摘要:

Hard‐to‐cook legumes (HTCL) have been observed for centuries. Different types of HTCL are recognized in freshly harvested crops or are developed during storage. Two types ofhard shell, which is due to seed coat impermeability to water, are identified: (1) thereversible hard shellthat occurs in freshly harvested seeds and disappear during storage; (2) the other type is theirreversible hard shellthat develops during storage.Scleremais due to unhydratable cotyledons (despite removal of seed coat) during soaking, and it may develop during storage. Some cases of reported hard shell may be due to sclerema, since no testing was done to prove seed coat impermeability.Hard textureandsandy texture(i.e., grainy or granular texture) have been noticed in freshly harvested and in stored legumes. In this paper, variations in the physical properties and the chemical composition of the seeds of different legumes and of different varieties are summarized in several tables. The following topics are discussed with regard to different types of HTCL: the environmental factors affecting their development; the structural and the chemical changes associated with their presence; the treatments which are used or suggested to control their development or to improve the texture of HTCL; and the possible relations between these subjects. Several propositions concerning the mechanisms involved in hard‐texture seeds are discussed. Soft texture is associated with ease of cell separation of the cotyledons in cooked legumes, indicating the significance of the middle lamella and the cell wall. At present, it seems that the main mechanisms include phytate, phenolic compounds, and divalent cations (Ca, Mg) and their interaction with pectic substances and proteins. Starch, lipids, tannins, and lignin may have a secondary effect. More knowledge is needed about cell wall components, structure, and interactions, and about the effect of environmental conditions on them.

ISSN:8755-9129    

DOI:10.1080/87559129209540938

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

Periwinkle is a potential source of good‐quality proteins. It contains most of the essential amino acids in adequate amount for human nutrition. The shellfish is capable of accumulating toxigenic microorganisms as well as toxic heavy metals if harvested from polluted water. Harvesting and processing are still mainly at artisanal levels—for example, in West Africa due to the clumsy methods of harvesting and removal of the meat from the shells. There is need for strict environmental control of the harvest areas and adequate processing of these marine animals in order to ensure safety and wider distribution of the product.

ISSN:8755-9129    

DOI:10.1080/87559129209540939

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

Although primarily used at low moisture levels, extrusion cooking with twin‐screw extruders also applies to food mixes with 40–80% moisture. Such levels reduce or prevent viscous dissipation of energy and product expansion, but facilitate operations such as fat emulsification, sterilization, protein gelation, restructuring and shaping of comminuted meat or fish, and microcoagulation and/or fibrillation of specific protein constituents. Fibrous gelled structures are obtained from (a) defatted soy flours or concentrates; (b) wheat gluten; and (c) mixes containing 70–80% surimi plus 30–20% soy concentrate or gluten, by extrusion cooking at 50–70% moisture, at barrel temperatures above 140°C, using long cooling dies. The continuous gelled bands are highly resistant to stretching in the longitudinal direction. They display a multilayer and partly fibrous structure. An extruded crab analog with a finely fibrous texture, made from Alaska pollack surimi plus egg white and 1% starch, is already commercialized in Japan. Three main phenomena are involved in the formation of these structures:(a) protein plastification (“melting”) within the extruder, which requires a barrel temperature of 140–180°C (at 60–70% water), a residence time close to 150 s, and high shear forces; (b) stability of extrusion conditions, without surging (often difficult to achieve); (c) presence of a long cooling die, exerting essential functions: upstream pressure generation, enabling high temperature, channel filling, and extrudate continuity; progressive reduction of the mechanical and thermal energy of the food mix, permitting proper shaping, while avoiding product expansion; alignment of dispersed protein particules along the shear gradient in the narrow die channel, leading to layer and fiber formation. The restructuring of mechanically deboned meat can be achieved through extrusion cooking (40–50% water) in the presence of high levels of binders such as starch or cereal flours. Such experiments were carried out without a cooling die and without fiber formation. Emulsified and gelled cheese analogs, with textures ranging from hard blocks to soft spreads, can be obtained with a single extruder pass, starting from cheddar or from caseinate plus various fats. The extents of fat emulsification and of casein “reassociation,” and the melting ability, depend on composition and process parameters. The extrusion of fibrous products similar to mozzarella‐based string cheese is attempted. Fat substitutes with a smooth and spread‐like consistency are also prepared by thermomechanical processing of caseinate and/or whey proteins in a twin‐screw extruder at an acid or neutral pH. Shear forces and several biochemical mechanisms concur to induce the “microcoagulation” of β‐lactoglobulin as small‐size particles (<20 μm). Other potential moist extrusion processes include the coagulation of skim milk powder into an insoluble acid casein coprecipitate, the encapsulation of small molecules into protein gels, and the formation of edible thin protein films.

ISSN:8755-9129    

DOI:10.1080/87559129209540940

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

Choices about what to eat to improve health and what substances should be prohibited in food to prevent harm both involve judgments that must be made in the absence of definitive information. Scientists and government regulators have refined the limited data on chronic toxicity, especially cancer, from low‐level exposure to chemicals in food by using quantitative risk assessment techniques. Quantitative risk assessment, which produces an exact numerical risk, facilitates decision making about food additives, pesticide residues, and other chemicals present in food. This article examines the feasibility and utility of a similar quantitative approach to the risks and benefits from dietary factors such as fats and fiber. The article concludes that although a more quantitative approach in this area is possible, it would be less useful than it is in regulating potentially carcinogenic food chemicals. Quantitative risk assessment for carcinogenicity is necessitated, in part, by serious gaps in our knowledge about whether and how chemicals induce cancer in people. Although this technique yields a precise measurement of risk, it has no verifiable relationship to what actually happens in the body. Somewhat paradoxically, a greater knowledge of how the diet influences health makes it less necessary to strive for exactness in describing it.

ISSN:8755-9129    

DOI:10.1080/87559129209540941

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

Mycotoxins, Cancer and Health. G. A. Bray and D. H. Ryan, eds. Pennington Center Nutritional Series, Vol. 1. Louisiana State University Press, Baton Rouge. 1991, 331 pages, $39.95.

ISSN:8755-9129    

DOI:10.1080/87559129209540942

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

ISSN:8755-9129    

DOI:10.1080/87559129209540943

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

ISSN:8755-9129    

DOI:10.1080/87559129209540937

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor