Abstract
Mussel cultivation results in tons of by-product, with 27% of the harvest considered as reject material. In this study, mussel by-products considered to be undersized (mussels with a cooked meat yield <30%), mussels with broken shells and barnacle-fouled mussels were collected from three different locations in the west, north-west and south-west of Ireland. Samples were hydrolysed using controlled temperatures and agitation, and the proteolytic enzyme Protamex® was added at an enzyme:substrate ratio of 1:50 (w:v). The hydrolysates were freeze-dried and analysed for protein content and amino acid composition, lipid content and fatty acid methyl ester (FAME) composition, ash and techno-functional and bioactive activities. The degree of hydrolysis was determined using the Adler-Nissen pH stat method and was found to be between 2.41% ± 0% and 7.55% ± 0.6%. Mussel by-products harvested between February and May 2019 had protein contents ranging from 36.76% ± 0.41% to 52.19% ± 1.78%. The protein content of mussels collected from July to October (the spawning season) ranged from 59.07% ± 1.375% to 68.31% ± 3.42%. The ratio of essential to nonessential amino acids varied from 0.68–0.96 and it was highest for a sample collected in November from the west of Ireland. All the hydrolysate samples contained omega-3 polyunsaturated fatty acids (PUFA), especially eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), which are known anti-inflammatory agents. Selected hydrolysates which had angiotensin-converting enzyme I (ACE-I; EC 3.4.15.1) and dipeptidyl peptidase IV (DPP-IV; EC 3.4.14.5) inhibitory activities were filtered using 3-kDa membrane filtration and the permeate fraction was sequenced using mass spectrometry (MS). Identified peptides were >7 amino acids in length. Following BIOPEP database mining, 91% of the by-product mussel peptides identified were found to be previously identified DPP-IV and ACE-I inhibitory peptides, and this was confirmed using in vitro bioassays. The ACE-I inhibitory activity of the by-product mussel hydrolysates ranged from 22.23% ± 1.79% to 86.08% ± 1.59% and the most active hydrolysate had an ACE-I inhibitory concentration (IC50) value of 0.2944 mg/mL compared to the positive control, captopril. This work demonstrates that by-product mussel hydrolysates have potential for use as health-promoting ingredients.
Highlights
Mussel cultivation for human consumption has been practiced for years through rope or raft cultivation systems, and the total global productivity of the common blue mussel (Mytilus edulis) is approximately 20,000 tons (9% of the total global mussel production) [1]
Three samples were obtained from Mulroy bay and were labeled MBF19, MBMay19 and MBJuly19, as they were sampled in the months of February, May and July 2019
In agreement with these published results, the present study showed relatively lower meat yields, hydrolysate yields and protein contents in mussel by-products harvested between with these published results, the present study showed relatively lower meat yields, hydrolysate yields
Summary
Mussel cultivation for human consumption has been practiced for years through rope or raft cultivation systems, and the total global productivity of the common blue mussel (Mytilus edulis) is approximately 20,000 tons (9% of the total global mussel production) [1]. Mussel by-products are a rich source of protein, lipids and essential amino acids. Bioprocessing of by-product mussels for high-value commercial ingredient development could contribute positively towards the circular economy. The harvesting season, by-product type, location and climate all have significant effects on the composition of mussel by-products. The spawning or the reproductive period for Mytilus edilus is spring to summer, whereas gametogenesis occurs during the winter season when the mussels get bigger prior to spawning. Depending on when the mussels are harvested, the size, meat yield and composition vary. A high meat yield, protein, lipid and pigment content (e.g., caretonoid) are often associated with the gametogenesis phase of maturation in mussels [3,4]
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