EFFECTS OF DIFFERENT DRYING TEMPERATURES ON THE PHYSICOCHEMICAL PROPERTIES OF Citrofortunella microcarpa (CALAMANSI) PEELS

1

CHAPTER I

1.1. General Introduction

Citrus fruit is a modified berry or a specialized berry (hesperidium)

resulting from single ovary (Ladaniya, 2008). The peel of Citrus is a potential

source of antioxidant. The plant of Citrus microcarpa is in the genus Citrus of

family Rutaceae. The genus Citrus is believed to have originated from Southeast

Asia. Nowadays, it comprises hundreds of varieties and hybrids as a result of

natural or artificial crossbreeding. Calamansi is considered as a natural hybrid of

mandarin and oval kumquat (Citrus reticulate x Citrus japonica). Citrus

microcarpa or Citrofortunella microcarpa, also known as calamondin, limau

kasturi, kesturi and kalamondin, has spread throughout Southeast Asia, India,

Hawaii, West Indies, Central and North America (Cheong et al., 2012).

Previous studies have showed that, in general, fruit peels contain higher

concentrations of antioxidant compounds than the flesh of the fruit. Therefore, it

is possible to utilize fruit peels as antioxidant food additive to produce value-

added food products for human consumption and they may play a role in the

prevention for risk of chronic diseases e.g., diabetes mellitus, cardiovascular

diseases and cancer (Samonte et al., 2013).

2

1.2. Problem Statement

The peel of Citrus microcarpa is a potential source of natural antioxidants.

However, the peels of the fruit are normally disposed as waste or at most used as

fertilizer and feeds. During processing, fruit peels in most cases are discarded

and treated as wastes due to their lack of commercial application. Wasted fruit

peels are consequently increase pollution problem. Although the peels are

commonly discarded after getting its juice, they may contain a high amount of

ascorbic acid that has been found to exceed that in the extracted juice (Manaf et

al., 2008). Accordingly, the study was carried out to determine the

physicochemical properties of the peel so as to gauge potential applications of

the peels.

1.3. Significant Of Study

The significant of this study is to investigate the extend of the usage of the

peels, for further processing. High temperature drying may deteriorate the natural

compound exists in the calamansi peel, especially ascorbic acid which is known

to be heat sensitive. Thus, a maximum temperature of 50oC for the hot air cabinet

drying is used, to preserve the antioxidant and other beneficial properties.

3

1.4. Objective Of Study

The objectives of this study are:

1. To examine the effects of different drying temperatures

within the study range on the moisture content, water

activity, pH, color and rehydration properties of Citrus

microcarpa peels.

2. To investigate the effects of different drying

temperatures on the antioxidant properties and total

phenolic content of the peels.

4

CHAPTER II

2.0 LITERATURE REVIEW

2.1. Characteristics Of Citrus

These citrus fruits are well-known for their refreshing fragrance, thirst

quenching ability, and providing adequate vitamin C as per recommended dietary

allowance (RDA). Besides that, the fruits contain several phytochemicals, which

play the role of neutraceuticals, such as carotenoids, limonoids, flavones, and

vitamin B-complex and related nutrients (thiamine and riboflavin) (Ladaniya,

2008).

The rind or peel is leathery- more so when it loses some moisture. It is

fragile and breaks on folding when turgid. Fruits usually have 8-16 segments.

Seeds vary in number from zero in a few cultivars in many, leading to quite

seedy fruit. Tahiti lime (C.latifolia) and navel oranges can be called truly

seedless and have almost no seeds, while grapefruit and pummel have 40-50

seeds. Seed size and shape also varies greatly among species (Ladaniya, 2008).

The pericarp (rind or peel) is divided into exocarp or flavedo, and

mesocarp or albedo. The flavedo consists of the outermost tissue layers, which

have cuticle-covered epidermis and parenchyma cells. The flavedo is the outer;

colored part and the albedo is the inner; colorless (white) or sometimes tinted

part (as in red grapefruit or blood oranges) (Fig 1) (Ladaniya, 2008).

5

Figure 1: Transverse Section of Citrus Fruit; source (Ladaniya, 2008)

The major pigments that give color to citrus fruits are chlorophylls

(green), carotenoids (yellow, orange, and deep orange), anthocyanins (blood red)

and lycopenes (pink or red). During growth and maturation, especially in the

immature stage, chlorophylls predominate in the peels of all citrus fruits. Due to

the presence of chlorophyll, immature fruits are capable of photosynthesis but

cannot make a significant contribution to the own nutrition (Ladaniya, 2008).

6

2.2. Citrofortunella Microcarpa

Also known as Citrus microcarpa or calamansi; is a mandarin-like fruit

with an oblate shape, but quite small (3-3.25cm in diameter) weighing 20-30 g,

peel that is smooth and very thin (1-2 mm). Its fruit is seeded with yellowish

orange colored flesh, which is acidic in taste, but the peel is sweet and edible. It

is commonly used for culinary purposes and for marmalade making (Ladaniya,

2008). This fruit is indigenous to the Philippines that are usually used in

beverages, or in sauces to enhance the flavor of food. It is sold cheap in the

market and can be found in residential backyards as ornaments.

The calamansi tree is evergreen and small, attaining a height of 2-7.5 m at

maturity. A three-year-old-tree can produce an average of 75 kg fruit and a ten-

year-old-tree can produce 50 kg of fruit. The fruits can be harvested either by

hand or by shear-clipping. They are able to be kept in good condition for two to

three weeks at 8-10oC and 90% relative humidity. The leaves are broadly egg-

shaped and dark green colored on top and pale green below. The small, white

fragment flowers are grouped in clusters. The fruit is round, with greenish yellow

to orange skin that is easy to peel. There are 6-10 segments in a fruit with an

orange colored, very acidic juice with approximately 4-11 seeds in each fruit

(Philipine Council for Agriculture, Forestry and Natural Resources Reseach and

Development, 2010).

The juice, as a drink, makes one of the best thirst-quenchers. The acid

content of lime is known to slow down the oxidation of fresh-cut fruits and

vegetables, thus preventing discoloration and acting as preservatives. Calamansi

7

has been proven to help alleviate depression and anxiety. It is also among the few

aromatics that not just masks bad smell, but completely neutralizes them, making

the essential oil a great additive to cleansing products.

2.2.1. Medicinal Properties

Health-promoting properties of citrus fruits have been ascribed to

their inherit phenolic compounds, including coumarins, flavonoids,

lignins, phenolic acids and tannins (Cheong et al., 2012).

Calamansi has several alternative medicinal uses, Like lightens

freckles, good as mouth wash, Cure coughs and expel phlegm, Helpful in

dealing with hangover, prevent and cure Osteoarthritis, Maintains kidney

health, great tonic for the liver, prevent Diabetes, lightens urine color,

lowers body cholesterol and as a perfume. Calamansi is also used in

medical purposes. In some medical products, Calamansi is used as a

Vitamin C supplement, because Calamansi is rich in Vitamin C. It is also

known to cure cough and colds because of its Vitamin C content.

Calamansi leaves can be an herbal tea that can also be used to cure

coughs.

8

2.2.2. Bioactive Compound

The flavonoids from citrus juices, particularly those from oranges

and grapefruit are effective in improving blood circulation and possess

anti-allergic, anti-carcinogenic, and anti-viral properties. Fresh citrus fruit

consumption is important because the nutrients and health-promoting

factors (especially antioxidants) from these sources are immediately

available to the body and the loss of nutrients is negligible compared to

processed juices (Ladaniya, 2008).

Phenolics are compounds possessing one or more aromatic rings

with one or more hydroxyl groups. They are broadly distributed in the

plant kingdom and are the most abundant secondary metabolites of plants,

with more than 8,000 phenolic structures currently known, ranging from

simple molecules such as phenolic acids to highly polymerized substances

such as tannins. Plant phenolics are generally involved in defense against

ultraviolet radiation or aggression by pathogens, parasites and predators,

as well as contributing to plants colors (Dai et al., 2010).

9

2.2.3. Antioxidant Activity

Antioxidants are defined as compounds that can delay, inhibit, or

prevent the oxidation of oxidizable materials by scavenging free radicals

and diminishing oxidative stress. Oxidative stress is an imbalanced state

where excessive quantities of reactive oxygen and/or nitrogen species

(ROS/RNS, e.g., superoxide anion, hydrogen peroxide, hydroxyl radical,

peroxynitrite) overcome endogenous antioxidant capacity, leading to

oxidation of a varieties of biomacromolecules, such as enzymes, proteins,

DNA and lipids. Oxidative stress is important in the development of

chronic degenerative diseases including coronary heart disease, cancer and

aging (Dai et al., 2010).

10

CHAPTER III

3.0 MATERIALS AND METHODOLOGY

3.1. Chemicals and reagents

Analytical grade chemicals and reagents used were including 2,2-

diphenyl-1-picrylhydrazyl (DPPH) free radicals, Folin-Ciocalteau reagent, gallic

acid, 7.5% sodium carbonate and pure methanol.

3.2. Sample preparation

The calamansi used were obtained from Pasar Borong Selangor. The fruits

were cleaned with cold running water and stems are removed completely. Then,

the fruits were cut and juice were extracted. The analyses were carried out for

both fresh and dried samples to compare the specific changes caused by different

drying temperatures. All experiments and analyses were conducted in triplicate.

Drying experiments were carried out by using freeze dryer (Labconco,

Benchtop Freeze Dry System) and cabinet dryer. The temperatures used for

cabinet dryer were 30oC, 40

oC and 50

oC on perforated stainless steel with airflow

of 2.62-2.82 m/s. Final weight of samples were obtained, or the drying process

ended when there until three consecutive weights were constant, indicating

equilibrium condition. Freeze dryer was carried out by pre-freezing the samples

for 24 hours. The samples were then placed in freeze drier for 3 days at -34oC. All

samples were blended into powder and stored in airtight containers for further

analyses. Extracts of the fruit were prepared using method proposed by Sagrin et

11

al. (2013), with some modifications. Five grams of dried and fresh samples were

added to 100ml of methanol. Mixtures were kept at room temperature for three

days and then filtered with Whatman filter paper (No.1). All filtrates were

collected and evaporated using a rotary evaporator at 50oC. The methanolic

extract was stored at 4oC for subsequent analysis.

3.3.Analyses

3.3.1. Moisture content determination

Moisture content was determined using Association of Official

Analytical Chemists (AOAC) methods. An oven was heated at 105oC.

Five grams of each samples was weighed into a crucible of known weight

and placed in the oven for 16 hours. The crucibles were then cooled in

desiccators. After cooling, the crucibles were weighed together with the

samples. Moisture content was calculated based on the percentage of wet

weight and expressed in percentage of moisture loss.

3.3.2. Water activity determination

The dried powder and fresh peels filled the sample cup halfway,

and constant readings of water activity were taken using a water activity

instrument (Aqua Lab, Series 3 & 3TE).

12

3.3.3. pH determination

The pH values of the samples were determined using a pH meter

(Jenway, 3505). Five grams of each sample was placed into a 100 mL

beaker, to which 50mL of distilled water was added. The mixture was

filtered with Whatman filter paper (No.1) and cotton wool.

3.3.4. Color determination

Color analysis was carried out using a colorimeter (Minolta,

CR300). The rates of lightness (L*), redness (a*), and yellowness (b*)

were measured. The samples were scanned and average values were taken.

3.3.5. Rehydration index determination

The rehydration index, R of the dried samples was measured as

reported by Claussen et al. (2007), with slight modifications.

Approximately one gram of sample was placed into 50ml of water at

20oC. The rehydration times were 30, 90 and 180 seconds. Then, the wet

products were placed into a Buchner tract for 2.5 minutes together with a

filter and suction. The weights of the rehydrated products were recorded,

and the index was calculated as follows:

13

whereby Mf is the weight of the wet product, Mp is the weight of dried

sample, and T is the percentage of dry weight in the dried sample. R

values were used to express the results.

3.3.6. Total phenolic content determination (Folin-Ciocalteau method)

Total phenolic content (TPC) was determined by the Folin-

Ciocalteau method, which was adapted from Lim et al. (2007). Three

hundred microlitre of each sample, 1.5 mL of Folin-Ciocalteau reagent

(diluted 10 times with deionized water), and 1.2 mL of sodium carbonate

(7.5% w/v) were mixed in test tubes. The tubes were vortexed and allowed

to stand in the dark at room temperature for 30 minutes. Absorbance was

measured at 765 nm using visible light spectrophotometer (Genesys 20,

4001/4). TPC was expressed in milligram gallic acid equivalents (GAE)

per gram extract, by using the following formula;

Whereby C is the total content of phenolic compounds in mg/g, in GAE

(gallic acid equivalent), c is the concentration of gallic acid established

from the calibration curve in mg/mL, V is the volume of extract in mL and

M is the weight of pure methanolic extract in g.

The results were expressed as the percentage of loss of TPC as

compared to the fresh or initial sample.

14

3.4. Statistical analyses

The results were expressed as the means of replicates standard

deviations. Significant differences at the 95% confidence level were calculated

based on Tukeys method using Minitab 16.

15

CHAPTER IV

4.0 RESULTS AND DISCUSSION

4.1. Moisture content

Table 1: Effects of drying temperatures on the moisture.

Drying temperature Moisture content Moisture reduction (%)

Fresh 79.183 0.635c -

Freeze dried 7.227 0.145a 90.873 0.247

a

30oC 10.113 0.136

b 87.227 0.075

b

40oC 7.890 0.212

c 90.213 0.493

a

50oC 7.117 0.106

c 90.833 0.408

a

Note: Means with different letters are significantly different at the 5% level

(P < 0.05).

16

Figure 2: Effect of drying temperature on the moisture.


(P < 0.05).

The initial moisture content of the calamansi peel is 79.18 0.64%. The

drying process conducted caused the significant loss of moisture in the peel.

Figure 2 shows the reductions in moisture content when compared to the fresh or

initial moisture content of the samples. The reductions were observed after a few

days of drying, or until there were no changes in the weights of the samples

being dried. The temperatures used for drying were freeze drying (-34oC),

cabinet drying (30oC, 40

oC and 50

oC). The values observed were 90.87 0.25%,

87.23 0.08%, 90.21 0.49% and 90.83 0.41% for freeze dried, 30oC, 40

oC

a 90.87 b

87.23

a 90.21

a 90.84

0

10

20

30

40

50

60

70

80

90

100

FD 30 40 50

Mo

istu

re r

edu

ctio

n (

%)

Temperature (C)

17

and 50oC samples respectively. For cabinet dried samples, the highest moisture

reduction was observed in the highest drying temperature, which was 50oC. This

is due to the higher temperature increases the drying rate and this occur as more

heat was applied to the samples and causes more moisture to evaporate from the

samples. These findings were also observed in Gupta et al., 2011 which uses

different drying temperatures in drying seaweeds.

As for freeze dried sample, the process involves the removal of moisture

from a pre-freezed sample by sublimation. Sublimation is a process when a

frozen liquid changes directly to the gaseous state without undergo liquid phase

and it allows the preparation of stable product and aesthetic in appearance. In

freeze drying, there are three major components in the system that ensures

effective drying; temperature and pressure, collector, and energy. When the

sample is frozen, the water was separated as it changes to ice. The rate of

sublimation of ice in the frozen sample depends on the difference in vapor

pressure of the sample compared to the vapor pressure in the ice collector; as

molecules migrate from the higher pressure sample to a lower pressure area. It is

also crucial that the temperature that maintains the frozen integrity and the

temperature that maximizes the vapor pressure of sample were balanced to

ensure an optimum drying. This is because, temperature and pressure are closely

related, and increasing the sample temperature will increase its vapor pressure, as

the vapor pressure of the sample is the one that forces the sublimation of water

vapor molecules from the frozen product matrix to the collector. Conditions in

the freeze drier were created to ensure free flow of water molecules from the

18

sample. A vacuum pump was used to lower the pressure of the environment

around the sample and a cold trap for collecting the moisture that leave the

frozen sample. The cold trap or collector condensed out all condensable gases

and vacuum pump removed all the non-condensable gases. Then, energy in the

form of heat was applied to the frozen sample to encourage the removal of water

in the form of vapor.

4.2. Water activity and pH

Table 2: Effects of drying temperatures on the water activity and pH.

Drying temperature Water activity (aw) pH

Fresh 0.963 0.0076a 3.433 0.0115

b

Freeze dried 0.451 0.0027d 3.447 0.0252

b

30oC 0.576 0.0021

b 3.567 0.0058

a

40oC 0.527 0.0289

c 3.443 0.0115

b

50oC 0.521 0.0015

c 3.380 0.0000

c


(P < 0.05).

From the results in Table 1, the initial water activity of calamansi peel was

0.963 0.0076. The highest reduction was in freeze dried sample, followed by

samples dried at 50oC, 40

oC and 30

oC with the values of 0.451 0.0027, 0.521

19

0.0015, 0.527 0.0289 and 0.576 0.0021 respectively. According to

Aberoumand, 2010, microorganisms have different minimum levels of water

activity for growth. Bacteria are generally most sensitive and nearly all are

inhibited at a water activity of less than 0.90-0.91, while molds and yeasts need

minimum of 0.70-0.80 and 0.87-0.94 for growth, respectively, thus, a water

activity of 0.60 or lower will prevent growth of all microorganisms.

The results showed that all of the samples possessed pH of a close range

of values. All of the values showed increment, except for the one dried at 50oC,

which showed a decrement. The values were 3.447 0.0252, 3.567 0.0058,

3.443 0.0115 and 3.380 0.0000 for freeze dried, 30oC, 40

oC and 50

oC

samples respectively. Guehi et al., 2010 mentioned that this pH reduction might

be due to the slow and gentle drying (cabinet drying) process that enable the

evaporation of more acid, and mainly because of the presence of citric acid.

20

4.3. Color analysis

Table 3: Effects of drying temperatures on the color of samples.

Lightness (L*) Redness (a*) Yellowness (b*)

Fresh 34.340 0.943d -4.833 0.068

c 22.720 0.737

c

Freeze dried 57.533 1.605a

-5.817 0.124d

22.533 0.840c

30oC 43.690 1.450

c -2.453 0.156

b 24.010 0.217

bc

40oC 48.630 0.560

b

-2.183 0.083ab

25.530 1.070b

50oC 48.040 0.792

b -1.997 0.127

a 29.940 1.128

a


(P < 0.05).

21

Figure 3: Fresh peel color and effect of drying temperature on the color.


(P < 0.05).

The fresh sample had values of 34.340 0.943, -4.833 0.068 and 22.720

0.737 for L*, a* and b* values respectively. From Figure 3, all of the drying

processes showed increase in lightness of the samples color, with the highest

increment in the freeze dried sample, followed by the 30oC, 50

oC and 40

oC with

values of 57.533 1.605, 48.630 0.560, 48.040 0.792 and 43.690 1.450

respectively. These increases in lightness were most probably due to degradation

of chlorophyll due to exposure to high temperatures during drying (Sagrin et al.,

d 34.34

a 57.53

b 48.63

c 43.69

b 48.04

c -4.83

d -5.82

b -2.45

ab -2.18

a -2.00

c 22.72

c 22.53

bc 24.01

b 25.53

a 29.94

-10.00

0.00

10.00

20.00

30.00

40.00

50.00

60.00

70.00

Val

ue

of

L*, a

*, b

*

Temperature (C)

L

a

b

Fresh FD 30 40 50

22

2013). Toontom et al., 2012 reported that freeze drying method significantly

improve the lightness of chili compared to other drying method.

The same observation was obtained for the values of redness (a*) of the

samples, which were increased in each dried sample. It means that all of the dried

samples had reduced its greenness gradually due to drying, with the highest

increment showed in 50oC samples, followed by 40

oC and 30

oC with the values

of -1.997 0.127, -2.183 0.083 and -2.453 0.156 respectively. However, for

freeze dried sample, it showed a decrement in redness value; increment in

greenness. According to Krokida et al., 2001, due to its drying process of

removing water by sublimation of ice at a low temperature, it prevented

enzymatic browning reactions during drying and retained its green color,

resulting in a relative stability of the color parameter. Toontom et al., 2012 also

reported that the minimal color deterioration during freeze drying method is an

indication of the appropriateness of this method to preserve nutraceutical foods.

As for the yellowness (b*), all of the drying temperatures gave out results

of increased values. The drying temperature of 50oC showed highest increment,

followed by 40oC, 30

oC and freeze dried samples, with 29.940 1.128, 25.530

1.070, 24.010 0.217 and 22.533 0.840 respectively. The fresh sample showed

a value of 22.720 0.737. As compared to freeze dried sample, there was no

significant difference in the values (P < 0.05). From the values also can be said

that the freeze drying method protect the samples from undergone enzymatic

browning, which can be observed its increment with the increase of drying

temperatures in the cabinet dried samples. Freeze drying method inhibits color

23

deterioration during drying, resulting in products with superior color compared to

those dried by other methods (Krokida et al., 2001).

4.4. Rehydration index

Table 4: Effects of drying temperatures on the water rehydration of dried samples.

Time (s) 30 90 180

Freeze dried 0.017ab

0.016b

0.026ab

30oC 0.014

bc 0.015

b 0.020

b

40oC 0.013

c 0.016

b 0.025

ab

50oC 0.018

a 0.021

a 0.031

a


(P < 0.05).

24

Figure 4: Effect of drying temperature on the water rehydration of dried

samples.

The rehydration indices gave increased values with the increase in drying

temperatures. It may be due to the fact that the rate of moisture removal at a

higher drying temperature is very fast and causes more shrinkage of the dried

samples (Jokic et al., 2009) which is shown in the sample dried at 50oC; with the

highest rehydration index. Rehydration has an increasing trend with increasing

temperature since it had an increasing effect on the shrinkage of samples which

makes the cellular structure of the sample more porous (Abasi et al., 2009) and

enabled more water adsorption. The sample that undergone drying at 30oC

30 90 180

FD 0.017 0.016 0.026

30 0.014 0.015 0.020

40 0.013 0.016 0.025

50 0.018 0.021 0.031

ab b

ab

bc b

b

c

b

ab a a

a

0.000

0.005

0.010

0.015

0.020

0.025

0.030

0.035

Re

hyd

rati

on

Ind

ex

Time (s)

FD

30

40

50

25

showed the lowest rehydration index, possibly due to reduced shrinkage, and in

line with the observation that the sample retain a high moisture content, thus

weaken the driving force of the water molecules into the sample (Sagrin et al.,

2013).

4.5. Total phenolic content (Folin-Ciocalteau assay)

Table 5: Effects of drying temperatures on the total phenolic content.

Total Phenolic

Content (nm)

GAE (mg/g extract) TPC Reduction (%)

Fresh 0.953 0.019a 3.561 -

Freeze dried 0.709 0.016b

2.385 33.032

30oC 0.948 0.036

a 3.538 0.633

40oC 0.738 0.009

b 2.525 29.101

50oC 0.923 0.005

a 3.418 4.022


(P < 0.05).

26

Figure 5: Effect of drying temperature on the loss of TPC.

Note: Means with different letters are significantly different at the 5% level (P <

0.05).

The data obtained were expressed in the percentage of total phenolic

compound loss in the peel, in relative to the fresh sample. All of the changes

obtained were significantly different after drying process. The highest percentage

of loss was found in the freeze dried sample, followed by cabinet dried at 40oC,

50oC and 30

oC with the values of 33.032%, 29.101%, 4.022% and 0.633%

respectively. The highest percentage of loss observed in freeze dried sample was

due to the binding of phenolic compounds to other peel components, such as

proteins, or because of an altered chemical structure caused by drying (Sagrin et

3.561

2.385

3.538

2.525

3.418 a 33.032

d 0.633

b 29.101

c 4.022

0

5

10

15

20

25

30

35

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

Fresh FD 30 40 50

Per

cen

tage

of

TPC

Red

uct

ion

(%

)

TPC

(G

AE,

mg/

g ex

trac

t)

Temperature (C)

TPC

27

al., 2013). Apart from that, in line with the highest percentage of moisture loss in

freeze dried sample, highest percentage of TPC reduction was found in the

sample, most probably due to loss of water-soluble phenolic compounds in the

peel during drying.

However, the percentage of loss of TPC at drying temperature of 50oC is

lower as compared to the one dried at 40oC. As reported by Gupta et al., 2011,

this increase could be related to the developmental changes and wound-like

response due to drying and that plants respond to wounding with increase in

phenolic compounds involved in the repair of wound damage.

28

CHAPTER V

5.0 CONCLUSION AND RECOMMENDATIONS

By analyzing all the results from this study, drying temperatures significantly

affects the physicochemical properties of dried peels as compared to the fresh peel. From

the values obtained, calamansi peels can be a source of phenolic compounds. Thus, the

results provide a rationale for broadening the usage of calamansi peels from this research.

However, this results include the non-edible part of the peels; the inner white part of the

peels. Therefore, further studies should be conducted to investigate the properties of only

the edible part of the calamansi peels.

29

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drying on the colour of dehydrated products. International Journal of Food Science

and Technology 36, 53-59.

Ladaniya, M., 2008. Citrus fruit, biology, technology and evaluation. London: Academic

Press.

Lim, Y.Y., Lim, T.T., Tee, J.J., 2007. Antioxidant properties of several tropical fruits: A

comparative study. Food Chemistry 103, 1003-1008.

Manaf, Y.N.A., Osman, A., Lai, O.M., Long, K., Ghazali, H.M., 2008. Characterisation

of musk lime (Citrus microcarpa) seed oil. Journal of the Science of Food and

Agriculture 88, 676-683.

Philippine Council for Agriculture, Forestry and Natural Resources Research and

Development (PCARRD), 2010.

Sagrin, M.S., Chong, G.H., 2013. Effect of drying temperature on the chemical and

physical properties of Musa acuminata Colla (AAA Group) leaves. Industrial Crops

and Products 45, 430-434.

Samonte, P.A.L., Trinidad, T.P., 2013. Dietary fiber, phytonutrients and antioxidant

activity of common fruit peels as potential functional food ingredient. J

Sharma, G.N., Dubey, S.K., Sati, N., Sanadya, J., 2011. Phytochemical Screening and

Estimation of total phenolic content in Aegle marmelos seeds. International Journal of

Pharmaceutical and Clinical Research 3, 27-29.

31

Toontom, N., Meenune, M., Posri, W., Lertsiri, S., 2012. Effect of drying method on

physical and chemical quality, hotness and volatile flavor characteristics of dried

chilli. International Food Research Journal 19, 1023-1031.

32

APPENDICES

Appendix 1: Calamansi

Calamansi Fruit. From Great food from the Phillipines: Calamansi,

(http://www.gardeningismyhobby.com/2013/02/28/calamansi-tree-oozing-with-

fruits/)

Calamansi Tree. From Calamansi Tree Oozing with Fruits,

(http://kikaymorena.blogspot.com/2011/02/calamansi-is-my-everything.html)

33

Appendix 2: One-way ANOVA for moisture content

Source DF SS MS F P

Factor 4 12148.85 3037.21 30430.95 0.000

Error 10 1.00 0.10

Total 14 12149.84

S = 0.3159 R-Sq = 99.99% R-Sq(adj) = 99.99%

Individual 95% CIs For Mean Based on

Pooled StDev

Level N Mean StDev -------+---------+---------+---------+--

Fr 3 79.183 0.635 (*

Fd 3 7.227 0.145 (*

30 3 10.113 0.136 *

40 3 7.890 0.212 *

50 3 7.117 0.106 (*

-------+---------+---------+---------+--

20 40 60 80

Pooled StDev = 0.316

Grouping Information Using Tukey Method

N Mean Grouping

Fr 3 79.183 A

30 3 10.113 B

40 3 7.890 C

Fd 3 7.227 C

50 3 7.117 C

Means that do not share a letter are significantly different.

Tukey 95% Simultaneous Confidence Intervals

All Pairwise Comparisons

Individual confidence level = 99.18%

Fr subtracted from:

Lower Center Upper ------+---------+---------+---------+---

Fd -72.805 -71.957 -71.109 *

30 -69.918 -69.070 -68.222 *)

40 -72.141 -71.293 -70.445 *)

50 -72.915 -72.067 -71.219 *

------+---------+---------+---------+---

-60 -40 -20 0

Fd subtracted from:


30 2.039 2.887 3.735 *)

40 -0.185 0.663 1.511 *)

50 -0.958 -0.110 0.738 *

------+---------+---------+---------+---

34

-60 -40 -20 0

30 subtracted from:


40 -3.071 -2.223 -1.375 (*

50 -3.845 -2.997 -2.149 (*

------+---------+---------+---------+---

-60 -40 -20 0

40 subtracted from:


50 -1.621 -0.773 0.075 (*

------+---------+---------+---------+---

-60 -40 -20 0

MOISTURE REDUCTION

Source DF SS MS F P

Factor 3 27.036 9.012 75.69 0.000

Error 8 0.952 0.119

Total 11 27.988

S = 0.3450 R-Sq = 96.60% R-Sq(adj) = 95.32%


Pooled StDev

Level N Mean StDev -------+---------+---------+---------+--

FD 3 90.873 0.247 (---*---)

30 3 87.227 0.075 (---*---)

40 3 90.213 0.493 (---*---)

50 3 90.833 0.408 (---*---)

-------+---------+---------+---------+--

87.6 88.8 90.0 91.2



N Mean Grouping

FD 3 90.8733 A

50 3 90.8333 A

40 3 90.2133 A

30 3 87.2267 B





FD subtracted from:

35

Lower Center Upper --------+---------+---------+---------+-

30 -4.5491 -3.6467 -2.7442 (--*---)

40 -1.5624 -0.6600 0.2424 (--*---)

50 -0.9424 -0.0400 0.8624 (---*--)

--------+---------+---------+---------+-

-2.5 0.0 2.5 5.0

30 subtracted from:


40 2.0842 2.9867 3.8891 (---*---)

50 2.7042 3.6067 4.5091 (--*---)

--------+---------+---------+---------+-

-2.5 0.0 2.5 5.0

40 subtracted from:


50 -0.2824 0.6200 1.5224 (--*---)

--------+---------+---------+---------+-

-2.5 0.0 2.5 5.0

36

Appendix 3: One-way ANOVA for water activity and pH values

Water activity

Source DF SS MS F P

Factor 4 0.497795 0.124449 687.31 0.000

Error 10 0.001811 0.000181

Total 14 0.499606

S = 0.01346 R-Sq = 99.64% R-Sq(adj) = 99.49%


Pooled StDev

Level N Mean StDev -+---------+---------+---------+--------

Fr 3 0.96333 0.00757 (*)

Fd 3 0.45100 0.00265 (*)

30 3 0.57633 0.00208 (*-)

40 3 0.52733 0.02888 (*)

50 3 0.52133 0.00153 (*)

-+---------+---------+---------+--------

0.45 0.60 0.75 0.90



N Mean Grouping

Fr 3 0.96333 A

30 3 0.57633 B

40 3 0.52733 C

50 3 0.52133 C

Fd 3 0.45100 D





Fr subtracted from:

Lower Center Upper -------+---------+---------+---------+--

Fd -0.54846 -0.51233 -0.47621 (*-)

30 -0.42313 -0.38700 -0.35087 (-*)

40 -0.47213 -0.43600 -0.39987 (-*-)

50 -0.47813 -0.44200 -0.40587 (-*-)

-------+---------+---------+---------+--

-0.40 -0.20 -0.00 0.20

Fd subtracted from:


37

30 0.08921 0.12533 0.16146 (-*-)

40 0.04021 0.07633 0.11246 (-*-)

50 0.03421 0.07033 0.10646 (-*)

-------+---------+---------+---------+--

-0.40 -0.20 -0.00 0.20

30 subtracted from:


40 -0.08513 -0.04900 -0.01287 (-*)

50 -0.09113 -0.05500 -0.01887 (-*-)

-------+---------+---------+---------+--

-0.40 -0.20 -0.00 0.20

40 subtracted from:


50 -0.04213 -0.00600 0.03013 (-*-)

-------+---------+---------+---------+--

-0.40 -0.20 -0.00 0.20

pH values

Source DF SS MS F P

Factor 4 0.056293 0.014073 75.39 0.000

Error 10 0.001867 0.000187

Total 14 0.058160

S = 0.01366 R-Sq = 96.79% R-Sq(adj) = 95.51%

Individual 95% CIs For Mean Based on Pooled StDev

Level N Mean StDev +---------+---------+---------+---------

Fr 3 3.4333 0.0115 (--*--)

Fd 3 3.4467 0.0252 (-*--)

30 3 3.5667 0.0058 (-*--)

40 3 3.4433 0.0115 (--*--)

50 3 3.3800 0.0000 (--*--)

+---------+---------+---------+---------

3.360 3.420 3.480 3.540



N Mean Grouping

30 3 3.56667 A

Fd 3 3.44667 B

40 3 3.44333 B

Fr 3 3.43333 B

50 3 3.38000 C


38




Fr subtracted from:

Lower Center Upper ---------+---------+---------+---------+

Fd -0.02335 0.01333 0.05001 (--*--)

30 0.09665 0.13333 0.17001 (--*--)

40 -0.02668 0.01000 0.04668 (--*--)

50 -0.09001 -0.05333 -0.01665 (---*--)

---------+---------+---------+---------+

-0.12 0.00 0.12 0.24

Fd subtracted from:


30 0.08332 0.12000 0.15668 (--*--)

40 -0.04001 -0.00333 0.03335 (--*--)

50 -0.10335 -0.06667 -0.02999 (--*---)

---------+---------+---------+---------+

-0.12 0.00 0.12 0.24

30 subtracted from:


40 -0.16001 -0.12333 -0.08665 (--*--)

50 -0.22335 -0.18667 -0.14999 (--*---)

---------+---------+---------+---------+

-0.12 0.00 0.12 0.24

40 subtracted from:


50 -0.10001 -0.06333 -0.02665 (--*--)

---------+---------+---------+---------+

-0.12 0.00 0.12 0.24

39

Appendix 4: One-way ANOVA for color analysis

(L*)

Source DF SS MS F P

Factor 4 853.17 213.29 163.87 0.000

Error 10 13.02 1.30

Total 14 866.19

S = 1.141 R-Sq = 98.50% R-Sq(adj) = 97.90%


Pooled StDev

Level N Mean StDev ---+---------+---------+---------+------

Fr 3 34.340 0.943 (-*-)

FD 3 57.533 1.605 (-*-)

30 3 43.690 1.450 (-*--)

40 3 48.630 0.560 (-*--)

50 3 48.040 0.792 (-*-)

---+---------+---------+---------+------

35.0 42.0 49.0 56.0



N Mean Grouping

FD 3 57.533 A

40 3 48.630 B

50 3 48.040 B

30 3 43.690 C

Fr 3 34.340 D





Fr subtracted from:

Lower Center Upper ----+---------+---------+---------+-----

FD 20.130 23.193 26.256 (-*--)

30 6.287 9.350 12.413 (--*-)

40 11.227 14.290 17.353 (--*-)

50 10.637 13.700 16.763 (-*--)

----+---------+---------+---------+-----

-12 0 12 24

FD subtracted from:


40

30 -16.906 -13.843 -10.780 (-*--)

40 -11.966 -8.903 -5.840 (--*-)

50 -12.556 -9.493 -6.430 (-*--)

----+---------+---------+---------+-----

-12 0 12 24

30 subtracted from:


40 1.877 4.940 8.003 (-*--)

50 1.287 4.350 7.413 (--*-)

----+---------+---------+---------+-----

-12 0 12 24

40 subtracted from:


50 -3.653 -0.590 2.473 (--*-)

----+---------+---------+---------+-----

-12 0 12 24

(a*)

Source DF SS MS F P

Factor 4 36.6734 9.1684 679.47 0.000

Error 10 0.1349 0.0135

Total 14 36.8083

S = 0.1162 R-Sq = 99.63% R-Sq(adj) = 99.49%


Level N Mean StDev +---------+---------+---------+---------

Fr 3 -4.8333 0.0681 (-*)

Fd 3 -5.8167 0.1242 (-*)

30 3 -2.4533 0.1557 (-*)

40 3 -2.1833 0.0833 (*)

50 3 -1.9967 0.1274 (*-)

+---------+---------+---------+---------

-6.0 -4.8 -3.6 -2.4



N Mean Grouping

50 3 -1.9967 A

40 3 -2.1833 A B

30 3 -2.4533 B

Fr 3 -4.8333 C

Fd 3 -5.8167 D


41




Fr subtracted from:


Fd -1.2952 -0.9833 -0.6715 (*)

30 2.0681 2.3800 2.6919 (-*)

40 2.3381 2.6500 2.9619 (-*)

50 2.5248 2.8367 3.1485 (*-)

-------+---------+---------+---------+--

-2.5 0.0 2.5 5.0

Fd subtracted from:


30 3.0515 3.3633 3.6752 (*-)

40 3.3215 3.6333 3.9452 (-*)

50 3.5081 3.8200 4.1319 (*-)

-------+---------+---------+---------+--

-2.5 0.0 2.5 5.0

30 subtracted from:


40 -0.0419 0.2700 0.5819 (*)

50 0.1448 0.4567 0.7685 (*)

-------+---------+---------+---------+--

-2.5 0.0 2.5 5.0

40 subtracted from:


50 -0.1252 0.1867 0.4985 (-*)

-------+---------+---------+---------+--

-2.5 0.0 2.5 5.0

(b*) Source DF SS MS F P

Factor 4 110.800 27.700 37.29 0.000

Error 10 7.427 0.743

Total 14 118.227

S = 0.8618 R-Sq = 93.72% R-Sq(adj) = 91.20%


Pooled StDev

Level N Mean StDev ----+---------+---------+---------+-----

Fr 3 22.720 0.737 (----*---)

Fd 3 22.533 0.840 (---*----)

30 3 24.010 0.217 (---*---)

40 3 25.530 1.070 (---*----)

50 3 29.940 1.128 (----*---)

42

----+---------+---------+---------+-----

22.5 25.0 27.5 30.0



N Mean Grouping

50 3 29.940 A

40 3 25.530 B

30 3 24.010 B C

Fr 3 22.720 C

Fd 3 22.533 C





Fr subtracted from:


Fd -2.500 -0.187 2.127 (----*---)

30 -1.024 1.290 3.604 (----*---)

40 0.496 2.810 5.124 (----*---)

50 4.906 7.220 9.534 (---*----)

---------+---------+---------+---------+

-5.0 0.0 5.0 10.0

Fd subtracted from:


30 -0.837 1.477 3.790 (----*----)

40 0.683 2.997 5.310 (----*----)

50 5.093 7.407 9.720 (----*---)

---------+---------+---------+---------+

-5.0 0.0 5.0 10.0

30 subtracted from:


40 -0.794 1.520 3.834 (----*----)

50 3.616 5.930 8.244 (----*---)

---------+---------+---------+---------+

-5.0 0.0 5.0 10.0

40 subtracted from:


50 2.096 4.410 6.724 (----*---)

---------+---------+---------+---------+

-5.0 0.0 5.0 10.0

43

Appendix 5: One-way ANOVA for rehydration index

(30 seconds)

Source DF SS MS F P

Factor 3 0.0000422 0.0000141 14.22 0.001

Error 8 0.0000079 0.0000010

Total 11 0.0000501

S = 0.0009946 R-Sq = 84.21% R-Sq(adj) = 78.29%


Pooled StDev

Level N Mean StDev -+---------+---------+---------+--------

FD 3 0.016067 0.001447 (-----*------)

30 3 0.013967 0.001328 (------*-----)

40 3 0.013200 0.000100 (------*------)

50 3 0.018000 0.000300 (------*------)

-+---------+---------+---------+--------

0.0120 0.0140 0.0160 0.0180



N Mean Grouping

50 3 0.0180000 A

FD 3 0.0160667 A B

30 3 0.0139667 B C

40 3 0.0132000 C





FD subtracted from:

Lower Center Upper

30 -0.0047012 -0.0021000 0.0005012

40 -0.0054679 -0.0028667 -0.0002655

50 -0.0006679 0.0019333 0.0045345

---------+---------+---------+---------+

30 (------*-----)

40 (------*-----)

50 (------*-----)

---------+---------+---------+---------+

-0.0040 0.0000 0.0040 0.0080

44

30 subtracted from:

Lower Center Upper

40 -0.0033679 -0.0007667 0.0018345

50 0.0014321 0.0040333 0.0066345

---------+---------+---------+---------+

40 (-----*------)

50 (-----*------)

---------+---------+---------+---------+

-0.0040 0.0000 0.0040 0.0080

40 subtracted from:

Lower Center Upper

50 0.0021988 0.0048000 0.0074012

---------+---------+---------+---------+

50 (------*------)

---------+---------+---------+---------+

-0.0040 0.0000 0.0040 0.0080

(90 seconds)

Source DF SS MS F P

Factor 3 0.0000658 0.0000219 14.20 0.001

Error 8 0.0000123 0.0000015

Total 11 0.0000781

S = 0.001242 R-Sq = 84.19% R-Sq(adj) = 78.27%


Level N Mean StDev --------+---------+---------+---------+-

FD 3 0.016333 0.000569 (-----*------)

30 3 0.014633 0.000569 (------*-----)

40 3 0.015667 0.000896 (------*-----)

50 3 0.020767 0.002173 (------*------)

--------+---------+---------+---------+-

0.0150 0.0175 0.0200 0.0225



N Mean Grouping

50 3 0.020767 A

FD 3 0.016333 B

40 3 0.015667 B

30 3 0.014633 B


45




FD subtracted from:


30 -0.004949 -0.001700 0.001549 (------*-----)

40 -0.003916 -0.000667 0.002582 (------*-----)

50 0.001184 0.004433 0.007682 (------*-----)

---------+---------+---------+---------+

-0.0050 0.0000 0.0050 0.0100

30 subtracted from:


40 -0.002216 0.001033 0.004282 (-----*------)

50 0.002884 0.006133 0.009382 (-----*------)

---------+---------+---------+---------+

-0.0050 0.0000 0.0050 0.0100

40 subtracted from:


50 0.001851 0.005100 0.008349 (-----*------)

---------+---------+---------+---------+

-0.0050 0.0000 0.0050 0.0100

(180 seconds)

Source DF SS MS F P

Factor 3 0.0002093 0.0000698 6.15 0.018

Error 8 0.0000908 0.0000114

Total 11 0.0003002

S = 0.003370 R-Sq = 69.74% R-Sq(adj) = 58.39%


Pooled StDev

Level N Mean StDev -----+---------+---------+---------+----

FD 3 0.026167 0.002503 (-------*------)

30 3 0.019567 0.001498 (-------*------)

40 3 0.024533 0.001450 (-------*------)

50 3 0.031267 0.005900 (------*-------)

-----+---------+---------+---------+----

0.0180 0.0240 0.0300 0.0360


46


N Mean Grouping

50 3 0.031267 A

FD 3 0.026167 A B

40 3 0.024533 A B

30 3 0.019567 B





FD subtracted from:


30 -0.015413 -0.006600 0.002213 (------*-------)

40 -0.010447 -0.001633 0.007180 (-------*------)

50 -0.003713 0.005100 0.013913 (------*-------)

-------+---------+---------+---------+--

-0.012 0.000 0.012 0.024

30 subtracted from:


40 -0.003847 0.004967 0.013780 (------*------)

50 0.002887 0.011700 0.020513 (-------*------)

-------+---------+---------+---------+--

-0.012 0.000 0.012 0.024

40 subtracted from:


50 -0.002080 0.006733 0.015547 (-------*------)

-------+---------+---------+---------+--

-0.012 0.000 0.012 0.024

47

Appendix 6: One-way ANOVA for total phenolic content (TPC)

Source DF SS MS F P

Factor 4 0.173439 0.043360 107.90 0.000

Error 10 0.004019 0.000402

Total 14 0.177458

S = 0.02005 R-Sq = 97.74% R-Sq(adj) = 96.83%


Pooled StDev

Level N Mean StDev -----+---------+---------+---------+----

Fr 3 0.95267 0.01893 (--*--)

FD 3 0.70900 0.01559 (---*--)

30 3 0.94800 0.03600 (---*--)

40 3 0.73800 0.00917 (--*--)

50 3 0.92300 0.00529 (--*---)

-----+---------+---------+---------+----

0.720 0.800 0.880 0.960



N Mean Grouping

Fr 3 0.95267 A

30 3 0.94800 A

50 3 0.92300 A

40 3 0.73800 B

FD 3 0.70900 B





Fr subtracted from:

Lower Center Upper +---------+---------+---------+---------

FD -0.29749 -0.24367 -0.18985 (---*--)

30 -0.05849 -0.00467 0.04915 (---*--)

40 -0.26849 -0.21467 -0.16085 (---*--)

50 -0.08349 -0.02967 0.02415 (---*---)

+---------+---------+---------+---------

-0.30 -0.15 0.00 0.15

FD subtracted from:


30 0.18518 0.23900 0.29282 (---*---)

40 -0.02482 0.02900 0.08282 (---*---)

50 0.16018 0.21400 0.26782 (--*---)

+---------+---------+---------+---------

48

-0.30 -0.15 0.00 0.15

30 subtracted from:


40 -0.26382 -0.21000 -0.15618 (---*---)

50 -0.07882 -0.02500 0.02882 (--*---)

+---------+---------+---------+---------

-0.30 -0.15 0.00 0.15

40 subtracted from:


50 0.13118 0.18500 0.23882 (--*---)

+---------+---------+---------+---------

-0.30 -0.15 0.00 0.15

Gallic acid (TPC)

Source DF SS MS F P

Factor 5 0.862754 0.172551 599.14 0.000

Error 12 0.003456 0.000288

Total 17 0.866210

S = 0.01697 R-Sq = 99.60% R-Sq(adj) = 99.43%


Pooled StDev

Level N Mean StDev ----+---------+---------+---------+-----

Blank 3 0.14000 0.02623 (*)

3.125 ppm 3 0.26567 0.00603 (*)

6.25 ppm 3 0.33933 0.02026 (*)

12.5 ppm 3 0.43700 0.00624 (*)

25 ppm 3 0.47800 0.01970 (*)

50 pm 3 0.83867 0.01290 (*)

----+---------+---------+---------+-----

0.20 0.40 0.60 0.80



N Mean Grouping

50 pm 3 0.83867 A

25 ppm 3 0.47800 B

12.5 ppm 3 0.43700 B

6.25 ppm 3 0.33933 C

3.125 ppm 3 0.26567 D

Blank 3 0.14000 E

49





Blank subtracted from:


3.125 ppm 0.07913 0.12567 0.17221 (-*)

6.25 ppm 0.15279 0.19933 0.24587 (-*)

12.5 ppm 0.25046 0.29700 0.34354 (*-)

25 ppm 0.29146 0.33800 0.38454 (-*)

50 pm 0.65213 0.69867 0.74521 (*)

--------+---------+---------+---------+-

-0.35 0.00 0.35 0.70

3.125 ppm subtracted from:


6.25 ppm 0.02713 0.07367 0.12021 (*)

12.5 ppm 0.12479 0.17133 0.21787 (*)

25 ppm 0.16579 0.21233 0.25887 (*)

50 pm 0.52646 0.57300 0.61954 (*-)

--------+---------+---------+---------+-

-0.35 0.00 0.35 0.70



12.5 ppm 0.05113 0.09767 0.14421 (-*)

25 ppm 0.09213 0.13867 0.18521 (*)

50 pm 0.45279 0.49933 0.54587 (*-)

--------+---------+---------+---------+-

-0.35 0.00 0.35 0.70



25 ppm -0.00554 0.04100 0.08754 (*-)

50 pm 0.35513 0.40167 0.44821 (*-)

--------+---------+---------+---------+-

-0.35 0.00 0.35 0.70

25 ppm subtracted from:


50 pm 0.31413 0.36067 0.40721 (*-)

--------+---------+---------+---------+-

-0.35 0.00 0.35 0.70

50

Gallic acid standard curve (TPC)

y = 12.438x + 0.2157 R = 0.9491

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

0.0000 0.0100 0.0200 0.0300 0.0400 0.0500 0.0600

Ab

sorb

ance

(n

m)

Concentration (mg/mL)

51

VITAE

Nur Afiqah binti Ab Aziz was born in Ipoh, Perak on 29th

July 1991. She is the

second child from five siblings; a brother and three sisters. Both of her parents were

alumni of University Putra Malaysia and currently work as teachers in Kelantan.

She received her early education in Peter and Jane Preschool. Later, she received

her education in Sekolah Kebangsaan Banggol Guchil, Kuala Krai, but then moved to

Sekolah Kebangsaan Seri Ketereh when she and her family moved to Ketereh. In her

early year of secondary school, she went to Sekolah Menengah Kebangsaan Ketereh; for

almost three years. Later, she went to Sekolah Menengah Kebangsaan Melor for her

Penilaian Menengah Rendah (PMR) in 2006 and Sijil Peperiksaan Malaysia (SPM) in

2008.

She obtained a result of 4As and 5Bs in her SPM and later pursue her study in

Kolej Matrikulasi Perak (KMPk) in Physical Science in 2009. During matriculation, she

showed a good performance, thus making her eligible to enroll into University Putra

Malaysia (UPM), one of the prestigious universities in Malaysia under a programme of

Faculty of Food Science and Technology for Bacelor of Food Science and Technology.

During her 4 years of study, she had learnt a lot of new things, gain new knowledge,

experience and friends, and improves herself for the better.

EFFECTS OF DIFFERENT DRYING TEMPERATURES ON THE PHYSICOCHEMICAL PROPERTIES OF Citrofortunella microcarpa (CALAMANSI) PEELS

Documents

fruit peels

peel of citrus microcarpa

citrus fruits

characteristics of citrus

plant of citrus microcarpa

antioxidant properties

significant of study

study range