Marine Cod (Gadus morhua) Head Hydrolysates - in vitro ACE inhibitory activity and investigation of structure-activity relationship
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Marine by-products contain valuable nutrients and there is an increasing interest in production of value-added products for human consumption. Cod (Gadus morhua) head hydrolysates produced by SINTEF Ocean in the pilot project HEADS UP were the base for analyses in this thesis. The hydrolysates were produced from cod harvested in Tufjord in February, March or May of 2017 with varying processing conditions, namely proteolytic enzymes (Bromelain + Papain or Protamex), concentration of enzymes and amount of water. One hydrolysate was produced with stick water, and two of the hydrolysates were added antioxidants. The thesis aimed to measure in vitro ACE inhibitory activity of the hydrolysates, and further investigate structure-activity relationship. All the cod head hydrolysates expressed ACE inhibitory activity in vitro, and IC50 values ranged from 2,60 4,91 mg protein/mL. The antihypertensive effect exerted by one of the hydrolysates was misleading and was therefore not included in this range. Compared to the antihypertensive drug Captopril (IC50 = 0,097 mg/mL), the ACE inhibitory activities of the hydrolysates were found to be relatively low. Four of the hydrolysates were fractionated by ultrafiltration. The fractions enriched in small peptides were found to exert less potent ACE inhibitory activity than the unfractionated hydrolysates. It is therefore suggested that fractionation is unnecessary to increase antihypertensive effects of the cod head hydrolysates. The hydrolysates were composed of amino acids that have been found to contribute to inhibition of ACE, including leucine, isoleucine, valine, phenylalanine and methionine, in addition to a balanced distribution and high content of essential amino acids (average content 38,8 11 %). The hydrolysates contained peptides with broad molecular weight distribution and contained low amounts of free amino acids. No correlation was found between degree of hydrolysis and IC50. No correlations were found between season of harvest and chemical composition of the cod head hydrolysates. Additionally, no correlations were found between processing parameters and ACE inhibitory activity and molecular properties of the hydrolysates. The use of stick water in the production of one hydrolysate did affect the sensory aspects, but not molecular properties. Cod head hydrolysates were found to be a promising potential food ingredient with antihypertensive effects, high solubility, no bitter taste and good nutritional value due to low amounts of free amino acids and high amounts of essential amino acids.