Imelda W.Y. Cheung

Angiotensin-I converting enzyme inhibitory activity of hydrolysates from oat (Avena sativa) proteins by in silico and in vitro analyses.

The potential for producing antihypertensive peptides from oat proteins through enzymatic hydrolysis was assessed in silico and confirmed in vitro. Thermolysin (EC 3.4.24.27) was predicted using BIOPEP database as the enzyme that would theoretically produce the most angiotensin I converting enzyme (ACE) inhibitory peptides from oat. Experimental evidence confirmed that strong ACE-inhibitory activity was produced under various hydrolysis conditions. Hydrolysates produced under high enzyme-to-substrate ratio (3%) short time (20 min) (HEST) and low enzyme-to-substrate ratio (0.1%) long time (120 min) (LELT) conditions had IC(50) values of 30 and 50 microg/mL, respectively. After simulated gastrointestinal digestion, the IC(50) of the HEST hydrolysate was 35 microg/mL whereas the IC(50) of the LELT hydrolysate was higher at 85 microg/mL. Ultrafiltration revealed that potent ACE-inhibitory peptides had molecular weights below 3 kDa. This study demonstrates the usefulness of in silico analysis to select enzymes for hydrolysis of proteins not previously examined as sources of bioactive peptides.

Pacific Hake (Merluccius Productus) Hydrolysates as Cryoprotective Agents in Frozen Pacific Cod Fillet Mince

Fish protein hydrolysates produced by proteolysis of Pacific hake (Merluccius productus) with Alcalase (FPH-A) or Flavourzyme (FPH-F) were investigated as a potential alternative to the 1 : 1 blend of sucrose-sorbitol (SuSo) commonly used for cryoprotection of frozen fish mince. The physicochemical properties of cod mince samples in the absence (control) or presence of 8% FPH-A, FPH-F, or SuSo were evaluated before and after 6 freeze-thaw cycles, with differences noted at the 5% significance level. Freeze-thawing of control sample increased expressible moisture (from 22% to 33%) and cook loss (from 3% to 16%). These poor water retention properties were improved in samples containing FPH or SuSo. Differential scanning calorimetry showed higher proportion of unfrozen water in freeze-thawed samples containing FPH-F or FPH-A (0.36 g/g) compared to SuSo (0.33 g/g) and control (0.24 g/g) samples. Textural analysis of cooked mince from unfrozen samples indicated greater hardness for FPH than SuSo and control samples, while freeze-thawing resulted in decreased hardness for FPH and SuSo samples. Content and surface hydrophobicity of extractable natural actomyosin (NAM) were maintained after freeze-thawing of samples containing FPH-F or SuSo, compared to 50% decrease in extractable NAM and a significant increase in surface hydrophobicity for the control. The presence of oligopeptides in both hydrolysates and the high levels of free amino acids including Asp, Glu, Arg, and Lys in FPH-F might be responsible for their cryoprotective action. This study provides strong evidence to support development of FPH as a new generation cryoprotectant to maintain quality of frozen fish.

Effects of fish protein hydrolysate and freeze-thaw treatment on physicochemical and gel properties of natural actomyosin from Pacific cod.

The properties of natural actomyosin (NAM) containing 2% or 8% fish protein hydrolysate (FPH-2, FPH-8) or 8% sucrose-sorbitol blend (SuSo) were compared to control NAM before and after freeze-thaw treatment. Surface hydrophobicity of control and FPH-2 increased after freeze-thaw treatment, while that of FPH-8 did not change, which may be related to greater thermostability of actin and myosin in FPH-8 as observed by differential scanning calorimetry. The cooked gel of freeze-thawed control had 39% expressible moisture after an 8.5% cook loss, whereas gels of freeze-thawed SuSo, FPH-2 and FPH-8 had significantly lower expressible moisture (15-22%) and no cook loss. Gels of freeze-thawed FPH-2 and FPH-8 were similar to unfrozen control gel in hardness, cohesiveness and gumminess. This study demonstrates that FPH effectively stabilised NAM protein structure and function during freeze-thaw treatment.

Application of taste sensing system for characterisation of enzymatic hydrolysates from shrimp processing by-products

The objective of this study was to investigate the potential of an instrumental taste-sensing system to distinguish between shrimp processing by-products hydrolysates produced using different proteases and hydrolysis conditions, and the possible association of taste sensor outputs with human gustatory assessment, salt content, and bioactivity. Principal component analysis of taste sensor output data categorised samples according to the proteases used for hydrolysis. High umami sensor outputs were characteristic of bromelain- and Flavourzyme-produced hydrolysates, compared to low saltiness and high bitterness outputs of Alcalase-produced hydrolysates, and high saltiness and low umami outputs of Protamex-produced hydrolysates. Extensively hydrolysed samples showed higher sourness outputs. Saltiness sensor outputs were correlated with conductivity and sodium content, while umami sensor responses were related to gustatory sweetness, bitterness and umami, as well as angiotensin-I converting enzyme inhibitory activity. Further research should explore the dose dependence and sensitivity of each taste sensor to specific amino acids and peptides.

Effects of Production Factors and Egg-Bearing Period on the Antioxidant Activity of Enzymatic Hydrolysates from Shrimp (Pandalopsis dispar) Processing Byproducts

The effects of production factors (protease used, percent enzyme, hydrolysis time, and water-to-substrate ratio) on the antioxidant activity of hydrolysates produced from shrimp processing byproducts (SPB) were assessed using Taguchis L16 (4(5)) fractional factorial design. SPB hydrolysates showed excellent ABTS radical scavenging activity, metal ion chelating capacity, and inhibition of lipid peroxidation, but weak DPPH radical scavenging activity and ferric ion reducing antioxidant power. The protease used significantly influenced antioxidant activities while hydrolysis time and percent enzyme affected radical scavenging activities and inhibition of lipid peroxidation, respectively. Differences in the lipid and amino acid contents observed between SPB collected early and late in the egg-bearing period may have contributed to the slight variance in antioxidant activities displayed by their hydrolysates. Nevertheless, SPB hydrolysates produced using Alcalase or Protamex had high antioxidant activity regardless of production factors and egg-bearing period.