The Girard-T reagent was used to recover the aldehydes from cold-pressed lemon, orange and grapefruit oils for subsequent quantitative gas chromatographic analysis. Optimum conditions for analysis were worked out with a known mixture of citral and the saturated aliphatic aldehydes which occur in major concentration in lemon oil. Isopropanol was used in the preparative step to eliminate acetal formation and isopentane in the final extractions to reduce losses of the lower-molecular-weight aldehydes during vacuum concentration of the sample for gas chromatographic analysis. Typical analyses are given for samples of domestic cold-pressed citrus oils.
The direct -effect of the free fatty acids themselves on flavor and aroma would depend on the kind of acids liberated. The metabolic liberation of fatty acids to supply energy in the depleted live pig may produce a pattern of acids different from that produced by autolysis in post-mortem fat. Relation of fat acidity to depletion was evident from the following observation. In the 14 back fat samples having acid numbers above 0.40, the liver glycogen values in milligrams per gram were distributed as follows: 7 at 2 or lower; 2 at 4 to 8; 3 at 12; and 2 at 25. In the 16 samples having acid numbers below 0.25, the liver glycogen values were: 13 at 41 to 97; lat28; and 2 at 12 to 14.A scattergram for fat flavor and acid numbers after a 24-week frozen storage (Figure 2) gave a strikingly different pattern from that shown in Figure 1. At that time, traces of peroxide had appeared in only four samples, but the flavor had deteriorated so far that 81% of the points were located in the region comparable to area D (Figure 1). Free fatty acid had increased 50 to 100% in most samples.
SUMMARYA method for estimating the total monoterpene hydrocarbon content of citrus oils is described. The procedure consists of adding an internal standard (n‐butylbenzene) to the oils, spotting the mixture on a chromatostrip, eluting the hydrocarbons, and analyzing the eluate by gas chromatography. The total monoterpene hydrocarbon content is calculated from the weights of n‐butyl‐benzene and citrus oil used and from the areas under the peaks of the monoterpene hydrocarbons and n‐butylbenzene on the chromatogram. The average percent total monoterpene hydrocarbon content and the standard deviation are given for a selected number of citrus oils. Data also show the relative monoterpene hydrocarbon composition of these oils.
SUMMARY
The variables included storage prior to processing, heavy and light juice‐extraction pressures, and various methods of juice finishing. Lemons stored for 15 weeks dropped 64% in l‐malic acid but increased 34% in the total amino acids. Total polyphenolics showed no significant change. Extremes of extraction pressure had a significant effect on the amino acid (increased), total polyphenolic (increased), and Z‐malic acid (decreased) values but not on the citric acid, sterol, carotenoid, and soluble pectin values. The finishing process affected only the pectin content. Changes in some of the constituents with extraction pressure were small in comparison with the natural range of values. The prediction of citric acid by the multiple‐regression approach, reported earlier, is independent of commercial fruit storage and processing practices.
The total amino acid and i-malic acid content of 61 samples of commercial California-Arizona lemon juice and lemon juice concentrates were studied. In characterizing these juices, relationships were observed between the natural citric acid content and the amounts of their total amino acids and l-malic acid. Total amino acids were determined by formol titration, while the l-malic acid was determined by measuring the optical rotation of a uranylmalate complex. Paper chromatograms of the individual amino acids are used to supplement these methods of analysis for characterizing lemon juice.
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