The researchers, from CSIRO Food and Nutritional Sciences, Australia, said that by using caffeic acid – a simple plant-derived phenolic compound – to form a natural cross-linking reaction, they were able to modify the material properties of gelatin.
“There is a growing need for the development of natural cross-linking agents that are non-toxic, non-specific, inexpensive and readily available,” said Shantha Lakshmi Kosaraju, from CSIRO.
“The results obtained in this study demonstrated the huge potential for exploiting the natural cross-linking process of proteins to obtain tailored properties for various applications,” said the researchers.
They added that by systematically varying reaction parameters, processors can control the cross-linking process of gelatin – thus altering gel strengths, setting and melting temperatures.
Kosaraj and her colleagues said that the process has great potential for developing natural cross-linking methods, to create new materials for a wide range of food based applications.
Chemical v.s. Natural
The authors said that the modification of proteins using chemical cross-linking mechanisms is used extensively for a number of biomedical applications. But, for food applications, the use of chemical cross-linking is limited and is not recommended due to potential issues with toxicity.
“Although enzymatic cross-linking has been used widely for food applications, there are many inherent disadvantages,” said the researchers.
However, there is now a trend towards natural cross-linking methods using green chemistry, said the authors.
They added that studies on the cross-linking of proteins using simple phenolic compounds derived from plant sources have been carried out in the past. However, they said that a lack of control over current natural cross-linking mechanisms hinder the future development of suitable food materials with desired properties.
They noted that there is a lack of systematic data to show the changes in gel properties under various conditions during irreversible cross-linking reactions using oxidised polyphenols.
The new study investigated the mechanisms of natural cross-linking of gelatin using caffeic acid.
The researchers tested the properties of cross-linked gels under differing conditions and at various stages of reactions in order to gain an understanding of how such changes affect the final properties of the gel.
Modified gels
Firstly, a cross-linking reaction was initiated by the oxidation of caffeic acid at pH 8 for 30 min. The researchers, however said that visual observations indicated there was no significant change in the viscosity of the reaction mixture with time – although there were changes to the setting and melting temperatures, which indicated some cross-linking.
An increase to pH 9 resulted in a steadily progressing reaction.
“There was gelation observed after 20 min of reaction at pH 9, and these conditions were optimised by following the changes in viscosity development with time,” said Kosaraju and colleagues.
“The formation of a pourable gel at pH 9/60 °C was observed for the first time in our work,” they added.
Changes in storage modulus, and setting temperatures were observed in cross-linked gelatins when compared to the properties of un-modified gelatin.
The authors also reported changes in melting temperatures, which increased with reaction time and when the cross-linking reaction time – they noted that after a 20 minute reaction at pH 9, the gel formed was stable at temperatures of up to 90°C.
Kosaraju and co workers added that gel strength was also found to steadily raise with increasing reaction time. They said that the strength of the gel cross-linked for 20 min was twice that of the uncross-linked gelatin gel.
“The formation of a thermo-irreversible gelatin gel after the reaction at 60 °C supported the formation of chemically cross-linked species,” they said.
Source: Food Research International
Volume 43, Issue 10, Pages 2385-2389, doi: 10.1016/j.foodres.2010.09.008
“Naturally cross-linked gelatin gels with modified material properties”
Authors: S.L. Kosaraju, A. Puvanenthiran, P. Lillford