Content uploaded by Edmundo Mercado-Silva
Author content
All content in this area was uploaded by Edmundo Mercado-Silva on Mar 19, 2019
Content may be subject to copyright.
1238 JOURNAL OF FOOD SCIENCE—Vol. 65, No. 7, 2000 © 2000 Institute of Food Technologists
Sensory and Nutritive Qualities of Food
JFS: Sensory and Nutritive Qualities of Food
Changes in the Quality of Fresh-cut Jicama
in Relation to Storage Temperatures
and Controlled Atmospheres
E.N. AQUINO-BOLAÑOS, M.I. CANTWELL, G. PEISER, AND E. MERCADO-SILVA
ABSTRACT: Intact jicama (Pachyrhizus erosus) roots are chilling sensitive, but quality of fresh-cut pieces (1.8 × 4.5
cm cylinders) was best maintained at low storage temperatures (0 to 5 °C). Respiration rates of different piece sizes
were similar, and averaged 2, 7 and 10 µL CO2·g–1·h–1 at 0 °C, 5 °C and 10 °C, respectively. Storage in air at 5 °C to
10 °C resulted in surface browning and was associated with increases in phenolics and phenylalanine ammonia
lyase and polyphenol oxidase activities. High CO2 atmospheres (5 to 10%) at 5 °C were very effective in retarding
microbial growth and discoloration. The source of jicama root notably affected the quality and shelf-life of the
fresh-cut pieces. Fresh-cut pieces from stored roots (2 wk at 19 to 22 °C) had lower visual quality and crispness
during subsequent storage than did pieces from recently harvested roots.
Key words: respiration, texture, color, acetaldehyde and ethanol, soluble solids, PPO, PAL
Introduction
JICAMA (PACHYRHIZUS EROSUS (L.) UR-
ban) is a tropical legume originally from
Mexico and Central America and cultivat-
ed by Precolombian cultures. It is current-
ly produced in Mexico (source of most jica-
ma in U.S. markets), Brazil, United States,
China, Indonesia, the Philippines, and Ni-
geria (Sørensen 1996; Fernández and oth-
ers 1996). The root consists of a light or
dark brown periderm, and a white, crisp,
succulent and sweet-starchy pulp. It is
consumed principally as a raw vegetable
with lime and chile, in salads, in soups,
stir-fried or conserved in vinegar with on-
ion and chile. Also it is used as a substitute
for the water chestnut (Eleocharis dulcis) in
Chinese food (Sørensen 1996).
Postharvest studies on jicama have
demonstrated that the intact root is very
sensitive to chilling injury when stored at
10 °C or below (Bergsma and Brecht 1992;
Cantwell and others 1992; Mercado-Silva
and Cantwell 1998; Paull and Chen 1988).
Different varieties of jicama may differ
significantly in their chilling susceptibility
(Mercado-Silva and others 1998b).
Processing of jicama by osmotic dehy-
dration, freezing, and juice preparation
has been reported (Juárez-Goiz and Pare-
des-López 1994). Since this root is usually
consumed raw, the preparation of a fresh-
cut jicama product provides an interesting
processing alternative. High quality fresh-
cut jicama should be white, crisp and juicy,
of characteristic odor and flavor, without
visible defects, and be microbiologically
sound.
Minimally processed vegetables offer
freshness and convenience to the con-
sumer, the main reasons for increased
sales of these products in both retail and
foodservice establishments (Watada and
others 1996). Other advantages of fresh-
cut products include the lack of additives
or preservatives, reduced transport and
storage space requirements, decreased
preparation time, and the possibility of of-
fering a product of uniform and consistent
quality (Garrett 1998).
Physical damage, inherent in the prep-
aration of minimally processed products,
causes an increase in respiration rates and
other metabolic reactions, and therefore an
increase in the rate of deterioration of
these products (Cantwell 1998; Saltveit
1997; Varoquaux and others 1990; Watada
and others 1990). The degree of damage
suffered by the product also affects the de-
gree to which metabolism is changed
(Cantwell 1998; Saltveit 1997). Undesirable
color changes are common defects of these
products. Biosynthesis, oxidation and poly-
merization of phenolic compounds are of-
ten associated with discoloration and other
color changes. Hyodo and others (1978)
and López-Gálvez and others (1996) re-
ported a high correlation between the ac-
tivity of phenylalanine ammonia lyase
(PAL) and the discoloration on intact and
cut lettuce leaves. Discoloration becomes
apparent when the phenolic compounds
are oxidized in reactions catalyzed by
polyphenol oxidase (PPO) and possibly
peroxidases (Hanson and Havir 1979).
Low temperatures are required to re-
duce metabolic activity, microbial growth,
and water loss of fresh-cut products
(Brackett 1987; Cantwell 1998). The bene-
ficial effect of modified/controlled atmo-
spheres on product quality has also been
demonstrated for many fresh-cut items
(Gorny 1997; López-Gálvez and others
1997; Portela and others 1997; Qi and Wat-
ada 1997; Rosen and Kader 1989). High
concentrations of CO2 may reduce respira-
tion rates, but concentrations of 20% or
more can result in the accumulation of
ethanol and acetaldehyde (Kader 1986;
Kader and others 1989; Kennedy and oth-
ers 1992) and consequently affect sensory
properties of the product. Concentrations
of CO2 from 10 to 30% can inhibit enzymes
of phenolic metabolism and delay darken-
ing (Siriphanich and Kader 1985; Mateos
and others 1993), softening and delay de-
velopment of decay organisms (Brackett
1987; Gorny 1997). The activity of en-
zymes involved in discoloration decreases
when oxygen concentrations are reduced
from 21% to 5–8% (Kader 1986). Low O2
and/or high CO2 concentrations change
intracellular pH and alter metabolic regu-
lation (Siriphanich and Kader 1985).
There are no reports on jicama as a
minimally processed product. It provides
a challenge as a fresh-cut vegetable since
the intact root is chilling sensitive and po-
tential benefits of modified atmospheres
are unknown. The objectives of this study
were to (1) determine the effects of low
temperature and controlled atmosphere
storage on quality changes of fresh-cut ji-
cama, (2) to evaluate quality changes in
relation to piece size, and (3) to gain some
understanding of variability due to raw
product source.
Vol. 65, No. 7, 2000
—
JOURNAL OF FOOD SCIENCE 1239
Sensory and Nutritive Qualities of Food
Changes in the Quality of Fresh-cut Jicama . . .
Materials and Methods
Raw material. Jicama roots produced in
Nayarit, Mexico were obtained from Frie-
das Produce (Los Angeles, Calif., U.S.A.) in
fall 1997 and are referred to as Nayarit ji-
cama. Other roots were obtained directly
from experimental fields at INIFAP, Gua-
najuato, Mexico in fall 1997 and are re-
ferred to as Bajio jicama. Roots were also
obtained from commercial fields in Mi-
choacan during February 1998 via a whole-
saler in Queretaro, Mexico and are referred
to as Michoacan jicama. Experiments with
the Nayarit and Bajio jicamas were con-
ducted at the Mann Laboratory, and the
experiment with Michoacan roots was con-
ducted at the laboratory in Querétaro.
Roots were free of visual defects and me-
chanical damage and were stored at 15 to
20 °C until used.
Preparation of fresh-cut pieces. Roots
were washed with potable water, the ter-
minal parts removed, leaving an equatori-
al section approximately 5 cm thick. Cylin-
ders (1.8 × 5 cm) were cut with a stainless
steel borer and then recut to 4.5 cm or to 1
cm for discs. For sticks, pieces (1 × 1 × 4.5
cm) were cut with a sharp stainless steel
knife. Pieces were placed in a tray on ice
and covered with moistened cheesecloth
to avoid dehydration during preparation.
The pieces were disinfected with a sodium
hypochlorite solution (50 ppm free chlo-
rine, pH 7) for 15 s. Excess water was re-
moved by draining and blotting with
damp cheesecloth. Three to 5 pieces in a
250 mL glass jar formed one repetition per
treatment.
Storage conditions of fresh-cut pieces.
The glass jars were covered with cheese-
cloth and placed in larger glass containers
through which a flow of humidified (> 95%
RH) air or different controlled atmo-
spheres passed. Flow rates were controlled
by capillaries calculated to maintain CO2
concentrations <0.5% in air storage. For
respiration measurements, pieces were
placed in jars individually connected to a
flow of humidified air at the indicated
temperatures. For the experiment on phe-
nolic metabolism, discs (1.8 × 1 cm) were
stored in a flow system of humidified air at
5 °C, 7.5 °C, and 10 °C, and samples were
taken daily.
Controlled atmospheres (CA) were ob-
tained by mixing appropriate volumes of
nitrogen, O2 and CO2 and then passing the
mixtures through water for humidifica-
tion. Three controlled atmosphere (CA)
experiments were carried out. In the first
CA experiment, atmospheres of 1, 3, and
21% O2 alone and in combination with 5
and 10% CO2 were tested at 5 °C on pieces
from Nayarit and Bajio jicamas. Evalua-
tions were conducted at 0, 8 and 12 d. In
the second CA experiment, atmospheres
of 0.3, 3 and 21% O2 alone in combination
with 10% CO2 were tested at 5 and 10 °C
on pieces from Bajio roots, and evalua-
tions were carried out on day 0, 4, 8, and
12. The third CA experiment was conduct-
ed on pieces from Michoacan roots stored
in air or air + 13 or 20% CO2 at 5 °C, with
evaluations at day 0, 8, and 14.
Gas measurements. Oxygen and CO2
concentrations were monitored daily dur-
ing the CA experiments. Gas samples of 1
mL were injected into an infrared gas ana-
lyzer (Horiba PIR-2000) or oxygen analyzer
(Applied Electrochemistry Inc. Model S-
3A). For calibration standard mixtures of 5
to 15% O2 and 5 to 15% CO2 were used. For
determination of respiration rates, CO2
gas samples were analyzed daily and cal-
culations were based on the difference be-
tween inlet and outlet CO2 concentrations.
A 0.5 % CO2 standard was used for calibra-
tion.
Storage of intact roots before process-
ing. Cylinders were prepared from Micho-
acan roots after 0 and 2 w storage in plastic
crates at ambient conditions (19 to 22 °C).
Prepared cylinders were evaluated at 5 °C
in air or CA (13 or 20% CO2 in air). Subjec-
tive and objective evaluations were car-
ried out at 0, 8 and 14 d storage.
Subjective Evaluations. Subjective
evaluations were carried out by the first 2
authors and were based on scales previ-
ously applied to jicama (Cantwell and oth-
ers 1992; Mercado-Silva and others
1998b). Overall visual quality was evaluat-
ed on a 9 to 1 scale, where 9 = excellent, no
defects, 7 = good, minor defects, 5 = fair,
moderate defects, 3 = poor, major defects,
1 = unusable. A score of 6 was considered
the limit of salability. Minor defects were
usually attributed to color changes; major
defects were usually due to decay. Brown-
ing was evaluated on a scale of 1 to 5,
where 1 = none, 2 = slight, 3 = moderate,
4 = severe, and 5 = extreme browning. De-
hydration and macroscopic decay were
evaluated on scales of 1 to 5, where
1 = none, 2 = slight (up to 5% surface af-
fected), 3 = moderate (5 to 20% surface af-
fected), 4 = moderately severe (20 to 50%),
and 5 = extreme (> 50% surface affected).
Flavor was scored on a 5 to 1 scale, where
5 = full, characteristic flavor, 4 = near full
typical flavor, 3 = moderate typical flavor,
2 = little typical flavor, and 1 = no flavor or
not typical flavor.
Objective Evaluations. Color of the flat
ends of the cylinders was determined with
a Minolta CR-200/300 spectrophotometer,
with illuminant A and a 10° viewing angle
and calibrated on a white tile. L*, a* and b*
values were recorded and chroma
(C* = (a*2+b*
2
)
½
) and hue (h °C = tan–1
(b* / a*)) were calculated.
Firmness was measured by a modifica-
tion of the conditions described by Merca-
do-Silva and Cantwell (1998) for intact ji-
cama. Maximum rupture force and dis-
tance to penetration were determined on
a TA-HD texture analyzer (Texture Tech-
nologies Corp., Scarsdale, N.Y., U.S.A.)
with a flat cylindrical 3-mm probe at a
penetration rate of 1 mm/s to a depth of 8
mm.
For phenylalanine ammonia lyase (PAL)
activity, 4 g of tissue were homogenized
with 0.4 g insoluble polyvinylpolypyrroli-
done, 16 mL borate buffer (50 mM pH 8.5)
and 14 (L 2-mercaptoethanol according to
Ke and Saltveit (1986). After filtering and
centrifugation at 12000 × g at 4 °C for 20
min, PAL activity in the supernatant was
determined at 40 °C using 100 mM L-phe-
nylalanine as substrate and measuring ab-
sorbance at 290 nm. One unit of PAL activi-
ty corresponded to the formation of 1 mmol
cinnamic acid in 1 hour.
Polyphenol oxidase (PPO) activity was
determined from 4 g of tissue homoge-
nized with 0.4 g insoluble polyvinylpoly-
pyrrolidone and 16 ml phosphate buffer
(50 mM pH 6.2) according to the method
described by Siriphanich and Kader
(1985). After centrifugation at 12000 × g
for 20 min at 4 °C, the supernatant was
used for determination of PPO. Caffeic
acid was used as substrate and absor-
bance was measured at 420 nm. One unit
of PPO activity corresponds to a change of
0.1 absorbance units in 1 min.
For total soluble phenolics, 8 g of finely
chopped jicama were homogenized with
15 mL 80% ethanol, filtered through 4 lay-
ers of cheesecloth and let stand 30 min be-
fore taking a 0.25-mL aliquot for spectro-
photometric determination according to
Hyodo and others (1978). A standard
curve of coumaric acid was used for quan-
tification.
Ethanol and acetaldehyde determina-
tions were based on a modification of the
method by Mateos and others (1993). A
2.5-g sample of chopped fresh tissue was
placed in a test tube closed with a rubber
stopper. Tubes were placed in a 60 °C wa-
ter bath for 1 h. Headspace samples of 0.5
mL were injected into a GC (Hewlett Pack-
ard Model 5890A) equipped with a
2 mm × 1.8 m 5% Carbowax 20 M column
(85 °C) and a flame ionization detector
(250 °C). Retention times and standard
curves of ethanol and acetaldehyde in wa-
ter solutions were used for peak identifica-
tion and quantification.
Microbiological examinations consisted
of aerobic plate counts of Nayarit and Ba-
jio samples after 0, 8, and 12 d storage in
air or controlled atmospheres at 5 °C. Piec-
es were removed from separate jars in the
large storage containers and a 25 g
chopped sample homogenized in 225 mL
Sensory and Nutritive Qualities of Food
1240 JOURNAL OF FOOD SCIENCE—Vol. 65, No. 7, 2000
Changes in the Quality of Fresh-cut Jicama . . .
distilled water. Total aerobic plate counts
were determined by a dilution series for
each treatment using SMA agar and incu-
bating at 29 °C (BAM 1984).
Experiments were conducted in a com-
pletely randomized design with a mini-
mum of 3 repetitions per treatment unless
otherwise specified. Data were calculated
as averages 6 standard deviations.
Results and Discussion
Physiology of intact roots and
minimally processed pieces.
Respiration rates of intact jicama roots
were relatively constant during 8 d storage
at 0 °C, 5 °C, and 10 °C (Figure 1A). The ji-
cama cylinders stored at 5 and 10 °C ini-
tially had respiration rates similar to those
of the intact roots, but after 4 and 2 d, re-
spectively, respiration rates increased
substantially (Figure 1B). At 0 °C, respira-
tion rates of intact and fresh-cut pieces
were similar and tended to decrease with
time. Respiration rates of cylinders aver-
aged 2, 7 and 10 µL CO2·g–1·h–1 over 7 d at
0, 5, and 10 °C, respectively. The Q10 (0 to
10 °C) values for intact and fresh-cut jica-
ma were 2.3 and 4.5, respectively. Similar
Q10 values have been reported for carrot
slices, melon cubes and salad lettuce
(Watada and others 1996).
Piece type and size did not greatly af-
fect the respiration rates of minimally pro-
cessed jicama (Figure 2), whereas rates
differed principally due to storage tem-
perature. Saltveit (1997) proposed that
the wounding response generally in-
creased with increased damage, and that
after reaching a certain severity, addition-
al injury would not increase the metabolic
response, suggesting an overlapping of
damaged areas. However for jicama, respi-
ration rates were similar for the cylinders,
discs and sticks although the cut surface
areas (30.5, 10.7, and 20.0 cm2, respective-
ly) were different. Others indicate that the
respiratory response to wounding de-
pends on the type of vegetable or fruit as
well as its state of development or maturi-
ty, and may not differ from that of the in-
tact product. For example, longitudinal
carrot slices had the same respiration rates
as the intact roots (Cantwell 1998). Rosen
and Kader (1989) reported that respiration
rates of pear and strawberry slices were
similar to rates of the intact products.
Changes in visual quality and color
in relation to storage temperature.
The visual appearance of minimally
processed jicama stored in air at 0 °C, 5 °C,
and 10 °C was excellent or very good dur-
ing the first 5 d of storage. After 10 d, cylin-
ders stored at 0 °C had an excellent ap-
pearance, while those at 5 °C were scored
as having good quality and those at 10 °C
had fair quality (Figure 3A). Discoloration
was the factor that most contributed to a
reduction in quality of pieces stored in air
at 10 °C. The relationship between chang-
es in visual appearance and hue values is
readily apparent in Figure 3B. Hue
changed drastically over 10 d at 10 °C, was
maintained at 5 °C and increased slightly
at 0 °C (this was associated with a translu-
cent appearance by d 10).
Another important factor in the loss of
quality of the minimally processed jicama
pieces was microbial growth. No macro-
scopic decay was found on Bajio jicama
pieces during 5 d at 0 °C, 5 °C, or 10 °C. By
10 d, decay was slight-moderate in pieces
stored at 10 °C, but still undetectable at
0 °C and 5 °C (Figure 3C). Firmness (maxi-
mum rupture force and distance to rup-
ture) measurements indicated that there
were no consistent differences in texture
during 10 d at the 3 storage temperatures
(data not shown).
These results indicate that quality of
minimally processed jicama is best main-
tained at low storage temperature. It was
necessary to store the fresh-cut pieces at
0 °C to 5 °C to prevent discoloration, mini-
mize respiration rates and retard microbial
growth, although the intact roots are very
Figure 1—Respiration rates of intact roots (A) and cylinders (1.8 × 4 cm) (B) of Bajio jicama
stored in air at 3 temperatures. Each data point is the average of 3 replications 6 std.
deviation
Figure 2—Respiration rates of cylinders
(1.8 × 4 cm), sticks (1 × 1 × 4 cm) and discs
(1.8 × 1 cm) of Bajio jicama stored in air at 5
and 10 °C. Each data point is the average of 3
replications 6 std. deviation.
Figure 3—Visual quality (A), hue color value
(B), and macroscopic decay (C) of cylinders of
Nayarit jicama stored in air at 3 temperatures.
Each data point is the average of 3 replica-
tions 6 std. deviation.
Vol. 65, No. 7, 2000
—
JOURNAL OF FOOD SCIENCE 1241
Sensory and Nutritive Qualities of Food
Changes in the Quality of Fresh-cut Jicama . . .
susceptible to chilling injury at 10 °C or
below (Cantwell and others 1992; Merca-
do-Silva and others 1998a). This apparent
contradiction is explained in part because
the assessment of chilling injury in intact
products usually occurs after transferring
the product to 20 °C. In the case of fresh-
cut pieces, however, it is appropriate to
evaluate them at storage temperature
without a transfer period. In addition,
benefits due to low temperature control of
microbial growth on fresh-cut products far
outweigh quality defects that may result
from the gradual onset of chilling injury.
Relationship between
discoloration and phenolic
metabolism
The synthesis of phenolic compounds
via PAL and subsequent oxidation by PPO
could be related to the observed changes
in color of jicama at 5 °C or above (Hanson
and Havir 1979). At 5 °C, PAL activity was
low and remained constant during the 9 d
of storage (Figure 4A); at 7.5 °C and 10 °C
maximum levels of activity were observed
at 6 and 4 d, respectively, and after this,
activity decreased. This pattern was simi-
lar to that observed in lettuce by Hyodo
and others (1978) and López-Galvéz and
others (1996). Creasy and others (1986), in
work on sunflower leaf discs, and Strack
(1996) proposed that this pattern of PAL
enzyme activity could be due to the syn-
thesis of a proteinaceous inactivator of
PAL.
PPO activity in jicama discs did not
change much at the different storage tem-
peratures, after an initial rapid increase
during d one (Figure 4B). PPO activity de-
clined after 4 d regardless of storage tem-
perature (Figure 4B). It is possible that the
initial stimulation in PPO activity is a di-
rect result of mechanical injury (Stevens
and Davelaar 1997).
The synthesis of phenolic compounds
soluble in alcohol increased during stor-
age at all temperatures, but the rate and
magnitude of the increase were directly
related to the storage temperature (Figure
4C). Total phenolic compounds increased
after the increases in PAL activity were ob-
served, but as PAL activities decreased lat-
er in storage, total phenolics continued to
increase. The production of phenolic com-
pounds has been associated with the pro-
cess of wound healing (Sukumaran and
others 1990; Walter and others 1990). On
fresh-cut jicama browning began on the
cut surfaces and then moved inward. This
suggests that the synthesis of phenolic
compounds in jicama pieces may also be a
wound healing response, and that tem-
peratures of 5 °C or below restrict the pro-
cess and therefore limit discoloration.
There was only a slight increase in PAL ac-
tivity of jicama pieces at 5 °C (Figure 4A).
Color changes at these intermediate
storage temperatures were best repre-
sented by calculations of chroma (Figure
4D). There was a high linear correlation
between chroma values and the concen-
tration of phenolics (r = 0.91). There was
also a good relationship between maxi-
mum PAL activity and phenolic accumula-
tion, results similar to those reported by
López-Galvéz and others (1996) for lettuce
pieces. Although PPO is involved in the
browning process and there were always
measurable levels of activity, there was
not a direct association between PPO ac-
tivity and browning, an observation re-
ported in other studies. Hyodo and others
(1978) working on lettuce in the presence
of ethylene, and Coseteng and Lee (1997)
studying different apple cultivars did not
observe a correlation between PPO activi-
ty and the development of browning.
Effect of controlled atmospheres at
5 °C and 10 °C on quality
parameters of fresh-cut jicama
Since there is no published informa-
tion regarding effects of controlled atmo-
sphere on quality of stored jicama, atmo-
spheres beneficial to other minimally pro-
cessed vegetables were selected for study
(Gorny 1997). In the first CA experiment,
atmospheres of 1, 3, and 21% O2 alone and
in combination with 5 and 10% CO2 were
tested at 5 °C on pieces from Nayarit and
Bajio jicama. There are notable differenc-
es in the intact roots of these two types of
jicamas. Nayarit roots have a thicker peri-
derm and less succulent pulp than Bajio
roots, and Mercado and others (1998b) re-
ported that Nayarit roots were less suscep-
tible to chilling injury than ‘Agua Dulce’
Bajio roots. Soluble solids concentrations
also differ, and in the present study aver-
aged 4.7 and 6.9% in pulp of Nayarit and
Bajio roots, respectively. Fresh-cut pieces
from both types of jicama maintained ex-
cellent or very good visual quality during 8
d independent of storage atmospheres
(data not shown). After 12 d, visual quality
was only maintained in atmospheres with
5 and 10% CO2. In addition, quality of the
Bajio pieces was lower than that of Nayarit
jicama, principally due to differences in
macroscopic decay. Aerobic plate counts
also differed between the two types of ji-
cama roots. After preparation on d 0, Na-
yarit and Bajio pieces had microbial loads
of 6.5 × 102 and 1.4 × 104, respectively. By
d 8, Nayarit air-stored pieces had microbi-
al counts of 2 × 107, counts on Bajio pieces
were 1 to 1.5 logs higher, and counts on
pieces in CO2 atmospheres were 0.5 to 1
logs lower than those of the corresponding
air-stored pieces.
In a second CA experiment on the more
perishable Bajio jicama pieces, CA mix-
tures with 10% CO2 at 10 °C maintained
excellent visual quality for 4 d, whereas air
and low O2 atmospheres resulted in a loss
of visual quality due to discoloration and
decay (Figure 5B and D). By 8 d, however,
the 10% CO2 atmospheres were insuffi-
cient to delay the onset of browning and
Figure 4—Phenylalanine ammonia lyase (PAL) activity (A), Polyphenyl oxidase (PPO) activity
(B), total phenolic compounds (C), and Chroma color values (D) of Bajio jicama discs stored in
air at different temperatures. Each data point is the average of 3 replications 6 std. devia-
tion.
Sensory and Nutritive Qualities of Food
1242 JOURNAL OF FOOD SCIENCE—Vol. 65, No. 7, 2000
Changes in the Quality of Fresh-cut Jicama . . .
decay (Figure 5B, D, and F). Controlled at-
mospheres at 5 °C maintained excellent
visual appearance of the jicama cylinders
during 8 d (Figure 5A). After 12 d, the 10%
CO2 atmospheres maintained visual quali-
ty of jicama pieces better than low oxygen
atmospheres alone or 3% O2 + 20% CO2
(Figure 5A). The 10% CO2 atmosphere with
3% O2 was not as effective as 10% CO2 com-
bined with air or 0.3% O2 due to microbial
growth (Figure 5E). Although discoloration
at 5 °C was slight, the 10% CO2 atmo-
spheres were more effective in retarding
discoloration than air or low O2 atmo-
spheres (Figure 5C). Pieces stored in 20%
CO2 were injured by this atmosphere as
evidenced by development of some dis-
coloration and an increased susceptibility
to microbial growth (Figure 5E).
Reduction in the rate of browning can
be explained by modifications in the syn-
thesis and/or degradation of phenolic
compounds due to reduced O2 concentra-
tions or low temperatures. Mateos and
others (1993) concluded that with CO2
concentrations < 20%, PAL activity of let-
tuce pieces was reduced as a result of de-
creased cytoplasmic pH. Siriphanich and
Kader (1985) demonstrated that cytoplas-
mic pH of air stored lettuce was 6.7, where-
as tissue exposed to 20% CO2 had a cyto-
plasmic pH of 6.3. Considering that the
pH optimum for PAL activity is 8.5, a re-
duction in pH would result in decreased
activity which in turn would result in a de-
creased rate of phenolic synthesis. This
could explain the lack of discoloration ob-
served on jicama pieces at 5 °C in 10% CO2
and the delay in discoloration observed in
pieces at 10 °C in high CO2 atmospheres.
Acetaldehyde concentrations in-
creased slightly during storage in air at
5 °C, whereas all controlled atmospheres
resulted in notable increases after 8 d (Fig-
ure 6A). In air + 10% CO2 acetaldehyde in-
creased 4 times, and 3% O2 resulted in a 6
fold increase. The 0.3% O2 + 10% CO2 or
the 20% CO2 atmospheres resulted in the
highest increases in acetaldehyde, about
10 times the concentrations of air-stored
pieces. Ethanol concentrations also varied
according to the O2 concentrations in the
CA mixture, and by 12 d, the pieces in the
0.3% O2+ 10% CO2 atmosphere had the
highest concentrations (Figure 6B). One of
the risks of atmosphere modification is the
induction of anaerobic respiration and the
consequent production of acetaldehyde
and ethanol. The concentrations of acetal-
dehyde and ethanol in jicama cylinders
did not correlate well with the develop-
ment of off-odors (data not shown). Ló-
pez-Gálvez and others (1997) found low
but highly significant correlations be-
tween off-odors and fermentative volatile
concentrations in lettuce pieces, and in-
Figure 6—Concentration of acetaldehyde (A) and ethanol (B) of Bajio jicama cylinders stored
at 5 °C in different controlled atmospheres. Each data point is the average of 3replications 6
std. deviation.
Figure 5—Changes in visual quality (A, B), browning discoloration (C, D), and macroscopic
decay (E, F) of Bajio jicama cylinders stored at 5 and 10 °C in different controlled atmo-
spheres. Each data point is the average of 3 replications 6 std. deviation.
Vol. 65, No. 7, 2000
—
JOURNAL OF FOOD SCIENCE 1243
Sensory and Nutritive Qualities of Food
Changes in the Quality of Fresh-cut Jicama . . .
terpreted this to indicate that other vola-
tiles must be contributing to off-odor de-
velopment. This may also be the explana-
tion in the case of jicama pieces.
Concentrations of soluble solids in-
creased from 4.5% on day 0 to an average
5.3 and 5.5% after 8 d at 5 °C and 10 °C, re-
spectively. An increase in soluble solids
concentrations of intact jicama stored be-
low 10 °C has been noted previously (Mer-
cado-Silva and others 1998a). Low temper-
ature sweetening is a common phenome-
non during storage of roots and tubers
(Wismer and others 1995). Marangoni and
others (1996) and Parkin and Schwobe
(1990) reported degradation of starch and
accumulation of sucrose and other sugars
in potatoes stored at 2 °C and 3 °C, respec-
tively.
Effect of intact root storage on
quality of fresh-cut pieces
Cylinders prepared from recently har-
vested jicama (2 d from harvest) were
compared with those prepared from the
same lot of roots stored 2 w at ambient
temperature. The visual quality of the cyl-
inders from unstored roots remained ex-
cellent or very good during 14 d at 5 °C
(Figure 7A) under air or high concentra-
tions of CO2. However, pieces obtained
from the stored jicama pieces had de-
creased quality by d 8. This loss of visual
quality corresponded to an increased yel-
lowing of the pieces (data not shown). The
13% CO2 atmosphere helped maintain vi-
sual quality in jicama from both fresh and
stored roots. Although maximum rupture
forces of pieces from unstored and stored
roots were similar (Figure 7B), the distance
to rupture increased in the pieces pre-
pared from the stored roots (Figure 7C).
This increase in distance to rupture is as-
sociated with less crisp or spongier jicama
tissue (Mercado-Silva and Cantwell 1998).
The data also suggest that the high CO2
atmosphere decreased the crispness of
the pieces from the stored roots. These re-
sults provide some indication that for best
shelf-life and quality of minimally pro-
cessed jicama pieces, the roots should be
prepared as soon as possible after harvest.
The effect of root storage is likely to be an
even more important consideration in the
case of jicama subjected to short periods
at chilling temperatures.
References
BAM 1984. Bacteriological Analytical Manual (FQA-BAM),
6th ed. Assn of Official Analytical Chemists. Washington
DC.
Bergsma KA, Brecht JK. 1992. Postharvest respiration, mois-
ture loss, sensory analysis and compositional changes in
jicama (Pachyrhizus erosus) roots. Acta Hort 318: 325-332.
Brackett RE. 1987. Microbiological consequences of mini-
mally processed fruits and vegetables. J Food Qual 10: 195-
206.
Cantwell M, Orozco W, Rubatzky V, Hernández L. 1992. Post-
harvest handling and storage of jicama roots. Acta Hort
318: 333-343
Cantwell M. 1998. Fresh-Cut Biology and Requirements. In:
Fresh-Cut Products: Maintaining Quality and Safety. Univ
California Davis Postharvest Hort Series No 10 Section 4b.
Coseteng MY, Lee CY. 1985. Changes in apple polyphenolox-
idase and polyphenol concentrations in relation to de-
gree of browning. J Food Sci 50(4): 985-989.
Creasy LL, Gupta SC, Chan BG, Elliger CA. 1986. Phenylala-
nine ammonia lyase inactivating system. Current Topics
Plant Biochem Physiol 5: 165-174.
Fernández MV, Marid WA, Loaiza JM, Martínez JJ, Serrano
A. 1996. Effect of planting methods on root characters of
jicama (Pachyrhizus erosus (L)Urban). Japan J Trop Agr
40(1): 26-28.
Garrett E. 1998. Overview of the fresh-cut industry. In: Fresh-
Cut Products: Maintaining Quality and Safety. Univ Cali-
fornia Davis Postharvest Hort Series No 10 Section 2a.
Gorny JR. 1997. A summary of CA and MA requirements and
recommendations for fresh-cut (minimally processed)
fruits and vegetables. In: Proc 7th Intl Controlled Atmo-
sphere Res Conf. Univ California Davis CA Postharvest Hort
Series No 19 Vol 5, p 30-66.
Hanson KR, Havir EA. 1979. An introduction to the enzymol-
ogy of phenylpropanoid biosynthesis, p 91-138. In: Swain
T, Harborne JB, and Sumere CF (eds). The Biochemistry of
Plant Phenolics Plenum Press. New York.
Hyodo H, Kuroda H, Yang SF. 1978. Induction of Phenylala-
nine-ammonia lyase and increase in phenolics in lettuce
leaves in relation to the development of russet spotting
caused by ethylene. Plant Physiol 62: 31-35.
Juárez-Goiz MS, Paredes-López O. 1994. Studies on jicama
juice processing. Plants for Human Nutrition 46: 127-131.
Kader AA. 1986. Biochemical and physiological basis for ef-
fects of controlled and modified atmospheres on fruits
and vegetables. Food Tech 40: 99-100, 102-104.
Kader A, Zagory D, Kerbel E. 1989. Modified atmosphere
packaging of fruits and vegetables. Critical Rev Food Sci
and Nutrition 28: 1-32.
Ke D. Saltveit ME. 1986. Effects of calcium and auxin on
russet spotting and phenylalanine ammonia-lyase activity
in Iceberg lettuce. HortScience 21: 1169-1171.
Figure 7—Visual quality (A), rupture force (B),
and rupture distance (C) of Michoacan jicama
freshly harvested or stored 14 d at ambient
temperature (19-22 °C) before processing.
Each data point is the average of 3 replica-
tions 6 std. deviation.
Kennedy R, Rumpho M, Fox T. 1992. Anaerobic metabolism
in plants Plant Physiol 100: 1-6.
López-Galvéz G, Saltveit M, Cantwell M. 1996. Wound-in-
duced phenylalanine ammonia lyase activity: factors af-
fecting its induction and correlation with the quality of
minimally processed lettuces. Postharvest Biol Tech 9: 223-
233
López-Galvéz G, Peiser G, Nie X, Cantwell M. 1997. Quality
changes in packaged salad products during storage. Z
Lebensm Unters Forsch A 205: 64-72.
Marangoni GA, Palma T, Stanley WD. 1996. Membrane ef-
fects in postharvest physiology. Postharvest Biol Tech 7:
193-217.
Mateos M, Ke D, Cantwell M, Kader A. 1993. Phenolic metab-
olism and ethanolic fermentation of intact and cut let-
tuce exposed to CO2 enriched atmospheres. Postharvest
Biol Tech 3: 225-233.
Mercado-Silva E, Cantwell M. 1998. Quality changes in jica-
ma roots stored at chilling and nonchilling temperatures.
J Food Quality 21: 211-221.
Mercado-Silva E, García R, Heredia-Zepeda A, Cantwell M.
1998a. Development of chilling injury in five jicama culti-
vars. Postharvest Biol Tech 13: 37-43.
Mercado-Silva E, Rubatzky V, Cantwell MI. 1998b. Variation
in chilling susceptibility of jicama roots. Acta Hort 467:
357-362.
Paull RE, Chen NJ. 1988. Compositional changes in yam bean
during storage. HortScience 23:194-196.
Parkin KL, Schwobe MA. 1990. Effects of low temperature
and modified atmosphere on sugar accumulation and chip
color in potatoes (Solanum tuberosum). J Food Sci 55:
1341-1344.
Portela S, Nie X, Suslow T, Cantwell M. 1997. Changes in sen-
sory quality and fermentative volatile concentration of
minimally processed cantaloupe stored in controlled at-
mospheres. In: Proc 7th Intl Controlled Atmosphere Re-
search Conf. University of California Davis CA Postharvest
Hort Series No 19 Vol 5 p 123-129
Qi L, Watada AE. 1997. Quality changes of fresh-cut fruits in
CA storage. In: Proc 7th Intl Controlled Atmosphere Re-
search Conf. University of California Davis CA Postharvest
Hort Series No 19 Vol 5 p 116-121.
Rosen JC, Kader AA. 1989. Postharvest physiology and qual-
ity maintenance of sliced pear and strawberry fruits. J Food
Sci 54: 656-659.
Saltveit M. 1997. Physical and physiological changes in min-
imally processed fruits and vegetables In: FA Tomás-Bar-
berán, RJ Robins (eds.). Phytochemistry of Fruit and Veg-
etables. Clarendon Press. Oxford p 205-220.
Siriphanich J, Kader A. 1985. Effects of CO2 on total pheno-
lics, phenylalanine ammonia lyase, and polyphenol oxi-
dase in lettuce tissue. J Amer Soc Hort Sci 110 : 249-253.
Sørensen M. 1996. Yam bean (Pachyrhizus DC) Promoting
the conservation and use of underutilized and neglected
crops. 2 Inst Plant Genetics and Crop Plant Research. 140
p. Gatersleben/Intl Plant Genetic Resources Inst Rome.
Stevens LH, Davelaar E. 1997. Biochemical potential of po-
tato tubers to synthesize blackspot pigments in relation
to their actual blackspot susceptibility. J Agric Food Chem
45: 4221-4226.
Strack D. 1996. Phenolic metabolism In Plant Biochemistry.
PM Dey, JB Harborne (eds.) Academic Press Great Britain
P 387-416.
Sukumaran NP, Jassal JS, Verma SC. 1990. Quantitative deter-
mination of suberin deposition during wound healing in
potatoes (Solanum tuberosum L). J Sci Food Agric 51: 271-
274.
Varoquaux P, Lecendre I, Varoquaux F, Souty M. 1990.
Change in firmness of kiwifruit after slicing. Sci Alim 10:
127-139.
Walter WM, Randall-Shadel B, Shadel WE. 1990. Wound
healing in cucumber fruit. J Amer Soc Hort Sci 115(3): 444-
452
Watada AE, Abe K, Yamaguchi N. 1990. Physiological activi-
ties of partially processed fruits and vegetables. Food Tech
44(5): 116-122.
Watada A, Ko N, Minott D. 1996. Factors affecting quality of
fresh-cut horticultural products. Postharvest Biol Tech 9:
115-125.
Wismer VW, Marangoni G, Yada YR. 1995. Low temperature
sweetening in roots and tubers. Hort Rev 17: 203-231.AC
This study was supported in part by a Postgraduate scholar-
ship to the first author and a Visiting Scholar Fellowship to
the second author, both provided by CONACyT Mexico.
The technical assistance of Xunli Nie is also appreciated.
Authors Aquino-Bolaños and Mercado-Silva are
with the Depto. de Investigación y Posgrado en
Alimentos. Univ. Autónoma de Querétaro,
Querétaro, México. Authors Cantwell and Peiser
are with the Vegetable Crops Dept., Mann Labo-
ratory. Univ. of California. Davis, CA 95616. USA.
Author Peiser is now at Fresh Express, Inc. Sali-
nas, Calif. Direct inquiries to author Cantwell.
(Email: micantwell@ucdavis.edu)