550

35 Edible Coatings and Films from Agricultural and Marine Food Wastes

used for further processing. Alkaline N-deacetylation of chitin will lead to chitosan

and is composed of (1-4)-linked 2-amino-2-deoxy-β-D-glucose monomers [7, 8]. It is a

cation polysaccharide with high molecular weight and also reported to have antimi-

crobial activities. It is advantageous to use chitosan in the film-forming due to its

nontoxic and biocompatible nature [34].

Chitosan has good film-forming properties and it can be used for food preserva-

tion. To be used as a film, chitosan needs to be solubilized into gel by the solvent

dissolution. Crude chitosan being only acid soluble and cannot be used for film mak-

ing, as pH plays a main role on its biocompatibility [35]. The main advantage of using

chitosan-based film is that it has antimicrobial activity. In one study [15], fish waste

was evaluated for chitosan generation. The author developed a chitosan coating for

commercial application to improve the quality of lettuce for 15 days at 4 ^∘C. It also

resulted in the reduction of microbial count, preservation of the chlorophyll pheno-

lic compounds, and antioxidant activity during the refrigerated storage period. The

chitosan utilization during the postharvest storage opened the possibility of valu-

ing the fish industrial waste. Sea urchin spines with chitosan gel were used for the

biodegradable film preparation. This provides a good hydrophobicity properties and

a smooth surface [8, 36].

Squid is the most abundant species in the aquaculture. Squid processing wastes

include its skin, viscera, tentacles, and muscle traces. Nearly, 200–400 g/kg of its total

weight produces the by-products. During skinning of the mantle, a large amount of

muscle waste is generated which is high in protein content. Valorization of these

components may lead to their commercialization. In another study [37], a film based

on the myofibrillar protein concentrate was developed. The edible films made from

the marine biowaste were shown in Table 35.2.

35.5

Film/Coating Formation Methods

All the components must be mixed properly in a solvent, such as water or other

solvent mixtures with a low-speed stirrer to obtain the homogenous layer. Adjust-

ing the pH, heating, degassing, and deforming of the solution is required to remove

the air micro-bubbles which after the suspension cause mechanical failure [3]. The

most commonly used film-forming methods are wet process or solvent casting and

dry extrusion process. However, for coating process dipping, spraying, and brushing

are used.

35.5.1

Solvent Casting

Dispersions of the edible materials are spread on appropriate base and then let it

to dry. This results in solvent evaporation leaving the polymer macromolecules to

align themselves to a cohesive free-standing layer (film). Careful controlling of dry-

ing rate and environmental conditions is needed because of their high effects on

film thickness and structural characteristics. Usage of infrared drying can fasten the

drying process. Removal of the film without tearing is done by peeling it off from