jicama

Introduction
Jicama or jam bean, a tropical legume with a pubescent vine growth habit, has
been cultivated in Mexico since the time of the Aztecs [1, 2]. These plants are
among the most vigorous-growing legumes. The edible light brown fleshy root
weighs 0.5 to 3 kg. Yields average 40 ton/ha but they may reach 80 ton/ha [3].
The commonly marketed tubers weigh 2 kg or less. They are crisp like an apple
and succulent, with a light sweet pleasant flavor. Under some conditions where
cool storage facilities are not available, it is common to store the root in the
soil until neede& Throughout the Latin American countries, jicama is mostly
eaten in raw slices and, to a lesser degree, lightly cooked or pickled. Importation of jicama into the United States in small quantities has been recorded
[4]; (E. S/mchez, personal communication).
On the other hand, it has been reported that membrane-processed vegetable
and fruit juices retain flavors and aromas that are normally volatilized and
partially lost in conventional processing during pasteurization and evaporation
[5, 6]. The sugars and amino acids present in juice, which undergo the
browning reaction when heated, are maintained at low temperature in the
membrane processes, thereby inhibiting off-flavor development.
There is no industrial product available in the market that takes advantage
of the high productivity and special sensory attributes of jicama. Immediately
after extraction j~cama juice starts to develop browning reactions followed by
a rancidity aroma. In view of these facts, the purpose of this preliminary

investigation was to try a ‘cold’ membrane process to retain flavor and aroma
components of fresh jicama juice.
Materials and methods
Jicama sample and fresh juice extraction. Jicama (Pachyrrhizus erosus Urban cv.
Agua Dulce) tubers, were harvested in Celaya, Gto. To improve juice extraction, the vegetable was peeled, and cut into slices of about 40 g each. Slices were
macerated and pressed in a centrifuge type laboratory extractor (Moulinex, SA,
model 140-t-05, Celaya, M6xico), equipped with a screen having 0.15mm
openings. Samples were passed through the extractor twice. Fresh juice was
kept at 4 °C before use.
Juice ultrafiItration. The screened juice was then subjected to UF, which was
conducted using a Pellicon Cassette System (Millipore Corp., Bedford, MA), at
a temperature lower than 25 °C. The polysulfone membrane had a molecular
weight cut-off of t0 000 daltons with 0.045 m 2 of membrane surface. UF was
performed at a transmembrane pressure of 130 to 170kPa with a flux
averaging 13 litres/m2h. Juice was circulated across the membrane until the
volume concentration ratio (initial volume of feed/final retentate volume) was
2.6.
Analytical methods. Fresh, retentate, and permeate juices plus bagasse residual
samples were analyzed, by AOAC procedures [7], for total solids (method
22.018), ash (method 7.009), total nitrogen (microKjeldahl, method 2.057),
and crude fiber (method 7.061). Total sugars were measured colorimetrically
by the phenol-sulfuric acid method of Dubois et al. [8]. Soluble solids (°Brix)
were assessed with a Bellingham and Stanley refractometer (Tunbridge Wells,
UK). Color of juices was measured using a Hunter-Lab D25-2 Color Difference Meter (Hunter Associates, Inc., Reston, VA). L (0 = black; 100 = white),
a (+ values = red; – values = green), and b (+ values = yellow;
-values = blue) were recorded. Total color difference (AE) was calculated
from the previous Hunter parameters [9]. The data are means of triplicate
determinations and were analyzed for standard deviation.
Results and discussion
Figure 1 shows the flow diagram of process used for producing jicama juices.
Original weight of jicama yielded 62% of screened juice for UF. Processing
trims showed that UF rendered juices, retentate and permeate, possessing
fresh-like aroma and flavor. Samples stored at 4 °C for two months appear to
retain their color, aroma and flavor. Various commercial procedures use
centrifugation (Fig. 1) to produce fruit and vegetable juices of acceptable.

sensory properties [10]. Ultrafiltration appears to give more versatility to
produce juices with stable aroma and flavor. Moreover, pasteurized UF
retentate and clarified samples may be recombined to give juices of various
total solid concentrations (e.g. equal to that of fresh jicama juice).
Analytical data on screened fresh juice and juice fractions are given in Table

  1. In relation to the fresh sample, total solids, total sugars, and nitrogen
    contents increased and decreased in the retentate and permeate juices, respectively, whereas ash and pH remained practically constant. The Brix degree
    changed only slightly.
    Color of fresh juice appeared to change by UF, as reported by Padilla &
    McLellan [11]. Thus, three Hunter color standards were used for comparison
    purposes. Concentrated and clarified juices exhibited decreasing L values
    compared to the control (Table 1). Determinations of total color difference
    showed that the fresh juice and UF retentate were closer to the yellow tile,
    whereas the UF permeate was nearer the green standard.
    General composition of jicama bagasse is also shown in Table 1. Contents
    of total solids and crude fiber were 23 and 16.4%, respectively. This residue
    should be investigated as a possible source of starch, as suggested by Hansberry et al. [12], and of dietary fiber.
    In summary, this initial study suggests that UF may be used to render a
    pleasant jicama juice with some commercial potential and, in view of its
    composition, some food applications may be found for the bagasse. However,
    further studies are needed on this process including sensory studies of juice.
    Also, storage and handling studies of jicama are pending.