Characterization of alkylmethoxypyrazines contributing to earthy/bell pepper flavor in farmstead cheddar cheese.

Farmstead Cheddar cheeses with natural bandage wrappings have a distinctive flavor profile that is appealing to many consumers. An earthy/bell pepper (EBP) flavor has been previously recognized in some of these cheeses. This study characterized the alkylmethoxypyrazine compounds causing EBP flavor in Farmstead Cheddar cheeses. Eight cheeses were divided into inner, outer, rind, and wrapper sections, and tested for descriptive sensory and instrumental analyses. To assess reproducibility of EBP flavor, cheeses from the same facilities were purchased and tested after 6 and 12 mo. EBP flavor was detected in four out of 8 Farmstead Cheddar cheeses by a trained sensory panel. 2-sec-butyl-3-methoxypyrazine and 2-isopropyl-3-methoxypyrazine were identified as the main sources of EBP flavor in these cheeses by GC/O and GC/MS. In general, those alkylmethoxypyrazines were prevalent in the wrapper (106 to 730 ppb) and rind (39 to 444 ppb) sections of the cheeses. They were either not detected in inner and outer sections of the cheeses or were present at low concentrations. These results suggest that 2-sec-butyl-3-methoxypyrazine and 2-isopropyl-3-methoxypyrazine are formed near the surface of the cheeses and migrate into the cheese during ripening. Threshold values in water and whole milk were 1 and 16 ppt for 2-sec-butyl-3-methoxypyrazine, and 0.4 and 2.3 ppt for 2-isopropyl-3-methoxypyrazine, respectively. Sensory analysis of mild Cheddar cheese model systems confirmed that direct addition of those individual alkylmethoxypyrazines (0.4 to 20 ppb) resulted in EBP flavor.

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.

The effect of transglutaminase crosslinking on the rheological characteristics of heated peanut flour dispersions.

Peanut flour (PF) is a high-protein ingredient prepared after the partial extraction of oil from roasted peanut seed. Microbial transglutaminase (TGase) catalyzes protein crosslinking via acyl-transfer reactions, resulting in the modification of functional properties such as viscosity, gelation, solubility, and water holding capacity. This work was conducted to observe changes in rheological properties of PF dispersions in the presence and the absence of TGase and amidated pectin (AP). Dispersions were characterized across a range of conditions, including controlled heating and cooling rates under both large- and small-strain deformations. Gelation occurred at temperatures above 78 degrees C using PF dispersions treated with TGase compared to untreated dispersions devoid of the enzyme (about 68 degrees C). The addition of AP (0.5%) resulted in a general increase in viscoelasticity for all dispersions. AP addition also minimized the shift in gel point temperature caused by TGase polymerization reactions. High-molecular-weight polymers were formed in TGase-treated PF dispersions in both the presence and the absence of AP; however, polymer formation was more rapid in PF dispersions without AP. Ortho-phthaldialdehyde assays indicated about 40% protein coupling in PF dispersions treated with TGase compared to about 20% in those containing both AP and TGase. Collectively, these data suggest potential applications of TGase-treated PF dispersions, both in the presence and the absence of AP, for use in peanut-base food products, including protein bars, shakes, and value-added baked goods.

Transglutaminase polymerization of peanut proteins.

Transglutaminase promotes protein cross-linking reactions through an acyl transferase mechanism involving protein-bound glutaminyl residues and primary amines including the epsilon-amino group of lysine residues in soy, myosin, gluten, oat globulin, casein, and whey. Herein, we present a first report of exogenous transglutaminase catalysis of several peanut protein fractions, including purified Ara h 1. In most cases, SDS-PAGE banding patterns revealed the formation of high molecular weight polymers while catalysis of Ara h 1 resulted in distinct dimer formation. Cross-linking effects were accomplished in the presence and absence of the reducing reagent, dithiothreitol. Ortho-phthaldialdehyde assays, used to quantify the degree of polymerization, indicated approximately 21% and approximately 30% coupling over a similar time interval, using either cold hexane extracted peanut protein fractions or lightly roasted flour dispersions, respectively. Rheological measurements established that transglutaminase-modified peanut extracts exhibited lowered viscosity readings compared to nontreated dispersions. Peanut protein polymers and glycoprotein conjugates, created by covalent linkage between protein substrates and monosaccharide amino sugars, exhibited similar IgE binding activity, compared to control solutions. These results suggested that potential allergic responses were not enhanced after enzymatic modification. Ultimately, these approaches may provide novel peanut-based food ingredients with unique functional characteristics for expanded applications within the world marketplace.

Non-detectable levels of trans-fatty acids in peanut butter.

The fatty acid composition of 11 brands of peanut butter and paste freshly prepared from roasted peanuts was analyzed with emphasis on isomeric trans-fatty acids. No trans-fatty acids were detected in any of the samples in an analytical system with a detection threshold of 0.01% of the sample weight. Hydrogenated vegetable oils are added to peanut butters at levels of 1--2% to prevent oil separation. Some hydrogenated vegetable oils are known to be sources of trans-fatty acids in the human diet. The addition of these products was not found to result in measurable amounts of trans-fatty acids in the peanut butters analyzed.

Occurrence of resveratrol in edible peanuts.

Resveratrol has been associated with reduced cardiovascular disease and reduced cancer risk. This phytoalexin has been reported in a number of plant species, including grapes, and may be one of the compounds responsible for the health benefits of red wine. Analytical methods for measuring resveratrol in wine and peanuts were adapted to isolate, identify, and quantify resveratrol in several cultivars of peanuts. Aqueous ethanol (80% v/v) extracts from peanuts without seed coats were purified over alumina/silica gel columns and analyzed by reversed phase HPLC using a C-18 column. Peanuts from each market type, Virginia, runner, and Spanish, produced in four different locations contained from 0.03 to 0.14 microg of resveratrol/g. Seed coats from runner and Virginia types contained approximately 0.65 microg/g of seed coat, which is equivalent to <0.04 microg/seed. Quantitative analysis of 15 cultivars representing 3 peanut market types, which had been cold stored for up to 3 years, indicated a range of 0.02-1.79 microg/g of peanut compared to 0.6-8.0 microg/mL in red wines.

Effect of maturity and curing on peanut proteins. Changes in protein surface hydrophobicity.

A hydrophobic fluorescence probe, 1,8-anilinonaphthalene sulfonate (ANS), was used to study the changes in protein surface hydrophobicity (PSH) occurring during peanut maturation and curing. PSH increased with the degree of maturity and during curing (windrow drying). The increase of PSH during curing or heating was more pronounced in immature peanuts than their mature counterparts, suggesting that more hydrophobic sites are hidden in the former proteins. PSH decreased when proteins were chemically modified with phenylglyoxal (an arginine-modifying agent), suggesting that arginine might play a role in hydrophobicity. The findings indicate that maturation and curing affect PSH, and that there is a relationship between PSH and peanut maturity. Possible factors contributing to the increase of PSH are discussed.

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 degrees 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 degrees C treatment compared to the 25 degrees C treatment, and data indicated that the higher soil temperature also favored growth and aflatoxin production by Aspergillus flavus in peanuts susceptible to contamination.

Color mutants of Aspergillus flavus and Aspergillus parasiticus in a study of preharvest invasion of peanuts.

A comparison of the invasion of flowers, aerial pegs, and kernels by wild-type and mutant strains of Aspergillus flavus or A. parasiticus along with aflatoxin analyses of kernels from different drought treatments have supported the hypothesis that preharvest contamination with aflatoxin originates mainly from the soil. Evidence in support of soil invasion as opposed to aerial invasion was the following. A greater percentage of invasion of kernels rather than flower or aerial pegs by either wild-type A. flavus or mutants. Significant invasion by an A. parasiticus color mutant occurred only in peanuts from soil supplemented with the mutant, whereas adjacent plants in close proximity but in untreated soil were only invaded by wild-type A. flavus or A. parasiticus. Aflatoxin data from drought-stressed, visibly undamaged peanut kernels showed that samples from soil not supplemented with a mutant strain contained a preponderance of aflatoxin B's (from wild-type A. flavus) whereas adjacent samples from mutant-supplemented soil contained a preponderance of B's plus G's (from wild-type and mutant A. parasiticus). Preliminary data from two air samplings showed an absence of propagules of A. flavus or A. parasiticus in air around the experimental facility.

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 degrees C. The lower limit was between 25.7-26.3 degrees C. That is, peanuts grown under drought stress with a mean geocarposphere temperature of 29.6 degrees C were highly contaminated while those at 31.3 degrees C were not contaminated. Likewise, those grown under drought stress with a mean geocarposphere temperature of 25.7 degrees C were not contaminated while those subjected to a mean geocarposphere temperature of 26.0 degrees C resulted in some categories becoming contaminated. Increasing the mean temperature up to 29.6 degrees C caused increasing amounts of contamination.

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 degrees, 25.5 degrees, 30 degrees and 20 degrees C, respectively. Peanut stem temperatures in all drought treatments reached a maximum of ca. 40 degrees C and for 6-7 h each day were as much as 10 degrees C warmer than irrigated peanut stems. Pod temperatures in drought-heated soil and drought treatments were ca. 34 degrees C and 30 degrees C, respectively, for several hours each day. As pod temperatures approached the optimum for A. flavus growth (ca. 35 degrees 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.

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 degrees C and 27 degrees C.

Effects of soil moisture and temperature on preharvest invasion of peanuts by the Aspergillus flavus group and subsequent aflatoxin development.

Four soil temperature and moisture treatment regimens were imposed on Florunner peanuts 94 days after planting in experimental plots in 1980. At harvest (145 days after planting), the incidence of the Aspergillus flavus group and the aflatoxin concentration were greatest in damaged kernels. Extensive colonization of sound mature kernels (SMK) by the A. flavus group occurred with the drought stress treatment (56% kernels colonized); colonization was less in the irrigated plot (7%) and the drought stress plot with cooled soil (11%) and was intermediate in the irrigated plot with heated soil (26%). Aflatoxin was virtually absent from SMK with the last three treatments, but it was found at an average concentration of 244 ppb (ng/g) in drought-stressed SMK. Colonization of SMK by the A. flavus group and aflatoxin production were greater with hot dry conditions. Neither elevated temperature alone nor drought stress alone caused aflatoxin contamination in SMK. When the ratio of SMK colonized by A. flavus compared with A. niger was greater than 19:1, there was aflatoxin contamination, but there was none if this ratio was less than 9:1. Irrigation caused a higher incidence of A. niger than drought did. This may have prevented the aflatoxin contamination of undamaged peanuts.

Effect of peanut tannins on percent seed colonization and in vitro growth by Aspergillus parasiticus.

The relationship between tannin content of mature, intact, cured peanut seed and percent seed colonization by Aspergillus parasiticus was examined. Tannin content in 9 cultivars, 7 of which were grown in both Tifton, Georgia and Puerto Rico, was significantly correlated with percent seed colonization. For data expressed as mg tannin/g intact seed and mg tannin/g seed coat, correlation coefficients with percent colonization were 0.74 and 0.76, respectively. Seed coat tannin, methanol-extracted, water-soluble material from peanut seed coats, was tested in vitro for effects on growth of A. parasiticus. As concentrations of tannins were increased to 7.5%, inhibition of fungal growth increased linearly to 88%; a concentration of 20% produced over 96% inhibition.

Lipoxygenase isozymes of peanut.

Lipoxygenase was isolated and partially purified from peanut seed by ammonium sulfate precipitation, gel filtration, and ion exchange column chromatography. Three isozymes of lipoxygenase were identified. Two had pH optima of 6.2, and the other an optimum of 8.3. Molecular weight of each isozyme was 7.3 x 10(4), as determined by gel filtration. The alkaline optimum isozyme was not inhibited by NaCN and was inhibited by CaCl2 except at very low concentrations. The acid optimum isozymes were inhibited by NaCN and were stimulated by CaCl2 concentrations up to ca. 0.7 mM.

Aerobic pentane production by soybean lipoxygenase isozymes.

The effects of oxygen on production of pentane and compounds absorbing at 234 nm and 285 nm by soybean lipoxygenase isozymes I and II were examined in a model system. Aerobic conditions increased pentane production. Differences in dienone formation (A285) and diene conjugation (A234) indicate the reaction sequences of the 2 isozymes are not the same.

Peanut alkaline lipase.

Peanut alkaline lipase, (glycerol ester hydrolase EC 3.1.1.3), pH optimum 8.5, was isolated from acetone powders prepared from developing and germinated peanut seed (arachis hypogaea L. var. NC-2). Enzyme activity/seed increased in successive developmental stages. The course of the hydrolytic reaction was linear with regard to enzyme concentration and all times tested up to periods exceeding 60 min. Km for the reaction was determined to be 2.6 times 10-4M. Molecular weight of peanut lipase, as estimated by Sephadex gel filtration and sodium dodecyl sulfate gel electrophoresis, was ca. 55,000.