Quality enhancement of alternative fish feeds using highpower ultrasound processing

Abstract

Background: The rising costs of current fish feeds has led to an increase in the demand for alternative sources of nutrients to supplement the feed with, in the hope of lowering the overall price. Fish nutrition involves an intricate balance of macro and micronutrients which need to be met to ensure the highest quality fish meat. Plant nutrients extracted from sustainable sources, namely Alaria esculenta, Chlorella vulgaris and Lemna minor; have been evaluated for their nutritional value, in an attempt to make the aquaculture industry more environmentally friendly. Furthermore, the implementation of green technology (mainly ultrasound) to extract these nutrients from the alternative biomasses was studied extensively and compared to more traditional techniques. Method: Various experiments were performed to establish the best parameters for nutrient extraction. Characterisation of raw material was performed initially. This included colorimetry, microscopy, water activity and moisture content assessments. The impact of different ultrasound set-ups was evaluated to determine which ultrasonic treatment is the most efficient out of bath sonicators and probe sonicators set at different amplitudes. The impact of ultrasound on biomass treatments was assessed to determine which ultrasonic treatment is the most efficient out of enzyme-assisted, conventional or alkali protein extraction methods. Results and discussion: The raw material characterisation gave insight on parameters that affect the quality of the end-product. The UP400St probe sonicator was the most efficient ultrasonic device. Ultrasound extraction using the probe sonicator resulted in a higher extraction yield overall. Ultrasound as a pre-treatment for enzyme-assisted extraction gave the best protein extraction yields. Conclusion: This study delved into relatively untouched territory in nutrient feeding ingredients in aquaculture research. Ultrasonic probe devices were found to be more efficient in extraction of compound than bath sonicators. Furthermore, ultrasound technology fared better than conventional or alkali extraction methods. Lemna minor was found to have the greatest extraction yield of nutrients, followed by Chlorella vulgaris and Alaria esculenta, respectively.