Effect of Salt and Ethanol Addition on Zein–Starch Dough and Bread Quality

Development of viscoelastic doughs from non‐wheat proteins allows for a wider range of gluten‐free products. Little work has been completed to describe mechanisms of zein functionality in food systems. To identify factors responsible for dough development in zein–starch mixtures and their influence on zein bread quality, a mixture of 20% zein–80% maize starch was mixed with water and various reagents. Salts, NaSCN, NaCl, and Na₂SO₄ were evaluated at concentrations from 0 to 2M for their influence on the properties of zein–starch dough systems. NaSCN at low concentrations produced softer dough. Ethanol treatments produced softer more workable dough in the absence of salts. Increasing concentrations of NaCl and Na₂SO₄ resulted in coalescing of the proteins and no dough formation. The addition of β‐ME had minimal softening effects on zein–starch dough. Specific volumes of zein–starch bread increased with decreasing NaCl addition in bread formulations. Likewise, including 5% ethanol (v/v) in the bread formula increased bread quality.     

Age Gelation,Sedimentation, and Creaming in UHT Milk: A Review

Demand for ultra‐high‐temperature (UHT) milk and milk protein‐based beverages is growing. UHT milk is microbiologically stable. However, on storage, a number of chemical and physical changes occur and these can reduce the quality of the milk. These changes can be sufficiently undesirable so as to limit acceptance or shelf life of the milk. The most severe changes in UHT milk during storage are age gelation, with an irreversible three‐dimensional protein network forming throughout, excessive sedimentation with a compact layer of protein‐enriched material forming rapidly at the bottom of the pack, and creaming with excessive fat accumulating at the top. For age gelation, it is known that at least two mechanisms can lead to gelation during storage. One mechanism involves proteolytic degradation of the proteins through heat‐stable indigenous or exogenous enzymes, destabilizing milk and ultimately forming a gel. The other mechanism is referred to as a physico‐chemical mechanism. Several factors are known to affect the physico‐chemical age gelation, such as milk/protein concentration, heat load during processing (direct compared with indirect UHT processes), and milk composition. Similar factors to age gelation are known to affect sedimentation. There are relatively few studies on the creaming of UHT milk during storage, suggesting that this defect is less common or less detrimental compared with gelation and sedimentation. This review focuses on the current state of knowledge of age gelation, sedimentation, and creaming of UHT milks during storage, providing a critical evaluation of the available literature and, based on this, mechanisms for age gelation and sedimentation are proposed.     

Distribution of storage proteins in low-glutelin rice seed determined using a fluorescent antibody

To compare the distribution of storage proteins in low-glutelin rice seed with that in other cultivars having normal protein compositions, immunofluorescence labeling with specific antibodies was applied to visualize the distribution of storage proteins in endosperm tissues. The endosperm tissues from five cultivars were reacted with anti-prolamin and anti-glutelin antibodies, and then observed by light microscopy and confocal laser scanning microscopy (CLSM). In low-glutelin rice, using microscopic analysis, a large proportion of storage proteins was observed in the endosperm tissue of 70% polished rice. To determine the localization of two types of protein bodies in endosperm tissues, images of the distribution of the type I protein body (PB-I) and the type II protein body (PB-II) were obtained by CLSM. The CLSM images showed that, in low-glutelin rice, prolamin which accumulates in PB-I remains in the center of 70% polished rice grains despite the elimination of 30% of the outer layer of brown rice grains. However, the other cultivars mostly contained glutelin which accumulates in PB-II and is distributed throughout the endosperm tissues. This shows that low-glutelin rice differs from the other cultivars not only in the major storage protein composition but also in the distribution of storage proteins in endosperm tissues.     

Isolation and purification of three antifungal proteins from sorghum endosperm

Three proteins potently inhibitory to the growth of Fusarium moniliforme, the grain mould pathogen have been identified from sorghum endosperm, using aqueous extraction, gel filtration and ion-exchange chromatography coupled with bioassay. The aqueous extract (Tris buffer, pH 6.8) of sorghum endosperm flour was separated into two fractions by passing through Sephadex G-50. The void volume fraction, showing antifungal activity was further fractionated by ion-exchange chromatography on SP Sephadex C-50. The most potent fraction was that which bound to the SP Sephadex column at pH 6.0. A less potent fraction with an 18 kDa protein as major component was released on shifting the pH to 8.5. The bound fraction at pH 8.5 was a much more potent inhibitor of fungal growth than the unbound fraction; and it was composed of two major polypeptides with molecular weights of 26 and 30 kDa. All three polypeptides were separated on SDS-PAGE gels, transferred onto Immobilon and tested for antifungal activity. The test showed that the 26 and 30 kDa proteins retained the antifungal activity even after electrotransfer. Antibodies raised against the electroeluted proteins were shown to abolish the antifungal activity of the endosperm extracts. These proteins appeared only in the endosperm of sorghum grains as revealed by dot immunobinding assay. The 26 and 30 kDa antifungal proteins were also present in pearl millet and maize, while the 18 kDa protein was found only in sorghum. Cross-reactivity of antibodies with the aqueous extracts of wheat, rice and ragi was not seen.     

Zein Characterisation of South African Maize Hybrids and Their Respective Parental Lines Using MALDI-TOF MS

Zeins are important storage proteins and play a role in grain texture and impact on processing. Having a technique to accurately quantify the individual zeins and the size of these proteins would allow for more precise understanding of the impact these individual protein have on grain texture and/or processing. Matrix-assisted laser desorption ionisation time-of-flight mass spectrometry (MALDI-TOF MS) was used to characterise zein protein profiles of five South African maize hybrids, grown at three locations, and their respective parental lines. A new, simplified and shortened zein extraction method was used to characterise the zein profiles and to determine any possible relationship between the hybrids and their parents. A matrix solution comprising two matrices, α-cyano-4-hydroxy-cinammic acid (CHCA) and 2-(4-hydroxyphenylazo) benzoic acid (HABA), was required to detect all major zein (α, β, γ and δ) classes. Within the set of hybrids and parents, additional peaks with molecular weights not previously reported were observed. These were identified as belonging to the δ-zein, β-zein and γ-zein. Relationships between the hybrids and their respective parental lines were observed indicating genetic variation for these zein classes exists. The MALDI-TOF MS method identified differences in individual zein proteins and these differences were observed between hybrids. The method shows a potential for accurately quantifying the presence and molecular size of zein proteins which may be important in milling and food processing. Storage proteins play an important role not only in grain composition but also in some processes such as milling, and variation in these individual proteins may impact on efficiency of processing.     

Chapter 3: Double‐Embryo,High‐Protein,High‐Oil Maize Produced Using a Cytokinin‐Based Flower Rescue

ABSTRACT: Maize is an important staple of human diets and animal feed.Improving the nutritional profile for both of these purposes is a desirable research focus and agricultural endpoint. Many mechanisms have been used to improve maize protein and oil content, including selective breeding to introgress desirable traits (Quality Protein Maize), introducing single natural or synthetic genes expressing desired traits, changing signal sequences (high methionine maize), and modifying metabolic pathways (high‐lysine maize, see Chapter 6). A novel approach was used to indirectly increase protein and oil content ( Young and others 2004 ). Maize produces unisexual florets. Within the maize spikelet,the meristem gives rise to an upper and lower floret and male (tassel)‐ and female (ear)‐specific florets are borne on separate inflorescences.The lower floret of each ear spikelet is aborted early in its devel‐opment,leaving the upper floret to mature as the only female floret.Expression of a bacterial cytokinin‐synthesizing isopentenyl transferase (IPT) enzyme,under the control of the Arabidopsis senescence‐inducible promoter SAG 12 (senescence associated gene), blocked the abortion of the lower floret and resulted in 2 functional florets per spikelet.The pistil in each floret was fertile,but the spikelet produced just 1 kernel composed of a fused endosperm with 2 viable embryos.The 2 embryos were genetically distinct, indicating that they had arisen from independent fertilization events. The embryo contains most of the protein and oil in the kernel and kernels that contained 2 embryos have more protein than conventional maize.The presence of 2 embryos in a normal‐sized kernel leads to displacement of endosperm growth, resulting in kernels with an increased ratio of embryo to endosperm content. The end result is maize with more protein and oil and less carbohydrate ( Young and others 2004 ).     

Optimising the determination of maize endosperm vitreousness by a rapid non‐destructive image analysis technique

A rapid non‐destructive image analysis technique was developed and optimised for the determination of maize endosperm vitreousness without the need for sample preparation. Maize kernel translucency measurements were optimised for a light system consisting of positioning whole kernels on top of round illuminated areas smaller than the projected areas of the kernels, allowing light to shine through the kernels. A correction factor to allow for constant illumination of kernels was developed to adjust for kernel size variation in relation to constant light area. The intensity of translucency in maize is linearly correlated to the percentage of kernel illumination (r = 0.99, p < 0.001). Significant correlations were found between corrected translucency values and endosperm yields determined by hand dissection. These were: translucency as a percentage of the whole kernel and vitreous endosperm (mass%), r = 0.77; translucency as a percentage of the whole kernel and opaque endosperm (mass%), (r = ?0.72); translucency as a percentage of endosperm and vitreous endosperm (mass%), r = 0.81; and translucency as a percentage of endosperm and opaque endosperm (mass%), r = ?0.77; with n = 245 in all instances. Translucency varied by 29.5% between the lowest and highest values, and vitreous endosperm (mass%) varied by 16.8% between the lowest and highest values. Correlations increased significantly after corrections for kernel thickness. A thickness increase of 1 mm in the maize will cause a decrease of 21.86% in translucency and vice versa. The method allows for large samples (at least 49 kernels min^?1) to be analysed for individual vitreous and opaque endosperm contents with no interferences with kernel structure. With further development of suitable automated sampling techniques, it could become a suitable potential method for in‐line quantification of maize endosperm contents. Copyright © 2004 Society of Chemical Industry     

Influence of the protein distribution of maize endosperm on ruminal starch degradability

This study was aimed at determining the influence of the protein distribution of maize endosperm on ruminal starch degradation using 14 maizes differing in endosperm texture (eight dent and six flint maizes). Ruminal starch degradability was determined by an in situ technique on ground samples with a particle size of 3 mm. The distribution of endosperm proteins was assayed by a method based on their differential solubilities in solvents. The (α,β,δ)‐zeins and the true glutelins were the predominant proteins in the endosperm. The (α,β,δ)‐zeins (66.1 and 70.1 g kg⁻¹ of recovered protein for dent and flint types respectively) and the true glutelins (21.8 and 18.4 g kg⁻¹ of recovered protein for dent and flint types respectively) were related to the vitreousness, ie the ratio of vitreous to floury endosperm. Ruminal starch degradability averaged 619 and 462 g kg⁻¹ for dent and flint maizes respectively. It was correlated negatively with the (α,β,δ)‐zeins and positively with the true glutelins. The (α,β,δ)‐zeins located in the protein bodies should limit the accessibility of starch granules to ruminal micro‐organisms and, as a consequence, the ruminal starch degradability. © 2000 Society of Chemical Industry     

Starch Granule-Bound Proteins and Polypeptides: The Influence of the waxy Mutations

Proteins are found as integral components of starch granule structure. The starch granule-bound proteins from the endosperm of nonmutant (normal) and waxy (glutinous) cereals were extracted and subsequently separated by electrophoresis on denaturing SDS-polyacrylamide gels. The silver stained gels revealed that for cereals the waxy protein (starch granule-bound starch synthase) was approximately 60 kD. The cereals containing the waxy mutation do not show this protein. Compared to the nonmutant genotypes of other cereals, the waxy protein of barley, Hordeum vulgare is greatly diminished. Based on this observation, there may be reason to suspect that starch synthesis in barley varies from that of other cereals. There are minor homologous proteins among the cereals studied, including, maize, teosinte, rice, millet, sorghum, and barley. Starch granules from all cereal genotypes studied exhibited a minor protein at 68 kD. Most (81%) genotypes showed a 65 kD protein, which may correspond to a minor isozyme of starch granule-bound starch synthase. Minor proteins occurred at 70 kD and 72 kD in 71% and 57% of the genotypes studied, respectively. The minor proteins could be isozymes of starch granule-bound starch synthase or the proposed granule-bound forms of branching enzyme and oligosaccharide synthase.     

Technical note: quantification of zeins from corn, high-moisture corn, and corn silage using a turbidimetric method: comparative efficiencies of isopropyl and tert-butyl alcohols

Zeins are corn endosperm storage proteins that encapsulate starch granules into a protein matrix, which can act as a barrier to starch accessibility and digestion. Laboratory methods to quantify zein are seldom used because they are considered arduous and time-consuming. A recently published rapid turbidimetric method (mTM) was reinvestigated by changing the solution originally used for the zein solubilization step. In particular, the aim was to explore whether, and to what extent, the use of tert-butyl alcohol (t-BuOH-mTM) in lieu of isopropyl alcohol (i-PrOH-mTM) was able to improve the quantification of zeins from dry corn, high-moisture corn, and corn silage samples. The nature of the alcohol influenced the zein extraction values, and t-BuOH-mTM gave higher zein values in corn (3.6 vs. 3.3 g/100 g of dry matter) and corn silage samples (1.2 vs. 0.9 g/100 g of dry matter) compared with i-PrOH-mTM. In contrast, similar zein extraction values were obtained for high-moisture corn (2.1 vs. 1.9 g/100 g of dry matter, respectively). Sodium dodecyl sulfate-PAGE analysis revealed no contamination by nonzein proteins with the use of tert-butyl alcohol. Overall, these findings indicated that tert-butyl alcohol has a greater ability to solubilize zein compared with isopropyl alcohol and thus the t-BuOH-mTM allowed greater extraction of zeins. Considering the growing interest of animal nutritionists in zein proteins, such results should provide useful information for routine laboratory analysis.     

Molecular aspects of legume seed storage protein synthesis

The seed proteins of crop plants will provide an ever‐increasing proportion of protein in the human diet in the future. Research is currently under way with a variety of crop plants to try to identify the molecular mechanisms that regulate the production of seed proteins. This review, however, will be limited to studies of soybean (Glycine max) and common bean (Phaseolus vulgaris). The accumulation of storage proteins during seed maturation, the characteristics of the different proteins, and the results of studies of the messenger RNAs encoding the seed proteins have revealed a number of similarities as well as differences between common beans and soybeans. Ongoing research in the isolation and characterization of the genes encoding the seed proteins will provide the much needed background to further explore the molecular mechanisms that regulate the synthesis of these proteins.     

Viscoelastic properties of concentrated aqueous ethanol suspensions of α-zein

Viscoelastic properties of α-zein dispersed in aqueous ethanol were studied using oscillatory strain rheometry. In 55-80% v/v aqueous ethanol, zein was only partially soluble, forming a gel at a sufficiently high zein concentration. The strain dependence of the storage modulus and the loss modulus of gelled systems exhibited features characteristic to closely-packed swollen particles. Close-packing was found to occur at a lower zein concentration with increasing ethanol concentration as the threshold for gelation decreased from a zein concentration of ca. 29 to 20% w/v with increasing ethanol concentration from 55 to 80% v/v. A contrasting trend in the effect of the solvent quality was revealed at a constant zein concentration of 30% w/v, at which the storage modulus decreased from ca. 12,000-700 Pa with increasing ethanol concentration from 55 to 80% v/v. The two major factors determining viscoelastic properties of the partially solvated zein systems were identified to be: (1) the degree of dissolution of zein into the continuous phase that was negatively correlated with the volume fraction of the dispersed phase and positively correlated with the osmotic pressure of the continuous phase; and (2) the degree of swelling of partially solvated zein particles that was positively and negatively correlated with the volume fraction and the storage modulus of the dispersed phase, respectively.     

Maize: A Paramount Staple Crop in the Context of Global Nutrition

Abstract: The maize plant (Zea mays), characterized by an erect green stalk, is one of the 3 great grain crops of the world. Its kernels, like other seeds, are storage organs that contain essential components for plant growth and reproduction. Many of these kernel constituents, including starch, protein, and some micronutrients, are also required for human health. For this reason, and others, maize has become highly integrated into global agriculture, human diet, and cultural traditions. The nutritional quality and integrity of maize kernels are influenced by many factors including genetic background, environment, and kernel processing. Cooking procedures, including nixtamalization and fermentation, can increase accessibility of micronutrients such as niacin. However, man cannot live on maize alone. For one‐third of the world's population, namely in sub‐Saharan Africa, Southeast Asia, and Latin America, humans subsist on maize as a staple food but malnutrition pervades. Strategies to further improve kernel macronutrient and micronutrient quality and quantities are under intense investigation. The 2 most common routes to enhance grain nutritional value are exogenous and endogenous fortification. Although exogenous fortification, such as addition of multivitamin premixes to maize flour, has been successful, endogenous fortification, also known as “biofortification,” may provide a more sustainable and practical solution for chronically undernourished communities. Recent accomplishments, such as low‐phytate, high‐lysine, and multivitamin maize varieties, have been created using novel genetic and agronomic approaches. Investigational studies related to biofortified maize are currently underway to determine nutrient absorption and efficacy related to human health improvement.     

125th Anniversary Review: The science of the tropical cereals sorghum,maize and rice in relation to lager beer brewing

Mainstream lager beer brewing using the tropical cereals sorghum, maize and rice, either as malt or as raw grain plus commercial enzymes, is becoming widespread. This review examines the differences in composition between these tropical cereals and barley and their impact on brewing processes and beer quality. All of these cereals have a starch gelatinization temperature some 10 °C higher than barley. The sorghum prolamin proteins are particularly resistant to proteolysis owing to disulphide cross‐linking involving γ‐kafirin. Unlike barley, the major endosperm cell wall components in sorghum and maize are arabinoxylans, which persist during malting. The rice cell walls also seem to contain pectic substances. Notably, certain sorghum varieties, the tannin‐type sorghums, contain considerable levels of condensed tannins (proanthocyanidins), which can substantially inhibit amylases, and probably also other brewing enzymes. Tropical cereal malts exhibit a similar complement of enzymic activities to barley malt, with the notable exception of β‐amylase, which is much lower and essentially is absent in their raw grain. Concerning beer flavour, it is probable that condensed tannins, where present in sorghum, could contribute to bitterness and astringency. The compound 2‐acetyl‐1‐pyrroline, responsible for the popcorn aroma of maize and also the major aroma compound in rice, presumably affects beer flavour. However, much more research is needed into tropical cereals and beer flavour. Other future directions should include improving hydrolysis of prolamins into free amino nitrogen, possibly using prolyl carboxypeptidases and investigating tropical cereal lines with useful novel traits such as high amylopectin, high protein digestibility and low phytate. Copyright © 2013 The Institute of Brewing & Distilling     

Distribution of antifungal proteins in maize kernel tissues using immunochemistry

This study examined the distribution of two antifungal proteins, ribosome-inactivating protein (RIP) and zeamatin, in maize kernel tissues. Proteins were extracted from endosperm (including aleurone layer) and embryo tissues of imbibed maize kernels. Western blot analyses revealed that RIP-like protein was present at higher levels in endosperm than in embryo tissues, whereas zeamatin-like protein was more concentrated in embryo tissues than in endosperm tissues. However, there were three protein bands in the endosperm and two bands in the embryo that reacted to anti-RIP antibody in Western blot analyses. Tissue prints were conducted to localize the antifungal proteins. Imbibed kernels were cut longitudinally and transversely and blotted onto nitrocellulose membranes. Using antibodies against maize RIP and zeamatin, RIP was found primarily in the aleurone layer of the endosperm and glandular layer of scutellum, whereas zeamatin was located mainly in the kernel embryo. These results provide insight into the potential functions of these antifungal proteins, especially since the presence of RIP and zeamatin within maize kernels uniquely protects kernels from pathogens.     

Characteristics of edible films made from dairy proteins and zein hydrolysate cross-linked with transglutaminase

The main objectives of this research were to develop whey protein or casein films incorporating zein hydrolysate and also cross‐linked by transglutaminase as to well as characterize the physical and mechanical properties of the film. Zein hydrolysate decreased the solubility of the whey protein film (P < 0.05), while treatment with transglutaminase did not change the solubility of the film significantly. Electrophoresis patterns demonstrated that casein molecules were cross‐linked by transglutaminase and the extent of this cross‐linkage was further increased when zein hydrolysate was added. In addition, the use of zein hydrolysate decreased the tensile strength of the whey protein film by 35–45%. The elongation of the casein film was increased by 41% because of the action of transglutaminase and zein hydrolysate (P < 0.05). The water vapour permeability of the films was not significantly different. As the addition of zein hydrolysate and treatment with transglutaminase improved the flexibility of the films, the level of plasticizer required to maintain film flexibility could be reduced without sacrificing their water vapour permeability.     

响应面法优化微波辅助提取玉米醇溶蛋白工艺研究

玉米皮含有大量玉米黄色素和醇溶蛋白;该研究首先对玉米皮进行脱色处理得到玉米黄色素,然后利用微波辅助提取玉米醇溶蛋白,并在单因素试验基础上利用响应面法优化玉米醇溶蛋白提取工艺;结果表明,最佳提取工艺条件为:乙醇浓度75%、液料比12、微波功率450 W、间歇式微波处理5次,共225 s,提取率为73.6%。     

Endosperm Properties and Extrusion Cooking Behavior of Maize Cultivars

Understanding the association between industrial quality and biochemical and biophysical properties of commercial maize cultivars may help breeders develop cultivars best adapted to diversified processing requirements, and processors choose cultivars best for specific requirements. The suitability of cultivars for extrusion cooking is important in this regard. To supply information useful to maize breeders and processors, biophysical (endosperm texture and hardness) and biochemical (protein and starch composition) properties of kernels, grits and extruded curls of several commercial maize cultivars were determined and related to extrusion performance. Results show that extrusion alters protein hydrophobicity and degree of aggregation, though differently between cultivars. Under conditions of this study, grits from harder maize expand more, consume less energy upon extrusion, and cook more rapidly than do grits from softer maize. These behaviors appear related to differing protein compositions and endosperm textures of cultivars. Results also suggest that reversed-phase high-performance liquid chromatography of zeins (the storage prolamin proteins of maize) may be valuable for predicting end-use properties of extruded maize products, and as a quality estimator during maize breeding.     

Characterisation of zein–oleic acid films and applications in fruit coating

Pure zein films are known to be very hydrophobic, but are inappropriate for edible coating applications because of their brittle nature. In an attempt to improve the flexibility of these coatings, the influence of low concentrations of oleic acid (OA) as a plasticiser on mechanical, topographical and wetting properties of zein thin films was evaluated. Films were first obtained by casting from aqueous ethanol solutions with 4.0% in mass of zein and additions of 0%; 0.25%; 0.50%; and 1.0% (w/w) of OA. The results indicate an improvement in mechanical properties with increasing plasticiser leading to a reduction in the elastic modulus. An increase in the elongation at break has been observed, but with minor influence on tensile strength. All plasticised zein films have similar initial contact angle (approximately 69°) with a time‐dependent receding drop behaviour. An increase in plasticiser concentration increases film’s affinity towards water. As measured by atomic force microscopy, a consistent linear relation (R² = 0.991) was estimated between film composition and surface adhesion and consequently on the hydrophilicity. Surface topography also varied with plasticiser addition, becoming smoother as the OA concentration increases. When tested as an edible coating on pears (Pyrus communis L.), a formulation with 0.25% wt of plasticiser achieved the best results in preserving the pear mass as measured during the evaluated storage time (12 days) at room temperature. A 0.5% concentration of plasticiser had no influence and higher amounts resulted in a reduction in fruit protection.     

Wet‐Milling of Grain Sorghum of Varying Seed Size Without Steeping

Experimental lines of hybrid grain sorghums were produced with thousand‐kernel‐weights (TKW) varying between 23.1–44.9 g. The proportion of germ in the normal‐seeded hybrids with TKW 23–27 g was ∼ 9.9–10.2% of dry kernel weight, whereas that in the large‐seeded hybrids with TKW 37–45 g was ∼ 10.8–11.2%. Starch in grain decreased ∼ 4% as kernel weight increased which was offset by an increase in protein level. Wet‐milling of the grain was done without steeping after an initial coarse‐grinding step in two parts of water with 0.3% sodium bisulfite. Three of four samples of large‐seeded and soft‐textured grain sorghums gave 77–82% recovery of starch with 0.5–0.7% protein, while one gave 59% recovery and 0.6% protein. The starches had < 0.5% damaged starch, gave no rancid off‐odor after storing 26 months at 25°C in a sealed glass container, and had lightness (L*) values of 93.1–93.7 vs. 95.2 for a commercial corn starch. Their pasting curves were similar to that of commercial corn starch. The bran/germ/endosperm fraction obtained by limited wet‐milling of one large‐seeded hybrid was separated by flotation to recover one‐half the germ in 98% purity as estimated by fat content.