166 Produce Degradation: Reaction Pathways and their Prevention
with no clear set of character-impact compounds yet identified [49,113,114]. Both
flavors are the result of a specific balance of several aroma compounds, and grapefruit
is distinguished from orange primarily on the basis of the sulfur-containing com-
pounds 1-p-menthene-8-ol and 4-mercapto-4-methylpentane-2-one. Nootkatone, a
peel oil constituent, is reported to possess a grapefruit-like character [57] but was
found to be of only moderate importance in grapefruit juice [49]. Mandarin (tan-
gerine) flavor is not as clearly defined as orange and grapefruit; methyl N-methy-
lanthranilate, β-pinene, γ-terpinene, and α-sinensal have been reported as potential
contributing compounds to its unique character [57,115]. A recent study indicated
the importance of 3-sec-butyl-2-methoxypyrazine, ethyl 2-methylbutanoate, 3-iso-
propyl-2-methoxypyrazine, and (Z)-3-hexenal in the aroma of clementine segments
[116]. Lemon flavor is dominated by citral, and other volatile components have
somewhat less impact. Citral also predominates in lime flavor, with possibly ger-
macrene B, linalool, β-pinene, and β-myrcene providing enough complexity to
differentiate lime from lemon flavor [117,118].
6.3.1.7 Tropical Fruit
Among the various tropical fruits, bananas and pineapples are of greatest economic
importance. The aroma of these fruits have, therefore, undergone extensive investi-
gation. In recent years, only relatively few studies have been conducted on the flavor
of some other important tropical fruits, including avocado (Persea americana L.)
[120,121], guava (Psidium spp.) [122–128], mango (Mangifera indica, Anacardi-
aceae) [129–131], passion fruit (Passiflora spp.) [44,47,132,133], and kiwifruit
(Actinidia spp.) [134–136]. The following discussion will present the current under-
standing of the key aroma constituents of banana and pineapple fruit.
6.3.1.7.1 Banana
The flavor chemistry of banana (Musa sapientum L.) has been extensively studied
for over 30 years. Over 350 volatile compounds have been identified, but only a few
components are considered to greatly affect banana aroma [55]. Esters, especially
3-methylbutyl acetate, and to a lesser extent 3-methylbutyl butanoate and various
3-methylbutanoate esters, are important aroma constituents [137,138]. Ester biogen-
esis in banana has received recent attention [138,139]. Some alcohol and aldehyde
constituents (e.g., 3-methyl-1-butanol and 3-methylbutanal) may also be important
in banana aroma [133,137,140].
6.3.1.7.2 Pineapple
Pineapple (Ananas comosus L.) flavor has been the subject of extensive study. Esters
were reported as the major volatile constituents of green and ripened pineapples
[11]. Takeoka et al. [11] used results of quantitative studies and calculated aroma
activity values to establish DMHF, methyl 2-methylbutanoate, ethyl 2-methylbu-
tanoate, ethyl acetate, ethyl hexanoate, ethyl butanoate, ethyl 2-methylpropanoate,
methyl hexanoate, and methyl butanoate as important contributors of pineapple
aroma. Additional thiol-esters and phenolic and furanoid compounds have recently
been identified in pineapple [142,143].