Relationship between the physicochemical properties of soybean protein isolate and its extrudate based on high-moisture extrusion torque.

This study investigated the relationship between nitrogen soluble index (NSI), bulk density, gel storage modulus of soybean protein isolate and torque during high-moisture (50%) extrusion, and analyzed the influence to extrudate texture by the moisture content and the expansion degree of extrudate. The results showed that in the range of NSI of 21-74%, bulk density of 0.41-0.47 g/cm3 , and gel storage modulus of 3,800-5,400 Pa, the torque and specific mechanical energy raised with the decrease in NSI and the increase in bulk density and gel storage modulus. The lower the moisture content of the extrudate was, the higher its hardness. Interestingly, as the extrudate expands, bubble cavities formed on the surface of the extrudate could cause its hardness to drop from 13,124 g/s to 11,736 g/s and 4,840 g/s. Overall, the hard extrudates can be produced from soy protein isolates with low NSI (<21%), high bulk density (>0.47 g/cm3 ), and gel storage modulus (>5,380 Pa) via high-moisture extrusion, at the same time appearing in an expanded structure that reduces the hardness test value of the extrudate.

Identifying changes in soybean protein properties during high-moisture extrusion processing using dead-stop operation.

To provide additional evidence and better understand the high-moisture texturing extrusion process of soybean protein isolate (SPI), the physico-chemical changes of SPI during extrusion were investigated. SPI in the extruder feeding zone, barrel zones 1 (80 °C) to 4 (135 °C), and the cooling die (80 °C) were obtained from a dead-stop operation. The lowest values associated with the denaturation enthalpy and the extractable protein occurred in zone 3 (150 °C). The minimum level of the protein subunit content was identified in zone 4. The highest value of the average protein molar mass occurred in zone 3. The ß-sheet ratio in the protein increased, and the unordered ratio decreased after extrusion. The surface hydrophobicity of the protein decreased with water injection in zone 1; however, it increased in zone 2 (110 °C). Overall, SPI undergoes swelling, denaturation, aggregation, and depolymerization due to water injection, heating, and shearing during high-moisture extrusion.

Effects of thermostable phytase supplemented in diets on growth performance and nutrient utilization of broilers.

Phytase is an enzyme that has the ability to release phosphorous (P) from phytate by hydrolyzing inositol-phosphate linkages. Recently, thermostable phytases have gained great consideration because the reduction in phytase activity was found when exposed to heat during feed pelleting. In this study, the effects of the granular thermostable phytase (Aspergillus niger) on growth performance and nutrient utilization of broilers were investigated. A total of 96 21-day-old Arbor Acres broilers were randomly distributed into six treatments including basal diet (control) and basal diet supplemented with 500, 1,000, 2,000, 4,000, 8,000 U of phytase/kg. In general, the metabolizable energy (ME) and the apparent and true availability of dry matter (DM), organic matter (OM), ether extract (EE), crude protein (CP), and amino acids (AA) showed both linearly (p < .01) and quadratically (p < .01) increase with increasing levels of phytase in the diet. Additionally, diet supplementation with phytase could improve (p < .05) body weight (BW), average daily gain (ADG), and feed/gain (F/G) on day 42 compared with the control. The results suggested that diet supplementation of the granular thermostable phytase in the crumbled pellets could improve chicken growth performance and nutrient utilization.

The forward and backward transport processes in the AOT/hexane reversed micellar extraction of soybean protein.

Soybean protein was taken as a model protein to investigate two aspects of the protein extraction by sodium bis(2-ethylhexyl) sulfosuccinate (AOT) reverse micelles: (1) the forward protein extraction from the solid state, and the effect of pH, AOT concentration, alcohol and water content (W0) on the transfer efficiency; (2) the back-transfer, the capability of the protein to be recovered from the micellar solution. The experimental results led to the conclusion that the highest forward extraction efficiency of soybean protein was reached at AOT concentration 180 mmol l(-1), aqueous pH 7.0, KCl concentration 0.05 mol l(-1), 0.5 % (v/v) alcohol, W0 18. Under these conditions, the forward extraction efficiency of soybean protein achieved 70.1 %. It was noted that the percentage of protein back extraction depended on the salt concentration and pH value. Around 92 % of protein recovery was obtained after back extraction.

Surface characterization of corn stalk superfine powder studied by FTIR and XRD.

Corn stalk superfine powder was ground by a special designed machine. The physical-chemical properties of corn stalk powders with particle sizes of >300, 300-150, 150-74, 74-37 and <15 µm were investigated. The particle size distributions of the powders were: d(90)=362, 147, 74, 40 and 12 µm. The size of corn stalk powders was smaller, the surface area (from 1.188 to 2.432 m(2)/g) and bulk density (from 0.103 to 0.1145 g/ml) were greater. Light microscopy (LM) and scanning electron microscopy (SEM) observations revealed the shape and surface morphology of five types of corn stalk powders. FTIR analysis showed that some position of absorbing peaks was shifted as the powder particle size decreased. X-ray diffraction analyses for corn stalk coarse and superfine powders revealed no evident changes in X-ray pattern. However, the crystallinity, intensity of crystal peaks and crystal size of corn stalk powders with particle sizes from >300 to 300-150 µm dropped, then, as the size of the powders decreased, the crystallinity, intensity of crystal peaks and crystal size increased in some degree.

Determination of the domain structure of the 7S and 11S globulins from soy proteins by XRD and FTIR.

BACKGROUND: The 7S and 11S fractions from soybean proteins have interesting high nutritional and excellent functional properties. The aim of this research was to improve the functional properties of soy proteins by studying the effect of bis(2-ethylhexyl) sodium sulfosuccinate (AOT) reverse micelles on the conformation of the 7S and 11S globulins using Fourier transform infrared and X-ray diffraction spectroscopy. RESULTS: Fourier transform infrared revealed that the intensity of the 7S and 11S globulin bands from AOT reverse micelle extraction at 1600-1700, 1480-1575, 1220-1300, 3330, 1448 and 1395 cm(-1) was higher than from aqueous buffer. X-ray diffraction data showed that the intensities of 7S globulin using two extraction methods at 2θ about 10° were significantly different (P < 0.05), about 22° slightly increased. The intensities of 11S globulin at 2θ about 10° and 22° were similar. The average distance between particles (dhkl ) for 7S globulin with aqueous buffer extraction at 2θ about 10° was greater than AOT reverse micelle extraction. CONCLUSION: This study showed the potential of reverse micelles as a protocol for extracting the 7S and 11S globulins for analytical purposes. The results represent a new avenue for determining the structures of the 7S and 11S globulins.

Reaction kinetics in food extrusion: methods and results.

Extrusion cooking is a highly efficient food processing technology. During the extrusion process, there are many desirable and undesirable reactions which will determine final product quality. While being heated and sheared simultaneously, food raw materials experience a non-isothermal process and their residence time in the extruder is distributed. All these factors contribute to the difficulties in determining the kinetic parameters for those reactions. Therefore, this paper attempts to review the reaction kinetics in food extrusion. First of all, the kinetic models for the reactions are outlined. After elucidating how to determine reaction time in an extruder, the methodological approaches for determining the reaction order, rate constant, and activation energy of a reaction under isothermal or non-isothermal conditions with or without residence time distribution (RTD) are presented. Then, different models relating the rate constant to its various impact factors, with especially focusing on shear stress, are reviewed. Subsequently, how shear stress is estimated in an extruder, is illustrated. In the last part of this paper, the reported data of rate constant, reaction order, and activation energy for the reactions occurring during food extrusion are summarized, with detailed impacts of temperature, moisture content, shear stress, and determination method on these kinetic parameters. Finally, future research needs are suggested.

Mechanochemistry in thermomechanical processing of foods: kinetic aspects.

In some food processing operations, raw materials sustain shearing and heating simultaneously. These thermomechanical treatments will induce chemical, physicochemical, and biochemical changes, such as starch degradation and gelatinization, protein denaturalization, loss of nutritious components, and inactivation of enzymes and their inhibitors. In this article, only kinetic aspects of these changes are reviewed. The Basedow and Zhurkov models are commonly used to describe shear effects on the rate constants of mechanochemical reactions. After a brief description of these 2 models, their applications in food are reviewed deeply, with emphasis on the activation energy reduction in the Zhurkov model and the shear activation energy in the Basedow model. Since the changes occurring in food systems often involve various interactions at the atomic, molecular, and supramolecular levels, they were described only phenomenonlogically by the mechanochemical kinetic models. The limitation, opportunity, and extension of the mechanochemical approach to modeling food kinetics are discussed.