Influence of ohmic heating in the composition of extracts from Gracilaria vermiculophylla

Abstract

Electric field-based technologies for extraction processes have been gaining importance due to sustainability concerns. This work aims to assess the potential of ohmic heating as an efficient and feasible tool for the extraction of different biocompounds from Gracilaria vermiculophylla and its effect on the extracts' composition. Different ratios of water/ethanol (0 to 75% ethanol, v/v) were used to target different families of biocompounds. The ohmic heating-based extraction was performed at 82 °C under electric field and frequency of 2–8 V/cm and 25 kHz, respectively. Conventional extractions without the presence of electric field were made keeping a temperature profile identical to the ohmic heating treatments, thus addressing the potential occurrence of electrical (non-thermal) effects. Extraction yields and extracts composition (content in polysaccharides, proteins, phenolic compounds and pigments) were evaluated. Further, as agar is the major commertially exploited compound from Gracilaria spp., the effect of ohmic heating on the extracted agar in terms of yield, carbohydrates' composition, monosaccharides profile, and gelling ability was also envisaged.Overall, significant differences in the extraction of each family of compounds between ohmic and conventional extractions were observed, being more pronounced at the best solvent for each compound (100% water for carbohydrates, 75:25 water/ethanol for proteins, 75:25 and 50:50 water/ethanol for phenolic compounds and 25:75 water/ethanol for pigments). Higher extraction yields were achieved for ohmic heating at 1 h, except for 100% water, probably indicating accelerated extraction kinetics promoted by the presence of electric field effects. Furthermore, the gelling ability of agar and the antioxidant activity were not impaired by the use of moderate electric fields. Therefore, ohmic heating is an interesting alternative, with reduced energy consumption and improved extraction performances, to recover functional ingredients or additives from seaweeds for the food industry.