DESIGN AND DEVELOPMENT OF POLYPHENOLIC BASED FLEXIBLE pH INDICATORS FOR SMART FOOD PACKAGING

Abstract

Food is a basic and daily necessity for the survival of humans. The constituents of food are complexly crafted by Mother Nature to meet the nutritional demands of the human body. Most of the food is categorized as a highly perishable commodity, meaning it can be devoured of its nutritional value by both extrinsic and intrinsic factors. Once they lose their nutritional value, they generate gigantic amounts of food losses and waste that can pose a threat to food safety and security. This has led to the idea of protecting and preserving food to extend its shelf life by maintaining its inherent properties. Packaging played a crucial role in executing the idea of protection and preservation by creating barriers between food and the external environment. Packaging has evolved rapidly through the years to meet consumer demands. Increased conscience over what is eaten in a day has necessitated fresh and minimally processed food. While food processing has been widely accepted in developing countries and there is no alternative, assuring the freshness of food remains challenging for the industry. Therefore, to enhance the communication functionality of packaging, a new age smart packaging system, specifically intelligent packaging, is the need of the hour. When concerned with the freshness of food, the simple and easiest way to analyze it is through sensory properties. Packed food cannot give consumers the convenience to truly sense the food. However, a reliable indicator of the package can get the job done. These indicators are capable of monitoring the dynamic shelf life and detecting the state of food. Some key deliverables that are expected from indicators are easily comprehendible, cheaper, do not interact with food constituents, and are safe. Two varieties of indicators are usually seen in intelligent packaging systems, namely internal and external indicators. The ones that monitor the inner atmosphere, like headspace gases, moisture content, and microbial growth, are called internal indicators, and the ones that are placed on the outer layer and give information on storage temperature and location are external indicators. The basic principle of indicators is that they chemically interact with volatile organic compounds released into the package headspace during food spoilage and convey through visual changes, most likely its color. These gases released by food are an indirect sign of pH changes in food. Hence, these indicators are broadly called pH indicators, and in addition, some indicators can detect the presence of unwanted gases like oxygen; ethylene comes under the category of gas indicators. Indicators consist of a base matrix and pH or gas-sensitive compound that readily reacts and detects their presence by color change. Synthetic pH-sensitive dyes and polymers were used to serve the purpose, but on the downside, they are carcinogenic and cause environmental pollution. The primary focus of this thesis is to investigate the viability of some natural colorants derived from plant phytochemicals (or) plant polyphenols as a replacement for synthetic dyes and examine their applicability in poultry packaging. Correspondingly, plant biomass-derived polymer matrices were explored to embed these natural pigments, which yields a biodegradable and flexible pH indicator for smart food packaging applications. Details of plant polyphenols and biopolymers, along with a literature review, are discussed in Chapter 1&2. In the third chapter, an attempt was made to investigate simple hydroxybenzoic acid as a pH-sensitive gas indicator, oxygen in particular. Oxygen is the major driving force for denaturation of proteins and lipid oxidation in foods. Scant traces of oxygen may promote the growth of microbes that eventually spoil within no time. Gallic acid is a simple hydroxybenzoic acid known for its radical scavenging activity. Therefore, gallic acid monohydrate (GA), 5 wt%, 10 wt%, 20 wt%, and 30 wt% coated pH-sensitive oxygen indicator labels were developed. Cellulose acetate was employed as a binder in the coating solution, and layer-by-layer coating was applied using a bar coater. Upon exposure to varying pH at atmospheric oxygen, the coated paper exhibited a color change from green to yellow for a pH range of 8-12, as evident from UV-visible spectra. FE-SEM, AFM images confirmed that coating led to a smoother surface with a decrease in roughness by approx. 60-80 %. ΔE values at pH 8 have the highest color difference at all concentrations. Hence, the fabricated gallic acid-coated oxygen indicator paper/label can serve as an intelligent packaging system to indicate the real-time quality of oxygen-sensitive food products. The present indicator will also act as a temper indicator, which will provide a clear optical indication of whether a sealed package has been tampered with during shipping. Despite the successful observation of color change, this polyphenol has a changed color only in alkaline media as gallic acid undergoes oxidation only after deprotonation leaving an option to explore other polyphenols further. Another polyphenol that has a broader spectrum of color changes was selected from the group of flavonoids called anthocyanins. They are a very well-known food colorant. The key focus of Chapter 4 is to extract anthocyanins from flower waste and develop a label out of it using a composite polysaccharide matrix. In addition, the biopolymer matrix was cross-linked using ionic cross-linkers to enhance the swelling index, and fillers like titanium dioxide were added to improve the color of the labels. The flower selected was butterfly pea flower (C. ternatea), and the polysaccharides opted for were flax seed mucilage and pectin. The brilliant blue hue of ternatins present in the flower was extracted using a simple maceration technique. The extract has changed from red to violet, blue to green, and finally yellow due to its structural changes from pH 2 to pH 12. The addition of 5 wt% TiO2 enhanced UV barrier property with a total color change (ΔE) of 23.441±0.54. After incorporating them into a biopolymer matrix, the performance of anthocyanins remains the same. It has taken about 21 days for the developed matrix without crosslinking to degrade completely. Although ionic crosslinking of polymers has decreased the swelling index, the label remains fragile when coming in contact with moisture, and leakage of anthocyanins from the label was noted during experimentation.