Wheat gluten in extruded fish feed: Effects on morphology and on physical and functional properties
Draganovic, V. ; Goot, A.J. van der; Boom, R.M. ; Jonkers, J. - \ 2013
Aquaculture Nutrition 19 (2013)6. - ISSN 1353-5773 - p. 845 - 859.
structural characteristics - lysine supplementation - salmonid feeds - rainbow-trout - oil uptake - products - protein - meal - microstructure - digestibility
This article focuses on understanding the role of vital wheat gluten on the structural parameters of extruded fish feed and its correlation to the physical and functional properties. Gluten–soy protein concentrate blends with five gluten concentrations (0–200 g kg-1) were produced. An abrupt reduction in oil uptake was observed with the 200 g gluten kg-1 blend. Inclusion of gluten from 100 to 200 g kg-1 resulted in unacceptable product properties. Sinking of feed pellets with 0 and 50 g gluten kg-1 was 100%, whereas only 36% of pellets with 200 g gluten kg-1 sank. We suspect that this is due to a relationship between morphological structure and oil impregnation during coating of feeds. The addition of gluten at 200 g kg-1 gave a smoother and non-porous outer surface. Pellets without gluten had a larger number of cells that were smaller than 200 µm (P <0.05) compared with pellets with 100 and 200 g gluten kg-1. More spherical cell shapes (P <0.01) and a compact structure were favoured in the presence of gluten. The closed porosity increased (P <0.05), whereas interconnectivity between pores decreased (P <0.01), with increasing gluten content from 0 to 200 g kg-1. The effects of the addition of gluten are probably related to the film-forming properties of gluten.
Opposite Contributions of Glycinin- and ß-Conglycinin-Derived Peptides to the Aggregation Behavior of Soy Protein Isolate Hydrolysates
Kuipers, B.J.H. ; Koningsveld, G.A. van; Alting, A.C. ; Driehuis, F. ; Voragen, A.G.J. ; Gruppen, H. - \ 2006
Food Biophysics 1 (2006)4. - ISSN 1557-1858 - p. 178 - 188.
heat-induced gelation - soybean proteins - structural characteristics - emulsifying properties - enzymatic-hydrolysis - limited proteolysis - physical-properties - alpha-lactalbumin - gel properties - whey proteins
The aggregation behavior as a function of pH was studied for hydrolysates obtained by hydrolysis of soy protein isolate (SPI) and glycinin- and ß-conglycinin-rich protein fractions with subtilisin Carlsberg. The substrates were hydrolyzed up to degrees of hydrolysis (DH) of 2.2% and 6.5%. Compared with nonhydrolyzed SPI, a decrease in solubility was observed for the hydrolysates of SPI [0.8% (w/v) protein, I¿=¿0.03 M] around neutral pH. At pH 8.0, glycinin hydrolysates had a much lower solubility (~43% and 60%, respectively, for DH 2.2% and 6.5%) than SPI and ß-conglycinin-derived hydrolysates, which were almost completely soluble. Peptides that aggregated were all larger than 5 kDa, and as estimated by size-exclusion chromatography their composition was almost independent of the aggregation pH. The solubility of hydrolysates of SPIs with a varying glycinin and ß-conglycinin composition showed that glycinin-derived peptides are the driving force for the lower solubility of SPI hydrolysates. The solubility of SPI hydrolysates at pH 8.0 was shown not to be the sum of that of glycinin and ß-conglycinin hydrolysates. Assuming that the separate hydrolysis of glycinin and ß-conglycinin did not differ from that in the mixture (SPI), this indicates that ß-conglycinin-derived peptides have the ability to inhibit glycinin-derived peptide aggregation.