Abstract
Simple SummaryAgro-industrial by-products are the waste from either agricultural crops or vegetable processing industries, and their disposal represents an environmental problem since they are potential pollutants. One of their most promising alternative uses is as feedstuffs in ruminant diets. The aim of this study was to assess the nutritive value of different by-products by analysing their chemical composition, in vitro digestibility and gas production kinetics. The results showed a high variability in chemical composition, in vitro digestibility and rumen fermentation kinetics among different by-products. In addition, samples of the same by-product from a different origin or subjected to different conservation processes showed a certain variability in the evaluated parameters. The variability among by-products was reflected in the results of the cluster analysis, which divided the materials in four groups based on the multivariate analysis. Most by-products showed the potential to be included as alternative ingredients in ruminant rations. They could be used as a source of energy, fibre or protein, replacing part of the ingredients in a conventional diet and therefore, reducing the risk of environmental pollution and contributing to develop a circular economy by recycling these wastes. In addition, their use as feedstuffs might reduce competition between ruminants and humans for food or land.The nutritive value of 26 agro-industrial by-products was assessed from their chemical composition, in vitro digestibility and rumen fermentation kinetics. By-products from sugar beet, grape, olive tree, almond, broccoli, lettuce, asparagus, green bean, artichoke, peas, broad beans, tomato, pepper, apple pomace and citrus were evaluated. Chemical composition, in vitro digestibility and fermentation kinetics varied largely across the by-products. Data were subjected to multivariate and principal component analyses (PCA). According to a multivariate cluster analysis chart, samples formed four distinctive groups (A–D). Less degradable by-products were olive tree leaves, pepper skins and grape seeds (group A); whereas the more degradable ones were sugar beet, orange, lemon and clementine pulps (group D). In the PCA plot, component 1 segregated samples of groups A and B from those of groups C and D. Considering the large variability among by-products, most of them can be regarded as potential ingredients in ruminant rations. Depending on the characteristic nutritive value of each by-product, these feedstuffs can provide alternative sources of energy (e.g., citrus pulps), protein (e.g., asparagus rinds), soluble fibre (e.g., sugar beet pulp) or less digestible roughage (e.g., grape seeds or pepper skin).
Highlights
The world’s human population is in constant growth, and estimated to reach 8.6 billion people by 2030 and 9.8 billion by 2050 [1]
Loadings of each variable used in the Principal Components Analysis (PCA) on principal components 1 and 2 explained the distribution of the samples in the plot
Samples with high Neutral detergent fibre (NDF), acid detergent fibre (ADF) and acid detergent lignin (ADL) contents and t1/2 values were positioned on the right of the plot, but the ones with high values of in vitro digestibility (IVDMD and In vitro NDF digestibility (IVNDFD)), fermentation kinetics parameters (A, c, Gas produced at 24 h (G24), Average gas production rate (AR), disappearance after 144 h of incubation (D144) and E), and non-structural carbohydrates (NSC) and ME contents were positioned on the left along the x-axis
Summary
The world’s human population is in constant growth, and estimated to reach 8.6 billion people by 2030 and 9.8 billion by 2050 [1]. Fresh vegetables and fruit production in Spain reached nearly. 38,600 hundred tons in 2017 (including olives and grapes) [2], so that Spain is the largest vegetable and fruit producing country in the European Union (EU) [3]. Throughout the plant-based food supply chain there is a loss or waste of material generated during the harvesting or processing of food for human consumption. These wastes are known as by-products and their disposal may represent an environmental problem, as they are perishable and potential pollutants [4]. Ruminants can digest plant fibre to produce high quality products available to humans such as milk or meat [7]
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