## 1 Introduction  
Legumes are a rich source of plant protein and are a viable alternative for crop rotation and biodiversity improvement. In particular, they are desirable in sustainable and ecological agriculture as they allow for limiting the use of fertilizers and pesticides [1]. Legumes are also a source of many non-nutritional compounds that exhibit biological activity. Their nutritional and functional properties can be improved by means of various processes, like dehulling and its combined treatment, enzyme and extraction treatments, heat treatment, fermentation, and germination. Lupin has been demonstrated to be an outstanding raw material source, superior to most crops and suitable for manufacturing foods with good antioxidant and nutritional properties [2]. Its sweet and bitter cultivars foster huge potential as alternative sources of protein and valuable non-nutritional compounds, such as the raffinose family of oligosaccharides. Lupin seeds may be a potential source of alimentary cellulose for the production of dietetic foods. Their high-protein fraction (25-40%) could be used as a substance for enriching different kinds of products, such as pastries, breads, chips, and milk substitutes, and also be the main food component when animal proteins are eliminated. Multiple processes have been proposed so far to improve the nutritional value of lupin seeds. In lupin seeds, the raffinose family of oligosaccharides and alkaloids, in the case of bitter cultivars, are the main non-nutritive compounds [3,4]. Germination is an easy and useful process to increase the nutritional value of legumes and cereals; additionally, it causes a reduction in the content of alkaloids, phytynians, and oligosaccharides [5]. Both fermentation and germination are effective processes for enhancing free radical scavenging ability. Thus far, many studies have been published on the germination of legume seeds and their fermentation [6,7]; however, the combination of these two processes has not been tested so far. It was reported that germination modified the quantitative and qualitative polyphenic composition of lupin (_Lupinus angustifolius_ L) seeds during different days of the process, leading to a significant increase in the antioxidant capacity [6].  
A variety of analytical methodologies have been deployed to study antioxidant capacity [8, 9, 10], including, among others, DPPH radical scavenging activity (DPPH assay), Trolox-equivalent antioxidant capacity (TEAC, known as the ABTS assay), ferric-reducing antioxidant power (FRAP assay), and oxygen radical absorption capacity (ORAC) as the most often used ones. In recent years, electrochemical methods and sensitive photochemiluminescence approaches have gained prominence for their rapid estimation of the antioxidant capacity of food extracts [11, 12, 13, 14]. Voltammetry, a widely used electrochemical technique, includes several methods such as cyclic voltammetry (CV), differential pulse voltammetry (DPV), and square-wave voltammetry (SWV). The photochemiluminescence assay (PCL) is suitable for measuring the radical scavenging properties of single antioxidants as well as more complex food systems in the nanomolar range [15].  
The aim of this study was to (1) evaluate the effects of germination and fermentation on the antioxidant capacity of sweet and bitter lupin seeds and sprouts fermented by yeast and (2) test different methods for assessing antioxidant capacity by means of the updated analytical strategy based on the recently recommended voltammetric, photochemiluminescence, and spectrophotometric methods.