In between, under specific conditions, the polymer-polymer interaction can precisely compensate the polymer-water interaction, which referred as theta condition. Under theta condition, the chain conformation is defined solely by bond angles and short-range interactions given by the hindrances to rotation about bonds and polymer coil dimensions [ 2 ].
Second virial coefficient A 2 , which describes the contribution of the pair-wise potential to the pressure of the gas, could reflect the polymer-water interaction. Good solvent, poor solvent, and theta condition can be indicated when the second virial coefficient is above, below, or equal to zero, respectively. In a real experiment, the second virial coefficient of the polysaccharides in aqueous solution can be determined by static light scattering using Zimm plot Figure 1 based on the Eqs.
Zimm plot of polysaccharide from seed of Artemisia sphaerocephala Krasch determined by SLS solvent, 0. Adopted from Guo et al. For example, A 2 of xyloglucans from flaxseed kernel cell wall was reported as 3.
This is because mild alkaline could break down the intermolecular hydrogen bonding, thus eliminating the aggregates in aqueous solution. The solubility of polysaccharides is determined by their molecular structures. Any structural feature that hinders the intermolecular association leads to higher solubility, such as branching structure, charged group carboxylate group, sulfate, or phosphate groups ; on the opposite, structural characters that promote the intermolecular association result in a poor solubility, such as linear chain, large molecular weight, and other regular structural characters.
Polysaccharides are polydisperse in molecular weight. Therefore the molecular weight of polysaccharides is mostly described in a statistic way, such as number average molecular weight Mn , weight average molecular weight Mw , and zeta average molecular weight Mz , as shown in the below equations Eqs.
Here Ci refers to the concentration of molecules that having molecular weight of Mi. The molecular distribution of polysaccharides can be described by the polydispersity index Eq. Most natural occurring polysaccharides demonstrated high PDI value above 2 :. The molecular weight and molecular weight distribution play a critical role for the solubility of polysaccharides. High molecular weight molecules normally have a large excluded volume Eq. Almost all carbohydrate polymers with degrees of polymerization DP less than 20 are soluble in water [ 7 ].
Solubility decreases with the increase of molecular weight. For example, the amylose and amylopectin in starch are reluctant to dissolve in cold water due to high molecular weight, while maltodextrin starch after chain cleavage by acid or enzyme with the DP value less than 20 demonstrates very good solubility in cold water.
The dissolution rate of polysaccharide samples is also highly affected by the molecular weight and molecular weight distribution. Higher molecular weight usually leads to lower dissolution rate, as disentanglement from the particle surface and subsequent diffusion to the bulk solution of large molecules take a longer time compared to that of small molecules.
It has also been reported that samples with high polydispersity dissolved about twice as fast as monodisperse ones of the same Mn [ 1 ]:. Charged polysaccharides are referred to polysaccharides that carry charged groups in the molecules, which include both negatively acidic polysaccharides and positively charged polysaccharides. The charged groups help with the solubility of polysaccharides, which is achieved by 1 increasing the molecular affinity to water and 2 preventing the intermolecular association due to the electrostatic effects posed by the charged group.
Acidic polysaccharides are polysaccharides containing carboxyl groups e. The acidic group may be free or as a simple salt with sodium, potassium, calcium, or ammonium or naturally esterified with methanol. Therefore, most of the natural occurring pectin is readily soluble in water due to the charged group, although high in molecular weight. It also should be noticed that adding salt or reducing pH value could shield the charged effect, which leads to gelation under some circumstances.
For example, high methyl ester pectin gel at pH 3. Low methyl ester pectin can react with calcium ions to form gel, even under relative high pH environment. Therefore, when dissolving the pectin into water, it is essential to avoid the gelling condition; similar to other hydrocolloids, the dissolution usually needs high shearing mixing [ 8 ]. Pectic polysaccharides from American ginseng. Adpated from Guo, et al.
Adopted from Cui et al. As one typical positively charged polysaccharide Figure 4 , chitosan is derived from the deacetylation of chitin. To our knowledge, this is the first report about digestibility, endocrine responses and metabolic responses in rats fed modified water-soluble starches. The findings may be useful in the development of liquid nutritional supplements.
At 5 wk of age, all of the rats were randomly divided into five groups. The four carbohydrate-fed groups contained nine rats in each group. A fifth group contained seven rats. The rats were individually housed in wire-bottomed cages.
The two modified soluble starches were supplied by Dr. At 5 weeks of age food was withheld overnight from all five groups of rats. At the start of the experiment, all rats were weighed. Seven rats from group 5 were killed by decapitation at the start of the feeding period between and h.
Liver, heart and epididymal fat pad weights were recorded. The body weights after exsanguination were also recorded. The contents of the gastrointestinal tracts were removed as much as possible. Each of the remaining four groups of rats were fed one of the four experimental diets for a 4-wk period with free access to the diets and water.
Body weight and food consumption were recorded weekly. In the last week of feeding, the fecal marker, 2. Food consumption was recorded daily and feces were collected daily for 6 d. After 4 wk of feeding 9 wk of age , all the rats were weighed and killed between and h by gassing with CO 2. Blood was collected by cardiac puncture. Because all 36 rats could not be killed in 1 d, 16 rats the first 4 rats in each group were killed on 1 d; the remaining 20 rats were killed on the following day.
Blood, tissues and carcasses were collected and treated as described above. The total food consumption over the 4-wk feeding period was calculated as the sum of the weekly food consumption. The total body weight gain was calculated as the difference between the final live body weight and the initial body weight. The precipitated starch samples were resuspended in water Hassid and Abraham The released glucose was determined enzymatically by the addition of 3.
Louis, MO. The fecal starch contents were calculated as glucose units. Fecal samples in which chromium excretion was at a constant level were used to calculate starch recovery. The results were calculated on a dry weight basis. Serum glucose was assayed with the glucose hexokinase reagent kit Sigma Chemical. Glucose was assayed by using the coupled enzymatic reactions catalyzed by hexokinase and bacterial glucosephosphate dehydrogenase and following the change in absorption of NADH at nm.
Serum triglycerides were determined with the triglyceride UV reagent kit Sigma. Triglycerides were enzymatically hydrolyzed to glycerol and free fatty acids by lipase EC 3. Serum free fatty acid concentration was analyzed by the enzymatic method described by Shimizu et al.
The absorbance of NADH was followed at nm. Serum total protein was assayed by using biuret reagent White et al. Determination of the composition of liver was not originally planned, but was analyzed after differences in liver weight among groups were noticed. Each liver was cut into small pieces and placed into a homogenizing tube followed by addition of 15 mL water. The liver was homogenized with the homogenizing tube in an ice bath. The water content of liver was calculated as fresh liver weight minus lyophilized liver weight.
The liver protein was assayed by using biuret reagent White et al. Because differences in liver weights were unexpected, the liver samples were not quickly frozen. Therefore, the glycogen contents of the livers were not assayed. The calculations of total liver composition were based on fresh liver weight.
Each frozen carcass, minus liver, was chopped into small pieces and homogenized in a 3. Water content of each carcass was calculated as the fresh carcass weight minus the lyophilized carcass weight. Total body water was calculated as water content of carcass plus water content of liver. Total body lipid was calculated as carcass lipid plus liver lipid. Then the digested samples were diluted and the resultant nitrogen was determined as NH 4 2 SO 4 colorimetrically at nm Chaney and Marbach The protein factor of 6.
The total body protein was calculated as carcass protein plus liver protein. The weight of the rat without its gastrointestinal contents was the weight used in the calculations of total body composition. Samples of the lyophilized diets and fecal samples were pressed into pellets that weighed between 1. The energy content of the diets and each fecal sample was determined by using the Parr adiabatic oxygen bomb calorimeter Parr Instrument, Moline, IL.
For body energy content determination, the same procedure was employed. Body energy gain was calculated as the difference between the final body energy content of each experimental rat and the average carcass energy content of the group killed at the start of the feeding period. Energy efficiency was calculated as the percentage of body energy gained divided by energy consumption during the feeding period. Data are presented as means. No significant differences in body weight and total body weight gain among all four dietary groups were observed during the 4-wk feeding period Table 2.
However, the total food consumption was much higher in the modified potato starch—fed group and the amylomaize-7 starch—fed group compared with the commercial cornstarch—fed and dextrose-fed groups. In the modified potato starch—fed group, food consumption was also significantly higher than in the amylomaize-7 starch—fed group Table 2. Body weight, body weight gain, food consumption and dietary energy consumption in rats fed control or modified carbohydrates The rats were fed experimental and control diets with free access to food from 5 to 9 wk of age as outlined in Materials and Methods.
The recovery of chromium in feces was calculated for 5 d during the last week of feeding. After 4 d of ingestion, fecal chromium recovery was stable Fig. At this point, the digestibilities of the four experimental carbohydrates were calculated and are shown in Table 3. The digestibility of the modified potato starch was significantly lower than that of the two control carbohydrates and the modified amylomaize-7 starch. Table 3 also shows the percentage of digestible energy of experimental and control diets.
The percentage of digestible energy of the two modified starch diets was significantly lower than that of the two control diets. Additionally, the percentage of digestible energy of the modified potato starch diet was the lowest of the diets studied. During the 4-wk feeding period, high bulk fecal output was observed in the two modified starch—fed groups, especially in the modified potato starch—fed group. At the time of dissection, we noted that the colons of both experimental starch-fed groups were extended with gas and undigested food even after overnight food deprivation.
The modified potato starch—fed group had extremely extended colons filled with much gas. The percentage of consumed chromium recovered in feces of rats fed control or modified carbohydrates for 4 wk. Values are the means of 5—9 samples per treatment.
The rats were freely fed the diets from 5 to 9 wk of age. At 8 wk, the fecal marker, 2. Feces were collected daily for 5 d during the last week of feeding. Fecal chromium content was determined as described as in Materials and Methods. The percentage of consumed chromium recovered in feces was calculated for each day. For the commercial cornstarch—fed, dextrose-fed, modified potato starch—fed, and modified amylomaize-7 starch—fed groups, the mean square of the error term MSE from ANOVA is Digestibility of experimental carbohydrates and dietary energy in rats fed control or modified carbohydrates Total body water did not differ among the four dietary groups Table 4 , but both the modified potato starch—fed and the amylomaize-7 starch—fed groups had significantly higher body water as a proportion of body weight than the two control groups.
Additionally, the percentage of body water in the modified potato starch group was significantly higher than in the amylomaize-7 starch group. Total body protein in the modified potato starch—fed group was significantly lower than in the dextrose-fed and the amylomaize-7 starch—fed groups, but did not differ from that in the commercial cornstarch—fed group. Both the commercial cornstarch—fed and the modified potato starch—fed groups had significantly lower body protein as a proportion of body weight than the dextrose-fed and the amylomaize-7 starch—fed groups.
Total body lipids and percentage of body lipids in the modified potato starch—fed group were significantly lower than those in the two control groups and were not different than those in the modified amylomaize-7 starch—fed group.
Body composition and energy in rats fed control or modified carbohydrates The average total body energy content of the group studied at base line was Cellulose and starch are different not only in overall structure and macroscopic properties. From a biochemical point of view they behave so differently that it is difficult to believe that they are both polymers of the same monosaccharide.
Enzymes which are capable of hydrolyzing starch will not touch cellulose, and vice versa. If there were not a sharp biochemical distinction between the two, the need for a bit more energy by the plant might result in destruction of cell walls or other necessary structural components.
Depending on molecular weight of amylose and because of its helical structure formed by two macromolecules makes it partly soluble in water. Heating amylose solution leads to formation of colloidal suspension of soluble fraction and remining insoluble higher molecular weight fraction of amylose does not dissolve.
On cooling this suspension, certain portion of polysaccharide precipitates. This is because of the glycosidic linkages between these glucose molecules. Reference Cuevas et al. Structural differences between hot-water-soluble and hot-water-insoluble fractions of starch in waxy rice.
Carbohydrate Polymers 81 3 Sign up to join this community. The best answers are voted up and rise to the top.
Stack Overflow for Teams — Collaborate and share knowledge with a private group. Create a free Team What is Teams? Learn more.
0コメント