Oligochitosan of 5 kDa and transglutaminase can be used to glycate and cross-link SPI. This approach is applicable to generate potential protein ingredient with good hydration and dispersive stabilisation. © 2016 Society of Chemical Industry.

Skimmed milk used for set-style yoghurt production was treated with lactase at 0.1 g/kg for 30 min to give partial lactose hydrolysis and then treated with horseradish peroxidase and glucose oxidase at 200 and 6 kU/kg protein to result in protein cross-linking. Two treatments conferred higher apparent viscosity on the milk, but led to the yoghurt prepared from it with insignificantly different chemical compositions to the counterparts (P > 0.05). The prepared yoghurt also showed decreased syneresis (about 17.7%), higher apparent viscosity and viscoelastic modulus, firmer texture and finer microstructure. This ternary enzyme system is a potential approach to improving the quality of set-style yoghurt.

Structure and property changes of soybean protein isolates resulted from the glycation and cross-linking by transglutaminase and a degraded chitosan Cambios en la estructura y en las propiedades del aislado de proteína de soja como resultado de la glicación y reticulación mediante transglutaminasa y chitosán degradado A glycated and cross-linked soybean protein isolate (GC-SPI) with the glucosamine content of 19.40 g/kg protein was prepared by using SPI, transglutaminase, and a degraded chitosan under fixed conditions, aiming to assess modified properties and potential application of GC-SPI. GC-SPI has less reactable -NH 2 groups than SPI (0.38 versus 0.48 mol/kg protein), and is verified by electrophoretic analysis to be a glycated and cross-linked protein product. Infrared spectroscopy and circular dichroism analyses demonstrate that GC-SPI contains more -OH groups, and has a more open secondary structure. In comparison with SPI, GC-SPI has higher surface hydrophobicity but lower in vitro digestibility due to protein cross-linking, and exhibits greater water-and oil-binding capacities (9.9 versus 6.4 and 3.7 versus 2.0 kg/kg protein). It is concluded that the glycation and cross-linking confer an open structure and modified properties of SPI, and GC-SPI is a potential ingredient with better hydration and oil-binding than SPI.Keywords: soybean protein isolate; degraded chitosan; transglutaminase; secondary structure; property Se preparó aislado de proteína de soja glicada y reticulada (GC-SPI) con un contenido de glucosamina de 19,40 g/kg de proteína utilizando SPI, transglutaminasa y chitosán degradado sometido a condiciones determinadas con el objetivo de estudiar las propiedades modificadas y las aplicaciones potenciales de GC-SPI. GC-SPI obtuvo menos grupos reactivos de tipo NH 2 en comparación con SPI (0,38 frente a 0,48 mol/kg de proteína) y se verificó mediante análisis electroforético para ser un producto proteínico glicado y reticulado. La espectroscopía infrarroja y el análisis de dicroísmo circular mostraron que el GC-SPI contiene más grupos OH y tiene una estructura secundaria más abierta. En comparación con SPI, GC-SPI tiene una mayor superficie de hidrofobia aunque una menor digestibilidad in vitro debido a la reticulación proteínica, además exhibe una mayor capacidad de retención de agua y de aceite (9,9 frente a 6,4 y 3,7 frente a 2,0 kg/kg de proteína). En conclusión, la glicación y la reticulación conceden una estructura abierta y unas propiedades modificadas en SPI. Además GC-SPI se trata de un ingrediente potencial con una mejor hidratación y capacidad de retención que SPI.Palabras clave: aislado de proteína de soja; chitosán degradado; transglutaminasa; estructura secundaria; propiedad

Sodium caseinate was modified by transglutaminase-catalyzed reaction in the presence of oligochitosan of 5 kDa at two different levels, aiming to generate two glycated and crosslinked caseinate products (GC-caseinate I and II) and to clarify their respective structure and property changes. Electrophoretic analysis with aid of protein and saccharide staining confirmed that both GC-caseinate I and II were glycated and crosslinked protein products, while high-performance liquid chromatrography analysis demonstrated that both GC-caseinate I and II contained glucosamine (12.8 and 30.8 g/kg protein, respectively). In comparison with sodium caseinate, GC-caseinate I and II also contained less reactable-NH 2 groups (0.50 and 0.52 versus 0.62 mol/kg protein), more-OH groups in their molecules, but they had more ordered secondary structure than sodium caseinate. In addition, GC-caseinate I and II showed higher water-binding capacity, larger hydrodynamic radius (173.9 and 168.2 versus 145.3 nm), and larger negative zeta-potential (-32.9 and-30.9 versus-27.6 mV) in aqueous dispersions, but they exhibited lower thermal stability (namely, greater mass loss) at temperature higher than 286ºC. Oligochitosan-glycated sodium caseinate at lower and higher extents was observed to be unfavorable and favorable to the in vitro digestibility of GC-caseinate I and II, respectively. It is concluded that application of transglutaminase and the oligochitosan can modify structure and property of sodium caseinate to generate new protein ingredients with good hydration and colloidal stability.