PHENOLIC PROFILE, DISTRIBUTION, AND ANTIOXIDANT CAPACITY OF WHITE LUPIN MICROGREENS

Microgreens are tender greens larger than typical sprouts but smaller than mature vegetables⁽¹⁾. They have been reported as rich sources of dietary bioactive compounds, particularly phenolic compounds with antioxidant properties⁽²⁾. Studies on microgreens from pulses such as mung beans⁽³⁾, chickpeas^(3,4), and peas^(5,6) have shown increased levels of bioactive compounds and antioxidant capacity compared with ungerminated seeds or sprouts. Nevertheless, information  on microgreens from other legume species remains limited, including Lupinus albus L. (white lupin), an important pulse crop cultivated in Chile^(7,8). Studies on sprouts from different Lupinus spp. species suggest that these matrices may represent a relevant dietary source of isoflavones^(9-13), compounds more commonly related to soybeans and their derivatives^(14,15).

This study aimed to characterize the profile and distribution of phenolic compounds in soluble and insoluble-bound (IB) fractions of Lupinus albus L. cv. Rumbo 12-day-old microgreens and to evaluate their in vitro antioxidant capacity.

Soluble and IB phenolic fractions were recovered from 12-day-old L. albus microgreen flour (from lyophilized plant material) through solid-liquid extraction and alkaline hydrolysis, respectively. For each fraction, total phenolic content (TPC) and total flavonoid content (TFC) were determined, and individual phenolic compounds were identified using HPLC-DAD. Antioxidant capacity was evaluated using the ferric reducing antioxidant power (FRAP) assay.

L. albus microgreens at 12 days of development showed a phenolic content of 596 ± 25 mg GAE/100 g of dry mass (dm) in the soluble fraction and 5.7 ± 0.5 mg GAE/100 g dm in the IB fraction (released after alkaline hydrolysis), and a total flavonoid content of 428 ± 3 mg QE/100 g dm in the soluble fraction and 0.5 ± 0.1 mg QE/100 g dm in the IB fraction. Regarding the phenolic profile, the soluble fraction was characterized by the presence of flavonoids, particularly the isoflavones genistin and genistein, followed by the flavanol catechin. In the IB fraction, catechin was the main phenolic compound detected. FRAP values were 1,041 ± 34 µmol TE/100 g dm in the soluble fraction and 23 ± 3 µmol TE/100 g dm in the IB fraction. Overall, the soluble fraction showed substantially higher phenolic and flavonoid contents and antioxidant capacity than the IB fraction.

This preliminary characterization highlights the potential of white lupin as a novel dietary source of isoflavones and other phenolic compounds, contributing to the valorization of this legume for human consumption.