An-I Yeh

Relationships between thermal, rheological characteristics and swelling power for various starches

Abstract The swelling powers (SP) of 10 kinds of starches from cereals, roots, tubers, and peas have been determined at 55°C to 95°C. SP increased with temperature for all the starches tested. When the temperature was reaching the peak temperature (Tp) from differential scanning calorimetric thermogram, there existed an increase in SP. Potato, tapioca, and waxy corn starch yielded high SP and exhibited a maximum value near 80°C. Low swelling starch, such as corn and rice starch, yielded greater peak storage modulus (G′max) in dynamic mechanical analysis. The corresponding loss tangent (tanδG′max) correlated fairly (r2=0.8) with SP measured at 75°C. Granule size, amylose content, or heat of gelatinization alone did not significantly correlate with the SP for all the data obtained. An equation consisting of temperature effect and tan δG′max was developed to explicate the relationships between thermal, rheological characteristics and SP.

Effects of screw speed and feed rate on residence time distribution and axial mixing of wheat flour in a twin-screw extruder

Abstract The residence time distribution of wheat flour with a moisture content of 40% in a twin-screw extruder was determined using erythrosin as the tracer. Both feed rate and screw speed affected the mean residence time and flow pattern in the extruder. Increasing the feed rate or screw speed reduced the mean residence time. The effect of feed rate was more pronounced than that of screw speed. The dispersion number, a reciprocal of the Peclet number, was used to describe the extent of axial mixing in the extruder. The value of dispersion number varied from 0·017 92 to 0·061 94. There existed a good correlation between the dispersion number and the ratio of feed rate to screw speed.

Modeling residence time distributions for single screw extrusion process

The residence time distribution (RTD) of rice flour during single-screw extrusion cooking at various operating conditions and screw profiles has been measured and a model describing RTD has been developed. Increasing the feed rate caused the reduction in residence time. High screw speed resulted in short residence time, but large dispersion number. The non-flight element yielded the longest residence, but smallest dispersion number among three screw elements tested. A mathematical model consisting of a plug flow reactor in series with a continuous stirred tank reactor cross-flowing with a dead volume fitted well the experimental data with correlation coefficients (r2) higher than 0.988. The analysis showed that P (fraction of plug flow reactor) varied from 0.38 to 0.65. A high screw speed or fitting a mixing disc induced more mixing action, and thus a low value of P. The use of the model with literature data demonstrated that the model was applicable to food and non-food single-screw extrusion process. The applications of different models were also discussed.

Effect of screw profile on residence time distribution and starch gelatinization of rice flour during single screw extrusion cooking

The effects of three types of screw elements, forward, mixing disc, and pin-mixing element, on residence time distributions of glutinous rice flour in a single screw extruder with different die opening areas have been investigated. Both mixing disc and pin-mixing element yield longer residence time, higher specific mechanical energy (SME), and higher extrudate temperature compared with those for the forward screw element. The variation in die diameter did not significantly affect the mean residence time when the forward element was used. Nevertheless, increasing die diameter from 20 to 40 mm significantly reduced the mean residence time when mixing disc was used. Based on SME ranging from 3.6 to 20 kJ/kg, the extruder used in this study was classified as a low shear extruder. Due to the high moisture content (45%) and large die opening area, the die pressure was lower than 11.5 kPa. The utilization of mixing disc was found to raise the die pressure. The degree of starch gelatinization in extrudates was a function of the mean residence time. Three models were employed to fit the RTD data. The flow pattern in different screw profiles was discussed based on the model analysis.

Effects of starch properties on rheological characteristics of starch/meat complexes

Abstract Ten kinds of starches from different botanical origin have been used to investigate their effects on rheological characteristics of starch/meat complexes (SM complexes). The rheological characteristics were determined using dynamic oscillatory measurements and texture profile analysis. The addition of starch resulted in a decrease in cooking loss and increase in both storage modulus ( G ′ ) and loss modulus ( G ′′ ). Adding starch also reduced the leaching out from meat protein. Potato SM complex yielded the highest cooking loss among all the SM complexes used. The temperature sweep showed that the dramatic increase in G ′ and G ′′ was associated with the gelatinization of starch. The correlations between starch properties and rheological characteristics of SM complex were discussed.

Physico-chemical characteristics of media-milled corn starch.

Nano/submicrometer scale corn starch particles have been prepared by using media milling. Molecular weight and pasting properties of milled starch were determined by HPSEC-MALLS-RI and an oscillatory rheometer, respectively. After 30-min of milling, the number-average diameter of the starch particle was reduced from 9.61 to 0.26 μm. Particle size was further reduced by extended milling. Microscopic observation confirmed the presence of particles smaller than 100 nm. As starch granules were being disintegrated, the mechanical energy imparted by media milling resulted in 43.7% of starch damage and 55% degree of gelatinization during the initial 30 min. In the meanwhile, the weight average molecular weight was reduced from 9.98 to 7.63 × 10(6) g/mol. The pasting properties were significantly altered by milling, which resulted in lower onset and peak temperature, and reduction in breakdown and set back. The importance of molecular weight on the physicochemical properties of milled starch was discussed.

Effects of Feed Rate and Screw Speed on Operating Characteristics and Extrudate Properties During Single-Screw Extrusion Cooking of Rice Flour

ABSTRACT Rice flour (37% moisture content) was used to examine the effects of feed rate and screw speed on the specific energy input during single-screw extrusion cooking. Torque, raised by decreasing screw speed or increasing feed rate, was found to be a power law function of the ratio of feed rate to screw speed (Fr/Ss) with r2 > 0.94. Specific mechanical energy (SME) calculated from torque also was a power law function of Fr/Ss with r2 >0.84 and negative power law indices. The SME obtained was in the 225–481 kJ/kg range. Thus the extruder can be considered low shear. Increasing SME raised the die temperature and decreased both intrinsic viscosity and water absorption index (WAI). The degree of gelatinization and intrinsic viscosity of extrudates also were power law functions of Fr/Ss. The intrinsic viscosity correlated well with the degree of gelatinization, WAI, and cooking loss, and appeared to be a good index of the extrudate properties. Different screw profiles also affect torque measurement.

Effect of Amylose Content on Expansion of Extruded Rice Pellet

ABSTRACT Rice pellets were prepared by single-screw extrusion cooking with an in-barrel water content of 50 wt%. Three different types of rice, indica glutinous, japonica, and indica, were used as raw materials. Reconstituted rice flour was made to study the effect of amylose content on pellet expansion. The glass transition (Tg) and expansion (Te) temperatures of extruded pellet were determined by differential scanning calorimetry (DSC) and noncontact infrared thermometer, respectively. The amylose content was not significantly affected by extrusion cooking. The reduction in intrinsic viscosity indicated that amylopectin experienced some degradation. The Tg and Te were not functions of amylose content, which affected the expansion ratio of the pellets. The Gordon-Taylor equation was applied to estimate the Tg of the rice pellets.

Process conditions for separating fatty acid esters by supercritical CO2

The solubilities of ethyl palmitate, ethyl oleate, ethyl eicosapentaenoate (EPA) and ethyl docosahexaenoate (DHA) in supercritical carbon dioxide were determined by a continuous flow method. The solubilities of fatty acid ethyl esters increased with pressure and decreased as the temperature was increased. An empirical equation, similar to Chrastils equation, was used to describe the relationship between solute solubility and the density of carbon dioxide. The empirical equation was further used to qualitatively estimate the separation efficiency of isolating EPA and DHA ethyl esters from fatty acid esters. The operating conditions yielding high solubility gave fast extraction rate but resulted in low separation efficiency. Experiments were conducted to separate ethyl EPA and ethyl DHA from a model mixture containing four fatty acid ethyl esters and from esterified squid visceral oil. The experimental data compared closely with the calculated values.

Effect of Goji (Lycium barbarum) on expression of genes related to cell survival.

This study investigated the interrelationship between Lycium barbarum (goji) and gene expression in mouse spleen. Oligomicroarray technology was employed to explore the comprehensive response of gene expression and to screen candidate marker genes in the spleens of mice fed a goji suspension. Goji was micronized by media milling and then used to evaluate the effect of size reduction. The average diameter of nano/submicrometer goji was about 100 nm, which exhibited no cytotoxicity to cell lines IEC-6 (rat normal small intestinal cell line) and Caco-2 (human colon adenocarcinoma cell line). It was found that three genes, TNF, Nfkb1, and Bcl-2, were up-regulated and two genes, APAF-1 and caspase-3, were down-regulated by goji. This phenomenon could be helpful for cytoprotection when cells undergo stress or damage that induces the apoptotic pathway. Size reduction into nano/submicrometer scale enhanced bioactivity.