Elsevier

Aquaculture

Volume 530, 15 January 2021, 735796
Aquaculture

Apparent digestibility coefficients of brewer's by-products used in feeds for rainbow trout (Oncorhynchus mykiss) and gilthead seabream (Sparus aurata)

https://doi.org/10.1016/j.aquaculture.2020.735796Get rights and content

Highlights

  • Brewery byproducts (spent yeast and spent grain) can be used for the formulation of aquafeeds.

  • Digestibility of spent yeast and spent grain was good enough to be considered new protein ingredients.

  • New trials with different inclusion levels of brewery byproducts are envisaged.

Abstract

A trial was conducted to test the effect of partial replacement of fishmeal by two brewery industry byproducts, yeast and spent grain, included in isoproteic (41% CP) and isolipidic (22% CL) diets for gilthead sea bream (Sparus aurata) and rainbow trout (Oncorhyncus mykiss), having in mind the availability of these byproducts. A first step before an ingredient is included in a commercial feed is to evaluate the nutritional quality of these raw materials by measuring their digestibility. Thus, the apparent digestibility coefficients of the diets and ingredients were determined after a 30 days feeding trial and faecal collection. Apparent digestibility coefficients of these by products in the case of rainbow trout varied between 75 and 88% whereas for gilthead seabream was between 71 and 88%. According to the results obtained, the inclusion of 20–30% of brewers' spent yeast and spent grain in the feed for carnivorous fish either from fresh (rainbow trout) or marine (gilthead seabream) gave similar results to a feed with fish meal as the main protein source and show a good protein, lipid and amino acid digestibility. Taking into account that these by-products are produced in large quantities in Europe, they can be a potential source of protein to reduce the use of plant proteins or fish/animal byproducts (trimmings) and increase the sustainability of both sectors, brewery industry and aquaculture.

Introduction

Aquaculture is one of the animal production industries with the highest growth worldwide, providing most fish for human consumption than capture fisheries since 2014 (FAO, 2018). Fish and fish products from world fisheries are processed into fishmeal and fish oil for the aquaculture sector in a significant, but declining, proportion (Green and Pearsall, 2018).They are considered excellent sources of high-quality protein, containing an optimal amino acid profile, long-chain omega-3 fatty acids, essential minerals and vitamins A, D and B (Gatlin et al., 2007), as well as high palatability and, initially, low cost and high availability (Oliva-Teles and Gonçalves, 2001). Currently, the most expensive component in aqua feeds is the protein fraction, due to the expansion of the aquaculture industry and the over-dependence and increasing demand of marine sources for feed production (Cheng et al., 2004). These prices show an increasing trend in the future, highly influencing the cost of intensive crops, which nowadays range between 40 and 50% of the total operating budget. However, the sustainability of aquaculture not only requires economic feasibility, but also reduction of the environmental impact. From the overfishing of the forage fish species used for feed production to the eutrophication of water column, due to overfeeding and lixiviation of aquaculture feedstuffs (Naylor et al., 2009), aquaculture suitability depends on the reduction of fishmeal use (Couto et al., 2016). This has special importance in carnivorous species of farmed fish, such as seabream (Sparus aurata) or rainbow trout (Oncorhynchus mykiss), which use protein as the main source of energy, preferably to lipids or carbohydrates (Green and Hardy, 2008).

Thus, the economic and environmental sustainability of aquaculture depends to a large extent on the identification and application of alternative raw materials to fishmeal, with highly digestible nutrients that improve fish performance, less waste production, available in the market in large regular quantities and at a competitive price and ease of handling and storage (Gatlin et al., 2007). Additionally, criteria for the selection and application of new foods are based on the health and performance of fish, as well as benefits for human health, and acceptance by the consumer (Naylor et al., 2009). In this way, alternative protein sources to fishmeal have been used in diets, but all of them have some feature that limits their use and inclusion level in aqua-feeds for piscivores (Naylor et al., 2009). Among those, vegetable proteins derived from grains, legumes or vegetable oils have anti-nutritional factors, fibre, insoluble carbohydrates, amino acid imbalances and low palatability that limit their use and increase waste, accentuating the environmental impact of aquaculture (Muzquiz and Wood, 2009; Naylor et al., 2009). Terrestrial animal by-products have a better nutritional composition for fish feed and are widely available at low cost in markets, but lack consumer acceptance (Naylor et al., 2009). In this sense, the economic and environmental interest in industrial by-products recovery, for the development of alternative sources of protein, has increased significantly in recent years due to its high and continuous production and its future perspective with great availability at a reduced cost (Barrows et al., 2008).

The brewer industry, with a world production exceeding 1.95 billion hectolitres in 2017 (Statista, 2019), generates large amounts of waste and by-products with great potential for its recovery as high nutritional value products (Aliyu and Bala, 2011). Large breweries, producing 1000HL beer per day, generate 40 tons of by-products per day to remove (Thomas and Rahman, 2006) and even small breweries must have careful waste management to ensure their economic and environmental feasibility. Since the bulk of organic waste, arising as brewer spent grain (BSG) and spent yeast (BSY), has been categorized as high quality food (Mussatto et al., 2006; Thomas and Rahman, 2006; Mussatto, 2009; Levic et al., 2010; Robertson et al., 2010; Zhou et al., 2018), leading breweries are seeking suitable ways to minimize losses and optimize production by increasing yields (Jurado and Sorensen, 2012). In the case of Europe 40 billion litres were produced in 2018 (Eurostat, 2019) generating 7 million tons of BSG and 0.9 million tons of BSY conventionally reused as animal feed and, in some cases, bioethanol production (Djuragic et al., 2010; Buffington, 2014). In this way, research efforts in Europe have been focused on brewer's by-products recovery through its inclusion in aqua feeds (Oliva-Teles and Gonçalves, 2001; Kaur and Saxena, 2004; Cheng et al., 2004; Ozório et al., 2012; Castro et al., 2013; Sealey et al., 2014; Campos et al., 2018; Zhou et al., 2018; Zhang et al., 2018).

Brewer's spent grain (BSG) is the major by-product of beer production, which is obtained after the mashing process of barley grains, corresponding to around 85% of waste generated by this industry (Mussatto et al., 2006). It has been used in human and livestock food (Faccenda et al., 2017; Murdock et al., 1981), crustaceans (Muzinic et al., 2004) and some fish species (Yamamoto et al., 1994; Kaur and Saxena, 2004; Cheng et al., 2004; Campos et al., 2018; Jayant et al., 2018) for being a raw material rich in fibre and proteins and containing lipids, minerals and vitamins (Mussatto et al., 2006). BSG has a rich essential amino acid composition (Aliyu and Bala, 2011), is a good source of unsaturated fatty acids (Thavasiappan et al., 2016), and has health benefits due to its content in biological active compounds such as polyphenols, flavonoids and β-Glucans (Farças et al., 2015; Tang et al., 2009). Even so, the chemical composition of BSG can vary depending on the variety of barley grain, harvest time and malting and maceration conditions during the brewing process (Robertson et al., 2010).

Brewer's Saccharomyces spent yeast (BSY) is the second major by-product of the brewing industry that, marketed as dry and inactive yeast (dead yeast cells), has been identified as a potential alternative to fishmeal in aqua-feeds (Oliva-Teles and Gonçalves., 2001; Ebrahim and Abou-Seif, 2008; Ozório et al., 2012; Sealey et al., 2014), as well as in feeds for porcine and ruminants (Huige, 2006). BSY has been used in the aquaculture industry since the early 1990's not only because its high content of cheap protein and excellent amino acid profile (Ovie and Eze, 2014), but also because of its rich content in other nutrients and bioactive compounds such as β-glucans, mannan oligosaccharides, vitamins, minerals and nucleic acids (Ferreira et al., 2010). In brewer's yeast, nitrogen from nucleic acids is mostly in the form of RNA, representing between 20 and 25%, fact that makes it toxic in humans and most of mono-gastric, due to the inability to excrete uric acid that is formed during its metabolic process. However, no negative effects have been found in fish, due to its high liver uricase activity (Rumsey et al., 1991).

As a first step before an ingredient is included in a commercial feed, it is essential to evaluate the nutritional quality of these raw materials by measuring their digestibility. Thus, the objective of this study was to determine the apparent digestibility coefficients (ADC) in vivo of the protein fraction of BSG and BSY, for possible commercial use in diets for rainbow and gilthead seabream.

Section snippets

Materials and methods

The experiment was designed to evaluate in vivo apparent digestibility coefficients (ADCs) of crude protein, in dried and hydrolysed, brewer spent grain (BSG) and brewer spent yeast (BSY). BSG and BSY, as experimental ingredients, were obtained from European breweries and tested in gilthead seabream (Sparus aurata), as a model of marine fish, and rainbow trout (Oncorhynchus mykiss) as a model of freshwater fish in South European countries.

Results

The biochemical composition of the test ingredients is shown in Table 2. Crude protein levels in brewers by products was 50% higher in BSY than in BSG and ranged from 217.92 to 478.50 g/kg. Hydrolysis of spent grain and spent yeast reduced the crude protein concentration by about 12% (29.15 g Kg−1) in H-BSG and around 3% (15.39 g Kg−1) in H-BSY. Hydrolysed H-BSG and H-BSY also had lower amino acid concentration as a result of low crude protein concentration. Amino acid concentration varied

Discussion

Fishmeal is becoming a limited feed source to be used as the main protein ingredient in carnivorous fish feeds and several new protein sources are being tested as alternatives, most of them derived from plants that generally are not well accepted because they contain carbohydrates that have low digestibility in carnivorous animals as well as anti-nutritional elements that affect feed intake, feed efficiency and health (Gatlin et al., 2007). Other important sources of protein that have been

Data Availability Statement

The data that support the findings of this study are available from the corresponding author upon reasonable request.

Author Statement

Joan Nazzaro.- Carried out the trial with Fish, collect the samples for analysis and collaborate in the writing of the manuscript.

David San Martin, Bruno Iñarra and Mikel Orive.- Provided the products (yeast and spent grain), developed the hydrolysis process and collaborate in the writing of the manuscript.

Anna Perez-Vendrell.- Performed the biochemical analyses, provided the information about the methods used and collaborate in writing the manuscript.

Lluis Padrell.- Helped in the formulation

Declaration of Competing Interest

The authors declare the following financial interests/personal relationships which may be considered as potential competing interests:

Acknowledgements

Life BREWERY project (LIFE16ENV/ES/000160) is co-funded by LIFE European Environment Programme, which is the EU's financial instrument supporting environmental, nature conservation and climate action projects throughout the EU. The implementation, updating and development of EU environmental and climate policy and legislation by co-financing projects with European added value are among its main priorities.

All the brewers by-products samples that have been used in this study have been provided

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