Protein from fermented prawn waste silage as an ingredient in the diet of seabass

Abstract

Prawn processing industries remain as one of the main marine activities in the world as well as in Malaysia and it normally generates large volumes of prawn waste. This waste product which contains high amounts of chitin (14 - 30%) and protein (15 - 40%) has been exploited to obtain chitin through chemical processes. However, this process renders the valuable protein useless. In this work, a lactic acid fermentation process was used to ferment the prawn waste and the performance of using the fermented prawn waste liquor (FPWL) as a protein source in seabass's diet was investigated. Initially, prawn waste with an addition of 10% (w/w) of glucose and 10% (v/w) starter culture was fermented for 60 days at 37°c. The pH value decreased from 7.51 to 4.00 within 24 hours and remained stable with no signs of spoilage up to 60 days. The fermentation produced solid chitin and protein liqour component, the latter of which contains 50 and 56% protein after 3 and 7 days of incubation period respectively and increased only slightly to 58% on day 60. After 3 days of fermentation period, 78% of the protein from the waste can be recovered as FPWL and 97% of chitin remained in the solid prawn waste. It was also observed that as the glucose concentration decreased, the lactic acid concentration and the bacterial growth increased. Similar fermentation was also succesfully conducted at ambient temperatures (27 to 33°c). Attempts were made to increase protein content of liquor by freeze drying into a powdered form and also by removing the calcium lactate through storage at -20°c. However, both processes despite producing a product which can be easily handled, is time and energy consuming while not improving the protein content. Thus, the usage of protein liqour in liquid form was more suitable. A feeding trial was conducted for 49 days to evaluate the effect of using FPWL as a substitute for fishmeal in seabass diet. The inclusions of FPWL were at 10, 20 and 30%. Growth performance of seabass with initial weight of 16.2g ± 0.4, fed with FPWL-based diet was not significantly different (P>0.05) compared to control diet which contain fishmeal. The most effective diet was 30%, 1.78 and 1.2 respectively. Overall, FPWL is feasible to be used as a protein source to partially substitute fishmeal in diet of seabass.