Extraction of lipids and astaxanthin from Northern Atlantic shrimp by-products: “green”/sustainable extraction process, statistical optimization study and mathematical modeling of kinetic extraction

Ahmadkelayeh, Sara (2022) Extraction of lipids and astaxanthin from Northern Atlantic shrimp by-products: “green”/sustainable extraction process, statistical optimization study and mathematical modeling of kinetic extraction. Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

The shrimp by-products from shrimp processing are typically disposed of as “waste” into landfills or the oceans, representing an environmental and economic cost. Shrimp processing by-products from harvesting and processing are a source of valuable biomaterials/bioactive materials (such as lipids and astaxanthin) for use in the pharmaceutical, cosmetic, food industries, and biomaterials. Extraction of these compounds would reduce the environmental burden and enhance the industry’s finances. However, in order to determine the feasibility, the quality and quantity of lipids/astaxanthin in the by-product as a function of extraction conditions and pre-treatment is required. This information on the quantity/quality of the extract in terms of lipid/FA and astaxanthin (ASX) compositions is required for product application (nutritional, medical, etc.). Traditionally, lipids and ASX are extracted using energy/waste intensive processes, which can degrade the product and/or by-products, are difficult to scale up, and/or operationally complex. However, the development of “green” valorization processes has made recovery of bioactive compounds from shrimp processing by-products feasible. In this study, we outlined (1) literature review on the advances in the field of value-added lipid/ASX recovery from shrimp and other crustacean processing by-products with a particular focus on SC-CO₂, (2) a comprehensive analysis of the quality and yield of lipid/ASX extract as a function of the extractant solvent used (Soxhlet) and pre-treatment (freeze-drying) of the by-products, (3) the viability of ASX extraction using waste fish/sunflower oils and optimization of waste fish oil extraction of ASX from wet and freeze-dried (FD) shrimp by-products as a function of water content and operating conditions (time, temperature and oil:waste ratio), (4) optimization of SC-CO2 extraction of lipid/ASX from FD shrimp by-products as a function of temperature/pressure; study of the impact of static co-solvents adding to SC-CO₂ on lipid/ASX yields, quality and lipid/fatty acids distributions, and (5) mathematical model to predict lipid/ASX extraction rates at certain operating conditions of temperature, pressure and flow rate. According to Soxhlet extraction results, in general, a mixture of polar/non-polar solvents maximized lipid/ASX yields, and the extract quality can be tuned with a proper solvent mixture to favour lipid yield, ASX yield, or a balance of both depending on the final application. ASX yields varied from 57-88 μg/gwaste depending on Soxhlet solvent(s) for wet shrimp by-product to 118-218 μg/gwaste for the freeze-dried. Lipid extracts are rich in omega-3 FAs and the composition of lipid classes varied with solvent(s) used and pretreatment. Overall, pre-treatment to remove water decreased lipid yield but increased ASX yield/quality. Edible waste oils are a potentially “green” solvent that could replace organic solvents and act to prevent degradation of the extracted ASX. This study investigates waste fish oil as a solvent for ASX extraction from Atlantic shrimp by-products (Pandalus borealis). This study observed that the higher the water content in the residues, the lower the ASX amount in the extract. As extended extraction times or high temperatures the ASX yield decreased; this is due to degradation of ASX with time/temperature. The optimal conditions to maximize the yield of ASX from both wet and freeze-dried shrimp by-products were 65 ˚C, 9:1 v/w and 1.5 h. ASX extractions were 40-60 % lower compared to Soxhlet, however the waste fish oil extracts were higher in triacylglycerols and omega-6 FAs. SC-CO₂ extracted the highest lipid yield at 50 ˚C and 30 MPa, and the highest ASX yield and total carotenoid content (TCC) at 60 ˚C and 32 MPa. Lipid/ASX recovery increased with an increase in pressure; however, temperature had a complex impact on lipid/ASX yield at a constant pressure. SC-CO₂ extract fractions had high percentages of neutral lipids but low phospholipids. Static co-solvent in SC-CO₂ provided the same lipid yield as and the higher ASX yield than the published papers using continuous co-solvent/SC-CO2. Polar co-solvent increased lipid/ASX recovery using SC-CO₂. Sunflower oil recovered higher ASX compared to waste fish oil. Polar co-solvents increased phospholipids and saturated fatty acids but decreased monounsaturated FAs and polyunsaturated FAs in the SC-CO₂ extract. Lipid compositions of sunflower oil extract was the same as sunflower oil, but the extract using waste fish oil in SC-CO₂ had higher sterols and free FAs compared to the lipid profile of waste fish oil. The highest lipid yield extracted using SC-CO₂ was 0.5 times of lipids extracted using ethanol in Soxhlet. The highest ASX yield with SC-CO₂ was 0.3 of ASX yield using a mixture of 40:60 vol% hexane/acetone in Soxhlet, and the highest TCC was 0.4 of the highest TCC obtained using Soxhlet (60:40 vol% hexane/isopropanol). The SC-CO₂ kinetic data were in good agreement with the mathematical model (Goto et al. 1993) used for both lipid/ASX extraction rates. The AARD values were 6 % for lipid extraction and 7.8 % for ASX extraction. Overall extraction rates of lipid/ASX were controlled by the strong solid–solute interaction.

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