Type II acid soluble collagen (CIIA), pepsin soluble collagen (CIIP) and type II gelatin (GII) were isolated from silvertip shark (Carcharhinus albimarginatus) cartilage and examined for their physicochemical and antioxidant properties. GII had a higher hydroxyproline content (173 mg/g) than the collagens and cartilage. CIIA, CIIP and GII were composed of two identical α1 and β chains and were characterized as type II. Amino acid analysis of CIIA, CIIP and GII indicated imino acid contents of 150, 156 and 153 amino acid residues per 1000 residues, respectively. Differing Fourier transform infrared (FTIR) spectra of CIIA, CIIP and GII were observed, which suggested that the isolation process affected the secondary structure and molecular order of collagen, particularly the triple-helical structure. The denaturation temperature of GII (32.5 °C) was higher than that of CIIA and CIIP. The antioxidant activity against 1,1-diphenyl-2-picrylhydrazyl radicals and the reducing power of CIIP was greater than that of CIIA and GII. SEM microstructure of the collagens depicted a porous, fibrillary and multi-layered structure. Accordingly, the physicochemical and antioxidant properties of type II collagens (CIIA, CIIP) and GII isolated from shark cartilage were found to be suitable for biomedical applications.

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BackgroundXylanase can replace chemical additives to improve the volume and sensory properties of bread in the baking. Suitable baking xylanase with improved yield will promote the application of xylanase in baking industry. The xylanase XYNZG from the Plectosphaerella cucumerina has been previously characterized by heterologous expression in Pichia pastoris. However, P. pastoris is not a suitable host for xylanase to be used in the baking process since P. pastoris does not have GRAS (Generally Regarded As Safe) status and requires large methanol supplement during the fermentation in most conditions, which is not allowed to be used in the food industry. Kluyveromyces lactis, as another yeast expression host, has a GRAS status, which has been successfully used in food and feed applications. No previous work has been reported concerning the heterologous expression of xylanase gene xynZG in K. lactis with an aim for application in baking.ResultsThe xylanase gene xynZG from the P. cucumerina was heterologously expressed in K. lactis. The recombinant protein XYNZG in K. lactis presented an approximately 19 kDa band on SDS-PAGE and zymograms analysis. Transformant with the highest halo on the plate containing the RBB-xylan (Remazol Brilliant Blue-xylan) was selected for the flask fermentation in different media. The results indicated that the highest activity of 115 U/ml at 72 h was obtained with the YLPU medium. The mass spectrometry analysis suggested that the hydrolytic products of xylan by XYNZG were mainly xylobiose and xylotriose. The results of baking trials indicated that the addition of XYNZG could reduce the kneading time of dough, increase the volume of bread, improve the texture, and have more positive effects on the sensory properties of bread.ConclusionsXylanase XYNZG is successfully expressed in K. lactis, which exhibits the highest activity among the published reports of the xylanase expression in K. lactis. The recombinant XYNZG can be used to improve the volume and sensory properties of bread. Therefore, the expression yield of recombinant XYNZG can be further improved through engineered strain containing high copy numbers of the XYNZG, and optimized fermentation condition, making bread-baking application possible.

The effects of microwave irradiation on the denaturation of collagen in acetic acid solution have been investigated in comparison with conventional heating. Circular dichroism measurements show that microwave irradiation can induce additional destructions of collagen triple helices due to nonthermal effect. Ultrasensitive microcalorimetry measurements further demonstrate the existence of nonthermal effect. The repeated exposure of collagen solutions to microwave along heating‐cooling cycles can only induce limited conformational changes measured with polarimetry. Our results indicate that thermal effect is the dominant factor leading to collagen denaturation, whereas nonthermal effect causes limited conformational destruction of the triple helices. PRACTICAL APPLICATION The thermal and nonthermal effects of microwave irradiation on biological system are still an open question. Whether nonthermal effect is associated with microwave irradiation and how it exerts influences if existing has no consistent statements so far. The present study helps to better understand the effect of thermal and nonthermal effects on the denaturation of protein upon microwave irradiation. The results suggest that microwave can be used in proteinous food processing safely because the total stereoisomers produced show no difference from conventional thermal denaturation of collagen.

The properties and structure of native taro starch and three modified starches (ultrasonically modified starch, malic acid modified starch, and ultrasound-malic acid modified starch) are compared and analyzed in this work. Experimental results demonstrate that ultrasound and malic acid change the properties and structure of taro starch. Compared with the native starch, the combination of ultrasound and malic acid (UM) leads to the decrease of the viscosity values and H, as well as the improvement of swelling power, water holding capacity, and oil absorption rate. In addition, scanning electron microscopy (SEM) microgram shows that UM results in the damage and degradation of starch granules. Laser diffraction analysis indicates that native starch and modified starches all exhibit bimodal distribution, and ultrasound leads to the decrease of starch particle size, while malic acid results in the increase. The FT-IR spectra suggest that UM changes the peak intensity and width of starch molecules and produces a new characteristic peak at 1741 cm −1 . In conclusion, UM is effective for modifying starch, and it can promote the taro starch process.