The future of pulsed electric fields in microgreen production: a comparative study

Santos, Mafalda de Aguiar Macedo e Ferreira dos

http://hdl.handle.net/10400.19/9510

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Authors

Santos, Mafalda de Aguiar Macedo e Ferreira dos

Advisor(s)

Costa, Daniela de Vasconcelos Teixeira Aguiar da

Guiné, Raquel de Pinho Ferreira

Redondo, Luís Manuel dos Santos

Abstract(s)

Abstract: Global demographic trends and increasing societal awareness of the need for sustainable, functional, and safe food products pose significant challenges to achieving the Zero Hunger goal proposed in the United Nations’ Agenda 2030. This reinforces the urgency of addressing contemporary issues in food systems. A combination of heritage farming practices and innovative technologies is crucial to overcoming these challenges. Pulsed Electric Fields (PEF), a sustainable, non-thermal, and purely physical technology, has shown potential to optimise and modulate germination, growth, and the physicochemical and nutritional properties of plants derived from PEFprimed seeds. This study investigates the effects of PEF seed priming on the growth and quality of microgreens of three species: Beetroot, Arugula, and Basil. A comparative analysis was conducted using Control and three PEF protocols (PEFA: 2 kV/cm, PEFB: 3 kV/cm, and PEFC: 4 kV/cm), examining physiological, biochemical, and sensory parameters. Key data collected during the first five days of germination included water uptake, electrical conductivity, radicle length, and germination indices. Following harvest, microgreens were analysed for Total Phenolic Compounds (TPC), antioxidant capacity (DPPH & ABTS), Total Soluble Solids (TSS), pigments (Chlorophylls & Carotenoids), and nutritional composition (macronutrients and amino acids) via FT-NIR. Photosynthetic pigments increased in Basil microgreens but decreased in Beetroot and Arugula. Sensory analysis was also conducted, using Quantitative Descriptive Analysis (QDA). Beetroot showed up to a +15% increase in TPC for PEFB and up to +12% improvement in antioxidant capacity (DPPH; PEFC), especially with ultrasound extraction (US). Arugula presented a +5% increase in DPPH antioxidant activity (PEFC). TSS increased by up to +7.5% in Beetroot (PEFC) but decreased by around 3 to 4% in Arugula. Extraction efficiency differed between Magnetic Stirring (MS) and US, with ultrasound generally yielding higher rates (p<0.001). In Basil, DPPH and ABTS scavenging assays presented distinct results, suggesting that the impact on ABTS-reactive compounds is not as dependent on PEF seed electropriming as DPPH. With respect to Nutritional Content, Fat and Protein increased in Beetroot (Fat: +41%, Protein: +34%) and Arugula (Fat: +91%, Protein: +11%) treated with PEFC. PEFB led to an increase in Starch in all species. Crude Fiber and Neutral Detergent Fiber decreased amongst all species. Methionine rose by 100% in Beetroot treated with PEFC. Although not statistically significant, sensory analysis revealed small increases in Sweet (Beetroot) and Aroma Intensity (Arugula), along with a reduced perception of the descriptor Hot in Arugula. Results demonstrated that PEF treatments significantly influenced water uptake, electrical conductivity, radicle length, and nutritional composition. Species-specific responses to different PEF protocols were observed. Optimal protocols appear to be PEFC for Beetroot, PEFB for Arugula, and PEFA/B for Basil. These findings not only suggest the potential of PEF as a tool for enhancing/modulating microgreen quality and nutritional profiles but also open the door for its utilisation in a wider agricultural context.