EVALUATION OF SOME TEXTURAL PROPERTIES OF FOODS WITH THE INSTRON UNIVERSAL TESTING MACHINE

Abstract. Analysis of published chewing force patterns indicates that the 'first bite' involves an approximately linear application of force. The Instron Universal Testing Machine also offers a linear pattern of force application making it possible to obtain information about textural properties identified during the 'first bite' from force-compression tests. However, the data obtained in such tests are influenced not only by the applied force but also by the rate at which it is applied. Both variables must be taken into account when analysing the data, since the applied force in chewing and also the rate of force application depend on the textural characteristics of the food being evaluated. Based on a correlation of sensory responses with instrumental force-compression-rate of force application data, a procedure is described for establishing the mechanical force conditions that should be used in Instron tests so that they simulate those associated with the sensory evaluation.     

Relative Role of Phospholipids, Triacylglycerols, and Cholesterol Esters on Malonaldehyde Formation in Fat Extracted from Chicken Meat

Fresh breast and leg meat was collected from 11-wk-old pullets fed a high protein-low fat starter ration. Lipid oxidation measured in malonaldehyde (MA) equivalents in total fat extracted from meat, and in phospholipids (PL), triacylglycerol (TG), and cholesterol ester (CE) fractions of total fat was determined by an improved TBA assay with antioxidant protection. It was found that breast meat had two-fold less fat than leg. Breast fat contained 70.1% PL, 22.2% TG, and 1.2% CE; leg fat contained 42.9% PL, 51.4% TG, and 0.8% CE. After separation by thin layer chromatography, the individual lipid classes were tested for TBA reactivity. The PL fraction was found to contribute approximately 90% of the MA measured in total fat from chicken meat.     

Coordination Chemistry in Mineral Processing

Abstract

In mineral processing industry, achieving an optimal extraction of valuable mineral components is an extremely important goal. The processes of leaching, solvent extraction and flotation are major methods of processing minerals under aqueous conditions in which coordination chemistry may play an important role, and in facilitating the realization of this goal. The success of some of these processes is ascribed to the ability of the chemical reagents to form stable coordination complexes with metal ions in the aqueous solution or on the surfaces of the mineral lattice. Leaching processes which involve complex formation usually result in increased dissolution of mineral values in aqueous solution, and may include cyanide, basic and chloride leaching. In solvent extraction, the extractant and masking reagents react with metal ions to form principally coordination complexes, which are either selectively extracted into the organic phase or retained in the aqueous raffinate. This is the basis underlying the concentration and purification of metal values by this process. Flotation processes, which employ collectors and depressants whose interactions with metal ions in aqueous solution lead to complex formation through coordinate bonding are believed to be more efficient than other analogous processes. In an effort to contribute to the understanding of the chemistry of these processes, the authors have attempted to review the role of coordination chemistry in mineral processing by flotation, leaching and solvent extraction.     

NEW DEVELOPMENTS IN STRUCTURAL OPTIMIZATION USING ADAPTIVE MESH REFINEMENT AND MULTIPOINT APPROXIMATIONS

Combining Shape Optimization (SO) with Adaptive Mesh Refinement (AMR) potentially offers a higher accuracy and higher computational efficiency, especially if the applied target error for AMR is reduced in the course of the optimization process. The disadvantage of that approach is that the rate of convergence of the corresponding optimization processes can be significantly lower as compared to processes which apply a fixed target error for AMR. In the present paper the so-called Multipoint Approximation Method (MAM) is used as a basis for SO in conjunction with AMR. Several techniques for improvement of the rates of convergence are presented and investigated. Firstly, alternative algorithms for determining the approximation functions using a weighted least squares method are investigated. The focus is on weights which depend on the discretization errors. Secondly, different strategies for moving and resizing the search sub-regions in the space of design variables are presented. The proposed methods are illustrated by means of several optimization problems in which the effect of AMR with changing discretization errors is modelled by artificially introduced numerical noise.     

BOOK REVIEWS

HEAT TRANSFER AND FOOD PRODUCTS. Bengt Hallström, Christina Skjölderbrand and Christian Trägårdh. Elsevier Applied Science Publishers, London and New York. 1988. pp. xiv + 263.
FLAVOUR ENCAPSULATION. (S. J. Risch and G. A. Reineccius, eds.) ACS Symposium Series 370, ACS, Washington D.C., 1988, 202 pp. $54.95 U.S. and Canada $65.95 Elsewhere.
POSTHARVEST PHYSIOLOGY OF VEGETABLES. (J. Weichmann, ed.) Marcel Dekker, New York and Basel. 1987. 597 pp. $150 U.S. and Canada, $180 all other countries.
PROGRESS AND TRENDS IN RHEOLOGY II. (editors H. Giesekus, M. F. Hibberd, P. Mitschka, P. Riha and J. Sestak, eds.) Steinkopf-Verlag, Darmstadt, Springer-Verlag, New York. 502 pp. DM 280.
HPLC IN FOOD ANALYSIS. (R. Macrae, ed.) Academic Press, London, 493 pp. $77.50 U.S. £55 elsewhere.
WATER ACTIVITY: THEORY AND APPLICATIONS TO FOODS. (L. B. Rockland and L. R. Beuchat, eds.) Marcel Dekker, New York 1987. ISBN 0-8247-7759-X; 404 pp.; $59.75 in the U.S. and Canada; $71.50 elsewhere.
GUMS AND STABILISERS FOR THE FOOD INDUSTRY. (G. O. Phillips, D. J. Wedlock and P. A. Williams) IRL Press, Oxford and Washington, 560 pp. £50 U.S. $100.
SAVOURY COATINGS. (D. B. Fuller and R. T. Parry, eds.) Elsevier Applied Science Publishers, New York. 130 pp., 1988. $47.00.
TOTAL QUALITY ASSURANCE FOR THE FOOD INDUSTRIES. W. A. Gould and R. W. Gould. CTI Publications, Baltimore. 1988. 394 pp. $50 in the U.S. $65 overseas.     

COMPARISON OF CATHEPSIN B, D, H AND L ACTIVITY IN FOUR SPECIES OF PACIFIC FISH

The activities of cathepsins B, D, H and L were compared in crude muscle extracts from four species of fish: Pacific whiting (PW), (Merluccius productus); arrowtooth flounder (ATF), (Atheresthes stomias); Alaska pollock (AP), (Theragra chalcogramma); and Pacific cod (PC), (Gadus macrocephalus). Both PW and ATF are known to undergo softening during post-mortem handling and cooking while AP and PC do not. Cathepsin B and L activities were both higher in extracts of PW and ATF than in AP and PC. Cathepsins B and L activities were both much higher in PW than in ATF. Cathepsin H activity was highest in AP followed by ATF with PC and PW having the lowest activities. Cathepsin D activity was extremely low in all four species. The heat stability of the various cathepsin activities showed cathepsin B to be the most heat labile and was inactivated by 50C heating for 15 min. Cathepsin H activity was inactivated at 60C, while cathepsin L required 70C for inactivation. Cathepsins B and L are the most likely responsible for softening in PW and ATF during holding and subsequent processing. However, during cooking, cathepsin L likely causes the most damage since it requires 70C for inactivation. The difference in heat stability of cathepsins B and L can be used to differentiate between their activities.