Production of low molecular weight pectins via electron beam irradiation and their potential prebiotic functionality

Pectic oligosaccharides, which can be obtained from depolymerisation of pectin, are an emerging family of prebiotics. In this work, pectin extracted from pomelo (Citrus Maxima) peels was used as a starting material. An electron beam (e-beam) was employed to degrade the pectin using the irradiation dosage ranging from 3 to 250 kGy. The irradiated pectins showed a diverse-range of molecular weights (MW), depending on the level of e-beam dosages, i.e. the higher the dosage, the lower the MW. Interestingly, the reduction in MW could be collapsed onto a master curve when expressing the degradation results between the normalised MW and irradiation dosage. The degree of esterification (DE) of pectin, when measured with FTIR, increased with increased e-beam dosage above 50 kGy. A previous study suggested that the increased DE measured by such method may be due to a greater content of radiolytically formed reducing carbonyl groups in the galacturonic residue of pectin. However, when measured explicitly using HPLC method, there was no significantly change in DE of irradiated pectin for e-beam treatment up to 125 kGy. Furthermore, the irradiated pomelo pectins showed a linearly proportional decrease in viscosity to the decrease in the molecular weight. To assess the prebiotic potential of the native and irradiated pomelo pectins, their abilities to promote growth of selected microbial species, including short chain fatty acid (SCFA)-producing bacteria, lactic acid bacteria (LAB), bifidobacteria and a pathogen, were evaluated. All pectin substrates showed the ability to exert growth-promoting effect on various beneficial microbes, but not the pathogen. The high-energy-treated pectin with decreasing molecular weight, i.e. MW = 2 kDa, became more fermentable to a butyric acid-producing Eubacterium maltosivorans strain. Furthermore, the pomelo-derived pectin substrates outperformed inulin or at least elicit the similar effect on stimulating growth of all indicator bacteria. Therefore, the results indicated the promising prebiotic functionality of both native pomelo pectin and e-beam-treated derivatives.