Structures, sensory activity, and dose/response functions of 2,5-diketopiperazines in roasted cocoa nibs (Theobroma cacao)

The taste compounds inducing the blood-like, metallic bitter taste sensation reported recently for a dichloromethane extract prepared from roasted cocoa nibs were identified as a series of 25 diketopiperazines by means of HPLC degustation, LC-MS/MS, and independent synthesis. Among these 25 compounds, 13 cis-configured diketopiperazines, namely, cyclo(L-IIe-L-Phe), cyclo(L-Val-L-Leu), cyclo(L-Pro-L-Pro), cyclo(L-IIe-L-Pro), cyclo(L-Val-L-Tyr), cyclo(L-Ala-L-Tyr), cyclo(L-Phe-L-Ser), cyclo(L-Ala-L-IIe), cyclo(L-Leu-L-Phe), cyclo(L-Pro-L-Val), cyclo(L-Pro-L-Thr), cyclo(L-Pro-L-Tyr), and cyclo(L-Val-L-Val) were identified for the first time in cocoa. In addition, the taste recognition thresholds for the metallic as well as the bitter taste of the diketopiperazines were determined, and after quantitative analysis by using two diastereomeric diketopiperazines as the internal standards, the sensory impact of the diketopiperazines was evaluated on the basis of their dose-over-threshold (DoT) factors calculated as the ratio of the concentration and the threshold concentration of a compound. These data revealed DoT factors above 1.0 exclusively for cis-cyclo(L-Pro-L-Val), cis-cyclo(L-Val-L-Leu), cis-cyclo(L-Ala-L-Ile), cis-cyclo(L-Ala-L-Leu), and cis-cyclo(L-Ile-L-Pro), whereas all of the other diketopiperazines were present below their individual bitter taste threshold concentrations and should therefore not contribute to the cocoa taste. Because the DoT factors do not consider the nonlinear relationship between the concentration and gustatory response of an individual compound, we, for the first time, report on the recording of dose/response functions describing the human bitter taste perception of diketopiperazines more precisely.     

Cataract development in sand and galactosemic rats fed a natural tomato extract

This study investigated the effect of a natural tomato extract (TE) on cataract formation in two animal models. A TE containing 5% lycopene was included in the diet of diabetic sand rats at 0.2%, and Sprague Dawley rats were fed a high-galactose diet (30 g/100 g of diet), supplemented with either the lycopene-rich extract at concentrations of 0.2, 0.4, and 0.8% or BHT (0.2%). TE had no significant effect on plasma glucose levels or cataract development in sand rats; however, in rats maintained on a diet rich in galactose, both BHT and TE decreased cataract incidence, and grades were lower than in control animals. In addition, lens protein and reduced glutathione levels were higher and aldose reductase activity was lower than in the control group. The results suggest that antioxidants act as protective agents when oxidative stress is a primary cause of cataract formation but may be less effective in preventing cataracts in hyperglycemic animals.     

Plant Responses of Ultra Narrow Row Cotton to Nitrogen Fertilization

ABSTRACT

Recent developments in cotton (Gossypium hirsutum L.) production technology in the Mississippi River Delta region include drill planting cotton. Production systems that include drill planting cotton are referred to as ultra narrow row (UNR). Ultra narrow row cotton production is a low input system designed to maximize economic returns. Cotton grown under UNR systems is generally lower yielding and lower returning than conventionally spaced cotton, but the inputs and input costs are also generally reduced compared to conventionally spaced cotton production systems. Studies were conducted for five location-years in southeastern and northeastern Arkansas to determine the optimum N-fertilizer rate for UNR cotton. Plant maturity was estimated using nodes above white flower (NAWF) measurements. The NAWF indicated that greater nitrogen (N)-rates delayed maturity of the crop, although differences were not always significant. Lint yields were significantly different in only three of five location-years. Yield responses of UNR cotton tended to maximize with N-treatments between 56 and 84 kg N ha^{? 1} when significant differences were observed. Plant height, similar to lint yield, was significantly different due to N-treatments in three out of five location-years, and generally increased with increasing N-fertilization up to 112 kg N ha^{? 1}. Boll load was significantly influenced by N-fertilization in only two of five location years. In these two instances, 84 kg N ha^{? 1} was sufficient to maximize boll load. Boll weight, a component of yield, was determined in the southern Arkansas location only. Significant differences in boll weight due to N-fertilization were found in only two of four years. Boll weight generally increased with increasing N-fertilization.     

Nearly singular magnetic fluctuations in the normal state of a high-Tc cuprate superconductor

Polarized and unpolarized neutron scattering was used to measure the wave vector- and frequency-dependent magnetic fluctuations in the normal state (from the superconducting transition temperature, Tc = 35 kelvin, up to 350 kelvin) of single crystals of La1.86Sr0.14CuO4. The peaks that dominate the fluctuations have amplitudes that decrease as T-2 and widths that increase in proportion to the thermal energy, kBT (where kB is Boltzmann's constant), and energy transfer added in quadrature. The nearly singular fluctuations are consistent with a nearby quantum critical point.     

Seismicity remotely triggered by the magnitude 7.3 landers, california, earthquake

The magnitude 7.3 Landers earthquake of 28 June 1992 triggered a remarkably sudden and widespread increase in earthquake activity across much of the western United States. The triggered earthquakes, which occurred at distances up to 1250 kilometers (17 source dimensions) from the Landers mainshock, were confined to areas of persistent seismicity and strike-slip to normal faulting. Many of the triggered areas also are sites of geothermal and recent volcanic activity. Static stress changes calculated for elastic models of the earthquake appear to be too small to have caused the triggering. The most promising explanations involve nonlinear interactions between large dynamic strains accompanying seismic waves from the mainshock and crustal fluids (perhaps including crustal magma).     

Sensory and instrumental measurement of french fry limpness

An instrument is described for measuring the apparent rupture stress and apparent elastic modulus of French fries objectively to evaluate French fry limpness. The fries are bent at a constant rate and the force and deflection recorded during this process. The instrumental results agree with sensory tests. Both instrumental and sensory tests indicate that French fry limpness and specific gravity of the fry are related.     

Potato response to split nitrogen timing with varying amounts of excessive irrigation

Irrigation and nitrogen management are two of the most important factors affecting production efficiency and environmental quality in potato cropping systems. Field studies were conducted in 1990 and 1991 to determine the interactive effects of irrigation amount and N timing on potato yield, quality and nitrate leaching potential. Sprinkler irrigation was applied at approximately 1.0, 1.2 or 1.4 times estimated evapotranspiration (ET) to Russet Burbank potatoes grown on a silt loam soil. Following tuber initiation, a total of 132 kg N/ha was applied through the irrigation system to N treatment subplots using either six weekly 22 kg N/ha applications or 3 biweekly 44 kg N/ha applications. Excessive irrigation reduced root zone and petiole NO₃-N concentrations during substantial portions of the tuber bulking period. Biweekly 44 kg N/ha applications in 1991 produced higher and more consistent earlyseason root zone NO₃-N concentrations in the 1.2 and 1.4 ET plots than did the weekly 22 kg N/ha applications. Late-season tuber dry weight, total plant dry weight and plant N uptake were not affected by irrigation rate or N timing. However, excessive irrigation reduced U.S. No. 1 yield and yield of tubers >284 g in both 1990 and 1991 and reduced total yield in 1990. Biweekly N applications produced higher U.S. No. 1 yields than weekly N applications at all irrigation levels. Excessive irrigation also reduced NO₃-N remaining in the top 60 cm of soil at the end of the growing season. These results show that irrigating at optimal rates and applying split N at two week intervals on a silt loam soil can maximize Russet Burbank yield and quality while minimizing NO₃-N losses.     

Stomatal behavior of potatoes under nonlimiting soil water conditions

Field studies were conducted to examine the relative effects of net irradiance (R_n), air vapor pressure deficit (VPD) and leaf water potential (Ψ₁), on leaf conductance, (C₁) of well-watered potatoes. Conductances of sunlit, surface-layer leaves for the cultivars Russet Burbank, Kennebec and Lemhi Russet were positively correlated with R_n (r²=0.79, 0.83 and 0.62, respectively) for R_n between 100 and 650 Wm^-2. Leaf conductance (cm s^-1) for all three cultivars was described by the linear relation: C₁=0.871 +0.0028 R_n (r²=0.73). Mean C¹ for a full Russet Burbank canopy, comprised of measurements from both sunlit and shaded leaves, was also linearly related to R_n. Although VPD and Ψ₁ were significantly correlated with C₁ (r²=0.44 and 0.46, respectively), the results of multiple regression analysis showed that they had no additional effect on C¹ beyond that attributed to R_n. These results indicate that potato leaf conductance is primarily related to irradiance under nonlimiting soil water conditions.