Ascorbic Acid Effectively Improved Lutein Extraction Yield from Australian Sweet Lupin Flour

Lutein is a xanthophyll, a bioactive phytochemical that presents itself as colourful pigments in plants. Australian sweet lupin flour has been incorporated as a food ingredient in wheat bread and pasta to improve their sensory property and nutritional quality. However, the amount of lutein in lupin flour has not yet been determined. This is the first study to quantify naturally occurring lutein in Australian sweet lupin flour after the extraction efficiency was optimised. Several organic solvents (acetone, isopropyl alcohol, ethyl acetate and hexane), the use of an ultrasonic bath or a probe, the need for saponification and addition of ascorbic acid (served as antioxidant) were tested to compare the extraction yield. HPLC was employed to analyse lutein in flour. Lowest lutein (68 μg/100 g) was determined in the hexane extract. Samples extracted using an ultrasonic bath (126-132 μg/100 g) contained higher lutein than those extracted using a probe (84-109 μg/100 g). Saponified samples showed significantly less lutein (30-64 μg/100 g) than their respective non-saponified ones (122-134 μg/100 g). Without added ascorbic acid, lutein that was extracted into isopropyl alcohol was 143 μg/100 g and was higher than those released into acetone (92 μg/100 g). When ascorbic acid was added, measured lutein in the extracts of isopropyl alcohol (155 μg/100 g) and acetone (138 μg/100 g) increased by 8 and 33%, respectively. Our results suggested that the choice of extraction solvents and addition of ascorbic acid was crucial for quantitative analysis of lutein, so that the lutein content in lupin flour can be accurately reported.