The black and purple rice (Oryza sativa L) are the indigenous rice varieties and are mostly available in North-East India. The bran of black and purple rice, a waste product from the rice milling process, contains high level of polyphenols such as anthocyanins (cyanidin-3-O-glucoside, peonidin-3-O-glucoside, and cyanidin-3-O-gentiobioside) and various type of phenolics (Catechin hydrate, Coumaric acid, Ferulic acid, Syringic acid, Vanillic acid, and gallic acid) and flavonoids in its composition.
The bran shows numerous antioxidant activities such as ferric reducing antioxidant power, Trolox equivalent antioxidant capacity, and scavenging effect on the 1,1-diphenyl-2-picrylhydrazyl free radical.
However, the use of extracted anthocyanins during food processing has been limited by their relative instability under varying light, oxygen, enzymes, thermal treatment, and pH conditions as well as other factors.
A latest study has applied microencapsulation technique for enhancing the shelf life and stability of anthocyanin. Different kinds of encapsulating materials have been tested for the microencapsulation of phenolic compounds.
The type of encapsulating material depends on the phenolic compounds and the type of food material in which it will be used. The stability of encapsulated phenolic compounds during food processing depends on the types of processing and processing parameters.
There are various types of microencapsulation techniques, such as a vibrational nozzle, centrifugal extrusion, spray drying, and co-crystallisation. The most commonly used technique is spray drying, due to its continuity in nature, low cost and less time which can produce particles with good quality.
For microencapsulation through the spray drying process, the selection of wall material is the primary step. Most commonly used wall materials are maltodextrin, gum arabic, and emulsifying starches. The maltodextrins and starches have properties like good solubility and low viscosity at high solids contents which are highly essential for an encapsulating agent.
However, native starch is insoluble in cold water and, when heated with water it forms a paste-like texture with high viscosity, which decreases the spray drying efficiency and increases the surface crack, thereby limiting its application for encapsulation using spray drying.
These limitations can be overcome by the modification of native starch. Therefore, this study is the first to report the use of microencapsulated anthocyanin from purple rice bran with modified glutinous rice starch using a spray-drying technique.
Further, to test the efficacy of the developed microencapsulated anthocyanin, authors have used extrusion technology for the new food product development and it has been observed that the use of microencapsulated anthocyanin increased the nutritional quality of the food product.
The extrusion cooking is carried out using a single screw extruder. After extrusion, the product is dried at 50 °C to maintain a moisture content of 10 per cent. The developed extruded showed higher 2,2-Diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity of extrudate due to the presence of anthocyanin.
It is manifested that microencapsulated anthocyanin from pigmented rice bran could efficiently be used in the food industry and could replace the synthetic antioxidants in the production of functional food and pharmaceuticals.
The utilisation of developed technology will provide a new horizon to valorize the pigmented rice bran of North-East India and will create new job opportunities in the agriculture and rural sector of the country.
About the authors-
Prof Chandan Das and Prof. Vaibhav Goud, faculties of Department of Chemical Engineering, and Associated faculties of International Joint M.Tech. Degree in Food Science and Technology (IMDFST), IIT Guwahati