Eunice C.Y. Li-Chan

Peptides Derived from Atlantic Salmon Skin Gelatin as Dipeptidyl-peptidase IV Inhibitors

The dipeptidyl-peptidase IV (DPP-IV)-inhibitory activity of peptides derived from Atlantic salmon skin gelatin hydrolyzed by alcalase (ALA), bromelain (BRO), and Flavourzyme (FLA) was determined. The FLA hydrolysate with the enzyme/substrate ratio of 6% showed the greatest DPP-IV-inhibitory activity. The hydrolysate was fractionated by ultrafiltration with 1 and 2.5 kDa cutoff membranes, and the <1 kDa fraction had the highest DPP-IV-inhibitory activity with an IC(50) value of 1.35 mg/mL. The F-1 fraction further isolated by HPLC showed the IC(50) value against DPP-IV of 57.3 μg/mL, and the peptide sequences were identified as Gly-Pro-Ala-Glu (372.4 Da) and Gly-Pro-Gly-Ala (300.4 Da). The synthetic peptides showed dose-dependent inhibition effects on DPP-IV with IC(50) values of 49.6 and 41.9 μM, respectively. The results suggest that the peptides derived from Atlantic salmon skin gelatin would be beneficial ingredients for functional foods or pharmaceuticals against type 2 diabetes.

Systematic experimental designs for product formula optimization

Abstract Food product development is a market-driven process and as such it is influenced by current consumer needs and trends, thus forcing food companies to respond rapidly to marketplace changes. The application of scientifically sound experimental designs enables companies to decrease the time between concept and marketplace. The ultimate objective of any product development, no matter how it is executed, is to generate products that perform as they were designed to do. A large number of experimental designs were available for the optimization of food product development. Fractional-factorial designs, especially Taguchi methods, have proved very useful in other industries as a quality improvement tool, and their use in the food product development area may be beneficial. Techniques such as response surface methodology and mixture designs are also effective in formula optimization. New optimization techniques are also emerging as alternative tools for the development of new foods.

Dietary requirement for lysine by juvenile Penaeus vannamei using intact and free amino acid sources

In a preliminary experiment, order-of-limitation of lysine, arginine and methionine was determined for wheat gluten fed to juvenile shrimp. Limitation diets were prepared by singular deletion of the crystalline component of one of the above amino acids from a control diet. Shrimp fed deletion diets had significantly less weight gain than those fed the control diet with the order-of-limitation being lysine ≥ methionine ≥ arginine with lysine being significantly more limiting than arginine. In a subsequent experiment, the dietary requirement for lysine was estimated using juvenile Penaeus vannamei and a 21-day experimental period. Shrimp were fed four different types of diets: (1) 35% crude protein, lysine supplementation via covalently lysine-enriched wheat gluten; (2) 35% crude protein, lysine supplementation via l-lysine HCl; (3) 45% crude protein, lysine supplementation via covalently lysine-enriched wheat gluten; and (4) 45% crude protein, lysine supplementation via l-lysine HCl. Diets containing 35% crude protein contained graded levels of lysine ranging from 3.43 to 6.57% of the protein. Lysine in the diets containing 45% crude protein ranged from 3.33 to 6.67% of the dietary protein. Apparent requirement for lysine was estimated by broken-line regression of instantaneous growth coefficient (IGR) against dietary lysine concentration. No significant difference (P < 0.05) in survival was observed among shrimp fed any of the four different types of diets. Irrespective of means of lysine supplementation, the apparent requirement for lysine by shrimp fed diets containing 45% crude protein was 4.67% of the protein. The apparent requirement for lysine by shrimp fed the diet containing 35% crude protein supplemented with wheat gluten and with l-lysine HCl was 4.49 and 5.19% of the protein, respectively.

In situ investigation of protein structure in Pacific whiting surimi and gels using Raman spectroscopy

Abstract Raman spectroscopy was used to study the in situ protein structure in raw and salted surimi from Pacific whiting, and in gels formed by setting (32 °C), cooking (86 °C) or setting followed by cooking. The set-cooked gel had a better gel strength and fold score than the gels which were only set or cooked. Large increases in relative intensity of a band near 530 cm−1 in the cooked and set-cooked gels indicated changes in disulfide bond stretching or aliphatic chain vibrations. Involvement of hydrophobic interactions of aliphatic chains in salting, setting and cooking was inferred from the decreased intensity of a band near 2930cm−1 assigned to C-H stretching vibrations. Changes in a doublet near 850 and 830 cm− suggested an increasing involvement of tyrosine residues as hydrogen bond donors in a non-polar environment after setting or setting-cooking, in contrast to increasing exposure to a polar environment in gels formed by cooking alone. Secondary structure estimation based on the amide I band indicated a change from predominantly α-helical structure in raw surimi to higher antiparallel β-sheet and lower α-helical contents after setting and particularly during the kamaboko stage.

Stability of bovine immunoglobulins to thermal treatment and processing

Abstract Thermal stability of bovine immunoglobulin (IgG) in model systems and in commercially processed milk products was investigated. Bovine serum IgG dissolved in either phosphate buffered saline (PBS), boiled milk or ultra high temperature (UHT) sterilized milk was heated at temperatures ranging from 62.7 °C to 80 °C. The D -values ranged from 90, 200 and 170 s at 80 °C to 25.5, 27.2 and 32.8 min at 72 °C for IgG in PBS, boiled milk and UHT milk, respectively. These results suggest slightly greater thermal stability of IgG in milk than in phosphate buffer. IgG content was not changed after 30 min at 62.7 °C, nor by holding for 24 h at either ambient temperature or 4 °C. Over the temperature range from 72 ° to 80 °C, z -values were 6.7, 8.9 and 8.5 °C, and energies of activation were 353.5, 258.2 and 298.5 kJ mol −1 for thermal destruction of bovine serum IgG in PBS, boiled milk and UHT milk, respectively. These findings in model systems suggest that commercial pasteurization processes should not result in complete destruction of IgG. Comparison of IgG content in raw milks and corresponding HTST-pasteurized milks of varying fat content indicated 59–76% retention after pasteurization, with no apparent effect by either homogenization, skimming or standardization to 1 or 2% fat levels. The IgG contents and specific antibody activity against lipopolysaccharide fractions of five bacteria were determined for several commercially processed milk products. HTST-pasteurized milks, reconstituted skim milk powder and whey from cheddar cheese production all showed high levels of IgG and specific antibody activity. However, canned evaporated milk and ultra high temperature (UHT) sterilized milk had little or no IgG. This study demonstrates the dependence of bovine IgG stability in milk products on severity of thermal treatment used in various commercial processes.

Binding and textural properties of beef gels as affected by protein, κ-carrageenan and microbial transglutaminase addition

Abstract The combined influence of κ-carrageenan (0.5%) and egg albumin or collagen isolate non-muscle proteins (NMP, 2%) on quality characteristics of beef gels processed without or with 0.5% microbial transglutaminase (MTG) was investigated. Beef gel properties were determined by measuring textural, hydration and colour characteristics. Substitution with NMP resulted in gels (8% total protein) which were less hard, chewy and elastic, and had poorer binding properties. Although MTG improved WHC and textural parameters, it could not restore texture of NMP substituted gels to that of non-substituted meat gels. κ-carrageenan favourably affected hydration properties and thermal stability, yielding lower cooking loss and purge and higher WHC for NMP substituted than non-substituted meat gels. It also restored hardness and fracturability of NMP substituted batters, but was unable to improve springiness or cohesiveness. Addition of NMP and κ-carrageenan significantly altered colour, while no significant influence of MTG on gel colour parameters was observed.

Inhibition of Dipeptidyl Peptidase (DPP)-IV and α-Glucosidase Activities by Pepsin-Treated Whey Proteins

Inhibitors of the enzymes dipeptidyl peptidase (DPP)-IV and α-glucosidase are two classes of pharmacotherapeutic agents used for the treatment of type 2 diabetes. In the present study, whey protein isolate (WPI), α-lactalbumin, β-lactoglobulin, serum albumin, and lactoferrin hydrolysates obtained by peptic digestion were investigated for their potential to serve as natural sources of DPP-IV and α-glucosidase inhibitors. Although inhibition of DPP-IV activity was observed in all pepsin-treated whey proteins studied, the α-lactalbumin hydrolysate showed the greatest potency with an IC50 value of 0.036 mg/mL. Conversely, only WPI, β-lactoglobulin, and α-lactalbumin hydrolysates displayed some inhibitory activity against α-glucosidase. This study suggests that peptides generated from whey proteins may have dual beneficial effects on glycemia regulation and could be used as functional food ingredients for the management of type 2 diabetes.

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.

Developments in the detection of adulteration of olive oil

Abstract The authenticity of products labelled as olive oil is of great importance from the standpoints of both commercial value and health aspects. Over the years, a high degree of sophistication has evolved in chromatographic methods for the analysis of both major and minor components of oils and fats. At the same time, spectroscopic methods are emerging as potential tools for rapid screening of samples for the detection of adulteration. However, the complexity and intrinsic variability of biological samples such as olive oil and its potential adulterants demands the application of multivariate calibration or pattern-recognition techniques to aid interpretation of the data obtained using these instrumental methods. Combination of the techniques of analytical chemistry and chemometrics is mandatory for unequivocal identification and quantification of the adulteration of olive oil.

Interactions of κ-carrageenan with whey proteins in gels formed at different pH

Abstract The objective of this study was to investigate the influence of κ-carrageenan on textural properties of whey protein isolate gels formed by heating at 80 °C for 30 min in the pH range from 1–12. In the absence of polysaccharide, very strong and elastic gels were obtained using 10% WPI at pH 7–8. In the presence of κ-carrageenan, the highest shear stress value was observed at pH 6, but strong gels were obtained over a broad pH range up to 11. WPI at a concentration of 3% did not form a self-supporting gel, but significantly enhanced the shear stress values of 0.5% κ-carrageenan, particularly at pH 6–7. A similar enhancing effect of 3% unheated milk protein on gk-carrageenan gels at pH 6.7 was also observed. At pH 6–7, where optimal gelation of mixtures was observed, the presence of κ-carra-geenan resulted in smaller increases in protein surface hydrophobicity after heating, as determined by the fluorescence probe 1-anilinonaphthalene-8-sulfonate. Under these conditions, small angle X-ray scattering studies indicated the formation of a mixed structure gel with attractive interparticle interactions.