Profile of Sweet Potato Fermentation using Leuconostoc

Mesenteroides as a Starter

Neti Yuliana

, Dewi Sartika, Sutikno and Edo Jatmiko

Teknologi Hasil Pertanian (THP), Faculty of Agriculture, Universityu of Lampung,

Sumantri Brpjonegoro #1, Bandar Lampung, Inodonesia

Keywords: EPS, Fermentation Profile, Mesenteroides.

Abstract: This study aimed to know the fermentation profile of yellow sweet potato (total lactic acid bacteria, total non-

lactic acid bacteria, total lactic acid, pH, total exopolysaccharides, and morphology changing on starch

granules) using Leuconostoc mesenteroides as a starter. The sample's withdrawal was performed at 0, 24, 48,

and 72 hours. The results showed that during 72 hours fermentation time, there was a linearly decreased of

pH (minimum at pH 3.80), a linearly increased of total lactic acid (0.0023% /h), reducing sugars (0.26

mg/ml/h), crude exopolysaccharides (EPS) (0.017 g/l/h), and total Lactic Acid Bacteria (LAB) (maximum at

log 8.40 cfu/ml), as well as a decreased of non-Lactic Acid Bacteria. Leuconostoc mesenteroides had

significant effect on granule of yellow sweet potato. There was an alteration of starch granules at the end of

fermentation time (at 72 hours).

1 INTRODUCTION

Yellow sweet potato is a source of carbohydrates, so

that it has good potential to be developed in support

of food diversification programs. Yellow sweet

potato is also a beta-carotene (provitamin A) sources

(Kammona et al., 2015). Some examples of sweet

potato-based processed products are baby food, salad

dressings, cake mix (Anggraeni & Yuwono, 2014),

pickle (Oke & Workneh, 2013; Oloo, 2013; Neti

Yuliana et al., 2013), and processing based on sweet

potato flour (Sebben et al., 2017). To produce more

applicable sweet potato flour, a modification process

is required. Modification of sweet potato flour can be

done by fermentation of lactic acid (Ajayi et al., 2016,

2018; Liao & Wu, 2017; Yuliana et al., 2018; .

Yuliana et al., 2017; Yuliana et al., 2014) The

application of lactic fermentation in flour

modification will produce flour that is easy to expand

and tastes better. Besides, fermentation with the help

of specific lactic acid bacteria has the advantage of

being able to produce exopolysaccharides (EPS)

(Yuliana et al., 2020; Zubaidah et al., 2014) which

have many benefits, including improving the

properties of flour..

https://orcid.org/0000-0003-2759-7735

The lactic acid fermentation process can occur with

the help of a lactic acid bacteria starter (LAB). One of

the LABs that produce EPS is Leuconostoc

mesenteroides (Li et al., 2020; Taylan et al., 2019).

These bacteria include heterofermentative lactic acid

bacteria, which break down glucose and produce 50%

lactic acid, ethanol, acetic acid, glycerol, mannitol,

and CO2 (Mora-Villalobos et al., 2020). In addition

to Leuconostoc mesenteroides, a lactic acid bacterial

starter can be obtained from a pickle liquid starter

with added salt (Yuliana et al., 2018). Lactic acid

bacteria can also be obtained from a spontaneous

fermentation process with added salt. In this study,

sweet potato fermentation was carried out using the

starter Leuconostoc mesenteroides from the culture

collection unit.

The success of the lactic acid fermentation

process is strongly influenced by optimizing the

desired LAB growth factors. These factors then

provide different conditions according to the LAB

environment, which ultimately affects the

fermentation process. Each LAB starter will also

show different growth patterns, the period needed to

grow and adapt, and the resulting metabolites (Yang

et al., 2018). Information about growth patterns and

metabolites produced is needed to determine the

Yuliana, N., Sartika, D., Sutikno, . and Jatmiko, E.

Proﬁle of Sweet Potato Fermentation using Leuconostoc Mesenteroides as a Starter.

DOI: 10.5220/0010514200003108

In Proceedings of the 6th Food Ingredient Asia Conference (6th FiAC 2020) - Food Science, Nutrition and Health, pages 64-68

ISBN: 978-989-758-540-1

fermentation efficiency as the growth and formation

of products affect the responsiveness of cells. During

growth, microorganisms require a substrate as the raw

material used for cell multiplication and the formation

of metabolite products (Utami et al., 2012; Zubaidah

et al., 2014) Thus, the fermentation profile related to

growth patterns, substrate consumption, and

metabolite production is needed to determine

fermentation's optimum conditions.

Fermentation of sweet potatoes using a starter of

lactic acid bacteria to improve the characteristics of

sweet potato flour has been reported (El Sheikha &

Ray, 2017). Yuliana et al., (2013) examined the

fermentation of yellow sweet potato pickles using

mixed LAB cultures, which produced the best

characteristics of pickles organoleptically with a total

lactic acid value of 0.5%, pH 3.39, and a total lactic

acid bacteria of 8.46 log CFU / mL. So far, research

on the sweet potato fermentation process has been

done a lot, but it is still limited to white sweet

potatoes. There is no information regarding the

growth patterns of lactic acid bacteria, changes in

starch granules, and exopolysaccharides during

yellow sweet potato fermentation. So that in this

study, the fermentation profile of yellow sweet potato

with the starter of lactic acid bacteria Leuconostoc

mesenteroides as a starter was studied

2 MATERIALS AND METHOD

2.1 Materials

The main ingredient used in this study was a yellow

sweet potato purchased at the traditional market in

Bandar Lampung, Indonesia. Leuconostoc

mesenteroides FNCC-0023 was from PAU Pangan

dan Gizi, University of Gajah Mada, Indonesia.

Media used were MRS broth, and MRS agar.

2.2 Method

The sweet potatoes were washed, peeled, sliced, and

added to glassware containing a boiled solution of

salt-sugar and were left at room temperature. The

sweet potato slices were fermented with Leuconostoc

mesenteroides FNCC-0023 as starters.. Observations

were performed on total LAB (Yuliana et al., 2013),

and biochemical changes: pH, total acidity as % of

lactic acid, total glucose of supernatant (phenol-

sulphuric method), and amount of crude

exopolysaccharide (Razack et al., 2013) 2013).

Sampels were withdrawal at 0 hours (H0), 24 hours

(H24), 48 hours (H48), and 72 hours (H72). A 72

hours of fermentation was selected for observation of

change in sweet potato starch granule by using

scanning electron microscopy.

2.3 Data Analysis

Experimental unit was repeated three times. All data

were analyzed to find the average and subjected to

polynomial trend line to find either linearly or

quadratically pattern in which the rate of the

parameter observed was determined.

3 RESULTS AND DISCUSSION

3.1 Change of Lactic Acid Bacteria,

Total Lactic Acid and Ph

During fermentation process, LAB utilized starch and

sugar in yellow sweet potato as an energy source for

cell multiplication and produced metabolites such as

lactic acid (Oloo, 2013) and exopolysaccharides

(Zubaidah et al., 2014) and resulting in a decrease in

pH (Yuliana et al., 2013). LAB activity will degrade

and modify starch granules (Liao & Wu, 2017;

Yuliana et al., 2014) and leave reducing sugars.

(Yuliana et al., 2013) The data recapitulation of

biochemical changes during fermentation is

presented in Figure 1.

There was a linear increase in total lactic acid

from 0.61 to 1.802% during fermentation. On the

other hand, there was a linier decreased in pH from

point 4.9 to 3.6. An increase of total lactic acid during

fermentation occurred at a rate of 0.2%, as

Leuconostoc mesenteroides FNCC-0023 starter

activity.

Figure 1: Trend line of pH, Lactic Acid Bacteria, Total

Lactic Acid, EPS and Reducing Sugar during Fermentation

of Yellow Sweet Potato with Leuconostoc mesenteroides.

Proﬁle of Sweet Potato Fermentation using Leuconostoc Mesenteroides as a Starter

Figure 1: Trend line of pH, Lactic Acid Bacteria, Total

Lactic Acid, EPS and Reducing Sugar during Fermentation

of Yellow Sweet Potato with Leuconostoc mesenteroides

(cont.).

The lowest pH value and the highest total acid

occurred at 72 hours of fermentation. The same

pattern was reported by (Oloo, 2013). In the

fermentation of orange sweet potatoes, there was an

increase in lactic acid's total content and a decrease in

pH during fermentation. The decrease in pH during

fermentation is caused by the accumulation of organic

acids, especially lactic acid produced by Leuconostoc

mesenteroides FNCC-0023.

During fermentation, the total LAB also increased

quadratically and reduced non-lactic acid bacteria

(Table 2). Addition of Leuconostoc mesenteroides

starter treatment increased the LAB population, and

then it was stationary until 72 hours. The growth of

LAB in yellow sweet potato fermentation have time

incubation dependent. The growth pattern of

Leuconostoc mesenteroides increased from 0 to 24

hours and afterward tended to be stationary from 24

hours to 72 hours. (Yuliana et al., 2013) study

showed that the growth pattern of Leuconostoc

mesenteroides continues to increase up to 12 days of

fermentation.

At the beginning of the yellow sweet potato

fermentation (0 hours), besides LAB, non-lactic acid

bacteria colonies were also found, namely mold, with

an average of 2 log CFU / mL. The addition of starter

cultures can cause the desired microbial dominance

and suppress the growth of competing microbes.

During fermentation, LAB experiences growth by

utilizing sugar sources as energy or nutrition. The

simple sugars that are used for the development of

LAB are partially converted into organic acids such

as lactic acid (Oloo, 2013) and then LAB produces

crude exopolysaccharides which are secreted outside

the cell. In this study, there was an increase in

residual reducing sugar and an increase in lactic acid

and EPS production during fermentation. Consent

ensures that the publisher has the Author’s

authorization to publish the Contribution.

The length of fermentation has a very significant

effect on the value of reducing sugar residual

fermentation of yellow sweet potato which increases

at a rate of 26.13%. The residual reducing sugar

content increased linearly with fermentation time

(Table 1). The residual reducing sugar in yellow

sweet potato fermentation could come from the starch

and sugar contained in the yellow sweet potato tissue.

Sanoussi et al., (2016) states that yellow sweet potato

contains starch 172.87-326.73 mg/g (DW) and total

sugar 24.23-42.64 mg/g (DW). During fermentation,

yellow sweet potato starch is degraded by enzymes

both from sweet potatoes and LAB into horter chains

(simple sugar) (Guo et al., 2019). The simple sugar is

then used by Leuconostoc mesenteroides FNCC-0023

6th FiAC 2020 - The Food Ingredient Asia Conference (FiAC)

as a source of energy or nutrition for its growth. Apart

from being used for the development of LAB, some

of the simple sugars will be converted into organic

acids such as lactic acid (Oloo, 2013). During

development, LAB produces exopolysaccharides and

is secreted outside the cell. The exopolysaccharide

level analysis showed the EPS value of yellow sweet

potato fermentation increased linearly during

fermentation at a rate of 1.6%. The results of this

study are in line with previous research which states

that EPS production with lactic acid bacteria will

increase with the length of incubation time (Onilude

et al., 2013; (Zubaidah et al., 2014) .

3.2 Morphology of Starch Granula

The results of Scanning Electron Microscopy can be

seen in Figure 2.

Figure 2a: Morphology of starch granule of yellow sweet

potatoes before fermentation (Magnification 2000 X).

Figure 2b: Morphology of starch granule of yellow sweet

potatoes after 72 hours fermentation (Magnification 2000 X).

Figure 1a shows the appearance of yellow sweet

potato starch granules (control), which do not look

hollow. Meanwhile, the yellow sweet potato starch

granules changed shape at the end of the fermentation

time (t = 72 hours), which was degraded by

Leuconostoc mesenteroides (2b).

The granule structure of control yellow sweet

potato starch and fermented starch resulted in a

significant difference in appearance and shape when

identified by Scanning Electron Microscopy. Figure

2b confirmed that there was a change in the starch

granule structure. Similar results were reported by

(Liao & Wu, 2017) on Lactobacillus plantarum

fermented yellow sweet potato starch granules.

(Yuliana et al., 2014) also reported spontaneous

fermentation of white sweet potato, causing starch

granules changes. According to (Liao & Wu, 2017),

the prolonged treatment of fermentation destroys the

crystal structure of yellow sweet potato starch and

significantly affects the crystalline and amorphous

parts. This change is thought to be caused by the

activity of lactic acid bacteria. Yuliana et al., (2014).

stated that the size of the starch granules in the

fermentation process of white sweet potato changes

after the fermentation process, which causes changes

in the amorphous structure of starch granules, size of

starch granules, chemical composition, and also

modifies the physical and rheological characteristics

of white sweet potato starch.

The form should be completed and signed by one

author on behalf of all the other authors. Figure 2.

Morphology of starch granule of yellow sweet

potatoes (magnification 2000 X).

4 CONCLUSIONS

The fermentation profile of yellow sweet potato with

starter Leuconostoc mesenteroides is as follows:

during fermentation, there was a linear increase in

total lactic acid (at a rate of 0.1%), residual reducing

sugar (at a rate of 26.13%), crude EPS (at a rate of

1.6%), and quadratically lowering the pH (with the

lowest point at pH 3.80) with total LAB (optimum at

8.63 log CFU / mL) and a decrease in non-LAB. The

morphology of yellow sweet potato starch granules

fermented with Leuconostoc mesenteroides starter

during 72 hours of fermentation caused starch

granules changes.

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