The impact of rhamnogalacturonan-I side chain monosaccharides on the rheological properties of citrus pectin

• Enzymes were used to modify citrus pectin side chain composition.
• Gel rheological performance changed depending on the side chain composition.
• Gel strength decreased for pectin gels with lower amount of side chains.
• Longer side chains were associated with increased entanglements between pectin molecules.

Citrus peel is the preferred raw material for pectin production, mainly due to its high pectin content but also due to the gelling capabilities. Especially the high galacturonic acid content and the high degree of methyl esterification make it an attractive starting material for further modification. Until now the presence of rhamnogalacturonan-I (RG-I) in commercial pectin has received less attention due to its relatively low abundance. Using a gentle industrial extraction process we discovered a slightly higher composition in neutral sugars of RG-I. In particular, the arabinose concentration in mildly extracted pectin was higher compared to conventionally extracted pectin. The use of enzymes specific for either arabinan or galactan allowed assessing the implications of varying neutral sugar composition on the gelling capabilities of pectin. A comparison between untreated and debranched pectin revealed a significant decrease in both gelling temperature (up to 20 °C) and gel strength (up to 38%), following the specific reduction in neutral sugars concentration. Coil-overlap and entanglement effects were analysed to further understand the impact of RG-I side chains on polymer rheology.

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