D90862 f4380767 e85 bcfce4431794 a6 f

Industrial Crops and Products 50 (2013) 557–562

Contents lists available at ScienceDirect

Industrial Crops and Products
journal homepage: www.elsevier.com/locate/indcrop

Changes of antioxidant constituents in pineapple (Ananas comosus)
residue during drying process
Diogo I.S. da Silva a , Geraldo D.R. Nogueira b , Alexandra G. Duzzioni b ,
Marcos A.S. Barrozo b,∗
a
b

Federal Institute of Mato Grosso, Campus Rondonópolis, Brazil
Federal University of Uberlândia, Chemical Engineering School, Brazil

a r t i c l e

i n f o

Article history:
Received 23 April 2013
Received in revised form 30 July 2013
Accepted 1 August 2013
Keywords:
Residue
Pineapple
Antioxidant activity

a b s t r a c t

Brazil is one of the three largest producers of fruit in the world. As a consequence, it has become one
of the largest producers of agricultural residues. Studies have shown that the residues of certain fruits
can present a higher antioxidant activity than the pulp. Although these residues are usually discarded, it
could be used as an alternative source of nutrients. The present paper investigates the drying of pineapple
residues in a fixed-bed dryer, analyzing the effect of the process variables on the antioxidant properties
of the residue. The content of phenolic compounds, flavonoids, and ascorbic acid were also quantified.
The results shown that the drying of the fruit residue in a fixed-bed was very efficient. The content of
some bioactive compounds was found to increase after drying. Therefore, a new type of product could
somehow be considered helpful to promote the nutritional value and extend the utilization of residues.
© 2013 Elsevier B.V. All rights reserved.

1. Introduction
Pineapple (Ananas comosus) belongs to the Bromeliaceae family,
and is originated from South America. Pineapple mainly contains
water, carbohydrates, sugars, vitamins A, C and beta carotene,
protein, fat, ash and fiber and antioxidants namely flavonoids in
addition to citric and ascorbic acid (Wai, 2009). It is commonly
consumed as fresh and as processed products such as pineapple
juice, which is a popular product due to its pleasant aroma and flavor (Rattanathanalerk et al., 2005). The world-wide total pineapple
production is between 16 and 19 million tons. Brazil is the second
largest producer of pineapple in the world (FAO, 2010) and has a
huge domestic market.
Sixty percent of fresh pineapple is edible and average yield in
processing ranges from 45% to 55% (Samson, 1986). Processing
residuals ranges between 45% and 65% an indication of serious
organic-side streams disposal challenges, which causes environmental pollution if not successfully utilized. Studies have shown
that the residues of certain fruits can present a higher antioxidant
activity than the pulp (Gorinstein et al., 2001). Antioxidants are the
substances that are able to prevent or inhibit oxidation processes in
human body and food products (Diaz et al., 1997) as ascorbic acid,

∗ Corresponding author at: Bloco K - Santa Mônica, 38400-902 Uberlândia, MG,
Brazil. Tel.: +55 34 96776099; fax: +55 34 32394188.
E-mail addresses: (D.I.S. da Silva),
(M.A.S. Barrozo).
0926-6690/$ – see front matter © 2013 Elsevier B.V. All rights reserved.
/>
phenolics and flavonoids. Thus, although these residues are usually discarded, it could be used as an alternative source of nutrients
to increase the nutritive value of poor people’s diets and to help
reduce dietary deficiencies.
Vitamin C, also known as ascorbic acid, is water soluble, meaning
it will dissolve in water and is not stored in the body. It is essential for collagen, l-carnitine and neurotransmitters biosynthesis
(Naidu, 2003). For adults, the recommended amount of vitamin C is
60–90 mg per day (Gordon, 2005). Vitamin C is found in fruits such
as oranges, lemons, acerola, pineapple and grapefruit, as well as in
vegetables including tomatoes, green peppers, and potatoes.
Phenolic compounds, in particular, are thought to act as
antioxidant, anti-carcinogenic, anti-microbial, anti-allergic, antimutagenic and anti-inflammatory, as well as reduce cardiovascular
diseases (Kima et al., 2003). Flavonoids are the most abundant
polyphenolic compounds present in fruits and vegetables and,
mainly present as coloring pigments in plants also function as
potent antioxidants at various levels. Some studies showed that
flavonoids could protect membrane lipids from oxidation (Terao
et al., 1994).
As said before, the recovery of fruit residues, to be used in food,
cosmetics and in the pharmacy industry can be an important alternative for the sustainable development. However, depending on
the type of fruit, the residues can contain a high moisture content
level (80–90%), that can contribute to the degradation at an accelerated pace (Makris et al., 2007). One of the methods to conserve
the sensorial properties and the bioactive compounds present in
these residues is the drying (Barrozo et al., 2001).

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D.I.S. da Silva et al. / Industrial Crops and Products 50 (2013) 557–562

The copper-constantan thermocouples used for measuring of
the dry and wet bulb temperatures were calibrated by means of a
thermostatic bath and a mercury thermometer with precision of
0.05 ◦ C (Felipe and Barrozo, 2003). The thermocouples were positioned in the tube of the air feeding.

2.4. Experimental procedure

Fig. 1. Experimental apparatus.

The present paper investigates the effects of the variables in
the drying process to define the best drying conditions in a fixedbed, bearing in mind the final quality of the product, regarding the
changes in the content of citric acid, ascorbic acid, of total phenolics and flavonoids, present in residue of pineapple taken after
processed juice. These bioactive compounds contents are compared
with the values obtained from the fresh pineapple pulp and skin.
2. Materials and methods
2.1. Material
The residues of pineapple taken from the industrial processing
of juices and pastes, used in the experiments, were given away by
the Lotus Solutions Company, located in the state of Minas Gerais
in mid-southern Brazil. The residues were separated in small portions, labeled and then frozen in a freezer. Before the analysis took
place, the frozen samples were taken out and put in fridges until
completely defrosted.
2.2. Drying conditions
The study of the drying process of the pineapple residue took

place in a fixed-bed dryer. The independent variables studied were
air velocity and air temperature. The experimental conditions were
chosen based on an experimental design of two levels of each variable (2k ).
2.3. Experimental apparatus
A scheme of the fixed bed in thin layer (Barrozo et al., 2005)
and the experimental apparatus is shown in Fig. 1. The unit is composed, basically, of a blower type fan radial (2), an electric heater (3)
provided with a variable voltage (4), thermocouples (6), gate valves
to control flow (1), a flowmeter type hot wire anemometer (5) and
a measuring cell. The cell consists of a cylindrical tube of diameter 8.1 × 10−2 m and length 3.0 × 10−2 m, having metallic screens
at the two extremities (details in Fig. 1). The system is thermally
isolated.

Initially the system was adjusted to the requested operating
conditions. An auxiliary cell, identical to the measuring cell, was
connected to the equipment. Next, the dry and wet bulb temperatures were measured. As soon as the desired conditions were
reached, the measuring cell was inserted into the equipment,
initiating the experiment (zero time). The measuring cell was
periodically withdrawn (to each 0.5, 1.0, 2.0, and 5.0 min in the
beginning, to each 10 min until the first hour and in the sequence
to each 20 min) and its mass determined on an analytical balance
with a precision of 1 × 10−5 kg. At the times of sample mass determination, which took about 7 s, the auxiliary cell was connected
to the unit in order to maintain thermal and fluid-dynamic equilibrium in the system (Barrozo et al., 2006). The drying time was
maintained constant and equal to 27,000 s (7.50 h) for all the experiments in order to maintain the standard for the analysis of the
bioactive compounds at the end of each experiment. At the end of
experiment, the dry mass of the residues was determined by oven
method 105 ± 2 ◦ C/24 h.
The moisture ratio was obtained as a function of the time.
The equilibrium moisture has been obtained by dynamic method
(Arnosti Jr. et al., 1999). The moisture ratio (MR) has been calculated
according to Eq. (1):

MR =

M − Meq
M0 − Meq

(1)

where MR is the moisture ratio, M is the moisture content (dry
basis) at any time, Meq is the equilibrium moisture content (dry
basis) and M0 is the initial moisture content (dry basis).

2.5. Quality parameters
2.5.1. Analysis of titratable citric acid (CA) and ascorbic acid (AA)
Acidity content of the samples was titrated with 0.1 N NaOH
and the results were expressed as the percentage of citric acid.
The titration method was based on the reduction of the sodium
salt of the blue dye 2,6-dichlorophenolindophenol by ascorbic acid
(AOAC, 1995). The results are expressed as milligrams of ascorbic
acid 100 g−1 samples (dry matter).

2.5.2. Determination of total phenolics content (TPC)
Total polyphenols were determined by the Folin Ciocalteu
method (Singleton and Rossi, 1965), using gallic acid as the
standard. The linear reading of the standard curve was from 0.2
to 2.0 mg gallic acid per milliliter. Total phenolics were expressed
as milligrams of gallic acid equivalents (GAE) 100 g−1 samples (dry
matter).

2.5.3. Determination of total flavonoids content (TFC)
Total flavonoids content were determined using a colorimetric

method described by Zhishen et al. (1999). The linear reading of the
standard curve was from 20 to 80 ␮g rutin acid per milliliter. Total
flavonoids were expressed as milligrams of rutin 100 g−1 samples
(dry matter).


D.I.S. da Silva et al. / Industrial Crops and Products 50 (2013) 557–562

1.0

Table 1
Drying kinetics models.
Equation

References

MR = exp(− kt)
MR = Aexp(−
 kt)

Lewis (1921)
Brooker et al. (1974)

1
9



exp(−9kt)

MR = exp(− ktn )
MR = exp − (kt)n

0.8

Henderson and Henderson (1968)
Page (1949)
Overhults et al. (1973)

V = 1,0 m s-1
T = 46 ° C
T = 60 ° C
Overhults

0.6

MR

MR = A exp(−kt) +

559

0.4

2.6. Statistical treatment

0.2

Table 1 shows the drying kinetics models analyzed in this work.
The parameters of these models were estimated by nonlinear

regression (Barrozo et al., 1996).
The selection of the model that best predicted the drying kinetics
considered: the significance of the parameters; residues distribution and the correlation coefficient (Duarte et al., 2004).
All analyses of antioxidant compounds were performed in triplicate and the results expressed in mean value ± standard deviation
(SD).

0.0

0

2000

4000

6000

20000
24000
8000
12000
16000
28000
22000
26000
10000
14000
18000

Time (s)
Fig. 2. Drying kinetics v = 1.0 m s−1 and experimental data and simulated by Overhults model.

1.0

3. Results and discussion

V = 1,5 m s-1
T = 46 ° C
T = 60 ° C
Overhults

0.8

3.1. Drying kinetics

Table 2
Parameters found for the kinetic model evaluated.
V (m s−1 )

T (◦ C)

1.0
1.0
1.5
1.5

46
60
46
60
R2 (Average)

Parameters of Overhults model
k

n

0.000239 ± 0.000008
0.000460 ± 0.000012
0.000395 ± 0.000011
0.000698 ± 0.000010

0.6608 ± 0.011662
0.5377 ± 0.010975
0.7419 ± 0.014611
0.8201 ± 0.009941
0.9965

MR

0.6

In the statistical discrimination of rival models (Table 1), considering all the statistical aspects, the kinetic model that showed better
results was the Overhults model. The quadratic correlation coefficient (R2 ) obtained with Overhults model was 0.997; while for
the other models the R2 were 0.948 (Lewis), 0.983 (Brooker), 0.996
(Page) and 0.991 (Henderson and Henderson). The Overhults model
also showed the best results to describe the drying of the organic
solid wastes from citrus juice industry, as showed by Perazzini et al.
(2013).
Table 2 shows the parameters of Overhults model for each operating conditions considering the experimental design of two levels
of each variable (2k ).
Figs. 2 and 3 show the experimental data and the prediction by

the Overhults model for the moisture ratio (MR) as a function of the
drying time (t). These figures show that Overhults equation could
well describe the drying kinetics of the pineapple residues and that
the water removal during drying of this material occurs mainly in
the falling-rate period, conform also observed for ginger by Gouveia
et al. (1997) and for kiwi by Simal et al. (2005).
The results of the Figs. 2 and 3 show that the drying kinetics of
the residues of pineapple is clearly influenced by air velocity and
temperature. The experimental drying results also show that the
time of 7.25 h was adequate to dehydrate the residue of pineapple. For the extreme conditions (60 ◦ C and 1.5 m s−1 ) occurred a
moisture reduction from 83.4% to 1.42% (Table 3).

0.4

0.2

0.0

0

2000

4000

6000

8000
12000
16000
20000

24000
28000
10000
14000
18000
22000
26000

Time (s)
Fig. 3. Drying kinetics v = 1.5 m s−1 and experimental data and simulated by Overhults model.

3.2. Physical–chemical analysis
The temperature and the drying conditions can affect the activity and stability of the bioactive compounds caused by chemical and
enzymatic degradation, by volatilization and/or thermic decomposition (Dorta et al., 2012). Thus, in this work, we evaluated the effect
of temperature and drying air velocity on the content of citric acid,
ascorbic acid, total phenolics and total flavonoids present in the
sample after drying.
The citric acid content (CA) obtained in the different samples of
pineapple was 6.72 ± 0.49 g citric acid 100 g−1 samples (dry base),
while for the dried samples the value obtained varied between
0.67 ± 0.03 g citric acid 100 g−1 samples and 0.39 ± 0.03 g citric acid
Table 3
Moisture (%) residue of pineapple before and after drying.
Drying kinetics variables
−1

V (m s
1.0
1.0
1.5

1.5

)

◦

Moisture

T ( C)

Before drying (%)

After drying (%)

46
60
46
60

82.240
82.670
83.170
83.396

5.012
2.724
3.123
1.419

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D.I.S. da Silva et al. / Industrial Crops and Products 50 (2013) 557–562

Fig. 4. Citric acid contents (CA) of fresh and dried pineapple residue.

Fig. 5. Acid contents (AA) of fresh and dried pineapple residue.

Fig. 6. Total phenolic contents (TPC) of fresh and dried pineapple residue.


D.I.S. da Silva et al. / Industrial Crops and Products 50 (2013) 557–562

561

Fig. 7. Total flavonoids contents (TFC) of fresh and dried pineapple residue.

100 g−1 samples (dry base) at 60 ◦ C and 1.5 m s−1 and 46 ◦ C and
1.0 m s−1 , respectively (Fig. 4).
The experimental results show that the highest value of
the ascorbic acid content (AA) was 84.27 ± 8.31 mg 100 g−1 for
pineapple pulp (dry base), while for the fresh residue we found
21.84 ± 2.67 mg 100 g−1 (dry base) and for the pineapple skin we
found 56.17 ± 6.40 mg 100 g−1 (Fig. 5). The higher values of the
ascorbic acid content (AA) for the dry residue were obtained with
the drying temperature of 60 ◦ C, with values close to the fresh
residue. In particular, vitamin C (ascorbic acid) is considered to be
a quality indicator of processed food due to its low stability during heat treatments (Podsedek, 2007). Hence, the drying method
studied in this paper can be considered effective as the dried product showed similar content of ascorbic acid compared to the fresh
residue.

As regard to content of phenolic (TPC), the experimental results
show that the highest value was found at 60 ◦ C and 1.5 m s−1
(13.79 ± 0.26 mg of gallic acid 100 g−1 samples, dry base). For the
fresh residue the content found was 1.41 ± 0.06 mg of gallic acid
100 g−1 sample, dry base (Fig. 6). The same trend was found by
Chang et al. (2006), which evaluated the content of phenolic compounds in tomatoes after drying and obtained higher values than
the fresh tomatoes. According to the authors, this behavior can
possibly be explained by the liberation of phenolic compounds
during the drying process. Chism and Haard (1996) has mentioned that fruits and vegetables normally contain high contents
of phenolic compounds in the outer parts, in other words, total
phenolics including all the phenolic acid compounds occur in
plants as the metabolic intermediates and usually accumulate in
the vacuoles. It is assumed that food processes might accelerate
more bound phenolic compounds releasing from the breakdown
of cellular constituents. Although, disruption of cell walls may
also trigger the release of oxidative and hydrolytic enzymes that
would destroy the antioxidants in fruits, however, high temperature processing would deactivate these enzymes and avoid the
loss of phenolic acids and, therefore, lead to the increase of total
phenolics.
It is also worth noting that the drying caused a more pronounced increase in the total phenolic of the pineapple residue
(13.79 ± 0.26 mg of gallic acid 100 g−1 sample, dry base) when
compared with fresh pineapple pulp (2.71 ± 0.13 mg of gallic acid
100 g−1 sample, dry base) and skin (4.16 ± 0.24). Therefore we can
realize the importance of recycling the residue of this fruit.

The total flavonoids content for pineapple residue after drying
and for fresh pineapple pulp and skin can be seen in Fig. 7. It can
be observed that at 46 ◦ C and 1.5 m s−1 , the content of this compound was at its highest level (580.70 ± 20.46 ␮g of rutin 100 g−1
sample). For the fresh residue, we found 114.40 ± 11.82 ␮g of rutin
100 g−1 sample (dry base). The effect of the drying on the content

of flavonoids was similar to that observed on content of phenolic
(Fig. 6). The content of flavonoids compounds in pineapple residue
after drying was higher than fresh pineapple pulp (197.10 ± 2.60 ␮g
of rutin 100 g−1 sample, dry base) and skin (76.93 ± 11.85 ␮g of
rutin 100 g−1 sample). The same behavior was found by Chang
et al. (2006) in their studies with tomatoes in which the dried
samples contained higher levels of total flavonoids compared to
fresh samples. Thus, the drying conditions play an important role
in determining the final quality of the product mainly in terms of
antioxidant constituents.

4. Conclusions
The drying kinetics of pineapple residues showed to be consistent in the range studied. It was observed that the behavior was
similar to other studies in the literature using similar fruit as study
material. The statistical discrimination of rival models shows that
the Overhults model (Overhults et al., 1973) was the kinetic model
that better represented the experimental data of the residues of
pineapple. The drying kinetics was clearly influenced by air velocity
and temperature.
As for the content of bioactive compounds analyzed in this work,
drying in a fixed-bed was very efficient. The content of some bioactive compounds was found to increase after drying. Higher values
of total phenolic and flavonoids content were found compared with
the same fresh residue. It can be explained by the fact that these
compounds in plants act as metabolic intermediates and normally
accumulate in vacuoles, and that the drying process accelerates the
release of these compounds by breaking down the cellular constituents.
The results presented in this paper indicated the drying process could enhance the nutritional value of pineapple residue. Thus,
once handled correctly, the residue from the extraction of pineapple pulp and juice industry can be reused for various purposes,
considering it as a source of bioactive compounds, thereby avoiding
the discharge to the environment. Therefore, a new type of product

562

D.I.S. da Silva et al. / Industrial Crops and Products 50 (2013) 557–562

could somehow be considered helpful to promote the nutritional
value and extend the utilization of pineapple residues.
Acknowledgments
The authors gratefully acknowledge the financial support of
the Brazilian research funding agencies FAPEMIG (Foundation for
Research Support of the State of Minas Gerais), CAPES (Federal
Agency for the Support and Improvement of Higher Education,
PNPD–National Postdoctoral Program) and CNPq (National Council
for Scientific and Technological Development).
References
AOAC, 1995. Official methods of analysis. Association of Official Analytical Chemists,
Gaithersburg, MD.
Arnosti Jr., S., Freire, J.T., Sartori, D.J.M., Barrozo, M.A.S., 1999. Equilibrium moisture content of Brachiaria brizantha. Seed Science and Technology 27 (1),
273–282.
Barrozo, M.A.S., Freire, F.B., Sartori, D.J.M., Freire, J.T., 2005. Study of the drying kinetics in thin layer: fixed and moving bed. Drying Technology 23,
1451–1464.
Barrozo, M.A.S., Henrique, H.M., Sartori, D.J.M., Freire, J.T., 2006. The use of the
orthogonal collocation method on the study of the drying kinetics of soybean
seeds. Journal of Stored Products Research 42, 348–356.
Barrozo, M.A.S., Souza, A.M., Costa, S.M., Murata, V.V., 2001. Simultaneous heat and
mass transfer between air and soybean seeds in a concurrent moving bed. International Journal of Food Science and Technology 36 (4), 393–399.
Barrozo, M.A.S., Sartori, D.J.M., Freire, J.T., Achcar, J.A., 1996. Discrimination of equilibrium moisture equations for soybean using nonlinearity measures. Drying
Technology 14 (7), 1779–1794.
Brooker, D.B., Bakker-Arkema, F.W., Hall, C.W., 1974. Drying Cereal Grains. AVI,

Westport, CT.
Chang, C.H., Lin, H.Y., Chang, C.Y., Liu, Y.C., 2006. Comparisons on the antioxidant
properties of fresh, freeze-dried and hot-air-dried tomatoes. Journal of Food
Engineering 77, 478–485.
Chism, G.W., Haard, N.F., 1996. Characteristics of edible plant tissues. In: Fennema,
O.R. (Ed.), Food Chemistry. Marcel Dekker, Inc., New York, pp. 943–1011.
Diaz, M.N., Frei, B., Vita, J.E., Keaney, J.F., 1997. Antioxidants and atherosclerotic heart
disease. Journal of Medicine and Nutrition England 337, 408–416.
Duarte, C.R., Vieira Neto, J.L., Lisboa, M.H., Santana, R.C., Barrozo, M.A.S., Murata, V.V.,
2004. Experimental study and simulation of mass distribution of the covering
layer of soybean seeds coated in a spouted bed. Brazilian Journal of Chemical
Engineering 21 (1), 59–67.
Dorta, E., Lobo, M.G., González, M., 2012. Using drying treatments to stabilise mango
peel and seed: Effect on antioxidant activity. LWT: Food Science and Technology
45, 261–268.
FAOSTAT, 2010. Food and Agriculture Organization of the United Nations Database,
Available at www.faostat.fao.org (accessed November 2010).

Felipe, C.A.S., Barrozo, M.A.S., 2003. Drying of soybean seeds in concurrent moving
bed: heat and mass transfer and quality analysis. Drying Technology 21 (3),
439–456.
Gordon, J., 2005. How Vitamin C Works, Atlanta, GA. Available at www.
howstuffworks.com/vitamin-c
Gorinstein, S., Zachwieja, Z., Folta, M., Barton, H., Piotrowicz, J., Zemser, M., Weisz, M.,
Trakhtenberg, S., Martın-Belloso, O., 2001. Comparative contents of dietary fiber,
total phenolics, and minerals in persimmons and apples. Journal of Agricultural
and Food Chemistry 49, 952–957.
Gouveia, J.P.G., Fernandez, F.R., Murr, F.E.X., Prado, M.E.T., 1997. Ginger desorption
rate. In: Inter-American Drying Conference, São Paulo, Proceedings, p. 26.
Henderson, J.M., Henderson, S.M., 1968. A computational procedure for deep-bed

drying analysis. Journal of Agricultural Engineering Research 13, 87–95.
Kima, D., Jeondb, S.W., Leea, C.Y., 2003. Antioxidant capacity of phenolic phytochemicals from various cultivars of plums. Food Chemistry 81, 321–326.
Lewis, W.K., 1921. The rate of drying of solid materials. Indian Chemical Engineer
13, 427.
Makris, D.P., Boskou, G., Andrikopoulos, N.K., 2007. Recovery of antioxidant
phenolics from white vinification solid by-products employing water/ethanol
mixtures. Bioresource Technology 98, 2963–2967.
Naidu, K.A., 2003. Vitamin C in human health and disease is still a mystery? An
overview. Nutrition Journal 2, 1–10.
Overhults, D.G., White, G.M., Hamilton, H.E., Ross, I.J., 1973. Drying soybeans with
heated air. Transactions of the ASAE 16 (1), 112–113.
Page, G.E., 1949. Factors Influencing the Maximum Rates of Air Drying Shelled Corn
in Thin-Layer. Purdue University, West Lafayette, IN.
Perazzini, H., Freire, F.B., Freire, J.T., 2013. Drying kinetics prediction of solid waste
using semi-empirical and artificial neural network models. Chemical Engineering and Technology 36 (7), 1193–1201.
Podsedek, A., 2007. Natural antioxidant and antioxidant capacity of Brassica vegetables: a review. LWT: Food Science and Technology 40 (1), 1–11.
Rattanathanalerk, M., Chiewchan, N., Srichumpoung, W., 2005. Effects of thermal
processing on the quality loss of pineapple juice. Journal of Food Engineering 66
(2), 259–265.
Samson, J.A., 1986. Tropical Fruits. Longman Incorporated Publishers, New York, pp.
44–56.
Simal, S., Femenia, A., Garau, M.C., Rosello, C., 2005. Use of exponential page’s and
diffusional models to simulate the drying kinetics of kiwi fruit. Journal of Food
Engineering 66, 323–328.
Singleton, V.L., Rossi, J.A., 1965. Colorimetry of total phenolics with
phosphomolibidic–phosphotungistic acid reagents. American Journal of
Enology and Viticu 16, 144–158.
Terao, J., Pinkula, M., Yao, Q., 1994. Protective effect of Epicatechim, Epicatechin
Gallate and Quercetin on lipid peroxidation in phospholipd bilayers. National
Food Research Institute, Ministry of Agriculture, Forestry and Fisheries, Tsukuba,

Ibaraki 308 (1), 278–284.
Wai, C.M., 2009. Supplementation of nitrogen sources and growth factors in
pineapple waste extract medium for Optimum yeast (Candida utilis) biomass
production. School of Industrial Technology, Universiti Sains Malaysia, Malaysia
(PhD thesis).
Zhishen, J., Mengcheng, T., Jianming, W., 1999. The determination of flavonoid
contents in mulberry and their scavenging effects on superoxide radicals. Food
Chemistry 64, 555–559.