Nixtamalized Instant Flour from Corn (Zea mays L.) Meal: Optimization of Nixtamalization Conditions

The present investigation provides a new method for the nixtamalization process wherein corn endosperm fractions (corn meal) are treated in an alkaline solution that yields quality masa or instant masa flour like traditional nixtamalization process (alkaline cooking of corn with lime). The objective of this work was to determine the best combination of nixtamalization process variables for producing nixtamalized instant flour (NIF) from corn meal. Nixtamalization conditions were selected from factorial combinations of process variables including nixtamalization time (NT 8–22 min) and cooking temperature (CT 78–88°C). A central composite rotable experimental design was chosen. Lime concentration was 1% (10 g of Ca(OH)₂/L of water) and ratio of corn meal to cooking medium was 1:4. At the end of each cooking, each treatment was steeped for 5 hr at room temperature (25°C). Nixtamalized corn meal was dried (55°C/12 hr) and milled to pass through 80 U.S. mesh to obtain NIF. Response surface methodology (RSM) was applied as an optimization technique over four response variables: masa firmness (MF), masa adhesiveness (MA), tortilla cutting force (CF), and tortilla tensile strength (TS). Predictive models for response variables were developed as a function of process variables. Conventional graphic methods were applied to obtain response variable values similar to the control (MASECA). Contour plots of each response variable applied superposition surface methodology to obtain a contour plot for observation and for selecting the best combination of nixtamalization time (NT 15 min) and cooking temperature (CT 83°C) for producing an optimized NIF from corn meal. Values of MF, MA, CF, and TS obtained from the predictive models were compared with those derived from experimental tests; a close agreement (coefficient of variance < 10%) between both values was observed.     

Thermal Properties of Starch from Selected Maize (Zea mays L.) Mutants During Development

The changes in thermal properties of maize starches during five stages of kernel maturity, (12, 18, 24, 30, and 36 days after pollination [DAP]), from three mutant genotypes, amylose extender (ae), sugary-2 (su₂), and waxy (wx) in an OH43 background, and the OH43 genotype were studied using differential scanning calorimetry (DSC). Within a genotype, DSC values of starches at 24, 30, and 36 DAP were similar to each other and often were significantly different (P < 0.05) from the values at 12 DAP, indicating possible differences in the fine structure of starch during endosperm development. For su₂ starches, the gelatinization onset temperature (T_oG) significantly decreased after 12 DAP and remained low throughout the study. The gelatinization range (R_G) had a similar pattern. For wx starches, T_oG at 18 DAP was significantly lower than at 12 DAP but tended to increase after 18 DAP. The R_G increased significantly after 12 DAP and significantly decreased after 30 DAP. Thus, thermal properties of starches during early development were different from those of their mature counterparts, and differences among the mutant genotypes and the normal starch originated from the earliest endosperm development stage studied (12 DAP).     

Effect of Potassium Supplies on the Nutritional Status of Maize (Zea mays L.)

The effect of soil potassium (K) supplies on the yield and nutritional status of maize and on interactions between the nutrients was examined in a long-term mineral fertilization experiment on maize. The experiment was set up in 1989 in Hungarian Great Plain, Szarvas on chernozem meadow soil calcareous in the deeper layers, with four levels each of nitrogen (N), phosphorus (P) and potassium (K) supplies. The present paper describes the results of K fertilization in the 7–19th years of the experiment, from 1996 to 2008. The ammonium (NH₄)-lactate (AL) potassium oxide (K₂O) content of the ploughed layer ranged from 200 to 550 mg kg^–1 depending on the K fertilization level. No significant yield surpluses were recorded in any of the 13 years in response to the better K supplies ensured by K fertilizer. The results of leaf analysis indicated that the K concentrations representing satisfactory K supplies at a grain yield level of 10–14 t ha^–1 were 2.3–4.3% at the 5–6-leaf stage and 1.5–2.6% at the beginning of tasselling. When the AL-K₂O content of the soil was above 200–320 mg kg^–1, K– calcium (Ca), K–magnesium (Mg) and K–copper (Cu) antagonism was observed in the nutrient concentrations of the maize leaves in most years. The limit values of satisfactory nutrient supplies for maize in the 5–6-leaf stage and at the beginning of tasselling were 0.25–0.60% for Ca, 0.15–0.40% for Mg, and 7–11 mg kg^–1 and 2–11 mg kg^–1, respectively, for Cu. In dry years the iron (Fe) and zinc (Zn) concentrations of maize leaves declined at higher soil K supply levels.     

Thermal Properties of Starch from 62 Exotic Maize (Zea mays L.) Lines Grown in Two Locations

The variability in thermal properties among 62 S₃ lines derived from a high-yielding exotic corn (Zea mays) population, Antigua 1 (PI 484990), was evaluated by differential scanning calorimetry (DSC). The S₃ lines were grown in Puerto Rico (1990–1991) and Georgia (1994). Separate single-kernel starch extractions for five kernels (five replicates) from each line grown in each location were performed, and the starch was analyzed. The DSC values reported included gelatinization onset (T_oG), range (R_G), enthalpy (ΔH_G), and peak height index (PHI) and retrogradation onset (T_oR), range (R_R), enthalpy (ΔH_R), and percent retrogradation (%R) (an indication of the stability of gelatinized starch after storing at 4°C for 7 days). Significant differences (P < 0.05) were found among the 62 lines of Antigua 1 for T_oG, R_G, and PHI and highly significant differences (P < 0.01) were found for ΔH_G. The starches from plants grown in Georgia (1994) had significantly (P < 0.05) greater T_oG, ΔH_G, and PHI but a significantly lower R_G than those from Puerto Rico (1990–1991). These data suggest that the starch from plants grown in Georgia (1994) might have a greater degree of crystallinity than that from Puerto Rico (1990–1991). None of the retrogradation values were significantly different among starches of the 62 lines of Antigua 1 and the starches from plants grown in the two locations.     

Maize (Zea mays L.) genetic factors for preventing fumonisin contamination

Fusarium moniliforme and Fusarium proliferatum are the most frequently isolated fungi from maize (Zea mays L.) in Spain. Both Fusarium species produce toxins potentially dangerous for animals and humans, the fumonisins being the most significant of those toxins. White maize is preferred for human consumption, and extra care should be taken to avoid kernel mycotoxin contamination. The objectives of this study were to identify and quantify kernel infection by Fusarium spp. and contamination by fumonisin on white maize hybrids, to search for white maize sources of resistance to infection by Fusarium spp. and mycotoxin contamination, and to preliminarily study the genetics involved in such resistances. Ten F(1) single crosses derived from a diallel mating design among five white maize inbreds were evaluated in a randomized complete block design with three replications in 2002 at two locations. Fusarium verticilloides and F. proliferatum were detected on kernels of white maize hybrids cultivated in northwestern Spain. No differences in fungal infection were found among maize genotypes, but differences in fumonisin contamination were significant and could be related, in part, to differences in husk tightness. Among the genotypes studied, general combining ability (GCA) effects were the most important for resistance to fumonisin contamination. Inbreds EP10 and EC22 showed the most favorable GCA effects for husk tightness and fumonisin content, and the cross between them, EP10 x EC22, had the most favorable specific combining ability (SCA) effect for husk tightness. Inbreds EP10 and EC22 showed favorable GCA effects for fumonisin contamination and husk tightness, and the cross EP10 x EC22 was the only one with an average fumonisin level below 1 mug/g. Although this should be confirmed with more extensive studies, white maize inbreds developed from white maize landraces could be sources of resistance to fumonisin contamination.     

玉米单倍体胚性愈伤的诱导与鉴定

为建立一套适合玉米单倍体胚性愈伤培养和快速筛选体系,以单倍体诱导系MT-1为父本,18-599红为母本进行单倍体诱导,设置暗培养、全光照培养和光暗周期培养3种光照培养方式,均分别培养0、1、5、10、20、40 h后,观察幼胚形态和颜色。结果表明,自交系18-599红的单倍体和二倍体幼胚均能正常诱导形成胚性愈伤组织;不同光照培养方式对紫色(二倍体)愈伤率的检出效果依次为光培养>光暗周期培养>暗培养。通过光照筛选的方法可在早期鉴定愈伤组织,其二倍体愈伤的筛选率在培养20 h时可达68%,40 h时为71%,剔除了大部分非单倍体愈伤,综合分析确定光照强度为2 000 lx、20℃处理20 h为最适光照筛选处理。染色体压片技术获得的拟单倍体愈伤中有二倍体愈伤的检出,但经流式细胞仪检出获得的拟单倍体愈伤再经染色体压片检测,无二倍体愈伤,表明流式细胞仪检测单倍体愈伤的准确性高于染色体压片技术。通过光照初步筛选结合流式细胞仪的精确鉴定,迅速从3 000个单倍体愈伤中获得110个单倍体愈伤,单倍体愈伤率3.67%。本研究结果为以玉米单倍体愈伤为转基因受体,快速获得转基因植株提供了一定的技术支撑和理论参考。     

Variability Among Maize (Zea mays L.) Inbred Lines for Seed Longevity

Genotypes conserved in active collections may suffer genetic erosion and modifications. The objective of this work was to investigate changes in germination and vigour in maize (Zea mays L.) inbred lines during cold storage in an active collection. Seeds of 16 maize inbreds produced along 16 years were evaluated for emergence and seedling vigour in a growth chamber. Linear and quadratic regressions of vigour and viability-related traits over seed age were calculated and tested for homogeneity. The seed of five production years of five inbreds that behaved differently in the regression analysis was multiplied in 1998, and original and renewed seed were evaluated in a growth chamber in 1999. Viability and vigour decreased linearly with age for most inbreds, particularly for B84 and EP10, varied at random for a few inbreds, and remained high for EP56 and A295. Aging caused reduction of vigour and loss of viability in most inbreds. There was variability for seed longevity among inbred lines; longevity was highest for inbred EP56. During storage, some seeds of each inbred died, while enduring seeds, when multiplied, produced new seed with enhanced viability and vigour compared to the average seed of the inbred, suggesting natural selection for viability and vigour during storage within inbred lines.     

The Role of Organic Soil Amendments on Soil Physical Properties and Yield of Maize (Zea mays L.)

The objective of this study is to examine the role of some organic (composted tobacco waste, CTW; bio-humus, BH; chicken manure, CM) soil amendments on soil physical properties and yield of maize. A 3-year field experiment was conducted at the Agricultural Research Farm of Ege University in Menemen, Izmir, Turkey from 2009 to 2011. The treatments, (1) control, (2) 4 t/ha CM+NPK, (3) 50 t/ha CTW, (4) 10 t/ha BH+NPK, were arranged in complete randomized block design with four treatment replications. Both of BH (composted plant residues) and CM were obtained from organic manure industry. Tobacco wastes were gathered from the cigarette industry and applied to maize (Zea mays L.) after composting period with the other amendments. During the experiment, two soil samples were collected in three different periods (3 June 2009–23 October 2009; 1 June 2010–5 November 2010; 13 July 2011–21 October 2011). The effects of CM, BH, and CTW on physical properties of the soil and yield were investigated. According to our results, all organic amendments increased porosity, structure stability index, field capacity, wilting point, and available water amount and decreased bulk density and particle density of soil when compared to the control. We additionally determined that these organic amendments positively affected grain yield.     

Maize (Zea mays L.) Grain Yield Response to Methods of Nitrogen Fertilization

ABSTRACT

In the developing world, fertilizer application is commonly achieved by broadcasting nutrients to the soil surface without incorporation. A commonly used nitrogen (N) source is urea and if not incorporated, can sustain N losses via ammonia volatilization and lower crop yields. This study evaluated the effect of planting, N rate and application methods on maize (Zea mays L.) grain yield. An experiment with a randomized complete block design (nine treatments and three replications) was established in 2013 and 2018 in Oklahoma. The planting methods included; farmer practice (FP), Oklahoma State University hand planter (OSU-HP), and John Deere (JD) mechanical planter. Side-dress N application methods included; dribble surface band (DSB), broadcast (BR), and OSU-HP. Nitrogen was applied at the rate of 30 and 60 kg ha^?1 as urea and UAN at V8 growth stage. On average, planting and applying N at 60 kg ha^?1 using OSU-HP resulted in the highest yield (11.4 Mg ha^?1). This exceeded check plot yield (5.59 Mg ha^?1) by 104%. Nitrogen application improved grain yield by over 57% when compared to the 0-N check (8.77 Mg ha^?1). Mid-season N placement below the soil surface using OSU-HP makes it a suitable alternative to improve grain yield.     

Antifungal and Plant Growth Promoting Activities of Indigenous Rhizobacteria Isolated from Maize (Zea mays L.) Rhizosphere

Plant growth promoting rhizobacteria (PGPR) enhance the plant growth directly by assisting in nutrient acquisition and modulating plant hormone levels, or indirectly by decreasing the inhibitory effects of various pathogens. The aim of this study was to select effective PGPR from a series of indigenous bacterial isolates by plant growth promotion and antifungal activity assays. This study confirmed that most of the isolates from maize rhizosphere were positive for PGPR properties by in vitro tests. Azotobacter and Bacillus isolates were better phosphate solubilizers and producers of lytic enzymes, hydrocyanic acid (HCN), and siderophores than Pseudomonas. Production of indole-3-acetic acid (IAA) and antifungal activity were the highest in Azotobacter, followed by Bacillus and Pseudomonas. The most effective Azotobacter isolates (Azt₃, Azt₆, Azt₁₂) and Bacillus isolates (Bac_10, Bac₁₆) could be used as PGPR agents for improving maize productivity. Further selection of isolates will be necessary to determine their efficiency in different soils.     

Growth Promotion of Maize (Zea mays L.) by Plant-Growth-Promoting Rhizobacteria under Field Conditions

Plant-growth promoting rhizobacteria (PGPR) play an important role in plant health and soil fertility. The experiment was conducted as factorial experiment with two factors of Azospirillum and Azotobacter. The bacterial strains were Azospirillum lipoferum s-21, A. brasilense DSM 1690, A. lipoferum DSM 1691, Azotobacter chroococcum s-5, and A. chroococcum DSM 2286. The results indicated that growth promotion by PGPR appears from early stages of growth, 45 days after inoculation (DAI). Beneficial effects of bacterial inoculation on ear growth were observed after 75 DAI. Inoculation with PGPR increased dry weights of leaf, stem, and grain and hence total biomass sampled at 90, 105, and 120 (harvest time) DAI. The greatest grain weight was produced by Azospirillum s-21 inoculation. Dual inoculation with Azotobacter s-5 + Azospirillum s-21 significantly increased total dry weight up to 115%. Results of this study showed that leaf area index and crop growth index were significantly affected by bacterial treatments.     

Maize (Zea mays L.) from the Saharan oasis: adaptation to temperate areas and agronomic performance

Saharan maize had been adapted to extreme conditions and could have developed resistance to different stresses. However, genebanks and breeding collections have poor representation from Saharan germplasm and, particularly, from Algeria. This is a preliminary approach to investigate the adaptation and agronomic performance of a representative sample of Saharan maize. We evaluated open-pollinated Saharan populations along with European and American cultivars during 2?years in humid and dry Spanish locations and in Algiers (Algeria). Saharan populations were able to grow in temperate environments, although results were not consistent over years and the genotype-by- environment interactions were very important. Some of the Algerian populations evaluated in 2010 showed promising yield and anthesis silking interval over environments, but none of the Algerian populations evaluated in 2009 were adequately adapted to Spanish conditions. These results suggest that there are wide ranges of variability within Saharan maize for adaptation to temperate conditions, and further evaluations of Saharan maize should identify potential base populations for breeding maize in either side of the Mediterranean Sea. However, this germplasm requires prebreeding for adaptation to temperate conditions in order to be adequate for breeding programs in temperate areas.     

Physicochemical and Nutritional Properties of Different Maize Races on Toasted Tortillas

Biodiversity contributes to nutrient production and, together with processing, is a critical factor in product quality. Physicochemical and nutritional properties of toasted tortillas (totopos) were evaluated in 1) maize samples from Oaxaca communities and 2) maize races of different endosperm texture. Texture profiles show that totopos elaborated from Zapalote Chico maize race showed the best performance (low breaking force) and higher crunchability, similar to commercial totopos. Quality of Zapalote Chico totopos was explained by flotation index (FI) and starch viscosity as well as thermal properties. FI was negatively correlated with texture that may related to end use. Zapalote Chico maize gelatinizes at higher (P < 0.05) pasting temperature (72.8–73.3°C) and it had higher (P > 0.05) peak viscosity (3,093–4,723 cP), suggesting a more organized starch structure. In hybrid and Tuxpeño samples, most of the starch granules (90%) were gelatinized and increased the hardness in totopos. The totopo samples increased the peak at 4.45 Å, a characteristic of type‐V diffraction of amylose‐lipid complexes (resistant starch). A small increase in resistant starch (0.6%) was found in totopos, which has important nutritional benefits for consumers. Our results support the preference of Oaxaca people for the totopos made from Zapalote Chico maize.     

Selective Nixtamalization of Fractions of Maize Grain (Zea mays L.) and Their Use in the Preparation of Instant Tortilla Flours Analyzed Using Response Surface Methodology

Using a continuous decorticating machine, white dent corn was efficiently separated, after brief steeping in water, into two fractions: the first (12.5%) consisting mainly of pericarp, germ, and tip cap (PGT); the second (87.5%) consisting of endosperm. Nixtamalization of the maize fractions in the presence of 0.6% (w/w) lime caused an increase in the hot‐paste viscosity at 90°C, while nixtamalization of PGT at lime inputs <0.6% (w/w) resulted in decreased viscosity. Three domains were found for the viscosity of nixtamalized endosperm at 90°C: lower concentrations of lime (< 0.15%, w/w) resulted in lower viscosity values; increased lime (0.15% – <0.3%, w/w) increased the viscosity values; and a lime concentration of 0.3% (w/w) resulted in a lower viscosity value. The response variables (water absorption index, water solubility index, initial viscosity, and viscosity at 90°C for nixtamalized PGT, and compression force and compression area of tortillas) indicated that the mathematical models fit the experimental data and the variance of the models was highly significant. Tortillas of good functional characteristics similar to tortillas produced by the traditional process were obtained when 5% nixtamalized fractions of PGT were blended with 95% nixtamalized endosperm.     

干旱胁迫对玉米根系生长及根际养分的影响

通过盆栽模拟干旱试验，测定了干旱胁迫下玉米根系生长情况和根际土壤中速效N、P、K的含量。结果表明，干旱胁迫抑制了玉米拔节期和抽雄-开花期玉米根系的生长，减弱了玉米根系的吸收能力。干旱胁追下玉米根际NH4^＋-N、NO3^--N、速效P和速效K均发生根际富集现象。其中有效N和速效K含量高于正常供水．而速效P却呈现低于正常供水的趋势。干旱胁追抑制玉米根系生长、减弱根系吸收能力是玉米减产的重要原因。     

Foliar nutrition of baby corn (Zea mays L.)

Abstract

Field experiments were conducted during late Rabi (January to March) and Kharif (June to September) seasons of 2002, to study the influence of foliar spraying of nutrients on growth and yield of baby corn (Zea mays L.). The experiment was laid out in randomized complete block design with three nutrients (phosphorous [P], potassium [K] and boron [B]) each at three concentrations along with control (water spray) and absolute control (no spray). Di-ammonium phosphate, Muriate of Potash and Borax are the sources of P, K and B nutrients respectively. Results showed that spraying of P favorably influenced the growth parameters, yield attributes and green cob and fodder yields of baby corn. Application of P at 0.75% concentration at 25 and 45 days after sowing (DAS) gave significantly higher growth parameters with thicker cobs and corns, increasing the individual cob weight, which in turn increased the green cob yield of baby corn. Increased growth parameters resulted in increased green fodder yield. Application of B and K with different concentrations and P (0.25 and 0.50%) failed to influence the growth and yield of baby corn.     

玉米苗期磷效率相关根系分泌物的QTL定位

为了充分利用现有的遗传信息和基因资源,揭示玉米磷营养高效的分子机制,本研究以磷高效玉米自交系082和磷低效玉米自交系掖107为亲本组配的F2世代为作图群体,采用SSR和AFLP分子标记构建了遗传连锁图,以两个时期,两个磷水平和两个地点共4种环境下的241个F2∶3家系各性状的平均值作为表型值,采用复合区间作图法定位了磷效率相关的3种根系分泌物的QTL。四种环境下检测表明,(1)检测到4个影响酸性磷酸酶活性的QTL,其中有两个QTL AP1-KXNP和AP9-KXNP被重复检测到,分别分布在第1和9二条染色体上,所在标记区间分别为bnlg1268a-umc1290a和P1M3/d-P1M3/g,在染色体上的位点分别为bin1.09和bin9.04,单个QTL解释酸性磷酸酶变异的9%～16%,2个QTL共解释酸性磷酸酶变异的25%;(2)检测到5个影响有机酸含量的QTL,其中只有1个在两种环境下被重复检测到,位于第9染色体上,标记区间为P1M3/f-P1M7/g,在染色体上的位点为bin9.03;(3)检测到5个影响H+含量的QTL,但没有一个被重复检测到。结果表明,影响酸性磷酸酶活性的两个QTL AP1-KXN...     

空间诱变对玉米自交系产量性状配合力的诱变效应

空间诱变育种具有诱变效率高、变异幅度大、育种周期短等特点,是创新种质、拓展种质基础、丰富种质资源的重要途径.为探明空间诱变对不同玉米自交系产量性状配合力的诱变效应,本研究以3份玉米(Zea mays L.)骨干自交系08-641、RP125和18-599为空间诱变基础材料,分别从诱变处理后代中选出优良诱变系为母本,以常用玉米自交系Mo17、478和黄早四等为父本配制杂交组合,在四川和云南两个环境条件下对各杂交组合进行田间试验鉴定,对单株产量性状进行配合力分析.结果表明,08-641和RP125诱变系单株产量一般配合力(GCA)有所降低,18-599诱变系Y2709和Y3235单株产量GCA极显著高于对照.空间诱变对三份玉米自交系单株产量性状配合力效应影响程度不同,总体表现为RP125诱变系变异幅度最大,18-599诱变系次之,08-641诱变系最小.对各杂交组合进行杂种优势分析结果显示,诱变系S1449、Y2803、Y3165和Y3235的杂种优势表现明显,可能具有较大的育种潜势.这些研究结果不仅丰富了玉米育种的物质基础,而且丰富了玉米诱变育种的理论内涵.     

Comparison of Flour Starch Properties in Half‐Sib Families of Opaque‐2 Maize (Zea mays L.) from Argentina

Since the discovery of the o2 mutation in maize, many studies have reported the characterization of the protein quality of opaque‐2 genotypes. However, few have reported the properties of their starch. The objective of this study was to characterize flour starch properties of 12 half‐sib families of opaque‐2 maize from Argentina. Chemical composition and thermal and pasting properties of whole grain flour were determined. Nonopaque genotypes were used as a control. Starch content of opaque‐2 genotypes did not show significant differences compared with nonopaque genotypes, yet amylose content was significantly lower. A high variability in pasting and thermal properties was observed in genotypes. Opaque samples showed a significantly higher peak viscosity and a lower pasting temperature compared with nonopaque samples, probably owing to larger and less compact starch granules in the floury endosperm. The higher the gelatinization enthalpy of opaque‐2 genotypes was, the lower the amylose content in relation to nonopaque varieties. Two retrogradation endotherms were observed in DSC analysis: one corresponding to amylopectin crystallization and the other to melting of amylose‐lipid complex. Both enthalpies were considered total starch retrogradation (ΔH _RT). A wide range of variation was obtained in ΔH _RT in opaque‐2 genotypes, but no significant differences between opaque and nonopaque genotypes were observed. The differences in starch properties found in this study would make it possible to identify opaque‐2 families with particular characteristics for the development of starchy food items adapted to specific processing traits.     

Phenolic Compounds and Antioxidant Activity of Extruded Nixtamalized Corn Flour and Tortillas Enriched with Sorghum Bran

Sorghum bran (SB) is a good source of phenolic compounds with high antioxidant capacity that increases the antioxidant activity (AOX) of tortillas prepared with extruded nixtamalized corn flour. The objective of this research was to study the effects of bran addition (0, 5, or 10%) before (ENBESB) or after (ENAFSB) extrusion, in the features and composition of baked tortillas in terms of total phenolic compounds (TPC), AOX, color (L , a , b, hue, chroma, and E value), and tortilla firmness. It was possible to retain more than 81.8 and 89.9% of TPC and AOX, respectively, in ENBESB‐10% flour. Tortillas prepared with ENAFSB‐10% flour retained more than 92 and 76% of TPC and AOX, respectively, compared with ENBESB. However, tortillas elaborated with ENAFSB flour showed a higher firmness and lower flexibility than counterparts produced from ENBESB. The use of extrusion to produce nixtamalized corn flours and the strategy of adding the SB to the corn meal before extrusion were essential to retain TPC and AOX and, additionally, to enhance texture of tortillas.