Fritura de Alimentos

1. Comparative study of physical and sensory properties
of pre-treated potato slices during vacuum and
atmospheric frying
Ponente: José David Torres González
Docente: Ramiro Torres Gallo
Reología y Textura de los Alimentos
Maestria en Ciencias Agroalimentarias
Universidad de Córdoba - Monteria, 2015
E. Troncoso*; F. Pedreschi**; R.N. Zuñiga***.
*Chemical Engineering Deparment, Universidad de Santiago de Chile (USACH), P.O. Box 10233, Santiago, Chile,
**Department of Food Science and Technology, Universidad de Santiago de Chile (USACH), P.O. Box 10233, Santiago, Chile
***Chemical & Bioprocess Engineering Department, Pontificia Universidad de Chile, P.O. Box 306, 6904411, Santiago, Chile
LWT - Food Science and Technology 42 (2009) 187–195

2. RESUMEN
The objective of this research was to study the effect of different processing conditions on physical and
sensory properties of potato chips.
Desirée and Panda varieties (diameter: 30 mm; thickness: 3 mm) were pre-treated in the following ways:
(i) control or unblanched slices without pre-drying.
(ii) blanched slices in hot water at 85 °C for 3.5 min and air-dried at 60 °C until a final moisture content of
∼0.6 kg water/kg dry solid.
(iii) control slices soaked in a 3.5 kg/m3 sodium metabisulphite solution at 20 °C for 3 min and pH adjusted
to 3.
Pre-treated slices were fried at 120 and 140 °C under vacuum conditions (5.37 kPa, absolute pressure) and
under atmospheric pressure until they reached a final moisture content of ∼1.8 kg water/100 kg (wet basis).
An experimental design (3 × 23) was used to analyze the effect of pre-treatment, potato variety, type of
frying and frying temperature over the following responses: oil content, instrumental color and texture and
sensory evaluation.

3. Vacuum frying increased significantly (p<0.05) oil content and decreased instrumental color and textural
parameters.
Sensory attributes, flavor quality and overall quality, were significantly improved using vacuum frying.
The higher frying temperature (140 °C) increased ΔE, maximum breaking force, hardness and crispness and
decreased L* and b* values. On the other hand, panda potato variety improved the color of the product.
A great improvement on color parameters was obtained using sulphited potato slices instead of the other
pre-treatments.
Although, the better flavor was obtained for control potato chips, no significant differences were found for
overall quality between control and sulphited potato chips.
Significant correlations (p < 0.01) between sensory and instrumental responses were found.
RESUMEN

4. Introduction
Deep-fat frying is one of the oldest and most popular food preparation techniques at
both domestic and industrial venues. Deep-fat frying can be defined as a thermal
food processing method in which food immersed in oil at a temperature of 150–190
°C, which is well above the boiling temperature of water.
The heat and simultaneous mass transfer of oil and air promote a number of chemical
changes, such as:
Water loss Denaturation protein
Oil uptake Reducing sugars
Crust formation Color via Maillard reactions
Starch gelatinization Hydrolysis or oxidation
Aromatization Oil polymerization
Fig. 1: Deep-Fat Frying Procesing (Aguilera, 1997)

5. Fig. 2: Scanning Electron Microscope of the crust
during deep fat frying potato (Singh, 1995).
Fig. 4: Phases during deep fat frying (Moreira, 1999)
Fig. 3: Mass and Heat Transfer during deep fat frying (Farkas, 1996)
1) Calentamiento inicial; 2) Ebullición superficial; 3) Velocidad
decreciente; 4) Punto final de burbujas (Baik y Mittal, (2003).

6. Pre-treatments for Deep-Fat Frying
Pretreatmentsbeforedeepfatfrying
Blanching (Escaldado)
Drying (Secado)
Biofilms (Recubrimientos)
Osmotic dehydration (Deshidr. Osmótica)
Frozen (Congelación)
Combined methods (Combinados)

7. Material and methods
-Potatoes (varieties Desirée and
Panda) vegetable oil.
-Stored in dark room at 8 °C and 95% relative humidity.
-Slices (thickness of 3 mm) were cut from the pith of
the parenchymatous region of potato tubers using an
electric slicing machine (Berkel, model EAS65, UK).
-A circular cutting mold was used
to provide chips with a diameter of
30 mm.
-Sugar contents of Desirée and Panda varieties were
21.79 ± 0.58 and and 22.54±0,42 respectively.

8. Sample Preparation
Potato slices were rinsed immediately after cutting for 1 min in distilled water
The following pre-treatments were used:
• (i) Control or unblanched slices without pre-drying.
• (ii) Blanched slices in hot water at 85 °C for 3.5 min were placed on a
wire tray, arranged in one layer of 28 samples, in a laboratory
convection dryer, with an average tray load of 1.75 kg/m2. Then the
samples were air-dried at 60 °C at an air velocity of 1.8 ± 0.1 m/s.
Weight loss was monitored periodically until the slices reached a final
moisture content of ∼0.6 kg water/kg dry solid.
• (iii) Potato slices were soaked in a 3.5 kg/m3 sodium meta-bisulphite
solution at 20 °C for 3 min and pH adjusted to 3.
The concentration of the metabisulphite
solution and the time of immersion was
chosen to obtain fried potato slices with a
sulphite level below 5 × 10−5 kg/kg,
according to the permissible limit the
General Standard for Food Additives
(GSFA) developed by the Codex
Committee on Food Additives and
Contaminants (CODEX STAN 192-1995,
1995).
After immersion, the samples were rinsed
and blotted with tissue paper before
frying.

9. Systems Deep-Fat Frying
V = 0.012 m3 y stainless steel (type 316) vessel electrically heated and a temperature controller system (PID) ± 3 °C. The
fryer was filled with 0.0035 m3 of oil, which was pre-heated for 1 h prior to frying and discarded after 6 h of use.
Fig. 5: Schematic of the frying system
-The vessel was connected to a vacuum
pump. Level maxim of 5.37 kPa and at this
pressure the boiling point of water is 34 °C.
-Once the oil temperature reached the
target value (120 °C or 140 °C), the pre-
treated slices were placed inside the fryer
basket (Fig. 5).
-The vessel was depressurized. When the
absolute pressure in the vessel achieved
5.4 kPa, the basket was lowered and
immersed in the oil.
Vacumm
-Temperature (120 °C or 140 °C), the basket was immersed in the oil.
-Finalized the frying time, the basket was raised and the samples were removed
from the fryer, blotted with tissue paper and allowed to cool to room temperature
before analyses.
Atmospheric

10. Experimental design and statistical analysis
• A statistical multifactorial experimental design was used to analyze simultaneously the effect of four
factors that affect the frying process through the following responses:
Factors
Pre-treatment
c: control
bd: blanched
and dried
s: sulphited
Potato variety
d: Desirée
p: Panda
Type of frying
a: atmospheric
v: vacuum
Frying
temperature
120°C
140°C
Responses
Oil content
Instrumental color
Instrumental texture
Sensory evaluation

11. Experimental Design And Statistical
Analysis
The randomization of the experiments as well as
the statistical analysis of the experimental data
was done with the software Statgraphics Plus
(version 5.1).
The statistical significance of the effects of the
factors, and their interactions, was analyzed
simultaneously by means of Pareto charts and
ANOVA tests (p<0.05).
Table 1. Standard matrix of the multifactorial experimental design 3×23 runs.

12. Design responses
Sensory evaluation
Instrumental texture
Instrumental color
by computer vision
Oil content
Was determined by rapid method of total lipid extraction and purification (Bligh & Dyer, 1959). was expressed
as kg oil/kg dry solid.
A computer vision system (CVS), previously implemented, was used to measure representatively and
accurately the color of the potato chips, using 15 samples for each analysis. Diferencia de color total (QRT)
fried potato slices was defined as:
Measurements at temperature (20 °C) by a puncture test with a speed test of 10 mm/s using a punch with a
diameter of 2 mm (probe model P/2) performed in a Texture Analyzer TA.XT2i (Stable Micro System, Surrey,
UK). The peak or maximum force, defined as the force at which the punch penetrates the outer layer of the
surface of the fried potato slices, was obtained using the software Texture Expert (version 1.16). Each analysis
was conducted using 10 samples.
Thirteen assessors (eight male and five female), 20 and 30 years. This panel was trained during 12 sessions (2 h
each one) for quantitative descriptive analysis (QDA) of potato chips. The response variables were obtained by
means of a QDA on a 10 cm non-structured linear scale (Meilgaard, Civille, & Carr, 1991), and a quality rating
test (QRT) (Muñoz, Civille, & Carr, 1992) on a 7-point numerical scale (1 = very bad, 7 = very good).

13. Other analyses
Moisture content
Moisture content of potato chips was measured by drying the samples in a vacuum convection oven (SHEL
LAB, model 1410-2E, USA) at 30 kPa (vacuum pressure) and 70 °C per 24 h until reaching constant weight
(AOAC, 1984).
Sulphite content
The determination of sulphite content was performed according to the optimized Monier-Williams method
(AOAC, 1995). The total concentration of sulphite was determined by a titrimetric method in which sulphite
is converted into sulphur dioxide and further oxidized to sulphuric acid using hydrogen peroxide and
subsequently titrating against alkali. The analysis of all samples was performed in triplicate

14. Results And Discussion
Table 2. Response values of the multifactorial experimental design (3×23)

15. Table 3. Effects of the multifactorial experimental design (3×23)

16. Table 4. Percent change in the response by switching from low to high level of the factors

17. Fig. 2. Effect of pre-treatment on the statistically significant quality parameters of fried potato slices. Bars with different
letters indicate significant differences (p<0.05).

18. Fig. 3. Image gallery of pre-treated potato chips (Desiree and Panda varieties) fried at 120 C under vacuum and
atmospheric frying.

19. Table 5. Percent change in the response by switching from low to high level of the pretreatment

20. Conclusions
Vacuum frying increased significantly oil content of potato chips and had a significant effect on the
instrumental and sensory parameters of color. Potato slices fried under vacuum had L* values significantly
higher than the values corresponding to the slices fried under atmospheric conditions. The a*, b* and ΔE
values were significantly higher for potato slices fried at atmospheric pressure than those for fried at the
vacuum conditions.
Sensory evaluation confirmed these results, the color of the potato slices fried at atmospheric conditions
was evaluated as “darker” and “worst” than the potato slices fried at vacuum conditions. Instrumental and
sensory textural parameters of chips, maximum breaking force, hardness and crispness, were significantly
decreased by using vacuum frying.

21. Nevertheless, texture quality was significantly “better” for vacuum fried chips and flavor quality and overall
quality were improved when vacuum frying was used instead of atmospheric frying. Frying temperature
affected significantly instrumental and sensory parameters of color and texture. The high level of frying
temperature (140 °C) decreased L* and b* and increased ΔE, maximum breaking force hardness and
crispness. Panda potato variety improved the color of the product and the pre-treatment affected
significantly the instrumental parameters of color, flavor and overall quality of potato chips.
In general, sulphited potato slices improved significantly color parameters in comparison with control and
blanched and dried pre-treatments. The better flavor was obtained for control potato chips, but no
significant differences were found for overall quality between control and sulphited potato chips. Significant
correlations (p<0.01) between sensory and instrumental responses were found indicating that both methods
are suitable for the measurement of color and texture parameters.

22. ¡¡¡GRACIAS!!!