The Effect of Ultraviolet and Heat Treatments on Microbial Stability, Antioxidant Activity and Sensory Properties of Ready-to-serve Tropical Almond Drink
There is a growing trend towards the production of ready to use multifunctional foods which has nutritional and medicinal value as well as good sensory properties. On the other hands, microbial safety of those foods is a major concern in food industry. Treatments used to ensure microbial safety of foods can affect the medicinal, nutritional and sensory properties of food. Aim of this study was to evaluate the affect of two such treatments namely UV irradiation and thermal processing on some important properties of ready to serve tropical almond drink. Prepared tropical almond ready to serve drink samples were subjected to UV irradiation and three different heat treatments. Then microbial stability, antioxidant activity and sensory properties of those treated samples were evaluated comparatively to non-treated samples. Two properties tested in this study, namely microbial stability and antioxidant activity was found to be affected by both treatments tested. Sensory properties of the product were found to be affected only by thermal processing. Compared to non-treated and thermal processed tropical almond ready to serve drinks, UV irradiated tropical almond ready to serve drinks were found to be microbiologically more safe and with preserved sensory properties. Hence, UV irradiation was identified as a suitable method to treat tropical almond ready to serve drinks to ensure microbial safety over thermal processing.
January 06, 2012; Accepted: January 10, 2012;
Published: January 21, 2012
Tropical almond (Terminaliya catappa) is primarily a coastal tree belonging
to the family combretaceae which commonly forms beach forests from sandy shores
in to the forests behind. However, it is also a feature of the landscape in
regions even far from the sea. This tree is reported to be indigenous to Andamans
and its neighboring islands. It is presently grown in countries such as Brazil,
India, Ghana, Malaysia, Myanmar, Papua New Guinea, Mexico, Peru, Puerto Rico,
The Philippines, Singapore, Sri Lanka, Taiwan etc. In Sri Lanka it is grown
in the lowland areas in various parts of the island, up to an elevation of about
300 m, as a beautification and fruit plant (Gunasena et
al., 2007). Tropical almond fruit is reported to be containing antioxidant,
anticancer and antidiabetic compounds and hence it is an important medicinal
plant (Lall et al., 1999; Nagappa
et al., 2003). There is a growing trend towards production of foods
with various functions as nutritious as well as medicinal value using medicinally
important plants (Muchuweti et al., 2007; Lee
et al., 2009). Ready to treat tropical almond drink is such product
produced concerning its nutritious as well as medicinal value.
Food can be contaminated by microorganisms at various stages of production,
processing, storage and distribution. Some of those microorganisms are pathogenic
to man and animals. So, it is safe to assume that food may carry risk of food-borne
illness if not properly handled and prepared before consumption (Loaharanu,
1996). The occurrence of illness due to consumption of contaminated unpasteurized
fruit juice has led some countries to establish microbial quality standards
to control such illnesses (Gabriel and Nakano, 2009;
Goodrich et al., 2005). As per these regulations,
to ensure the microbial safety, manufacturers of juice products are compel to
subject those juice products to a processing step or combination of processes
capable of reducing populations of target pathogens by a given amount (Goodrich
et al., 2005). Thermal processing, ultraviolet and gamma irradiation,
osmotic dehydration etc., are used by food manufacturers in this regards. However,
many factors should be considered in the selection of a suitable method, out
of those methods for a particular food, which has minimum effect to the characters
of the food. Effect of these microbial control methods to antioxidants activity
and sensory properties of food is major concern as they directly effect the
medicinal value and consumer preference of the food respectively (Chipurura
and Muchuweti, 2010; Chipurura et al., 2010).
Thermal processing has very long history as an effective means of juice pasteurization.
Moreover, thermal processing has been recognized as an efficient method of pasteurization
which ensures microbial safety and enhances the self life of fruit juice (Donahue
et al., 2004). However, many fruit juice manufacturers elect not
to apply thermal processing due to its affect to the nutritional and sensory
properties of the product. Therefore, methods such as ultraviolet and gamma
irradiation, pulsed electric field application are been considered by fruit
juice manufacturers as alternative methods (Noci et al.,
2008). In UV irradiation food products are exposed to germicidal light with
a wavelength of 220-300 nm which inactivates microbial contaminants. UV irradiation
causes the cross-linking of neighboring pyrimidine nucleotide bases in the same
DNA strand of microbial cells which eventually case cell death (Sizer
and Balasubramaniam, 1999).
Many studies have been carried out on the effect of thermal processing on different
qualities of different foods (Mozolewski et al.,
2004; Jeong et al., 2004; Agbede,
2004; Enujiugha and Akanbi, 2005; Terpinc
et al., 2011; Chipurura and Muchuweti, 2010).
Moreover, research has been carried out to study the affect of UV and gamma
irradiation on different qualities of different foods (Lee
et al., 2009; Chipurura et al., 2010).
However, affect of those to qualities of ready to serve drinks and ability to
use UV irradiation to substitute thermal processing has not been studied. This
study was conducted to evaluate the ability of thermal processing and UV irradiation
to ensure the microbial safety and their affect to antioxidant activity and
sensory properties of ready to serve tropical almond drink.
MATERIALS AND METHODS
Preparation of RTS: Ready to serve tropical almond drink was prepared
by the following procedure. Fruit flesh (150 g) was blended well and pulp was
separated using sieve. Then 1000 mL of water was added into pulp and mixed well.
Then 6 g of citric acid 220 g of sugar and 0.3 g of SMS was added and 12°
Brix RTS was produced. Then, prepared RTS drink was filled into bottles and
Preparation of bacterial cultures: Five bacterial species were used
in this study namely, Salmonella enteritidis, Salmonella typhimurium,
Vibrio parahaemolyticus, Escherichia coli O157:H7 and Listeria
monocytogenes. Bacterial samples for heat and ultra violet inactivation
test were prepared by following procedure as explained by Lee
et al. (2009). Individual test bacterium was loop-inoculated from
Nutrient Agar slant stock culture into a sterile 10 mL nutrient broth tube and
incubated at 37°C. The bacteria were harvested for inactivation studies
18-24 h post incubation. The cells were harvested by spinning 1.0 mL of the
Nutrient broth suspension on a bench top centrifuge at 8000 rpm for 5 min. The
supernatant liquid was then decanted and the cell pellets were re-suspended
in 1.0 mL of prepared RTS drink. The re-suspended cells were allowed to acclimatize
in the suspending medium for 15-30 min prior to the inactivation studies.
Ultraviolet irradiation and heat inactivation: RTS samples inoculated with five test bacteria and acclimatized were used for UV irradiation and heat inactivation studies. Prior to UV exposure, 0.5 mL of the acclimatized, re-suspended cells were diluted with 4.5 mL of prepared RTS. Then, another 10-fold dilution was done by mixing 2.5 mL of the resulting suspension with 22.5 mL of the prepared RTS. Eventually, 5 mL of the final suspension were aspirated into sterile 43 mm plastic petri plates where the contained volume had a height of 5.0 mm.
For the UV irradiation studies, each prepared plate were exposed to UV radiation for 0-2 min in a biological safety cabinet with a pair of 15 UV light source at a lamp-to-juice surface distance of 55.0 cm.
For the heat inactivation studies, 9.9 mL of inoculated RTS samples in glass test tubes were heated to reach desired temperatures (55, 65 and 75°C) on a water bath. The medium temperature was measured by inserting a thermometer through the cold point of a control tube. When the cold point temperature reached desired temperature, 0.1 mL of the RTS samples inoculated with five test bacteria and acclimatized were pipetted into each of the tubes and heated up to 2 min while agitated manually. After heat treatments, tubes were immediately immersed in an ice bath and kept until survivor enumerations.
Survivor enumeration and decimal reduction times calculations: RTS samples
obtained at five different time intervals after treatments (0, 0.5, 1.0, 1.5,
2 min) were used for survivor enumeration and decimal reduction time calculations.
All UV-irradiated and heat inactivated samples were serially diluted using sterilized
distilled water and pour plated on nutrient agar. Plated dilutions were then
incubated at 37°C. Emerging colonies were enumerated 24-48 h post incubation.
The decimal reduction times (D value) of each of the test sample were then determined
by plotting the log10 of the calculated colony-forming units versus irradiation
or heating time. The Survivor Curve (SC) was then determined by tracing the
best-fitted straight line in the survivor plots. The D value was equivalent
to the number of minutes of irradiation or heating that resulted to 90% loss
in the viability of the test organism and graphically equivalent to the negative
inverse of the slope of the survivor curve (Jay et al.,
Total phenolic contents, DPPH (1,1-diphenyl-2-picrylhydrazyl) radical scavenging
activity and Ferric reducing antioxidant power (FRAP): Total phenolic contents
of all treated samples and control were measured using the Folin-Ciocalteau
colorimetric method as explained by Gao et al. (2000).
Phenolic contents were expressed as gallic acid equivalents. DPPH free-radical
scavenging effect was estimated according to the method proposed by Blois
(1958). The FRAP (ferric reducing/antioxidant power) assay was performed
as described by Benzie and Strain (1996) using a spectrophotometer.
In this assay, reductants in the sample reduce the Fe(III)/tripyridyltriazine
complex, present in the stoichiometric excess, to the blue ferrous form, with
an increase in the absorbance at 593 nm wave length . Absorbance readings were
taken after 0.5 sec and every 30 sec thereafter during the monitoring period
for 5 min and the readings at 4 min were used as the FRAP value (mM g-1)
as described by Lee et al. (2009).
Sensory evaluation: All RTS samples which were subjected to UV and heat
treatments and control sample were evaluated for their sensory properties by
a panel of 15 expert members. Seven point hedonic scale ranging from dislike
extremely to like extremely was used to evaluate six different sensory
properties namely, odor, color, taste, off odor, off taste and overall acceptance.
Each sample was labeled with three digit code and about 50 mL of each sample
were given individually to the panelists for evaluation. Water was provided
to wash the oral cavity after testing of each sample. The sensory test was carried
out three times and average values of those were used for the analysis (Meilgaard
et al., 1999).
RESULTS AND DISCUSSION
Microbial analysis: The calculated D values per test bacterium in UV-irradiated
and heat treated samples are summarized in Table 1. The bacteria
Listeria monocytogenes were shown to be significantly more resistant
than the other organisms in all treatments. The bacteria Salmonella enteritidis
and E. coli O157:H7 were shown to be significantly less resistance to
all treatments. These results are in agreement to the results obtained in previous
studies using different food matrices. In Gabriel and Nakano
(2009) had obtained similar results for inoculated PBS and apple juice samples
subjected to UV irradiation. In Beltran and Canovas (2005)
also reported that Listeria had better resistance to UV irradiation compared
to E. coli when suspended in apple juice.
When consider heat treatments, the results were not in agreement with the results
reported by Gabriel and Nakano (2009) for inoculated
apple juice samples and results reported by Sharma et
al. (2005) for inoculated watermelon juice. In those studies, E.
coli was reported to be more heat resistant than Listeria monocytogenes
but in the present study results was vice versa. Mak et
al. (2001) and Mazzotta (2001) also reported
that E. coli O157:H7 is more heat resistant than L. monocytogenes
and Salmonella in their studies conducted using inoculated apple juice.
However, results of the present study for heat treatments were in agreement
with some other studies. In a study conducted by Murphy
et al. (2004), L. monocytogenes had greater resistance than
Salmonella spp. and E. coli O157:H7 when heated at 55°C in
ground pork. In another study conducted by Sharma et
al. (2005), L. monocytogenes was found to be relatively more
heat resistant than E. coli O157:H7 and Salmonella spp. when heated
at 57°C in cantaloupe juice.
|| Decimal reduction values (D) of test pathogens in UV irradiated
and heat treated tropical almond ready to serve drinks
|Values with different letters (a-d) within the same column
and values with different letters (w-z) within the same row are significantly
different at p<0.05
||Values of tests, Total phenolic content (TPC), DPPH activity
and FRAP assay of UV irradiated, heat treated and non-treated tropical almond
ready to serve drink
|Values with different letters (a-d) within the same column
are differ significantly (p<0.05)
Hence an appropriate universal target organism for evaluating the lethality
of thermal processes of food cant be identified and different studies
should carried out to identify suitable organisms for different food matrixes.
When compare the results obtained for UV irradiated samples and heat treated
samples, UV irradiation found to be significantly effective than heat treatments
except samples of Salmonella typhimurium, Vibrio parahaemolyticus and
Listeria monocytogenes treated by 75°C. These results confirm the
possibility of using UV irradiation to replace heat treatments in food industry
to ensure the microbiological safety.
Total phenolic contents, DPPH activity and FRAP assay: Values of total phenolic content, DPPH radical scavenging activity and ferrous reducing antioxidant power assay for UV irradiated, heat treated and non-treated (control) tropical almond ready to serve drink are summarized in Table 2.
Total phenolic contents (TPC): Compared to control sample, significantly
high Total Phenolic Contents (TPC) was observed in UV eradiated samples. This
significant increase of TPC in irradiated samples may be due to the degradation
of larger phenolic compounds into smaller phenolic compounds by irradiation
as previously explained by Harrison and Were (2007).
When irradiated, radicals such as hydrated electrons, hydroxyl radicals and
hydrogen atoms are produced by radiolysis of water in the samples (Fan
and Mastovska, 2006). In addition to that, these radicals may break glycosidic
bonds in larger phenolic compounds and produce smaller phenolic compounds (Lee
et al., 2009). Total phenolic content of the heat treated samples
were also significantly higher compared to control sample. Moreover, total phenolic
content of heat treated samples were significantly higher than the UV irradiated
samples. Total phenolic content was found to be increased with the increase
of treatment temperature as previously explained by Jeong
et al. (2004) and Terpinc et al. (2011)
for other foods.
DPPH activity: Number of research have been carried out to investigate
the effect of UV and gamma irradiation on the DPPH radical scavenging activity.
However results of those studies are not consistence. In some of those research
irradiation found to be effecting to increase the DPPH radical scavenging activity
(Ahn et al., 2004; Variyar
et al., 2004; Jo et al., 2003). In
some of those studies irradiation found to be effecting to decrease the DPPH
radical scavenging activity (Ahn et al., 2005;
Suhaj et al., 2006). In some cases, no significant
changes of the radical scavenging abilities were observed (Byun
et al., 2002; Byun et al., 1999).
In the present study DPPH radical scavenging activity of irradiated samples
was found to be significantly increased compared to fresh samples.
|| Sensory values of UV irradiated and heat treated tropical
almond ready to serve drink
|Values with different letters (a-d) within the same row are
significantly different at (p<0.05)
When consider heat treatments, as previously explained by some other authors
for some other foods (Jeong et al., 2004; Terpinc
et al., 2011), DPPH radical scavenging activity was found to be significantly
increased by the heat treatment compared to the control. However, significant
difference of DPPH radical scavenging activity was not observed UV irradiated
samples with heat treated samples or in different heat treatments.
FRAP assay: The FRAP (ferrous reducing antioxidant power) assay is commonly
used for assessing antioxidant activity, since it has high sensitivity and is
rapid and inexpensive. In this assay, inactivation of oxidant by the reductants
(antioxidants in the sample) is used as the principle to asses the antioxidants.
In the present investigation, significantly high antioxidant activity was observed
in UV and heat treated samples compared to the control. However, no significant
difference was observed in antioxidant activity of different heat treated samples.
The antioxidant activity of UV irradiated samples was significantly higher than
all other samples tested. This could be due to formation of Maillard reaction
products by irradiation which have the ability to scavenge hydroxyl radical
and superoxide as explained by Chawla et al. (2007).
Sensory evaluation: Table 3, shows the sensory evaluation
results of odor, color, taste, overall acceptance, off odor and off taste. A
significant difference in the sensory scores was observed in the irradiated
ready to use tropical almond drink when compared to that of heat treated samples.
These samples were highly preferred by the sensory panel. The sensory data for
the samples heat treated by 55 and 65°C were not significantly different.
Sensory data of the sample heat treated by 75°C were significantly different
from the other and were least preferred by the sensory panel. These results
indicate that irradiation by UV treatments helps to maintain sensory qualities
compared to heat treatments. Moreover, the results shows that sensory qualities
are highly affect when high temperature conditions are used. Some comparative
studies have been carried out to compare the sensory qualities of different
fresh and irradiated foods (Song et al., 2007)
and no significant changes were observed. Those results are supportive to the
results obtained in this study. However, the present study is the first study
which compares the effect of heat and UV treatments to the sensory qualities
of ready to serve drinks.
Thermal processing was found to be affecting all parameters tested namely, microbial stability, antioxidant activity and sensory properties of tropical almond ready to serve drink. UV irradiation found to be effecting two of those parameters namely, microbial stability and antioxidant activity. Compared to thermal processed tropical almond ready to serve drinks, UV irradiated tropical almond ready to serve drinks were found to be with preserved sensory properties and microbiologically more safe. In conclusion, UV irradiation was identified as a substitute for thermal processing in tropical almond ready to serve drink production.
Agbede, J.O., 2004. Compositional studies of differently processed ornamental plant seed flour: Caesalpinia pulcherima. Pak. J. Nutr., 3: 222-227.
CrossRef | Direct Link |
Ahn, H.J., J.H. Kim, C. Jo, M.J. Kim and M.W. Byun, 2004. Comparison of irradiated phytic acid and other antioxidants for antioxidant activity. Food Chem., 88: 173-178.
Ahn, H.J., J.H. Kim, J.K. Kim, D.H. Kim, H.S. Yook and M.W. Byun, 2005. Combined effects of irradiation and modified atmosphere packaging on minimally processed Chinese cabbage (Brassica rapa L). Food Chem., 89: 589-597.
Beltran, G.J.A. and B.G.V. Canovas, 2005. Reduction of Saccharomyces cerevisiae, Escherichia coli and Listeria innocua in apple juice by ultraviolet light. J. Food Process Eng., 28: 437-452.
Benzie, I.F. and J.J. Strain, 1996. The Ferric Reducing Ability of Plasma (FRAP) as a measure of antioxidant power: The FRAP assay. Anal. Biochem., 239: 70-76.
CrossRef | PubMed |
Blois, M.S., 1958. Antioxidant determinations by the use of a stable free radical. Nature, 181: 1199-1200.
CrossRef | Direct Link |
Byun, M.W., H.S. Yook, K.S. Kim and C.K. Chung, 1999. Effects of gamma irradiation on physiological effectiveness of Korean medicinal herbs. Radiat. Phys. Chem., 54: 291-300.
Byun, M.W., J.H. Son, H.S. Yook, C. Jo and D.H. Kim, 2002. Effect of gamma irradiation on the physilogical activity of Korean soybean fermented foods, Chungkookjang and Doenjang. Radiat. Phys. Chem., 64: 245-248.
Chawla, S.P., R. Chander and A. Sharma, 2007. Antioxidant formation by γ-irradiation of glucose-amino acid model system. Food Chem., 103: 1297-1304.
Chipurura, B. and M. Muchuweti, 2010. Effect of irradiation and high pressure processing technologies on the bioactive compounds and antioxidant capacities of vegetables. Asian J. Clin. Nutr., 2: 190-199.
Chipurura, B., M. Muchuweti and F. Manditseraa, 2010. Effects of thermal treatment on the phenolic content and antioxidant activity of some vegetables. Asian J. Clin. Nutr., 2: 93-100.
CrossRef | Direct Link |
Donahue, D.W., N. Canitez and A.A. Bushway, 2004. UV inactivation of E. coli O157: H7 in apple juice: Quality, sensory and shelf-life analysis. J. Food Process. Preserv., 28: 368-387.
Enujiugha, V.N. and C.T. Akanbi, 2005. Compositional changes in African oil bean (Pentaclethra macrophylla Benth) seeds during thermal processing. Pak. J. Nutr., 4: 27-31.
CrossRef | Direct Link |
Fan, X. and K. Mastovska, 2006. Effectiveness of ionizing radiation in reducing furan and acrylamide levels in foods. J. Agric. Food Chem., 54: 8266-8270.
Gabriel, A.A. and H. Nakano, 2009. Inactivation of Salmonella, E. coli and Listeria monocytogenes in phosphate-buffered saline and apple juice by ultraviolet and heat treatments. Food Control, 20: 443-446.
Gao, X., L. Bjork, V. Trajkovski, M. Uggala, 2000. Evaluation of antioxidant activities of rosehip ethanol extracts in different test systems. J. Agric and Food Chem., 80: 2021-2027.
Goodrich, R.M., K.R. Schneider and M.E. Parish, 2005. The juice HACCP program: An overview. Inst. Food Agric. Sci., 15: 1-4.
Direct Link |
Gunasena, H.P.M., D.K.N.G. Puspakumara and V.P. Singth, 2007. Under utilized fruit trees in Sri Lanka. World Agroforestry Centre, 1: 437-451.
Harrison, K. and L.M. Were, 2007. Effect of gamma irradiation on total phenolic content yield and antioxidant capacity of almond skin extracts. Food Chem., 102: 932-937.
Jay, J.M., M.J. Loessner and D.A. Golden, 2005. Modern food Microbiology. 6th Edn., Springer, New York.
Jeong, S.M., S.Y. Kim, D.R. Kim, S.C. Jo, K.C. Nam, D.U. Ahn and S.C. Lee, 2004. Effect of heat treatment on the antioxidant activity of extracts from citrus peels. J. Agric. Food Chem., 52: 3389-3393.
CrossRef | Direct Link |
Jo, C., J.H. Son, M.G. Shin and N.W. Byun, 2003. Irradiation effects on color and functional properties of persimmon (Diospyros kaki L. folium) leaf extract and licorice (Glycyrrhiza uralensis Fischer) root extract during storage. Radiat. Phys. Chem., 67: 143-148.
Lall, S.B., B. Singh, K. Gulati and S.D. Seth, 1999. Role of nutrition in toxic injury. Ind. J. Exp. Biol., 37: 109-116.
Lee, J.W., J.K. Kim, P. Srinivasan, J. Choi and J.H. Kim et al., 2009. Effect of gamma irradiation on microbial analysis, antioxidant activity, sugar content and color of ready-to-use tamarind juice during storage. LWT-Food Sci. Technol., 42: 101-105.
Loaharanu, P., 1996. Irradiation as a cold pasteurization process of food. Vet. Parasitol., 64: 71-82.
Mak, P.P., B.H. Ingham and C. Ingham, 2001. Validation of apple cider pasteurization treatments against Escherichia coli O157:H7, Salmonella, and Listeria monocytogenes. J. Food Prot., 64: 1679-1689.
Mazzotta, A.S., 2001. Thermal inactivation of stationary-phase and acid-adapted Escherichia col O157:H7, Salmonella, and Listeria monocytogenes in fruit juices. J. Food Prot., 64: 315-320.
Meilgaard, M., G.V. Civille and B.T. Carr, 1999. Sensory Evaluation Techniques. CRC Press LLC, USA.
Mozolewski, W. and S. Smoczynski, 2004. Effect of culinary processes on the content of nitrates and nitrites in potatoe. Pak. J. Nutr., 3: 357-361.
CrossRef | Direct Link |
Muchuweti, M., C. Mupure, A. Ndhlala, T. Murenje and M.A.N. Benhura, 2007. Screening of antioxidant and radical scavenging activity of Vigna ungiculata, Bidens pilosa and Cleome gynandra. Am. J. Food Technol., 2: 161-168.
CrossRef | Direct Link |
Murphy, R.Y., B.L. Beard, E.M. Martin, L.K. Duncan and J.L. Marcy, 2004. Comparative study of thermal inactivation of Escherichia coli O157:H7, Salmonella and Listeria monocytogenes in ground pork. J. Food Sci., 69: FMS97-FMS101.
Nagappa, A.N., P.A. Thakurdesai, N.V. Rao and J. Singh, 2003. Antidiabetic activity of Terminalia catappa Linn fruits. J. Ethnopharmacol., 88: 45-50.
CrossRef | Direct Link |
Noci, F., J. Riener, M. Walkling-Ribeiro, D.A. Cronin, D.J. Morgan and J.G. Lyng, 2008. Ultraviolet irradiation and pulsed electric fields (PEF) in a hurdle strategy for the preservation of fresh apple juice. J. Food Eng., 85: 141-146.
Sharma, M., B.B. Adler, M.D. Harrison and L.R. Beuchat, 2005. Thermal tolerance of acid-adapted and unadapted Salmonella, Escherichia coli O157:H7, and Listeria monocytogenes in cantaloupe juice and watermelon juice. Lett. Applied Microbiol., 41: 448-453.
Sizer, C. and V. Balasubramaniam, 1999. New intervention processes for minimally processed juices. Food Technol., 53: 64-67.
Song, H.P., M.W. Byun, C. Jo, C.H. Lee, K.S. Kim and D.H. Kim, 2007. Effects of gamma irradiation on the microbiological, nutritional and sensory properties of fresh vegetable juice. Food Control, 18: 5-10.
Suhaj, M., J. Racova, M. Polovka and V. Brezova, 2006. Effect of g-irradiation on antioxidant activity of black pepper (Piper nigrum L.). Food Chem., 97: 696-704.
Terpinc, P., T. Polak, P.N. Ulrih and H. Abramovic, 2011. Effect of heat treatment of camelina (Camelina sativa) seeds on the antioxidant potential of their extracts. J. Agric. Food Chem., 59: 8639-8645.
Variyar, P.S., A. Limaye and A. Sharma, 2004. Radiation-induced enhancement of antioxidant contents of soybean (Glycine max Merrill). J. Agric. Food Chem., 52: 3385-3388.