Yeast from papaya processing wastes as aquaculture feed supplement

Abstract

The Pacific Island is facing the challenge of short in cost-effective aquafeed. The protein source is the most costly ingredient in feed supplements. Yeast is enriched with protein and has been reported to be able to enhance shrimp's immune system, survival rate and average body weight. Hawaii produces million tons of fruit and food by-products each year which may have the potential to be upgraded into protein enriched value-added products. This study plans to develop a bioprocess procedure to convert fruit processing wastes into yeast biomass, to establish design and operational criteria for yeast production in batch and/or continuous/semi-continuous flow system, to evaluate the nutrient potential of the bioprocessed product as shrimp feed and the cost of the proposed production system. Papaya processing waste collected from a food company in Honolulu was used for yeast growth (S. cerevisiae) in a 14-L fermenter mixing at 200 rpm under room temperature (22±2°C). PH, oxidation reduction potential (ORP) and dissolved oxygen (DO) were monitored with the change of soluble chemical oxygen demand (SCOD) removal and suspended solids increase in the growth medium to determine the required reaction time for maximum desirable product formation. An initial SCOD concentration ranged from 12,000 to 25,000 mg/l with 8-12h aeration was found for optimal and economical operation in the batch production system. It was able to remove more than 70% SCOD and produce 40-45% crude protein in suspended solid. Preliminary work of continuous/semi-continuous flow operation, shrimp (L. vannamei) feed trail and economic analysis on the batch production system indicated the successful development of the bioprocess system would be a mutual beneficial solution for local aqua-industries and environmental pollution control. In addition, the bioprocess could be applied widely to other agri-food by-products to produce the value-added products for the sustainability of agriculture production and environmental protection.