John D. Craske

Comparative studies on volatile components of non-fragrant and fragrant rices

Volatile compounds (70 in all) were identified in cooked fragrant and non-fragrant rice. The most important compounds were alkanals, alk-2-enals, alka-2,4-dienals, 2-pentylfuran, 2-acetyl-1-pyrroline and 2-phenylethanol, but many other compounds were identified that contributed to the total aroma profile. Non-fragrant rice (Pelde) contained much more n-hexanal, (E)-2-heptenal, 1-octen-3-ol, n-nonanal, (E)-2-octenal, (E)-2,(E)-4-decadienal, 2-pentylfuran, 4-vinylguaiacol and 4-vinylphenol, than the fragrant rices (Basmati, Jasmine, Goolarah, YRF9). Jasmine and Goolarah had much more indole, Goolarah and YRF9 had higher amounts of 2-acetyl-1-pyrroline compared with those of Pelde, whilst Basmati had the highest amount of 2-phenylethanol and the lowest content of n-hexanal among all the rice types examined. Results of the sensory evaluation showed that YRF9 and Goolarah had the highest pandan-like aroma whilst Basmati had the highest popcorn-like aroma.

The Change of Total Anthocyanins in Blueberries and Their Antioxidant Effect After Drying and Freezing

This study examined the effects of freezing, storage, and cabinet drying on the anthocyanin content and antioxidant activity of blueberries (Vaccinium corymbosum L). Fresh samples were stored for two weeks at 5°C while frozen samples were kept for up to three months at −20°C. There were two drying treatments, one including osmotic pretreatment followed by cabinet drying and the other involving only cabinet drying. Total anthocyanins found in fresh blueberries were 7.2 ± 0.5 mg/g dry matter, expressed as cyanidin 3-rutinoside equivalents. In comparison with fresh samples, total anthocyanins in untreated and pretreated dried blueberries were significantly reduced to 4.3 ± 0.1 mg/g solid content, 41% loss, and 3.7 ± 0.2 mg/g solid content, 49% loss, respectively. Osmotic treatment followed by a thermal treatment had a greater effect on anthocyanin loss than the thermal treatment alone. In contrast, the frozen samples did not show any significant decrease in anthocyanin level during three months of storage. Measurement of the antioxidant activity of anthocyanin extracts from blueberries showed there was no significant difference between fresh, dried, and frozen blueberries.

Analysis of fatty acid methyl esters with high accuracy and reliability. IV. Fats with fatty acids containing four or more carbon atoms

Those aspects of the quantitative methanolysis of fats with fatty acids containing four or more carbon atoms and the gas liquid chromatographic analysis of the methyl esters which have not been adequately dealt with to date were investigated. Accurate analysis of the esters requires the optimization of the total chromatographic system using a carefully prepared methyl ester primary standard and applying, as the only correction factors, the theoretical flame ionization detector response factors of Ackman and Sipos. These factors now have also been shown to be highly accurate for short chain saturated fatty acid methyl esters, in particular methyl butyrate and methyl caproate. Under the conditions specified by the international methods for the methylation (methanolic KOH) of fats with fatty acids containing four or more carbon atoms, saponification of the esters, once formed, proceeds much more rapidly for short chain than for long chain esters. This problem is easily overcome by neutralizing the catalyst, which then leads to very stable solutions and contributes to column life. This step should be mandatory in the international procedures. Tristearin methylated more slowly than other triacylglycerols under the standard conditions, but there was no difficulty in the case of unsaturated fatty acids of this chain length. Satisfactory results could not be obtained when sodium methoxide was the catalyst. The optimum procedure rendered unnecessary the use of methyl pentanoate as an internal standard for the accurate quantitation of methyl butyrate.

Analysis of fatty acid methyl esters with high accuracy and reliability. V. Validation of theoretical relative response factors of unsaturated esters in the flame lonization detector

Because unsaturated fatty acid methyl esters (FAME) are subject to autoxidation, it is virtually impossible to obtain and maintain high purity standards. Accordingly, it is not possible to determine flame ionization detector response factors by the usual technique of analyzing standard mixtures of known composition. In an alternative approach, the response factors of methyl oleate, methyl linoleate, methyl linolenate, methyl arachidonate and methyl 4,7,10,13,16,19-docosahexaenoate relative to methyl stearate were estimated by determining the peak areas before and after quantitative hydrogenation in the presence of an internal standard. The estimates showed excellent agreement in all cases with the theoretical factors predicted by Ackman and Sipos and thus constitute an independent and unambiguous proof that the theoretical factors are highly accurate for all olefinic unsaturated FAME. Whereas it is common practice to determine an empirically derived correction factor for each FAME by analyzing standard mixtures of known composition, the thesis is now proposed that, for both saturated and olefinic unsaturated FAME, the proper approach to accurate analysis requires that peak areas be corrected using the theoretical response factors as the only correction factors. If the correct result cannot be obtained when analyzing a primary standard of saturated FAME, it is an indication of faulty technique or equipment, and the only acceptable resolution of the problem is to locate and correct the fault(s).

Gas liquid chromatography analysis of the fatty acid composition of fats and oils: A total system for high accuracy

The generally accepted approach to the analysis of fatty acid methyl esters (FAME) by gas liquid chromatography (GLC) is to analyze a standard mixture of known composition and to determine empirical correction factors for individual FAME. These correction factors, which are a composite of the theoretical flame ionization detector (FID) relative response factors and an empirical factor to correct for any system errors that may be present, then are used to correct the raw peak areas of the individual FAME of the sample undergoing analysis. It is proposed that this approach is fundamentally unsound as a means of generating consistently accurate results. Rather, it has been proven that theoretically calculated FID relative response factors are valid, both for the saturated and unsaturated FAME commonly encountered in edible oils, and that these should be used as the only response factors for the correction of raw peak areas. Thus, the proper approach to the generation of highly accurate results is to optimize both equipment and operator technique so that a correct answer is obtained for a primary standard when these theoretical factors are used, rather than to introduce an empirical correction factor other than the theoretical response factor to take account of faulty practice. Eight facets of equipment operation or operator technique have been identified which must be addressed to optimize accuracy.

Changes in Volatile Components of Paddy, Brown and White Fragrant Rice During Storage

Paddy rice from an Australian fragrant variety, YRF9, was dehulled and milled. A total of three samples—the original paddy and the resulting brown and white rices obtained by dehulling and/or milling—were then stored for 3 months at 30°C and 84% relative humidity under atmospheric pressure, or under a vacuum of about 150 Pa. Before storage, a sample was dehulled and milled and the volatile components were isolated from the resulting white rice using a modified Likens–Nickerson simultaneous distillation–extraction unit (SDE). After storage, the paddy and brown rices were dehulled and/or milled as appropriate and the volatile components were isolated from the resulting white rices, as well as that stored in the white rice form, using the same SDE technique. Rice stored under both sets of conditions acquired a slightly musty, rancid odour, the more so for the sample stored in air. During storage in air, there was an increase in the level of total volatile compounds in all three forms of rice, which was far greater for the white rice. This increase was largely due to aldehydes and ketones commonly formed as a result of lipid oxidation processes. This indicates that, when stored in air, the fragrant aroma character was retained better in brown and paddy rice than in white rice, because the development of off-flavours was inhibited by the protective layers of bran and hull. However, during vacuum storage, total and neutral volatiles decreased in all stored rices, with acidic and basic fractions being relatively unchanged. The volatiles profile of white rice stored under reduced pressure was closer to that of the fresh rice than were those of the equivalent storage samples of either the brown or paddy rices. During storage, the content of 2-acetylpyrroline, a compound that contributes greatly to the favourable character of fragrant rices, decreased to the extent of around 40–50% no matter what the form of the rice, or the condition of storage. It is thus concluded that, while it was found possible to inhibit the development of off-flavours to some extent, no way was found to assist the preservation of the desirable flavour compound, 2-acetylpyrroline.

Analysis of fatty acid methyl esters with high accuracy and reliability. VI: Rapid analysis by split injection capillary gas-liquid chromatography

Of the several facets of technique that must be addressed to allow the generation of highly accurate results by gas chromatographic analysis of fatty acid methyl esters, that of split injection to capillary columns has long been a major problem. A practical solution of this problem is now proposed. Three factors were found to be of major importance in achieving highly accurate results viz. avoidance of needle discrimination when injecting, very rapid vaporisation of the sample and complete homogenisation of the sample with the carrier gas stream. High speed of injection was found to be a highly effective means of avoiding needle discrimination. Rapid vaporisation of the sample was achieved by the use of relatively dilute solutions of analyte in the solvent, the smallest sample size commensurate with obtaining a chromatogram that could be accurately quantitated and, particularly, by the use of injector temperatures considerably higher than those generally adopted. Good mixing of the vaporized sample with the carrier gas was achieved with a number of injector insert designs, but, with improvement of design, it was found possible to achieve linear splitting over a wide range of operating conditions. The most controversial recommendation is to use very high injection temperatures, but it has been shown that the commonly held view that this may cause pyrolysis of fatty acid methyl esters is not true, even when the esters are highly unsaturated.

Effects of drying treatments on the composition of volatile compounds in dried nectarines

The effects of drying treatments including dryer type, drying conditions, and sample preparation on the composition of volatile compounds in two cultivars of dried Australian nectarines were investigated in this study. A cabinet dryer, a tunnel dryer, and a heat pump dryer were evaluated. The sample preparation included halving or slicing the fruit to different slice thickness and in different directions. The volatile compounds in fresh and dried nectarines were isolated using Likens Nickerson simultaneous distillation and extraction technique and identified by gas chromatography. The results indicated that a heat pump dryer was the best system for preservation of volatile compounds in sliced dried fruit in terms of lactones and terpenoids followed by cabinet dryer and tunnel dryer.

Separation of instrumental and chemical errors in the analysis of oils by gas chromatography: A collaborative evaluation

Thirty-five analysts studied the concept that, in the gas chromatographic (GC) analysis of fatty acid composition, errors can be separated into those caused by poor chromatograph optimization and those related to inefficient conversion of triacylglycerols (TAG) to fatty acid methyl esters (FAME). A primary standard mixture of FAME was used to determine how well the participants had optimized their chromatographs. A primary standard of the equivalent TAG was used to determine total error of analysis. “Chemistry error” was calculated as the difference between the absolute errors found for the FAME and the TAG standards. Grades of analysis were computed for the FAME and TAG results and for the chemistry errors calculated from these analyses.Only four analysts achieved grades of analysis for the FAME standard that can be considered excellent or good. These four analysts used different injector/column configurations, indicating that, when properly optimized, a GC with a flame ionization detector is an extremely accurate instrument. Conversely, it is evident that there is the potential for most analysts to improve their instrumental optimization. In agreement with published information, AOCS method Ce 2-66 and AOAC method 969.33 gave low chemistry grades, but a number of analysts used modifications of these methods, and some achieved much better grades. It would appear that many of the standard methods that are in common use are capable of producing improved results, but that critical parameters need to be better specified to ensure minimization of error. The concept of separating errors into those of instrument origin and those caused by the chemical component of the total method would appear to be a useful concept for the validation of analytical methods.

Effect of overload of capillary gas-liquid chromatographic columns on the equivalent chain lengths of C18 unsaturated fatty acid methyl esters

Abstract Column overload causes errors in the estimation of equivalent chain lengths (ECLs) of fatty acid methyl esters (FAMEs), and the extent of these errors on fused-silica open tubular columns has been investigated. Load limits for several common FAMEs were accurately determined utilizing a synchronized, rapid automatic liquid sampler. The findings were applied to obtain estimates of ECLs of a range of C 18 unsaturated FAMEs to a precision (repeatability) of about ± 0.001 ECL units. Three stationary phases, DEGS, SP-2330 and Supelcowax 10, were studied, each at three temperatures.