Robert L. Jackman

Perspectives in the textural evaluation of plant foods

Abstract Texture is a major quality attribute that determines the acceptance of plant foods. However, the term is still often poorly defined and applied. As texture is dictated by the underlying composition and organization of plant tissues, it is crucial for food scientists to be aware of the structure of plant foods. The texture of plant foods can be attributed mainly to the structural integrity of the cell wall and middle lamella, as well as to the turgor pressure generated within cells by osmosis. Recent models of the cell wall envision a cellulose-hemicellulose structural domain embedded in a second domain consisting of pectic substances, while a third domain contains covalently crosslinked protein units. Textural problems in plant foods, arising from diffusion, ripening and processing factors, for example, are directly related to the architecture of the plant cell. Thus, an increased understanding of the structural basis of texture and also of the fundamentals of texture measurement should assist in overcoming quality problems in plant foods.

Ultraviolet Absorption and Fluorescence Properties of Whey-Potato and Whey-Pea Protein Composites

Abstract Several whey-potato and whey-pea protein composites were prepared by wet-blending and their ultraviolet (UV) absorption and fluorescence properties were measured at pH 4 to 8. A significant (p

Multivariate Analysis of Functional and Structure-Related Properties of Whey-Vegetable Protein Composites

Several multivariate statistical techniques were applied to ultraviolet absorption, fluorescence emission and extrinsic fluorescence data to investigate the relationship between functionality and structure-related properties of whey-potato and whey-pea protein composites over the pH range of 4 to 8. Multiple regression analysis resulted in highly significant (p<0.001) equations predicting solubility, thermocoagulability, foaming capacity and emulsion properties. Cluster and principal component analyses delineated variables into three distinct groups reflecting solubility and/or surface-active properties, surface hydrophobicity and tryptophan exposure. Stepwise linear discriminant analysis led to correct differentiation of individual samples into their respective composites, based solely on significant (p<0.05) contributions to discriminant functions by variables characterizing surface hydrophobicity and solubility and/or surface-active properties. Results from this study support the hypothesis that hydrophobic residues play a key role in functional properties displayed by whey-vegetable protein composites.

Protein engineering: Methodology, applications and status

Abstract Developments in recombinant DNA (rDNA) technology have made selective alteration of primary amino acid sequences of proteins possible. Such manipulation using genetic engineering techniques has been referred to as protein engineering. Although this technology has seen only limited application in food research to date, this emerging and rapidly expanding technology offers exciting approaches to protein/enzyme modification studies, and may aid in the development of novel processes and/or more functional and nutritious proteinaceous foods. This review outlines some basic protein engineering methodology and strategies. In addition, examples are provided in which site‐directed mutagenesis has been used advantageously in the specific modification of the enzymes subtilisin, lysozyme and chymosin, and of the casein proteins in milk and the storage proteins of potato tubers. These examples indicate the potential of protein engineering technology in investigations of structure‐function relationships, stabi...