Timothy H. Sanders

Interrelationship of kernel water activity, soil temperature, maturity, and phytoalexin production in preharvest aflatoxin contamination of drought-stressed peanuts

Samples of Florunner peanuts were collected throughout a period of late-season drought stress with mean geocarposphere temperatures of 29 and 25 °C, and determinations of maturity, kernel water activity (aw), percent moisture, capacity for phytoalexin production, and aflatoxin contamination were made. Results showed an association between the loss of the capacity of kernels to produce phytoalexins and the appearance of aflatoxin contamination. Kernel aw appeared to be the most important factor controlling the capacity of kernels to produce phytoalexins. Mature peanuts possessed additional resistance to contamination that could not be attributed solely to phytoalexin production. Kernel moisture loss was accelerated in the 29 °C treatment compared to the 25 °C treatment, and data indicated that the higher soil temperature also favored growth and aflatoxin production by Aspergillus flavus in peanuts susceptible to contamination.

Mean geocarposphere temperatures that induce preharvest aflatoxin contamination of peanuts under drought stress.

Apparently undamaged peanuts grown under environmental stress in the form of drought and heat become contaminated with Aspergillus flavus and aflatoxin in the soil prior to harvest. The upper mean temperature limit for aflatoxin contamination in undamaged peanut kernels grown under drought stress the latter 4–6 weeks of the growing season was between 29.6–31.3°C. The lower limit was between 25.7–26.3°C. That is, peanuts grown under drought stress with a mean geocarposphere temperature of 29.6°C were highly contaminated while those at 31.3°C were not contaminated. Likewise, those grown under drought stress with a mean geocarposphere temperature of 25.7°C were not contaminated while those subjected to a mean geocarposphere temperature of 26.0°C resulted in some categories becoming contaminated. Increasing the mean temperature up to 29.6°C caused increasing amounts of contamination.

Effect of geocarposphere temperature on pre-harvest colonization of drought-stressed peanuts by Aspergillus flavus and subsequent aflatoxin contamination

Florunner peanuts grown in research plots were subjected to 5 soil temperature and moisture treatment regimes resulting in A. flavus infestation and subsequent aflatoxin contamination in drought-stressed peanuts. Treatments imposed beginning 85 days after planting were drought, drought with heated soil and 3 drought treatments with cooled soil. The incidence of A. flavus in drought-stressed, unshelled, sound mature kernels (SMK) decreased with decreases in the mean 5 cm deep soil temperature. The incidence of A. flavus was greater in inedible categories and in damaged kernels than in SMK. The mean, threshold, geocarposphere temperature required for aflatoxin development during the latter part of the peanut growth cycle was found to be between 25.7° C and 27° C.

Fatty acid composition of lipid classes in oils from peanuts differing in variety and maturity

ABSTRACTOils from three varieties of mature peanuts and from one variety at seven physiological maturity stages were extracted with petroleum ether and fractionated into lipid classes. The fatty acid composition of the whole oils and fractions were then determined. The fractions from the Starr variety generally contained more 16:0 and 18:2 and less 18:1 than those from the Florunner and Florigiant varieties. Long chain fatty acids (C20–C24) were generally more predominant in thesn-1,3-diacylglycerol fraction than in other fractions, and only traces of long chain acids were found in the sn-1,2(2,3)-di-acylglycerol fraction. An unusual compound associated with thesn- 1,3-diacylglycerol fraction was detected by GLC. Fatty acid compositions of classes in the different maturity stages showed that, generally, the concentration of 18:1 increased and that the concentrations of all other fatty acids decreased with maturity.

Effect of drought on occurrence ofaspergillus flavus in maturing peanuts

Florunner peanuts were grown in experimental plots with soil moisture and soil temperature modified during the last third of the growing period to produce drought, drought with cooled soil, irrigated and irrigated with heated soil treatments. Twice each week, beginning 97 days after planting, random samples were harvested and maturities of individual pods were determined without destroying pod integrity. The nature and quantity of the microflora associated with the pods and kernels were subsequently assessed. Drought and lower soil temperature resulted in maturity distributions containing higher proportions of immature pods. On peanuts with no visible damage to the pod or kernel, colonization byAspergillus flavus was more frequent in immature than mature kernels. Drought stress increased the incidence ofA. flavus and irrigation decreased it, except when soil temperatures were modified.A. flavus infestation was greatly increased at all maturity levels by pod damage.

The effect of refrigerated and frozen storage on butter flavor and texture.

Butter is often stored for extended periods of time; therefore, it is important for manufacturers to know the refrigerated and frozen shelf life. The objectives of this study were to characterize the effect of refrigerated and frozen storage on the sensory and physical characteristics of butter. Fresh butter was obtained on 2 occasions from 2 facilities in 113-g sticks and 4-kg bulk blocks (2 facilities, 2 package forms). Butters were placed into both frozen (-20 degrees C) and refrigerated storage (5 degrees C). Frozen butters were sampled after 0, 6, 12, 15, and 24 mo; refrigerated butters were sampled after 0, 3, 6, 9, 12, 15, and 18 mo. Every 3 mo, oxidative stability index (OSI) and descriptive sensory analysis (texture, flavor, and color) were conducted. Every 6 mo, peroxide value (PV), free fatty acid value (FFV), fatty acid profiling, vane, instrumental color, and oil turbidity were examined. A mixed-model ANOVA was conducted to characterize the effects of storage time, temperature, and package type. Storage time, temperature, and package type affected butter flavor, OSI, PV, and FFV. Refrigerated butter quarters exhibited refrigerator/stale off-flavors concurrent with increased levels of oxidation (lower oxidative stability and higher PV and FFV) within 6 mo of refrigerated storage, and similar trends were observed for refrigerated bulk butter after 9 mo. Off-flavors were not evident in frozen butters until 12 or 18 mo for quarters and bulk butters, respectively. Off-flavors in frozen butters were not correlated with instrumental oxidation measurements. Because butter is such a desirable fat source in terms of flavor and textural properties, it is important that manufacturers understand how long their product can be stored before negative attributes develop.

Effect of soil temperature and drought on peanut pod and stem temperatures relative to Aspergillus flavus invasion and aflatoxin contamination

Peanut stem and pod temperatures of plants growing in irrigated, drought, drought-heated soil, and drought-cooled soil treatments were determined near the end of the growing season. Mean soil temperatures of the treatments during this period were 21.5°, 25.5°, 30° and 20 °C, respectively. Peanut stem temperatures in all drought treatments reached a maximum of ca. 40 °C and for 6–7 h each day were as much as 10 °C warmer than irrigated peanut stems. Pod temperatures in drought-heated soil and drought treatments were ca. 34 °C and 30 °C, respectively, for several hours each day. As pod temperatures approached the optimum for A. flavus growth (ca. 35 °C), the proportion of kernels colonized and aflatoxin concentrations increased. Increased plant temperature without accompanying pod temperature increases (drought-cooled soil) resulted in colonization percentages and aflatoxin concentrations only slightly higher than those of the irrigated peanuts.

Compositional and mechanical properties of peanuts roasted to equivalent colors using different time/temperature combinations.

Peanuts in North America and Europe are primarily consumed after dry roasting. Standard industry practice is to roast peanuts to a specific surface color (Hunter L-value) for a given application; however, equivalent surface colors can be attained using different roast temperature/time combinations, which could affect product quality. To investigate this potential, runner peanuts from a single lot were systematically roasted using 5 roast temperatures (147, 157, 167, 177, and 187 °C) and to Hunter L-values of 53 ± 1, 48.5 ± 1, and 43 ± 1, corresponding to light, medium, and dark roasts, respectively. Moisture contents (MC) ranged from 0.41% to 1.70% after roasting. At equivalent roast temperatures, MC decreased as peanuts became darker; however, for a given color, MC decreased with decreasing roast temperature due to longer roast times required for specified color formation. Initial total tocopherol contents of expressed oils ranged from 164 to 559 μg/g oil. Peanuts roasted at lower temperatures and darker colors had higher tocopherol contents. Glucose content was roast color and temperature dependent, while fructose was only temperature dependent. Soluble protein was lower at darker roast colors, and when averaged across temperatures, was highest when samples were roasted at 187 °C. Lysine content decreased with increasing roast color but was not dependent on temperature. MC strongly correlated with several components including tocopherols (R(2) = 0.67), soluble protein (R(2) = 0.80), and peak force upon compression (R(2) = 0.64). The variation in characteristics related to roast conditions is sufficient to suggest influences on final product shelf life and consumer acceptability.

Content of Some Nutrients in the Core of the Core of the Peanut Germplasm Collection

Abstract The usefulness of core collections of germplasm collections has been well established. The U.S. germplasm collection for peanuts was selectively reduced based on morphological characteristics to a mini core or “Core of the Core” collection composed of 112 of the 7432 accessions in the whole collection to make it more efficient for study. Of these samples, 108 were available from one location in the same year and were therefore exposed to one set of environmental conditions wherein genetic variability could also be examined. These samples were analyzed for total and individual amino acid content, fatty acid content, tocopherols, and folic acid content. These data provide a starting point for establishing nutrient composition within these accessions and provide an early indication of currently important characteristics in these lines which might be suited for use in random breeding initiatives.

DIELECTRIC PROPERTIES OF IN-SHELL AND SHELLED PEANUTS AT MICROWAVE FREQUENCIES

Dielectric properties (..,.. ) of ground samples of in-shell and shelled peanuts (Arachis hypogaea L.) were measured for several densities, temperatures, and moisture contents in the range of 300 to 3000 MHz. Dielectric mixture equations were used to correlate the dielectric properties with density. The coefficients of quadratic and linear dielectric mixture equations are tabulated for 915 and 2450 MHz, for different temperatures and moisture contents. The values of the dielectric constant (..) and loss factor (.. ) of bulk in-shell and shelled peanuts were determined by extrapolation of the firstand second-order polynomials that relate .. and .. with density. An equation that determines the dielectric properties of “nominal” peanut pods (in-shell peanuts) and kernels (shelled peanuts) as a function of their temperature and moisture content was determined by using multiple linear regression.