Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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Background o the Invention
Field of Invention: The invention relates to and
has among its objects the provision of novel processes
for peeling fruits and vegetables. Further objects of
~ the invention will be evidence from the following de;crip-
- tion wherein parts and percentages are by weight unless
otherwise specified.
~ escription of the Prior Art: In conventional
- practice in food processing plants, many fruits and
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vegetables are peeled by dipping them in hot lye (NaOH~
solutionr and then removing the loosened skin ~ wiping
with rotatingr soft rubber discs, or by flushing with
jets of water. Although such lye-peeling procedure is
e~fective, it presents several disadvantages. In the
first place, high peeling losses occur because the caustic
removes a substantial proportion of the softer tissue in
the flesh of the fruit or vegetable as well as the peel.
It is evident that hi~h peeling losses are economically
undesirable. Al$o, the peeled products do not have an
at~ractive appearance because of removal of some of
the flesh. This is, of coursel a disadvantage where
the product is intended for canning in the whole state.
Another disadvantage of lye-peeling is that it yields
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a waste having a high MaOH
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content so that it is difficult to dispose of; many communi-
ties require that the waste be neutralized prior to releasing
it into sewage plants, and even such neutralization, which is
a considerable expense, does not alter the detrimental effect
of its high sodium content.
To increase peeling efficiency in the lye-peeling method,
various surfactants are added to the caustic peeling solution.
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For example, minor amounts of sodium 2-ethylhexylsulfate,
sodium mono- and dinaphthalene sulfonates, or certain aliphatic
acids have been used in conjunction with lye to peel fruits and
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. vegetables. However, although peeling efficiency is increased,
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the use of caustic solutions containing surfactants is still
? subject to the same disadvantages as outlined above for caustic
alone.
Peeling of fruits and vegetables is also accomplished
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using hot water, steam, or simple abrasion. These methods also
have the disadvantage of high peeling losses, i.e., loss of
valuable flesh, and uneven peeling.
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Summary of the Invention
Accordingly, this invention provides a process for peel-
ing edible plant products, which comprises:- (a) contacting
the unpeeled edible plant product with an aqueous dispersion
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containing a 2-18 carbon carboxylic acid as the sole peel-
loosening agent in a concentration and for a period of time
and at a temperature sufficient to loosen the peel, and
` (b) removing the so-loosened peel.
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The primary advantage of the-invention is that the peel -
; of the fruit or vegetable can be removed without removal of or
damage to the flesh. Obviously, this is an economic advantage
- 30 since the flesh is the salable commodity. Furthermore, an
;~ attractive appearance for the whole fruit or vegetable is re-
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tained, thus maintaining or increasing the marketability of
the peeled material.
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Another advanta~e of the invention is that the
carboxylic acids employed are biodegradable. Consequently,
disposal of spent peeling solutions is not a serious
problem. The peeling solutions are compatible with
municipal waste treatment facilities and agricultural
land disposal systems. Also, the waste can be dried and
used directly as an animal feed or as a fertilizer without
prior neutralization and the like.
A further advantage of the invention is that lower
temperatur~s may ~e employed as compared to peeling with
lye, hot water, steam, etc. Consequently, less energy
is consumed, thus making the instant process more econ-
omicalO Further, lower peeling temperatures result in
a better quality fruit or vegetable. Various desirable
nutritional and physical at~ributes, such as color, cell
` structure, protein, pectin, and vitamin content, etc., are
retained.
The peeling dispersion of the invention is not
caustic or alkaline. Thus, an~ther advantage ~f the
- 20 invention is that lysinoalanine formation is avoided.
Lysinoalanine is a substance recently suspected to be
carcinogenic; it is formed when proteins are treated with
- alkali. In alkaline peeling of fruits and vegetables,
then, some lysinoalanine is formed. The instant invention
avoids t~is prohlem ~ecause the peeling medium is acidic.
A further advantage is that the peeling solutions
are safer to handle. Hot al};aline solutions used in other
peeling methods are extremely caustic and, therefore,
dangerous to personnel and equipment.
Descr~ption of t~e Preferred Embodiments
In the following description emphasis is placed on
the peeling of tomatoes. This emphasis is by way of illus-
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tration and not limitation. The invention has wide
applicability and can ~e employed to remove the skin fro~
any edible plant product such as fruits, including pears,
apples, peaches, figs, grapefruit segments, etc., and
vegeta~les, including tomatoes, potatoes (both sweet and
white), carrots, beets, parsnips, turnips, pimentos,
onions, squash, etc.
The term "dispersion" used herein includes disper-
sions, solutions, emulsions, suspensions, mixtures and
.,
P 10 the like.
In a practice of the invention the tomatoes are
contacted with a dilute a~ueous dispersion of carboxylic
acid, This is best done ~y immersing the tomatoes in the
acid dispersion. Alternatively, the acid dispersion may
be applied by spraying, brushing, or the li~e. ~enerally,
the dispersion will contain about 0.1 to 2Q% of the acid
and is kept hot, i.e., about 7Q to 210F., pre~erably,
about 140~150F. It should ~e noted that the tomatoes
can be effic~ent~ peeled using a peelin~ dispersion
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; 20 containing ~ater and a minor proportion of carboxylic
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acid as the sole peel~loosening agent~-no caustic or
r;~ i alkaline material is necessary. Contact between the
tomatoes and the fatt~ acid di$persion should be main
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tained for a period long enough to loosen the peel of
the tomato. The amount of time is dependent on a number.',
o~ factors, such as type and maturity of the tomatoes,
; the concentration of aliphatic acid in the solution,
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~i the temperature of the peeling ~ath, etc. Usually, the
peel can be loosened by contacting the tomatoes ~ith the
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peeling bath for about 0.1 to 10 minutes. It should ~e
- obvious that neither the concentration o~ acid, nor the
temperature of the bath, nor the duration of contact should
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be great enough -to cause damaye to the tomato fle~h~
Acids which may be used in the process of ~he
invention include 2-18 carbon carboxylic acids such as
ethanoic (acetic~ acid, propanoic acid, butano~c (butyric)
acid, pentanoic acid, hexanoic ~caproic~ acid, heptanoic
acid, octanoic ~caprylic~ acid, nonanoic acid, deconoic
(capric~ acid, undecanoic acid, dodecanoic Clauric)
acid~ tridecanoic acid, tetradecanoic (myristic~ acid,
pentadeca-octadecanoic (stearic) acid, benzoic acid, 10-
undecenoic acid, cis-9-octadecenoic (oleic) acid, cis, cis-
9,12-octadecadienoic (linoleic) acid, cis, cis, cis-9,12,15-
octadecatrienoic (linolenic) acid. Preferred for purposes
of the invention are the even numb red 2-12 carbon ali-
phatic acids. It is also within the purview of the invention
to employ 2 to 18 carbon polycarboxylic acids, i.e., those
with more than one carboxylic acid function, to loosen the
tomato peel. It should be noted that the peeling bath of the
invention may contain only one of the above acids or mixtures
of two or more of the aforementioned acids. Furthermore,
it is not meant to limit the invention merely to the above-
named acids; the above examples are merely representative.
Some of the carboxylic acids mentioned above,
although effective in loosening the peel, possess an un-
pleasant odor. Consequently, such acids should be avoided
where aroma of the peeled product is important. However, '
undesirable odors from the acid may be removed by contact-
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ing the tomatoes, either before or after removal of the
- loosened peel, with dilute aqueous carbonate or bicarbonate.
Other means for avoiding undesirable aroma in the peeled
products will be obvious to those skilled in the art.
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Af-ter the peel of the tomato is loosened by appli-
cation o~ a carboxylic acid dispersion, the tomato is treated
to mechanically remove the so-loosened peel. Excellent results
are obtained using a rubber~disc peeler as described in U.S.
Patent 3,618,651. Other means for removing the loosened
peel, such as dry-brushing, water spraying, etc., will be
suggested to those skilled in the art.
-~ XAMPLES
The invention is further demonstrated by the
following illustrative-examples.
EXAMPLE 1
Peeling of Tomatoes
A batch of tomatoes (Tropic variety grown in
Sinoloa, Mexico~ was divided into several lots, each lot
being treated as follows:
Lot A: The tomatoes were weighed and then immersed
in a 1% aqueous solution of octanoic acld at 150F. for one
minute to loosen the peel. The tomatoes were removed from the
solution, and the loosened peel was removed by means of a
rubber disc peeler as descrihed in U.S. Patent 3,618,651.
The so-treated tomatoes were weighed and the difference in
weight was designated as the peel loss (4.8%). The peeled
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- tomatoes had a smooth surface with a uniform red color
resulting from the fact that the entire deep red sub-
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;;- cuticular layer was undisturbed. In essence, the peel of the
tomato was removed without loss of valuable tomato flesh.
Lot B: The tomatoes were weighed and then immersed
in an aqueous mixture containing 11% sodium hydroxide and 0.2%
sodium 2-ethylhexyl sulfate (SES) at 210F. ~or 0.5 min.
.; 30 (commercial peeling process). The tomatoes were separated
from ~he solution and the peel was removed as described above
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for Lot A. The peel loss was 12.4%. Peeling was not uniform;
small amounts of peel adhered to the tomato. Furthermore,
the flesh of the tomato was removed on parts of the tomato
surface. The white vascular tissue was much more prominent
than in the peeled Lot A tomatoes.
Lot C: The procedure described for Lot B was
repeated except that 0.2% of Faspeel (a commercial aliphatic
acid mixture produced by BASF Wyandotte Corporation) was
used in place of sodium 2-ethylhexyl sulfate.
The peeling loss was 11.7%. As in Lot B, the
peeled Lot C tomatoes had an uneven surface with peel adher=~
ing to part of the surface and flesh removed from part of
the surface.
Lot D: The tomatoes were weighed and immersed in
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hot (2120F., water for 1.0 minute. The tomatoes were then
removed from the water and cooled. The peel was intact and
was not removed when subjected to the action of the rubber
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discs.
hot E: The procedure described above for Lot D
was repeated except that the tomatoes were immersed for 1.5
minutes.
The so-treated tomatoe;s were overcooked and the
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Lot F: The procedure described above for Lot D was
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repeated except that the tomatoes were immersed for 2.0 minutes.
The so-treated tomatoes were overcooked and
exhibited pronounced surface cracking and splitting.
The extent of peeling was rated as total (complete
removal of peel) or partial ~incomplete removal of peel). The
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3Q appearance was rated as excellent, good, fair, or poor, depend-
ing upon the amount of flesh removed by the treatment. A
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rating of excellent meant that no flesh was removed, whereas
a rating of poor indicated substantial removal of flesh or,
in the case of the hot water treatments, substantial splitting
of the tomato surface.
The results are summarized below.
Lot Peeling medium Temp. Time Peeling Extent of Appearance
(F.) (min.) loss (%) peeling
A 1% Cc~noic acid 150 1 4.8 Tbtal Excellent
i Bl 11~ NaOH ~ 0.2% SES 210 0.5 12.4 lbtal Poor
cl 11% NaOH + 0.2% Faspeel 210 0.5 11.7 lbtal Poor
; D Water 212 1.0 UhpePled N~ne
- E Water 212 1.5 do. None Poor (tomato
cooked)
; F2 Water 212 2.0 do. None Poor do.
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1 Not in accordance with the invention but provided for
purposes of comparison; both peeling media are used commercially~.
Not in accordance with the invention but provided for
purposes of comparison; generally used to peel tomatoes on
a small scale such as in the home. The fact that peeling did
not take place i~dicates the difficulty of peeling this part-
'~ icular variety of tomato.
, EXAMPLE 2
Peeling of Tomates
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A batch of tomatoes (same variety as in Example 1) was
, divided into several lots and each lot was treated in accordance
i with the procedure outlined in Example 1, Lot A, with changes
, as indicated in the table belowO
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Lo-t Peelin~ medium '~ra- TLme Peeling Extent of Ap~ance
ture ( F.) tmino) loss (~) Peelmg
G 1~ Hexanoic acid 120 2.5 5.5 Tbtal Excellent
H do. 120 5 7.9 Tbtal Excellent
J do. 80 51 12.7 To~l ~x~
K 1% Butyric 150 1 5.2 Tbtal Excellent
L do. 120 5 5.4 ~btal Good
M 10% Acetic acid 150 2 7.5 Tbtal Good
N 5% ~cetic acid 150 2 2.6 Partial Pcor
P 1% Oleic acid 150 1 1~0 Partial Poor
R 11% NaO~ + 0.2% SES 210 0.5 12.4 Total Poor
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, 1 Not in accordance with the invention but provided for
purposes of comparison; the peeling medium is used commercially.
It should be noted that the odor of the peeled pro-
duct may be undesirable due to the presence of trace amounts
of the carboxylic acid employed in the peeling process. In
addition, in the case of those carboxylic acids which are
solid at ambient temperature, an undesirable residue may be
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`-: left on the peeled material. In both cases, these undesirable
`~ 10 effects were removed by washing the peeled product in dilute
aqueous sodium bicarbonate.
EXAMPLE 3
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Peeling of Pears
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Ripe Anjou pears were divided into lots and treated
as follows: -
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Lot S: The pears were immersed in a 1% aqueous octanoicacid solution at 150F. for 3 minutes to loosen the peel. The
pears were removed from the solution, and the loosened peel
~, was removed by means of a rubber disc peeler as described in
`' 20 Example 1. The peeled pears had a smooth surface resulting
; from the total removal of the peel without removal of the flesh.
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` Lot T: The pears were treated in accordance with the
procedure described for Lot S but were immersed for 10
minutes in the peeling medium.
Lot U: These pears were immersed in water at 150F.
for 5 minutes, removed from the bath, and cooled.
The results are tabularized below.
:
IDt Peeling medium Tem~erature Time Extent of Appearance
.~ (min.)peeling
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`;S 1~ Octanoic acid 150 3 Ibtal Gcod
T do. 150 10 Tbtal Pcor
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` ~~ater 150 5 None PuDr
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:~ 1 Not in accordance with the invention but provided for compari-
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son.
EXAMPLE 4
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Peeling of Carrots
Ripe carrots were divided into lots and treated
i,~ as -follows:
~ Lot V: Treated in the same manner as described for
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~ the pears in Lot T of Example 3.
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Lot W: Treated in the same manner as the pears of Lot
- U in Example 3 except that the immersion time was 30 minutes
The results are summarized in the -following table:
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~:~; Lot Peeling medium Temperature Time Extent of Appearance
~`! tOF.) (min.) peeling
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;~ V 1~ Cctanoic acid 150 10 Partial Poor
Water 150 30 None Poor
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!~p 20 1 Not in accordance with the invention but provided for
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~ comparison.
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