The use of protein from palm kernel meal in diets of seabass (lates calcarifer)

Abstract

Malaysia has an abundant supply of palm kernel meal (PKM) as a plant protein source as it contains up to 20 % crude protein. It has the potential to at least partly reduce the dependency on the soybean meal presently used in fish diets. However, the nutritive value of PKM limits its incorporation in fish diets due to the presence of high fibre content. A preliminary study on the use of raw PKM indicated that it could be included up to 15% inclusion level in the diets of juvenile seabass without affecting fish growth performance and feed efficiency. A series of problemsolving experiments were conducted to optimise the utilization of PKM as a feed ingredient in the diets of seabass (Lates calcarifer). Initially a chemical extraction of protein involving acid and bases was conducted. Less than 3% (w/w protein) soluble protein from PKM was obtained after 30 min in either acid (pH 2.7) or alkaline (pH 12.5) conditions. However, this amount increases to about 50% (w/w) when left for a longer period of time (3 h) at 28 oC and in alkaline condition (pH 10 and above). Increasing the extraction temperatures (60 oC, 80 oC, 105 oC or 121 oC) did not substantially improve the amount of extracted protein. The low recovery by the chemical extraction method could probably be due to the protein being hindered by layers of cell wall. Thus, pre-treatment on the raw PKM by physical elements such as pressure and heat using the fibre explosion process were attempted. However, it also did not substantially improve protein recovery compared to untreated raw PKM (P > 0.05). Hence, another strategy to expose the binding or entrapment of protein by polysaccharides was to treat PKM with urea at 80:750 g kg-1 (urea:water). A series of feeding trial were then conducted to evaluate the effect of using raw PKM and chemically-treated PKM using urea (UTPKM) as feed ingredients in diets on growth performance of juvenile seabass L. calcarifer. Seabass juveniles fed 7.5% PKM and 15% PKM or 7.5% UTPKM, 15% UTPKM and 22.5% UTPKM diets showed similar growth performance (P > 0.05) with control diet. However, fish fed 22.5% PKM diet showed poor growth performance and feed efficiency (P < 0.05) than fish fed the control diet. On the other hand, there were significant differences (P < 0.05) in terms of protein efficiency ratio (PER) as fish fed the control diet giving the best PER compared to fish fed either 22.5% PKM, 15.0% UTPKM or 22.5% UTPKM. Net protein utilization (NPU) of fish fed 15.0% PKM and 22.5% PKM diets were substantially lower (P < 0.05) than fish fed the control diet. In general, fish growth performance and feed efficiency were shown to be better when fish fed diets with up to 22.5% inclusion of UTPKM than fish fed 22.5% PKM diets. It was concluded that raw PKM has the potential to partially replace soybean meal in the diets of juvenile seabass and that urea treatment on PKM may further improve the utilization of this by-product from the oil palm industry.