Multi-response surface optimisation of extrusion cooking to increase soluble dietary fibre and polyphenols in lupin seed coat

The seed coat of the legume lupin which is rich in insoluble dietary fibre is a major by-product in human food applications. Extrusion cooking has been demonstrated to increase desirable soluble dietary fibre in the Australian sweet lupin seed coat. In this study, processing condition of twin-screw extrusion cooking was optimised using a central composite rotatable design to increase soluble dietary fibre in lupin seed coat from 44.17 g/kg up to 113.69 g/kg dry basis. The high levels of polyphenols in the seed coat were retained. The optimal extrusion conditions which achieved maximum levels of soluble dietary fibre, total free phenolic content and total free individual phenolic content simultaneously were identified and validated. The extrusion cooking largely had no or slight effects on bioaccessibility and bioavailability of the selected minerals and individual polyphenols. The extrusion cooked lupin seed coat could be a natural antioxidant dietary fibre source for human consumption.

Automated summary

This study optimized the processing conditions of twin-screw extrusion cooking to increase soluble dietary fiber in lupin seed coat while retaining high levels of polyphenols. The extrusion cooking had minimal effects on the bioavailability of minerals and polyphenols. The extrusion cooked lupin seed coat could be a natural antioxidant dietary fiber source for human consumption.