Robert C. Lindsay

Evaluation of compounds contributing characterizing fishy flavors in fish oils

AbstractsVacuum steam-deodorized fish oils oxidized under flourescent light (950 lux) at 21°C initially developed green flavors which were caused principally by t,c-2,6-non-adienal, but some green-type flavor notes were contributed byt-2-hexenal and 1,c-5-octadien-3-one. Diminishment of green flavor notes resulted from the depletion of 2,6-nonadienal and the formation ofc-4-heptenal (>1 ppm) which contributed oxidized, burnt flavor notes. Concomitant formation oft,c,c- andt,t,c-2,4,7-decatrienal (>1 ppm) yielded characterizing burnt/fishy or cod liver oil-like flavors in fish oils. Two unidentified compounds exhibiting minnow-bait-bucket and trout-like odor qualities, respectively, were encountered in oxidizing fish oils. Hexanal, 2,4-heptadienals and 2,4-decadienals contributed general oxidized, painty flavors to fish oils.

Ascorbate and transition-metal mediation of methanethiol oxidation to dimethyl disulfide and dimethyl trisulfide

Abstract Headspace-gas chromatography was employed to study the behavior of methanethiol in buffer solutions (pH 6·3) in the presence of transition metals and ascorbate. In the presence of Cu(II) (1 ppm), methanethiol (2 ppm) was depleted within 30 min at 30°C by 70% and 30% under aerobic and anaerobic conditions, respectively. Under similar conditions, Fe(III) alone catalyzed the oxidation of methanethiol to only a very limited extent (15%). However, ascorbate plus Fe(III) mediated a rapid formation of dimethyl trisulfide at 30°C in a model system containing methanethiol and hydrogen sulfide. A partial inhibition of dimethyl trisulfide formation by benzoate in the ascorbate plus Fe(III) system suggested that the hydroxyl radical was involved in the pathway leading to the formation of dimethyl trisulfide.

Retro-aldol degradations of unsaturated aldehydes: Role in the formation ofc4-heptenal fromt2,c6-nonadienal in fish, oyster and other flavors

Alterations of cucumber-, melon-like notes in aromas and flavors caused by retro-aldol degradations oft2,c6-nonadienal were confirmed using gas chromatographic measurements of volatile compounds in model systems. The data indicated that 3-hydroxy-c6-nonenal was formed first by the addition of water to the alpha/beta double bond oft2,c6-nonadienal, and this was followed by a retro-aldol condensation of 3-hydroxy-c6-nonenal to yieldc4-heptenal and ethanal. Compared to the reaction rate in aqueous systems at neutral pH, formation ofc4-heptenal was enhanced substantially at alkaline pH, but was greatly diminished at acidic pH values. Heating (to 90 C) of aqueous model systems oft2,c6-nonadienal held at neutral pH also enhanced the rate of formation ofc4-heptenal substantially compared to that at ambient temperature (21 C). Rates of formation ofc4-heptenal in aqueous model systems held under air or nitrogen atmospheres were similar.c4-Heptenal was not formed whent2,c6-nonadienal was held at 21 C for 96 hr under air or nitrogen in nonaqueous commercial corn oil.

Musty Aroma Compounds Produced by Selected Molds and Actinomycetes on Agar and Whole Wheat Bread

Musty aroma compounds produced by cultures of Streptomycetes odorifer , Streptomycetes griscus , Penicillium roqueforti , Aspergillus flavus , Aspergillus niger , and Botrytis cineria when grown on agar and whole wheat bread were isolated and identified using headspace entrainment and GC-MS analysis. Actinomycete cultures produced the most intense musty aromas, which were attributed to the presence of 2-methylisoborneol and geosmin, whereas P. roqueforti and B. cineria cultures produced an overall musty-fruity odor quality caused by the combination of 2-methylisoborneol and 8-carbon alcohols and ketones. Several musty compounds in the cultures were not identified including an intensely musty, cat-like aroma compound produced by A. flavus . Seven musty aroma-type categories are proposed to assist in defining musty taints produced by microorganisms in food and feedstuffs.

Toxicological properties of thio‐ and alkylphenols causing flavor tainting in fish from the upper Wisconsin River

EC50 Microtox (5 min, 25 degrees C) assay values for 2-isopropylphenol, 3-isopropylphenol, 4-isopropylphenol, 2,4-diisopropylphenol, 2,5-diisopropylphenol 2,6-diisopropylphenol, 3,5-diisopropylphenol, carvacrol, thymol, thiophenol, and thiocresol ranged from 2 x 10(-2) mM for thymol (least toxic) to 2 x 10(-4) mM for 2,4-diisopropylphenol and 4-isopropylphenol (most toxic).

Chemical Intervention Strategies for Substantial Suppression of Acrylamide Formation in Fried Potato Products

Prototype processes were developed for the substantial suppression of acrylamide formation (40-95% compared to untreated controls) in cut surface fried potato products using potato chips (crisps) as the primary model. The most efficacious procedures employed sequentially both surface preparation and subsequent acrylamide precursor complexation and/or competitive inhibition processing steps. Surface preparation processing involved either various low-temperature (50-75 degrees C) aqueous (5-30 min) or ca. 80% ethanol blanch solutions for various times (1-5 min) combined with aqueous leaching steps (1-10 min) to reduce concentration of acrylamide precursors in the critical frying zone of cut potato surfaces. Acrylamide precursor complexation and/or competitive inhibition processing strategies included immersion exposure of prepared cut potato surfaces to solutions or dispersions of various combinations of either calcium chloride, phytic acid, chitosan, sodium acid pyrophosphate, or N-acetylcysteine.

Model systems for evaluating factors affecting acrylamide formation in deep fried foods.

Simulated food pieces constructed from fiberglass pads (models for French fries and chips) were used as carriers for defined aqueous solutions, dispersions of test substances and ingredients to evaluate acrylamide formation. The pads were loaded with a solution containing asparagine and glucose (10 mM each) plus selected reaction modulators before deep fat frying and analysis for acrylamide. Data from fiberglass models along with companion sliced potato samples were used in developing hypotheses for the mechanisms involved in the suppression of acrylamide formation by polyvalent cations, polyanionic compounds, pH, and altered food polymer states in fried potato products.

Controlling acrylamide in French fry and potato chip models and a mathematical model of acrylamide formation: acrylamide: acidulants, phytate and calcium.

We previously reported that in potato chip and French fry models, the formation of acrylamide can be reduced by controlling pH during processing steps, either by organic (acidulants) or inorganic acids. Use of phytate, a naturally occurring chelator, with or without Ca++ (or divalent ions), can reduce acrylamide formation in both models. However, since phytate itself is acidic, the question remains as to whether the effect of phytate is due to pH alone or to additional effects. In the French fry model, the effects on acrylamide formation of pH, phytate, and/or Ca++ in various combinations were tested in either blanching or soaking (after blanching) steps. All treatments significantly reduced acrylamide levels compared to control. Among variables tested, pH may be the single most important factor for reducing acrylamide levels, while there were independent effects of phytate and/or Ca++ in this French fry model. We also developed a mathematical formula to estimate the final concentration of acrylamide in a potato chip model, using variables that can affect acrylamide formation: glucose and asparagine concentrations, cut potato surface area and shape, cooking temperature and time, and other processing conditions.

Volatile compounds in flavor-tainted fish from the upper Wisconsin river

Fillets from Walleye pike (Stizostedion vitreum) and Northern pike (Esox lucius) captured from the Upper Wisconsin River were analyzed for volatile components using simultaneous steam distillation-extraction and GC-MS techniques. Based on comparative odor assessments of eluting GC fractions and GC-MS analysis between control and tainted fish, trace amounts (ppb) of alkylphenols (2-isopropyl-, 4-isopropyl-, 2,4-diisopropyl-, 2,5-diisopropyl-, 2,6-diisopropyl-, 3,5-diisopropyl-, 5-methyl-2-isopropyl-, and 2-methyl-5-isopropyl-) and thiophenol were identified as the principal contributors to flavor-tainting found in fish during the spring of the year. Geosmin and 2-methylisoborneol were major contributors to mustiness flavor-tainting occurring in fish captured in the late summer and were more abundant in downstream fish than in upstream control fish.

Development and characterization of an improved silicic acid-KOH arrestant column for routine quantitative isolation of free fatty acids

An improved silicic acid-KOH arrestant column method for the quantitative isolation of free fatty acids (FFA) is described. The method involves preparation of samples in acidified silicic acid caps that are placed directly above alkaline arrestant column portions in glass Chromatographic tubes. Neutral lipids are eluted with solvents whereas FFA are stopped as K-salts. FFA are recovered by elution with formic acid-containing solvents. The accuracy and reproduci-bility of existing methods were greatly improved by minimizing and stabilizing the extent of alkali-induced glyceride hydrolysis. The improved method is suitable for adaptation to a wide variety of food products and biological systems.