Effect of high temperature on condensed tannin accumulation in leaf tissues of big trefoil (Lotus uliginosus Schkuhr)

Plants from three clones of big trefoil (Lotus uliginosus Schkuhr) having low, medium and high concentrations of tannin in their leaves were subjected to growing conditions with normal (20°C) and high (30°C) temperature regimes. Plants were tested every 3 weeks for foliar condensed tannin content using the vanillin-HCl and the butanol-HCl assays. Plants from clones growing under high temperatures matured more quickly and by 14 days had condensed tannin levels substantially greater than plants from the same clones grown under normal temperatures. Clones remained consistent with respect to their parental tannin levels throughout two trials. Leaves from high-temperature clones suffering additional nutrient stress symptoms had very low levels of foliar condensed tannins and cross-sections of chlorotic leaves revealed an absence of large tannin vacuoles. It is concluded that high-temperature stress can induce the formation of additional condensed tannin in the leaves of this species.     

Condensed tannins from Lotus corniculatus and Lotus pedunculatus exert different effects on the in vitro rumen degradation of ribulose‐1,5‐bisphosphate carboxylase/oxygenase (Rubisco) protein

Condensed tannins (CT) or proanthocyanidins (PA), which occur in a restricted range of forages, have the ability to interact with proteins and enzymes and can influence the digestion of plant protein in the rumen. We compared the effects of CT extracts from Lotus corniculatus and pedunculatus on degradation of the principal leaf protein, ribulose‐1,5‐bisphosphate carboxylase/oxygenase (Rubisco), by rumen microorganisms. Total soluble leaf protein extracted from white clover (Trifolium repens ) was incubated with fresh rumen fluid from sheep and a range of concentrations of each CT extract. The rate of degradation of the large (LSU) and small subunit (SSU) of Rubisco was quantified by fractionating the proteins in samples taken from in vitro rumen incubations using sodium dodecyl sulphate–polyacrylamide gel electrophoresis (SDS‐PAGE) and imaging densitometry. To deduce the effects of the CT extracts, experiments were performed in the presence (CT inactive) and absence (CT active) of polyethylene glycol (PEG; MW 3350). The two CT extracts differed markedly in their effects on the degradation of the LSU and SSU of Rubisco. At concentrations of 0.89 and 1.79 mg CT mg ⁻¹ total soluble leaf protein, the CT extract from L pedunculatus was more effective at preventing the degradation of the LSU and SSU by rumen microorganisms than the CT extract from L corniculatus. At a concentration of 1.79 mg CT mg ⁻¹ total soluble leaf protein, the CT extracts from L corniculatus and pedunculatus prevented about 0.75 and 0.83 of the LSU and about 0.69 and 0.86 of the SSU, respectively, from being degraded. Addition of PEG removed the inhibition and almost complete degradation of these proteins occurred, as was the case in incubations without CT extracts. The results of this study suggest that the concentration of CT in the diet and the chemical structure which affects the activity of the CT needs to be considered when assessing the effects of CT on protein metabolism in ruminants. © 1999 Society of Chemical Industry     

Concentration of indoles and other rumen metabolites in sheep after a meal of fresh white clover,perennial ryegrass or Lotus corniculatus and the appearance of indoles in the blood

The objective of this study was to determine the effect of feeding three fresh forage diets, white clover (WC), perennial ryegrass (PRG) and Lotus corniculatus (LC), on the formation of indole and skatole in the rumen of sheep. The formation of indole and skatole in the rumen and their appearance in the blood were also compared. Peak rumen indole and skatole concentrations per kg crude protein intake (CPI) were significantly higher when feeding WC compared with PRG and LC (P < 0.05) and this was associated with a significantly higher rumen concentration per kg CPI of ammonia, branched chain volatile fatty acids, total nitrogen and soluble nitrogen (P < 0.05). Greater indole and skatole concentrations when feeding WC can be attributed to high solubility and rapid degradation of the forage protein. LC had a similar nutrient composition to WC, but the condensed tannins in LC slowed protein degradation and reduced indole and skatole formation. Indole and skatole concentrations peaked in the plasma 1–2 h after the end of feeding, indicating that skatole and indole are rapidly absorbed from the rumen into the blood. High indole and skatole formation with low intakes of WC indicates that the WC component of traditional New Zealand pastures may be the primary cause of undesirable pastoral flavours that result from the presence of indoles in meat. To ameliorate undesirable flavours, producers reliant on pastoral systems will need to consider using alternative forages such as LC to reduce protein solubility and degradation rate. Copyright © 2007 Society of Chemical Industry     

Milk pH as a function of CO2 concentration, temperature, and pressure in a heat exchanger

Raw skim milk, with or without added CO2, was heated, held, and cooled in a small pilot-scale tubular heat exchanger (372 ml/min). The experiment was replicated twice, and, for each replication, milk was first carbonated at 0 to 1 degree C to contain 0 (control), 600, 1200, 1800, and 2400 ppm added CO2 using a continuous carbonation unit. After storage at 0 to 1 degree C, portions of milk at each CO2 concentration were heated to 40, 56, 72, and 80 degrees C, held at the desired temperature for 30 s (except 80 degrees C, holding 20 s) and cooled to 0 to 1 degree C. At each temperature, five pressures were applied: 69, 138, 207, 276, and 345 kPa. Pressure was controlled with a needle valve at the heat exchanger exit. Both the pressure gauge and pH probe were inline at the end of the holding section. Milk pH during heating depended on CO2 concentration, temperature, and pressure. During heating of milk without added CO2, pH decreased linearly as a function of increasing temperature but was independent of pressure. In general, the pH of milk with added CO2 decreased with increasing CO2 concentration and pressure. For milk with added CO2, at a fixed CO2 concentration, the effect of pressure on pH decrease was greater at a higher temperature. At a fixed temperature, the effect of pressure on pH decrease was greater for milk with a higher CO2 concentration. Thermal death of bacteria during pasteurization of milk without added CO2 is probably due not only to temperature but also to the decrease in pH that occurs during the process. Increasing milk CO2 concentration and pressure decreases the milk pH even further during heating and may further enhance the microbial killing power of pasteurization.