Ruminal fermentation of propylene glycol and glycerol

Bovine rumen fluid was fermented anaerobically with 25 mM R-propylene glycol, S-propylene glycol, or glycerol added. After 24 h, all of the propylene glycol enantiomers and approximately 80% of the glycerol were metabolized. Acetate, propionate, butyrate, valerate, and caproate concentrations, in decreasing order, all increased with incubation time. Addition of any of the three substrates somewhat decreased acetate formation, while addition of either propylene glycol increased propionate formation but decreased that of butyrate. R- and S-propylene glycol did not differ significantly in either their rates of disappearance or the products formed when they were added to the fermentation medium. Fermentations of rumen fluid containing propylene glycol emitted the sulfur-containing gases 1-propanethiol, 1-(methylthio)propane, methylthiirane, 2,4-dimethylthiophene, 1-(methylthio)-1-propanethiol, dipropyl disulfide, 1-(propylthio)-1-propanethiol, dipropyl trisulfide, 3,5-diethyl-1,2,4-trithiolane, 2-ethyl-1,3-dithiane, and 2,4,6-triethyl-1,3,5-trithiane. Metabolic pathways that yield each of these gases are proposed. The sulfur-containing gases produced during propylene glycol fermentation in the rumen may contribute to the toxic effects seen in cattle when high doses are administered for therapeutic purposes.     

Metabolite production during in vitro colonic fermentation of dietary fiber: analysis and comparison of two European diets

Metabolite production and antioxidant released during colonic fermentation of naturally occurring dietary fiber (DF) from two European diets (Mediterranean and Scandinavian) were determined. With this aim, DF and associated components were isolated from both whole diets, as well as from cereals and fruits and vegetables comprising the diets. DF was used as substrate for colonic fermentation in a dynamic in vitro model of the colon, samples were collected, and fermentation metabolites were analyzed. Statistical differences between samples were observed in the concentrations of short-chain fatty acids and ammonia and in the ratio acetate/propionate/butyrate. Whole grain cereal DF generated a larger amount of propionate than refined flour cereal DF. Fruit and vegetable DF generated higher amounts of butyrate than cereal DF. Most antioxidant compounds were released from DF during in vitro colonic fermentation. It is concluded that different sources of DF may play a specific role in health maintenance mediated by metabolites produced during colonic fermentation.     

In Vitro Digestion of RS4‐Type Resistant Wheat and Potato Starches,and Fermentation of Indigestible Fractions

RS4‐type resistant wheat starch (RWS) and resistant potato starch (RPS) were subjected successively to in vitro digestion with pepsin and pancreatin‐bile, and the indigestible residues (82.1% db and 74.1% db, respectively) were recovered and subsequently fermented by in vitro techniques using fresh human fecal microbiota as inoculum. Scanning electron microscopy of the indigestible residues showed surface erosion on the residual granules. Total gas production during the in vitro fermentation increased almost linearly over time with the two resistant starches exhibiting similar gas production rates, as well as a similar rate of production of total short‐chain fatty acids (SCFA). The indigestible fractions from both starches produced acetate as the major SCFA and relatively higher levels of butyrate than propionate, but wheat starch tended to produce more butyrate over time than potato starch. Fractional molar ratios of acetate, propionate, and butyrate from the RWS and RPS were 0.586:0.186:0.228 and 0.577:0.200:0.223, respectively. The calculated caloric contributions of the RWS and RPS are ≈33% lower than for unmodified starch and are comparable to those reported in the literature for RS2 and RS3 high‐amylose maize starches.     

Volatile fatty acid production with alfalfa (Medicago sativa) and glucose in denitrifying soil at different temperatures

Summary A laboratory study was done to determine how, if at all, temperatures affect the production of volatile fatty acids and the rate of denitrification in soil. Glucose and alfalfa were compared as C substrates at temperatures of -2, 10, and 25°C under anaerobic conditions. At -2°C (soil not frozen), the denitrification rate was slow but was as rapid with alfalfa as glucose. This indicated that the production of volatile fatty acids by fermenters or other C substrates from alfalfa were adequate to sustain denitrifiers. No volatile fatty acids were apparently produced with glucose at -2°C whereas acetate and propionate were produced with alfalfa during the 26-day incubation period. During the 8-day incubation period at 10°C, there were also greater accumulations of acetate and propionate with alfalfa than with glucose. At 25°C, there was no major difference in the denitrification rate between glucose and alfalfa over a 4-day period. In a contrast to the other temperatures, more butyrate than propionate was produced at 25°C, especially with alfalfa. Acetate was the dominant volatile fatty acid produced and generally increased with temperature, especially after NO₃ exhaustion at 10 and 25°C. This indicated that acetate was a source of C for denitrifiers.     

C2-C4有机酸和醇作为潜在种子引发剂:基于灰色关联分析的综合评估

【目的】 种子作为植物生长发育的起点,承载了全部的遗传因素以及作物发芽所需要的营养物质,其质量的好坏很大程度上影响着植物的后续发展以及最终的产量。化学浸种处理是促进幼苗快速,均匀田间出苗的有效途径。寻求环境友好和经济可行的化学品应用于种子引发,可为促进作物生长提供一条经济有效的途径。 【方法】 以低成本的C2-C4有机酸和醇作为氨基酸的替代化学浸种剂,进行了玉米、小麦和绿豆种子浸种试验。在试验研究中,甘氨酸、乙酸盐、丙酸盐、丁酸盐的各供试浓度同为10、20、30、40、50 mg/L,乙醇、丙醇和丁醇的各供试浓度同为3、5、8、10、13 mg/L。在25℃下浸泡24 h,然后置于25℃和80%湿度的环境下待发芽,5 d后计算发芽率,2周后测量枝条长度、根长度及幼苗生物量。使用灰色关联分析来整合发芽率、枝条长度、根长度和幼苗生物量对作物后续生长的影响,将发芽率的权重设为0.4,枝条长度、根长度及幼苗生物量的权重均设为0.2。依据归一化数据计算出的灰色关联系数,对引发化学物进行了全面评估。 【结果】 将数据带入公式进行计算,20 mg/L乙酸盐获得0.797的最高引发等级,作为诱导玉米种子的最佳化学试剂,而甘氨酸的最佳浓度为40 mg/L,引发等级为0.701;40 mg/L丙酸盐在绿豌豆种子上获得0.730最高引发等级,在小麦种子上获得0.799的最高引发等级,高于最佳浓度为30 mg/L的甘氨酸处理中获得的引发等级0.699。 【结论】 这项工作证明了低分子有机酸和醇是合适的生长调节物质。以40 mg/L 乙酸盐在玉米、40 mg/L丙酸盐在小麦和绿豆上的效果最佳。      

In vitro fermentability of differently substituted xylo-oligosaccharides

Xylo-oligosaccharides (XOS) with various substituents were fermented in vitro by fecal inocula (FI) from four human volunteers to study the influence of substitution on the ability and rate of fermentation and on the production of short-chain fatty acids (SCFA) and lactate. By all FI used nonsubstituted XOS (nXOS) and arabino-XOS (AXOS) were fermented more quickly than the more complex structures of acetylated XOS (AcXOS) and XOS containing a 4-O-methylglucuronic acid group (GlcA(me)XOS). In the first stage (0-40 h) of the fermentations of nXOS and AXOS mainly acetate and lactate were formed. The fermentations of AcXOS and GlcA(me)XOS resulted in a lower lactate production, whereas the concentration of propionate and butyrate increased. These results put emphasis on the detailed elucidation of the structural features of nondigestible oligosaccharides in general to understand their fermentation mechanisms more precisely.     

Digestion residues of typical and high-beta-glucan oat flours provide substrates for in vitro fermentation

In vitro fermentabilities of the oat flour digestion residues (ODR) from two commercial oat lines with 4.7 and 5.3% beta-glucan and from two high-beta-glucan experimental lines with 7.6 and 8.1% beta-glucan were evaluated and compared with fermentations of lactulose, purified oat beta-glucan (POBG), and purified oat starch (POS). Substrates were fermented by using an in vitro batch fermentation system under anaerobic conditions for 24 h. The progress of the fermentation was studied by following the change in pH of the fermentation medium, production of short-chain fatty acids (SCFA) and gases, and consumption of carbohydrates. The substrate from the flour with the greatest amount of beta-glucan tended to have the greatest pH decline and the greatest total SCFA production. A significant correlation occurred between gas production and SCFA formation (R 2 = 0.89-0.99). Acetate was produced in the greatest amounts by all of the substrates except POBG, by which butyrate was produced in the greatest amount. More propionate and butyrate, but less acetate, were produced from high-beta-glucan ODR. With the given fermentation conditions, >80% of the total carbohydrate was depleted by the bacteria after 24 h. Glucose was the most rapidly consumed carbohydrate among other available monosaccharides in the fermentation medium. Overall, the high-beta-glucan experimental lines provided the best conditions for optimal in vitro gut fermentations.     

In vitro digestion and fermentation characteristics of temulose molasses, a coproduct of fiberboard production, and select temulose fractions using canine fecal inoculum

It is of interest to discover new fermentable carbohydrate sources that function as prebiotics. This study evaluated the hydrolytic digestibility, fermentative capacity, and microbiota modulating properties of Temulose molasses, four hydrolyzed fractions of Temulose molasses, short-chain fructooligosaccharides (scFOS), and a yeast cell wall preparation (Safmannan). These substrates resisted in vitro hydrolytic digestion. Each substrate was fermented in vitro using dog fecal inoculum, and fermentation characteristics were quantified at 0 and 12 h. All Temulose molasses substrates decreased pH by at least 0.64 unit and resulted in greater (P < 0.05) butyrate and total short-chain fatty acid (SCFA) production compared to scFOS and Safmannan. Temulose molasses substrates resulted in higher (P < 0.01) or equal Bifidobacterium spp. concentrations compared to scFOS. Temulose molasses substrate and its fractions demonstrated prebiotic characteristics as indicated by low hydrolytic digestibility, high fermentability, and enhanced growth of microbiota considered to be beneficial to health.     

Enzyme-linked immunosorbent assay of aflatoxin B1 in naturally contaminated corn and cottonseed

Naturally contaminated corn and cottonseed samples were screened for aflatoxin B1 (AFB1) by a direct competitive enzyme-linked immunosorbent assay (ELISA). Samples were blended 5 min in an extraction solvent of methanol-water-dimethylformamide (70 + 29 + 1) and filtered. Filtrates were assayed by direct competition between AFB1 in the corn and cottonseed samples and AFB1-peroxidase conjugate for binding to specific antibody adsorbed to a solid phase microtiter plate. Standard curves prepared using the extract of AFB1-free corn and cottonseed samples, and extraction solvent only, showed negligible interference by the sample extract in the performance of ELISA. The AFB1 content in corn and dehulled cottonseed samples as determined by ELISA ranged from 7 to 422 micrograms/kg and 7 to 3,258 micrograms/kg, respectively. When ELISA estimates of AFB1 in corn were compared with values obtained by thin layer chromatography (CB method), the correlation coefficient (n = 10) was 0.95. Average interassay and subsample coefficients of variation for ELISA in corn were 21.4 and 22.0%, respectively. When ELISA estimates of AFB1 in cottonseed were compared with values obtained by liquid chromatography (Pons method), the correlation coefficient (n = 15) was 0.96. Using this ELISA, 36 duplicate sample extracts can be screened for AFB1 in less than 2 h.     

中温和高温环境下乙酸和丙酸厌氧发酵产甲烷动力学特征

采用不同浓度的乙酸和丙酸在中高温下进行厌氧发酵批次试验,采用修正的Gompertz模型和产甲烷的一级动力学模型分析,研究酸浓度和温度对发酵产气动力学的影响。研究表明,当乙酸和丙酸浓度较低时降解较快,高浓度酸抑制产气。乙酸在中温条件下降解较快,质量浓度为5 000 mg/L时中温反应有最大产甲烷速率101 mL/d;质量浓度为10 000 mg/L时高温条件下有最大产甲烷速率77 mL/d,随酸浓度增加,最大产甲烷速率减小,高温反应器对酸的耐受度较高。丙酸在高温条件下更易降解,浓度为4 000 mg/L时,中高温反应均有最大产气速率：78 mL/d（中温）和96 mL/d（高温）。另外,高浓度乙酸和丙酸厌氧降解产气具有滞后性,且随酸浓度的增加滞后期延长,降解过程受到抑制,一级动力学常数减小。温度对厌氧降解的影响大于酸浓度对厌氧降解的影响。     

Substrates Influence Stimulatory Effect of Mevalonic Acid on Carotenoid Production in Red Yeasts

Stimulation of carotenogenesis in carotenoid producing red yeasts, algae, or bacteria for enhanced carotenoid production has been achieved by mevalonic acid addition. Recently, carotenoid‐enriched feed was produced by Phaffia rhodozyma fermentation of inexpensive animal feeds. Because mevalonate improves carotenoid yield in P. rhodozyma in synthetic medium, this study tested whether a similar enhancement was possible in biobased substrates. Four concentrations, 0, 0.02, 0.04, and 0.1% of mevalonate as a precursor of P. rhodozyma production of astaxanthin and β‐carotene were evaluated in five substrates: defatted rice bran, full fat rice bran, wheat bran, corn whole stillage, and synthetic media. Additionally, four concentrations, 0, 0.05, 0.1, and 0.5% of apple pomace and tomato pomace were also evaluated as precursors of carotenogenesis in P. rhodozyma fermentation of corn whole stillage and rice bran. Mevalonic acid, tomato pomace, and apple pomace enhanced carotenoid yields in all substrates in that order. However, the optimal concentration of precursor and the percent increase of carotenoid yield in each substrate were variable, potentially indicating substrate influence on carotenoid stimulation. Among animal feed substrates, mevalonic acid in corn whole stillage resulted in the best astaxanthin yield of 220 μg/g and β‐carotene of 904 μg/g. Tomato pomace resulted in 29% astaxanthin and β‐carotene enhancement in corn whole stillage, and apple pomace increased β‐carotene production by 26% in whole stillage. The use of expensive mevalonate is offset by the inexpensive process of producing carotenoid‐enriched DDGS. Optimization of tomato or apple pomace addition may further enhance the carotenoid yields.     

In vitro fermentation of bacterial cellulose composites as model dietary fibers

Plant cell walls within the human diet are compositionally heterogeneous, so defining the basis of nutritive properties is difficult. Using a pig fecal inoculum, in vitro fermentations of soluble forms of arabinoxylan, mixed-linkage glucan, and xyloglucan were compared with the same polymers incorporated into bacterial cellulose composites. Fermentation rates were highest and similar for the soluble polysaccharides. Cellulose composites incorporating those polysaccharides fermented more slowly and at similar rates to wheat bran. Bacterial cellulose and cotton fermented most slowly. Cellulose composite fermentation resulted in a different short-chain fatty acid profile, compared with soluble polysaccharides, with more butyrate and less propionate. The results suggest that physical form is more relevant than the chemistry of plant cell wall polysaccharides in determining both rate and end-products of fermentation using fecal bacteria. This work also establishes bacterial cellulose composites as a useful model system for the fermentation of complex cell wall dietary fiber.     

Carotenoid Value Addition of Cereal Products by Monoculture and Mixed‐Culture Fermentation of Phaffia rhodozyma and Sporobolomyces roseus

Carotenoid value addition of corn whole stillage by red yeast fermentation has yielded astaxanthin‐ and β‐carotene‐enriched distillers dried grains with solubles (DDGS) for animal feed. In this study, commonly used animal feeds (rice bran, wheat bran, milo whole stillage, and soybean products) were subjected to carotenoid value addition. Phaffia rhodozyma and Sporobolomyces roseus monoculture and mixed‐culture submerged fermentation of these substrates supplemented with 5% glycerol were analyzed for astaxanthin, β‐carotene, and residual glycerol. Among all the substrates, full‐fat rice bran and full‐fat soy flour resulted in the highest astaxanthin (80 μg/g by P. rhodozyma) and β‐carotene yields (836 μg/g by S. roseus). P. rhodozyma produced the highest astaxanthin yield on each substrate, whereas depending on the substrate, either the mixed culture or S. roseus monoculture produced the highest β‐carotene yield. Soy hull was a poor substrate for carotenoid value addition. Both yeasts used glycerol as a carbon source for carotenoid production. This study shows that substrates influence the carotenoid yield. However, it is impossible to dissect the effect of specific nutrients on carotenoid production in complex biological substrates. Carotenoid value addition of these substrates provides as much as or more than the required daily dosage of carotenoids in animal feed.     

Evaluation and Strategies to Improve Fermentation Characteristics of Modified Dry‐Grind Corn Processes

New corn fractionation technologies that produce higher value coproducts from dry‐grind processing have been developed. Wet fractionation technologies involve a short soaking of corn followed by milling to recover germ and pericarp fiber in an aqueous medium before fermentation of degermed defibered slurry. In dry fractionation technologies, a dry degerm defiber (3D) process (similar to conventional corn dry‐milling) is used to separate germ and pericarp fiber before fermentation of the endosperm fraction. The effect of dry and wet fractionation technologies on the fermentation rates and ethanol yields were studied and compared with the conventional dry‐grind process. The wet process had the highest fermentation rate. The endosperm fraction obtained from 3D process had lowest fermentation rate and highest residual sugars at the end of fermentation. Strategies to improve the fermentation characteristics of endosperm fraction from 3D process were evaluated using two saccharification and fermentation processes. The endosperm fraction obtained from 3D process was liquefied by enzymatic hydrolysis and fermented using either separate saccharification (SS) and fermentation or simultaneous saccharification and fermentation (SSF). Corn germ soak water and B‐vitamins were added during fermentation to study the effect of micronutrient addition. Ethanol and sugar profiles were measured using HPLC. The endosperm fraction fermented using SSF produced higher ethanol yields than SS. Addition of B‐vitamins and germ soak water during SSF improved fermentation of 3D process and resulted in 2.6 and 2.3% (v/v) higher ethanol concentrations and fermentation rates compared with 3D process treatment with no addition of micronutrients.     

食用菌栽培对棉籽壳营养价值及山羊瘤胃动态降解率的影响

为了研究4种食用菌栽培后对栽培基质棉籽壳的营养价值和山羊瘤胃动态降解率的影响,选用6只年龄(10月龄)、体重[(35.42±3.96)kg]接近并装有永久瘤胃瘘管的槐山羊羯羊,通过化学分析法测定了棉籽壳和4种菌糠的化学成分,并采用尼龙袋技术,分5批次测定了棉籽壳、平菇菌糠、木耳菌糠、金针菇菌糠和白灵菇菌糠瘤胃动态降解率。结果表明:(1)4种菌糠干物质(DM)和有机物(OM)含量分别比其栽培原料棉籽壳的含量降低13.09%~19.67%(P<0.01)和14.13%~39.52%(P<0.01),粗蛋白(CP)含量分别比棉籽壳提高40.20%~34.29%(P<0.01),中性洗涤纤维(NDF)和酸性洗涤纤维(ADF)含量分别比棉籽壳降低3.07%~39.72%和17.80%~45.91%(P<0.01);(2)木耳菌糠、金针菇菌糠、白灵菇菌糠的DM和OM在瘤胃内的有效降解率和a+b值(快速降解部分和慢速降解部分之和)均极显著高于棉籽壳(P<0.01),平菇菌糠的DM和OM在瘤胃内的有效降解率显著高于棉籽壳(P<0.05);平菇菌糠、金针菇菌糠、白灵菇菌糠的CP在瘤胃内的有效降解率和a+b值均极显著高于棉籽壳(P<0.01);4种菌糠的NDF和ADF在瘤胃内的有效降解率分别比棉籽壳提高76.72%~702.63%(P<0.01)和137.41%~575.31%(P<0.01)。因此,在棉籽壳上栽培4种食用菌均能改善棉籽壳的营养价值和提高山羊瘤胃消化率,栽培食用菌后的菌糠更有利于作为反刍动物饲料进行利用。     

玉米秸秆与污泥的腐解物对盐碱地化学指标的影响

为探索发酵后的玉米秸秆对内蒙古地区盐碱化土壤化学性质(有机质、ESP,pH值、EC、土壤代换性Na~+)的影响,在实验室条件下以污泥作为接种物,将玉米秸秆在不同发酵的条件下以不同梯度的秸秆还田量施加到盐碱化土壤中,以施加未发酵的玉米秸秆为对照。结果显示:(1)施加玉米秸秆对土壤的部分化学性质有着一定的改善,且发酵后的玉米秸秆比未发酵的玉米秸秆效果要好;(2)当玉米秸秆与污泥的配比为2∶1且秸秆还田量为75%时,土壤的有机质含量上升幅度最大,土壤的ESP、pH值、土壤代换性Na~+降低幅度最大;(3)施加玉米秸秆对土壤的EC作用不明显,反而使EC的含量有所上升,施用发酵后的玉米秸秆尤为明显。综合考虑,在本试验条件下针对该土壤最佳参数为:玉米秸秆与污泥配比为2∶1,发酵后的玉米秸秆还田量为75%。     

苜蓿中金属肽酶对青贮过程中蛋白降解的作用

为探讨金属肽酶在苜蓿青贮过程中对蛋白的降解作用,以苜蓿（Medicago stativa L.）绿汁发酵液模拟青贮发酵过程,添加金属肽酶抑制剂后,测定发酵后第0.5、1、1.5、2、2.5、3、4、5、7和14天时绿汁发酵液的蛋白组分。结果表明,在苜蓿发酵液发酵过程中添加金属肽酶抑制剂能够降低pH值、非蛋白氮、游离氨基酸和氨态氮含量,增加乳酸含量;发酵第14天时,抑制剂处理组非蛋白氮、游离氨基酸和氨态氮质量分数为483.98 g/kg TN,256.98 g/kg TN和26.11 g/kg TN,与对照组相比分别降低28.92%,38.59%和67.08%。金属肽酶对苜蓿发酵液蛋白降解起着一定的作用;添加金属肽酶抑制剂能够提高发酵液发酵品质。     

瘤胃真菌与酿酒酵母仿生共培养提升秸秆发酵产乙醇量

玉米秸秆中具有较高的纤维素、半纤维素含量,是一种具有稳定产率、可集中处理、可代替木材作制浆原料的生物质材料。为了研究厌氧微生物与酵母共培养预处理玉米秸秆的产物,该研究模拟反刍动物消化玉米秸秆的过程,从羊瘤胃液中分离出厌氧真菌（Pecoramyces sp.）。以玉米秸秆茎皮碎为底物,与厌氧真菌、酿酒酵母菌S1145在39℃进行共培养72 h,分析发酵对秸秆茎皮降解及其代谢产物的影响。结果表明,在瘤胃真菌作用下,添加不同量的酿酒酵母可对代谢产物中乙醇含量产生影响,其中添加5 mL酿酒酵母时产生的乙醇含量最高,占总代谢产物比例为32.09%,相对于未添加酿酒酵母的对照组,乙醇含量提高了23.04百分点。研究表明,在厌氧真菌与酿酒酵母共培养预处理玉米秸秆茎皮的过程中,添加酿酒酵母可提高乙醇产量,为玉米秸秆高效资源化处理和生物质燃料生产提供了一种可靠的方法。     

蒸汽爆破预处理和微生物发酵对玉米秸秆降解率的影响

为了提高玉米秸秆的利用效率,首先对玉米秸秆进行蒸汽爆破预处理（压力2.5 Mpa,维压200 s）,然后再进行米曲霉发酵,研究物理和生物学处理对秸秆成分及相关酶活变化的影响。结果表明,蒸汽爆破使秸秆中纤维素、半纤维素和木质素的降解率分别达到8.47%、50.45% 和36.65% （p＜0.05）。爆破预处理的秸秆再经米曲霉发酵6 d后,秸秆中纤维素和半纤维素的降解率分别为27.89%和64.80% （p＜0.05）,发酵秸秆中的滤纸酶、羧甲基纤维素酶、淀粉酶和蛋白酶活力分别达到335.10、1138.92、1954.20和201.99 U/g。爆破预处理后进行米曲霉发酵,对于提高玉米秸秆的降解率具有非常重要的意义。