Twin-Screw Extrusion Modification of a Corn Fiber and Corn Starch Extruded Blend

Surface response modeling was used to characterize the effect of extrusion processing on the functional properties of corn fiber/corn starch formulations. Process parameters evaluated included screw speed (200-500 rpm), temperature (90-150°C) and pH (3-11). Generally, the water holding capacity of starch increased with increasing extrusion temperature while the water holding capacity of the fiber decreased with increasing extrusion temperature. The foam stability decreased, while the residual moisture increased, with an increase in fiber concentration. X-ray diffraction profiles indicated that extrusion did not affect fiber crystallinity. No significant changes in the ratio of soluble to insoluble fiber were found as a result of extrusion.     

Enzymatic Starch Hydrolysis of Extruded Potato Peels

Potato peels discarded by potato processors are a potential source of dietary fiber and starch. This starch may be hydrolyzed for fermentation to value-added products. Dried steam peels were extruded at 135°C and 22% feed moisture and digested with α-amylase and/or amyloglucosidase. Two barrel temperatures and feed moistures were also studied. Glucose was measured colorimetrically at O,1,2,4,8 and 24h of incubation. All peels treated with either no enzymes or α-amylase alone produced minimal glucose. Nonextruded peels digested with both enzymes produced more glucose than did those treated with amyloglucosidase alone. Complete digestion of starch occurred in extruded peels digested with amyloglucosidase, but not when α-amylase was used.     

大豆挤压膨化物显微结构的研究

针对大豆挤压膨化预处理浸油时,浸出率提高,浸出时间缩短这一现象进行研究,应用了樾的显微技术中的石蜡制片法和显微摄影技术,分别对大豆挤压膨化物和大豆轧胚胚片制成切片,切片染色后显微摄影。指出大豆挤压膨化预处理较轧胚预处理具有明显的优势。     

Starch Lipids: A Reappraisal

It is proposed that lipids on the surface of starch granules should be called “starch surface lipids”, and that those inside the granules should be called “internal starch lipids”. Starch surface lipids appear to be derived from the “non-starch lipids” which are either free or bound to proteins in the starch-bearing tissues. In cereals the internal starch lipids are exclusively monoacyl lipids, and they are quite different in composition from the starch surface lipids and non-starch lipids. In some recent publications lipids purporting to be internal starch lipids evidently include substantial quantities of non-starch or surface lipids.     

Effect of Lipids on the Properties of Extruded Products

Corn gluten having 3.9, 1.8 and 0.2%, lipid (dry basis, db) was blended with defatted soy protein concentrate in the ratio of 25:75 w/ w. The blends were made up of 20, 30, and 40% moisture (db) and then extruded through 4.24, 3.0, and 2.12 mm diameter dies at screw speeds of 60, 120, and 180 rpm. The dependent variables measured were puff ratio, bulk density, shear strength, and water-holding capacity. Shear strength increased when lipids decreased from 3.9% to 1.8% but then decreased when lipids were reduced to 0.2%. Water-holding capacity and puff ratio increased with decreasing lipids. Bulk density was unaffected by lipid concentration.     

Starch Lipids and Their Effect on Rice Starch Properties

The properties of starch lipids and the effect of defatting on properties of starch granules from eight rice sorts were studied. Content of lipids associated with starch prepared by sodium dodecyl benzene sulfonate (DoBS) extraction of protein from rice flour ranged from 0.03 to 0.44%. Major lipids were free fatty acids and lysophosphatidyl choline. Major fatty acids were linoleic, palmitic, and oleic or myristic acid. Defatting reduced the gelatinization temperature and the gel viscosity of starch. Various methods of starch preparation were compared.     

Selected Properties of Extruded Potato and Chicken Meat

Chicken thigh meat (CTM), (0–40%) was mixed with instant mashed potato and twin-screw extruded. Feed moisture content (FMC), (15 or 20%) and screw speed (SS) (250 or 300 rpm) were varied. CTM affected expansion, bulk density, mean cell size, plateau stress, fracturability and solubility. Protein, fat, free fatty acid and ash increased and carbohydrate decreased as CTM increased. Extrudates produced at low feed moisture (15%) had higher compressive resistance, fracturability and solubility. Extrudates produced at high feed moisture (20%) had higher bulk density and mean cell size. Screw speed had no influence except on expansion degree (p≥0.05). Increased CTM changed microstructure from rough, thread-like sheets to a flat, agglomerated carbohydrate-protein laminar phase. Panelists reported no differences in overall acceptability among 0% CTM extruded at 20% FMC, 20% CTM extruded at 15% FMC and 20% CTM extruded at 20% FMC.     

挤压剪切活化对添加耐高温α-淀粉酶脱胚玉米淀粉结构和理化特性的影响

本研究通过偏光显微镜、扫描电子显微镜、热台显微镜、X射线衍射、差示扫描量热分析、傅里叶变换红 外光谱分析等手段,研究原脱胚玉米、挤压脱胚玉米和添加耐高温α-淀粉酶挤压脱胚玉米的淀粉结构及性质变化, 并探究其相互关系,揭示挤压剪切活化对脱胚玉米的淀粉颗粒机械力化学效应。研究表明：与原脱胚玉米和挤压脱 胚玉米相比较,挤压处理对添加耐高温α-淀粉酶脱胚玉米的淀粉结构及性质产生显著影响,酶解力和糊化度增大,碘 蓝值、直链淀粉含量减小。添加耐高温α-淀粉酶挤压脱胚玉米淀粉颗粒形貌破坏,偏光十字破坏,结晶度变小;升温糊 化过程中,焓变降低;挤压使淀粉颗粒的结晶结构破坏,淀粉颗粒发生聚集,破损淀粉颗粒易糊化和裂解。     

Surface Energy of Extruded and Jet Cooked Starch

Contact angles of water and other liquids were measured on films and extruded ribbons of normal, high amylose and waxy cornstarch using a Chan dynamic contact angle analyzer. The contact angles were then used to calculate the critical surface energy of the starch via a Zisman plot. Attempts were also made to use the contact angles to calculate the surface energy of starch via the harmonic-mean method. No differences were found for the critical surface energy due to starch type. Using a composite of all contact angles for the three different starches, an average critical surface energy of 40 dynes/cm was calculated. This value was close to the literature value of 39 dynes/cm found for starch. The surface energy of starch, calculated from the harmonic-mean method, was more variable and ranged from 35-42 dynes/cm. The harmonic-mean method not only calculates the surface energy, but it also estimates the polar and non-polar components of surface energy. The estimate calculated for the polar portion for the surface energy of starch was too low for a polar solid like starch. Values for the polar component range from 0.3 to 10 dynes/cm. A theoretical argument is made for the surface energy of starch being greater than the 39 dynes/cm now reported in the literature.     

不同淀粉挤压面条的品质研究

采用双螺杆挤压机对小麦淀粉、玉米淀粉、木薯淀粉、马铃薯淀粉以及它们的复配粉进行挤压处理并获得相应的面条,通过测定面条的拉伸特性、剪切特性及TPA特性来研究不同淀粉对挤压面条品质的影响。结果发现,马铃薯淀粉挤压面条品质最好,木薯淀粉次之,小麦淀粉、玉米淀粉挤压面条品质略差,含小麦淀粉的复配粉挤压面条品质低于对应的单一品种淀粉,含薯类淀粉的复配粉挤压面条品质好于小麦、玉米淀粉的复配粉。研究认为,薯类淀粉及含薯类淀粉的复配粉挤压面条品质优良,可以满足糖尿病肾病患者对低蛋白主食产品多样性的需求。     

Contribution of Lipids to Volatiles Generation in Extruded Corn-Based Model Systems

Volatile compounds generated by model systems of zein, corn amylopectin and corn oil extruded at barrel temperatures of 120°C and 165°C were analyzed by GC and GU/MS. The largest quantities of lipid oxidation products were detected in systems containing all three components. In each system, the quantity of 2,4-decadienal was low relative to the quantities of hexanal, heptanal, and benzaldehyde. Identification of the Maillard reaction products, 2-methyl-3(or 6)-pen-tylpyrazine, 2-methyl-3(or 6)-hexylpyrazine, and 2,5-dimethyl-3-pen-tylpyrazine, suggested that lipid-derived aldehydes might be involved in the formation of substituted pyrazines.     

Interactions between Starch,Lipids, and Proteins in Foods: Microstructure Control for Glycemic Response Modulation

In real food, starch is usually forming part of a matrix with lipids and proteins. However, research on this ternary system and interactions between such food components has been scarce so far. The control of food microstructure is crucial to determine the product properties, including sensorial and nutritionals ones. This paper reviews the microstructural principles of interactions between starch, lipids, and proteins in foods as well as their effect on postprandial glycemic response, considering human intrinsic differences on postprandial glycemic responses. Several lines of research support the hypothesis that foods without rapidly digestible starch will not mandatorily generate the lowest postprandial glycemic response, highlighting that the full understanding of food microstructure, which modulates starch digestion, plays a key role on food design from a nutritional viewpoint.     

Degradation of Wheat Starch in a Single Screw Extruder: Characteristics of Extruded Starch Polymers

Wheat starch was processed in a 19 mm diameter, single screw extruder to study the physical and structural modifications that occur during extrusion cooking. Structural modification of the starch polymers was investigated using gel permeation chromatography (GPC), enzymatic digestions and dilute solution viscometry. Both the GPC and intrinsic viscosity results showed that the average molecular size significantly decreased as a result of extrusion processing. The relative amount of material excluded by Bio-Gel A150m was considerably lower for extruded samples than for unprocessed wheat starch and this size reduction of the amylopectin fraction was attributed to mechanical rupture of covalent bonds. The characterization of the structural modifications of the starch polymers is reported.     

Glass Transition of Extruded Wheat,Corn and Rice Starch

Commercial wheat, corn and rice starch were extrusion cooked under a specific mechanical energy input (SME) ranging from 81 to 365 Wh/kg (288 to 1314 kJ/kg). Extrusion cooking at low and high SME resulted in products having significant differences in molecular weight distribution and having crystalline structures of the V‐ and E‐type, as determined by gel permeation chromatography and X‐ray diffraction analysis. Differential scanning calorimetry revealed that the glass transition temperature (T_g) of the extruded starches was independent of the botanical source, the degree of extrusion‐induced molecular fragmentation and the formation of the V‐ and E‐type crystalline structures. The obtained master curve, defined by the relationship between water content and T_g of the amorphous starch, may be used as a predictive tool in modelling the extrusion process of starch or starch containing blends, especially with regard to the formation of the morphological structure and texture attributes of directly expanded products.     

用玉米淀粉制备交联淀粉的工艺

以玉米淀粉为原料,以柠檬酸和乙酸酐为交联剂制取交联淀粉,通过反复试验研究了不同混合酸的用量、不同混合酸比例、不同反应时间、不同反应温度条件对交联淀粉交联效果的影响,最后采用正交试验优化了制备交联淀粉的工艺条件,为制备交联淀粉提出了新工艺。     

魔芋淀粉改性研究

用魔芋淀粉,氯乙酸和氢氧化钠为原料,在乙醇溶液中制备高粘羧甲基淀粉,用正交试验设计试验考察了物料配比、反应温度和反应时间对产品性质的影响,确定了最佳反应条件。     

The Lipids of Various Sizes of Wheat Starch Granules

Starches have been prepared from two wheat cultivars having contrasted hot-pasting characteristics. The granules have been separated by successive sedimendations into several size classes and their lipid compositions determined. In agreement with previous work, the lipid is mainly lysophosphatidylcholines of palmitic and linoleic acids in nearly equal quantities. The saturated acid predominates in the smallest granules. The amounts of lipid per granule tend to be proportional to the granule surface areas of the larger granules but proportional to the volumes of the smaller granules. There was no distinction between contents or types of lipid in the two cultivars, suggesting that their contrasted pasting qualities were not a function of lipid composition.     

Wheat Starch Modification Through Biotechnology

Natural mutations that affect the amylose/amylopectin ratio in starch are unlikely to develop naturally in wheat due to its allohexaploid genome (2n=6x; AABBDD). One of the strategies to modify wheat starch structure involves identification of germplasms with null alleles for starch biosynthetic genes, followed by exchange of functional alleles with the identified null alleles through classical plant breeding. This technique has successfully been used to combine the three null alleles for granule-bound starch synthase I (GBSSI) to develop a wheat line that produces amylopectin-rich (>95%) starch (waxy starch). Another strategy to alter expression levels of starch biosynthetic genes employs recent advances in molecular biology and genetic engineering of wheat. For this approach, various monocot vectors have been developed that drive expression of wheat starch branching enzyme I (SBEI) cDNA sequences in the anti-sense orientation. Several of the wheat cell lines transformed with the anti-sense vectors express branching enzyme (BE) activity at a significantly lower level than non-transformed cells. One transgenic wheat plant expressing the anti-sense SBEI RNA produces a ten-fold lower level of BE activity in kernels than wild-type wheat. Analysis of starch produced from the transgenic plant shows that starch structure and properties have been altered.     

Some Effects of Starch Lipids on the Thermal and Rheological Properties of Wheat Starch

Thermal and rheological properties of starches from two different wheat varieties were examined in relation to differences in surface distribution of lipids in the starch granules. The lipids present on the outside of the granules were extracted by isopropanol and the lipids in the amylose lipid complexes were extracted by water-saturated butanol. These amylose lipid complexes influence both the thermal properties of the starch, measured by differential scanning calorimetry, and the viscosity of the starch. The starch with the greatest amount of lipids extractable by water-saturated butanol began to gelatinize at a higher temperature and the gelatinization enthalpy was lower. Furthermore the viscosity began to increase at a higher temperature and the maximum viscosity was achieved at a higher temperature for this starch.