Bitterness in enzymatically-produced hydrolysates of commercial shrimp (Pandalopsis dispar) processing waste

The shrimp processing industry produces a huge amount of waste which can potentially be converted into value-added products by enzymatic hydrolysis. Nevertheless, bitterness in hydrolysates is a common problem that needs to be addressed. In this study, 16 protein hydrolysate samples were produced from commercial shrimp (Pandalopsis dispar) processing wastes using Taguchi's L16 (45 ) experimental design. Four factors, namely water-to-substrate ratio, percent enzyme, time of hydrolysis and type of protease, were investigated. The properties of the shrimp waste hydrolysates were assessed by three responses: product yield, degree of hydrolysis and bitterness. It was found that the type of protease had the most significant impact on hydrolysate properties. Hydrolysates produced from the proteases had significantly higher soluble product yields compared to the controls incubated without added protease. Moreover, the yield from treatments with Alcalase or Protamex reached over 30%, which was six times higher than the control samples. In terms of degree of hydrolysis (DH), Alcalase, Flavourzyme and Protamex gave higher DH than bromelain, which had a DH similar to the controls. Despite the high soluble yields and DH for Alcalase and Protamex hydrolysates, their bitterness was intense and the 10% (w/v) solutions of these samples were evaluated to be greater than 2000 ppm caffeine. Bromelain and Flavourzyme samples had significantly lower bitterness close to 1500 ppm caffeine but these samples were still significantly more bitter than the controls, which contained nearly no bitterness. A sample (blended in 2:1 water-to-substrate ratio and hydrolyzed with 4% Alcalase for 4 hours) that gave a soluble yield of 37.64%, a DH of 2.30 meq/g and bitterness of 2300 ppm was selected for further fractionation by size and hydrophobicity to study the characteristics of the bitter substances. Results showed that bitter substances were small having molecular weight under 3 kDa and contained a large amount of hydrophobic amino acid residues such as Tyr, Phe, Leu, Ile and Lys. Therefore, it was concluded that Flavourzyme had the best potential to be used to produce protein hydrolysates from shrimp processing discards and small hydrophobic peptides were the major contributors to the bitterness.Land and Food Systems, Faculty ofGraduat