Grapefruit - Tropical and Subtropical Fruits: Postharvest Physiology, Processing and Packaging - page 356

juice must possess a bright, typical color and distinct canned
grapefruit juice concentrate flavor (Downing, 1996a).
The blended grapefruit-orange juice may contain up to
50% orange juice. The grapefruit-orange juice blend may
be packed with or without added sugar/sweeteners and pro-
cessed in the same manner as grapefruit juice (Downing,
1996a). A 250 ml serving of grapefruit-orange juice blend
has 120 calories, 28 g total carbohydrates (22 g sugars),
470 mg potassium, and vitamin C at 110% of the daily
recommended value (Anon, 2011).

In electric field processing, the primary process param-
eters that affect microbial inactivation are the electric field
strength, number of pulses, duration and shape of pulses,
and initial product temperature. Most commercial PEF ap-
plications have been applied to liquid products such as
juices. Lebovka et al. (2003) showed that application of
PEFs affects textural property of the food.

By-product utilization
Grapefruit peel waste has been transformed by enzymatic
hydrolysis into useful by-products (Wilkins et al., 2007).
The peel by-product of most fruits has significantly higher
levels in the range of 5-10% of total phenolic compounds,
total flavonoids, ascorbic acid (Wu et al., 2007), and an-
tioxidant activity as compared with the pulp and seeds.
Flavonoids, which have high levels in grapefruit, have been
reported to enhance the antibacterial, antiviral, or anticancer
activities of compounds such as naringenin (Brackle et al.,
1999; Ho et al., 2000). Grapefruit seed extract has been
demonstrated to have an antibacterial effect on food-borne
pathogens, hence its application in the preservation of min-
imally processed vegetables (Xu et al., 2007).
Citrus fruit waste materials, especially peels, are rich
in pectin, cellulose, and hemicellulosic polysaccharides;
these compounds can be hydrolyzed into sugars and fer-
mented into alcohol (USDA, 2006). Lab-scale and up to
1,000-gallon batch level experiments were successful in
producing ethanol. In Florida alone, citrus processing yields
approximately 5 million tons of wet waste annually, equiv-
alent to 1.2 million tons of dry waste. Traditionally, most
dried peel residue has been marketed as low-value cattle
feed. It was estimated that Florida's citrus peel waste could
yield up to 80 million gallons of ethanol per year (USDA,
2006).
Some processors quarter and shave peels to recover citrus
oil; the cold-pressed oil is a valuable by-product of the
grapefruit industry. Major commercial processors produce
dry citrus peel, citrus molasses, and d'limonene (Downing,
1996a).

Canned grapefruit
For processing purposes, tree-ripened grapefruit is used, es-
pecially for canning, to obtain maximum flavor. Overripe,
plugged, or split fruit must be discarded due to the poten-
tial of soil, insect, or microbial contamination (Downing,
1996b). For canning, lye peeling and, to a lesser extent,
manual peeling with knives are used. Though available
commercially, grapefruit is not among the most commonly
canned, frozen, or dehydrated fruits in the tropical regions
as compared to other fruits. However, investigation has
been done on the effect of thermal treatment and storage
on the stability of organic acids and the functional value of
grapefruit juice (Igual et al., 2010b). Typical canning pro-
cess steps are as follows: Receiving fruit → Inspection →

Washing Filling into cans

→ Syruping (30 ◦ -50 ◦ Brix) → Can closure → Processing
(180 ◦ -195 ◦ F for 25-50 min, depending on can size) →
Cooling to 95 ◦ -105 ◦ F (Downing, 1996b).

→ Peeling → Sectioning fruit →

Innovative processing technologies
Fruits can be processed by novel nonconventional or “non-
thermal” methods such as irradiation, high hydrostatic pres-
sure (HP), ultrasound, filtration, use of antimicrobials, and
electrical methods such as pulsed electric fields (PEFs),
ohmic, microwave, radiofrequency, light pulses, and oscil-
lating magnetic fields. These methods are attractive to the
food industry because they produce more freshlike, flavor-
ful, colorful, and nutrient-rich preserved foods (Gonzalez
and Barrett, 2010), especially HP and PEF—the two most
prominent new technologies being adopted by the food in-
dustry. Although many of these technologies were classified
as “nonthermal,” heat at relatively low temperatures may
still be generated during application of these processes. A
good example of successful HP-treated foods at commer-
cial level is fruit jams (Cano and de Ancos, 2005). How-
ever, some effects of HP on plant tissues includes changes
in lipids (Cano and de Ancos, 2005), and textural changes
(Basak and Ramaswamy, 1998).

NUTRITIONAL PROFILE AND
HEALTH BENEFITS

Nutrient composition
Grapefruit, like other citrus fruits, is an excellent source
of vitamin C, dietary fiber, vitamin A, potassium, folic
acid, and vitamin B-5. It is also a source of calcium and
phosphorus (Table 19.4). Each nutrient is followed by the