Lipoxygenase inactivation kinetics and quality-related enzyme activities of narrow-leafed lupin seeds and flakes

• First-time determination of enzyme activities during lupin seed maturation.
• Opposed change of LOX activity compared to lipase and peroxidase.
• Effective LOX reduction by hydrothermal treatment of seeds and de-oiled flakes.
• Ea and DT values for integral seeds significantly lower than for flakes.
• Conditioning of integral seeds at 80 °C strongly recommended.

Lupin seeds are promising sources for the production of vegetable proteins. However, these proteins are associated with green and bean-like flavour, which is attributed to endogenous enzyme activities. Therefore, the objective was to develop a suitable process for the thermal inactivation of quality-affecting enzymes for lupin (Lupinus angustifolius cv. Boregine) seeds and de-oiled flakes. After monitoring the specific activities of lipoxygenase (LOX), peroxidase (POD) and lipase during seed maturation, LOX was selected as the most appropriate indicator enzyme to assess inactivation as lipase and POD activities extensively declined at full maturity. Effective reduction of LOX activity was achieved by various hydrothermal treatments at 70–100 °C for up to 30 min and 100% relative humidity. The calculation of kinetic parameters revealed a first-order reaction, whereby the k values increased from 0.09 to 0.58 min−1 and 0.06 to 0.62 min−1 for seeds and flakes, respectively. The activation energies were significantly lower for inactivation in seeds (60.5 kJ mol−1) than in de-oiled flakes (78.0 kJ mol−1), suggesting the application of whole seeds for LOX inactivation. Based on these results, a gentle inactivation process at 80 °C for 7 min for lupin LOX is proposed.