Abstract
Seaweed is gaining attention as a possible alternative and sustainable source of proteins. This study investigates three protein extraction methods and their effect on protein yield and quality when applied to Ulva fenestrata. Two of the methods included alkaline extractions (pH-shifts); one version solubilizing the proteins at pH 8.5 and one solubilizing them at pH 8.5 followed by pH 12 (pH 8.5 + 12). The third method was a mechanical pressing, using a double screw press. All extraction methods were followed by isoelectric precipitation to concentrate the proteins. Extraction at pH 8.5 gave the significantly highest total protein yield after the isoelectric precipitation, followed by extraction at pH 8.5 + 12 and lastly mechanical extraction gave the lowest yield. Proteins extracted with both alkaline methods had a significantly higher solubility at pH 7 and pH 9, compared to proteins from the mechanical pressing. There were no significant differences between the three methods in total D/L-amino acid ratio. Amino acid cross-links measured as lysinoalanine (LAL) and lanthionine (LAN) where found in significantly higher amounts in alkali-extracted proteins compared to mechanically extracted, however not to a degree that expect to compromise functional or nutritional quality. Further, no significant difference in protein in vitro digestibility was found between extraction methods. In conclusion, results indicated that protein extraction at pH 8.5 can be recommended, especially regarding total protein yield and solubility of the final protein extract.
Highlights
There is a need for new and sustainable protein sources generated by the increasing world population [1,2]
This study investigates three protein extraction methods and their effect on protein yield and quality when applied to Ulva fenestrata
Protein extraction using the pH-shift method where proteins were solubilized at pH 8.5 gave the statistically highest total protein yield of 8.95 ± 0.79%
Summary
There is a need for new and sustainable protein sources generated by the increasing world population [1,2]. The high productivity as well as a relative high content of essential amino acids (EAA) (36–42% of total amino acids) [8,9,10] makes e.g. green seaweeds of the genus Ulva interesting for protein extraction. Based on a biomass productivity of 70 t dry matter (DM) ha− 1 year− 1 for commercially cultivated Ulva ohnoi in a land-based integrated aqua culture facility, Ulva spp. have been described as having a protein pro duction potential competitive to production of protein rich soybean meal [11]. The protein content in Ulva depends on several factors, such as season, nutrient availability and geographic location [12] and is often between 10 and 26% (DM) [9,13], which is a relatively low protein amount compared to e.g. soybean. Extraction of protein from Ulva spp. has been shown to increase in vitro protein digestibility
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