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Many bioactive peptides have been reported from various food proteins through the conventional activity-guided-purification approach; however, the rationale behind the selection of conditions for the production of the bioactive peptides has not been extensively explored. The purposes of the study were to provide the rationale behind the selection of conditions, and to develop an innovative strategy to explore the most potent peptides within egg proteins through an integrated QSAR and bioinformatics approach. Thermolysin-pepsin hydrolysate of ovotransferrin was predicted as the best condition for production of ACE-inhibitory peptides. Three predicted peptides, IRW, LKP and IQW, were successfully released from ovotransferrin. Simulated gastrointestinal incubation showed IQW was stable while IRW and LKP can be degraded into dipeptides (IR and KP respectively). Peptides produced from the study will have the potential to be developed as functional foods and nutraceuticals for the prevention of hypertension, a disease affecting ~ 31% of the adult population. / Food Science and Technology

Profiles of plasma estradiol and testosterone concentrations, cathepsin D, L, and B activities, and quantitative and qualitative protein content were developed and evaluated in four commercial strains of channel catfish, Gold Kist (2), Thompson and NWAC-103 for one year (age 2 to age 3). Great variation between individuals of the same strain precluded the identification of any significant, strain-specific differences for the variables under investigation. When variables from fish of all strains were collectively evaluated over time, both estradiol and testosterone concentrations significantly increased in July and then later from February to April. The increase in hormone concentration was accompanied by oocyte growth and increases in proteolytic activity of cathepsins D, L, and B, supporting the role of estradiol in regulating vitellogenesis. Vitellogenin was enzymatically broken down into smaller protein units by cathepsins L, D, and B that were separately predominant at different stages of oocyte development. During oocyte development, there were sequential relationships among hormone concentration, cathepsin activity, protein content, and predominant oocyte proteins. This observation was associated with high levels of activity of cathepsin L in February, suggesting an important role in protein degradation during that time, while high activity of cathepsin B occurred, stimulating during November to January. Cathepsin B is more important in oogenesis or early vitellogenesis, and cathepsin L assumes a principal role during middle vitellogenesis. Twenty hours subsequent to the injection of fish with either carp pituitary hormone or luteinizing hormone releasing hormone, increases in the concentration of plasma estradiol and testosterone, activities of cathepsins L, D, and B, egg size, and egg protein content occurred, stimulating the process of oocyte maturation. The percentages of spawning obtained were 18.8% of LHRH injected fish, 12.4% of CPE injected fish, 9.4% of fish not injected, and 0% of saline injected fish. Injection of females with LHRH can potentially serve as a tool to increase spawning success in appropriate commercial settings, particularly for improving three year old catfish spawning success early in the spawning season. Low estradiol levels in all three-year-old fish suggest that insufficient stimulation of vitellogenin production by estradiol may underlie the lack of vitellogenin incorporation into developing oocytes. In the present study, the measurement of the activities of the cathepsins and their relationships to other parameters were evaluated for the first time. This is also the first study to report plasma estradiol and testosterone concentrations, protein content, and egg size in 2 to 3-year old channel catfish. All of the parameters collectively evaluated may serve to assist in the selection of the best 2- year old channel catfish female broodstock, and to determine the optimal timing of treatments of hormone injection to increase reproductive performance.