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Background and Objectives:
- To assess frying performance of selected vegetable oils and frying fats during
production of french fries.
- To understand the role of endogenous minor components in frying performance.
- To establish the relation ship between composition and content of minor components and
performance during frying and effect on quality of french fries.
Procedure and
Project Activities:
Oils and Fats
Following industrially processed oils and fats were used in the
frying experiments: regular and low linolenic canola (RCO, LLCO), Mid Oleic sunflower
(MOSUN), hydrogenated canola and soybean fats (HCO, HSO) and low linolenic, high oleic low
linolenic canola oil (NATREON).
Analytical Procedures
Peroxide Value - Fresh oils were analysed for peroxide value using the AOCS procedures Cd
8-53.
Conjugated Dienes - Content of these components was analysed by the AOCS procedure Ti
1a-64.
Anisidine Value - Was analysed according to AOCS procedure Cd 18-90.
Free Fatty Acid - According to AOCS procedure Ca 5a-40.
Polar Components - Content of polar components formed during frying was analysed by the
AOCS column chromatography method Cd 20-91.
Colour of Oil - Colour of oils used in frying were measured at wavelength of 490 nm using
spectrophotometer in standard 1 cm cuvette, applying fresh oil as reference.
Tocopherols - Tocopherols were analysed using AOCS procedure Ce 8-89 with modification of
mobile phase to 5% t-butyl methyl ether in hexane.
Fatty acid - Composition of fatty acids was analysed using AOCS procedure Ce 1-62.
Odour Evaluation of French Fries
The objective of this study was to determine
the overall odour quality of french fries fried in vegetable oils/fats for an extended
period of time.
Sample Preparation
For each test two vegetable oils were placed into two
Garland institutional fryers as follows: Frying 1 - low linolenic/high oleic canola oil
(NATREON) and sunflower oil (MOSUN); Frying 2 - hydrogenated canola oil (HCO) and low
linolenic canola oil (LLCO); Frying 3 - regular canola oil (RCO) and hydrogenated soybean
oil (HSO). Oils were heated to 178oC ±2oC and maintained for eight
hours a day for a period of seven days. Fresh oils were heated first 30 minutes without
french fries frying to condition them. Parfried frozen french fries were fried in the oils
four times per day, 1 kg fries per fried batch. Sensory evaluation took place on 1, 3, 5
and 7 day of the frying. Fries from the fourth frying batch of the day being used for the
sensory evaluation.
The reference oil, hydrogenated canola oil (HCO), was placed in a household fryer and
was heated to 165oC ± 5oC and maintained at this temperature for a
period of one hour during two consecutive days. Parfried frozen french fries were fried in
the oil only during the day when sensory analysis have been performed.
After frying, french fries were placed on trays and kept under heat lamps while
portioning into 250 mL styrofoam cups. Approximately 20 g (4 french fries each 8 cm long)
were placed into the cups and kept under heat lamps. As panelists arrived cups were capped
with plastic lids for presentation. The reference sample was presented each time with
label REF and evaluated first followed by the two samples coded with 3 digit numbers.
Training Sessions
Eleven panelists were recruited based on their willingness
and availability to participate in sensory evaluation. Three 45 minutes training sessions
were completed. During the first session panelists learned the method to evaluate the
odour of the french fries. Two samples of french fries were presented, a reference sample
labeled REF which consisted of french fries fried in fresh HCO and a coded sample, the
french fries fried in RCO which was used for eight days of frying. For each sample,
starting with the reference, on an individual basis, panelists evaluated the odour for the
french fries. Discussion followed after each sample evaluation. Panelists noted that the
reference sample was "fresher" than the sample of fries fried in RCO used for
eight days of frying. At this session, panelists were introduced to eight standard odour
as shown in Table 1.
During the second session panelists evaluated the reference sample for intensity of the
following odour attributes: potato, fresh oil, hydrogenated and buttery. Quality was also
discussed given the quality scale adapted from the AOCS procedure Cg 2-83. The reference
sample was given score of 8 points and odour attributes were described as "typical of
good quality product, moderate characteristic odours, no off-odours". The ballot for
this session incorporated the reference attributes as well as the eight standard odour
attributes with five intensity levels - very weak, weak, moderate, strong, very strong.
Panelists were instructed to check the odour attribute(s) with the corresponding
intensity(s) present in the coded sample. With these attributes and intensities the
quality score could be determined based on the presence/absence of characteristic french
fry odour (as it appeared in the reference sample) and the presence/intensity of
off-odours (stale, fishy, painty, grassy, cardboard, browned, any other noted off-odours,
in addition to hydrogenated for the five non hydrogenated oils). Three coded samples were
presented in the second session including french fries fried in RCO, LLCO and in HCO,
these oils were held at frying temperature for eight, one and eight days, respectively.
Panelists were instructed to define the intensity and type of odour attributes present in
the sample. After individual assessment, samples were discussed regarding the attributes
as well as the intensity scores.
The third session provided additional practice with fries fried in LLCO, NATREON and
RCO oils which were held at frying temperature for five, one and seven days, respectively.
The REF sample was presented with each set. Discussion of the attributes and intensity
found in the samples took place after evaluation of the each set to master the scoring
procedure.
Testing Sessions
Testing sessions took place in individual booths equipped with
red fluorescent light to mask possible colour differences which may have influenced the
evaluation of the french fry odour. Panelists came in two groups, 10 minutes apart. French
fries were prepared as described above in "Sample Preparation".
The eight standard odour samples were available for evaluation if the panelists needed
to refresh their memories regarding the odours. These standards were held in the
refrigerator, checked daily and prepared fresh weekly.
Data Analysis
Averages and standard deviations were calculated for the six vegetable oils for each of
the four frying days tested. Frequencies of odour attributes for all samples were
tabulated.
Results and Discussion:
Composition of Oils/Fats
In Table 2, basic composition of oils/fats used
in frying experiments is presented. As expected, hydrogenated fats contained the highest
amounts of trans isomers.
 Natreon contained significant amounts of tocopherols, more than HCO, MOSUN and LLCO.
Sunflower oil contains mainly alpha isomer of tocopherol, while in other oils gamma isomer
was predominant but with significant contribution of alpha tocopherol. Plastochromanol - 8
is a derivative of gamma tocotrienol which have side chain twice longer, and this
component has good antioxidant quality.
TOTOX value represents total description of the oil/fat quality, oxidation status and
presence of degradation products formed from previous oxidation. Values for RCO and MOSUN
were the highest among all oils analysed.
Anisidine Value
Anisidine value describes oxidative and thermal degradation of
oil. This method measures carbonyl (aldehydes and ketones) components, which are formed
during deterioration of oils. Generally, values increased as the frying time extended.
Accumulation of carbonyl components was different in analysed oils during frying. The
amount of these components indicate rate and degree of deterioration, if value are smaller
better stability in frying can be expected. Hydrogenated and regular canola oils showed
the lowest and the highest accumulation of carbonyls, respectively. Natreon was more
resistant to degradation during frying than regular and low linolenic canola and
hydrogenated soybean oils, but was slightly outperformed by MOSUN oil.
Conjugated Dienes
Similarly to anisidine value, conjugated dienes describe
oxidative degradation of oils, resistance to oxidation, higher value indicates faster
degradation. Pattern of conjugated dienes formation was similar to anisidine value where
RCO, HSO and LLCO formed cluster with the fastest rate of these components formation.
Natreon showed similar degradation rate as MOSUN, but slightly faster than HCO.
Additionally, at the end of frying, sunflower oil had higher amount of dienes, but Natreon
showed some kind of plateau in formation of these components. Slope of the curve indicates
rate of oxidative degradation of the fatty acid in oils. The rates were similar for HCO
and Natreon, whereas sunflower oil showed faster degradation.
Polar Components
Polar components provide direct measurement of compounds
formed during frying including effect of product fried in an oil. Faster rate of formation
is a cumulative indication of degradation of the oil during frying and interaction of
fried product residues present in the oil during and after frying. Again slope of the
curves indicate rate of formation, steeper slope faster formation. Natreon, MOSUN and HCO
showed similar rate of polar components formation, slower rates were observed for these
oils than for other oils. HSO showed the fastest accumulation of polar components at the
beginning of frying till the day 5. RCO and LLCO showed the fastest accumulation of these
components indicating low resistance to degradation during frying. Formation of polar
components showed similar pattern as previously discussed indicators.
Free Fatty Acid
Main cause for FFA formation is hydrolysis, water present in
fried products and elevated temperature stimulate this process. Usually, with frying time
the amount of FFA increase, similar data were observed in this project. Relatively low
levels of FFA were observed in frying with different oils, probably due to not extensive
frying done. Pattern of FFA formation was similar to other parameters measured, where
Natreon was found in the middle but closer to more stable oils such as MOSUN and HCO.
Indicating better resistance to degradation by hydrolysis.
Fat Absorption
Data from this measurement showed minimal difference between
oils and most of fat was absorbed during final frying, about 80% of total fat. Natreon
showed slightly lower amount absorbed similarly to HCO and MOSUN.
Colour of Oil
Changes in colour of oils during frying is a complex process
where components of oil, such as pigments and food fried are involved and main cause of
darkening of oil with frying time, higher absorption indicates darker colour of oil.
Natreon showed better colour stability than RCO and LLCO, but was slightly more
intensively coloured than MOSUN. At the end of frying after 24 hours of oil use, Natreon
showed lighter colour than other oils but slightly darker than MOSUN.
Tocopherols
Changes of tocopherols during frying has been analysed using HPLC
in normal mode with fluorescent detector. Disappearance of tocopherols was different in
analysed oils. Rate of degradation of tocopherols was about 30% faster in hydrogenated
canola oil than in regular canola oil. Similar decomposition was observed in hydrogenated
soybean oil and low linolenic canola oil. These data clearly indicate that it is not
direct relation between content of polyunsaturated fatty acids (PUFA) and degradation of
tocopherols. Slow degradation of these components in sunflower oil during frying can
suggest that type of tocopherol is more important to the stability than content of PUFA.
Sensory Results
 Table 3 shows the mean odour quality scores obtained for
evaluated oils. Hydrogenated soybean oil received the lowest quality score for each of the
frying days with scores ranging from 5.1 (day 1) to 6.3 (day 7). Standard deviations
ranged from 1.5 to 2.8 indicating that significant differences among the frying days were
unlikely.
The HCO seemed to be the least affected over the frying period with a range of odour
quality scores from 6.8 (day 1) to 7.1 (day 7). Natreon odour quality scores ranged from
6.0 (day 3) to 6.8 (day 7), MOSUN scores from 6.3 (day 3) to 7.2 (day 1) , LLCO scores
from 6.2 (day 1) to 7.4 (day 5) and RCO scores from 6.6 (day 1 and 7) to 7.3 (day 3).
Significant differences between these oils over frying time were not found. As indicated
by standard deviation, flavour score of analysed oils was similar in intensity.
Abbreviations:
HSO - Hydrogenated Soybean Oil; MOSUN - Mid Oleic Sunflower Oil;
Plastochromanol - 8 - gamma tocotrienol derivative which have similar antioxidant
properties as tocotrienols and is mainly present in canola, rapeseed, mustard and flax
seeds/oils. TOTOX Value = 2 PV + AV - two peroxide values plus anisidine value.
Conclusions from Sensory Evaluation
Quality scores for the odour of the
french fries fried in analysed six oils were similar throughout the seven day frying
period. Panelists assigned lower mean for overall odour quality scores for french fries
fried in all of the six oils than for reference sample (HCO).
French fries fried in hydrogenated soybean oil were ranked the lowest in odour quality
scores of 5 and described them as "no characteristic odour, moderate
off-odours", whereas french fries fried in the other five oils obtained quality
scores of 6 and 7.
Conclusions:
- NATREON oil showed better performance than RCO and LLCO in all measurements done
during evaluation of frying performance.
- Some differences have been observed between Natreon and MOSUN, and HCO last two oils
are usually perceived as the best frying media. These differences were rather small
indicating good frying performance and stability of Natreon.
- Natreon showed similar frying stability and quality of frying product as MOSUN and
HCO.
- Sensory evaluation showed no differences between oils in the quality of fried
products. HSO showed slightly lower sensory scores than other oils.
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