TRANSGLUTAMINASE IN DAIRY PRODUCTS: CHEMISTRY, PHYSICS, APPLICATIONS

Literature on the effects of microbial transglutaminase on various dairy‐based systems is discussed. Beginning with a short synopsis on the development of microbial transglutaminase as a functional tool for modifying foods, the principles of reactions catalyzed by transglutaminase and their structural implications, as well as the mechanisms of formation and cleavage of isopeptide bonds are reviewed. After summarizing the present knowledge on the specificity of microbial transglutaminase towards milk proteins, including reactions determined by individual lysine and glutamine residues, emphasis is placed on the effects of enzymatic cross‐linking on physicochemical properties in foods and, particularly, dairy‐based systems. Discussed are implications of cross‐linking on acidified milk gels including yogurt and effects on single milk protein fractions, with respect to several physicochemical properties including rheology and mechanical properties of these systems, but also syneresis, and emulsification behaviour.     

Biochemical and Physicochemical Properties of Actomyosin from Pre- and Post-spawned Hake (Merluccius hubbsi) Stored on Ice

Biochemical and physicochemical properties of natural actomyosin (NAM) from pre- and post-spawned hake stored on ice were studied. At the beginning of storage both reduced viscosity and ATPases activities of NAM from post-spawned hake were about 3 times higher than those of the pre-spawned ones, except for the Mg²⁺-(Ca²⁺)-ATPase. Higher loss of functional components during pre-spawned hake NAM purification was found compared to NAM from post-spawned fish. Reduced viscosity and Mg²⁺-(EGTA)-ATPase activity of NAM from both pre- and post-spawned hake decreased following ice storage. SDS-PAGE patterns of NAM from pre-spawned hake showed an absence of the myosin heavy chain and the presence of a 160 kDa component at zero time of storage. No proteolysis occurred in ice-stored fish caught in both gonadal stages.     

Amino Acid Profiles of Fermenting Wheat Sour Doughs

The free amino acid patterns of unfermented and fermented wheat sour doughs started with Lactobacillus plantarum were related by factor analysis to dough yield, ash content of flour, fermentation temperature and presence/absence of yeast, from data corresponding to a central composite design of samples. Individual levels of hydrophobic, acid and basic amino acids as well as total amino acid content positively correlated with extraction rate of flours. The presence of yeast promoted metabolism of histidine, aspartic acid and asparagine, particularly in samples made with whole and wholemeal flours. Proliferation of predominant amino acids by enzymatic release was more notable at higher fermentation temperatures and wholemeal samples. Sour doughs with maximum levels of hydrophobic and basic amino acids were started with no yeast bacterial cultures, made with whole and wholemeal flours and fermented at 35°C.     

Some Further Contributions to “A Model Reference Adaptive Control System using a Cost Function Criterion for Driers and other Dead-time Processes”—The use of a Dynamic Model

An earlier paper developed an iterative hill climbing procedure for optimizing the performance of a static process model, using a performance criterion which could readily take into account the desigu objectives of the process.

This paper extends the work to the dynamic case. The preferred mode is the impulse response of the process, which can be determined by experimental methods which are already in an advanced stage of development. The particular optimizing programme described gives assured convergence with a short computing time, which is substantially independent of the order of the system.

The choice of sampling interval is considered and it is shown that a value of l/10th of the system dominant time constant is suitable for most applications.     

Sub‐100‐nanometre resolution in total internal reflection fluorescence microscopy

Combining total internal reflection fluorescence microscopy with structured illumination allows optical wide‐field imaging with sub‐100‐nanometre resolution. We present a novel objective‐launch set‐up for standing wave illumination that takes advantage of a tunable transmission diffraction grating and transparent phase shifters actuated by electro‐active polymers to control the excitation pattern in three dimensions. Image acquisition is completed in less than 1 s. To reconstruct the extended image spectrum, we apply a new apodization function that results in a lateral resolution of 89 nm for green emission wavelength.     

ELECTRICAL CONDUCTIVITIES OF SOME METAL SALT FILMS UNDER ANODIC CONDITIONS

Recently determined electrical conductivities of anodic AgCl, AlCl₃, TiBr₄, and MgCl₂ films are compared to well established conductivities of anodic Ta₂O₅ and Al₂O₃. All of these films exhibit high-field barrier layer condition. The exponential constant, β is about the same value for the salts as for oxides but the preexponential constants and conductivities are orders of magnitude larger for the salts. The salts, AlCl₃, TiBr₄, and MgCl₂, in addition, have a series ohmic resistance which is attributed to an outer, continuously-forming and dissolving, hydrated salt layer.     

SWEETNESS AND ACCEPTANCE OPTIMIZATION IN COLA FLAVORED BEVERAGES USING COMBINATIONS OF ARTIFICIAL SWEETENERS — A PSYCHOPHYSICAL APPROACH

This paper develops a quantitative model relating concentration of sweeteners, perceived sweetness, offtaste, and overall acceptability for cola beverages sweetened with artificial sweeteners. The psychological rules of sensory perception that govern reactions to pure aqueous systems of sweeteners are shown to hold for complex beverages that are normally drunk. By means of sensory assessments of products, acceptance and rejection limits can be specified both in terms of consumer reactions, and in terms of ingredients, once a model is developed which interrelates these variables.     

MAKING BETTER USE OF NATURAL LIGHT WITH A LIGHT-REDIRECTING DOUBLE-GLAZING SYSTEM

The subject of the present paper is a fixed daylighting system known as the LIF light guide. The system consists of a fixed arrangement for capturing sunlight incident at various angles and re-directing it by means of an optical wave-guide which provides diffuse ceiling illumination. The light guide is generally sandwiched between two glass panes and mounted above the windows to avoid obstructing visibility. Its intended function is to furnish offices and other working areas with a uniform level of natural illumination while avoiding glare.     

USE OF SEMITRAINED PANEL MEMBERS IN THE SENSORY EVALUATION OF HAKE (MERLUCCIUS MERLUCCIUS, L) ANALYZED STATISTICALLY

Abstract The main objective of this study was to evaluate the responses of semitrained sensory assessors to parameters traditionally used in the sensory analysis of hake and to compare their performance with that of trained inspectors. Appropriate statistical methods were used to validate this objective.
The study was carried out with whole gutted hake stored for 7 and 12 days in a controlled atmosphere consisting of 60%/15%/25% (CO₂/O₂/N₂), followed by conventional storage in ice. The hake stored under the CA conditions were preserved better than the control hake at 7 days and at 12 days the difference was even more in favor of the CA storage. Ten parameters evaluated in the sensory tests could be reduced to five with no loss in essential information. The evaluations of the semitrained assessors largely correlated with those of trained inspectors. A model using five parameters and semitrained assessors could be routinely used to evaluate the quality of cooked hake previously stored in ice.     

The influence of a dielectric window near the open end of a circular waveguide on the reflection and transmission coefficients

Modifications to the reflection and transmission coefficients of a circular waveguide radiating into free space due to the presence of a dielectric window are considered. The reflection and transmission coefficients as functions of several factors (for example, the thickness, the location and the dielectric and attenuation constant of the dielectric window) are analysed. Some experimental results are presented