Effect of extrusion on the nutritional value of peas (Pisum sativum), chickpeas (Cicer arietinum) and faba beans (Vicia faba) and inclusion in feeds for European seabass (Dicentrarchus labrax) and gilthead seabream (Sparus aurata)

Abstract

The current general economic and food crises have generated an unsettled future for food and feed production and prices in general. Increasing demand, prices and fluctuations in supply in world markets for fishmeal, fish oil, soybean meal, maize and wheat meal emphasize the need to reduce the dependence of the fish feed industry on these ingredients by increasing choices among a wider range of raw materials. Legume seed such as peas, chickpeas and faba beans are promising ingredients for aquafeeds due to their high protein compared to cereals but also for their energy content. The objective of the present study was to investigate the use of these legumes in both high and low inclusion level in diets for the two main species farmed in the Mediterranean countries namely, European seabass (Dicentrarchus labrax L.) and gilthead seabream (Sparus aurata L.). In Chapter 3 the effects of different processing conditions were examined on whole seed flours of tested ingredients with respect to both nutritional and antinutritional factors and physical characteristics of the experimental diet pellets including high and low levels of each legume. Extrusion of raw material resulted in a clear reduction in trypsin inhibitors (TI) with chickpeas showing a decrease of up to 90% and complete inactivation for wheat flour, while for peas and faba beans reduction was less than 50% in most cases. Extrusion processing was less effective in the reduction of phytic acid and total tannins, occasionally reaching 22% and 18% respectively. Oligosaccharides and total NSP were not drastically affected by processing, however faba bean NSP showed greater reduction. A redistribution of soluble and insoluble NSP fractions was noted for chickpea and pea flours after extrusion. Physical characteristics of the pellets were not negatively affected for any of the tested diets. In Experiment I the effects of total or partial wheat substitution by legumes were investigated on nutrient digestibility, gastrointestinal evacuation rate and serum glucose response of European seabass. Use of legumes in seabass and seabream diets resulted in an overall increase in gastrointestinal evacuation time and a delay in glucose load. Specifically, gastric evacuation time was greatly delayed when seabass was fed a diet with high levels (30%) of chickpeas, while foregut evacuation time was mostly delayed by the diet including a high level (30%) of faba beans. In addition, glucose levels in seabass serum were also affected by the type of carbohydrates ingested with wheat starch showing more rapid increase and decrease of glucose compared to fish fed pea and chickpea diets, while faba bean starch resulted in a lower glucose peak. In Experiment II growth, digestibility, hematological parameters, histological effects and fillet organoleptic characteristics and the interaction between starch inclusion level (8% and 16% or 17% and 35% of legumes respectively) and legume type were estimated when tested legumes replaced wheat in European seabass diets. Digestibility coefficients were satisfactory for all nutrients (>93%) while legume diets at a low level had beneficial effects on growth parameters when compared to the control diet, with chickpeas showing a significant improvement in SGR (P<0.05). High level legume diets did not result in any negative effect on growth. HSI was increased with increasing starch/legume inclusion in the feed and serum glucose also increased for fish fed high levels of faba beans and chickpeas. Carcass proximate composition was not affected by replacement of wheat in the diets, excluding the increase of fat content in fish fed chickpeas. Sensory analysis showed no differences between fish fed the control and high legume inclusion diets. Lastly in Experiment III growth, hematological parameters, histological effects and the interaction between starch inclusion level (low and high) and legume type were evaluated when tested legumes were included in gilthead seabream diets. Decreased, but not significantly so, growth was observed for all diets including legumes compared to the control. Poorer SGR were observed for pea and faba bean diets when these legumes were included at high levels. Liver glycogen increased with increasing starch level, but HSI did not differ significantly for any of the diet treatments. Histological examination of hindgut did not show pathological effects, such as enteritis, for in either species or for any of the diets. Increased absorptive vacuoles were found for control and pea diets (high level) only for seabass. The findings of this thesis showed that the two important species cultivated in Mediterranean countries responded differently to the same raw materials used at high levels in the diets. Overall legumes had a strong effect on gastrointestinal evacuation reducing the rate of feed or digesta passage. Peas, chickpeas and faba beans successfully replaced wheat in seabass diets resulting in improved growth coefficients. However, when the same legumes included in seabream diets growth performance was not improved compared to the wheat based diet.