Historical review of citrus flavor research during the past 100 years.

Citrus juices are a complex mixture of flavor and taste components. Historically, the contributions of taste components such as sugar (sweet) and acid (sour) components were understood before impactful aroma volatiles because they existed at higher concentrations and could be measured with the technologies of the 1920s and 1930s. The advent of gas chromatography in the 1950s allowed citrus researchers to separate and tentatively identify the major citrus volatiles. Additional volatiles were identified when mass spectrometry was coupled to capillary GC. Unfortunately, the major citrus volatiles were not major influences of citrus flavor. The major aroma impact compounds were found at trace concentrations. With the advent of increasingly more sensitive instrumental techniques, juice sample size shrank from 2025 L in the 1920s to 10 mL today and detection limits fell from percent to micrograms per liter. Currently gas chromatography-olfactometry is the technique of choice to identify which volatiles in citrus juices possess aroma activity, determine their relative aroma strength, and characterize their aroma quality but does not indicate how they interact together or with the juice matrix. Flavor equations based primarily on nonvolatiles and other physical measurements have been largely unsuccessful. The most successful flavor prediction equations that employ instrumental concentration values are based on a combination of aroma active volatiles and degrees Brix (sugar) values.

A comparison of citrus blossom volatiles.

The objective of this study was to identify the major volatiles and their relative concentrations in intact grapefruit, sweet orange, sour orange, mandarin, lemon, lime and pummelo blossoms. Volatiles from freshly picked blossoms were collected and concentrated using static headspace solid-phase microextraction and then separated and identified using GC-MS. Seventy volatiles were detected, 66 identified, of which 29 were identified for the first time in citrus blossoms. Major volatiles consisted of linalool, beta-myrcene, alpha-myrcene, limonene, (E)-ocimene, methyl anthranilate and indole. In terms of total volatiles: pummelo >> grapefruit approximately = sweet orange > sour orange approximately = mandarin approximately = lemon-lime > Volkamer lemon > Kaffir lime. Principal component analysis of blossom volatiles demonstrated that there were three widely separated, tightly clustered groups which consisted of mandarin, lemon-lime and pummelo. Other cultivars of possible mixed parentage produced non-overlapping values within the boundaries of these three clustered groups. The first two Eigenvectors explained 83% of the total variance. Linalool, limonene and myrcene had the highest loading values. Those cultivars requiring insect pollination such as pummelo produced highest levels of total volatiles as well as highest levels of known honeybee stimulants such as 1-hexanol and linalool.