International Journal of Food Science and Technology 2009, 44, 445–455
445
Original article
Anthocyanin-rich sweet potato lacto-pickle: production, nutritional
and proximate composition
Smita Hasini. Panda, Satarupa Panda, P. Sethuraman Sivakumar & Ramesh C. Ray*
Regional Centre of Central Tuber Crops Research Institute, P.O. Dumduma Housing Board, Bhubaneswar 751 019, Orissa, India
(Received 9 November 2006; Accepted in revised form 14 January 2008)
Summary
Anthocyanin pigment-rich sweet potato (SP) cubes were pickled by lactic fermentation by brining the cut and
blanched cubes in common salt (NaCl, 2–10%) solution. They were then inoculated with a strain of
Lactobacillus plantarum (MTCC 1407) and incubated for 28 days. Treatment with 8–10% brine solution was
found to be organoleptically most acceptable. The final product with 8% and 10% brine solutions had a pH
(2.5–2.8), titratable acidity (TA) (1.5–1.7 g kg)1), lactic acid (LA) (1.0–1.3 g kg)1), starch (56–58 g kg)1) and
anthocyanin content (390 mg kg)1) on fresh weight basis. Sensory evaluation rated the anthocyanin-rich SP
lacto-pickle acceptable based on texture, taste, aroma, flavour and after taste. Principal component analyses
reduced the eleven original analytical and proximate variables (pH, TA, LA, starch, total sugar,
anthocyanin, organic mater, ash, fat, protein and calories) to three independent components (factors),
which accounted for 91% of the total variations.
Keywords
Fermentation, lactic acid, lacto-pickle, sweet potato.
Introduction
Lactic acid (LA) fermentation of vegetable products
applied as a preservation method for the production of
finished and half-finished products is considered to be
an important technology. It is further investigated
because of the growing amount of raw materials
processed in this way in the food industry. The main
reasons for this interest are the nutritional, physiological
and preservation aspects of the process and their
corresponding implementation and production cost
(Karoviĉova et al., 2001; Karoviĉova & Kohajdovă,
2002). Most vegetables can be LA fermented in presence
of salt, although so far cucumber, cabbage and olives
are the only vegetables that are fermented in large
volumes for human consumption (Maifreni et al., 2004;
Montet et al., 2006). Lactic-fermented vegetables commonly produced in Asia are gundruk (LA fermentation
of mustard, radish and cauliflower leaves), dhamuoi
(fermented cabbage) and dakguadong (fermented mustard leaves). LA fermentation not only produces LA but
also imparts taste and flavour to the fermented product.
Ascorbic acid, phenols and coloured pigments (b-carotene and anthocyanin) are also preserved. These pigments are considered as anti-oxidants (Shivashankara
*Correspondent: Fax: 91 674 2470528;
e-mail: [email protected]
et al., 2004). Therefore, there are agricultural, nutritional, sensory and preservation reasons for evaluating
LA fermentation as a potential process for making
fermented products from other vegetables such as sweet
potato (SP) (Ipomoea batatas L.).
SP is the world’s seventh most important food crop
after wheat, rice, maize, potato, barley and cassava.
India is considered as one of the leading producers of SP
in the world with production of 1.35 million tonnes of
roots annually. SP roots are consumed in India as fresh
vegetable or as boiled or baked in normal human diet of
rural and tribal people (Ray & Ravi, 2005). The swollen
roots are rich in starch, sugars, vitamin C, provitamin
A, iron and minerals (Ray & Ward, 2006). SP roots of
some varieties contain coloured pigments such as
b-carotene, anthocyanin and unidentified flavonoids
(Matsui et al., 2003). These pigments are regarded as
anti-oxidants (Matsui et al., 2003) having several physiological attributes such as anti-oxidation, anti-cancer,
anti-immunodilation, protection against cataract, aging,
macular degeneration and liver injury (Kaur et al.,
2002). Very recently, SP is labelled as an antidiabetic
food because of animal studies in which SP helped to
stabilise blood sugar levels and lowered insulin resistance (Kusano & Abe, 2000). Since SP roots are rich in
sugar, starch, minerals, vitamins and dietary fibres, they
have high potential for undergoing fermentation into
value-added commodities like pickles, vinegar, curd,
doi:10.1111/j.1365-2621.2008.01730.x
2008 The Authors. Journal compilation 2008 Institute of Food Science and Technology
446
Anthocyanin-rich sweet potato lacto-pickle S. H. Panda et al.
yoghurt, wine and ethanol (Panda et al., 2006; Ray &
Ward, 2006; Mohapatra et al., 2007).
LA fermentation of vegetables is a sequential process
that uses a mixture of natural Lactic acid bacteria (LAB)
from surface microflora, i.e. Lactobacillus spp., Leuconostoc spp., Pediococcus spp., etc. (Gardner et al., 2001;
Adeniyi et al., 2005); however, the use of ‘starter culture’
provides consistency and reliability of performance
(McFeeters, 2004). Lactobacillus plantarum is the
‘starter’ most frequently used in LA fermentation of
plant materials (Molin, 2001; Montet et al., 2006).
In this paper, the purpose was to investigate methods
of making anthocyanin-rich SP pickles using Lb. plantarum MTCC 1407 as a controlled starter culture and to
evaluate nutritional and compositional changes during
LA fermentation at different salt concentrations.
Materials and methods
Preparation of starter culture
Good quality sweet grapes (Var. Bangalore Blue)
(100 g) were selected and washed under running tap
water. These grapes were mashed in a Mixer-cum
Grinder (TTK Prestige Ltd, Bangalore, India) and the
juice was extracted by using a juice squeezer. The
volume of juice (filtered through cheese cotton cloth)
was measured and equal volume of water was added.
The mixture was boiled for 10–15 min on a hot plate
and was cooled at room temperature of 28 ± 2 C.
After cooling the grape juice was inoculated with Lb.
plantarum culture from the stock culture under laminar
flow (Klenzoides, Bombay, India) and was incubated at
30 C for 24 h.
Pickling of sweet potato
Freshly harvested and unbruised anthocyanin-rich SP
roots (Var. ST-13) (starch, 178 g kg)1, total sugar,
26 g kg)1 and anthocyanin 755 mg kg)1 fresh SP cubes)
were collected from the experimental farm of Regional
Centre of Central Tuber Crops Research Institute,
Bhubaneswar during the month of November 2005
(day temperature, 28 ± 2 C and night temperature,
20 ± 2 C). The roots were used within 24 h after
harvest. SP roots were cleaned in running tap water to
remove surface dirt, peeled and cut into small cubes
(1 cm · 1 cm, approximately). These cubes were
blanched in boiling water for 1 min at 70 C. These
blanched SP cubes (140 g) were dispensed in 500 mL
plastic jars (Polypet, Bombay, India). Brine solution of
five different salt concentrations (2–10%) were prepared
by dissolving common salt (NaCl) (Tata Salt, Bhav
Nagar, India) in distilled water and 300 mL of the
prepared brine solution was added to each bottle. Three
replicates were maintained for each salt concentration
International Journal of Food Science and Technology 2009
and the data on biochemical analyses were calculated as
a means of three replications. One table spoon (7 mL)
(1 · 107 CFU mL)1) of starter culture was inoculated
into each bottle and capped tightly. In this way, SPs
were fermented in brine solution and jars were kept on
the laboratory bench at room temperature of
28 ± 2 C. The flowchart for making SP lacto-pickle
(LP) is given in Fig. 1. Although sourness developed
after 7 days of fermentation, the fermentation was
allowed to continue up to 28 days for the pickle to
season before preservative, i.e. potassium metabisulphite
(100 lg g)1) was added to prevent the growth of salttolerant microorganisms such as Aspergillus spp.
Biochemical and proximate analysis
Data were collected for pH and biochemicals [starch,
total sugar, anthocyanin, titratable acidity (TA) and LA]
constituents of SP LPs. pH was determined by pH meter
[Model 351, Systronics (India), Pvt. Ltd, Ahmedabad,
India] using glass electrode. TA was estimated by titration
method and LA by spectrophotometric method using a
UV–Vis Spectrophotometer (Model C-7250; Cecil Instruments, Cambridge, UK) (Amerine & Ough, 1980) and the
data were expressed as equivalent of g LA kg)1 SP LP
cubes and g L)1 LP brine solution. The starch and total
sugar contents were estimated by the procedure given by
Mahadevan & Sridhar (1993) and the values were
expressed in g kg)1 SP LP cubes and g L)1 LP brine
solution. Anthocyanin content was estimated by spectrophotometric method (Ahmed et al., 2004) and expressed
as mg kg)1 SP LP cubes and mg L)1 LP brine solution.
The proximate compositions of SP LP were determined as follows. Protein [total nitrogen (N) · 6.25] and
N was determined by Kjeldahl and ash by the muffle
furnace methods (CTCRI, 2000). Fat (ether extracts)
was estimated by Soc. Tech. Instruments (Pelican
Equipments, Chennai, India) and gross energy (kcal g)1
SP LP) by using an Adiobatic Bomb calorimeter (Parr
Scientific Equipments, Michigan, MI, USA) following
the procedure given by USDA (1984). Organic matter
was estimated by the procedure described by USDA
(1984). Protein, fat, organic matter and ash contents
were expressed as g kg)1 SP LP.
Lactobacillus counts
Lactobacillus counts were reported as colony forming
units (CFU mL)1) of SP LPs (homogenised) on MRS
agar Petri plates (100 mm · 18 mm).
Sensory evaluation assay
Sensory attributes (texture, taste, aroma, flavour, colour ⁄ appearance and after taste) of SP pickles prepared
using 2–10% salt solutions only after 28 days of
2008 The Authors. Journal compilation 2008 Institute of Food Science and Technology
Anthocyanin-rich sweet potato lacto-pickle S. H. Panda et al.
Anthocyanin rich
Sweet potato
Washing, cleaning by tap water and peeling
Cut in to small cubes 1×1 cm approx.
Blanching
(Dip in hot water at 70 ºC for 10–15 min)
Dip the blanched sweet potato cubes in brine solution [2–10%NaCl (w/v)]
Add the brine solution treated sweet potato cubes in
plastic jars
Inoculation with starter culture
Inoculation with Lb. plantarum starter culture [use 48 h old starter culture at 7%
(v/v)]
Fermentation (at 28 ± 2 ºC for 28 days)
Add 100 µg g–1 potassium metabisulfite (preservative)
Final packing (plastic jars sealed anerobically)
Figure 1 Flowchart for preparation of sweet
potato (SP) lacto-pickles.
fermentation were evaluated using a 5-point Hedonic
scale (where 1, dislike extremely and 5, like extremely).
A semi-trained sensory panel of twenty-four members
(gender, fourteen women and ten men; age group: 32–
45) was selected from the local people and staff of
several horticulture departments who usually consume
pickles and other lactic-fermented products. Samples
were served in polypropylene transparent cups which
had been labelled with a three-digit random number.
Questionnaires and water for mouth rising between each
tasting were provided. Prior to evaluation, a session was
held to familiarise panelists with the product. Panelists
were asked to read through the questionnaires and the
2008 The Authors. Journal compilation 2008 Institute of Food Science and Technology
Sweet potato lacto-pickle
meaning of each attribute (texture, taste, aroma, flavour, colour ⁄ appearance and after taste) was explained
to the panelists to avoid any misinterpretation (Kilcast
& Subramanian, 2000). Prior to each evaluation, a
session was held to familiarise panelists with the
product. Another set of LPs were evaluated as replication 2 (n = 2) the following day. The sensory evaluation
data were presented as the mean of the panelists’ score.
Statistical methods
For the evaluation of the analytical, proximate and
sensory results, the data were analysed by Factorial
International Journal of Food Science and Technology 2009
447
448
Anthocyanin-rich sweet potato lacto-pickle S. H. Panda et al.
anova through General Linear Model procedure. When
significant differences in anova (P < 0.05) were detected, the Fischer’s least significant difference (LSD)
multiple comparison test was applied to compare the
factor level differences. An alpha level of 0.05 was set a
priori (Cass, 1980). The multivariate statistical methods:
correlation analysis and principal component analysis
(PCA) were also applied to analyse the analytical and
proximate data of SP pickles produced after 28 days of
fermentation using only 10% brine. The analyses were
performed using spss (SPSS Software for Windows
release 10.0l SPSS Inc., Chicago, IL, USA).
Results and discussion
The biochemical changes during LA fermentation of SP
lacto-pickling process are described below. We have
ignored the amount of salt if any, which might have
interfered while expressing the quantity of LA, TA,
starch, etc., in g kg)1 LP. Because, the study was a
submerged fermentation; unlike solid state or surface
fermentation, little salt might have adhered to or
penetrate into pickle surface which would not alter the
general trend of the data.
Changes in pH
Table 1 shows the changes in pH of pickled SP during
fermentation. On day 7 of fermentation, pH decreased
rapidly from initial 5.7 (0 day) to 3.02–3.04. Beyond
7 days the decrease in pH was gradual up to the end of
fermentation period (28 days). The anova revealed that
the salt concentration [F(5, 30) = 41.195, P < 0.001]
and days of fermentation [F(4, 30) = 12 513.731,
P < 0.001] significantly affected pH. Post-hoc tests
exhibited that the salt concentrations of 0 and 4 did
not differ significantly from each other. But, other
treatment means differed significantly (P < 0.05; LSD).
Post-hoc tests showed that salt concentration means
except 0% and 4% differed significantly from each other
(P < 0.05; LSD). The mean pH values of all the days of
fermentation also differed significantly from each other
Table 1 pH values of SP lacto-pickles during fermentation
Salt
concentration (%)
7 Days
14 Days
21 Days
28 Days
0
2
4
6
8
10
3.03
3.04
3.02
3.04
3.04
3.04
3.02
2.96
2.80
2.81
2.82
2.82
2.48
2.20
2.50
2.60
2.72
2.90
2.13
2.15
2.26
2.40
2.50
2.80
±
±
±
±
±
±
0.13
0.13
0.13
0.13
0.15
0.14
±
±
±
±
±
±
0.06
0.05
0.04
0.04
0.10
0.10
±
±
±
±
±
±
0.10
0.10
0.15
0.10
0.12
0.15
±Standard deviations.
Initial (0 day) pH value of SP cubes was 5.7.
International Journal of Food Science and Technology 2009
±
±
±
±
±
±
0.12
0.11
0.12
0.14
0.16
0.13
(P < 0.01; LSD). It seems that there might be a very
active fermentation initially (up to 7 days) and organic
acids formed during this period could reduce microbial
action in course of fermentation. Mugula et al. (2003)
reported a similar change in pH, i.e. from 5.87 to 3.24
during 24 h fermentation of Togwa, a Tanzanian food
using starter culture of LAB and yeasts. Karoviĉova
et al. (2001) reported a similar change in pH during the
first 7 days of fermentation (i.e. from 5.87 to 3.86) of
cabbage–carrot juices using Lb. plantarum as an inoculant. The situation was also similar to other vegetable
ferments like table green olives, cucumbers, Irish potato,
etc. (Spyropoulou et al., 2001; Adeniyi et al., 2005). A
rapid decrease in pH at the beginning of fermentation is
of great importance for the texture and quality of
fermented products (Bobillo & Marshall, 1992). Further, with the increase in salt concentrations from 0% to
10%, the decrease in pH was arrested because of
probably less LA accumulation at 8–10% salt concentrations. Most of the LA bacteria tolerate NaCl
concentrations ranging from 15 to 20 g L)1 during
fermentation (Montet et al., 2006). The salt tolerance
gives them an advantage over less tolerant species and
allows LA fermentation that inhibits growth of nondesirable organisms and activity of potential pectinolytic
and proteolytic enzymes that cause vegetable softening
(Rao et al., 2004). The strain Lb. plantarum MTCC 1407
could tolerate salt up to 10% (data not given) which was
conducive for SP fermentation.
Changes in titratable acidity
The initial TA value of raw material was somewhat low,
i.e. 0.75 g kg)1, for SP cubes and 0.12 g L)1 for brine
(Table 2) which increased significantly during the course
of fermentation (0–28 days). For example, at 4% brine
solution the TA values were 3.2 g kg)1 and 4.9 g L)1 for
SP LPs and brine, respectively, at the end of fermentation period. The treatment was more or less similar to
other brine concentrations. The anova analysis of LP
brine samples revealed that salt concentration had
significant effect on TA [F(5, 30) = 102.795,
P < 0.001]. To identify significant difference among
pairs, post-hoc comparisons were made using LSD. All
the salt concentrations, except 0% and 2%, differ
significantly from each other (P < 0.01; LSD). As the
days of fermentation increased, there was a significant
increase in TA [F(4, 30) = 536.701, P < 0.001]. Posthoc analysis showed significant differences in TA level
between 7 and 28 days of fermentation (P < 0.01;
LSD), whereas it did not differ between 14 and 21 days
(P = 0.28; LSD). In LP cubes, the salt concentration
significantly affected TA level, too [F(5, 30) = 249.619),
P < 0.001]. Post-hoc analysis revealed that all the salt
concentrations differed significantly (P < 0.05; LSD).
As the days progressed, there was a significant increase
2008 The Authors. Journal compilation 2008 Institute of Food Science and Technology
Anthocyanin-rich sweet potato lacto-pickle S. H. Panda et al.
)1
a
)1
Table 2 Titratable acidity (TA) concentrations of SP lacto-pickles (g kg ) and brine (g L ) during fermentation
Salt concentration (%)
7 Days
0
2
4
6
8
10
5.40
4.4 0
2.50
2.2 0
1.3 0
1.1
±
±
±
±
±
±
0.20 (5.90 ± 0.40)
0.30 (5.4 0 ± 0.20)
0.20 (4.30 ± 0.20)
0.10 (3.80 ± 0.30)
0.20 (3.20 ± 0.20)
0.2 (1.9 0 ± 0.10)
14 Days
21 Days
28 Days
5.80
4.60
2.80
2.60
2.20
1.6
5.20
4.80
3.40
2.90
2.50
2.0
4.70
4.50
3.20
2.80
1.70
1.5
±
±
±
±
±
±
0.30 (6.20 ± 0.40)
0.30 (5.90 ± 0.30)
0.20 (5.60 ± 0.30)
0.10 (4.40 ± 0.20)
0.10 (4.00 ± 0.20)
0.1 (2.8 0 ± 0.10)
±
±
±
±
±
±
0.20 (5.80 ± 0.30)
0.20 (5.30 ± 0.20)
0.10 (5.10 ± 0.20)
0.10 (4.90 ± 0.20)
0.20 (4.20 ± 0.20)
0.1 (2.70 ± 0.10)
±
±
±
±
±
±
0.20 (5.20 ± 0.20)
0.20 (5.30 ± 0.30)
0.20 (4.90 ± 0.30)
0.10 (4.60 ± 0.20)
0.10 (4.10 ± 0.10)
0.1 (2.70 ± 0.10)
±Standard deviations.
Initial (0 day) TA value of SP cubes was 0.75 g kg)1 and for brine was 0.12 g L)1.
a
Figures in parentheses indicate the corresponding values for lacto-pickle brine.
in TA level of LP cubes [F(4, 30) = 260.323),
P < 0.001]. Post-hoc comparisons revealed that TA
level significantly differed among the treatments
(P < 0.05; LSD). It appears that a significant amount
of organic acid was leached out of the SP into brine
which resulted in increase of TA in brine. The rate of
increase was maximum between 0 and 7 days as
compared with other period of incubation and TA
concentration did not vary substantially in the later
stage of fermentation (after 7 days). The increase in TA
during fermentation is normally associated with the
increase in organic acids mainly LA which minimises the
influence of spoilage bacteria (Steinkraus, 1997; Spyropoulou et al., 2001). Further the increase in TA was
inversely proportional to the increase in salt concentration in the LP brine as well as in the pickles. Maifreni
et al. (2004) reported a similar increase in TA during
fermentation of turnip (Brassica rapa) using a mixed
culture of lactobacilli (Lactobacillus spp., Pediococcus
spp., etc.).
LA concentration in brine was higher in comparison to
SP pickles. This study was a submerged fermentation of
SP in brine. Hence, it is presumed that most of the salt
added remained dissolved in brine and very less amount
was penetrated into SP pickles. As a consequence, there
might have been a difference in osmotic pressure
between LP brine and cubes causing leaching out a
substantial amount of LA from cubes into the brine to
maintain equilibrium (Montet et al., 2006). It was also
observed that in SP treated with 0% and 2% brine
solution, the LA concentration was higher in comparison to 8–10% brine concentrations. Higher salt concentration may have inhibited the growth of Lb.
plantarum (Gardner et al., 2001). Etchells et al. (1996)
reported an increase in LA during pure culture fermentation of green olives. Gardner et al. (2001) reported an
increase of LA during fermentation of cabbage, carrot,
beet and onion using a strain of Lb. plantarum NK312
as the inoculant. According to anova results, the salt
concentration [F(5, 30) = 101.362, P < 0.001] and
days of fermentation [F(4, 30) = 436.923, P < 0.001]
had significant effect on LA in LP brine samples. In salt
concentration, all the treatment combinations were
found to differ from each other in the mean values
(P < 0.05; LSD). In LP cubes, the anova established
the treatment means differed significantly for salt
concentration [F(5, 30) = 43.73, P < 0.001) and days
of fermentation [F(4, 30) = 242.95, P < 0.001]. Post-
Changes in lactic acid
Initially the LA concentration was almost negligible
(0.2 g kg)1 for SP cubes and 0.0 g L)1 for brine). But
after fermentation for 7 days with Lb. plantarum, the
LA concentration in the fermentation medium increased
significantly (Table 3). Further it was observed that the
)1
a
)1
Table 3 Lactic acid (LA) concentrations of SP lacto-pickles (g kg ) and brine (g L ) during fermentation
Salt concentration (%)
7 Days
0
2
4
6
8
10
1.20
1.10
0.80
0.6 0
0.40
0.90
±
±
±
±
±
±
14 Days
0.10
0.10
0.01
0.02
0.05
0.04
(1.80 ± 0.10)
(1.60 ± 0.20)
(1.3 0 ± 0.1)
(0.90 ± 0.01)
(0.70 ± 0.04)
(0.50 ± 0.04)
1.90
1.60
1.40
1.30
1.10
0.90
±
±
±
±
±
±
0.12
0.06
0.20
0.14
0.12
0.02
21 Days
(2.40
(2.20
(2.10
(1.80
(1.40
(1.20
±
±
±
±
±
±
0.10)
0.12)
0.13)
0.2)
0.02)
0.1)
2.20
2.00
1.70
1.50
1.30
1.10
±
±
±
±
±
±
0.12
0.02
0.03
0.12
0.12
0.12
28 Days
(3.50
(2.90
(2.70
(2.40
(2.00
(1.80
±
±
±
±
±
±
0.30)
0.13)
0.03)
0.2)
0.2)
0.05)
2.00
1.80
1.60
1.20
1.30
1.00
±
±
±
±
±
±
0.15
0.13
0.12
0.05
0.12
0.06
(3.10 ± 0.05)
(2.70 ± 0.03)
(2.6 0 ± 0.12)
(2.20 ± 0.03)
(1.90 ± 0.06)
(1.70 ± 0.12)
±Standard deviations.
Initial (0 day) LA value of SP cubes was 0.20 g kg)1 and for brine was 0.00 g L)1.
a
Figures in parentheses indicate the corresponding values for lacto-pickle brine.
2008 The Authors. Journal compilation 2008 Institute of Food Science and Technology
International Journal of Food Science and Technology 2009
449
450
Anthocyanin-rich sweet potato lacto-pickle S. H. Panda et al.
)1
a
)1
Table 4 Starch concentrations of SP lacto-pickles (g kg ) and brine (g L ) during fermentation
Salt concentration (%)
7 Days
0
2
4
6
8
10
165.3
158.0
146.2
134.3
123.9
122.0
±
±
±
±
±
±
14 Days
7.5
5.9
6.4
8.2
5.9
6.8
(23.4
(21.9
(18.5
(16.4
(15.8
(12.4
±
±
±
±
±
±
1.8)
1.9)
3.2)
2.8)
2.5)
0.4)
136.1
128.0
126.1
115.20
120.1
107.0
±
±
±
±
±
±
3.1 (20.1
6.4 (19.5
7.5 (15.2
6.1 (13.7
6.6 (10.4
6.10 (9.0
±
±
±
±
±
±
1.2)
2.3)
1.1)
1.4)
1.3)
0.8)
21 Days
28 Days
104.0
95.1
90.2
84.30
72.1
64.0
88.4
78.5
69.6
65.40
58.2
56.2
±
±
±
±
±
±
2.90 (18.9 ± 1.2)
0.1 (16.3 ± 1.4)
3.9 (13.1 ± 1.3)
3.4 (11.5 ± 1.8)
3.2 (8.6 ± 1.6)
3.4 (8.2 ± 0.5)
±
±
±
±
±
±
1.4
1.3
1.2
1.2
1.2
2.8
(17.4 ± 1.6)
(15.6 ± 1.5)
(12.8 ± 0.4)
(10.6 ± 0.2)
(7.5 ± 0.3)
(7.0 ± 0.1)
±Standard deviations.
Initial (0 day) starch value of SP cubes was 178.0 g kg)1 and for brine was 0.0 g L)1.
a
Figures in parentheses indicate the corresponding values for lacto-pickle brine.
hoc analysis revealed that both salt concentrations and
day means differed significantly (P < 0.05; LSD).
Changes in starch
Initially the starch content of SP cubes was 178.0 g kg)1.
After fermentation for 7 days the starch content
decreased marginally to 122–165.3 g kg)1 SP LP which
subsequently decreased significantly to 56.2–88.4 g kg)1
SP LP at the end of 28 days of fermentation depending
on the salt concentration in the brine (Table 4). Kim
et al. (2000) reported that tomato, carrot, Chinese
cabbage and spinach gave relatively higher fermentability than other vegetables (olive, beet, cucumbers, etc.) as
they have more fermentable saccharides. But the starch
concentration of brine during fermentation was very low
in comparison to SP pickles. It is because starch is
insoluble in cold water while some organic acids are
soluble. Therefore, the starch concentration in brine
containing exudate remained very low despite the high
concentration of starch in fermented SP pickles. The
decrease in starch concentration in SP pickles was
probably due to amylolytic activity of Lb. plantarum
(Morlon-Guyot et al., 2001; Naveena et al., 2004). The
strain Lb. plantarum MTCC 1407 used in our study is
amylolytic by virtue of processing a-amylase that
converts starch into sugar (Panda et al., 2006; Mohapatra et al., 2007). The anova results for LP brine
)1
samples indicated that both salt concentration [F(5,
30) = 30.428, P < 0.001] and days of fermentation
[F(4, 30) = 146.767, P < 0.001] were significant. Posthoc analysis revealed that salt concentration of 4% and
6% as well as 8% and 10% did not differ significantly
from each other. Starch content differed significantly on
0, 7 and 14 days (P < 0.001; LSD), and on 21 and
28 days showed no mean differences. Both salt concentration [F(5, 30) = 51.026, P < 0.001] and days [F(4,
30) = 593.893, P < 0.001] produced significant effects
on starch content of LP cubes. Post-hoc tests revealed
that salt concentrations of 6%, 8% and 10% did not
differ and mean values of all the days exhibited
significant mean differences (P < 0.001; LSD).
Changes in sugar
Table 5 shows the changes in sugar content of pickled
SP during LA fermentation. Sugar concentration was
found to decrease significantly with increase in the
duration of fermentation from 7 to 28 days. Lu et al.
(2001) reported a similar change during cucumber
fermentation using a strain of Lb. plantarum MOP3M6 as an inoculant. In LP brine samples, the anova
revealed that there was significant mean difference
among
salt
concentration
[F(5,
30) = 8.879,
P < 0.001] and days of fermentation [F(4,
30) = 251.893, P < 0.001]. Post-hoc tests indicated all
)1
a
Table 5 Total sugars concentrations of SP lacto-pickles (g kg ) and brine (g L ) during fermentation
Salt concentration (%)
7 Days
0
2
4
6
8
10
15.70
12.20
12.50
12.40
10.10
9.70
±
±
±
±
±
±
14 Days
0.40
2.10
1.10
1.30
2.80
1.60
(13.10 ± 0.80)
(12.10 ± 0.70)
(11.00 ± 0.50)
(10.04 ± 2.50)
(9.03 ± 0.40)
(7.84 ± 1.30)
11.20
11.40
9.16
8.87
8.33
7.27
±
±
±
±
±
±
1.70
2.80
1.50
1.40
2.30
1.20
21 Days
(5.20
(5.60
(4.12
(3.90
(2.50
(2.40
±
±
±
±
±
±
0.20)
0.30)
0.20)
0.80)
1.10)
0.10)
3.50
3.66
2.50
1.66
1.44
1.41
±
±
±
±
±
±
0.40
0.80
0.20
0.10
0.10
0.10
28 Days
(3.80
(3.20
(2.20
(3.40
(2.30
(2.10
±
±
±
±
±
±
0.30)
0.20)
0.20)
0.30)
0.20)
0.10)
1.66
1.39
1.27
1.19
1.13
1.10
±
±
±
±
±
±
0.20
0.80
0.20
0.20
0.30
0.20
(2.90
(2.40
(2.00
(2.10
(2.00
(2.20
±
±
±
±
±
±
0.50)
0.10)
0.30)
0.10)
0.20)
0.20)
±Standard deviations.
Initial (0 day) total sugar value of SP cubes was 26.00 g kg)1 and for brine was 0.00 g L)1.
a
Figures in parentheses indicate the corresponding values for lacto-pickle brine.
International Journal of Food Science and Technology 2009
2008 The Authors. Journal compilation 2008 Institute of Food Science and Technology
Anthocyanin-rich sweet potato lacto-pickle S. H. Panda et al.
the salt concentration levels significantly differed from
0% with only 10% was distinct from others (P < 0.05;
LSD). The sugar level significantly differed as the days
progressed with only 21 and 28 days remained same
(P < 0.01; LSD). In LP cubes, the anova showed
significant effects for salt concentration [F(5,
30) = 3.418, P < 0.05] and days of fermentation [F(4,
30) = 439.003, P < 0.001]. Post-hoc tests established
the salt concentration means were not different, whereas
days of fermentation showed significant differences
(P < 0.001; LSD).
concentration during all the days of fermentation
differed significantly (P < 0.001; LSD).
Proximate analysis
Preliminary studies showed that SP LP prepared with
8–10% brine was organoleptically most acceptable.
Further studies were made with LPs prepared with
these two salt concentrations. The proximate composition of pickled SP is shown in Table 7. As the
fermentation period increased, the organic matter, ash
and protein contents decreased significantly irrespective
of salt concentrations. However, there were no significant variations among calorific value and fat contents
during the fermentation period. Adeniyi et al. (2005)
reported a similar decrease in ash content during
spontaneous fermentation of Irish potato in brine
solution. The reduction in carbohydrates (organic matter) is an advantage and medically recommended for
diabetic patients (Kusano & Abe, 2000). The anova
results showed only days had significant effect on the
organic matter content of LP cubes [F(4, 15) = 3.395,
P < 0.05]. The ash, fat and protein content had
significant effect on both salt concentration [F(2,
15) = 15.297,
P < 0.001],
[F(2,
15) = 25.278,
P < 0.001] and [F(2, 15) = 13.141, P < 0.01] and days
[F(4, 15) = 29.212, P < 0.001], [F(4, 15) = 7.678,
P < 0.001] and [F(4, 15) = 42.782, P < 0.001], respectively. Besides, the ash and protein content at 7 and 14
as well as 21 and 28 days did not significantly differ from
each other. Two-way anova revealed that both salt
concentration and days of fermentation did not have
significant effect on calories.
Anthocyanin content
Initially the anthocyanin content of fresh SP cubes was
755 mg kg)1 which degrades to 690 mg kg)1 cubes
after blanching in hot water (Ahmed et al., 2004).
After 7 days of fermentation the anthocyanin concentration was found in the range of 418–654 mg kg)1 in
SP LP, which further decreased significantly at the end
of 28 days of fermentation to 104–421 mg kg)1 in SP
LP. Anthocyanin content in brine varied between 37
and 58 mg L)1 during 7–28 days of fermentation
(Table 6). After 28 days fermentation, there was more
pigment in SP pickles at 0% and 2% salt compared
with 4–10%, which may be explained by osmotic
pressure variations in different brine concentrations or
because of suppression of the growth of Lb. plantarum
MTCC 1407 at higher (8–10%) salt concentrations.
Anthocyanin concentrations of LP brine was significantly influenced by salt concentration [F(5,
30) = 7.093, P < 0.001] and days of fermentation
[F(4, 30) = 105.917, P < 0.001]. However, the interaction was not significant. All the salt concentration
and fermentation (days) means were not significantly
different from each other. Similarly, anthocyanin content of LP cubes was influenced by salt concentrations
[F(5, 30) = 11.276, P < 0.001] and days of fermentation [F(4, 30) = 279.874, P < 0.001]. Post-hoc tests
indicated that salt concentrations significantly differed
from each other (P < 0.05; LSD). Anthocyanin
Microbiology
There was a slight increase in lactobacilli population up
to 14 days of fermentation. After that, the population
remained more or less static up to 28 days (Table 8).
Further, Lb. plantarum MTCC 1407 culture was susceptible to the increase in salt up to 10% level. Similar
)1
)1
a
Table 6 Anthocyanin concentrations of SP lacto-pickles (mg kg ) and brine (mg L ) during fermentation
Salt concentration (%)
7 Days
0
2
4
6
8
10
654.10
598.20
564.00
487.80
423.40
418.00
14 Days
±
±
±
±
±
±
24.20
23.60
13.20
22.90
32.60
12.10
(58.40
(46.40
(39.00
(37.80
(37.60
(36.80
±
±
±
±
±
±
8.40)
5.20)
3.00)
11.70)
2.70)
1.50)
434.30
512.20
474.20
443.00
404.20
401.00
±
±
±
±
±
±
21 Days
12.90
33.20
25.90
27.40
21.70
21.40
(56.20
(44.20
(38.10
(37.20
(36.90
(36.70
±
±
±
±
±
±
8.10)
2.90)
6.80)
4.60)
4.50)
2.50)
298.50
456.00
433.20
412.40
394.60
392.20
±
±
±
±
±
±
28 Days
22.20
18.60
12.40
22.00
31.90
21.60
(48.90
(42.00
(38.00
(36.90
(36.70
(36.70
±
±
±
±
±
±
7. 10)
3.90)
3.70)
2.50)
2.50)
2.50)
104.80
264.30
421.00
409.30
390.10
390.00
±
±
±
±
±
±
6.40 (48.70 ± 2.10)
11.70 (42.00 ± 2.90)
10.10 (38.00 ± 1.70)
21.80 (36.70 ± 3.50)
31.90 (36.40 ± 2.40)
31.80 (36.60 ± 3.50)
±Standard deviations.
Initial (0 day) anthocyanin value of SP blanched cubes was 690.00 ± 15 mg kg)1 and for brine was 0.00 mg L)1.
a
Figures in parentheses indicate the corresponding values for lacto-pickle brine.
2008 The Authors. Journal compilation 2008 Institute of Food Science and Technology
International Journal of Food Science and Technology 2009
451
452
Anthocyanin-rich sweet potato lacto-pickle S. H. Panda et al.
Salt
concentration (%)
0
8
10
Days
Organic matter
(g kg)1)
Ash (g kg)1)
0
7
14
21
28
0
7
14
21
28
0
7
14
21
28
236.0
228.2
215.1
203.5
198.2
230.7
224.7
216.9
195.2
189.8
233.2
216.0
213.2
181.9
179.2
972.5
956.5
934.9
804.8
791.8
972.5
810.2
783.1
775.3
763.1
972.5
786.8
774.0
748.1
746.8
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
13.1
12.6
13.6
12.5
13.0
21.9
21.5
21.9
22.2
21.5
22.9
12.1
18.9
17.5
15.2
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
30.0
35.0
36.2
28.3
28.6
28.3
39.2
36.7
15.8
15.2
20.0
16.1
15.1
13.4
12.8
Fat (g kg)1)
Protein
(g kg)1)
Calories
(kcal g)1)
11.2
20.2
10.9
10.2
10.2
12.4
12.2
9.8
9.4
8.3
11.2
6.3
3.5
2.9
2.2
78.1 ±
51.3 ±
49.0 ±
32.4 ±
29.8 ±
72.4 ±
66.4 ±
59.4 ±
45.7 ±
32.4 ±
69.8±
45.3 ±
34.3 ±
27.1 ±
24.2 ±
3.69
3.59
3.74
3.78
3.69
2.98
3.07
3.64
3.10
3.10
3.20
3.17
3.12
3.09
3.04
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
1.3
4.9
1.2
1.3
1.2
2.5
1.3
0.9
0.8
0.5
0.8
0.8
0.4
0.5
0.7
4.9
3.8
3.5
2.5
1.4
5.2
10.3
4.2
3.6
3.5
6.9
4.2
3.3
3.2
2.2
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
Table 7 Proximate composition of SP
lacto-pickles during fermentation
0.6
0.5
0.3
0.5
0.3
0.5
0.3
0.4
0.3
0.2
0.5
0.5
0.6
0.4
0.3
±Standard deviations.
6
Table 8 Lactobacillus counts (1 · 10 ) of SP lacto-pickle
Fermentation (days)
Salt concentration (%)
7
14
21
28
0
8
10
12.2
14.4
10.5
16.8
16.2
13.7
18.2
16.9
12.4
18.9
15.8
12.6
findings were recorded with different strains of Lb.
plantarum (Hubert & Dupuy, 1994).
Sensory evaluation
A twenty-four member semi-trained sensory panel
evaluated the SP LPs prepared in 2–10% brine after
28 days of fermentation (Table 9). The sensory evaluaa
Table 9 Sensory evaluation of the SP lacto-pickles in different salt
concentrations
Salt concentrations (%)
Attributes
2
Texture (A)
Aroma (B)
Taste (C)
Colour ⁄
appearance (D)
Flavour (E)
After taste (F)
1.5
1.1
1.6
1.2
4
±
±
±
±
0.2
0.3
0.7
0.3
1.3 ± 0.5
1.5 ± 0.8
1.6
1.4
1.3
1.6
6
±
±
±
±
0.4
0.3
0.3
0.8
1.6 ± 0.8
1.6 ± 0.9
2.7
2.9
2.8
2.4
8
±
±
±
±
0.3
0.4
0.6
0.9
2.4 ± 0.9
2.8 ± 0.7
3. 6
4.5
3.1
3.6
10
±
±
±
±
0.6
0.7
0.8
0.3
3.8 ± 0.7
3.2 ± 0.6
3.8
4.7
4.3
3.6
±
±
±
±
0.7
0.8
0.5
0.3
4.2 ± 0.8
3.9 ± 0.7
±Standard deviations.
n = 48.
1, dislike extremely; 2, like moderately; 3, like much; 4, like very much; 5,
like extremely.
a
Values are means of the panelist’s scores.
International Journal of Food Science and Technology 2009
tion scores of antho-pickles at salt concentrations of
2–10% were subjected to one-way anova. The results
indicated that the salt concentrations had significant
effect on texture [F(4, 115) = 261.652, P < 0.001],
aroma [F(4, 115) = 567.104, P < 0.001], flavour [F(4,
115) = 106.679, P < 0.001], taste [F(4, 115) =
148.753, P < 0.001], colour [F(4, 115) = 85.172, P <
0.001] and aftertaste [F(4, 115) = 52.987, P < 0.001].
Post-hoc analysis revealed that only 2% and 4% were
not significantly different. All other combinations are
different from each other (P < 0.05; LSD). Although
the pickles prepared in 8% and 10% brine were equally
good in some aspects, taste and aftertaste-wise pickles
prepared in 10% brine were most preferred (Fig. 2).
Statistical evaluation of the results of the analytical and
proximal data of sweet potato lacto-pickles (prepared with
10% brine after 28 days fermentation)
The correlation analyses among the proximate + analytical variables are presented in Table 10. The most
important correlations were pH – TA (0.806), starch –
LA (0.781), organic matter – sugar (0.794), calories –
protein (0.902), ash – organic matter (0.842) and
fat – TA (0.914). Furthermore pH and TA were
significantly correlated with most of the attributes like
starch, fat, LA, calories and protein.
Using PCA, the original proximate and analytical
variables were reduced to three principal components
(PC 1–PC 3), which had eigenvalues larger than one and
retained for rotation. PC 1 accounted for 58%, whereas
PC 2 and PC 3 accounted for 24% and 9%, respectively,
of the total variations (Fig. 3).When combined, PC 1–
PC 3 together accounted for 91% of the total variations.
To assist interpretation of dimensions, the factor pattern
was rotated using varimax method. Based on the
2008 The Authors. Journal compilation 2008 Institute of Food Science and Technology
Anthocyanin-rich sweet potato lacto-pickle S. H. Panda et al.
Texture
5
4
3
Aftertaste
Aroma
2
2%
4%
6%
8%
10%
1
0
Flavour
Taste
Colour
Figure 2 Comparison of sensory scores of sweet potato (SP)
lacto-pickle prepared in various (2–10%) salt concentrations.
guidelines provided by Stevens (1992), an attribute was
considered to load heavily on a given component if the
factor loading was >0.72. A total of eleven proximate
and analytical attributes loaded heavily on three dimensions, while the loading of calories did not meet Stevens
guidelines (<0.72). Six analytical variables, i.e. pH
(+ve), TA (+ve), LA (+ve), starch (+ve), fat (+ve)
and protein (+ve) were loaded heavily on PC 1,
indicating strong correlations among these attributes.
Therefore, the combination of these variables loading on
PC 1 may be broadly referred to as the ‘taste axis’ or
‘nutrient axis’ as these components are responsible for
major nutrients in SP LP. Further interpretation reveals
that the factor loadings of sugar (+ve), organic matter
(+ve) and ash (+ve) may be designated as ‘carbon axis’
which were loaded on PC 2 and only anthocyanin ()ve)
was loaded heavily on PC 3 (‘colour axis’) despite
having higher factor values.
There are several studies where PCA was applied for
the evaluation in food product analysis. Destefanis et al.
(2000) used PCA for the study of relationships between
chemical, physical and sensory variables (eighteen variables) measured on various beef meat specimens. The
first three components accounted for 63% of the total
variance (PC 1, 34%; PC 2, 20.6% and PC 3, 38%).
Lawlor et al. (2003) used PCA for study of sensory
characteristics and consumer preference for cooked
chicken breasts from organic, corn-fed, free-range and
conventionally reared animals. PCA accounted for 74%
of the total variance. Elmore et al. (1999) have evaluated
the sensory characteristics of vanilla pudding to consumer responses using PCA and reduced sixteen attributes to just one independent component, which
accounted for 81% of the total variance. A total of
thirteen attributes loaded heavily on the dimensions. PC
1 accounted for 50%, whereas PC 2 and PC 3 accounted
for 18% and 13% of the total variance, respectively.
Harper et al. (1991) applied PCA for sensory ratings
of commercial plain yoghurts by consumers and
descriptive panels. The first principal component accounted for 27%, the second component for 22% and
the third for 12% of the total variance, respectively.
Similarly, Mohapatra et al. (2007) applied PCA in
analysing nutritional and proximate composition of
SW curd. PCA reduced the fourteen original analytical
(proximate) variables (starch, total sugar, LA, b-carotene, etc.) to four independent components (factors),
which accounted for 97% of the total variations. In the
present study, the six analytical variables were reduced
to just two by application of PCA.
Conclusions
The LP is rich in starch, sugar, anthocyanin pigment and
LA, which imparts flavour and sour taste and possesses
useful probiotic properties of LAB. Anthocyanin-rich SP
Table 10 Correlation coefficients for analytical + proximate variables of SP lacto-pickle
pH
TA
LA
Starch
Sugar
Anthocyanin
OM
Ash
Fat
Protein
Calories
1.000
0.806**
1.000
0.714
0.611
1.000
0.875**
0.670**
0.781**
1.000
0.175
0.372
0.308
)0.035
1.000
)0.361
)0.356
0.087
)0.304
0.271
1.000
)0.151
0.068
0.085
)0.396
0.744
0.332
1.000
)0.554*
)0.396
)0.169
)0.673**
0.544*
0.514*
0.842**
1.000
0.961**
0.914**
0.689**
0.831**
0.268
)0.379
)0.073
)0.516*
1.000
0.894**
0.907**
0.584*
0.833**
0.093
)0.466
)0.311
)0.695**
0.949**
1.000
0.717**
0.812**
0.365
0.708**
)0.116
)0.591*
)0.408
)0.763**
0.790**
0.902**
1.000
*Correlation is significant at the 0.05 level (two-tailed).
**Correlation is significant at the 0.01 level (two-tailed).
2008 The Authors. Journal compilation 2008 Institute of Food Science and Technology
International Journal of Food Science and Technology 2009
453
Anthocyanin-rich sweet potato lacto-pickle S. H. Panda et al.
1.00
OM
Sugar
Ash
Principal component 2
454
0.50
TA
Anthocyanin
LA
Fat
0.00
pH
Protein
Calories
–0.40
0.00
0.40
Principal component 1
LPs would be a novel product similar to lactic-fermented
cucumber, cabbage and garlic, and its regular consumption would be helpful in rectifying gastro-intestinal
disorders, aging and related ailments because of antioxidant principles. SP LPs prepared using Lb. plantarum
as the starter culture would be a good prospect for
commercialisation in small-scale industries.
Acknowledgments
The authors thank Dr S. Edison, Director of CTCRI,
for valuable suggestions and facilities and Dr S.K.
Sahoo for analysis of proximate composition of SP LP.
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International Journal of Food Science and Technology 2009
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Figure 3 Graphical representation of principal components (PC 1 vs. PC 2) of analytical + proximate variables of sweet potato
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