## 3 Results and Discussion
### Free Amino Acid Content  
The free amino acid content of the generated hydrolysates ranged from 3.77% for sample MBF19 to 11.91% for sample MBMay19 of the total amino acid content. The free amino acid content depends on the enzyme used during hydrolysis, the time of hydrolysis and the resulting degree of hydrolysis. Amino acid contents of 30% were previously reported for marine samples with higher degrees of hydrolysis (35%-40%) [33]. Taurine was the only amino acid found in a higher concentration in the free amino acid fraction of the mussel hydrolysates when compared to the total amino acid fraction. It is known that taurine, a free amino acid, is not part of the protein polypeptide chain and hence is found in a greater proportion in the free amino acid fraction. Figure 2 shows the relative abundance of free and total amino acids in the mussel by-product hydrolysates for sample KHN18, which had an ACE-I inhibitory activity of 86.08% \(\pm\) 1.59% when assayed at a concentration of 1 mg/mL compared to the control. Cooked Meat Yield, Hydrolysate Yield and Protein Content across Different Seasons and By-Product Types  
The meat yield and corresponding hydrolysate yield are dependent on the type of by-product mussel and the season of harvest. Seed mussels' cooked meat yields ranged from 9.75%-15.34% compared to undersized/broken shells or a combination of seed and broken sells, which had meat yields ranging from 22%-26.77%. Seed mussel samples in this study showed heterogeneity and some samples contained seed mussels \(<\) 1 cm in length, resulting in no retrievable meat and thus lower meat yields/250 g of sample in comparison to larger seed mussels. The cooked meat yield for the by-products analysed varied between 9.75% (MBF19) to 26.77% (KHN18), and was always less than 30%. For _Mytilus edulis_ mussels, the gamete development phase is between November and May, during which time the cells reach sexual maturation, and there is a record drop in meat yield in the month of May [34]. In agreement  
Figure 1: The Degree of hydrolysis (DH) of mussel by-product Protamex® hydrolysates (H) determined using the Adler-Nissen pH stat method. The 9 samples from the three sampling sites Mulroy bay (MB), Killary harbour (KH) and Ardgeroom (A), collected from November 2018 to October 2019, were used for hydrolysis. Analysis was performed in triplicate (n = 3). Bars sharing the same letter are not significantly different according to [PERSON]’s honestly significant difference (HSD) test. Figure 2: Free and total amino acid % composition (_w/w_) of mussel by-product Protamex® hydrolysate for the Killary harbour November 2018 (KHN18) sample. The amino acids were quantified using a Jeol JLC-500/V amino acid analyser (Joul Ltd., Garden city, Herts, UK) fitted with a Jeol Na+ high performance cation exchange column. Glutamate was the most abundant amino acid, whereas taurine was the most abundant free amino acid, as seen from the average values displayed on the two bars. Analysis was performed in triplicate (n = 1). with these published results, the present study showed relatively lower meat yields, hydrolysate yields and protein contents in mussel by-products harvested between February and May, as shown in Figure 3. The meat protein content is high between July and October, months associated with the spawning season. A higher amount of storage tissue accumulates during this season, which corresponds to the higher protein content observed. Furthermore, in February and March, lower meat yields were found in comparison to samples harvested from September and November, though the effect was not as pronounced as the hydrolysate yields and protein contents observed. Figure 3: Changes in meat yield (% _v/v_), hydrolysate yield (% _v/v_) and protein content (% _v/v_) for mussel by-products and Protame® hydrolysates. The 10 samples from the three sampling sites Mulroy bay (MB), Killary harbor (KH) and Ardrogom (A), collected from November 2018 to October 2019, were used for analysis.