appeared to be suitable parameters to predict the baking performance of wheat flour. All other quality parameters were not or were only weakly correlated and unsuitable for predicting baking performance.     

Changes in the Element Composition of Flours during Maturation of the Winter Wheat Kernel

Abstract

An underappreciatel field of plant analysis is the change in the nutrient concentration of flours from winter wheat (Triticum aestivum L.) during maturation. The knowledge of these processes is important because breeding solely for higher yield has caused a decrease in the nutrient concentrations important for human nutrition. The difference in nutrient concentration of flours from grains of different spike positions is also an interesting field of plant analysis. The objective of this study was to study these processes to better understand the effect of these factors on flour quality. The concentration and amount of macro (nitrogen, phosphorus, potassium, calcium, magnesium) and micronutrients (copper, manganese, iron, zinc) were determined in the flours of grains of two genotypes from basal, central, and apical grain positions, from the 14th day to the 42th day after anthesis. Genotype and sampling time both affected the concentration of nutrients. The grain position on the head also influenced the N, Ca, K, Mn, P, and S concentrations. The amount of assimilated nutrients in flours increased until the middle of maturity, and then remained around specific values in the case of some elements. We describe the changes in concentrations of these nutrients based on changes in the assimilated mass.     

Influence of Cooking Conditions on the Protein Matrix of Sorghum and Maize Endosperm Flours

To understand the influence of the sorghum and maize endosperm protein matrix honeycomb structure on starch hydrolysis in flours, three‐dimensional fluorescence microscopy was applied to floury and vitreous endosperm flours cooked under various conditions. Cooking caused the collapse and matting of the sorghum and maize vitreous endosperm matrices, with the effect being greater in sorghum. The effect of cooking was rather different in the floury endosperm in that the protein matrices expanded and broke up to some extent. These effects were a consequence of expansion of the starch granules through water uptake during gelatinization. Cooking in the presence of 2‐mercaptoethanol caused an expansion of the vitreous endosperm matrix mesh due to breakage of disulfide bonds in the protein matrix. Mercaptoethanol also caused an increase in the proportion of β‐sheet structure relative to α‐helical structure of the endosperm proteins. Increased energy of cooking caused collapse of the sorghum matrix. Disulfide bonding and an increase in β‐sheet structure occurred with cooking, with the increase in disulfide bonding being greatest in sorghum vitreous endosperm. The tendency for the sorghum protein matrix to collapse and mat more with cooking than the maize matrix appears to be due to greater disulfide bonding. This is responsible for the observed low starch digestibility of cooked sorghum flour as a result of the more disulfide‐bonded protein matrix limiting the expansion of the starch granules and hence amylase access.     

Size‐Exclusion HPLC of Protein Using a Narrow‐Bore Column for Evaluation of Breadmaking Quality of Hard Spring Wheat Flours

The objective of this study was to investigate whether a narrow‐bore column (NBC) (300 × 4.5 mm, i.d.) improved analyses of unreduced proteins in flour by size‐exclusion HPLC (SE‐HPLC) and subsequent evaluation of breadmaking quality of hard spring wheat flours. Total protein extracts and SDS buffer extractable and unextractable proteins were analyzed by SE‐HPLC. NBC separated proteins in 10 min at a flow rate of 0.5 mL/min with similar resolution to a regular column (300 × 7.8 mm, i.d.) which took 30 min. SE‐HPLC absorbance area (AA) data obtained from an NBC showed comparable or superior repeatability and correlations with flour breadmaking characteristics when compared with those of a regular column. AA values of total protein that were calculated by adding AA values of SDS extractable and unextractable proteins showed greater repeatability and correlations with quality characteristics than those of actual total protein extracts. The improvements including employment of an NBC in SE‐HPLC provide enhancement of rapid quality evaluation and decreased consumption of hazardous organic solvents.     

Relationships of Free Lipids with Quality Factors in Hard Winter Wheat Flours

Hard winter wheat (Triticum aestivum L.) flours (n = 72) were analyzed for free lipids (FL) and their relationships with quality parameters. The two main glycolipid (GL) classes showed contrary simple linear correlations (r) with quality parameters. Specifically, kernel hardness parameters, flour yields, and water absorptions had significant negative correlations with monogalactosyldiglycerides (MGDG) but positive correlations with digalactosyldiglycerides (DGDG). MGDG showed negative correlations with gluten content but positive correlations with gluten index. The percentages of DGDG in FL had significant positive correlations among cultivars (n = 12) with mixograph and bake mix times (r = 0.71, P < 0.01 and r = 0.67, P < 0.05, respectively), mixing tolerance (r = 0.67, P < 0.05), and bread crumb grain score (r = 0.71, P < 0.01). These results suggest that increasing DGDG in FL could contribute to enhancing wheat quality attributes including milling, dough mixing, and breadmaking quality characteristics. FL content and composition (ratio of MGDG or DGDG to GL) supplement flour protein content to develop prediction equations of mixograph mix time (R² = 0.89), bake mix time (R² = 0.76), and loaf volume (R² = 0.72).     

Use of Solvent Retention Capacity Profile to Predict the Quality of Triticale Flours

The solvent retention capacity test (SRC) was used to evaluate flour functionality for end use applications and select wheat for production of flour with required functionality, but there is little information about SRC test application on triticale flour quality. The ability of flour to retain a set of four solvents produces a flour quality profile for predicting bakery performance. The objective of this study was to evaluate the capacity of SRC and its micro test to determine the potential quality of 25 triticale flours, as well as studying the relationship between the SRC parameters and flour chemical composition. The SRC parameters of triticale flours were correlated with the flour components that have been proposed by the method: sucrose SRC‐pentosan (r = 0.57), carbonate SRC‐damaged starch (r = 0.80), lactic SRC‐glutelin (r = 0.42), water SRC‐all hydrophilic constituents (damaged starch [r = 0.72], protein [r = 0.61], glutelin [r = 0.66], pentosan [r = 0.46]). Triticale flours have shown higher water and sodium carbonate SRC, similar sucrose SRC, and lower lactic SRC values than published results of typical flours used for cookie production. Summarizing, the high level of association found between SRC and micro SRC parameters with flour composition and quality flour tests evidence that either the SRC profile or the micro test SRC could be used to determine the potential quality of triticale flours.     

Effect of Roller Mill Extraction Rate on the Chapatti-Making Quality of Canadian Flours

The effect of roller mill extraction rate on the chapatti-making potential of Canadian wheat from six different classes was assessed. Objective measurement of texture including pliability, puncturability, and tearing force, in conjunction with color, discerned significant differences due to flour extraction rate as well as wheat class. The 85% extraction yield was determined by sensory panelists to yield the best chapatti. Analyses of objective measurements, HunterLab values L*, a*, and b*, in conjunction with sensory assessments, suggested that the optimum chapatti have a brightness (L*) of 75–79, redness (a*) of 1.5–4.0, and a yellowness (b*) >17. Sensory scoring compared with objective measurement indicated that a tearing force of <4.0 kg was necessary to achieve optimum panelist evaluation of tearing and chewability. The primary reasons for a fair rating were attributable to either a too white and nonwheaty taste for the low extraction flours or, in the case of the 95% extraction material, dark chapattis with a slightly off flavor. No chapatti prepared from any of the wheat classes or varying extraction rate flours resulted in an unacceptable rating. Evidence suggests that removal of low-extraction mill-streams, up to 40%, from a 85% extraction yield flour did not have a detrimental effect on chapatti quality.     

Free Lipids in Air‐Classified High‐Protein Fractions of Hard Winter Wheat Flours and Their Effects on Breadmaking Quality

Free lipids (FL) were extracted from straight‐grade flours (SF) and the air‐classified high‐protein fractions (ACHPF) of nine hard winter wheats. The mean values of FL contents in 10 g (db) SF and ACHPF were, respectively, 92.8 and 178.5 mg for total FL, 74.1 and 141.9 mg for nonpolar lipids (NL), 12.8 and 20.9 mg for glycolipids (GL), and 4.9 and 12.0 mg for phospholipids (PL). FL compositions of SF and ACHPF showed nonsignificant differences in NL (80.7 and 81.1% of the FL) but significant differences in GL (13.9 and 12.0% of the FL) and PL (5.4 and 6.9% of the FL). Fortification of SF with ACHPF by blending to reach 13% protein content increased gluten quantity and thereby loaf volume but decreased gluten index, loaf volume regression, and crumb grain scores. NL contents showed significant relationships with dry gluten contents (r = 0.79) and gluten index (r = ‐0.83) values, indicating that high NL content in ACHPF could decrease gluten quality of fortified flours. Thus, an optimum balance should be maintained during fortification.     

Impact of Characteristics of Different Wheat Flours on the Quality of Frozen Cooked Noodles

In this study, the impact of characteristics (physicochemical, rheological, and pasting properties) of different wheat flours on the quality of frozen cooked noodles was investigated. In this sample set, results showed the cooking loss of noodles related negatively to flour swelling power. The water absorption of noodles related negatively to the dough stability time, the area, and the resistance to extension. The wheat flour with higher dough development time resulted in frozen cooked noodles with higher hardness, chewiness, and adhesiveness. Springiness of noodles correlated negatively to degree of softening. The tensile properties of frozen cooked noodles were influenced by rheological and pasting properties of wheat flours. The present study indicated high quality of frozen cooked noodles demanded wheat flours with high dough gluten strength, peak viscosity, and final viscosity and with low pasting temperature.     

Effect of Steeping Conditions (Sulfur Dioxide,Lactic Acid,and Temperature) on Starch Yield,Starch Quality,and Germ Quality from the Intermittent Milling and Dynamic Steeping Process (IMDS) for a Brazilian Corn Hybrid

Effect of lactic acid, SO₂, temperature, and their interactions were assessed on the dynamic steeping of a Brazilian dent corn (hybrid XL 606) to determine the ideal relationship among these variables to improve the wet‐milling process for starch and corn by‐products production. A 2×2×3 factorial experimental design was used with SO₂ levels of 0.05 and 0.1% (w/v), lactic acid levels of 0 and 0.5% (v/v), and temperatures of 52, 60, and 68°C. Starch yield was used as deciding factor to choose the best treatment. Lactic acid added in the steep solution improved the starch yield by an average of 5.6 percentage points. SO₂ was more available to break down the structural protein network at 0.1% than at the 0.05% level. Starch‐gluten separation was difficult at 68°C. The lactic acid and SO₂ concentrations and steeping temperatures for better starch recovery were 0.5, 0.1, and 52°C, respectively. The Intermittent Milling and Dynamic Steeping (IMDS) process produced, on average, 1.4% more starch than the conventional 36‐ hr steeping process. Protein in starch, oil content in germ, and germ damage were used as quality factors. Total steep time can be reduced from 36 hr for conventional wet‐milling to 8 hr for the IMDS process.     

滹滏平原地下水资源脆弱性时变分析

采用灰色关联度法和BP神经网络法计算各指标权重,然后用综合指数法分别对滹滏平原1984年和2000年地下水资源脆弱性进行了评价。2000年相对于1984年,地下水资源脆弱性分布特征发生了明显的变化,而且脆弱性级别升高。地下水资源脆弱性具有时变性,制定地下水合理利用模式时应当结合现状实际地下水资源脆弱性。     

水库水质之时间数列分析研究

本研究将以德基水库中总磷资料计算 TSI（Trophic Status Index）优养指数,并利用相乘性分解方法（multiplicative decomposition method）进行德基水库水质优养化时间数列分析研究,用以了解德基水库水质之优养化变化情形。研究显示,德基水库季节变化（S）之水质优养化变动情形每年有一高峰期,从 4～10月,总长度达 7个月之久。此外,德基水库优养指数长期趋势（T）乃显示随时间（t）呈缓慢成长状态,其间的关系可表示为 T =51.4231+ 0.0605t,其中 t=1,2,3……,161。至于在循环变动（C）的研究中则发现,循环变动周期自早期的 2～3年,逐渐缩减至 1年左右。由此可知,德基水库水质优养化的情形有日益严重的趋势。     

Relationship Between Physicochemical Properties of Starches and White Salted Noodle Quality in Japanese Wheat Flours

This study describes the effect of starch properties of Japanese wheat flours on the quality of white salted noodles (WSN). Starch was isolated from 24 flours of 17 Japanese cultivars and amylose content was determined along with pasting properties by Rapid Visco Analyser (RVA), thermal properties by differential scanning calorimetry (DSC), and the distribution of amylopectin chain length by high‐performance anion exchange chromatography (HPAEC). Twenty flours were used to prepare WSN. As expected, 5–6% lower amylose content was associated with good WSN quality (higher scores in softness, elasticity, and smoothness). RVA analysis indicated that the pasting temperature had the greatest influence on WSN quality, while breakdown and setback showed slight effects on WSN quality. DSC results showed that lower endothermal enthalpy (ΔH) in the amylose‐lipid complex was associated with good WSN quality. Chainlength distribution of amylopectin by HPAEC was not an important factor in relation to WSN quality.     

窟野河流域生态系统服务功能变化及其驱动因素分析

[目的] 窟野河流域地处黄河流域重要补给段,是黄河中上游侵蚀最强烈的地区之一,其生态环境不仅影响自身的发展,还影响黄河下游的区域生态发展。[方法] 为了对窟野河流域生态系统服务功能有更加全面的认识与理解,运行InVEST模型定量评估1990-2020年生态服务功能(碳储量、土壤保持、水源涵养、生境质量),并采用地理探测器分析其驱动因素。[结果] (1)在土地管理政策的驱动下,建设用地的面积显著增加,未利用地的面积明显减少,主要土地类型以草地为主,植被覆盖度呈波动上升的趋势。(2)窟野河流域生态服务功能均表现出在2000年左右下降,2010年后波动升高,生境质量指数基本稳定在0.22~0.24,整体生境质量较差。(3)土壤保持和生境质量指数在流域内以低-低聚集的冷点分布为主,碳储量和水源涵养量冷点和热点的空间分布较为分散,高值和低值在空间上呈现交错分布。(4)近30年碳储量、生境质量主要受土地利用影响,土壤保持和水源涵养主要受地形、土壤类型和降水影响。[结论] 研究结果可为窟野河流域生态服务综合效益的提升和水土保持措施的配置提供科学的依据。     

冷海水预处理时间对竹筴鱼冻藏品质的影响

为评价冷海水预处理时间对竹筴鱼冻藏品质的影响,本试验比较了未处理(CK)、冷海水预处理4 h(T1)和48 h(T2)的竹筴鱼在冻藏12个月内,鱼体的细菌总数(APC)、挥发性盐基氮(TVB-N)、脂肪氧化(TBARS、POV)、盐溶性蛋白含量的变化趋势。结果表明,随着冻藏时间的延长,各组竹筴鱼鱼体APC和TVB-N值均呈上升趋势,其中上升幅度为CKT1T2;贮藏第12个月,CK、T1和T2竹筴鱼样品的TVB-N值分别是30.24、27.03、26.28 mg·100g~(-1)。此外,冷海水预处理加速了鱼体TBARS和POV值的上升及肌原纤维蛋白的溶出。综合分析,冷海水预处理可减缓鱼体品质下降,延长货架期,本研究为渔品的冻藏预处理提供了有效的技术手段。