Production and characterization of chicken blood hydrolysate with antihypertensive properties

Chicken blood has limited utilization despite its high protein content. Production of a blood hydrolysate exhibiting angiotensin I-converting enzyme (ACE)-inhibitory activity would be means of valorizing chicken blood. The optimized conditions used to produce chicken blood corpuscle hydrolysate (BCH) by Alcalase were 51.1°C, 4% enzyme, and pH 9.6 for 6 h, resulting in a 35.8% degree of hydrolysis and 37.7% ACE inhibition at a peptide concentration of 0.2 mg/mL. The permeate of a 1-kDa membrane, BCH-III, showed a 2.5-fold increase in ACE inhibition compared with that of BCH. BCH-III was resistant to in vitro gastrointestinal digestion, whereas the BCH digesta exhibited an increased ACE-inhibitory activity after digestion. Both BCH and BCH-III were rich in hydrophobic amino acids. A single administration of BCH and BCH-III to spontaneously hypertensive rats at concentrations of 600 and 100 mg/kg, respectively, lowered the systolic blood pressure by -57.7 and -70.9 mmHg, respectively, 6 h after oral administration compared with the control group. The blood pressure-lowering effect of the 600 mg/kg BCH dose was comparable with that of the 100 mg/kg BCH-III dose after 4 wk of oral administration. Both BCH and BCH-III could be developed for use as nutraceutical products with antihypertensive effects.

Acceleration of Thai fish sauce fermentation using proteinases and bacterial starter cultures

A means to accelerate fish sauce fermentation without adversely affecting fish sauce quality was investigated. Starter cultures prepared from Virgibacillus sp. SK33, Virgibacillus sp. SK37, and Staphylococcus sp. SK1-1-5 were added separately to anchovy that was hydrolyzed by 0.25% Alcalase at 60 degrees C for 2 h followed by 0.5% Flavourzyme at 50 degrees C for 4 h. The mixtures were then adjusted to contain 25% solar salt and incubated at 35 degrees C for 4 mo. alpha-Amino contents of all inoculated samples were higher than the control (without the addition of starter culture) during the course of fermentation. After 4-mo fermentation, the samples inoculated with Staphylococcus sp. SK1-1-5 contained the highest alpha-amino content of 733.37 +/- 13.89 mM while that of the control was 682.67 +/- 3.33 mM. Amino acid profiles of inoculated samples showed similar patterns to that of commercial product fermented for 12 mo, with glutamic, aspartic, and lysine being predominant amino acids. Virgibacillus sp. SK33 appeared to decrease histamine content of fish sauce by 50% when compared to the control. Volatile compounds analyzed by GC-MS of all inoculated samples fermented for 4 mo exhibited a similar pattern to those of the 12-mo-old commercial product. Samples inoculated with Staphylococcus sp. SK1-1-5 produced higher levels of volatile fatty acids and showed similar sensory characteristics to the commercial fish sauce fermented for 12 mo. Staphylococcus sp. SK1-1-5 is a potential strain that can be applied to produce fish sauce with overall sensory characteristics of traditional fish sauce in shorter time.

NaCl-activated extracellular proteinase from Virgibacillus sp. SK37 isolated from fish sauce fermentation

Virgibacillus sp. SK37 exhibited high extracellular proteolytic activity in skim milk broth containing 10% NaCl. Optimum conditions of the crude proteinase were at pH 8.0 and 65 degrees C. The proteinase was strongly inhibited by phenylmethanesulfonyl fluoride (PMSF) and preferably hydrolyzed Suc-Ala-Ala-Pro-Phe-AMC, suggesting the serine proteinase with a subtilisin-like characteristic. Proteolytic activity increased with NaCl concentration up to 20%. Ca(2+) activated the enzyme activity but reduced enzyme stability at 65 degrees C. Several proteinases with dominant molecular mass (MW) of 81, 67, 63, 50, 38, and 18 kDa were detected on native-polyacrylamide gel electrophoresis (native-PAGE) activity staining in the absence and presence of 25% NaCl. These results demonstrated that Virgibacillus sp. SK37 produced salt-activated extracellular proteinases. Virgibacillus sp. SK37 could be a promising strain for starter culture development used in fish sauce fermentation.

Proteolysis and gelation of fish proteins under ohmic heating

Pacific whiting surimi gels heated slowly in a water bath exhibited poor gel quality, while the ohmically heated gels without holding at 55 degrees C showed more than a twofold increase in shear stress and shear strain over conventionally heated gels. Degradation of myosin and actin was minimized by ohmic heating, resulting in a continuous network structure. Ohmic heating with a rapid heating rate was an effective method for maximizing gel functionality of Pacific whiting surimi without enzyme inhibitors. In linear heating, slow heating rates increased proteolysis in Pacific whiting surimi as shown by degradation of myosin heavy chain and low shear stress and shear strain. Proteolysis of whiting surimi was decreased by the presence of beef plasma protein (BPP) to a greater extent at rapid heating rates (20 and 30 degrees C/min) than at slow heating rates (1 and 5 degrees C/min). Shear stress of Alaska pollock surimi gels with or without BPP increased as heating rate decreased, but shear strain was unaffected. An increase in shear stress was accompanied by an increase of cross-linked myosin heavy chain.