Microencapsulation strategies for long term protection of ascorbic acid

Ascorbic acid (AA) has essential roles in human health; however it is a relatively unstable component of foods. In a preliminary study of using AA as a fortificant during the preparation of instant Asian noodles showed high losses of AA at each stage of processing. These results demonstrate the need for a strategy to enhance retention by which AA is effectively protected during the processing and preparation of food products.

A range of wall materials were trialled and various combinations used to encapsulate AA by spray drying on a pilot scale. The observations on the capsules included: high yields (75 and 93%), low moisture contents (2.7 to 8.2%) and low water activity (0.15 to 0.48). The recovery of the AA during spray drying was also consistently high which shows the effectiveness of this technique for microencapsulation purposes for AA. The capsules had particle size distributions reflecting uniformity and relatively small size (10 to 60 µm). Electron microscopy confirmed that for all of the encapsulating agents, the capsules that were uniform in size and the outer surfaces had good integrity with the structures remaining intact.

A long term storage trial for samples of the microcapsules was performed for varying time periods (0 to 15 months) and at a range of temperatures (20, 30, 37 and 48 μC). Statistical analysis of the results demonstrated excellent stability of AA for a number of the microcapsule combinations, even under the harshest temperature conditions used. The rates of loss for AA varied widely depending on the selection of encapsulating agents and the five combinations which were most effective in enhancing the retention of AA were maltodextrin F30 with Instant 449; maltodextrin F30 with Instant MAPS; Hi CAP™100; maltodextrin F17 with Instant 449; as well as maltodextrin F30 with gum Arabic and Hi Maize™1043.

For those combinations where different dextrose equivalent of maltodextrins and Hi Maize™1043 were incorporated, these did not appear to strongly impact on the retention of AA during storage trial. Higher levels of AA loading resulted in significantly increased retention at each of the temperatures trialled in this study. The calculated values for starch crystallinity obtained from an X-ray study demonstrated a negative relationship with the retention of AA. For those microcapsules having only amorphous structure, retention was higher than for those showing crystallinity. This might be related to the presence of lower molecular weight carbohydrate fragments in the walls of the capsules with amorphous structure, providing enhanced protection of the AA that has been encapsulated. Finally, spray drying has been found to provide a practical approach to microencapsulation of AA. The primary conclusion of this research is that five of the thirteen combinations of wall materials which were evaluated showed excellent potential for enhancing retention of AA. Accordingly further studies are warranted and it is recommended that these microcapsules be further assessed through incorporation into a range of food products.