Pregelatinized Corn Starch Research Articles

Viscoelastic Properties of Extruded Cereal Melts

Hydrophilic biopolymer systems reach a state of maximum plasticization at a concentration of water designated as Wg′. The thermomechanical behaviour of various extruded cereals were investigated at concentrations above and below Wg′ to determine the significance of Wg′ on the viscoelastic properties in the rubbery region above Tg. Cereal melts were produced via extrusion cooking using a twin-screw extruder at in-barrel moisture contents ranging from 25 to 42% (wb). Dynamic mechanical thermal analysis (DMTA) was used to determine the viscoelastic properties for melts obtained from degermed corn meal, oat flour, pregelatinized corn starch and pregelatinized waxy maize. All of the extruded melts displayed reductions in the storage modulus of about two orders of magnitude from the glassy to rubbery regimes. At temperatures greater than 320K, another transition is apparent for extruded oat flour. These losses may be attributed to a reduction in physical crosslinks and/or entanglements. With respect to the other melts investigated, differences in the oat flour melts at temperatures above Tgmay be due to the increased presence of protein and lipid. Given the apparent partly crystalline nature of these melts at moisture contents <Wg′, the most appropriate representation of the viscoelastic properties may be isotimic plots of the viscoelastic functions. These contour plots provide a more comprehensive guide to material behaviour than the ‘traditional’ state diagrams found throughout the literature. An important point is that prediction of viscoelastic properties above Tgfor polymers where the internal structure changes with temperature or moisture content, cannot be predicted using the same methods of reduced variables as for amorphous polymers. Thus rather than using these methods, experimental data, such as given here, may prove to be necessary to design or understand processes involving cereal melts based on their viscoelastic properties.

Reaction of Starch and Cellulose with Products of Thermal Decomposition of Mono‐ and Disaccharides

AbstractD(—)‐Fructose, dextrose and sucrose were thermally decomposed in the presence of native and pregelatinized corn starch, cellulose as well as its mixtures with native corn starch. Several products were obtained in which reactive intermediates thermally generated from lowmolecular saccharides were involved. When starch either was not gelatinized or it could not gelatinize on reaction, the preference for the formation of a physical mixture of caramel with starch and starchsugar complexes was observed. Otherwise products of substitution of starch with reactive intermediates and inclusion complexes were formed. Cellulose appeared to be more reactive. It was grafted to starch by reactive intermediates thermally generated from dextrose.

Utilization of different carbohydrates by the European eel ( Anguilla anguilla)

The present study was conducted to compare the utilization of several different carbohydrate sources and to evaluate the effect of two different methods of feed-processing in eel feeding. Five experimental isoenergetic diets were formulated (all containing 28.5% protein, 8% fat and 40% carbohydrate in dry matter), differing in the carbohydrate source: raw wheat starch (RWS diet), corn malto-dextrins (MD diet), manioc ( Manihot dulcis) meal (MAN diet) and pregelatinized corn starch (PCS1 diet). These four diets were manufactured by extrusion in a Clextral BC-45 extruder. A fifth diet was prepared with the same pregelatinized corn starch (PCS2 diet) but by using a customary laboratory procedure: pellets were made in a mincing machine after mixing dry premix with water and thereafter dried under hot-air flow. Each experimental diet was supplied to three lots of European eels. Feed acceptance, growth, feed efficiency, digestibility, dietary protein utilization, and effects on body composition were evaluated. All extruded diets were well utilized and promoted similar growth rates, irrespective of the origin and nature of the carbohydrate source. Diet PCS1 resulted in more tough pellets and was poorly accepted by the eels; besides its digestibility was clearly lower, so growth rate and feed conversion were the poorest. Results confirm the ability of eels to use high dietary carbohydrate levels and demonstrated the importance of selecting an appropriate processing method when these high carbohydrate levels are to be utilized.

Adaptation of digestive enzymes to dietary protein, carbohydrate and fibre levels and influence of protein and carbohydrate quality inPenaeusuannameilarvae (Crustacea, Decapoda)

Resume Activity of digestive enzymes (trypsin, chymotrypsin and amylase) was studied in relation with food in Penaeus vannamei larvae first stages. Microparticles containing casein involved the decrease of soluble protein content and enzyme activities. Specific trypsin activity but not chymotrypsin was correlated (p< 1 %) to casein level between 10 and 60% in microparticles. Cellulose fibres in food seemed to have little effect on digestive enzymes. Starch, between 1 and 20% in microparticles, had no influence on specific amylase activity. The effect of different feeding conditions were also tested on growth. No clear relationship between growth and enzyme is established since only trypsin is concerned in the case of a casein dose effect in the food. The protein source (casein, gelatin, squid meal or fish protein soluble concentrate) as well as the carbohydrate quality (soluble starch, standard corn starch, amylopectin corn starch or pregelatinized corn starch) were tested. Squid meal stimulated significantly chymotrypsin activity @<2 %) while trypsin activity decreased with fish protein soluble concentrate @<5 %). Source of carbohydrate seemed very important, amylase activity increased significantly (p <2 %) with corn starch. These adaptations are not correlated to growth performances since squid meal or fish protein soluble concentrate improved lama1 development until zoe 3 substage. These results suggest a specific induction of digestive enzymes to the food quality in larvae independent of growth performances.

Prediction of the compression behaviour of powder mixtures by the Heckel equation

The compression behaviour of plastically flowing microcrystalline cellulose and pregelatinized corn starch and fragmenting α-lactose monohydrate and dicalcium phosphate dihydrate, and their binary mixtures was evaluated using the Heckel equation. Powders were compressed using an instrumented eccentric tablet press. The Heckel plots for both plastically flowing materials and their binary mixtures were linear in shape. In contrast, on the Heckel plots of the fragmenting materials and their mixtures, an obvious curvature was seen. The mean yield pressures were linearly proportional to the mixture composition of two plastically flowing materials. When mixed with a fragmenting material, a plastically flowing component had a greater effect on the compression behaviour of the mixture than a fragmenting mixture component had. This was explained by the more pronounced effect of plastic flow on volume reduction. When two fragmenting materials were compressed, the densification of their binary mixture was strongly influenced by the less compressible material with higher mean yield pressure. It was concluded that in the mixtures of two fragmenting materials the particles of the less compressible material constituted a firm structure, like a skeleton, which tended to dominate the compression behaviour of the binary mixtures. For binary mixtures of fragmenting materials the mean yield pressures were thus not linearly proportional to the mixture composition. Compression behaviour of powder mixtures seemed to be strongly dependent on the deformation properties of plain materials to be compressed. On the other hand, one mixture component may dominate the compression behaviour of the mixture, and the compressibility may change non-linearly with mixture composition. Therefore, caution is needed when the Heckel equation is applied for predicting compression behaviour of powder mixtures.

Continuous Restructuring of Mechanically Deboned Chicken Meat by HTST Extrusion‐Cooking

ABSTRACTThe continuous restructuring of mechanically deboned chicken meat (MDM) was attempted using twin‐screw extrusion‐cooking at high moisture contents (50‐80%), high temperatures (ca 150°C), short residence times (30‐240 sec) and low pressures (below 6 bars). The hardness, cohesiveness and water‐holding capacity of the nonexpanded moist extruded samples are optimal and resemble those of meat‐loaf when 10‐20% wheat flour or pregelatinized corn starch are added to MDM. Incorporation of 25% soy protein isolate gives a solid gel matrix containing dispersed meat particles. Scaling up this process could lead to the continuous production of simulated meat chunks or slices for use in canned or frozen dishes.

EXTRUDED FRENCH FRIES FROM DEHYDRATED POTATO GRANULES PROCESSED BY A FREEZE‐THAW TECHNIQUE

ABSTRACTSome physicochemical properties of dehydrated potato granules were studied in relation to their suitability for extruded French fries. The freeze‐thaw granules exhibited higher water‐binding capacity (WBC), lower bulk density and larger particle size than the add‐back granules. Microscopic examination revealed that relatively rapid and complete rehydration was associated only with the freeze‐thaw granules. The add‐back granules indicated a thin membrane of insoluble, completely retrograded amylose that was revealed immediately on contact with water while the interior granule absorbed water slowly. These differences were attributed to the respective processing techniques. Trials indicated that the ratio of 1:2.6 rather than 1:2 of granules to water (w/v) is superior for reconstitution and French fry extrusion of the freeze‐thaw granules. Production of good quality extruded French fries from these granules is possible with the use of a mixture of binders such as guar gum, stabilized high amylose corn starch, crosslinked pregelatinized corn starch, and hydroxypropylmethylcellulose.