F. Hsieh

Effects of lipids and processing conditions on lipid oxidation of extruded dry pet food during storage

Abstract Effects of fat type (beef tallow and poultry fat), fat content (0–0.75 g kg −1 ) and processing conditions (initial moisture: 1.6–2 g kg −1 ; screw speed: 200–400 rpm) on lipid oxidation of extruded dry pet food were studied. The results showed that the lipid oxidation rate constant of the extruded dry pet food was a function of fat types, added fat content and feed moisture content. Control (no fat) samples had the highest lipid oxidation rate, as compared to the samples with fat addition. Samples with poultry fat had a higher lipid oxidation rate than those with beef tallow addition. Samples containing a higher fat content resulted in a lower rate of lipid oxidation during storage. Feed moisture content had the same effect as the fat content; the extrudates with a higher moisture content resulted in a lower lipid oxidative rate. Pet foods extruded at 300 rpm had a significantly higher lipid oxidation rate than the ones produced at 200 and 400 rpm. Lipid oxidation of the extrudates appeared to be affected mainly by the degree of extrudate expansion. Products with a higher degree of expansion, which had larger cells and thinner cell walls, were more susceptible to oxidation.

System analysis as the basis for control of density of extruded cornmeal

Abstract The increase in the use of twin-screw extruders for the production of directly expanded products can be attributed to the unique versatility of this machine and the products that may be produced with it. However, complex relationships between process inputs, system variables and unmeasurable product quality attributes make control of the process difficult. Understanding the effects of particular inputs on product properties will improve the general understanding of the fundamental phenomenon underlying the extrusion process. Using a system analysis approach, the effect of moisture and screw speed on percentage torque, specific mechanical energy (SME), product temperature and die pressure was determined. Corn meal was adjusted to 16%, 19% and 22% moisture and extruded at 200, 300 and 400 rev./min in an APV-Baker MPF 50, twin-screw extruder. Extrudates were characterized by their specific volume, longitudinal expansion index (LEI) and sectional expansion index (SEI). SME could be described as a linear combination of moisture and screw speed. Product temperature was highly correlated with SME regardless of whether changes in SME were a result of changes in moisture or screw speed. However, specific volume was found to be a function of both SME and moisture content. Longitudinal expansion was linearly correlated with SME alone, whereas radial expansion was not correlated with SME input. Based on these results, an algorithm for indirect control of specific volume was developed based on on-line measurement of SME and calculation of the actual in-barrel moisture content.

Mechanical properties of extruded high amylose starch for loose-fill packaging material

Extrudates of corn starch containing 700g/kg amylose, which may have potential as a loose-fill packaging material, were prepared using an APV Baker MPF50/25 twin-screw extruder. Their moisture sorption isotherm was established by equilibrating them over saturated salt solutions at 25°C. The salts used and their water activities (in parentheses) were: LiCl (0.11), CH 3 COOK (0.23), MgCl 2 (0.33), K 2 CO 3 (0.42), Mg(NO 3 ) staggered2 (0.53), NaNO 2 (0.63), and NaCl (0.75). Energy index (3–19.3 N·m/m 3 ), compressive strength (34–162 kPa), and spring index (58–79%) of the packaging materials were determined from their stress-strain curve using the Instron Universal Testing Machine with a data acquisition system. Both energy index and compressive strength increased with increasing water activity levels up to 0.53 and then decreased. The spring indices were not present at water activities 0.11 and 0.23, and behaved in a similar manner to compressive strength at higher water activities.

Model and strategies for computer control of a twin-screw extruder

Abstract The dynamics of twin-screw extrusion of corn meal was studied. Second-order transfer functions with numerator dynamics were used to model the dynamic responses of process variables to step changes in extruder operating parameters. Step changes in screw speed, feed rate and barrel temperature set-point caused inverse responses in die pressure and motor torque. Overshoot responses were found for die pressure and motor torque to step changes in feed moisture. Product temperature always displayed an over-damped second-order response for step changes of all extruder operating parameters. These models were validated and the implications of using these models for computer control of a twin-screw extruder were discussed.

Puffing of okara/rice blends using a rice cake machine.

Okara is the insoluble byproduct of soymilk and tofu manufactures. It is cheap, high in nutrients, and possesses great potential to be applied to functional human foods. In this study, a puffed okara/rice cake product was developed with blends of okara pellets and parboiled rice. Consumer preference and acceptance tests were conducted for the product. Okara pellets were prepared by grinding the strands obtained from extruding a mixture of dried okara and rice flour (3:2, w/w) with a twin-screw extruder. Okara pellets and parboiled rice were blended in 4 ratios, 90:10, 70:30, 40:60, and 0:100 (w/w), and tempered to 14% and 17% moisture. The blends were puffed at 221, 232, and 243 degrees C for 4, 5, or 6 s. The okara/rice cakes were evaluated for specific volume (SPV), texture, color, and percent weight loss after tumbling. Overall, the decrease in okara content and increase in moisture, heating temperature and time led to greater specific volume (SPV) and hardness, lighter color, and lower percent weight loss after tumbling. The consumer tests indicated that the okara/rice cake containing 70% okara pellets was preferred and the 90% one was liked the least. The possible drivers of liking for the puffed okara/rice cakes could be the okara content, hardness, SPV, bright color, and percent weight loss after tumbling.

Processing parameters and product properties of extruded beef with nonmeat cereal binders

Ground beef chuck was extruded with yellow corn flour, white corn flour and white corn flour with soy fibre acting as the nonmeat binders. Extrusion temperature was found to affect torque, specific mechanical energy, die temperature, die pressure, residence time, extrudates visual appearance, expansion ratio, colour, and texture profile analysis. Extrudates storage stability was not affected by either extrusion temperature nor cereal flour type. The additions of soy fiber did not significantly affect product properties nor processing variables. However, addition of yellow corn flour increased the extrudates yellowness due to the presence of carotenoids.

Laser Scanning System for Real-Time Mapping of Fiber Formations in Meat Analogues

High moisture extrusion has been used to produce vegetable meat analogues that resemble real animal meat and can provide significant health benefits. Since visual and textural properties are key factors for consumer acceptance, assessing fiber formation in the extruded products is important for quality control purpose. Recently, we developed a nondestructive photon migration method to quantify fiber formation in meat analogues. In this study, we implemented this technique in a real-time optical scanning system. This system can scan the entire sample area in real-time and provide 2-dimensional maps to visualize the degree of fiber formation and fiber orientation in the sample. The new system has a potential to provide a fast, nondestructive means for online monitoring of the fiber formation in meat analogues.

Nondestructive real-time monitoring of fiber formation in meat analogs

High moisture extrusion technology is capable of producing meat analogs which assemble real meat. Since visual and textural properties are the key factor for consumer acceptance, assessing fiber formation in extruded products is important for producing quality meat analogs with a great texture. Recently, we developed a photon migration method to assess fiber formation in meat analogs. In this paper, we present an implementation of this method in a real time scanning system. Acquired images were processed to characterize the fiber formation. This system provides a fast, non destructive means to determine the fiber formation in meat analogs.

Quantifying fiber formation in meat analogs under high moisture extrusion using image processing

High moisture extrusion using twin-screw extruders shows great promise of producing meat analog products with vegetable proteins. The resulting products have well defined fiber formations; resemble real meat in both visual appearance and taste sensation. Developing reliable non-destructive techniques to quantify the textural properties of extrudates is important for quality control in the manufacturing process. In this study, we developed an image processing technique to automatically characterize sample fiber formation using digital imaging. The algorithm is based on statistical analysis of Hough transform. This objective method can be used as a standard method for evaluating other non-invasive methods. We have compared the fiber formation indices measured using this technique and a non-invasive fluorescence polarization method and obtained a high correlation.