Food Hydrocolloids: Characteristics, Properties and Structures

Abstract

An edible film is defined as a thin layer, which can be consumed, coated on a food or placed as
barrier between the food and the surrounding environment. For the past 10 years, research on edible
films and coatings in foods is driven by food engineers due to the high demand of consumers for longer
shelf–life and better quality of fresh foods as well as of environmentally friendly packagings [1-4]. The
most familiar example of edible packaging is sausage meat in casing that is not removed for cooking
and eating. Such films can mechanically protect foods, prevent the contamination from
microorganisms, prevent quality loss of foods due to mass transfer (e.g. moisture, gases, flavours, etc.).
Indeed, edible films and coatings can be used as a vehicle for incorporating natural or chemical
antimicrobial agents, antioxidants, enzymes or functional ingredients such as probiotics, minerals and
vitamins [5-7]. The edible films are classified into three categories taking into account the nature of
their components: hydrocolloids (containing proteins, polysaccharides or alginates), lipids (constituted
by fatty acids, acylglycerols or waxes) and composites (made by combining substances from the two
categories) [8].
Thus, the objective of this work is to present and discuss only some aspects of hydrocolloid
edible films and coatings. In particular, the film-forming materials is presented and the physical
properties (e.g. thickness, mechanical, optical and thermodynamic properties, water and gases barrier)
of the film and coating are examined. The main techniques used to form edible coatings as spray
systems or immersion procedures are detailed as well as the solvent casting and the extrusion processes
for the edible films. The main disadvantage of these techniques is the lost of quality of the edible
coatings and films since there is no control over the shape, size and size distribution of the dispersed
elements (e.g. additives, ingredients, etc.) in the support structure matrix is poor. An other disadvantage
of these techniques is that the thickness of the films is generally no constant and no controlled. Finally,
microfluidic applications are presented and discussed to solve some of these problems and to improve
film qualities.