Antioxidant activities of two sericin proteins extracted from cocoon of silkworm (Bombyx mori) measured by DPPH, chemiluminescence, ORAC and ESR methods.

Recent efforts have focused on the use of sericin proteins extracted from cocoons of silkworm as a healthy food source for human consumption. In this study, we focused on the antioxidative properties of sericin proteins. The antioxidative properties were measured in sericin proteins extracted from the shell of the cocoon, designated hereafter as white sericin protein and yellow-green sericin protein, as well as bread without sericin protein and bread to which white sericin powder had been added using four measurement methods: 1,1-Diphenyl-2-picrylhydrazyl (DPPH), chemiluminescence, oxygen radical absorbance capacity (ORAC) and electron spin resonance (ESR). High antioxidative properties of sericin proteins were indicated by all four methods. A comparison of the two types of sericin proteins revealed that yellow-green sericin protein exhibited high antioxidative properties as indicated by the DPPH, chemiluminescence and ORAC methods. By contrast, a higher antioxidative property was determined in white sericin protein by the ESR method. Consequently, our findings confirmed that sericin proteins have antioxidative properties against multiple radicals. In addition, the antioxidative property of bread was enhanced by the addition of sericin powder to the bread. Therefore, findings of this study suggest that sericin proteins may be efficiently used as beneficial food for human health.

Supplementation with Japanese bunching onion (Allium fistulosum L.) expressing a single alien chromosome from shallot increases the antioxidant activity of Kamaboko fish jelly paste in vitro.

Kamaboko is a traditional type of processed seafood made from fish jelly paste that is unique to Japan. We supplemented Kamaboko with Japanese bunching onion (Allium fistulosum L.) with an alien monosome from shallot (Allium cepa L. Aggregatum group) and we measured in vitro the oxygen radical absorbance capacity (ORAC) value, an index of antioxidant activity. We also evaluated the results of sensory testing. The ORAC value of plain Kamaboko was 166±14 µmol trolox equivalent (TE)/100 g fresh weight (FW). The values of the edible Alliaceae powder, i.e., Japanese bunching onion (JBO, genome FF, 2n=2x=16) and the alien addition line of JBO carrying the 6A chromosome from shallot (FF+6A, 2n=2x+1=17), were 6,659±238 and 14,096±635 µmol TE/100 g dry weight (DW). We hypothesized that the 6A chromosome encoded the enhancement of polyphenol production. Subsequently, we created Kamaboko containing 4.8% JBO powder or 4.8% FF+6A powder. The ORAC value of each modified Kamaboko product was increased to 376±24 µmol TE/100 g FW for the JBO powder and to 460±16 µmol TE/100 g FW for the FF+6A powder, respectively. We next created Kamaboko containing 9.0% JBO powder or 9.0% FF+6A powder and the ORAC values of the respective modified Kamaboko products was increased to 671±16 and 740±21 µmol TE/100 g FW, i.e., 4.1- and 4.5-times the value of plain Kamaboko. Consequently, taking into consideration the sensory evaluation regarding taste and appearance as well, the use of Kamaboko supplemented with 4.8% FF+6A powder is recommended.

Cloning of the thaumatin I cDNA and characterization of recombinant thaumatin I secreted by Pichia pastoris.

Thaumatin is a sweet-tasting protein comprising a mixture of some variants. The major variants are thaumatins I and II. Although the amino acid sequence of thaumatin I was known and the nucleotide sequence of cDNA of thaumatin II was elucidated, the nucleotide sequence of thaumatin I has been controversial. We have cloned two thaumatin cDNAs from the fruit of Thaumatococcus daniellii Benth. One is the same nucleotide sequence as that of thaumatin II already reported, and the other is a novel nucleotide sequence. The amino acid sequence deduced from the novel cDNA was the same amino acid sequence as that of thaumatin I, the only exception being the residue at position 113 (Asp instead of Asn), indicating that the novel thaumatin cDNA is that for thaumatin I. This thaumatin I cDNA was transformed into Pichia pastoris X-33, and the recombinant thaumatin I expressed was purified and characterized. The threshold value of sweetness of the recombinant thaumatin I was the same as that of the plant thaumatin I, although several unexpected amino acid residues were attached to the N-terminal of the recombinant thaumatin I. These indicate that the N-terminal portion of thaumatin is not critical for the elicitation of sweetness.

Effects of heating at neutral and acid pH on the structure of beta-lactoglobulin A revealed by differential scanning calorimetry and circular dichroism spectroscopy.

The structural change of beta-lactoglobulin A (betaLG A) on heating was measured at pH 3.0 and 7.5 with UV absorption difference spectra, differential scanning calorimetry (DSC), and circular dichroism (CD). At pH 3.0, betaLG A showed a reversible structural change by heating at 80 degrees C, while an irreversible change was observed and molecular aggregates of betaLG were formed by heating at 95 degrees C. DSC analysis of betaLG A gave endothermic peaks at 75 degrees C and 90 degrees C at pH 7.5, and 90 degrees C at pH 3.0. At pH 7.5, betaLG A modified with N-ethylmaleimide (NEM-betaLG A) gave two endothermic peaks: at 72 degrees C and 90 degrees C. CD spectra of betaLG A heated at various temperatures and pHs were measured and the spectra at pH 3.0 and 7.5 were not changed by heating to 95 degrees C and 80 degrees C, respectively. Unheated NEM-betaLG A gave a spectrum similar to that of heated betaLG A, suggesting that the secondary structure was changed by NEM treatment.

Cloning, expression and characterization of recombinant sweet-protein thaumatin II using the methylotrophic yeast Pichia pastoris.

Thaumatin, an intensely sweet-tasting protein, was secreted by the methylotrophic yeast Pichia pastoris. The mature thaumatin II gene was directly cloned from Taq polymerase-amplified PCR products by using TA cloning methods and fused the pPIC9K expression vector that contains Saccharomyces cerevisiae prepro alpha-mating factor secretion signal. Several additional amino acid residues were introduced at both the N- and C-terminal ends by genetic modification to investigate the role of the terminal end region for elicitation of sweetness in the thaumatin molecule. The secondary and tertiary structures of purified recombinant thaumatin were almost identical to those of the plant thaumatin molecule. Recombinant thaumatin II elicited a sweet taste as native plant thaumatin II; its threshold value of sweetness to humans was around 50 nM, which is the same as that of plant thaumatin II. These results demonstrate that the functional expression of thaumatin II was attained by Pichia pastoris systems and that the N- and C-terminal regions of the thaumatin II molecule do not -play an important role in eliciting the sweet taste of thaumatin.