VALORIZATION OF VEGETABLE BY-PRODUCTS AS SUSTAINABLE RAW MATERIALS FOR AQUACULTURE FEED
Introduction
The nutritional requirements of Solea senegalensis are scarcely known, which explains the limited availability of commercial feed for this specie. Juveniles and market size fish need high levels of dietary protein, about 56% (Rema et al., 2008, Borges et al., 2009), and 8% of dietary lipid levels (Borges et al., 2012), showing low tolerance to dietary lipid levels higher than 12% either in juvenile (Borges et al., 2013) or market size sole (Valente et al., 2011). Nonetheless, replacement of dietary fish meal protein by a mixture of plant origin protein sources did not adversely affect feed intake, growth or protein utilisation of large size sole (Valente et al., 2011). In this framework, vegetable by-products could be used as new raw materials in feeds for sole, making sole aquaculture more sustainable.
Almost three quarters of vegetable by-products produced from food industry and retail trade end up in landfills. In the Basque Country, the region in Spain where this study is placed, potato industry by-products, rests of fruit and vegetables produced by supermarkets, and brewery yeast by-products have a high potential to be included in aquafeeds, taking into account production volumes, spatial dispersion and their nutritional value.
However, it is necessary to guarantee their nutritional quality and safety, from production to processing, together with the economic profitability and the environmental benefit obtained from their use in aquafeeds.
Hence, the aim of this study is to find a sustainable solution, from the valorization of the vegetable by-products alternative raw material to fish meal.
Material and methods
Information of the total amount of vegetable by-products available and the conditions in which they are produced were obtained from the most important producers in the Basque Country by using questionnaires. The nutritional value and safety of each by-product was assessed and once these aspects were guaranteed, specific drying methodology was developed to obtain stabilized meal to be included into aquafeeds. The meal prototypes obtained were also analyzed in order to evaluate their adequacy to national markets and legal EU requirements for feeds. Then, a theoretical Action Plan was defined to establish the main guidelines to manage appropriately the selected by-products, and to guarantee their sanitary and technical feasibility.
Finally, in order to assess the environmental benefits of the proposed valorization, a Life Cycle Assessment (LCA) was performed for the obtained vegetable meals.
Results
According to the questionnaires, the availability of the vegetable by-products studied produced in Basque Country was approx. 9,000 tons / year.
All by-products were nutritionally suitable based on the analytical results obtained (table 1). Moreover, the sanitary feasibility was guaranteed, taking into account that all undesirable substances were below legal limits.
The proposed Action Plan includes a drying process at 85ºC, to avoid the decrease of protein digestibility that appears when processing temperatures above 65 ºC are used and to ensure the economic feasibility of this process.
From an environmental point of view, the LCA suggested that, the proposed Action Plan caused less impact than managing the by-products as waste (which is the actual management option).
Discussion and conclusion
This study showed that the selected vegetable by-products can be used in feeds for Solea senegalensis due to their nutritional value, legal adequacy and the environmental benefits observed. However, a suitable Action Plan is a key factor to make this option profitable for aquaculture feed companies. Thus, it is necessary to develop economic strategies to make their inclusion into feeds more profitable. This includes: improving the drying process or increasing the total amount of by-products used in feeds, by mixing them with by-products produced in neighboring regions.
References
Rema P., Conceição L.E.C., Evers F., Castro-Cunha M., Dinis M.T. and Dias J, 2007. Aquaculture Nutrition, 14: 263-269.
Borges, P., Oliveira, B., Casal, S., Dias, J., Conceição, L., Valente, L.M.P., 2009. Br. J. Nutr. 102, 1007-1014.
Borges, P., Medale, F., Dias, J., Valente, L.M.P., 2012. Br. J. Nutr. 1-9.
Borges P, Medale F, Dias J, Valente LM., 2013. British Journal of Nutrition, Apr 28; 109(8):1373-81. doi: 10.1017/S0007114512003418. Epub 2012 Aug 20.
Valente, L.M.P., Linares, F., Villanueva, J.L.R., Silva, J.M.G., Espe, M., Escórcio, C., Pires, M.A., Saavedra, M.J., Borges, P., Medale, F., Alvárez-Blázquez, B., Peleteiro, J.B., 2011. Aquaculture 318, 128-137.
