ISSN:8755-9129    

DOI:10.1080/87559129309540973

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

To improve the functional properties of food protein, physical and enzymatic treatments are effective and attractive. As an example of physical treatment, heat treatment of egg protein under various conditions is shown. Egg albumin and egg white usually give turbid (white) gel on heating. However, we have learned that a transparent gel can be prepared by regulating conditions of the medium. The molecular mechanism for formation of such gels and the physical properties of transparent and turbid gels are shown. Proteolytic enzymes are often used to improve the properties of food protein, but sometimes bitter peptides are formed. Therefore, a limited pro‐teolysis rather than nonspecific hydrolysis is preferable and effective in order to change the functional properties. We have shown that pepsin promotes limited proteolysis under pH control. Not only proteolytic enzyme, but other enzymes are also useful for improving food protein. Possibilities of the use of enzymes for food processing are shown here.

ISSN:8755-9129    

DOI:10.1080/87559129309540974

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Coagulation of proteins into moist particles of 0.1–20 μm diameter constitutes the basis of several patents for producing protein‐based replacers for fats and oil/water (O/W) emulsions. The thermo‐mechanical coagulation of a whey protein concentrate at acid pH (US patent 4,734,287, 1988, J. Labatt Ltd.) or that of egg white proteins on the surface of casein micelles at neutral pH (International Application WO 89/05,587, 1989, NutraSweet Co.) provides in both cases spherical particles with a diameter ranging from 0.1 to 2.0 μm. Precipitation of soluble proteins at their isoelectric point (European Application 0,400,714, 1990, NutraSweet Co.) or from ethanol solutions (International Application WO 90/03,123, 1990, Enzytech Inc.) provides particles with a diameter below 10 μm, when carried out under controlled stirring conditions. Formation of complexes between electrically charged proteins and polysaccharides embedded in modified starch (US Patent 4,308,294, 1981, General Foods Corp.) or fragmented under high shear forces (European Application 0,340,035, 1989, Kraft Co.) can provide particles in the size range 0.5–15 μm. These and a few other patents are analyzed in terms of coagulation and particulation mechanisms, optimal processing conditions, and food applications. For those patents that have led to the commercial fat replacers Simplesse 100 and 300, details are given concerning available structural, rheological, and nutritional characteristics of these products. However, their resistance to pH changes, heat processing, or freeze‐thaw, before or after incorporation into various foods, has not yet been reported in a systematic manner. Our own studies deal with the thermomechanical coagulation of a whey protein isolate (free from fat and lactose) either at acid pH (3.5–3.9) or at neutral pH (6.5–6.7) in association with calcium caseinate, used as an inhibitor against extensive protein aggregation. The thermomechanical process is carried out in a long‐barrel twin‐screw extruder (water content ∼ 77%; protein content ∼ 20%; barrel temperature = 85°‐100°C; screw rotation speed = 100–200 rpm; feed rate = 20 kg/h). The resulting semisolid spreads displayed high nitrogen solubility: 43–47% and 69–70% for the acid and the neutral products, respectively. The β‐lactoglobulin constituent was totally soluble in 1% SDS in the case of the acid product, while the degree of solubility depended on the process conditions in the case of the neutral product. Differential scanning calorimetry indicated 80% and 70% whey protein unfolding for the acid and neutral products, respectively. Laser diffractometry revealed for both products that over 50% of the particles had a diameter range within 6 and 11 μm (on a volume basis). Viscoelasticity characteristics were studied with an oscillatory rheometer. The texture of these fat replacers was only slightly affected by freezing and thawing. Their utilization for the preparation of given low‐fat or fat‐free foods showed that they were easily dispersed at a 5–10% level, developed desirable “creaminess,” and withstood to some extent the heat process given to the final food.

ISSN:8755-9129    

DOI:10.1080/87559129309540975

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Proteins are very surface‐active substances, which means that they readily adsorb onto O/W and A/W interfaces, even if present in very low concentration. They do not yield a very low interfacial tension. Adsorption, conformation in the interface, and the various interfacial properties resulting from their adsorption are briefly reviewed, especially in relation to formation and stability of emulsions and foams. Displacement from the interface by small‐molecule surfactants is also discussed. It is concluded that most effects of adsorbed proteins on the various kinds of physical instability of emulsions and foams are semiquantitatively understood, but that the variation among proteins in the production of small droplets and bubbles during emulsification and foaming, respectively, still largely defies explanation. It makes little sense to classify proteins according to their suitability for emulsification or foaming, because each of the physical properties of these systems may depend in a different way on protein species and on physicochemical conditions.

ISSN:8755-9129    

DOI:10.1080/87559129309540976

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Proteins occur as natural and engineered assemblies in foods. This paper focuses on the microstructural aspects of some protein assemblies and their relation to processing and functionality. Examples discussed include: (a) disassembly of protein bodies in seeds during aqueous extraction;(b)freeze‐texturization and gelation of muscle proteins; (c) formation of large protein aggregates during caking of fish hydrolysate powders;(d)transformation of globular to fibrous aggregates and the role ofTgduring extrusion cooking;(e)formation of mixed and filled dairy gels; and (f) kinetics of aggregation of β‐lactoglobulin.

ISSN:8755-9129    

DOI:10.1080/87559129309540977

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Two of the most important properties in the food context are the three‐dimensional structure and dynamical properties. These account for the structural and functional behavior of the proteins, and the manipulation of these during processing is an important part of food manufacture. One of the main tools for examining proteins is nuclear magnetic resonance (NMR). Historically this is long‐established but the advent of three‐ and four‐dimensional spectroscopy, together with the availability of very high magnetic fields, has opened up a new range of possibilities allowing the determination of solution‐state structure together with detailed dynamical information. At the same time, relaxation time and solid‐state measurements can give useful information about proteins in solid and quasi‐solid systems. The vibrational spectra of proteins are potentially a rich source of structural information. In the past both infrared and Raman methods have been difficult to apply. Infrared has suffered from

ISSN:8755-9129    

DOI:10.1080/87559129309540978

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Flesh proteins, in the context of this article, are taken to be the component proteins of the contractile muscle of animals used for food (i.e., meat, poultry, and fish). Attention is given to the similarities and differences between the proteins from these different sources and in particular to the effects on them of freezing and frozen storage. It is believed that myosin and action, the main contractile proteins, are largely responsible for the functional properties of flesh foods, and that on frozen storage, myosin, in particular, undergoes aggregation reactions which lead to toughening of the muscle and a loss in water‐holding capacity. Variation in stability of flesh of different species on frozen storage can be attributed to some extent to the intrinsic characteristics of the respective myosins. Myosin from fish is generally less stable than its mammalian or avian counterparts and this is reflected in the stability of the flesh on frozen storage. Cryoprotectants, usually in the form of low molecular weight polyhydroxy compounds, are added to some processed products such as surimi to counter the denaturation process. Theories on the mechanism of protein denaturation and of the action of cryopro‐tectants are reviewed. The potential of using the freezing process to form textures from comminuted flesh or protein dispersions is also discussed.

ISSN:8755-9129    

DOI:10.1080/87559129309540979

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

The recent interest of the food industry in the high‐pressure processing of food materials as an alternative or in addition to temperature treatment requires fundamental studies on the pressure‐temperature behavior of macromolecular food constituents such as proteins. In this paper we review some basic knowledge on the effects of high pressure on proteins. These effects are reversible or nonre‐versible and include changes in intra‐ or intermolecular interactions (noncovalent bonds), in conformation and in solvation. In general, reversible effects are observed below 1–2 kbar (e.g., dissociation of polymeric structures into subunits). Above 2 kbar, nonreversible effects may include complete inactivation of enzymes and denaturation of proteins (unfolding of monomeric proteins, aggregation, and gelation phenomena). Particular attention is directed to pressure denaturation, a complex phenomenon depending on protein structure, on pressure range, and on other external parameters, for example, temperature, pH, and solvent composition (presence of sugars, salts, and other additives).

ISSN:8755-9129    

DOI:10.1080/87559129309540980

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

ISSN:8755-9129    

DOI:10.1080/87559129309540981

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

ISSN:8755-9129    

DOI:10.1080/87559129309540982

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor