Impact of trace element addition on degradation efficiency of volatile fatty acids, oleic acid and phenyl acetate and on microbial populations in a biogas digester

The effect of trace element addition on anaerobic digestion of food industry- and household waste was studied using two semi-continuous lab-scale reactors, one (R30+) was supplied with Fe, Co and Ni, while the other (R30) acted as a control. Tracer analysis illustrated that methane production from acetate proceeded through syntrophic acetate oxidation (SAO) in both digesters. The effect of the trace elements was also evaluated in batch assays to determine the capacity of the microorganisms of the two digesters to degrade acetate, phenyl acetate, oleic acid or propionate, butyrate and valerate provided as a cocktail. The trace elements addition improved the performance of the process giving higher methane yields during start-up and early operation and lower levels of mainly acetate and propionate in the R30+ reactor. The batch assay showed that material from R30+ gave effects on methane production from all substrates tested. Phenyl acetate was observed to inhibit methane formation in the R30 but not in the R30+ assay. A real-time PCR analysis targeting methanogens on the order level as well as three SAO bacteria showed an increase in Methanosarcinales in the R30+ reactor over time, even though SAO continuously was the dominating pathway for methane production. Possibly, this increase explains the low VFA-levels and higher degradation rates observed in the R30+ batch incubations. These results show that the added trace elements affected the ability of the microflora to degrade VFAs as well as oleic acid and phenyl acetate in a community, where acetate utilization is dominated by SAO.     

Evaluation of predictions of volatile fatty acid production rates by the Molly cow model

Predicting ruminal volatile fatty acid (VFA) production is important, as VFA are an energy source to the animal, affect nutrient partitioning, and dictate methane production. The VFA production submodel in the Molly cow model was evaluated using data from 8 publications that reported VFA production rates for cattle. Evaluations were conducted with ruminal water balance predictions enabled and the ruminal VFA stoichiometry coefficients set to “mixed” for all diets, or “mixed” when forage represented between 20 and 80% of the diet, “concentrate” when <20% forage, or “forage” when >80% forage. Prediction errors were relatively insensitive to changes in VFA coefficients by diet type. Root mean square prediction errors (RMSPE) were 63, 63, and 49% for acetate, propionate, and butyrate production rates, respectively. A large proportion of the error was slope bias for acetate and butyrate, and a modest proportion for propionate. Because interconversions between acetate and propionate represent approximately 15% of the variation in net production rates, lack of such consideration in the model may contribute to the substantial model prediction errors. The potential of using thermodynamic equations to predict interconversions was assessed using observed ruminal pH and VFA concentrations from 2 studies and assuming constant hydrogen pressure and concentrations of CO₂, H₂O, adenosine diphosphate, ATP, and inorganic P. Rate constants for conversion of acetate to propionate and propionate to acetate were derived independently from the control treatments and used to predict the fluxes for the other treatment. The observed changes in VFA concentrations and pH explained the observed changes in conversion of acetate to propionate, but overpredicted the change in the propionate to acetate flux in one study. When applied to the other study, the equations predicted the increase in propionate to acetate flux, but failed to predict the observed reduction in acetate to propionate flux. The inability to predict responses accurately may be due to a lack of data for controlling factors other than pH and VFA concentrations.     

Mass transfer of water and volatile fatty acids in cocoa beans during drying

In order to elucidate the phenomena involved in the remnant acidity of cocoa beans dried artificially, the diffusivities of water, and volatile fatty acids (VFAs: acetic, propionic, butyric and iso-butyric acids) in cocoa beans during drying were evaluated. Experimental drying kinetics of the acids were conduced at 40–60 °C with and without shell. Samples were taken at different drying times for moisture and acids content evaluation. VFAs content was evaluated by GC in a methanolic extract, and moisture content by a vacuum oven. Mass diffusivity was estimated from the fitting of experimental kinetics to a theoretical model that takes into consideration the beans’ shape. Acetic, propionic and butyric acids diffusivities were significantly (p < 0.05) smaller than water diffusivities both with and without shell. VFAs diffusivities were between 1/6 and 1/22 diffusivities values for water. Iso-butyric acid diffusivity was not statistically significant but the value was smaller than for the other VFAs. The diffusivities of VFAs may explain the remnant acidity in artificially dried cocoa beans.     

Volatile compounds of fresh and dry-cured loin as affected by dietary conjugated linoleic acid and monounsaturated fatty acids

Three levels (0%, 1% and 2%) of an enriched conjugated linoleic acid oil (CLA) were combined with two levels of monounsaturated fatty acids (MUFA) (low (19%) average and high (39%) average) for pig feeding. The profile of volatile compounds of fresh and dry-cured loin as affected by dietary CLA, MUFA and CLA × MUFA interaction was studied by headspace-solid phase microextraction coupled to gas chromatography–mass spectrometry. A total of 27 and 69 compounds were identified in fresh loin and dry-cured loin, respectively. Identified compounds were alcohols, aldehydes, aliphatic hydrocarbons, aromatic hydrocarbons, esters, furans, ketones, nitrogen compounds, sulphur compounds and terpenes. No qualitative differences in volatile compounds caused by the assayed treatments were found neither in fresh loin nor in dry-cured loin. Dietary CLA, MUFA and their interaction did not affect the level of most detected volatiles. Nevertheless, in fresh loin, the level of heptanal significantly increased due to dietary CLA (p = 0.001) and the area units (AU) for ethyl benzene and 1,3-dimethyl benzene increased at 1% CLA (p < 0.05). In the case of dry-cured loin, the AU of heptanal, nonanal and 2-nonenal contents increased due to dietary CLA (p = 0.016, 0.024 and 0.019, respectively).     

Effect of forage:concentrate ratio on fatty acid composition of rumen bacteria isolated from ruminal and duodenal digesta

Four dairy cows were used to examine the effect of the dietary forage:concentrate ratio [35:65, 50:50, 65:35, and 80:20 on a dry matter (DM) basis] on the fatty acid composition of rumen bacteria isolated from the liquid (LAB) and solid (SAB) phase of the rumen and duodenal digesta. Rumen contents were sampled 4 h after the morning feeding. Solid and liquid phases were separated from rumen contents and duodenal bacteria from a composite duodenal sample by differential centrifugation. Total fatty acid content in bacterial DM was 1.6 to 2.8 times higher in SAB compared with LAB, and increased with dietary concentrate. In combination with published reports, the data show that bacterial fatty acid content and composition is closely related to dietary fatty acids except for C18:2n-6 and C18:3n-3. A decrease in forage:concentrate ratio increased bacterial concentration of trans-10 C18:1, and this increase was 3.4 times higher in LAB compared with SAB. Analysis of odd- and branched-chain fatty acids showed large differences between SAB and LAB, which probably reflected a difference in species composition. The variation in odd- and branched-chain fatty acids between SAB and LAB was used to estimate their relative proportions in duodenal bacteria by means of linear programming, and showed an increased proportion of SAB from 64.7 to 74.8% with increasing forage:concentrate ratio. In addition, increasing the proportion of dietary forage was closely related to the proportion of anteiso C15:0 in total odd- and branched-chain fatty acids (r_pearson = −0.771). The bacterial concentration of iso C17:0 closely reflected the bacterial growth rate as shown by the relation with cytosine:N (r_pearson = −0.729). These strong relationships suggest that odd- and branched-chain fatty acids might be used as tool to evaluate nutrient supply to rumen bacteria.     

Evaluation of volatile compounds and free fatty acids in set types yogurts made of ewes’, goats’ milk and their mixture using two different commercial starter cultures during refrigerated storage

Six different types of yogurt were manufactured from Damascus goat milk, Awassi ewe milk and a mixture of equal portions of the 2 species of milk using 2 types of commercial yogurt cultures (CH-1 and YF-3331). Yogurts were chemically analysed at 1, 7, 14 and 21 days of storage. Results showed that cultures significantly affected acetaldehyde (P < 0.05), acetone (P < 0.05) and diacetyl (P < 0.001) contents. Type of milk significantly influenced acetaldehyde (P < 0.05), diacetyl (P < 0.001), acetoin (P < 0.001) and ethanol (P < 0.05) levels. Significant variations occurred in acetaldehyde (P < 0.001) and acetoin (P < 0.05) contents during the storage. Short-chain free fatty acids were the highest in ewes’ milk yogurt made with culture YF-3331, and increased during storage, while the levels of medium-chain free fatty acids, except for decanoic acid, were unchanged and the amount of long-chain free fatty acids decreased during storage. Cultures used and types of milk had no effect on long-chain free fatty acids in yogurts.     

光强和温度对球等鞭金藻（Isochrysis sphaerica）生长及其脂肪酸的影响

本研究测定了光照强度为16～58μmol／（m^2·s）和15～30℃条件下球等鞭金藻（Isochrysissphaerica）的生长曲线以及脂肪酸组成和含量。结果表明,在设置的光照强度范围内,光照强度越强,微藻的生长速度越快。光强对各种脂肪酸的含量影响有差异,过低和过高都不利于藻体内多不饱和脂肪酸（PolyunsaturatedFattyAcids,PU—FAs）的积累。当光强为24μmol／（m^2·s）时二十二碳六烯酸（DoeosahexaenoicAcid,DHA,C22：6n～3）的积累量最高,占总脂肪酸的11．77％。球等鞭金藻的最适生长温度在20～25℃之间,低温条件有利于不饱和脂肪酸的积累。光强20μmol／（m^2·s）、温度20℃条件下总不饱和脂肪酸（TotalUnsaturatedFattyAcids,TUFAs）含量最高,达64．99％;同样的光强,温度15℃条件下DHA占总脂肪酸的12．19％。可见适宜的光强和温度是利用球等鞭金藻收获PUFAs的关键。     

Stability of fatty acid composition after thermal,high pressure,and microwave processing of cow milk as affected by polyunsaturated fatty acid concentration

Interest has been increasing to enhance the contents of healthy polyunsaturated fatty acid (PUFA) in milk. However, trans fatty acids and conjugated linoleic acid (CLA) can be altered after thermal processing and high pressures disrupt the milk fat globule membrane, exposing the lipid core and helping its oxidation. The objective of the present research was to study whether processing can alter the fatty acid composition of milk and if these changes are affected by PUFA concentration as previous studies suggest. Two cow milk batches (500 L each), one naturally enriched in PUFA, were processed to obtain pasteurized; high temperature, short time; UHT; high pressure; and microwave pasteurized samples. The detailed fatty acid composition was analyzed with special attention to trans fatty acids and CLA isomers. Results showed that after high temperature, short time processing, total CLA content increased in both milk batches, whereas sterilization resulted in a sigmatropic rearrangement of C18:2 cis-9,trans-11 to C18:2 trans-9,trans-11. The extent of these effects was greater in milks naturally enriched in PUFA.     

Oxidative changes of fresh loin from pig,caused by dietary conjugated linoleic acid and monounsaturated fatty acids,during refrigerated storage

Three levels (0%, 1% and 2%) of a conjugated linoleic acid enriched oil (CLA) were combined with two levels of monounsaturated fatty acids (MUFA) (19% and 39% average) for pig feeding. Changes in instrumental colour, lipid oxidation (thiobarbituric acid reactive substances, TBARS) and volatile profile of fresh loin chops, as affected by dietary CLA, MUFA and CLA × MUFA, were studied throughout 7 days of refrigerated storage. Lightness (L∗) evolution was conditioned by dietary CLA, whereas changes in redness (a∗) and yellowness (b∗) were unaffected by dietary supplements. Dietary CLA at 2% led to higher TBARS values of loin chops at day 7 of refrigerated storage (p < 0.05), while MUFA supplementation and CLA × MUFA interaction did not affect lipid oxidation. Dietary CLA, MUFA or CLA × MUFA did not affect most volatile compounds of loin chops after 7 days of storage.     

Effect of dietary conjugated linoleic acid in combination with monounsaturated fatty acids on the composition and quality traits of cooked loin

Three levels (0%, 1% and 2%) of a conjugated linoleic acid oil (CLA) were combined with two levels of monounsaturated fatty acids (MUFA) (low – 19% average and high – 39% average) for pig feeding (n = 48, eight animals per treatment). The composition and quality traits (fat content, cooking losses, lipid oxidation, fatty acid profile, volatile profile and sensory analysis) of cooked loin, as affected by dietary CLA, MUFA, and CLA × MUFA interaction were studied. CLA and CLA × MUFA did not affect the intramuscular fat content, cooking losses, lipid oxidation, volatile profile and sensory traits of cooked meat. Therefore, CLA could be supplemented to the pig diet without detriment of the measured quality traits of cooked meat, and regardless of the MUFA level of pig diets. Dietary CLA increased the content of SFA and decreased the level of MUFA of meat, and led to a CLA enrichment, regardless the MUFA level of pig diets, but the content of CLA isomers of fresh meat decreased after the cooking process.     

Response of forage fiber degradation by ruminal microorganisms to branched-chain volatile fatty acids,amino acids,and dipeptides

This study evaluated the effect of branched-chain volatile fatty acids (VFA; isobutyric acid, isovaleric acid), amino acids (valine, leucine), and dipeptides (valine-valine, leucine-leucine) on neutral detergent fiber (NDF) degradation by rumen microorganisms in vitro. The CP (%) and in situ NDF degradation rate (%/h) for alfalfa, bermudagrass, and pangolagrass hays, and napiergrass silage were 17.2 and 7.5, 4.7 and 3.1, 8.3 and 5.3, and 9.6 and 3.4, respectively. In vitro NDF digestibility was the lowest for bermudagrass; alfalfa and napiergrass were the highest. When the incubation contained more ammonia initially, digestibilities increased, but relative differences among forages were unchanged. Adding branched-chain VFA (2 mM) to incubations increased digestibilities more than controls on 15 out of 16 occasions. The effectiveness varied with isoacids and forages used. Amino acid (2 mM) or dipeptide (1 mM) addition consistently increased digestibility over controls. Amino acids further increased digestibility over corresponding isoacids on 14 occasions. Improvement in digestibility over control by leucine appeared to be greater than that by valine. Digestibilities with dipeptides were always greater than those with isoacids, except for one case. Dipeptide addition further increased digestibility significantly over corresponding amino acids on only six occasions, while percent improvement in digestibility numerically by dipeptides occurred in 10 cases. Valine-valine seemed to exert different effect than leucine-leucine, depending on initial ammonia availability. The results indicate that dipeptides could be more effective than isoacids and amino acids in improving NDF digestion. Forages with high CP content or rapid NDF degradation rate appeared to respond to additives to smaller degrees.     

Effects of ruminal ammonia and butyrate concentrations on reticuloruminal epithelial blood flow and volatile fatty acid absorption kinetics under washed reticulorumen conditions in lactating dairy cows

The effect of reticuloruminal epithelial blood flow on the absorption of propionate as a volatile fatty acid (VFA) marker in 8 lactating Holstein cows was studied under washed rumen conditions. The cows were surgically prepared with ruminal cannulas and permanent catheters in an artery and mesenteric, right ruminal, and hepatic portal veins. The experiment was designed with 2 groups of cows: 4 cows adapted to high crude protein (CP) and 4 to low CP. All cows were subjected to 3 buffers: butyric, ammonia, and control in a randomized replicated 3 × 3 incomplete Latin square design. The buffers (30 kg) were maintained in a temporarily emptied and washed rumen for 40 min. The initial concentration of VFA was 84.2 mmol/L. Butyrate was increased from 4 to 36 mmol/L in butyric buffer by replacement of acetate, and ammonia (NH₃) was increased from 2.5 to 22.5 mmol/L in ammonia buffer by replacement of NaCl. Increasing amounts of deuterium oxide (D₂O) were added to the buffers as the order of buffer sequence increased (6, 12, and 18 g of D₂O). Ruminal clearance of D₂O was used to estimate epithelial blood flow. To increase accuracy of the epithelial blood flow estimates, data of ruminal liquid marker (Cr-EDTA), and initial and final buffer volumes were fitted to a dynamic simulation model. The model was used to estimate ruminal liquid passages, residual liquid, and water influx (saliva and epithelia water) for each combination of cow and buffer (n = 24). Epithelial blood flow increased 49 ± 11% for butyric buffer compared with control. The ruminal disappearance of propionate (marker VFA) was affected by buffer and followed the same pattern as for epithelial blood flow. The correlation between ruminal disappearance of propionate and epithelial blood flow (r = 0.56) indicates that the removal of propionate can be limited by epithelial blood flow. The ruminal disappearance of propionate increased 30 ± 12% for the butyric compared with ammonia buffer and 12.5 ± 8% when compared with control. The net portal flux of propionate increased 32 ± 6% in butyric compared with control. In conclusion, rumen epithelial blood flow is positively correlated with ruminal disappearance of propionate and affects the kinetics of ruminal VFA absorption.     

Production of conjugated fatty acids by lactic acid bacteria

Conjugated fatty acids have attracted much attention as a novel type of biologically beneficial functional lipid. Some isomers of conjugated linoleic acid (CLA) reduce carcinogenesis, atherosclerosis, and body fat. Considering the use of CLA for medicinal and nutraceutical purposes, a safe isomer-selective process is required. The introduction of biological reactions for CLA production could be an answer. We screened microbial reactions useful for CLA production, and found several unique reactions in lactic acid bacteria. Lactic acid bacteria produced CLA from linoleic acid. The produced CLA comprised a mixture of cis-9,trans-11-octadecadienoic acid (18:2) and trans-9,trans-11-18:2. Lactobacillus plantarum AKU 1009a was selected as a potential CLA producer. Using washed cells of L. plantarum AKU 1009a as a catalyst, CLA production from linoleic acid reached 40 mg/ml under the optimized conditions. The CLA-producing reaction was found to consist of two successive reactions, i.e., hydration of linoleic acid to 10-hydroxy-12-octadecenoic acid and dehydrating isomerization of the hydroxy fatty acid to CLA. On the basis of these results, the transformation of hydroxy fatty acids by lactic acid bacteria was investigated. Lactic acid bacteria transformed ricinoleic acid (12-hydroxy-cis-9-octadecenoic acid) to CLA (a mixture of cis-9,trans-11-18:2 and trans-9,trans-11-18:2). Castor oil, which is rich in the triacylglycerol form of ricinoleic acid, was also found to act as a substrate for CLA production by lactic acid bacteria with the aid of lipase-catalyzed triacylglycerol hydrolysis. L. plantarum AKU 1009a produced conjugated trienoic fatty acids from alpha- and gamma-linolenic acid. The trienoic fatty acids produced from alpha-linolenic acid were identified as cis-9,trans-11,cis-15-octadecatrienoic acid (18:3) and trans-9,trans-11,cis-15-18:3. Those produced from gamma-linolenic were cis-6,cis-9,trans-11-18:3 and cis-6,trans-9,trans-11-18:3. The conjugated trienoic fatty acids produced from alpha- and gamma-linolenic acid were further saturated by L. plantarum AKU 1009a to trans-10,cis-15-18:2 and cis-6,trans-10-18:2, respectively.     

Analysis of pea lipid content by gas chromatographic and microgravimetric methods. genotype variation in lipid content and fatty acid composition

Two methods were developed for the analysis of total lipid content in dried peas. The first measured total fatty acid methyl esters (total FAME) by gas chromatography. The second was a microgravimetric method. Both methods gave equally precise results with a skilled analyst but the total FAME method required less sample, was easier to use and was preferred for the analysis of large numbers of samples. Using the total FAME method a wide range of pea genotypes including primitive or wild forms, field peas, and round and wrinkled garden peas were analysed. The lipid content, expressed as percentage by weight, of dry whole pea flours prepared from 166 genotypes ranged from 1.4–4.0% and exhibited a bimodal distribution. The lower lipid population corresponded to round peas and the higher lipid population to wrinkled peas. Although only five fatty acids occurred in significant quantities in the total lipid there was considerable variation in their individual contents. In decreasing order of content, in the vast majority of genotypes, the fatty acids were linoleic (18:2), oleic (18:1), palmitic (16:0), linolenic (18:3) and stearic (18:0). In a few genotypes, however, oleic acid predominated over linoleic acid. Linolenic acid ranged from 2.5–14.9% of the total fatty acids. A positive linear correlation (r=0.98) was found to exist between total FAME values (L_F) and corresponding gravimetric lipid values (L_G) for a combined population of round and wrinkled peas. An initial calibration was derived by regression analysis of data obtained by the FAME method and a large scale gravimetric method. This was tested and found to give satisfactory prediction of L_G on a second set of samples analysed by the FAME method and the microgravimetric method.     

Effects of diet fermentability and supplementation of 2-hydroxy-4-(methylthio)-butanoic acid and isoacids on milk fat depression: 1. Production,milk fatty acid profile,and nutrient digestibility

The objectives of this experiment were to determine the effects of increased diet fermentability and polyunsaturated fatty acids (FA) with or without supplemental 2-hydroxy-4-(methylthio)-butanoic acid (HMTBa), isoacids (IA; isobutyrate, 2-methylbutyrate, isovalerate, and valerate) or the combination of these on milk fat depression (MFD). Ten Holstein cows (194 ± 58 DIM, 691 ± 69 kg BW, 28 ± 5 kg milk yield) were used in a replicated 5 × 5 Latin square design. Treatments included a high-forage control diet (HF-C), a low-forage control diet (LF-C) causing MFD by increasing starch and decreasing neutral detergent fiber (NDF), the LF-C diet supplemented with HMTBa at 0.11% (28 g/d), the LF-C diet supplemented with IA at 0.24% of dietary dry matter (60 g/d), and the LF-C diet supplemented with HMTBa and IA. Preplanned contrasts were used to compare HF-C versus LF-C and to examine the main effects of HMTBa or IA and their interactions within the LF diets. Dry matter intake was greater for LF-C versus HF-C, but milk yield remained unchanged. The LF-C diet decreased milk fat yield (0.87 vs. 0.98 kg/d) but increased protein yield compared with HF-C. As a result, energy-corrected milk was lower (28.5 vs. 29.6 kg/d) for LF-C versus HF-C. Although the concentration of total de novo synthesized FA in milk fat was not affected, some short- and medium-chain FA were lower for LF-C versus HF-C, but the concentrations of C18 trans-10 isomers were not different. Total-tract NDF apparent digestibility was numerically lower (42.4 vs. 45.6%) for LF-C versus HF-C. As the main effects, the decrease in milk fat yield observed in LF-C was alleviated by supplementation of HMTBa through increasing milk yield without altering milk fat content and by IA through increasing milk fat content without altering milk yield so that HMTBa or IA, as the main effects, increased milk fat yield within the LF diets. However, interactions for milk fat yield and ECM were observed between HMTBa and IA, suggesting no additive effect when used in combination. Minimal changes were found on milk FA profile when HMTBa was provided. However, de novo synthesized FA increased for IA supplementation. We detected no main effect of HMTBa, IA, and interaction between those on total-tract NDF digestibility. In conclusion, the addition of HMTBa and IA to a low-forage and high-starch diet alleviated moderate MFD. Although the mechanism by which MFD was alleviated was different between HMTBa and IA, no additive effects of the combination were observed on milk fat yield and ECM.     

Deodorisation of fish oil by nanofiltration membrane process: focus on volatile flavour compounds and fatty acids composition

This study focuses on the investigations for the deodorisation of tuna oil and squid oil through n‐hexane extraction and nanofiltration membrane process with a molecular weight cut‐off of 360 Da. The change of the odour and the fatty acids composition were analysed. Volatile components analysed by monolithic material sorptive extraction (MMSE) combined with gas chromatography–mass spectrometry (GC‐MS) suggested that nanofiltration membrane process could remove the majority of the volatile components, and the removal rate was approximate to 80%. The odour activity values (OAVs) of the volatile components in tuna oil and squid oil were significantly reduced from 125.23 to 17.47 and 129.76 to 10.06 (P < 0.05), respectively. On the other hand, the contents of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) were increased as expected. These results indicated that the organic solvent nanofiltration technique had obvious effects on deodorisation of fish oil, and it would be a promising deodorisation method in fish oil refining industry.     

Studying different dimensions of amylose–long chain fatty acid complexes: Molecular, nano and micro level characteristics

Recently amylose inclusion complexes, or V-amylose, have drawn much attention as a possible vehicle for the nanoencapsulation of unsaturated fatty acids. This study aimed to study three different structural strata of V-amylose, the molecular attributes using XRD, DSC and ¹³C CP/MAS NMR and the nanostructures using SAXS. Using these methods it was noted that decreased degree of fatty acid unsaturation induces the formation of more organized and well defined structures. Specifically, calculations based on SAXS data show that regardless of the crystallization temperature saturated SA yields the highest values for parameters like average crystalline lamellar thickness (φ = 0.26) and characteristic particle dimension (R_g = 9.6). SEM shows this trend extends even into the microscopic level. Overall, this study shows that in the case of long chain fatty acids, increased fatty acid unsaturation impairs the structure of amylose inclusion complexes.     

Enhancement of survival of probiotic and non-probiotic lactic acid bacteria by yeasts in fermented milk under non-refrigerated conditions

The effects of yeasts on the survival of probiotic and non-probiotic lactic acid bacteria (LAB) were studied in fermented milk under non-refrigerated conditions (30 °C) with a view to develop ambient-stable fermented milk with live LAB. Five yeasts tested (Saccharomyces bayanus, Williopsis saturnus var. saturnus, Yarrowia lipolytica, Candida kefyr and Kluyveromyces marxianus) enhanced the survival of Lactobacillus bulgaricus (but not Streptococcus thermophilus) in a mixed yoghurt culture in yoghurt by ~ 10² to 10⁵-fold. Seven yeasts examined (Candida krusei, Geotrichum candidum, Pichia subpelliculosa, Kloeckera apiculata, Pichia membranifaciens, Schizosaccharomyces pombe and Y. lipolytica) improved the survival of Lactobacillus rhamnosus in fermented milk by ~ 10³ to 10⁶-fold. W. saturnus var. saturnus enhanced the survival of Lactobacillus acidophilus, L. rhamnosus (probiotic) and Lactobacillus reuteri by up to 10⁶-fold, but the same yeast failed to improve the survival of Lactobacillus johnsonii (probiotic), S. thermophilus and L. bulgaricus in fermented milk. These results provide definitive evidence that yeasts possess stability-enhancing effects on LAB and that the specific effects of yeasts on LAB stability vary with yeasts as well as with LAB. However, the molecular mechanism of such interaction of yeasts with LAB remains to be found.     

Production of short‐chain fatty acids following in vitro fermentation of saccharides,saccharide esters,fructo‐oligosaccharides,starches, modified starches and non‐starch polysaccharides

A range of carbohydrates including modified starches and short‐chain fatty acid esters of di‐, tri‐, tetra‐ and polysaccharides were subjected to an in vitro fermentation using human‐derived faecal bacteria. The production of the short‐chain fatty acids (SCFAs) acetate, propionate and butyrate was monitored at 6, 12, 24 and 36 h for all substrates; however, it was found that the proportions of acids produced were reasonably constant after 6 h. Between substrates there was variation in both the proportions and quantities of acids produced. Relative substrate fermentability as measured by total acid production at 24 h was: sucrose octa‐acetate > sucrose > stachyose > pregelatinised starch > Raftilose^® > verbascose > raffinose > starch acetate > bleached starch > phosphated distarch phosphate > locust bean gum > corn starch > oxidised starch = starch sodium octenyl succinate > di‐starch phosphate > acetylated di‐starch adipate = gum arabic > acid‐treated starch > gum tragacanth > gum guar > acetylated di‐starch phosphate = hydroxypropyl di‐starch phosphate > hydroxypropyl starch > pectin > raffinose undeca‐acetate > stachyose acetate > gum karaya = cellulose propionate > cellulose acetate > cellulose > cellulose butyrate > hydroxypropyl methyl cellulose > carrageenan > methyl cellulose. Chemically modified starches were similar to corn starch in the amounts of total SCFAs produced at 24 h. Synthetic sugar esters could have potential application as vehicles to deliver supraphysiological amounts of SCFAs during in vivo studies of colonic fermentation. © 2000 Society of Chemical Industry