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Annals of Biology 37 (2) : 267-271, 2021
Evaluation of Various Methods of Preparing Kinnow (Citrus nobilis X
Citrus deliciosa) Peel Candy
HARJINDER KAUR AND GURPREET SINGH*
Department of Horticulture, School of Agriculture, Lovely Professional University, Phagwara-144 411 (Punjab),
India
*(e-mail : gurpreetraje@rediffmail.com; Mobile : 8435002901)
(Received : April 22, 2021; Accepted : June 10, 2021)
ABSTRACT
Kinnow pee l is a citrus proce ssing waste that can be collected from discarded fruits. In the present
study, research work was conducted to utilize the peel in the form of Kinnow candy. Methods of candy
preparation were standardize d by varying the treatme nts to reduce bitterness with concentration and
time. Different samples of Kinnow peels were subjected to nine different treatments : T1 : Single boiling
(15 min), T2 : Multiple boiling (3 times for 8 to 10 min), T3 : Soaking in baking soda (2% sodium bicarbonate
for 12 h), T4 : Soaking in 5% vinegar (pure) for 30 min, T5 : Soaking in 2% alum for 24 h, T6 : Boiling in salt
solution (2% brine for 20 min), T7 : Boiling in bottle gourd juice for 20 min, T8 : Boiling in cucumber juice
for 20 min, T9 : Control (no boiling). Further cooked in 750 Brix sugar syrup solutions and steeping in
sugar syrup for 24 h. Treatment of multiple boiling (for 8 to 10 min) with cooked in 750 Brix sugar syrup
solution for 5-8 min and steeping in sugar syrup for 24 h gave the best result with re spect to overall
acceptability, taste, flavour, TSS, ascorbic acid and other biochemical parameters.
Key words : Pe el, citrus, waste-utilization, candy, processing
INTRODUCTION
Citrus fruits o ccupy a dominant place i n
thoroughly grown as tropical and sub-tropical
fruit crop all over the world. Kinnow is one of
th e imp ortant mem be rs of citrus g roup.
Kinnow (Citrus reticulata Blanco) is a hybrid of
King and Willow Leaf and belongs to the citrus
family (Arora et al., 2018). It is the major fruit
crop grown in Punjab. It is principally grown
in Abohar, Hoshiarpur, Mansa, Muktsar and
Bathinda regions. Citrus peels are the richest
sources of bi oactive phe nolic compounds,
especially bioflavonoids, with comparatively
higher polyphenol content compare d to the
pulp (Safdar et al., 2017). Different parts of
Kinnow fruit are used for different purposes
(i.e. fruit and peel). Fresh fruits are consumed
for its juicy placental hairs. Peels are used in
various cookies, cake s, marmalades, as well
as candied peels. Many fruits and vegetables
like guava, apple, carrot, mango and citrus
rind (peel) are used in making candies. Its
worldwide production is over 88 million tonnes
and on e -t h i rd o f th e crop is processed.
Ho wever, i n th at process, more than 40
mill ion tonne s (MT) per annum of citrus
was te s a re produce d b y the in du s t r i es
indulged in juice processing which accounts
for 50% of the origin al whole frui t mass
(Sharma et al., 2017).
During manufacturing, 30-40% of Kinnow peel
is obtained as a major by-product (Rafiq et al.,
2018; Yaqoob et al. 2020a, b). These by-products
po l lu te th e atmo sphere w he n dis c arde d
withou t adequate tre atment and disposal
methods. Peels consist of Beta carotene, which
pr ot ec t s again s t in fe ctio n , cance r,
cardiovascular disease, and slows plaque build-
up in arteries as a precursor to vitamin A.
Prote c ts agai nst di abete s, i nfl amm ati o n,
apopto sis, hepatic steato sis, fibros is and
oxidative stress, among other things. Lutein
has been linked to anti-inflammatory effects,
improved eye and cardiovascular health, the
pr eve n ti on o f ag e -re l at ed m a c u lar
degeneration, and a reduction in the risk of
cervical cancer. Cryptoxanthin possesses an
anti-obesity benefit, anti-oxidant, and anti-
cancer properties (Buscemi et al., 2018; Elvira-
Torales et al., 2019; Jiao et al., 2019).
Shamrez et al. (2013) studied the preparation
of citron peel candy. These were checked for
organoleptic properties after a half-year of
storage at room temperature (25-30°C). Nearly
half year candies are usually stored securely
in polythene sacks. Citron peel (sliced) + 40%
sugar + po t a s s i u m me ta b i s u lp h i te was
Impact Factor : 0.32
(Scop us)
discovere d to be most favo u red candie s.
Aggarwal and Michael (2016) also investigated
the effect of replacing sucrose with fructose
on the p h y si co- c h e mical and s e n sory
characte r i st ics of Ki n no w ca n d y.
Organoleptically, the candy made with 100%
fructose was the highest, but the candy made
with a ratio of 25 : 75 sucrose to fructose was
al so e xce lle nt . In most of the meth o ds,
complicated methods were adopted to prepare
candy from citrus peel. Efforts are being made
to search for the simple and easy method for
candy preparation. Kinnow peel is a waste
product of the citrus manufacturing industry
that can be utilized for preparation of candy
but due to bi tterness of peel, most of the
candies are not relished by the consumers
which determine the acceptability of the peel
candy. The present investigation was carried
out to find the simple and easy method of
preparing the Kinnow peel can dies with
maximum shelf life.
MATERIALS AND METHODS
Re se a r c h work was carrie d out in the
Department of Horticulture Laboratory, Lovely
Professional University, Phagwara, Punjab
(India). Fresh and mature citrus fruits were
harvested from the Kinnow farm of Hoshiarpur,
Punjab. It was ensured that the fruit was free
from any kind of blemishes, bruising, damaged
or infested. The citrus fruits were peeled and
then peels were used for the preparation of
candy. Different samples of Kinnow peels were
subjected to nine different treatments : T1 :
Single boiling (15 min), T2 : Multiple boiling (3
times for 8 to 10 min), T3 : Soaking in baking
soda (2% sodium bicarbonate for 12 h), T4 :
Soaking in 5% vinegar (pure) for 30 min, T5 :
Soaking in 2% alum for 24 h, T6 : Boiling in
salt solution (2% brine for 20 min), T7 : Boiling
in bottle gourd juice for 20 min, T8 : Boiling in
cucumber juice for 20 min, T9 : Control (no
boili ng). Coo ked in 75° Brix sug ar syru p
solutions and steeping in sugar syrup for 24 h.
Peels of four Kinnow fruits were taken in each
replication. The se pe els we re subjected to
above mentioned treatments and candies were
prepared.
For preparing candies, peels of Kinnow were
thoroughly washed under running water. White
piece (albedo) of internal side from the peel
was taken out. At that point, peels of Kinnow
were air-dried under the fan. Then peel was
cut consistently in 5-6 cm length and 0.5-1.0
cm in breath. After, peels were subjected to
various treatments as mentioned above. Then
Kinnow peels were cooked in 75° Brix sugar
syrup solution for 5-8 min and steeping in
sugar syrup for 24 h. After draining, excess
syrup candies were dried in tray dryer at 70°C
for 6 h and samples were packed in plastic
containers and stored at room temperature up
to 30 days for storage studies. Observations on
physico-chemi cal properties viz., moisture
content (%), total solids (% ), pH, total soluble
solids (%), ascorbic acid (mg/100 g), sugars (%
total reducing sugars), titrable acidity (%),
pec tin (% ) and tannin (mg/100 g) and on
organo leptic quality viz., colour, tex tu re,
flavour and overall acceptability (hedonic scale)
were taken for freshly prepared candy as well
as after 30 days of storage. These observations
were analyzed with completely randomized
design (CRD).
RESULTS AND DISCUSSION
Mean score for total soluble solids increased
from 69.09% to 75.19% (Table 1). After 30 days
of storage of candy, T2–Multiple boiling (3 times
for 8 to 10 min) showed the maximum value of
total soluble solids (75.30%) and T9–Control (no
boiling) showed the minimum value of total
soluble solids (69.23% ) at the end of storage.
TS S increased s i g n ificantly, du e to the
hydrol y s is mec h an i s m conv e rti ng
polysaccharides into sugars. Similar results
were found by Priya and Khatkar (2013) in aonla
and by Aggarwal and Michael (2016) in Kinnow
candy.
A significant decrease in the ascorbic acid was
observed during the storage of candy at 5%
level of significance. Mean score for ascorbic
acid decreased from 10.38 to 5.26. After 30 days
of storage of candy, T2–Multiple boiling (3 times
for 8 to 10 min) showed the maximum value of
ascorbic acid (9.60 mg/100 g) and T9–Control
(no boiling) showed the minimum value of
ascorbic acid (3.85 mg/100 g) at the end of
storage (Table 1). The decrease in ascorbic acid
content was due to the dehydroascorbic acid
was formed as a result of oxyge n oxidation.
Kumar et al. (2015) and Priya and Khatkar
(2013) reported similar results in citrus peel
and papaya leather, respective ly.
A significant increase in the total sugars
268 Kaur and Singh
content was observed during the storage of
candy at 5% level of significance. Mean score
for total sugars increased from 44.09 to 62.98
(Table 1). After 30 days of storage of candy, T2–
Multiple boili ng (3 time s for 8 to 10 min)
showed the maximum value of total sugars
content (63.24) and T9–Control (no boiling)
showed the minimum value of total sugars
content (43.54) at the end of storage. Kinnow
peel candy had a steady and noticeable rise in
total sugars that can be attributed to the loss
of moisture content from the products thereby
concentrating sugars. Muzzaffar et al. (2016)
in pumpkin candy, Babariya et al. (2014) in
papaya candy and Priya and Khatkar (2013) in
aonla preserve showed similar results.
Mean score for titrable acidity decreased from
0.63 to 0.40 (Table 2). After 30 days of storage
of candy, T2–Multiple boiling (3 times for 8 to
10 min) showed the maximum value of titrable
acidity (0.62% ) and T9–Control (no boiling)
showed the minimum value of titrable acidity
(0.40% ) at the end of storage. The effect of salt
treat ment and a cid retention with basic
minerals, or the interaction binding of acid
with peel component with time, could explain
the decrease in acidity of Kinnow peel candy.
Kumar et al. (2015) found similar results during
the studies on development of value-added
product from citrus peel and by Priya and
Khatkar (2013) in papaya leather, respectively.
A significant decrease in the pectin content
was observed during the storage of candy at
5% level of significance. Mean score for pectin
Table 1. Effect of various methods of preparing Kinnow peel candy on total soluble solids (%) 0Brix, ascorbic acid (mg/100 g) and
total sugars (%) at different days of intervals
Treatment Storage period (days)
Total soluble solids (%) °Brix Ascorbic acid (mg/100 g) Total sugars (%)
0 15th 30th Mean 0 15th 30th Mean 0 15th 30th Mean
T1–Single boiling 74.60 74.73 74.87 74.73 11.11 10.22 9.48 10.27 58.63 58.86 59.09 58.86
T2–Multiple boiling 75.07 75.20 75.30 75.19 11.21 10.33 9.60 10.38 62.74 62.96 63.24 62.98
T3–Soaking in baking soda 71.93 72.07 72.17 72.06 7.55 5.50 4.33 5.79 51.70 52.09 52.36 52.05
T4–Soaking in vinegar 73.63 73.73 73.87 73.74 8.20 6.31 5.23 6.58 53.15 53.14 53.42 53.24
T5–Soaking in alum 74.03 74.17 74.27 74.16 10.46 9.81 9.25 9.84 53.64 53.82 53.99 53.82
T6–Boiling in salt solution 72.50 72.63 72.77 72.63 8.00 6.03 4.84 6.29 52.94 53.31 53.61 53.29
T7–Boiling in bottle gourd juice 69.93 73.13 70.30 71.12 7.10 5.23 4.25 5.53 49.85 50.17 50.43 50.15
T8–Boiling in cucumber juice 70.43 70.50 71.27 70.73 7.40 5.52 4.46 5.79 51.62 51.89 52.13 51.88
T9–Control (no boiling) 68.93 69.10 69.23 69.09 6.95 4.99 3.85 5.26 43.75 43.99 44.52 44.09
Mean 72.34 72.81 72.67 72.61 8.66 7.10 6.14 7.30 53.11 53.36 53.64 53.37
C. D. 0.47 3.012 0.363 NA 2.548 0.861 0.622 0.516 0.639
S. Em 0.157 1.006 0.121 1.337 0.851 0.287 0.208 0.172 0.213
S. Ed 0.222 1.423 0.171 1.891 1.203 0.407 0.294 0.244 0.302
NA–Not available.
Table 2. Effect of various methods of preparing Kinnow peel candy on titrable acidity (%), pectin (% Cal. pectate) and tannins
(mg/100 g) at different days of intervals
Treatment Storage period (days)
Titrable acidity (%) Pectin (% Cal. pectate) Tannins (mg/100 g)
0 15th 30th Mean 0 15th 30th Mean 0 15th 30th Mean
T1–Single boiling 0.43 0.41 0.40 0.41 1.38 1.28 1.26 1.31 55.87 55.62 55.36 55.62
T2–Multiple boiling 0.64 0.63 0.62 0.63 1.50 1.43 1.36 1.43 53.16 52.91 52.64 52.90
T3–Soaking in baking soda 0.62 0.61 0.60 0.61 1.43 1.31 1.30 1.35 67.80 67.60 67.35 67.58
T4–Soaking in vinegar 0.56 0.55 0.54 0.55 1.61 1.49 1.38 1.49 64.15 63.94 63.72 63.94
T5–Soaking in alum 0.63 0.62 0.61 0.62 1.65 1.51 1.35 1.50 73.17 72.86 72.64 72.89
T6–Boiling in salt solution 0.45 0.44 0.43 0.44 1.63 1.54 1.51 1.56 74.42 74.22 74.04 74.23
T7–Boiling in bottle gourd juice 0.63 0.62 0.61 0.62 1.55 1.45 1.38 1.46 59.28 58.97 58.64 58.96
T8–Boiling in cucumber juice 0.63 0.62 0.61 0.62 1.51 1.42 1.32 1.42 70.50 69.94 69.35 69.93
T9–Control (no boiling) 0.43 0.40 0.39 0.40 1.41 1.30 1.25 1.32 53.01 52.77 52.48 52.75
Mean 0.56 0.55 0.54 0.55 1.52 1.41 1.35 1.43 63.34 63.06 63.06 63.20
C. D. 0.017 0.017 0.017 0.141 0.093 0.107 0.502 0.607 0.552
S. Em 0.006 0.006 0.006 0.047 0.031 0.036 0.168 0.203 0.184
S. Ed 0.008 0.008 0.008 0.067 0.044 0.051 0.237 0.286 0.261
Preparation of Kinnow peel candy 269
decreased from 1.56 to 1.31. After 30 days of
storage of candy, T6–Boiling in salt solution (2%
brine for 20 min) showed the maximum value
of pectin content (1.51% Cal. pe ctate) and T9–
Control (no bo iling) showed th e minimum
value of pectin content (1.25% Cal. pectate) at
the end of storage (Table 2). Decrease in pectin
content in Kinnow peel candy during storage
was due to degradation of pectin into pectic
acids. Muzzaffar et al. (2016) also sh owed
similar results in pumpkin candy and Priya
and Khatkar (2013) in aonla preserves.
Mean score for tannins decreased from 55.62
to 52.90 (Table 2). After 30 days of storage of
candy, T6–Boiling in salt solution (2% brine for
20 min ) sh o w e d the max i mu m v a lue of
tannins content (74.04 mg/100 g) and T9–
Control (no bo iling) showed th e minimum
value of tannins content (52.48 mg/100 g) at
the end of storage. Tannins in Kinnow peel
candy decreased because tannins were highly
volatile and oxidized to given brown products
of high molecular weight. Priya and Khatkar
(201 3 ) s h o w e d s i m i l a r re s u l t s in aonla
preserves and Muzzaffar et al. ( 201 6) in
pumpkin candy.
A significant decrease in the flavour was
observed during the storage of candy at 5%
level of significance. Mean score for flavour
decreased from 8.34 to 6.41. After 30 days of
storage of candy, T2–Multiple boiling (3 times
for 8 to 10 min) showed the maximum value of
flavour (8.20) and T9–Contro l (no boiling )
showed the minimum value of flavour (6.33)
at the end of storage (Table 3). Decrease in
flavour of Kinnow peel candy during storage
was due to some oxidative changes and also it
was a sensory attribute it depended upon
human perception. Shamrez et al. (2013) also
showed similar results in preparation and
evaluation of candies from citron peel. Kumar
et al. (2015) observed similar results from
citrus peel.
Mean score for overall acceptability decreased
from 7.86 to 6.27 (Table 3). After 30 days of
storage of candy, T2–Multiple boiling (3 times
for 8 to 10 min) showed the maximum value of
overall acceptability (7.67) and T9–Control (no
boiling) showed the minimum value of overall
acceptability (6.10) at the end of storage.
Decrease in overall acceptability was due to
decreased scores in colour, texture and flavour
of candy during storage. Shamrez et al. (2013)
and Kumar et al. (2015) also showed similar
result s i n pre parati o n and evaluation of
candies.
CONCLUSION
It may be concluded that candies prepared by
multiple boiling (for 8 to 10 min) cooked in 75°
Brix sugar syrup solution for 5-8 min and
steeping in sugar syrup for 24 h (treatment
T2) produced the best quality candie s with
respect to overall acceptability, taste, flavour,
TSS, ascorbic acid and othe r biochemical
parameters. This treatment did not include
any chemical or any other herbal extract/juice
to reduce the bitterness of the peel. Clean and
pure water was relatively available with more
ease as it was cheapest method of bitterness
removal. It gave the acceptable colour due to
the caramel ization of sugar. The candie s
prepared with T1–Single boiling (15 min) cooked
in 75 °Brix sugar syrup for 5 to 8 min also gave
second most acceptable results.
Table 3. Effect of various meth ods of preparing Kinnow peel candy on flavour and overall acceptability at different
days of inter vals
Treat ment Storage period (days)
Flavour Overall accept ability
0 15th 30th M ean 0 15t h 30th M ea n
T1–Single boiling 8. 20 8. 03 7. 87 8. 03 7.80 7. 60 7. 40 7. 60
T2–Mult iple boi li ng 8. 50 8. 33 8. 20 8. 34 8.07 7. 83 7. 67 7. 86
T3–Soaking in baking soda 7.1 3 7. 0 0 6. 8 7 7. 00 6. 80 6. 60 6. 47 6. 62
T4–Soa kin g in vine gar 7.40 7. 27 7. 1 0 7. 26 7. 23 7. 03 6. 83 7. 03
T5–Soaking in alum 7. 60 7. 50 7. 37 7. 49 7. 53 7. 30 7. 0 3 7.2 9
T6–Boilin g in salt solut ion 7 . 20 7 . 07 6 . 93 7. 07 7. 0 0 6. 8 0 6. 60 6.80
T7–Boiling in bottle gourd juice 6. 67 6. 53 6. 37 6. 52 6. 47 6. 20 6. 1 3 6.2 7
T8–Boiling in cucumber juice 6.77 6. 63 6. 5 0 6. 63 6 . 53 6. 33 6.20 6. 35
T9–Control (no boiling) 6 . 50 6 . 40 6 . 33 6.41 6.43 6.27 6. 1 0 6.2 7
Mean 7. 33 7. 20 7. 06 7. 20 7 . 10 6 . 88 6.71 6.90
270 Kaur and Singh
ACKNOWLEDGEMENT
Th e auth o rs are hi g h l y thankf u l to t h e
De p a rt m e nt of Hor ti c u lture , Love ly
Professional University, Phagwara, Punjab
(India) for providing the material and their
continuous support to conduct this research
work.
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Preparation of Kinnow peel candy 271
