December 1965 B-1046

Fruits o)‘ Chico variety scalded in 25 percent NaOH (230° F.) for 2O seconds, 45 percent
CaC/z (250°  for 30 seconds and water (212° F.) for 90 seconds, respectively. The
fruits were photographed immediately after scalding.

emical Pel  Tomatoes

  

Fruits of Homestead variety scalded in 25 percent NaOH (230° F.) for 20 seconds, 45
percent CaCl, (250° F.) for 3O seconds and water (212° F.) for 90 seconds, respectively.
The fruits were photographed immediately after the cans were opened.

Summary

Tomato fruits of the Chico and Homestead
varieties were scalded in solutions of water, NaOH
and CaClz at various concentrations, times and tem-
peratures. Fruits were weighed before and after
peeling to determine percent Weight loss and were
visually rated for percent peel removed. After can-
ning and subsequent storage the fruits were sub-
jectively evaluated for firmness and color.

Graphic presentation of the data provided a
basis for selecting desired scalding treatments ac-
cording to variety and chemical in terms of percent
peel removed and percent Weight lost.

Both NaOH and CflCl2 solutions were more
effective for peeling tomatoes than the standard
water treatment. More complete peel removal was
obtained with equal or less weight loss and the
fruits generally were firmer and possessed a more
attractive red color. The CaClz-treated fruits were
particularly firm and attractive after thermal process-
ing and storage. (See Photos)

IiQTEXAS A8<M UNIVERSITY AGRICULTURAL EXPERIMENT STATION R. E. Patterson, Director, College Station, Texas

Cbgmgkal  0f TOTnflIQQf l Gerald C. Heddins and E. E. Burns‘;

i he tomato, Lycope-rricum erculentum Mill, is widely

grown for both fresh market and processing. Toma-
toes are processed into many forms; one of the most highly
prized is canned whole tomatoes. However, before the
fruits are placed into the cans the peels must be removed.
This phase of the processing procedure greatly affects the
quality of the finished product. It is also time consuming
and laborious.

REVIEW OF LITERATURE

Early canners removed the peel entirely by hand with
the aid of sharp knives  This method was later
replaced by a technique that has been the standard process
for many years. The fruits are passed through boiling
water or live steam, cooled in water, and the peels are
removed by hand (9, 11).

Through the years there have been several new meth-
ods proposed for peeling tomatoes, but most have not been
adopted by canners. Cagnoni. (6, 7) developed a process
which involves immersing fruit in a freezing solution.
The skin is superficially frozen, and upon thawing the
peel separates from the fruit and is removed, leaving the
remainder of the pericarp intact.

Brown and Murnane (3) proposed a process whereby
tomatoes are quickly heated to 240°-260° F. under 10-15
pounds steam pressure. Cold water then is injected into
the pressure tank, causing a partial vacuum to be produced.
This induces rupturing of the peel, making it easily
removable.

In recent years some processors, especially those in
California (1, 9), have added NaOH to the scalding
water. The literature does not indicate clearly the con-
centrations, temperatures or time intervals utilized. Con-
siderable information is available regarding the lye peeling
of peaches, apricots, sweet potatoes and carrots, but specific
information regarding the lye peeling process for tomatoes
is very limited. However, when the lye is used in peeling
peaches and sweet potatoes the terms for describing the
peel removal indicates a dissolution or cauterization of the
cells (5, 9).

Childs et al. (8) states that high concentrations of
CaC12 may be used at high temperatures to cause a separa-
tion of the peel from the ‘remainder of the pericarp and
to firm the exposed tissues.

According to Campbell et al. (5), Proper scalding is
very important because of the resultant effects on quality,
yield and rapidity with which the fruits may be peeled.

*Respectively, superintendent of industries, Texas Department
of Corrections, Sugar Land; and associate professor, Department
of Soil and Crop Sciences, Texas A&M Universitv-

   
  
 
   
   
    
  
  
  
  
   
  
  
   
   
  
 

Cruess (9) stressed this factor by stating that 20-50
cent of the fruit is lost when peeling is done by the 
scalding method. The amount hand trimming 
sary is partially related to the effectiveness of the s g
process (5). '

Wholeness of the fruit is an important fact
determining grades and prices for canned to
Wholeness of canned tomatoes can be reduced by ex
heat penetration and related softening of fruit d)
scalding (5). Excessive handling of the fruit 
peeling lines is another factor. Proper scalding, m
handling and the addition of fruit firming chemic “I
adjuncts to maintaining wholeness of fruit (4). i.

Kertesz et al. (10) investigated practical meth
using CaC12 for firming canned whole tomatoes. i
addition of CaC12 just prior to sealing the cans 1
processing is now an accepted practice and is of con
able importance for the tomato canning industry. i

The purpose of this research was to establish 1|
able times, temperatures and concentrations of CaClzi
NaOH for peeling tomatoes. '-

MATERIALS AND METHOD

Fresh fruits of Chico and Homestead tomato vari
were collected in the same general production area r;

TEMPERATURE (O F)

30-
28-
1? 26-
u
c‘.
O
U
OJ
Y’, 24-
5
Z
S 22-
2
E
20-
18-
16-
14-
Percent peel removed
___ Percent weight loss ~ ___
12 I 1 r J‘ “‘~-

I I I
25 25 25 25

NaOH (Percent)

Figure ‘l. Percent peel removed and weight loss for Chico 
(U. S. No. 'l) at varying times, temperatures and concentroti _‘
NaOH.

      
   
 
   
  
   
 
  
  
 
  
  
  
  
 
 
 
 
 
 
   
  
   
   
   

TEMPERATURE (° F)
220
I

100%

227.

20%
95%

90%

 ___Percent peel removed
 - m.

 
 
 

Percent weight loss

| | 707.

I I I

25 25 25 3O 35
NaOH (Percent)

2. Percent of peel removed and weight loss for Homestead
71(U.S. No. I) at varying times, temperatures and concentra-
l‘. NaOH.

_g The samples were harvested and subjectively
‘- nto one maturity class. The class was U.S. No. 1
rmined by comparison with the United States De-
 of Agriculture Tomato Red Color Standards.

e fruits were also selected for uniformity of size.
p ico variety ranged in size from 1% to 2 inches in
 The size of the Homestead variety was from 2
 inches in diameter. The fruits underwent pre-
p grading at harvest, but final selection was made
riot to treatment. The fruits were stored overnight
i° F. and used as quickly as possible the following

iEach fruit was weighed to the nearest hundreth gram
ndividually scalded according to one of the following
 es:

f1. 25 percent NaOH (212°  25 percent NaOH
' (25o° F.), 55 percent NaOH (250° F.) for 1o,
2O and 30 seconds, respectively.

25 percent CaC12 (212° F.), 25 percent CaC12
(230° F.), 45 percent CaClg (250° F.) for 10,
V, 2O and 50 seconds, respectively.

,3. Water (212° F.) for 90 seconds.

jThe various treatapernts were replicated six times.
i scalding, the fruits were idipped in running water
passed individually through a revolving drum washer.
 fruit emerged from the washer it was given a
t? rating from 0 to 10, based on the amount of peel
‘ved from the fruit. Zero was given to those with the
(‘completely intact, 1O to those with the peel com-

pletely removed and gradation in between relative to
the estimated ercent of eel removed.
P P

After the scalded fruits were rated for peel removal,
the adhering peels were removed and the fruits were
placed on a 0.5-inch mesh screen for 2 minutes to drain
off excess water. Each fruit then was weighed to the
nearest hundredth gram.

The fruits were canned separately in No. 505 cans
according to commercial methods (9). The fill juice for
all cans was from one lot of Chico tomatoes and had
approximately the same pH and percent soluble solids.
The canned fruits were stored at room temperatures for
about 5 months. The cans were opened and the fruits
were subjectively examined for color and firmness.

RESULTS AND DISCUSSION

Peeling Test

The large number of variables involved in the peeling
test and the presence of two response surfaces (peel rating
and weight loss) rendered the drawing of statistical
inference impractical. However, desired NaOH and
CaC12 peeling treatments can be selected from Figures
1, 2, 3, and 4. The procedure for using the tables is
to follow an iso-peel curve corresponding to the specified
percent peel removal desired until a temperature and
concentration is reached which corresponds to the smallest
percent weight loss. This point often appears in the
upper right-hand margin of the figures involving CaC12
treatments. The CaC12 treatments are dependent on a
high solution temperature of about 250° F.

TEMPERATURE (° F)

 

200 210 220 230
I I I I
I I I
30--
28-:-
Zfiq-
'5? 24.1-
ra
r:
o
U
o
i5
a ZZI-
H
Z
f3 20--
g
18--
16--
14"- Percent peel removed
___...Percerit weight loss
1? I l I I

I I I
25 25 25 25 35 45
CaCl 2 (Percent)

Figure 3. Percent of peel removed and weight loss for Chico variety
(U. S. No. 1) at varying times, temperatures and concentrations of
CaClg.

 

‘TEMPERATURE (O F)

200 210 220 21.30
I
I I I I
3°" s07.
28--
26-1:-
° 7oz
A 24mm
fi
'0
l:
o
u
GI
Y} 22..-
g 60%
l-l
g 2Q--
l-l
2
g 18--
50%
16--
407.
14--
Percent peel removed
__._ Percent weight loss
l
12 g : l I I l»

I I I
25 Z5 25 25 35 45
CaClz (Percent)

Figure 4. Percent of peel removed and weight loss for Homestead
variety (U. S. No. 1) at varying times, temperatures and concentra-
tions of CaCl2.

Since the standard hot-water treatment involves only
one time (90 seconds) and one temperature (212° F.);
figures comparable to 1, 2, 3, and 4 could not be formulat-
ed. Table 1 represents results obtained when U.S. N0. 1
fruits were scalded by the standard hot water method.
These results are averages of six replicates.

The immersion time of the hot water treatment
was considerably longer than the NaOH or CaC12 treat-
ments. More time and effort also was required to remove
that portion of the peels which adhered to the fruits after
scalding and washing.

The top cover photo illustrates fruits of the Chico
variety scalded with 25 percent NaOH (230° F.) for 2O
seconds, 45 percent CaC12 (250° F.) for 3O seconds and
water (212° F.) for 9O seconds. The fruits scalded in 25
percent NaOH were fairly firm; however, the white vas-
cular bundles were exposed. This was due to the caustic
action of the NaOH on the outer tissues. The white color
of the vascular bundles reduced the redness of the fruits.

Fruits scalded in 45 percent CaC12 were firm and
possessed an attractive red color. During the CaC12 scald-
ing process, the peel separated from the fruit and exposed
the outer portions of the fruit to the high calcium
concentration in the solution. These tissues were firmed
by the apparent reaction of the calcium with the fruit
pectins forming calcium pectate. This prevented sloughing
of the outer portion of the pericarp and greatly reduced
weight loss and exposure of the vascular bundles.

According to McCollum (12), the total carotenoids
are highest in the outer portion of the pericarp wall. The

photo.

 
    
    
 
 
 
  
   
 
   
  
  
   
 
  
   
   
  
    
   
   
   
   
    
  
  

Table 1. Percent peel removed and weight loss,
standard hot water treatment

Percent W

Variety Temperature Time h
(° F seconds peel i.‘

removed per f,

Chico 212 9Q 25 1 A

Homestead 2 1 2 90“ 48 1 l:

retention of these highly pigmented cells and the la J
exposed underlying vascular bundles would explain;
more attractive red color of the CaC12-scalded fruits. A -:_

The fruits scalded in water were slightly softer =1
those scalded in NaOH solution and were conside
softer than those scalded in CaC12 solution. The col A
the fruits was similar to that of the NaOH-treated f t
The outer tissues were softer and sloughed readily. A

Effects of Thermal Processing _

Samples of fruits peeled by the methods discus w
the previous section were used in this test. The b0‘
cover photo illustrates fruits of the Homestead v if
peeled by three methods, canned and stored for 5 mo .
The fruits subjected to the NaOH and water treat I
appeared similar, but the water-treated fruits were r.
and lost moisture rapidly. This can be noted by
moisture circles that appear around the fruits in the bol

The CaC12-treated fruits were very firm and p,
their shape similar to that of fresh fruits. The color 
attractive and there was little evidence of thermal 
ing. The cover photos illustrate the small quay
of moisture lost by the CaCIQ-treated fruit.

LITERATURE CITED

1. Anonymous. Feb., 1963. Fourteen steps in succ
tomato canning. Canner Packer 29-31. 

2. Bitting, A. W. 1937. Appetizing, or The Art of Ca "
The Trade Press Room, San Francisco. 

3. Brown, H. D. and Cecilia Murnane. 1944. The expla
vs. usual method of peeling vegetables and fruits. VJ
Amer. Soc. Hort. Sci. 44:190-192. q

4. Burns, E. E., P. W. Leeper, T. E. Stephens and A. l"?
1958. Evaluation of tomatoes for processing in the L

Rio Grande Valley, Tex. Ag. Expr. Sta. Prog. Rept. 2

5. Campbell, H. C., R. A. Isker, and W. A. McClinn. 
Campbell’s Book, A Manual on Canning, Packing and 
serving. Vance Pub. Corp., Chicago, Ill. 222 pp. "

6. Cagnoni, D. 1955. Mechanical peeling of tomatoes
means of cold. Ricerca Sci. 25: (5):1115-1120. f_

7. Cagnoni, D. 1955. Refrigeration peeling and the ind '
of peeled tomatoes. Ricerca Sci. 25 (3):519-529. 

8. Childs, D., A. E. Braun, and j. Hanson. 1948, P . _
for treating tomatoes. U. S. Patent Office. Patent 
2,431,957. :

9. Cruess, W. V. 1958. Commercial Fruit and Vegi
Products. McGraw-Hill Book Co., Inc.; New York. 884

10. Kertesz, Z. I., T. G. Tolmon, j. D. Loconti, and E,-
Ruyle. 1940. The use of calcium in the commercial j
ning of whole tomatoes. N. Y. Sta. Agr. Expt, Sta.
Bull. No. 252. ._

11. Magoon, C. A. and C. W. Culpepper. 1942. Scaldi f
vegetables for canning. U. S. Dept. Agr, Bull. 1265, j

12. McCollum, j. P. 1955. Distribution of carotenoids irii
tomato. Food Research, 20. (1):55-59. °