Role of pectic polysaccharides in structural integrity of apple cell wall material

Texture modulating properties of aqueous dispersions of apple cell wall material differed from those of tomato or kiwifruit, particularly under high shear. It was previously hypothesized that this may be due to the fact that the apple cell wall showed less in vivo solubilization of pectic polysaccharides during ripening compared to tomato or kiwifruit. However, in vitro solubilization of the pectic polysaccharide content of apple CWM by endo-polygalacturonase and/or extraction with 0.05 M sodium carbonate, did not affect the loss in wall integrity shown by tomato or kiwifruit CWMs under shear. In addition, the pectin-depleted residue after Na₂CO₃ extraction possessed better water retaining and viscosity generating properties than the original cell wall material. Following treatment of apple CWM with cellulase, the viscosity of suspensions decreased, emphasising the role that the cellulose–hemicellulose network plays in the water-retaining capacity of the cell wall. Residue from CWM after cellulase treatment consisted of ∼85% pectic polysaccharides. Surprisingly, the integrity of these “cellulose-free” walls was maintained after shear. It is concluded that differences in structural properties of the CWMs of apple compared to kiwifruit or tomato are not simply related to pectin solubilization but to a fundamental difference in the architecture of the apple cell wall.     

Impact of accessibility and chemical composition on cell wall polysaccharide degradability of maize and lucerne stems

Although lignification of forages is generally accepted as limiting cell wall degradability, prediction of degradation from cell wall composition is often difficult when forages are of similar maturity. It has been proposed that rumen microbe accessibility to potentially degradable cell walls is limited by the presence of non‐disrupted cells in forage particles with lignified middle lamella/primary walls acting as barriers to microbial access. We tested this accessibility hypothesis by evaluating the impact of reducing particle size of maize and lucerne stems to the level of individual cells by ball‐milling, in order to eliminate accessibility as a limiting factor. While cell wall concentration and composition were not influenced by ball‐milling compared with grinding to pass a 1 mm screen in a cyclone‐type mill, degradability of total cell wall polysaccharides was dramatically increased. However, only those polysaccharides (cellulose and xylan) which are most abundant in cell types with lignified middle lamella/primary and secondary walls increased in degradability owing to particle size reduction. Degradability of pectins, which are abundant in non‐lignified tissues in lucerne, did not respond to ball‐milling. Contrary to our expectations, ball‐milled forages showed fewer correlations for cell wall composition with degradability than observed for the larger‐particle‐size grinding treatment. Many components of the cell wall were correlated with polysaccharide degradation for the cyclone‐ground samples; however, the results were inconsistent as to which cell wall components were correlated with degradation among and within forages. This observation does not clarify the role of cell wall chemical structure as a limiting agent to wall degradation in the absence of accessibility barriers, but this study does provide support for the hypothesis that lignified middle lamella/primary walls act as barriers to microbial access for degradation. © 2000 Society of Chemical Industry     

Chemical composition and ruminal degradability of lucerne (Medicago sativa) products

A study was conducted to determine the chemical composition and in situ nutrient ruminal degradability of three lucerne products. These were dehydrated pellets, sun‐cured pellets and cubes. Results of the chemical analysis showed that sun‐cured pellets had the highest (P < 0.05) neutral and acid detergent fibre as well as total carbohydrate levels, followed by cubes and dehydrated pellets respectively. Crude protein (CP) content was highest (P < 0.05) for dehydrated pellets (204.3 g kg^?1), intermediate for sun‐cured pellets (160.0 g kg^?1) and lowest for cubes (153.2 g kg^?1). Intermediately degradable CP (buffer‐insoluble CP minus neutral detergent‐insoluble CP) was the main protein fraction in the three products and was higher (P < 0.05) in cubes than in dehydrated and sun‐cured pellets. Estimated net energy of lactation was highest (P < 0.05) for dehydrated pellets (5.9 MJ kg^?1), intermediate for cubes (5.23 MJ kg^?1) and lowest (P < 0.05) for sun‐cured pellets (5.15 MJ kg^?1). Results of the in situ experiment indicated that dehydrated pellets had higher (P < 0.05) ruminal protein degradability than sun‐cured pellets and cubes. The estimated ruminal escape protein values for dehydrated pellets, sun‐cured pellets and cubes were 361, 420 and 498 g kg^?1 CP respectively. It was concluded that differences in chemical composition and ruminal degradability among the three lucerne products were mainly due to differences in stage of maturity. It was also concluded that the dehydration process failed to increase the ruminal escape protein value of dehydrated pellets relative to sun‐cured pellets and cubes. © 2001 Society of Chemical Industry     

Ensiling characteristics and ruminal degradation of Italian ryegrass and lucerne silages treated with cell wall-degrading enzymes

Two experiments were carried out to investigate the effect of added cell wall-degrading enzymes at ensiling on the fermentation and in situ degradation of grass and legume silages. Primary growths of Italian ryegrass (Lolium multiflorum Lam) and lucerne (Medicago sativa L) were wilted and ensiled in laboratory-scale silos with or without enzymes. Silages were opened at 2, 5, 15 and 45 days after storage; the fermentation quality and the contents of cell wall components (NDF, ADF, ADL) were determined. The 45 day silages were subjected to in situ incubation experiments, and the kinetics of DM and NDF degradation was estimated. The enzyme treatment enhanced the lactic acid production (P < 0.01) and reduced the pH value (P < 0.01) of both Italian ryegrass and lucerne silages. The contents of cell wall components, however, were not affected by enzymes, except for NDF of Italian ryegrass silage. The in situ incubation experiments revealed that added enzymes increased the rapidly degradable DM (P < 0.01) and appeared to decrease the rate of degradation of DM and NDF of Italian ryegrass silage. The rapidly degradable DM was not altered when lucerne was treated, but the rate of degradation of NDF was significantly reduced (P < 0.05). These results suggest that although added cell wall-degrading enzymes could improve the preservation of grass and legume silages, the effects on ruminal degradation may be different according to the herbage treated. Enzymatic hydrolysis during ensilage may be restricted to easily digestible cell walls, leaving relatively less digestible components that would be retained in treated silages. © 1999 Society of Chemical Industry     

Rumen degradation of cell wall polysaccharides in untreated and alkali-treated straws and cereal brans

Rumen degradation of cell wall polysaccharide constituents using the in sacco technique was studied for untreated cereal brans (oats, wheat and barley) and nine technically alkali-treated batches of barley straw. The alkali treatment included four ammonia treatments, two dry sodium hydroxide treatments and three wet sodium hydroxide treatments. On degradation of the cell wall polysaccharides, their main constituents, xylose and glucose, were released at about the same rate for the ammonia treatments and the dry sodium hydroxide treatments. For the wet sodium hydroxide treatments the degradation of the xylose residues was faster than the liberation of the glucose residues. For all treatments the liberation of the arabinose residues was faster than that of the xylose and glucose residues. The reason for the increased digestibility of the cell wall polysaccharides is suggested to be the breaking of ester and hydrogen bonds and the breaking of alkali-labile linkages in lignin, as well as changes in the surface layer of the straw. For the wet sodium hydroxide treatments the larger amount of water present during the alkali treatment processes is suggested to increase the diffusion of the alkali into the straw and to translocate a part of the hemicellulose. On the degradation of wheat and barley bran the liberation of xylose residues was fast whereas xylose and arabinose residues in oat bran were slowly liberated.     

Degradation of cell wall material of apple and wheat bran by human faecal bacteria in vitro

The effect of the structures of plant cell walls and their component polymers on the degradability of dietary fibre by bacteria of the human colon was investigated by inoculating culture media containing cell wall materials of apple and wheat bran with slurries of human faeces which were then incubated for periods of up to 72 h. In the apple substrates the amounts of pectic polysaccharides were extensively depleted after 12 h, and after 24 h over 90% of the initial carbohydrate had been degraded. Material which remained after incubation was probably comprised of highly branched fragments of rhamnogalacturonans, cross-linked by phenolics and proteins, highly branched fragments of cross-linked xyloglucans, and degraded cellulose. In wheat bran the aleurone layer was preferentially degraded, but the glucuronoarabinoxylans, which were cross-linked by phenolic groups, and the lignified outer layers of the bran were very resistant to attack. Bacteria adhered mainly to the broken or damaged surfaces of the plant cell walls, and in the more resistant tissues only penetrated the intercellular regions.     

1-甲基环丙烯对硬溶质型桃果实细胞壁多糖降解特性的影响

以硬溶质型桃"晚湖景"为试材,20℃下用1μL/L 1-甲基环丙烯(1-MCP)密闭处理24h,研究1-MCP处理对细胞壁降解过程中多糖组分变化、单糖解离特性以及细胞壁多糖降解相关酶的影响。结果表明:1-MCP处理可以明显抑制硬溶质型桃果实硬度的下降,降低乙烯释放量。1-MCP处理的硬溶质型桃果实中CDTA-2、Na2CO3、KOH和CWM-残渣组分在贮藏过程中下降速率都明显低于未处理果。1-MCP处理能延缓CDTA溶性果胶多糖的解离。同时还抑制了Na2CO3溶性果胶多糖中半乳糖醛酸和鼠李糖构成的主链和阿拉伯糖、半乳糖支链的降解,对半纤维素和纤维素多糖成分降解有一定程度的抑制作用。1-MCP处理可能通过抑制参与细胞壁多糖降解相关酶的活性,从而抑制硬溶质型桃果实细胞壁多糖降解及单糖解离,达到延缓果实软化的目的。     

Ethephon‐induced fractional changes of pectic polysaccharides in developing cape gooseberry (Physalis peruviana L) fruits

Pectic polysaccharides extracted from fruit tissue of cape gooseberry (Physalis peruviana L) at different maturity levels were fractionated and analyzed for galacturonic acid backbone molecules. Preharvest spray of the fruits at 7 days old with ethephon resulted in a higher accumulation of water‐soluble and oxalate‐soluble pectic fractions than non‐treated fruits, while this treatment effectively enhanced the polygalacturonase enzyme activity necessary for maintenance of pectin degradation. Treatment with ethephon not only enhanced the solubilization rate but also resulted in a net increase in total pectic polymer content in developing cape gooseberry fruits. Copyright © 2005 Society of Chemical Industry     

微生物的天然多糖及其组成结构

微生物是一种能生产多糖的可再生资源，发酵工业己经提供了一部分具有独特性质可用于食品工业或其他工业的新产品。一部分微生物多糖是由一种单糖单位组成的同多糖。它们之中有许多是仅包含D-毗喃葡萄糖残基的葡聚糖。另外，也可以是含有两个或更多单糖的杂多糖。随着对多糖的使用的不断增加，人们也不断开发出微生物来源的或是用化学方法合成的多糖，满足人们的需要。     

碱法破壁-酶法提取葡萄酒废酵母细胞壁多糖的工艺研究

以工业发酵产生的葡萄酒废酵母泥为材料,过筛法除去葡萄果皮、果籽等杂质后,以细胞破壁液蛋白质含量、多糖提取率为评价指标,通过单因素试验和正交试验对碱法破壁-酶法提取细胞壁多糖工艺进行优化,以期提高多糖提取率。结果表明,最佳工艺条件为细胞破壁碱（KOH）处理温度为60 ℃,碱（KOH）质量浓度为70 g/L,处理时间为1.5 h,80 kHz超声辅助;酶法提取多糖最佳工艺为酶作用温度50 ℃,酶解时间1.5 h,中性蛋白酶添加量0.3%,初始pH值7.0。在此优化条件下,葡萄酒废酵母多糖提取率为21.08%。     

酵母细胞壁多糖分子量分布和结构的初步分析

以啤酒酵母细胞壁多糖为研究对象,比较了Sevage法和三氯乙酸（TCA）法脱蛋白效果,利用凝胶渗透色谱法（GPC）测定了细胞壁多糖的分子量分布,用葡聚糖凝胶G-100对多糖进行了纯化,最后用红外光谱法分析了多糖组分D的结构,结果表明:Sevage法脱蛋白效果较好,GPC测定结果得出酵母细胞壁多糖有5个组分,其重均分子量为1.31745×105、7.0863×104、3.6988×104、1.8277×104、8.342×103。红外光谱分析得出多糖组分D在890.51cm-1和808.48cm-1有特征吸收,为β-D-吡喃型结构,在844cm-1处没有吸收峰,不含有或含有少量的α-型糖苷键。      

碱不溶性酵母胞壁多糖苯酚-硫酸测定法的研究

为了测定碱不溶性酵母胞壁多糖含量,采用硫酸溶液水解碱不溶性酵母胞壁多糖,苯酚-硫酸法测定水解液的糖含量。通过单因素和正交实验对硫酸溶液水解碱不溶性酵母胞壁多糖的条件进行了优化,优化后的水解条件为:称取碱不溶性酵母胞壁多糖10mg,加入3mol/L H2SO4溶液20m L置于100℃水浴中水解90min。水解液定容至250m L,测定其糖含量。该方法的精密度RSD为0.30%,稳定性RSD为0.67%,重现性RSD为0.29%,样品的平均加标回收率为99.87%,RSD为1.16%,是测定碱不溶性酵母胞壁多糖含量的有效方法。      

Evaluation of models to describe ruminal degradation kinetics from in situ ruminal incubation of whole soybeans

Different mathematical models were evaluated as candidates to describe ruminal dry matter (DM) and crude protein (CP) degradation kinetics of raw and roasted whole soybeans from data obtained using the in situ polyester bag technique. Three models were used: segmented with up to 3 straight lines (model I), negative exponential (model II), and rational function or inverse polynomial (linear over linear; model III). A fourth, a generalized sigmoidal model, was also considered but the data did not exhibit sigmoidicity, so it was dropped from the analysis. Lagged and nonlagged versions of each model were fitted to the DM and CP disappearance curves of 6 different feeds (2 cultivars of raw or differently heat-processed whole soybean). The comparison between lagged and nonlagged versions of each model, based on statistical and behavior characteristics, showed for all models that the discrete lag parameter did not significantly improve the fit to ruminal DM and CP disappearance curves. The comparison between models (using nonlagged equations) showed that models I and II gave better goodness-of-fit than model III. Based on biological characteristics, models II and III underestimated the undegradable DM and CP fractions, but there was no significant difference between models for extent of degradation.     

Polyamines and cell wall organization in Saccharomyces cerevisiae.

Cells of Saccharomyces cerevisiae 179-5, an ornithine decarboxylase mutant (spe-1), showed several ultrastructural abnormalities when cultivated in the absence of polyamines. Besides the appearance of microvacuole-like spaces in the cytoplasm and of deformed nuclei, the most important alterations seemed to be located in the cell wall, which was thicker and of heterogeneous texture, and in the cell membrane, of irregular contour. These modifications could not be evoked by general stress conditions elicited by lack of nutrients. The relative levels of cell wall polysaccharides were altered in polyamine-deprived organisms, giving an envelope with increased mannan and decreased glucan content; this cell wall was incompletely attacked by the lytic enzyme zymolyase. Polyamine depletion led also to some abnormalities in the budding pattern. The above observations suggest the involvement of polyamines in the correct structure and organization of the yeast cell.     

Subacute ruminal acidosis challenge changed in situ degradability of feedstuffs in dairy goats

This study investigated the effects of wheat-induced subacute ruminal acidosis (SARA) on rumen bacterial populations and in situ degradabilities of NDF, starch, and crude protein of feeds. Four multiparous dairy goats (BW = 60 ± 3.3 kg) fitted with ruminal cannulas were assigned to a 2 × 2 crossover design (28-d treatment periods separated by a 7-d washout interval). The treatment diets consisted of 2 levels of cracked wheat: 0 (control, corn based concentrate) and 35% (diet-induced SARA, wheat-based concentrate), with a constant forage- (45% alfalfa hay and 5% corn silage of DM) to-concentrate (50% of DM) ratio. Results indicate that diets with a 35% wheat decreased ruminal pH (6.21 vs. 5.98) and increased the duration (1.13 vs. 4.72 h/d) and area (0.12 vs. 0.78 pH × h/d) of ruminal pH below 5.6 and induced SARA. The SARA increased ruminal total volatile fatty acid concentration, from 105.0 to 123.8 mM, and decreased the acetate molar proportion (62.8 vs. 56.6 mol/100 mol) and the acetate-to-propionate ratio (3.5 vs. 2.8). Compared with the control group, SARA decreases the relative abundance of Fibrobacter succinogenes (−59.3%) and Ruminococcus flavefaciens (−68.4%), whereas it increased Succinimonas amylolytica (198.1%) and Ruminobacter amylophilus (125.2%). The SARA decreased 24- and 48-h dry matter (DM) and neutral detergent fiber (NDF) degradabilities of corn silage. The 48-h degradabilities of DM (51.0 vs. 48.2%) and NDF (40.3 vs. 36.0%) in alfalfa hay were not affected by SARA, but the SARA tended to reduce the 24-h DM (49.6 vs. 46.3%) and NDF (37.8 vs. 33.2%) degradabilities. The effective ruminal degradabilities of DM and NDF in alfalfa hay and corn silage were reduced during SARA. In situ degradability parameters of DM and starch of wheat were not affected by SARA, but starch degradability of corn (9.5 vs. 13.3%/h) increased. The SARA reduced in situ 12-h degradabilities of DM and crude protein of soybean meal and extruded soybean without affecting the degradabilities of the other protein supplements (corn gluten meal, cottonseed meal, corn dried distillers grains with solubles, rapeseed meal, and wheat germ meal). These results indicated that the cracked wheat-induced SARA reduced the degradation of NDF in roughages and that of protein in soybean meal (−19.8%) and extruded soy (−18.9%) and increased the starch degradability in corn, due to the increased amylolytic bacteria and decreased cellulolytic bacteria counts in the rumen.     

Interactions between cell wall polysaccharides and polyphenols

In plant-based food systems such as fruits, vegetables, and cereals, cell wall polysaccharides and polyphenols co-exist and commonly interact during processing and digestion. The noncovalent interactions between cell wall polysaccharides and polyphenols may greatly influence the physicochemical and nutritional properties of foods. The affinity of cell wall polysaccharides with polyphenols depends on both endogenous and exogenous factors. The endogenous factors include the structures, compositions, and concentrations of both polysaccharides and polyphenols, and the exogenous factors are the environmental conditions such as pH, temperature, ionic strength, and the presence of other components (e.g., protein). Diverse methods used to directly characterize the interactions include NMR spectroscopy, size-exclusion chromatography, confocal microscopy, isothermal titration calorimetry, molecular dynamics simulation, and so on. The un-bound polyphenols are quantified by liquid chromatography or spectrophotometry after dialysis or centrifugation. The adsorption of polyphenols by polysaccharides is mostly driven by hydrophobic interactions and hydrogen bonding, and can be described by various isothermal models such as Langmuir and Freundlich equations. Quality attributes of various food and beverage products (e.g., wine) can be significantly affected by polysaccharide–polyphenol interactions. Nutritionally, the interactions play an important role in the digestive tract of humans for the metabolism of both polyphenols and polysaccharides.     

Effect of Barley Supplement on Microbial Fibrolytic Enzyme Activities and Cell Wall Degradation Rate in the Rumen

Three ruminally cannulated dry cows were used in a Latin square design to investigate the relationship between microbial fibrolytic enzyme activities and in sacco cell wall degradation of two gramineous hays, in which cell wall content ranged from 510 g kg⁻¹ DM for the regrowth to 687 g kg⁻¹ DM for the late harvested hay. Animals were fed twice daily a diet consisting of wheat straw, cocksfoot hay and ground barley in the ratios 10: 90: 0 (w/w), 10: 60: 30 (w/w) and 10: 30: 60 (w/w). For each diet and each hay, the in sacco degradation of cell wall polysaccharides and phenolic acids was determined. After 2 h and 23 h incubation time in the rumen, pH was measured in the bags, and fibrolytic activities (xylanase, avicelase, β-glycosidases) of the microbial population colonising hays in sacco were measured. Supplementation above 30% barley decreased the degradation rate of the cell wall polysaccharides, concomitantly with a decrease in polysaccharidase activities. The decrease in degradation rate was more marked for the regrowth than for the late harvested hay, for hemicelluloses than for cellulose and for ferulic than for p -coumaric acid. These differences did not appear to be related to microbial activities, which were similar between hays and between polysaccharidases, but rather to differences in accessibility of cell wall components to microbial enzymes, related to the composition of the forage and the cell wall architecture.     

Mango ripening: changes in cell wall constituents in relation to textural softening

Ripening of mango (Mangifera indica L., cv. Alphonso) fruit is characterized by a series of biochemical changes resulting in gradual textural softening. From unripe to ripe stage, the starch content came down from 18% to 0.1%; pectin from 1.9% to 0.5%; cellulose from 2% to 0.9% and hemicelluloses from 0.8% to 0.2%. Concomitantly, the total soluble solids increased from 7% to 20%, total soluble sugars from 1% to 15% and pH increased from 2.8 to 5.1. The increase in activity of several of the carbohydrate‐degrading enzymes, which resulted in solubilization of the various polysaccharide fractions, correlated with fruit‐softening phenomenon. Efficient distribution of ¹⁴C‐starch into glucose, fructose and sucrose revealed considerable sugar interconversions indicating active gluconeogenesis during mango fruit ripening. Copyright © 2005 Society of Chemical Industry