The microbiological safety of seaweed and insect larvae as novel and sustainable fish feed ingredients

Abstract

The capacity of global aquaculture to feed nine billion people by 2050 requires replacement of unsustainable fishmeal and plant ingredients in aquafeed with innovative ingredients such as seaweed-fed insect larvae. Dipteran (fly) larvae offer a protein composition similar to fishmeal, whilst seaweed provides omega-3, essential for both fish and human health. However, seaweed is readily colonised in the coastal environment by potentially pathogenic bacteria, and there are no bacteriological standards for seaweed manufactured for animal feed. Bacteriological standards for insect products are not yet adequate given the unknown risks associated with different insect species. To demonstrate the public health safety of seaweed-fed dipteran larvae entering the feed and food chain, this thesis sought to produce a bacteriological risk assessment of the entire production chain. Seaweed flies (Coelopidae) were shown to be capable of enhancing the spatio-temporal distribution and persistence of E. coli O157:H7 in decaying wrack and beach sand, thus increasing opportunities for contamination of living seaweed. Screening of seaweed-fed black soldier fly larvae (Hermetia illucens; BSFL) for bacteriological hazards during trial production demonstrated that incoming raw feed materials and the production environment are sources of bacteriological contamination, which processing of BSFL into finished products can eradicate. Simulated manufacture of meal from seaweed supporting biofilms of pathogenic bacteria revealed that drying seaweeds at a temperature that maintains their nutritive content (50 °C) can encourage pathogen persistence in stored powder due to the interacting effects of temperature, water activity, bacterial species and strain during processing. BSF prepupae reared on pathogen contaminated seaweed powder supplement selectively reduce E. coli levels in their guts. A survey of the seaweed industry suggested that feed producers and the public currently rely on remoteness of harvesting sites from anthropogenic disturbance as a measure of bacteriological water quality and thus product safety. Based on the identification of critical control points (CCPs) throughout the feed-food production chain, it is recommended that existing microbiological criteria for Shellfish Harvesting areas should be applied to freshly harvested seaweed. Microbiological criteria for ready-to-eat (RTE) food products are recommended as standards for freeze-thawed seaweed for Coelopidae, and powdered seaweed for BSFL. By demonstrating that seaweed-fed insect products pose no bacteriological threat to consumers, this thesis will contribute to transformation of global aquaculture into a sustainable food production system.