VOLATILE CONSTITUENTS OF VINEGAR. I. A SURVEY OF SOME COMMERCIALLY AVAILABLE MALT VINEGARS

Gas liquid chromatography was used to fractionate the alcohols, esters, carbonyls and acids in commercial malt vinegars. A qualitative and quantitative study was made using two different stationary phases; methyl formate, acetaldehyde, ethyl acetate, ethyl alcohol, isobutyl acetate, n-propyl alcohol, n-butyl acetate, isobutyl alcohol, amyl alcohol, acetoin, propionic acid and acetic acid were identified and estimated in eleven different malt vinegars. The results of this survey were compared with the information previously found for malt and other types of vinegars. A preliminary assessment has been made of the origins of these volatiles.     

VOLATILE CONSTITUENTS OF VINEGAR. IV. FORMATION OF VOLATILES IN THE FRINGS PROCESS AND A CONTINUOUS PROCESS OF MALT VINEGAR MANUFACTURE

Gas liquid chromatography was used to fractionate and measure volatiles formed during the Frings process and during a continuous process of malt vinegar manufacture. Acetaldehyde, ethyl alcohol, iso-amyl alcohol, acetic acid, n-propyl alcohol, sec-butyl alcohol, isobutyl alcohol, n-amyl alcohol, and also sec-butyl acetate, isobutyl acetate and n-amyl acetate were detected during the alcoholic fermentation but propionic acid, isobutyric acid and acetoin were produced during acetification. The increase in the number and concentration of the volatiles of these processes has been compared with those found for the Quick method.     

VOLATILE CONSTITUENTS OF VINEGAR. II. FORMATION OF VOLATILES IN A COMMERCIAL MALT VINEGAR PROCESS

Gas liquid chromatography was used to fractionate the alcohols, esters, carbonyls and acids formed in a commercial process of vinegar manufacture. Ethyl, n-propyl, sec-butyl, iso-butyl, n-amyl and iso-amyl alcohols, and iso-butyl, sec-butyl and n-amyl acetates were produced during the initial alcoholic fermentation. During acetification, propionic acid, iso-butyric acid and acetoin were produced. There was no increase in the number of volatiles or in their concentration during the maturing process of the charging wort or the subsequent treatments and storage period of the vinegar after acetification. A loss in the lower boiling point volatiles occurred during the storage of all the samples examined. An assessment has been made of the formation of these volatiles both before and after acetification.     

Fatty acid composition and volatile compounds of selected marine oils and meals

BACKGROUND: Although volatile compounds characterising seafood have been studied extensively, no similar data are available regarding the volatiles of raw materials used in fish feed. Therefore the aim of this study was to make an initial screening of the volatiles of various common marine raw materials used in the aquaculture feed industry. Nine commercial marine oils (German (GFO1, GFO2 and GFO3) and Norwegian (NFO) fish oils and salmon (SO1 and SO2), tuna (TO), sardine (SRDO) and shrimp (SHO) oils) and eight commercial marine meals (Peruvian (PFM1 and PFM2), Danish (DFM1 and DFM2) and prime quality (PQFM1 and PQFM2) fish meals and Antarctic krill meals (KM1 and KM2)) were analysed for their fatty acid profiles and volatile flavour compounds. The relation between fatty acids and volatiles was examined. RESULTS: The highest polyunsaturated fatty acid and eicosapentaenoic acid (20:5ω3) contents and ω3/ω6 ratio were found in NFO. The fatty acid composition of all marine meals except krill meals was found to be more variable among batches than that of marine oils. Regarding volatiles, all marine raw materials were characterised by the complete absence or negligible levels of eight‐ and nine‐carbon alcohols and carbonyls. All marine oils were found to have high 2‐ethyl furan, 2‐methylenebutyl cyclopropane, hexanal, 2,4‐octadiene and 3,5‐octadiene contents. Marine meals, unlike marine oils, were characterised by the almost complete absence of unsaturated and cyclic hydrocarbons and terpenes and very low levels of furans. CONCLUSION: Volatiles of marine meals differ from those of marine oils. Unlike fatty acids which give useful traceability information, volatiles seem to fail in this role owing to their strong variability. Copyright © 2008 Society of Chemical Industry     

APPLICATION OF MULTIVARIATE STATISTICS FOR THE QUALITY CLASSIFICATION OF SINGLE-STRENGTH GRAPEFRUIT JUICE

Grapefruit juice volatiles were collected and analyzed by gas-liquid chromatography for 24 samples of commercial single-strength grapefruit juice from different production days and storage conditions. With the help of multivariate statistics, attempts have been made to classify them according to the chromatographic data and sensory evaluation of the juice. The data was analyzed by canonical and cluster analysis. As a typical result, it was found that using three constituents, the samples could be classified into four different quality classes. From the point of view of sensory interpretation, the canonical analysis also proved to be an interesting approach. Of the three more significant constituents, nootkatone and an unknown constituent have positive contribution, while another unknown constituent give a reverse contribution.     

INFLUENCE OF HEATING END-POINT TEMPERATURE ON VOLATILES FROM POULTRY MEAT - A REVIEW

During heating of muscle foods, numerous volatile flavor components are generated. Both the identity and quantity of these volatiles are influenced by cooking end-point temperature (EPT) and post-cooking storage. Methods for assessing flavor volatiles include sensory tests and gas chromatographic (GC) methods. Static headspace GC techniques either with a packed or capillary column have been used to determine the volatiles individually and they are simpler in operation compared to sensory tests. High correlations between EPTs and several compounds in heated chicken breast and leg meat patties have been obtained. Samples prepared in model systems are more uniform in EPTs as compared to processed products. Good resolution and reproducibility in the analysis of volatiles from chicken meat have been reported by using a dynamic headspace-capillary column approach. More than one half of all compounds increased linearly or quadratically as EPT increased. Controlling the heating EPT is important in ensuring the quality and stability of precooked poultry.     

Ruminant fat volatiles as affected by diet. A review

Volatile compounds in meat have been widely studied for their favourable or undesirable effects on meat flavour, or for their potential use in tracing the animal feeding system. To date, the chemical mechanisms causing the appearance of volatile compounds in meat have been largely understood. Several variables are involved in the accumulation of volatiles in animal tissues and among them animal diet plays a key role. The purpose of the present review is to highlight the effects of different dietary regimes (concentrate, green grass and fat-enriched diets) on the appearance of fat volatile compounds in ruminant meat. Grain-based diets induce greater accumulations in meat of branched-chain fatty acids, some aldehydes, and lactones while meat fat from grazing animals contains high levels of phenols, terpenes, indoles and sulphur compounds. Fat-enriched diets exert their effect mainly on those volatiles which originate from polyunsaturated fatty acids. Cooking procedures have been considered for their contribution to fat volatiles in meat by reactions induced by high temperatures.     

PERSISTENCE OF PHOSPHINE GAS IN FUMIGATED IRAQI DATES

Phosphine gas (PH₃) is a widely used fumigant for stored fruits and grains. Previous studies indicated that all residues of this gas are eliminated by normal aeration but the exact time has never been determined.
The objective of this work was to determine the time required for desorption of phosphine from fumigated dates relative to aeration time and temperature. Flame photometric detection by gas chromatography was used for the detection of sorbed phosphine.
Results indicate that the initial residue level of PH₃ falls rapidly within 24 h after fumigation but residues persist for at least nine days. Higher residue levels were found in dates stored at low temperatures (4°C) than at 28°C. It is recommend that fumigated dates be marketed after longer periods of aeration, especially those aerated at temperatures of 4°C or less.     

真菌固定床反应器发酵L(+)-乳酸的初步研究

研究了在5L发酵罐中采用纤维床固定化技术发酵生产乳酸过程不同溶氧量和固定化面积对乳酸发酵过程的影响,测定了不同固定化面积发酵过程中的氧传质系数。在通气率为1.0vvm和固定化面积为400cm2条件下,产酸速率为2.13g/(L·h),发酵液中乳酸最终浓度为73.1g/L,L(+)-乳酸光学纯度为98.9%,证明提高发酵过程中菌体层内部溶氧传质系数有助于增加乳酸产率。乳酸发酵液浊度0.49NTU,显著改善发酵液的流体力学条件,为应用膜生物反应器技术连续发酵生产乳酸奠定了基础。     

MONITORING LIPID OXIDATION AND ANTIOXIDANT EFFECTS OF PHOSPHOLIPIDS BY HEADSPACE GAS CHROMATOGRAPHIC ANALYSES OF RANCIMAT TRAPPED VOLATILES

Two of the most frequently used techniques to follow oxidation patterns of fats are headspace gas chromatography (HS-GC) and gas chromatography/mass spectrometry (GC/MS). The HS-GC technique offers the advantages of rapidity and multiple sample analyses, whereas GC/MS offers the advantages of GC separation coupled with the ability of MS to identify volatile compounds separated via GC. No previous information exists in the literature on the use of the volatiles trapped in water contained in the measuring vessel of the Rancimat and HS-GC to monitor lipid oxidation, as was the objective of this study. Oxidative secondary breakdown products of fish oil model systems trapped in water contained within the measuring vessel of the Rancimat were subjected to HS-GC analyses for quantitation of individual volatiles. Results from this study showed that oxidation induction time and products of oxidation can be monitored by the combined use of the Rancimat and HS-GC, and that trapped volatiles are representative of typical by-products of lipid oxidation and of oil type being examined. Addition of phospholipids (PL) to salmon and menhaden oils significantly influenced the production of volatile compounds. The molecular weights of the volatiles identified ranged from 30 to 212 daltons. The reproducibility of the method (std. dev. ≈ 2.04) was good but can be greatly improved through the use of a capillary column. PL having antioxidant activity generated lower concentrations of total volatiles than those found to be prooxidants.     

Major volatiles in Sri Lankan arrack, a palm wine distillate

Arrack is a potable spirit produced in Sri Lanka by fermenting sap usually obtained from the coconut palm. In this study the major volatiles present in several commercial samples of arrack are found to be similar to those in other potable spirits although their individual concentrations differ. The variation between brands is attributed to differences in the quality of the fermented toddy used. This is thought to result from the uncontrolled and mixed nature of the fermentation. Ethyl lactate was found in all samples analysed and it is thought that production of this ester is a characteristic feature of mixed lacticalcoholic fermentations.     

The oviposition attractant for the mushroom phorid Megaselia halterata: The identification of volatiles present in mushroom house air

Neutral volatiles present in the air of a mushroom house during the spawn running phase of commercial production of the mushroom Agaricus bisporus have been identified and their source has been investigated. A group of polychloroanisoles emanated from broiler-house sweepings used in making wheat straw-chicken manure compost. Most of the straw volatiles were lost during the process of composting. With certain exceptions, most of the volatiles identified were metabolic products of A. bisporus, but the source of some cyclic monoterpenoids remains uncertain. Preliminary information suggests that some A. bisporus C₈ aliphatic alcohols and ketones are attractive to gravid females of the phorid Megaselia halterata.     

THE ORIGIN AND OCCURRENCE OF VOLATILE SULPHUR COMPOUNDS IN BRITISH ALES AND LAGERS

A flame-photometric sulphur detector was used to identify, measure and determine the sources of the sulphur volatiles produced during the commercial processing of British ale and lager. Dimethyl sulphide was the main sulphur volatile present in malt but traces of hydrogen sulphide, diethyl sulphide, and dimethyl disulphide were also detected. Hops contained hydrogen sulphide, methyl mercaptan, dimethyl sulphide, diethyl sulphide, methional and dimethyl disulphide. Most of this material extracted into commercial worts was driven off during boiling. Brewing yeasts produced only traces of organo-sulphur volatiles both in laboratory fermentations of wort and during the processing of commercial ales and lagers. In contrast, brewery bacteria, particularly wort spoilage organisms, could generate dimethyl sulphide and sometimes traces of other sulphur volatiles in laboratory cultures. t-Butyl mercaptan was the only organo-sulphur volatile detected in significant concentrations during the primary fermentation and conditioning of commercial beers and this was attributable to the activity of wort-spoilage bacteria. Attempts to identify a volatile compound causing ‘sulphury’ smells in beer were unsuccessful but there was some evidence that it might not contain sulphur.     

Short communication: Comparison of 3 rapid methods for analysis of vitamin degradation compounds in fluid skim milk

Vitamin fortification of dairy products, including fluid milk and fortified whey protein beverages, is an industry standard but can lead to the development of off-flavor compounds that are difficult to extract and detect by instrumental methods. Previous work has identified these compounds and their specific role in off-flavors in skim milk, but efficient extraction and quantification of these compounds remains a challenge. Three rapid methods (stir bar sorptive extraction, solvent-assisted stir bar sorptive extraction, and solid-phase microextraction) were compared for their ability to effectively recover vitamin degradation volatiles from fluid skim milk. The performance of the 3 methods for detecting and quantifying vitamin degradation-related volatile compounds was determined by linear regression of standard curves prepared from spiked standards of 5 vitamin degradation volatiles, the reproducibility on the same day and between days as measured by the average relative standard deviation of each standard curve, and the limits of detection and quantitation. Measurement of vitamin degradation compounds in commercial pasteurized fortified skim milks was also conducted using each method. Detection of selected vitamin degradation volatiles was linear in skim milk (0.005–200 μg/kg). Coefficient of determination values differed between methods and compounds. Within-day and between-day percentage of relative standard deviation also varied with compound and method. Limits of detection and quantitation values for all methods except solid-phase microextraction were lower than concentrations of selected volatile compounds typically found in commercial milk. Solvent-assisted stir bar sorptive extraction with a 10-mL sample volume provided the most consistent detection of selected compounds in commercial milks. Based on linearity, relative standard deviation, and limits of detection and quantitation, cyclohexane solvent-assisted stir bar sorptive extraction with 10-mL sample volume is recommended for the quantitation of vitamin degradation-related volatiles in fluid skim milk.     

ESTIMATION OF VOLATILE SULPHUR COMPOUNDS IN BEER

A method has been developed for the quantitative estimation of volatile sulphur compounds in beer at levels below 0.1 μg litre^?1. The method relies on the concentration of beer headspace volatiles onto a porous polymer followed by injection into a capillary gas chromatographic column using a thermal desorption cold trap injector. The volatile components are separated using temperature programming and detected by a flame photometric detector specific for sulphur compounds. The mean concentrations and the estimates of r₉₅ (μg litre^?1) for volatile sulphur compounds measured in a commercial lager were respectively: methanethiol (0.33, 0.30); dimethyl sulphide (19.3, 5.3); carbon disulphide (0.42, 0.32); ethylene sulphide (0.37, 0.05); 1-propanethiol (0.11, 0.02); methyl thioacetate (11.7; 2.7); methyl disulphide (0.34, 0.42). The method is a significant improvement over previous techniques for the quantification of sulphur-containing volatiles in beer .     

CONTENTS OF CYTOCHROMES IN YEAST

The contents of cytochromes in yeast were determined quantitatively from the absorption spectra, using a solid cell paste of intact yeast. During the industrial production of baker's yeast, the contents of the cytochromes, particularly of cytochrome aa₃ at successive stages, increased gradually with increasing aeration. In semi-aerobically grown baker's yeast, the contents of cytochromes aa₃, b and c were 0·9, 2·9 and 2·9 × 10^?5 moles/litre of fresh yeast (total amount 6·7 × 10^?5 moles/litre), while in vigorously aerated commercial baker's yeast the respective values were 2·3, 4·8 and 5·2 × 10^?5 moles/litre (total amount 12·3 × 10^?5 moles/litre). In brewer's yeasts separated after the brewing process, the contents of cytochromes were markedly lower than in baker's yeast grown with limited aeration, whereas in top-fermenting yeast the total cytochrome content, aa₃ + b + c, was in some samples markedly higher, 7·1 × 10^?5 moles/litre, than in bottom-fermenting brewer's yeast, 2·4 × 10^?5 moles/litre. When brewer's bottom yeast was grown on a laboratory scale under increasing aeration, a maximum appeared in the cytochrome contents when aeration was moderate, and increased aeration inhibited the formation of cytochromes. The cytochrome contents in brewer's bottom yeast may exceed the amounts found in commercial baker's yeast. In addition to aeration, the type of metabolism influences the amounts of cytochromes in yeast.     

BARLEY MATURITY AND THE EFFECTS OF STEEP AERATION ON MALTING

Micromalting experiments were carried out with barleys varying in maturity. During steeping, which included water changes, the barleys were either allowed to remain static (the controls) or were mixed at intervals or were mixed continuously in continuously aerated water. No significant improvement in the uniformity of endosperm hydration, relative to controls, was found where grains had been mixed or were continuously aerated during steeping. Mature barley responded to continuous aeration with rapid germination during the steeping process, resulting in high malting losses. Periodic mixing during steeping had little effect on malt quality. It is suggested that, where air-rests are provided and mixing is not required to alleviate pressure, aeration (air-sparging) may be of no benefit when malting mature barley. Water-sensitivity was partially overcome by constant aeration, although periodic mixing was ineffective, hence aeration may be useful in malting water-sensitive barleys. The use of intermittent or continuous aeration inhibited the germination of undried dormant barleys. It is suggested that this effect was due to the excessive proliferation of microorganisms where aeration and mixing were provided.     

Effect of terroir on the volatiles of Vitis vinifera cv. Albariño

The effect of terroir on volatiles of Vitis vinifera cv Albariño was studied. Twelve commercial Albariño wines from Galicia, Spain, were analysed. The content of varietals and fermentative volatile compounds was determined by gas chromatography. The numerous significant differences found for most of the aromatic compounds studied show the influence of the terroir. The Albariño wines from northern Galicia showed the highest total concentration of volatiles analysed. The volatile components showing the greatest differences in Albariño wines from different areas were terpenes and higher alcohols. Among the terpenes found, geraniol was markedly abundant in the north, while nerol and linalool were most abundant in the south. Among the alcohols, 2‐phenyl ethanol and benzyl alcohol showed the highest concentrations in the south and in the north, respectively. Cluster analysis and principal component analysis revealed two clearly defined main groups of Albariño wines from different terroirs. Albariño wines from the south were more heterogenic than those of the north. Copyright © 2007 Society of Chemical Industry     

Study by means of H nuclear magnetic resonance of the oxidation process undergone by edible oils of different natures submitted to microwave action

The oxidation processes of virgin olive, corn and linseed oils, repeatedly submitted to the effect of microwave heating until the temperature reached 190 °C, have been studied by means of ¹H nuclear magnetic resonance. These oxidation processes are very different to those produced at 70 °C with aeration; differences have been found not only in the rate of degradation and in the oxidation mechanisms but also in the nature and proportions of the aldehydes generated. It has also been shown that these oxidative conditions affect the three oils studied in very different ways; virgin olive oil is the least affected by this process and in addition its degradation produces lower proportions of harmful aldehydes.     

Trapping of soursop (Annona muricata) juice volatiles on porapak Q by suction

The trapping technique of Singleton and Pattee, in which the volatiles are swept to a Porapak Q trap by suction rather than by a sweeping gas, was modified and used to isolate soursop juice volatiles. Using fixed, low vacuum and operating conditions determined specifically for soursop volatiles, very high reproducibility was obtained. The majority of the peaks had a coefficient of variation less than 0.10. The relative amounts of the volatile components obtained by direct headspace sampling was fairly well maintained in the Porapak Q concentrate. The chromatograms showed distinct differences between two commercial brands or between lots of the same brand of soursop juice. The trapping technique appear to have wide applicability provided that the operating conditions are adapted to each product studied.