Surface Phenomena In Food Disperse Systems
SURFACE PHENOMENA IN FOOD DISPERSE SYSTEMS
T.O. Didorenko, G.N. Gordiychyk, V.N. Tischenko
Odessa State Academy of Food Industry, Kanatnaya st. 112, 65039 Odessa, Ukraine e - mail profAIK@ipss.net
The majority of foodstuff, is a composite polydisperse system, in which the dispersed phase is both in ionic – molecular state, and as particles of colloidal dispersion degree. It is impossible to define rigorous line between dispersed phases, as water solutions of some substances are a dispersion medium for other substances. Any changes in the content and state of constituents can give lead to destruction of all equilibrium system of foodstuff and losses of stability of its components.
The study of surface phenomena happening on interphase borders of edible disperse systems, has allowed developing a nonstandard colloidal – chemical method for the solution of a problem of stabilization of such edible disperse systems as juices with pulp and not purified juices. The offered approach to stabilization of the not clarified juices and juices with plump, is based on viewing them as hydrophilic biocolloids of compound composition. The preliminary examinations allow making a deduction that for maintenance of stability the colloidal systems of the not clarified juices and juices with plump should contain substances, which are stabilizers of these systems. Stabilizers can be ions of electrolytes, neutral molecules and micelles of reversible colloids forming a part of a dispersed phase of these systems [1]. The stability of disperse systems is bound up first of all with interaction of particles of a dispersed phase among themselves. This interaction also determines adhesion of particles to macrosyrface and structuring in disperse systems [2]. Therefore in a basis of any stability theory the relation between attractive forces and repulsion of particles lays. Utilizing the theory DLFO and taking into account the structure of particles of a dispersed phase of fruit juices is adsorptive - solvate factor it is schematically possible to present as follows.
The ions with potential jS are adsorbed on colloid particles plump of juices; in immediate proximity from them there are gegenions generating dense adsorptive bed. Other part of gegenions diffuses in a depth of a dispersion
medium under activity of thermal agitation, forming diffuse bed with potential jd. The thickness of diffuse bed can be major enough and depends on properties and composition of system.
The double electrical bed can also be formed due to orientation of polar molecules of conjugate phases as a result of their interaction. On such mechanism the double electrical bed is formed as a result of adsorption andissociable of polar molecules which are in a solution. Apparently, such system can be operated, changing electrolytic composition of a solution, рН of medium or selectively fortifying concentration in system of stabilizers (for example of pectin\’s or organic acids), i. e. substances, capable to be selectively adsorbed on a surface of particles of a dispersed phase, incrementing electrokinetic potential. The introduction juices of inert electrolyte in colloidal system on the contrary compresses double electrical bed that results in diminution of an electrokinetic potential, loss of a charge by a colloid particle and subsequent coagulation of all colloidal system.
The complex examinations, carried out by us based on viewing of dispersible composition, adsorptive, electrosurface and reological behavior of fruit juices with pulp have shown:
1. The dispersity of particles can vary (in short intervals) self-maintainedly by processes of adsorption and desorption by particles of a dispersed phase electrolytic of a phone.
2. In an isoelectric state there is an integration of particles as a result of losses of a charge by them, and consequently of aggregate stability.
3. It is possible that the stabilization of particles by preferential adsorption or introduction in system of microquantities of stabilizers – substances which are capable to increment a charge of particles and preclude to their integration. As stabilizers the substances, which form composition of juice (pectin, hemicelluloses, protein and other substances) can be used.
The above-stated point of view completely proves to be true by the results of electrokinetic and reological examinations. The carried out examinations show that the targeted study and regulation of the colloidal – chemical descriptions of edible disperse systems enable to operate processes of their stabilization and destabilization.
References
1. Борисов B. О., Загібалов O. Ф., Дідоренко Т. O. Наукові праці ОДАХТ, 1995, Вип. 15, С. 30.
2. Пилипенко Л. М., Борисов B. О., Калінков O. Ю., Дідоренко Т. O. Наукові праці ОДАХТ, 1999, Вип. 19, С. 138.
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