Individual pectin methylesterase isozymes for pectin modifications to increase emulsion stability
Rivner, Joshua Scott
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Pectin methylesterase (PME), extracted from Valencia pulp, was fractionated into 36 kDa, 27 kDa, and 13 kDa isozymes and isozyme combinations using a series of ion exchange columns. The 36 and 27 kDa isozymes were salt independent while the 13 kDa isozymes lost 50% of activity without salt. The 27 and 13 kDa fractions were unstable to heat at 70 oC for 10 minutes while the 36 kDa fraction retained activity. Partial amino acid sequences were determined using mass spectrometry analysis. The isozymes fractions were used to create charge modified pectin whose molecular weight remained the same as the unmodified control pectin. In all modified pectin samples, GGG/GGE and GG peaks increased in frequency and the EE peaks decreased in frequency compared to the control pectin. The calcium sensitivity test found a linear correlation between G’ and degree of esterification (%DE) (R2= 0.568). A correlation was observed between G’ and GGG/GGE frequencies (R2= 0.776). A smaller correlation was observed between G’ and GG frequencies (R2= 0.421). A correlation was observed between GGG/GGE frequencies and ζ-potential (R2=0.693). These tests show that both %DE and the distribution of DE play a role in determining the functionality of the pectins. Larger blocks of continuous charge affected the functionality of the pectin more than small blocks of charge. Pectins charge modified by separated pectin methelesterase (PME) isozymes were used to form complexes with whey protein to test their ability to stabilize an oil-in-water emulsion. No differences in emulsion activity (EA) measurements were observed between emulsions formulated with modified pectin samples. Initial EA stability was higher in emulsions with pectin and protein versus just pectin or just protein. Back scattering (BS) profiles of the emulsions showed the samples were subject to creaming, phase separation, and coalescence or flocculation.
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