Introduction
The expansion of the aquaculture production has been linked with the need for a rapid increase in the production of aqua feed products. Among alternative ingredients, the plant ones have been extensively studied. The European Union is highly depended on soybean imports for its domestic use and is highly vulnerable to risks linked to global trade. In this frame, the key of bridging the gap between consumption and demand is to identify alternative forage plant ingredients for sustainable production. For livestock production, forage legumes are promising candidates and highly valued feed components, however, the presence of several antinutritional factors (ANFs) still limits their use in feeds (Kaushik et al., 2018). The digestibility of many ingredients can be improved with inclusion of exogenous enzymes due to their ability of breaking down the complex cell wall structure that encapsulates nutrients present in plant based feed (Ojha et al., 2019). In addition, by increasing access to protein for digestive proteases, carbohydrases can act as enhancers to improve nitrogen and amino acid utilisation (Tahir et al., 2008). Aim of the present study was to evaluate the replacement of soybean meal by lupin meal treated with exogenous enzymes in European sea bass nutrition.
Materials and methods
Lupin seeds (Lupinus albus cv. Tennis) were grounded to produce lupin meal. A product fermented by Aspergillus niger containing several exogenous enzymes (Synergen™, Alltech Inc) was added at 0.05%. Moisture of lupin meal was adjusted to 45% and the lupin meal was treated for 4 hours at 50°C. Four commercial type diets, one control containing soybean meal as the sole plant protein at an inclusion level 15g/100g diet and three diets replacing soybean meal by treated lupin meal at three different levels (7.5 g/100g, 10 g/100g and 12.5 g/100g, Table 1) were formulated to be isonitrogenous (48%), isolipidic (17%) and isoenergetic. European sea bass juveniles (11.2g) were distributed in 12 tanks (50 fish/tank) in triplicate groups per diet. The experimental trial was conducted for 83 days in recirculation aquaculture system. Fish were fed ad libitum the experimental feeds three times per day. For a 2-week period prior to the end of the trial, faeces were collected, to evaluate nutrients digestibility.
Results and discussion
Cooking of legumes is a commonly used process that greatly improves the nutritional value of foods by reducing their ANFs (Patterson et al. 2017). In addition, the use of exogenous enzymes increases nutrient digestibility and bioavailability. In the current study inclusion of lupin meal, treated with exogenous enzymes, revealed positive results. Specifically, fish fed the Lupin1 diet showed significant higher final weight compared to the fish fed the control diet. Even though weight increase did not show significant differences, a trend (P=0.05) for higher weight was observed for fish treated with Lupin1 compare to those treated with control diet. Similar trend reflected also in feed conversion ratio (FCR) and specific growth rate (SGR) for the same groups. The growth parameters evaluated were not affected by the total replacement of soybean meal with treated lupin meal (Lupin3). Somatometric indices were fluctuated at similar levels, however, population fed the treated lupin meal presented lower liposomatic indices. Incorporation of exogenous enzymes treated lupin meal affected the digestibility of nutrients, the retention of protein and the activity of digestive enzymes (results are not shown). The present findings showed that lupin is a promising alternative to soyabean meal in the diet for D. labrax when treatment with exogenous enzymes is adopted.
Acknowledgements
The project is cofounded by Greece and the European Union under the Fisheries and Maritime Operational Program 2014-2020. https://www.aqualegumes.gr/
References
Kaushik, G., Singhal, P., & Chaturvedi, S. (2018). Food processing for increasing consumption: The case of legumes. In Food processing for increased quality and consumption (pp. 1-28). Academic Press.
Ojha, B. K., Singh, P. K., & Shrivastava, N. (2019). Enzymes in the animal feed industry. In Enzymes in food biotechnology (pp. 93-109). Academic Press.
Patterson, C. A., Curran, J., & Der, T. (2017). Effect of processing on antinutrient compounds in pulses. Cereal Chemistry, 94(1), 2-10
Tahir, M., Saleh, F., Ohtsuka, A., & Hayashi, K. (2008). An effective combination of carbohydrases that enables reduction of dietary protein in broilers: importance of hemicellulase. Poultry science, 87(4), 713-718.