Effect of microbial transglutaminase crosslinking

Authors: Min Yang Ying Shi Qi Liang

Publish Date: 2015/06/17

Volume: 96, Issue: 1, Pages: 39-51

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Abstract

Microbial transglutaminase mTGase crosslinking is a useful method for significantly improving the physical functionality of proteins This study focused on the effect of mTGase modification on the functional properties of yak and cow caseins including solubility emulsifying property water and oil absorption capacity foaming property and stability in the presence of Na+ Ca2+ and Mg2+ The results showed that the crosslinking degree of yak and cow caseins differed at the same mTGase concentration but the change in functional properties of cow and yak caseins was similar After mTGase crosslinking the solubility of caseins decreased while the emulsifying properties increased because of casein polymerization MTGase crosslinking was very effective in improving water and oil absorption properties stability in the presence of Na+ Ca2+ and Mg2+ and foaming activity but did not affect the foam stability of cow acid caseins caseins content of 9422  w/w and yak acid caseins caseins content of 9428 w/w The results could be used as a reference for selecting the proper modification method to improve the predetermined functional properties of caseins according to industrial processing requirementsGood functional properties of proteins are essential characteristics for the production of a wide range of food products Caseins are the main protein in milk and are largely used as ingredients in the food industry To expand the application of caseins transglutaminases TGase crosslinking has been used to enhance their stability and functional properties It was found that the nitrogen solubility of crosslinked sodium caseinate was improved at pH 20 30 and 50 and the emulsifying activity index and stability were improved at pH 50 and 100 Flanagan et al 2003 Lorenzen 2000 reported that the stability and viscosity of emulsions prepared with crosslinked sodium caseinate increased but the foam volume and stability of crosslinked sodium caseinate decreased compared to noncrosslinked sodium caseinate The strength and kinetics of casein gelation sensitivity to heat treatment and syneresis behavior changed after TGase treatment Vasbinder et al 2003 It was also found that the casein gels produced by TGase crosslinking had higher viscoelastic moduli and gel stiffness they formed quickly and exhibited no syneresis even after a long storage time Ardelean et al 2013 Schorsch et al 2000a b Some researches have shown that TGase treatment improved the stability of casein micelles Flanagan et al 2003 Huppertz and de Kruif 2007 Partschefeld et al 2007 Smiddy et al 2006In recent years there has been a concerted effort toward developing yak caseins as highquality ingredients in the food industry This is because the composition of yak milk differs from cow milk It was showed that yak milk has a high concentration of total proteins 462–584 gL−1 and total caseins 402 gL−1 Li et al 2010 The high content of βcasein more than 45 and consequently the lower proportion of αscasein about 40 together with the high content of κcasein 15 in yak milk make it with a good proportion of individual caseins which is similar to the proportion found in human milk and more favorable for infant nutrition Li et al 2010 It also found the high content of minerals and micellar size of yak milk Wang et al 2013 Yang et al 2014b To develop yak caseins for use as good ingredients in the food industry their physicochemical and functional properties must be improvedSome researchers have found that a TGasecatalyzed reaction is influenced by various parameters such as the conformation of proteins the chemical reagents the ionic strength and so on while the neighboring amino acids of lysine residues could influence reactivity of lysine residues toward TGase crosslinking Jaros et al 2006 The amino acid sequence the content of minerals the proportion of yak casein monomers and the size of yak casein micelles are different from those of cow caseins Therefore the effect of microbial transglutaminase mTGase modification on the functional properties of yak caseins should differ from cow caseinsThe objective of this study was to assess the effect of mTGase crosslinking on the functional properties of yak caseins which were compared to cow caseins The finding could provide basic data on the functional properties of mTGasecrosslinked yak caseins and the results can be used as a reference for selecting the proper modification method to improve the predetermined functional properties of yak caseins according to industrial processing requirementsYak and cow acid caseins provided by Gansu hualing Biotechnology company had a caseins content of 9428 and 9422 w/w respectively MTGase 99 maltodextrin 1 enzyme 100 Ug−1 was purchased by Yiming Biological Products Co Ltd Jiangsu China The enzyme was used without any further purificationThe caseins were dissolved in 100 mL distilled water at 5 mgmL−1 by constant mixing at 3000 rpm 40 °C Three samples of casein solution were prepared meanwhile The pH of the solutions was kept at 70 with 1 M NaOH After caseins were completely dissolved they were mixed with mTGase which was preincubated at 37 °C with 30 min at the ratio of 15 Ug−1 caseins The mixtures were incubated at 40 °C for 135 min The TGase reaction was inactivated by heating the sample at 85 °C for 5 min followed by rapid cooling to room temperature in cold running water within 3 min The treated samples were acidified to pH 4–5 with 1 M HCl and then centrifuged TDD5M Changsha Pingfan Instrument Co Ltd Changsha China at 4000×g for 10 min at 20 °C The pellet was freezedried to constant weight Then three batches of crosslinked caseins were achieved which were used to determine the extent of crosslinking individually and mixed together to measure the other propertiesWater and oil absorption capacities of caseins samples were determined according to Matemu et al 2011 Briefly distilled water or oil was added to caseins and mixed by a vortex shaker QL866 Qilinbeier Instrument Manufacturing Co Ltd Jiangsu China at 3000 rpm for 1 min every 10 min for 30 min The contents were allowed to stand at room temperature for 2 h and centrifuged at 3000×g for 30 min Free water or oil was removed carefully The amount of absorbed water or oil was determined by weight difference

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