Steven J. Mulvaney

The combined application of supercritical fluid and extrusion technology

The supercritical fluid extrusion (SCFX) process has the potential for producing a range of puffed food products, such as ready-to-eat cereals, pasta and confectionery products, with improved texture, color and taste. The conventional extrusion process has some limitations with regard to the process-related product characteristics. The SCFX process has been successful in overcoming some of these limitations, making extrusion a more versatile and controllable process. Some novel products produced using the SCFX process are presented in this article in the light of the above remarks. The principles of the SCFX process are described with particular focus on the thermodynamic and rheological fundamentals underlying the process improvements.

Role of Gluten and Its Components in Determining Durum Semolina Dough Viscoelastic Properties

ABSTRACT Gluten was isolated from three durum wheat cultivars with a range in strength. Gluten was further fractionated to yield gliadin, glutenin and high molecular weight (HMW) and low molecular weight (LMW) glutenin subunits (GS). The gluten and various fractions were used to enrich a base semolina. Enriched dough samples were prepared at a fixed protein content using a 2-g micromixograph. Mixing strength increased with addition of gluten. Dynamic and creep compliance responses of doughs enriched with added gluten ranked in order according to the strength of the gluten source. Gliadin addition to dough resulted in weaker mixing curves. Gliadin was unable to form a network structure, having essentially no effect on dough compliance, but it did demonstrate its contribution to the viscous nature of dough (increased tan δ). Source of the gliadin made no difference in response of moduli or compliance. Addition of glutenin to the base semolina increased the overall dough strength properties. Glutenin source ...

Advanced process control techniques for the food industry

Abstract The proper design and application of process controllers is essential for minimizing both operating costs and out-of-specification waste products in food processing operations. In this regard, advanced process controllers may perform significantly better than classical controllers. This article describes how advanced process controllers, particularly model-based controllers, are created and discusses the design criteria used to tune these controllers in the context of controlling food processes. A number of examples are reviewed that demonstrate the feasibility of applying model-based controllers to a variety of food processes. Guidelines for selecting appropriate advanced control strategies for particular types of dynamic processes are also presented.

Rheological properties of gelatin from silver carp skin compared to commercially available gelatins from different sources.

Gelatin is used as a functional ingredient in many foods, pharmaceuticals, and cosmetics as a stabilizing, thickening, and gelling agent. The rheological properties of gelatins are important in the potential functionality of gelatin. This study is designed to determine the rheological properties of gelatin extracted from the skins of silver carp (Hypophthalmichthys molitrix Valenciennes 1844). The extracted gelatin is compared with commercially available gelatins from different sources. The results indicate that the stress-strain relationship of gelatin gels remained in the linear region over a broad range of strains and stresses and gave similar elastic moduli at varying frequency, stress, and strain levels. One exception was a commercial high molecular weight fish skin gelatin that gave a lower elastic modulus indicating that its gel strength was low compared to the other gelatin samples studied. Gel strength varied between 220 and 1230 g while viscosity varied between 4.53 and 6.91 cP among the samples. Melting and gelling temperatures varied between 14.2 and 32.3 °C and 3.2 and 25.4 °C, respectively. Texture profile analysis was done at 2 deformation levels, 25% and 75%, and the results correlated well with gel strength. The correlations between hardness, cohesiveness, and gumminess and gel strength were 0.98, 0.82, and 0.99, respectively, at 25% deformation but lower at 75% deformation. The results suggest that rheological measurements might be used to quickly estimate gel strength using less material. In addition, the silver carp skin gelatin seemed to be of equal quality to some of the commercial gelatins.

Modeling and process control of twin-screw cooking food extruders

Abstract Twin-screw extruders exhibit highly non-linear and interactive dunamic behavior which makes their modeling and control difficult. Transfer function models determined from experimentally observed behavior are not only adequate in capturing the dynamics of the extrusion process, but are also invaluable tools in the design of multivariable control strategies for extruders. Suitable forms of transfer function models are taken from the literature to characterize a typical process used in cornmeal extrusion. The parameters for the transfer function models are also adapted from the literature and are used as an example in process control analysis and design. The degree of process loop interactions expected in this extrusion process for various controlled variable/manipulated variable pairings is studied using the relative gain array (RGA) technique. For minimal interaction, the MIMO system with screw speed and barrel heating as manipulated variables and product temperature and motor torque as controlled variables was found best. This system, using feed rate and moisture content as input disturbances and with realistic constraints on the manipulated variables, was simulated using standard software for controlled system performance. PID controllers without additional decoupling gave adequate performance results for various controlled system requirements.

On-line system identification and control design of an extrusion cooking process: Part I. System identification

Abstract A systems analysis of an extrusion cooking process for puffed corn snack products revealed that the specific mechanical energy (SME) and screw speed (SS) was a desirable pairing of measured and manipulated variables, respectively for regulating extrudate density. To facilitate the design of an SME model-based control system, a discrete-time transfer function that depicts the dynamic response of motor load (ML) to changes in SS is required. The research literature describes several off-line techniques for developing such transfer function models but no methods for on-line system identification were found. This paper represents the first of two articles that describe our investigations into the use of on-line system identification for automatic tuning and adaptive control of a high-shear twin-screw extrusion process. This paper reports results for using various system identification schemes in combination with relay-feedback as a way to derive, in real-time, a transfer function model that accurately depicts the dynamical behavior of an extrusion cooking process. A Wenger TX-52 co-rotating twin screw extruder was subjected to relay feedback during the processing of cornmeal for a breakfast cereal formula under different moisture and screw speed conditions. The data obtained from these experiments were used to derive first-, second- and third-order discrete-time transfer functions. An analysis of the resulting transfer functions revealed that a first-order lead-lag transfer function structure adequately described the dominant dynamic behavior of the process in all cases. Next, batch and recursive implementations of least-squares, extended least-squares, output error, maximum likelihood, Box–Jenkins and predictive error algorithms were used to derive parameters for the first-order transfer function. Overall, the batch output error method provided good transfer function estimates over the range of product and process conditions studied.

On-line system identification and control design of an extrusion cooking process: Part II. Model predictive and inferential control design

Abstract A non-linear model-based predictive control law to regulate specific mechanical energy (SME) using screw speed is developed. Operating variable setpoints are determined using an inferential model that correlates SME with product density and melt moisture content. Additionally, a ratio control strategy is used to regulate melt moisture content and an output noise filter is added to attenuate sensor noise. When combined with an on-line system identification procedure, the resulting system provides good servo and regulatory control response that is robust to modeling errors and disturbances. This paper represents the second of two papers that describe our investigation into the use of on-line system identification for automatic tuning and adaptive control of high-shear twin-screw extrusion processes. The resulting control design addresses the need for a comprehensive system that can be used to regulate extrudate density in extrusion cooking and puffing processes.

Effects of extraction and fractionation pressures on supercritical extraction of cholesterol from beef tallow

Edible beef tallow was extracted by supercritical CO2 in a dynamic mode at pressures from 138 to 345 bars and temperatures of 40 and 50°C. The lipid fractions were collected at 34.5 bar/40°C. A retrograde behavior of lipid solubility was observed around 170–175 bar. The ranges of the cholesterol concentration [chol.], were 300–450 mg/100 g and 50–200 mg/100 g lipid for the fractions extracted at 138 bar and 345 bar, respectively. Beef tallow was also extracted with sequentially varied pressures of 138, 345 and 138 bars at 40°C and collected at 34.5 bar/40°C. The results showed that after 20 kg CO2 was used for extracting 100 g of loaded beef tallow the weight of the residual beef tallow remaining in the extractor was 23 g with [chol.] of 49 mg/100 g lipid. The lower [chol.] of the residual beef tallow represents a 60–70% reduction in cholesterol content, when compared with untreated beef tallow where [chol.] ranges from 130 to 160 mg/100 g lipid. To isolate lipid fractions containing higher [chol.], beef tallow was extracted at 345 bar/40°C and then fractionated into three separators connected in series with decreasing pressures of 173 bar, 117 bar, and 34.5 bar at 40°C, respectively. The results showed that the fractions collected from the third separator (34.5 bar) contained concentrated [chol.] ranging from 272 to 433 mg/100 g lipid. The fatty acid analysis revealed that the fractions containing high [chol.] generally consisted of high concentrations of myristic and palmitoleic acids but low concentrations of stearic and oleic acids.

Dynamic modeling and computer control of a retort for thermal processing

Abstract The process dynamics and evaluation of analog pneumatic control and digital control of a batch retort were studied. Sensor dynamics of the analog controller resulted in poor control for arbitrary set-point tracking of the retort temperature. The retort dynamics were determined to be nonlinear in terms of the process gain, and time constant for changes in the steam supply input. A model was developed to describe this behavior and a digital proportional-integral controller was designed from simulation studies. This controller, with an anti-windup feature, was an excellent controller for regulation of the retort temperature to within ± 0.1 °C. It was also shown that to maintain this level of control the controller parameters need to be scheduled according to steam supply conditions and processing set-point.

Effect of moisture content on viscoelastic properties of hydrated gliadin

ABSTRACT The effect of moisture content on the linear viscoelastic properties of gliadin hydrated to 30 and 40% moisture content [gliadin(30%) and gliadin(40%), respectively] was determined. These two moisture contents bracketed the equilibrium moisture content of gliadin, which was 37.6%. Time-temperature-superposition was used to develop master curves of the elastic modulus (G′), viscous modulus (G″), dynamic viscosity (η′), and tan δ (G″/G′) from isothermal frequency sweep data obtained at 25–80°C. Smooth master curves were obtained for all of the viscoelastic functions for both gliadins. G′ and G″ showed a power law dependency on frequency (with G″ > G′) for frequencies <0.1 rad/sec for gliadin(30%) and <1 rad/sec for gliadin(40%). The low-frequency-limiting slopes on log-log coordinates for G′ and G″ were 0.700 and 0.646 for gliadin(30%), respectively. Corresponding values were 0.658 and 0.614 for gliadin(40%). G′ crossed over G″ at a frequency of ≈0.3 rad/sec for gliadin(30%), while G′ and G″ for gl...