Guibing Chen

Novel Rhamnogalacturonan I and Arabinoxylan Polysaccharides of Flax Seed Mucilage

The viscous seed mucilage of flax (Linum usitatissimum) is a mixture of rhamnogalacturonan I and arabinoxylan with novel side group substitutions. The rhamnogalacturonan I has numerous single nonreducing terminal residues of the rare sugar l-galactose attached at the O-3 position of the rhamnosyl residues instead of the typical O-4 position. The arabinoxylan is highly branched, primarily with double branches of nonreducing terminal l-arabinosyl units at the O-2 and O-3 positions along the xylan backbone. While a portion of each polysaccharide can be purified by anion-exchange chromatography, the side group structures of both polysaccharides are modified further in about one-third of the mucilage to form composites with enhanced viscosity. Our finding of the unusual side group structures for two well-known cell wall polysaccharides supports a hypothesis that plants make a selected few ubiquitous backbone polymers onto which a broad spectrum of side group substitutions are added to engender many possible functions. To this end, modification of one polymer may be accompanied by complementary modifications of others to impart functions to heterocomposites not present in either polymer alone.

Effect of microfluidisation on antioxidant properties of corn bran.

The microfluidisation process was used to reduce the particle size and loosen the tight microstructure of corn bran. This process significantly increased corn brans antioxidant activity exhibited through a surface reaction phenomenon and the extractability of phenolic compounds after alkaline and acid hydrolysis. For corn bran microfluidised through an 87 μm interaction chamber for 5 passes, the two most largely increased phenolic acids released after alkaline hydrolysis were p-coumaric acid (51.1%) and ferulic acid (45.1%). On the other hand, high shear stress during microfluidisation caused partial dispersion or dissolution of free phenolic compounds in water which was lost after the process. It was also found that bran residues after alkaline and acid hydrolysis still exhibited strong antioxidant activity via a surface reaction phenomenon, probably indicating the conventional method based on solvent extraction and relatively mild alkaline and/or acid hydrolysis underestimates the total phenolic content and antioxidant activity of corn bran.

An optimization algorithm for estimation of microbial survival parameters during thermal processing.

Isothermal microbial survival curves are usually described by either linear or nonlinear time-dependent models, from which non-isothermal survival curves can be generated if the parameters describing the survival kinetics of the microbial population are known. In order to estimate these parameters, an algorithm based on the steepest decent optimization method was developed. The algorithm searches the values of the survival parameters which minimize the sum of the squared differences between the experimental data and the calculated values provided by the model. The difference of the proposed algorithm with a typical optimization technique is that each data point used is not necessarily coming from the same thermal treatment; instead, data from different non-isothermal processes can be used. The developed algorithm was tested by using published non-isothermal survival data of Salmonella. The data showed that the survival curves can be described by the Weibull model, an already accepted and frequently used nonlinear model. Salmonellas survival parameters were estimated from the end points and all data points, respectively, of three non-isothermal survival curves. The results obtained showed that the number of survival data points must be sufficiently large to obtain true or statistically sound values of the survival parameters. A suitable way to achieve this is to implement the algorithm using all data points of multiple non-isothermal survival curves or a large number of end points of non-isothermal treatments. Mathematically, the developed algorithm should be applicable to any microbial survival kinetics accurately describing the inactivation of the microorganisms because no specific survival kinetics has to be pre-assumed to run the algorithm.

Numerical solution of a microbial growth model applied to dynamic environments

The Baranyi and Roberts model is one of the most frequently used microbial growth models. It has been successfully applied to numerous studies of various microorganisms in different food products. Under dynamic conditions, the model is implicitly formulated as a set of two coupled differential equations which could be numerically solved using the Runge-Kutta method. In this study, a simplified numerical solution of the coupled differential equations was derived and used to simulate microbial growth under dynamic conditions in Microsoft Excel. As expected, the results obtained were the same as those from solving the coupled differential equations using a MATLAB Solver. In addition, model parameters were accurately identified by fitting the numerical solution to simulated growth curves under dynamic (time-varying) temperature conditions using the Microsoft Excel Solver.

Physicochemical, Micro-Structural, and Textural Properties of Different Parts from Farmed Common Carp (Cyprinus Carpio)

ABSTRACT The fish body of cultured common carp (Cyprinus carpio) was divided into six sections, including the upper back, lower back, jaw, chest, belly, and tail. Differences in the physicochemical, micro-structural, and textural properties of different muscle tissues were investigated. The upper and lower back, with high content of protein, low content of fat, high water-holding capacity, and desirable textural properties, was proven to be the most valuable part of common carp from both a nutritional point-of-view and an organoleptic perspective. This could provide a theoretic basis for the comprehensive utilization of freshwater fish.

Explicit numerical solutions of a microbial survival model under nonisothermal conditions

Abstract Differential equations used to describe the original and modified Geeraerd models were, respectively, simplified into an explicit equation in which the integration of the specific inactivation rate with respect to time was numerically approximated using the Simpsons rule. The explicit numerical solutions were then used to simulate microbial survival curves and fit nonisothermal survival data for identifying model parameters in Microsoft Excel. The results showed that the explicit numerical solutions provided an easy way to accurately simulate microbial survival and estimate model parameters from nonisothermal survival data using the Geeraerd models.

On-line correction of in-pack processing of foods and validation of automated processes to improve product quality

Publisher Summary This chapter addresses the on-line correction of in-pack processing of foods, presenting a short review of the work done on batch retorts and a description of new developments on continuous retorts. The primary purpose of on-line correction of process temperature deviations is to automatically vary the process time to ensure that all containers receive the heat treatment necessary to achieve the required sterilization at the cold spot (the slowest heating point) of the food product. The critical part of the control system, specifically for batch retort operations, is to implement a fast method for accurately determining the new process time necessary to compensate for the process temperature deviations. In an on-line correction algorithm, the target process lethality is the most important constraint utilized to calculate the required new processing time. The traditional approach to evaluate the efficacy of a thermal process is based on the assumption that the inactivation of microbial cells and spores follows a first-order kinetic model. However, there is a growing concern about its validity because curvilinear isothermal survival curves are frequently observed. The Weibull model has been shown to be able to provide a more accurate estimation of microbial inactivation by heat and also by other inactivation sources: pressure and chemical agents. This model is of special interest to thermal processes of low-acid canned foods. Given the importance of non-linear kinetics in the evaluation of thermal processes, the chapter discusses on-line correction strategies for continuous retorts by using both first-order kinetics and the Weibull model.

Prediction of swelling behavior of crosslinked maize starch suspensions

Rheological properties of starch are affected by swelling of the granules that is in turn controlled by the degree of crosslinking. A previously developed model for swelling of starch granules was extended to account for electrostatic interactions. Maize starch was crosslinked with sodium trimetaphosphate. Granule swelling of 8% suspension of crosslinked maize starch when subjected to heating to 70,75,80,85 and 90 °C was more pronounced at higher temperatures eventually approaching equilibrium with the swelling ratio decreasing with increase in extent of crosslink. The number of crosslinks in the starch network was inferred from equilibrium swelling and related to peak viscosity and zeta potential. Chemical potential profile as well as the temperature profile within the granule at different times were predicted which were then employed to evaluate the evolution of granule size. The proposed model is able to describe the effect of crosslinking on swelling behavior.