Effects of rumen-protected γ-aminobutyric acid on performance and nutrient digestibility in heat-stressed dairy cows

This experiment was conducted to investigate the effects of rumen-protected γ-aminobutyric acid (GABA) on performance and nutrient digestibility in heat-stressed dairy cows. Sixty Holstein dairy cows (141 ± 15 d in milk, 35.9 ± 4.3 kg of milk/d, and parity 2.0 ± 1.1) were randomly assigned to 1 of 4 treatments according to a completely randomized block design. Treatments consisted of 0 (control), 40, 80, or 120 mg of true GABA/kg of dry matter (DM). The trial lasted 10 wk. The average temperature-humidity indices at 0700, 1400, and 2200 h were 78.4, 80.2, and 78.7, respectively. Rectal temperatures decreased linearly at 0700, 1400, and 2200 h with increasing GABA concentration. Supplementation of GABA had no effect on respiration rates at any time point. Dry matter intake, energy-corrected milk, 4% fat-corrected milk, and milk fat yield tended to increase linearly with increasing GABA concentration. Supplementation of GABA affected, in a quadratic manner, milk protein and lactose concentrations, and milk protein yield, and the peak values were reached at a dose of 40 mg of GABA/kg. Milk urea nitrogen concentration responded quadratically. Total solids content increased linearly with increasing GABA concentration. Supplementation of GABA had no effect on milk yield, lactose production, total solids, milk fat concentration, somatic cell score, or feed efficiency. Apparent total-tract digestibilities of DM, organic matter, crude protein, neutral detergent fiber, and acid detergent fiber were similar among treatments. These results indicate that rumen-protected GABA supplementation to dairy cows can alleviate heat stress by reducing rectal temperature, increase DM intake and milk production, and improve milk composition. The appropriate supplemental GABA level for heat-stressed dairy cows is 40 mg/kg of DM.     

Nonstarter lactic acid bacteria biofilms and calcium lactate crystals in Cheddar cheese

A sanitized cheese plant was swabbed for the presence of nonstarter lactic acid bacteria (NSLAB) biofilms. Swabs were analyzed to determine the sources and microorganisms responsible for contamination. In pilot plant experiments, cheese vats filled with standard cheese milk (lactose:protein = 1.47) and ultrafiltered cheese milk (lactose:protein = 1.23) were inoculated with Lactococcus lactis ssp. cremoris starter culture (8 log cfu/mL) with or without Lactobacillus curvatus or Pediococci acidilactici as adjunct cultures (2 log cfu/mL). Cheddar cheeses were aged at 7.2 or 10°C for 168 d. The raw milk silo, ultrafiltration unit, cheddaring belt, and cheese tower had NSLAB biofilms ranging from 2 to 4 log cfu/100 cm². The population of Lb. curvatus reached 8 log cfu/g, whereas P. acidilactici reached 7 log cfu/g of experimental Cheddar cheese in 14 d. Higher NSLAB counts were observed in the first 14 d of aging in cheese stored at 10°C compared with that stored at 7.2°C. However, microbial counts decreased more quickly in Cheddar cheeses aged at 10°C compared with 7.2°C after 28 d. In cheeses without specific adjunct cultures (Lb. curvatus or P. acidilactici), calcium lactate crystals were not observed within 168 d. However, crystals were observed after only 56 d in cheeses containing Lb. curvatus, which also had increased concentration of d(−)-lactic acid compared with control cheeses. Our research shows that low levels of contamination with certain NSLAB can result in calcium lactate crystals, regardless of lactose:protein ratio.     

Sensitive electrochemical determination of luteolin in peanut hulls using multi-walled carbon nanotubes modified electrode

A simple and highly sensitive electrochemical method was developed for the determination of trace-level luteolin, based on the multi-walled carbon nanotubes (MWNTs) modified glassy carbon electrode (GCE). The electrochemical behaviours of luteolin indicate that MWNTs modified glassy carbon electrode (MWNTs/GCE) can greatly enhance the electrocatalytic activity towards the redox of luteolin. It leads to a considerable improvement of the redox peak current for luteolin and allows the development of a highly sensitive voltammetric sensor for the determination of luteolin. A series of experimental parameters including the pH of supporting electrolyte, accumulation potential and time were optimised. The results showed that the oxidative peak currents increased linearly with the concentration of luteolin in the range of 2.0 × 10⁻¹⁰ to 3.0 × 10⁻⁹ M, with a detection limit of 6.0 × 10⁻¹¹ M (S/N = 3). The analytical performance of this sensor has been evaluated for detection of luteolin in peanut hulls as a real sample.     

Lactation performance and amino acid utilization of cows fed increasing amounts of reduced-fat dried distillers grains with solubles

The use of a solvent-extraction process that removes corn oil from distillers grains produces a reduced-fat co-product (RFDG). To determine the optimal concentration of RFDG in mid-lactation diets, 22 multiparous and 19 primiparous Holstein cows were used in a completely randomized design for 8 wk, including a 2-wk covariate period. The RFDG was included at 0, 10, 20, and 30% of the diet on a dry matter basis, replacing soybean feedstuffs. Increasing RFDG in diets had no effect on dry matter intake (23.1 kg/d) or milk production (35.0 kg/d). Milk fat percentage increased linearly from 3.18 to 3.72% as RFDG increased from 0 to 30% of the diet. Similarly, milk fat yield tended to increase linearly from 1.08 to 1.32 kg/d. Milk protein percentage (2.99, 3.06, 3.13, and 2.99% for diets with RFDG from 0 to 30%) responded quadratically, whereas protein yield was not affected by treatment. Milk urea N decreased linearly from 15.8 to 13.1 mg/dL. The efficiency of N utilization for milk production was not affected by including RFDG (26.1%), whereas the efficiency of milk production (energy-corrected milk divided by dry matter intake) tended to increase linearly with increasing RFDG in the diet. Similarly, concentrations of plasma glucose increased linearly. Arterial Lys decreased linearly from 66.0 to 44.8 μM/L, whereas arterial Met increased linearly from 16.5 to 29.3 μM/L. Arteriovenous difference of Lys decreased linearly from 42.6 to 32.5 μM/L, whereas that of Met was unaffected. The extraction of Lys by the mammary gland increased linearly from 64.3 to 72.2%, whereas that of Met decreased linearly from 71.6 to 42.7%. Feeding up to 30% of RFDG in a mid-lactation diet supported lactation performance similarly to cows fed the soybean protein-based diet (0% RFDG).     

Gas-flushed packaging contributes to calcium lactate crystals in Cheddar cheese

Gas-flushed packaging is commonly used for cheese shreds and cubes to prevent aggregation and loss of individual identity. Appearance of a white haze on cubed cheese is unappealing to consumers, who may refrain from buying, resulting in lost revenue to manufacturers. The objective of this study was to determine whether gas flushing of Cheddar cheese contributes to the occurrence of calcium lactate crystals (CLC). Cheddar cheese was manufactured using standard methods, with addition of starter culture, annatto, and chymosin. Two different cheese milk compositions were used: standard (lactose:protein = 1.47, protein:fat = 0.90, lactose = 4.8%) and ultrafiltered (UF; lactose:protein = 1.23, protein:fat = 0.84, lactose = 4.8%), with or without adjunct Lactobacillus curvatus. Curds were milled when whey reached 0.45% titratable acidity, and pressed for 16 h. After aging at 7.2°C for 6 mo, cheeses were cubed (1 × 1 × 4 cm) and either vacuum-packaged or gas-flushed with carbon dioxide, nitrogen, or a 50:50 mixture of carbon dioxide and nitrogen, then aged for an additional 3 mo. Heavy crystals were observed on surfaces of all cubed cheeses that were gas-flushed, but not on cheeses that were vacuum-packaged. Cheeses without Lb. curvatus exhibited l(+)-CLC on surfaces, whereas cheeses with Lb. curvatus exhibited racemic mixtures of l(+)/d(−)-CLC throughout the cheese matrices. The results show that gas flushing (regardless of gas composition), milk composition, and presence of nonstarter lactic acid bacteria, can contribute to the development of CLC on cheese surfaces. These findings stress the importance of packaging to cheese quality.     

Sulfamethazine detection with direct-binding optical waveguide lightmode spectroscopy-based immunosensor

A direct-binding optical waveguide lightmode spectroscopy-based immunosensor detecting sulfamethazine (SMZ) was prepared, followed by the measurement of its specificity and sensitivity. System construction was undertaken with a peristaltic pump, an injector and the main unit comprising a sensor holder, two signal-harvesting photodiodes, a beam mirror, shutter and He–Ne laser source emitting a monochrome light (λ = 632.8 nm), plus a PC. Antibody immobilization was performed in situ by covalent binding of an anti-SMZ antibody over the surface of a glutaraldehyde-activated 3-aminopropyltriethoxysilane-treated sensor chip. The reaction buffer for the system was 4 mM Tris–HCl (pH 7.2) that showed a medium surface coverage and stable baseline. Sensor response was quite specific to antibody–antigen complexation, as judged from no sensor response caused by bovine serum albumin immobilization. The sensor responses according to SMZ concentrations from 10⁻⁸ to 10⁻² M increased linearly in a semi-logarithmic scale, with the limit of detection of 10⁻⁸ M. The immunosensor was favorably reusable for SMZ screening.     

Headspace-solid phase microextraction (HS-SPME) analysis of oxidized volatiles from free fatty acids (FFA) and application for measuring hydrogen donating antioxidant activity

Volatile compounds from thermally oxidized free fatty acids (FFA) at 93 °C for 200 min were analyzed by headspace-solid phase microextraction (HS-SPME)-gas chromatography (GC). Commercially available mixtures of FFA were used instead of selecting specific vegetable oils with various fatty acid compositions. As oxidation time increased, total volatiles and some individual volatiles including hexanal, 2-hexenal, 2-heptenal, 2,4-heptadienal, 2-octenal, and 2,4-decadienal increased linearly with 0.99 coefficient of determination (R²) at specific oxidation time against conjugated dienoic acid (CDA) or p-anisidine value (p-AV). Total volatiles showed the highest linearity (R²) of 0.99 and 2-heptenal showed the highest increasing slope in peak areas for 200 min oxidation. Not all oxidized volatiles increased linearly during oxidation. Availability of HS-SPME method for determining hydrogen donating antioxidant activity was tested using FFA containing serially diluted butylated hydroxytoluene (BHT) at 93 °C for 60 min. 2-Heptenal and total volatiles showed higher linearity against BHT concentration than hexanal. HS-SPME could be a useful method to determine the hydrogen donating antioxidant activity from FFA using total volatiles or 2-heptenal as oxidation markers.     

Potential use of antioxidative mungbean protein hydrolysate as an anticancer asiatic acid carrier

This study investigated the potential use of mungbean (Vigna radiata (L.) Wilczek) protein hydrolysate (MPH) prepared from tryptic hydrolysis as an antioxidative hydrolysate and as a carrier for anticancer asiatic acid (AA). The antioxidant capacity of MPH was 0.67 and 0.46 ??mol Trolox equivalent (TE)/mg protein, as measured by oxygen radical absorbance capacity-fluorescein (ORAC_FL) and Trolox equivalent antioxidant capacity (TEAC) assays, respectively. Freeze-drying in lactose excipient reduced the antioxidant capacity of MPH to 0.48 ??mol TE/mg protein in ORAC_FL assay (P < 0.05) but did not alter antioxidant capacity determined by TEAC assay (P ≥ 0.05). The genotoxicity of H₂O₂ (50 ??M, 30 min) on hepatoblastoma HepG2 could be alleviated after HepG2 cells had taken up MPH after H₂O₂ exposure (P < 0.05). Moreover, the inhibition concentration (IC₅₀) of AA in HepG2 was lowered from 58.5 ??g mL^− 1 of AA alone to 38.5 ??g mL^− 1 when AA was freeze-dried with MPH in lactose excipient (P < 0.05). This study suggested that the efficacy of anticancer pentacyclic triterpene AA against hepatoblastoma HepG2 could be increased by co-drying with antioxidative mungbean protein hydrolysate in lactose excipient.     

Optimization of ionic liquid based ultrasonic assisted extraction of puerarin from Radix Puerariae Lobatae by response surface methodology

Ionic liquid (IL) based ultrasonic assisted extraction (ILUAE) was developed for the effective extraction of puerarin from Radix Puerariae Lobatae (RPL). The ILUAE parameters including the type of ILs, IL concentration, RPL amount, ultrasonic power and time were optimized by single-factor experiment and response surface methodology. Under the optimized experimental conditions, the best results were obtained using RPL amount 0.43 g in 10 mL 1.06 mol L⁻¹ 1-butyl-3-methylimidazolium bromide aqueous solution, ultrasonic time 27.43 min and ultrasonic power 480 W. Scanning electron microscope images of RPL samples were obtained to provide visual evidence of the sonication effect. Compared with the conventional ultrasonic assisted extraction and refluent extraction, the proposed ILUAE offered shorter extraction time and remarkable higher efficiencies due to the higher penetration ability and solubility of IL and the cavitation phenomenon produced in the solvent by the passage of an ultrasonic wave, which further supported the suitability of the proposed approach.     

Ultrasonic characterization of lactose crystallization in gelatin gels

Ultrasonic velocity and attenuation measurements (2.25 MHz center frequency) were used to follow bulk crystallization of lactose (43% and 46%) from gelatin (1.5% and 3%) gels at 25 °C, and compared to turbidity (500 nm) and isothermal calorimetric measurements. Ultrasonic velocity decreased slightly (approximately 0.5%) during crystallization while ultrasonic attenuation was low in the absence of lactose crystals and increased progressively during crystallization. The lag time before the onset of crystallization decreased and the maximum rate of increase in attenuation during crystallization increased with increasing lactose supersaturation but was not affected by gelatin concentration (P < 0.05). Similar results were seen in turbidity and isothermal calorimetric measurements. Ultrasonic attenuation measurements have the potential to measure crystallization kinetics in complex food matrices and to be applied on-line. Practical Application: Many foods contain crystals that affect their taste and texture (for example, lactose crystals can give a grainy defect in ice cream). The formation of crystals is often hard to predict so methods to measure the development of crystals inside real foods are useful. In this study, we show that as lactose crystallizes in a gelatin gel the ultrasonic attenuation--capacity to absorb sound--increases and can be related to the amount of crystals present. Ultrasound is easier to apply in real food processing than the existing methodologies.     

An improvement in the immersion freezing process for frozen dough via ultrasound irradiation

The ultrasound-assisted freezing (UAF) process, the influence of UAF on the quality and microstructure of frozen dough, were investigated. Dough cylinders were immersion frozen in an ultrasonic bath with 25 kHz frequency and five different power levels. The results showed that UAF process was consists of three stages: a liquid-state temperature decrease stage, a phase-transition stage, and a solid-state temperature decrease stage; ultrasound enhanced heat transfer more efficiently in the latter two stages than in the first stage, due to more heat generation in the first stage. At 288 or 360 W power levels, the total time for dough freezing shortened more than 11% significantly (P < 0.05), and the required time for each stage was reduced. Moreover, crystal nucleation was also enhanced by ultrasound with the formation of a large number of tiny ice crystals inside the frozen dough, and the maximum penetration force of ultrasound-assisted frozen dough increased.     

Lactulose production from milk concentration permeate using calcium carbonate-based catalysts

Milk concentration permeate (MCP), a low-value by-product of ultrafiltration plants and calcium carbonate-based catalysts were used for lactulose production. The results obtained show the effectiveness of oyster shell powder and limestone for lactose isomerisation as a replacement for egg shell powder. With the reaction conditions of 12 mg/ml catalyst loading, reflux time of 120 min at 96 °C, a maximum yield of 18–21% lactulose was achievable at a cost of <50% of original lactose degradation (measured by HPLC). De-proteination of MCP by acidification prior to isomerisation helped lactulose formation in the earlier stages, but did not significantly increase the yield. The resulting lactulose MCP (40 °B) incorporated at the rate of 3–4% was effective in enhancing the growth rate and acid production of Lactobacillus acidophilus (LA-5) in probiotic products.     

Effects on milk urea concentration,urine output,and drinking water intake from incremental doses of potassium bicarbonate fed to mid-lactation dairy cows

Large variation exists in the potassium content of dairy cow feeds and also within a feed type due to soil type and fertilization. Increased ration K concentration causes a subsequent increase in urinary volume and could be expected to also lower milk urea concentration. Six multiparous mid-lactation Swedish Red dairy cows, all fitted with rumen cannulas, were subjected to 3 different levels of K intake in a Latin square experiment with three 2-wk periods to evaluate the effects on concentrations of milk urea and rumen ammonia, urinary output, and drinking water intake. The treatments were achieved by K supplementation on top of a low-K basal ration fed at individual allowances fixed throughout the experiment. The basal ration, consumed at 20.2 kg of dry matter (DM)/d, provided 165 g of crude protein/kg of DM and consisted of grass silage, concentrates, and urea in the proportions 39.3:60.0:0.7 on a DM basis. Potassium bicarbonate supplementation was 0, 616, and 1,142 g/d, respectively, to give total ration K concentrations that were low (LO; 12 g/kg of DM), medium (MED; 23 g/kg of DM), or high (HI; 32 g/kg of DM). Production and composition of milk was not affected by treatment. A linear effect on milk urea concentration was detected, being 4.48, 4.18, and 3.77 mM for LO, MED, and HI, respectively, and a linear tendency for rumen ammonia concentration with 6.65, 6.51, and 5.84 mg of NH₃-N/dL for LO, MED, and HI, respectively. Milk urea concentration peaked about 3 h after the rumen ammonia peak from the morning feeding, at a level 1.3 mM over the baseline. Urinary urea excretion declined linearly (105, 103, and 98 g of urea-N/d for LO, MED, and HI, respectively). Linear increases occurred in urinary output (0.058 ± 0.001 kg of urine/g of K intake; no intercept; coefficient of determination = 0.997) and drinking water intake (65.9 ± 2.02 + 0.069 ± 0.004 kg of water/g of K intake; coefficient of determination = 0.95). Urinary K concentration leveled off at 12.4 g/L. Urinary creatinine excretion was not affected by K addition, but allantoin excretion increased linearly by 27% from LO to HI, suggesting increased rumen microbial growth. Rumen pH, acetate proportion of total volatile fatty acids, and digestibility of DM, organic matter, and neutral detergent fiber increased linearly with increasing potassium intake. We concluded that increased ration K concentration lowers milk urea concentration with a magnitude significant for the interpretation of milk urea values, but other sources of variation, such as sampling time relative to feeding, may be even more important.     

Longer milking intervals alter mammary epithelial permeability and the Udder's ability to extract nutrients

Increasing the milking interval decreases milk yield and modifies milk composition. To gain a clearer understanding of the regulation of milk yield and composition, a study was conducted to establish the response curves of nutrient extraction by the mammary gland and mammary epithelial permeability in response to increasing milking intervals. Four multiparous lactating dairy cows were milked at 8-, 12-, 16-, or 24-h intervals over a period of 7 d using a Latin square design. Between the 8- and 24-h milking intervals, milk yield and milk protein levels fell curvilinearly from 38.2 to 29.2 kg/d and from 1,086 to 827 g/d, respectively. Milk fat yield decreased linearly from 1,475 to 1,235 g/d. Indicators of the opening of tight junctions increased linearly with increasing milking intervals: milk BSA increased from 148 to 207 mg/L and plasma lactose increased from 22.9 to 32.0 mg/L. The mammary gland's ability to extract nutrients decreased with increasing milking intervals. Extraction rates of glucose, β-hydroxybutyrate, and total glycerol decreased significantly (from 27.2 to 23.3%, from 42.3 to 34.4%, from 36.6 to 30.8% between 8- and 24-h milking intervals, respectively), and not significantly for α-amino nitrogen (from 23.2 to 20.0%). The extraction rate of acetate remained constant. Moreover, the extraction of milk fat precursors appeared to be less regulated than those of the precursors of milk protein and lactose, which could partly explain why milk yield and milk protein yield decreased more than milk fat yield. The arteriovenous differences of β-hydroxybutyrate and total glycerol remained constant, whereas those of glucose decreased significantly from 0.98 to 0.87 ± 0.05 mmol/L and not significantly from 0.74 to 0.64 ± 0.12 mmol/L for α-amino nitrogen. As a result, the mammary gland's ability to extract nutrients appears to be downregulated explaining partly the decrease in daily milk yield observed in response to increased milking intervals.     

Electrochemical sensor based on graphene and mesoporous TiO2 for the simultaneous determination of trace colourants in food

Currently, synthetic colourants draw much attention as food additives. This paper investigated the simultaneous electrocatalytic oxidation of sunset yellow and tartrazine, two yellow colourants commonly present in food together, with a novel voltammetric sensor based on graphene and mesoporous TiO₂ modified carbon paste electrode. Due to the high accumulation effect and great catalytic capability of graphene and mesoporous TiO₂, the developed sensor exhibited well-defined and separate square wave voltammetric peaks (i.e., 272 mV) for sunset yellow tartrazine. The peak currents of sunset yellow and tartrazine increased linearly with their concentration in the ranges of 0.02–2.05 μM and 0.02–1.18 μM, respectively. And the detection limit was 6.0 and 8.0 nM for sunset yellow and tartrazine, respectively. This new sensor was applied to determine sunset yellow and tartrazine in several food sample extracts. Results suggested that the proposed sensor was sensitive, rapid and reliable.     

Short communication: Effect of estrogen supplemented at dry-off on temporal changes in concentrations of lactose in blood plasma of Holstein cows

The objective was to determine the effect of supplemental estrogen (estradiol cypionate, ECP) at dry-off on temporal changes in concentrations of lactose in blood plasma of Holstein cows as an indicator of rate of mammary involution. Thirty-two Holstein cows (8/group) were assigned randomly to 4 treatment groups: 30-d dry, 30-d dry + ECP, 60-d dry, and 60-d dry + ECP. A single injection (7.5 mL) of cottonseed oil (30- and 60-d dry) or ECP (15 mg) in oil (30- and 60-d dry + ECP) was administered intramuscularly at dry-off. Blood samples were collected from the coccygeal vein of all cows 24 h before dry-off and at dry-off, and then 8 samples were collected throughout the subsequent 48 h to monitor concentrations of lactose in blood plasma. No significant effects of ECP on the overall mean concentrations of lactose were detected. Concentrations of lactose increased and were greatest in blood collected 20 h (520.4 ± 54.1, 268.1 ± 48.2, 345.0 ± 52.3, 418.4 ± 49.8 μM, for the 4 treatment groups respective to the order listed above) after supplemental ECP and final milk removal. At 40 h, concentrations approached those observed 24 h before dry-off (140.5 ± 52.1, 57.6 ± 47.1, 90.1 ± 51.4, 61.2 ± 48.4 μM, respectively). Concentrations of lactose at 20 h were positively correlated with milk yield of cows at dry-off. Similar temporal profiles of lactose in blood plasma of cows supplemented or not with ECP indicated that ECP at dry-off did not markedly alter the course of tight junction leakage that typically occurs in mammary epithelial tissue during progressive early involution when milk removal is discontinued.     

Effects of monensin and dietary soybean oil on milk fat percentage and milk fatty acid profile in lactating dairy cows

The objective of this study was to investigate the effect of monensin (MN) and dietary soybean oil (SBO) on milk fat percentage and milk fatty acid (FA) profile. The study was conducted as a randomized complete block design with a 2 × 3 factorial treatment arrangement using 72 lactating multiparous Holstein dairy cows (138 ± 24 d in milk). Treatments were [dry matter (DM) basis] as follows: 1) control total mixed ration (TMR, no MN) with no supplemental SBO; 2) MN-treated TMR (22 g of MN/kg of DM) with no supplemental SBO; 3) control TMR including 1.7% SBO; 4) MN-treated TMR including 1.7% SBO; 5) control TMR including 3.4% SBO; and 6) MN-treated TMR including 3.4% SBO. The TMR (% of DM; corn silage, 31.6%; haylage, 21.2%; hay, 4.2%; high-moisture corn, 18.8%; soy hulls, 3.3%; and protein supplement, 20.9%) was offered ad libitum. The experiment consisted of a 2-wk baseline, a 3-wk adaptation, and a 2-wk collection period. Monensin, SBO, and their interaction linearly reduced milk fat percentage. Cows receiving SBO with no added MN (treatments 3 and 5) had 4.5 and 14.2% decreases in milk fat percentage, respectively. Cows receiving SBO with added MN (treatments 4 and 6) had 16.5 and 35.1% decreases in milk fat percentage, respectively. However, the interaction effect of MN and SBO on fat yield was not significant. Monensin reduced milk fat yield by 6.6%. Soybean oil linearly reduced milk fat yield and protein percentage and linearly increased milk yield and milk protein yield. Monensin and SBO reduced 4% fat-corrected milk and had no effect on DM intake. Monensin interacted with SBO to linearly increase milk fat concentration (g/100 g of FA) of total trans-18:1 in milk fat including trans-6 to 8, trans-9, trans-10, trans-11, trans-12 18:1 and the concentration of total conjugated linoleic acid isomers including cis-9, trans-11 18:2; trans-9, cis-11 18:2; and trans-10, cis-12 18:2. Also, the interaction increased milk concentration of polyunsaturated fatty acids. Monensin and SBO linearly reduced, with no significant interaction, milk concentration (g/100 g of FA) of short- and medium-chain fatty acids (<C16). Soybean oil reduced total saturated FA and increased total monounsaturated FA. These results suggest that monensin reduces milk fat percentage and this effect is accentuated when SBO is added to the ration.     

Effects of particle size and its distribution on specific cake resistance during rice wine microfiltration

The effects of particle size and its distribution on permeate flux and specific cake resistance (α) of rice wine suspensions were determined. Specific cake resistance decreased as the ratio of particles having size larger than 45 μm increased. For rice wine suspensions with particle sizes in the range of 1-20 μm (mean diameter of 5-6 μm), α increased linearly with total suspended solids concentration. The dependence of α on total suspended solids concentration was minimal when particles with size greater than 20 μm were present. Specific cake resistance was independent of total suspended solids concentration when rice wine suspensions contained greater than 50% by weight of particles having size larger than 45 μm.     

Production of galactooligosaccharides using a hyperthermophilic β-galactosidase in permeabilized whole cells of Lactococcus lactis

Galactooligosaccharides (GOS) are novel prebiotic food ingredients that can be produced from lactose using β-galactosidase, but the process is more efficient at higher temperatures. To efficiently express the lacS gene from the hyperthermophile Sulfolobus solfataricus, in Lactococcus lactis a synthetic gene (lacSt) with optimized codon usage for Lc. lactis was designed and synthesized. This hyperthermostable β-galactosidase enzyme was successfully overexpressed in Lc. lactis LM0230 using a nisin-controlled gene expression system. Enzyme-containing cells were then killed and permeabilized using 50% ethanol and were used to determine both hydrolysis and transgalactosylation activity. The optimum conditions for GOS synthesis was found to be at pH 6.0 and 85°C. A maximum production of 197 g/L of GOS tri- and tetrasaccharides was obtained from 40% initial lactose, after 55 h of incubation. The total GOS yield increased with the initial lactose concentration, whereas the highest lactose conversion rate (72%) was achieved from a low lactose solution (5%). Given that a significant proportion of the remaining lactose would be expected to be converted into disaccharide GOS, this should enable the future development of a cost-effective approach for the conversion of whey-based substrates into GOS-enriched food ingredients using this cell-based technology.     

The effect of lactose, NaCl and an aero/anaerobic environment on the tyrosine decarboxylase activity of Lactococcus lactis subsp. cremoris and Lactococcus lactis subsp. lactis

The aim of this work was to study, under model conditions, combined effects of the concentration of lactose (0-1% w/v), NaCl (0-2% w/v) and aero/anaerobiosis on the growth and tyramine production in 3 strains of Lactococcus lactis subsp. lactis and 2 strains of L. lactis subsp. cremoris. The levels of the factors tested were chosen with respect to the conditions which can occur during the real process of natural cheese production, including the culture temperature (10 ± 1 °C). In all strains tested, tyrosine decarboxylation was most influenced by NaCl concentration; the highest production of tyramine was obtained within the culture with the highest (2% w/v) salt concentration applied. Two of the strains L. lactis subsp. lactis produced tyramine only in broth with the highest NaCl concentration tested. In the remaining 3 strains of L. lactis, tyramine was detected under all conditions applied. The tested concentration of lactose and aero/anaerobiosis had a less significant effect on tyramine decarboxylation. However, it was also found that at the same concentrations of NaCl and lactose, a higher amount of tyramine was detected under anaerobic conditions. In all strains tested, tyramine decarboxylation started during the active growth phase of the cells.