Individual
flavonoids were analyzed by HPLC. The results showed that naringin, narirutin, quercetin and naringenin
were the most abundant flavonoids in grapefruit juice. In general, although every pasteurization treatment
caused a significant reduction in the content of all the studied flavonoids, the treated samples were more
stable during storage. While fresh squeezed juice (FS) and conventional pasteurized juice (CP) were better
preserved under refrigeration conditions, microwave pasteurized juice (MP) conserved better when frozen
stored. In fact, after 2 months, frozen MP samples showed the greatest flavonoid retention. From this point of
view, microwave treatment can be considered a good alternative to conventional pasteurization.
Industrial relevance: Flavonoids are polyphenolic compounds present in fruits and vegetables relevant not
only in terms of quality, as they influence the visual appearance and taste, but also from a therapeutical point
of view, as they appear to be associated with the prevention of degenerative diseases. The consumption of
grapefruit juice is fairly widespread among the population. Traditionally, juices have been pasteurized by heat
treatment to prolong their shelf life. However, this process may cause irreversible losses of nutritional quality
and antioxidant activity and, in consequence, may affect their health-related properties. In this sense, the use
of microwaves can be considered an alternative to conventional thermal pasteurization. Microwave energy
was applied as alternative to conventional heating for grapefruit juice pasteurization. The results obtained in
this study showed that when the effect of pasteurization process and storage is considered together, the use of
microwave energy led to a greater retention of all the analyzed flavonoids, thereby representing a good
alternative to conventional pasteurization. In this case, frozen storage of processed product would be
recommended to better preserve these compounds.