(463f) Zero-Waste Processing of Protein Rich Side-Streams

Background

This study evaluates possibilities of complete exploitation of selected high protein and high oil containing industrial co-streams by applying environmentally benign biomechanical processing technologies. Value components for food and skin care products are main focus. Remaining residue is simultaneously exploited for soil improvement. Rapeseed and fish processing co-streams have been chosen as raw materials, as they have high enough quality for food applications.

The quantities of these side-streams are significant. For example, if the volume of the co-stream from Norwegian salmon aquaculture is 275 000 t annually, there are 55 000 t of lipids and 41 000 t of proteins available. Likewise if 270 000 t of rapeseed press cake is produced by SME cold pressers in Germany, there are 27 000 t of lipids and 95 000 t of protein available for refining.

This study presents three developed process concepts for zero-waste processing of food side-streams: (i) thermo-enzymatic process for recovery fish oil and protein hydrolysate from fish side-stream, (ii) enzymatic process for fractionating proteins and peptides from rapeseed press-cake, and (iii) co-generation of heat and fertilisers out of residue from previous processes, namely fish bones, hulls or solids from hydrolysis.

The main emphasis of this study is to evaluate techno-economic feasibility of proposed process concepts. Mass and energy balances of concepts are estimated, raw material demand, utilities used and intermediates or products produced are calculated and variable production costs are evaluated. In addition, rough estimates for the fixed operating costs and investment costs are given. Finally, a profitability analysis is conducted based on the variable costs and fixed costs.

As the degree of uncertainty is high at early stages of process design, Monte Carlo simulation are applied when estimating variable and fixed costs in order to cope with this uncertainty. By applying this methodology, ranges and distribution can be used for the main process parameters, prices and also for investment. As a result of calculations, a probability distribution of outputs, e.g. profit, is obtained.

Processing rapeseed press-cake

Rape-seed press cake is milled and enzymatically treated. Mixture is flash heated and possibility of CO2 extraction to remove oil fraction is evaluated. Second enzymatic hydrolysis is conducted. To reduce water consumption in the process, it is proposed that consistency of enzyme treatments and extractions can be increased to at least 15% or dry methods to be used. Solid residue and hydrolysate is obtained after phase separation. Hydrolysate might be concentrated or precipitated. Solid residue is dried and can be used as raw material for co-generation of heat and fertilisers.

Processing fish filleting co-stream

Proposed concepts for fish-filleting co-stream process combine the gentle thermal treatment and the enzymatic hydrolysis. This thermo-enzymatic process begins with mechanical grinding of the fresh fish filleting co-stream. Moist raw material is then heated up for separation of the premium oil. Phase separation is utilised in order to recover the first oil fraction. The remaining raw material is further processed by enzymatic means. The flow of raw material into the enzymatic stage decreases due to the preliminary heat treatment resulting in a decreased amount of enzymes needed. After enzymatic treatment, the raw material is heated up in order to terminate the enzymatic activity. Phase separation conducted in a tri-canter is used to recovery second oil fraction. The solid fraction containing insoluble proteins, lipids and bones can be used as material for extraction valuable ingredients like phospholipids or can be dried and used as feed. Fish protein hydrolysate can be further concentrated by utilising an evaporator or dried depending on the specifications of the final product.

Co-generation of energy and fertilisers out of residue

Due to the seasonal nature of the need for fertilisers, a process for improving the preservability of residue, especially from fish side-stream processing, is needed. A process with anaerobic digestion of residue and cattle manure on a regional scale is proposed. The function of a biogas plant, regardless of the end use of the biogas generated and organic fertiliser obtained, is to provide treatment capacity for the residues. Process includes storage capacity for residue at ambient temperatures. Liquid manure and residue are mixed together before feeding to the anaerobic digester. The anaerobic digestion process was assumed to be a wet, single stage, continuously fed process operating at mesophilic temperatures and a hydraulic retention time of 40 days. Operation of the biogas plant requires heat and electricity which is generated from an on-site CHP plant using biogas as a fuel. Remaining substrates are used as fertilisers on fields.

Summary

This study presents three process concepts for zero-waste processing of food-industry side-stream. Raw materials are fish filleting side-stream and rapeseed press-cake. End-products are food and skin-care products as well as oil, feed, biogas and fertilisers. This study focuses mainly evaluates the techno-economic feasibility of proposed processes and provide insight of the opportunity to utilise these food processing side-streams.

Acknowledgements

The APROPOS project is part funded by the European Commission’s SeventhFramework Programme for research and technological development over the period 2007 to 2013.