A comparative study of microencapsulation agents and techniques for vitamin fortification of cereal foods
1School of Applied Sciences, RMIT University, Melbourne, Victoria
2Defence Science and Technology Organisation, Scottsdale, Tasmania
Bread is a major source of B vitamins for most people. However, significant losses occur during the baking process. Vitamins are sensitive to heat, light, oxidation and pH is an important factor influencing stability and retention (Gregory, 1996). Microencapsulation potentially provides a way to protect the vitamins and allow for their release at an appropriate time or under specific conditions. The technique basically involves an active ingredient, e.g. the vitamin, being protected by an encapsulating agent e.g. hydrocolloids gums. There are now a variety of commercial applications of microencapsulation in foods. These include the encapsulation of volatile flavour and aroma compounds. One of the ongoing challenges has been to find ways to encapsulate water-soluble molecules whilst providing a system that releases these effectively. The purposes of this study have been firstly to investigate the technique of spray drying in conjunction with hydrocolloid gums as encapsulating agents for the B-vitamins. Secondly the encapsulated products have been used to evaluate relative stability of the vitamins during the baking process
Materials and methods
Preparation of microcapsules by spray drying
Solutions of various hydrocolloid gums (0.5 to 1%) were stirred overnight before rice starch was added. Prior to spray drying, B-group vitamins were dissolved and pH adjusted to 4.0. A Niro Atomiser minor (Niro, Copenhagen) unit was used and the drying conditions were: flow rate 7mL/min, air pressure 5kg/m2, inlet temperature 120°C, and outlet 80-90°C (Zhao & Whistler, 1994).
Ingredients (breadmaking flour, yeast, sugar, shortening, improver & water) and microcapsules (~1g) were baked in Panasonic bread makers using the Rapid Bake Program. For all trials and controls, duplicate loaves were baked and analysed.
Samples were taken after kneading (20 min from start), mid proof stage (50 min), end proof (1hr 20 min) and end bake (after 1hr 55min). All samples were collected in duplicate and stored in the freezer awaiting preparation.
Extraction and analysis of B-vitamins
These were based on the procedure of Esteve et al., (2001). Flour, dough and bread (1g) were extracted with 0.1M HCl by autoclaving. For thiamin, an aliquot was oxidised with potassium ferrocyanate (ferricyanide) solution. After neutralisation and filtration samples were analysed by HPLC using a C-18 column and fluorescence detection.
Results and discussion
A variety of different gums were used in preliminary trials to produce microencapsulated thiamin and riboflavin by spray drying. In each case the capsule preparations were free-flowing fine powders with yields ranging from 60 to 92%. The highest recoveries were for microcapsules prepared with rice starch and equal amounts of alginate and low methoxy pectin. Electron microscopy demonstrated that these had relatively uniform particles with diameters in the range of 15-50μm.
A procedure for analysis of riboflavin using HPLC was set up, validated and applied to analysis of the spray dried capsules. Samples of capsules were incorporated into bread formulations and baked using a rapid dough process. The levels of riboflavin at various stages in the process were analysed and an example of the results is presented in Figure 1.
Figure 1. The levels of riboflavin at different stages of the baking process when microcapsules were added to the formulation
There was virtually no loss of riboflavin during the baking process. The small difference in contents from before mixing to after baking was probably due to the small amount of unprotected riboflavin present in the flour. There was some variation in the apparent losses for the different gums used. Microencapsulation with alginate and low methoxy pectin was the most effective in protection of riboflavin.
Thiamin levels were also analysed for samples taken during baking, with and without addition of encapsulated thiamin (Figure 2). For the control, the thiamin levels in the ingredients were as expected and declined rapidly during processing with approx 50% losses. When encapsulated thiamin was added the only losses found were attributable directly to the unencapsulated thiamin in the flour. The most effective encapsulation was found for the combination of alginate and pectin, with κ-carrageenan, carob galactomannan and alginate alone also minimising the loss of thiamin.
Figure 2 The levels of thiamin at different stages of the baking process for a formulation incorporating microcapsules compared to a control
The encapsulation of the B-vitamins by spray drying using hydrocolloid gums and rice starch gave good yields of a practical product that was readily usable in breadmaking. The most effective encapsulation was achieved with alginate and pectin. Further studies to optimise the conditions for encapsulation are recommended.
A special thanks to Renuka Mayadunne (RMIT Applied Chemistry) for help during the initial stages of the HPLC analyses.
Esteve, M.J., Farre, R., Frigola, A. & Cantabella-Garcia, J.M. (2001). Journal of Agricultural and Food Chemistry, 49: 1450-1454.
Gregory, J.F. (1996). Vitamins. In O.R. Fennema, (Ed.), Food Chemistry, (3rd ed., pp. 532-610). New York: Marcel Dekker.
Zhao, J. & Whistler, R.L. (1994). Food Technology, 48: 104-105.