| Pectin describes a family of structural hetropolysaccharides that have common features, but are extremely diverse in their fine structure. Pectins extracted from plants have been used widely as gelling agent, thicker, texturizer in food, pharmacy and cosmetic area. There is growing interest in low methoxyl pectin. However, LMP has to be prepared from HMP by reducing the DM through acid demethoxylation, alkali demethoxylation, or demethoxylating reaction of pectin methyl esterase. These methoxylations are complex and may cause potential depolymerization. An alternative approach for manufacturing LMP is to ’mine’ plant cell walls that are enriched with LMP. Creeping fig (Ficus pumila Linn) seeds and Premna microphylla turcz leaves have been used to prepare a "Liangfen" and "Shenxian tofu", respectively by local Chinese people. However, their making secret have not been explored. Preliminary experiments indicated that both resources contain high amount of pectic polysaccharides. However, extraction, physicochemical and rheological properties of pectin was rarely reported. In this study, pectic polysaccharides were extracted from Creeping fig seeds and Premna microphylla turcz leaves using kinds of extracting agent, then the physicochemical properties and gelling capability of resulting pectin were investigated to explain why "Liangfen" and "Shenxian tofu" would be manufactured in the traditional methods. The pectin isolated from creeping fig seeds was fractionated into two components by ion exchange column, techniques such as X-ray diffraction were used to explain the reason why two fractions have significant different solublities. During investigation, we also pay attention to the effect of dialysis solution on properties of pectin, and degradation of pectin induced by dynamic high pressure microfluidization (DHPM). We found out that low methoxyl pectin tends to absorb metal ions from dialysis solution. After characterizing the extent of degradation of pectin induced by DHPM, the mechanism of degradation was discussed. This technique was also used to produce pectic oligosaccharides (POS), the resulting POS exhibit a notable prebiotic properties. Main conclusions are summarized as follows: 1. Gelling material was extracted from creeping fig seeds using water, ammonium oxalate and hydrochloric acid, respectively. Results showed the main component of three extracts is low methoxyl pectin. The pectin locates in a transparent layer on the surface of seeds, as revealed by an inverted microscope. Hence, explained the feasibility of the squeezing and rubbing method in traditional handcraft. Comparing with the other methods, water-extracted pectin has high galacturonic acid content, viscosity-average molecular weight and intrinsic viscosity but low degree of methoxylation. This pectin forms the major component of WE, together with the high amount of calcium ions present in WE, it suggests the spontaneous gelation may be based on the’egg-box’formation.2. The water-extracted pectin (WEP) from creeping fig seeds can be fractionated into two components (WEP-0.3and WEP-0.4) by ion exchange column. These two fractions showed a notable difference in dissolution behavior, WEP-0.3can be easily dissolved into water while89.5%of WEP-0.4become insoluble after dialysis against running water and distilled water later and freeze-dried. This phenomenon was contradicted with the results of FTIR spectrum where WEP-0.4have lower degree of methoxylation should have better solubility. For WEP-0.4, partial crystal was observed by X-ray diffraction and noodle like-shape was found by environmental scanning electronic microscopy. In the case of WEP-0.3, it’s surface topography was relatively loosely and it has amorphous structure. These results indicated a microgel was formed for WEP-0.4in the process of dialysis. The formation of microgel may due to the adsorption of Ca2+by WEP-0.4, as reflected in a high calcium content in WEP-0.4.3. Premna microphylla turcz leaves (PMTL) have been used for preparing a "Shenxian tofu" by Chinese for a long history. Cell-wall material of PMTL extracted as alcohol insoluble solids (AIS) was analyzed. The AIS recovery accounted for77.82g/100g dried leaves, while the total, insoluble dietary fiber and galacturonic acid content was69.45,56.35and23.94g/100g of the AIS, respectively. A sequential extraction, using water, ammonium oxalate, hydrochloric acid and sodium hydroxide, was used to extract different pectic fractions. Oxalate-soluble pectin (OXSP) was found to be the major pectic fraction (59.48%), which contains high amounts of galacturonic acids (76.15%) with mainly homogalacturonan, and has low degree of methoxylation (14.90%) and high average molecular weight (980.67kDa). All of these characteristics have contributed an excellent gelling capability of OXSP. The results might allow an improved use of PMTL as a resource of dietary fiber and low-methoxyl pectin.4. Pectin sequentially isolated from Premna microphylla turcz leaves were dialyzed against running tap water or deionized water. It was found that dialysis solution has significant impact on appearance, final yield, ash and protein content, and surface topography of pectin. Water soluble pectin, oxalate-soluble pectin and alkali-soluble pectin formed or partial formed gels. The formation of gel would be due to low methoxyl pectin associated with calcium, which absorbed into dialysis tube when dialysis against running taping water. This deduction agrees with that a high amount of calcium and ash content were detected in these samples. The morphology of plant cell wall after each isolation step was observed. The results showed that sequential isolation steps are processes, which gradually release pectin from plant cell wall materials. The most remarkable change of morphology of cell wall material was found when ammonium oxalate were used as extracting agent, indicating ammonium oxalate is suitable for isolation of pectin in Premna microphylla turcz leaves.5. High-methoxyl pectin was degraded by dynamic high pressure microfluidization (DHPM). It was found that apparent viscosity, average molecular weight and particle size of pectin decreased, whereas the amount of reducing sugars increased with increasing DHPM pressure. At the same time, the surface topography of pectin was changed from large flake-like structure to smaller porous chips. The mechanism of DHPM-induced degradation of pectin was also investigated. Fourier transform infrared spectra showed DHPM had no effect on the primary structure of pectin. On the other hand, reducing sugars content increased linearly with decreasing average molecular weight, suggesting the degradation may derive from the rupture of glycosidic bond. The breakdown of glycosidic bond may not only result from intensive mechanical forces but also from acid hydrolysis, which was evidenced in the reduction of degradation when the concentration of H+was lowered. In addition, neither P-elimination nor demethoxylation occurred with DHPM. Based on these results, a model was proposed to illustrate the degradation of pectin induced by DHPM.6. Pectic-oligosaccharides (POS) were prepared from apple pectin by dynamic high-pressure microfluidization. Operating under selected conditions (pectin concentration1.84%, solution temperature63℃, DHPM pressure155MPa and number of cycles6passes),32.92%of the pectin was converted into POS. The resulting POS contains29.56%galacturonic acid and58.53%neutral sugars. The prebiotic properties of POS were then evaluated using a fecal batch culture fermentation. The POS increased the number of Bifidobacteria and Lactobacilli, and produced a higher concentration of acetic, lactic, and propionic acid than their parent pectin. Furthermore, POS decreased the number of Bacteroides and Clostridia while their parent pectin increased them. Moreover, the effects of POS on the growth of these bacteria and production of short-chain fatty acids are comparable to those of the most studied prebiotic, fructooligosaccharide. These results indicated that the POS prepared by DHPM has a potential to be an effective prebiotic. |
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