Authors D. Bajer, K. Janczak, K. Bajer,
Active, bio-friendly and natural-based materials are one of the innovative concepts in the field of research on packaging materials. Development of systems involving the employment of completely biodegradable polymers and natural bioactive components is currently a major challenge for plastic processing plants and packaging manufacturers. Due to its antimicrobial components, such an active packaging material can be an effective way to protect food or other perishable products (e.g. cosmetics) against accelerated biodegradation caused by activity of microorganisms which colonize the product surface. The possibility of reduction in the use of preservatives directly in the material, which undoubtedly increases the final product safety by protecting consumers against developing skin and food allergies, is an additional advantage of such packaging. However, current trends must take into account not only biodegradability, but also the oxidative resistance of such materials. The combined use of natural raw materials, i.e. antioxidants, anti-microbial agents incorporated into the biopolymer matrix constituting a base could contribute to an increase in their application efficiency. Currently, obtaining naturally originating materials resistant to photo- and biodegradation, simultaneously characterized by the desired mechanical strength, capabilities and constant processing parameters, transparency and physico-chemical properties (e.g. hydrophobicity, permeability to steam and gases, solubility, wettability, adhesion, cohesion etc.) constitutes a huge challenge to researches. Starch, a natural polysaccharide, is one of the most commonly occurring biopolymers. As a raw material of differentiated botanical origins, a reserve material in most plants, it has become a basic nutrient for mammals. Although the chemical structure of starch is commonly known, its origin and source are responsible for a large variety of its chemical composition (amylose to amylopectin ratio), (poly)dispersity, granules shape and size, as well as its molecular order and average molecular weight. Both, starch and its chemically and physically modified products, could find their applications in many sectors of industry (e.g. food, cosmetics, paper, and textile) and, more recently, as raw materials for biodegradable packaging production due to their availability, low acquisition costs and biodegradation. Despite many advantages, starch remains a difficult processing material owing to its cold-water insolubility, susceptibility to retrogradation, gelatinization, and high hydrophilicity. Moreover, its processing is characterized by high variability and instability and does not give reproducible results, which directly results from the botanical origin of starch or climatic conditions of plants growth. Starch-based films are brittle and not resistant to water activity, which directly limits the possibility of its industrial use. Thus, a suitable physico-chemical modification of native starch is aimed at modifying its properties according to industrial requirements and applicability. It concerns improving the starch processing methods, but it is also intended to obtain a material preventing biocompatible or antimicrobial properties. For this purpose, chitosan with its good gel- and film-forming abilities, anti-microbial and anti- oxidative properties as well as biodegradability seems to be a good modifier and a valuable material which has gained scientific attention. Its functional properties have been widely reported in literature in recent years. Moreover, it is safe and non-toxic; thus, there are no contraindications to its use in for food packaging production. Furthermore, as expected, chitosan can improve the mechanical properties of starch films which could strongly affect the possibility of its use on a large scale. Due to its higher hydrophobicity, if compared with that of starch, chitosan reduces water vapor transport and consequently increases resistance to moisture in starch/chitosan blends. A possibility to bond chemically with bioactive particles owing to the presence of reactive carbonyl and/or hydroxyl groups is an important advantage of such biopolymers. Thus, anti-bacterial properties of starch-/chitosan-based films could be intensified with biocompatible Aloe vera (AV) gel incorporated into the polymer matrix. It broadens the scope of applications for such biomaterial which turn out to be effective also for therapeutic and dressing purposes. Aloe vera plant is characterized by antimicrobial activity due to the presence of antiseptic ingredients i.a. salicylic acid, cinnamonic acid, sulfur, lueol. Moreover, its components such as glycoproteins, prostaglandins, muccopolysaccharides and gamma-linoleic acid are effective against E.coli, K. pneumoniae and S. aureus, whereas its anti-oxidative potential results from phenolic and polyssaccharide components, for example mannan, acemannan, glucomannan. In addition, by acting synergistically with other substances present in Aloe vera gel, e.g. enzymes or vitamins, biopolymer (starch/chitosan) films gain many pharmacological properties which are of great interest to medicine as well as food, cosmetic and pharmaceutical industries. Plant extracts which Aloe vera gel contains are a rich source of antioxidants, e.g. flavonoids, flavanols, polyphenols, organic acids (for example citric acid), etc., which can additionally improve plasticizing properties and influence bio-based films flexibility. In addition to the afore mentioned ingredients, there are more than 75 chemically active substances in Aloe vera gel. Among them, enzymes and minerals, essential and non-essential amino acids, sterols, saponins, anthraquinones (aloin, emodin) etc., can be listed. They are a part of dry, only 0.51.5% solid fraction, while water is the dominant component (98.599.5%) of the gel. Producing dressing materials based on biopolymers with AV gel incorporated in polymer films or hydrogels are a new research challenge. They are expected to elicit wound healing acceleration protecting at the same time against microbial attack; thus, such materials are of great interest for tissue engineering, drug delivery, and wound-dressings purposes. A novel system based on Aloe vera gel blended into the chitosan matrix was explored, and a strong interaction between these two components was proved. This combination caused a decrease in water solubility and vapor permeability noticed together with an increase in Aloe gel concentration. Moreover, mechanical properties of the prepared films were improved. Additionally, antimicrobial activity against S. aureus was higher in chitosan membranes enriched with higher Aloe vera gel content.
