
Lactic acid bacteria in traditional cheeses / Kalkan et al._______________________________________________________________________________
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INTRODUCTION
Cheese is a food product with high nutritional value, obtained
by pre–treating milk and usually fermenting it, and consumed
with pleasure all over the world. In addition, cheese is one of
the oldest fermented food products made by human [1]. France,
Netherlands, and Italy were famous for cheeses. Also, Turkey is
a very rich country in terms of cheese diversity [2]. Nowadays,
4,000 different variety of cheese are present in the world. Turkey
manufactures approximately 200 variety of cheese [3]. Although
the production methods of these cheese varieties are similar to
each other, their chemical, physical and sensory properties vary
depending on the milk, microflora or starter culture, environmental
factors such as climate and region. The Black Sea Region is one of
the regions of Turkey with rich cheese varieties. More than 30 types
of cheese are manufactured in this region. The most well–known
cheese types in the Black Sea Region are Civil Cheese, Kargi Tulum
Cheese, Imansiz Cheese, Kurchi Cheese, Minzi Cheese and Kolot
Cheese [4]. Kargı Tulum Cheese is a traditional cheese originating
from the Kargı district in Çorum province, Turkey. It is crafted using
a variety of milks, such as cow, sheep, or buffalo milk, depending
on local availability and preferences. It is typically made from
milk collected during the autumn season, which contributes to
its rich, high–fat content. Telli cheese is a traditional cheese from
the central districts of Trabzon and Artvin, as well as the Sürmene
and Akçaabat administrative districts of Trabzon in Turkey. It is
made primarily from cow’s milk. Telli cheese has thicker threads
compared to the thinner threads of Civil Cheese, which is also
sourer and salt–free in flavor. Artvin Şor cheese is made in the
Savsat district of Artvin and its vicinity. Its name derives from the
word Şor which means “bitter” in the region. This cheese is of a
dark yellow color, is very salty and has a bitter taste [4].
In recent years, due to the increasing demand of consumers
for natural products, interest in local cheese varieties has
increased [5]. It is possible that local cheese varieties will be
produced industrially and delivered much more and subsequently
become a demanded product in the world market [6]. However,
cheese industrially produced with starter cultures is different
from traditional cheese with spontaneous lactic microflora
(i.e. nonstarter lactic acid bacteria) regarding sensory quality
properties. Starter lactic acid bacteria (LAB) are deliberately added
to the milk for the production of acid during cheese processing.
However, nonstarter lactic acid bacteria or indigenous microflora
are inherently present in raw milk and play an important role in
the developing of cheese flavor [3, 7].
The presence of numerous enzymes and indigenous lactic acid
bacteria in milk improves quality properties of traditional cheeses.
Native LAB develop texture and flavour properties of cheeses with
microbiological and biochemical changes [7]. In industrial cheese
production, the main lactic acid bacteria utilized as starter cultures
are Lactobacilus casei, Lactobacillus helveticus and Lactobacillus
delbrueckii subsp. bulgaricus [8]. In order to produce traditional
cheese industrially, it is essential to determine the microflora of
the local cheese. Additionally, the characterization of the dominant
microflora provides whether it is possible to use as a starter culture
[9]. Recently, molecular methods have been utilized to identify
lactic acid bacteria. Especially, the sequences of the gene 16S
of the ribosomal RNA is highly effective method to describe the
phylogenetic degree of relatedness among bacteria. Hence, 16S
rRNA sequence analysis has been progressively performed to
characterize the bacterial diversity of various cheeses [10].
The dairy industry works with the limited variety of starter
cultures. However, there is a need for indigenous LAB strains as
starters to produce more flavorful cheeses [11]. A few studies
have reported to determine indigenous lactic acid bacteria in the
traditional cheese of the black sea region. This research aims to
identify lactic acid bacteria in the traditional cheese of the black
sea region by using PCR based molecular techniques.
MATERIALS AND METHODS
Cheese samples
Cheese samples were obtained from Black Sea Region in Turkey.
Traditional Turkish cheeses of Black Sea Region used in this study
are Telli cheese (TP) from Tonya/Trabzon, Şor cheese (AŞ) from
Artvin, Tecen cheese (TC) from Giresun, Kargı Tulum cheese (KT)
from Kargı/Çorum and Kesik cheese (OK) from Ordu.
Isolation and enumeration of lactic acid bacteria in traditional
cheeses
Cheese sample (25 g) was diluted with 225 mL of peptone
water (Sigma) and then homogenized with stomacher for 2 min
at 10 strokes per second. Serial dilution method is used for the
enumeration of lactic acid bacteria. Using a 1/10 dilution rate, the
homogenate was diluted to a dilution level of 10
7
. By taking 0.1 mL
from the appropriate dilutions, the homogenate was cultivated in
petri dishes containing the selective medium. The two selective
media were utilized for enumeration and isolation of bacteria. LAB
with mainly lactococci are grown on M17 agar acc. to TERZAGHI
(M17 Agar, Merck, Germany) at 30°C for 48–72 h under anaerobic
conditions; LAB with mainly lactobacilli are grown on de MAN,
ROGOSA and SHARPE (MRS) Agar (Merck, Germany) at 37°C for
48–72 h under anaerobic conditions. For anaerobic conditions,
anaerobic jars and anaerocult A were applied. Following incubation,
the colonies grown on M17 and MRS plates were enumerated.
From each cheese sample, approx. Ten colonies with distinct
morphological characteristics were selected from MRS and M17
agar plates and subsequently transferred to fresh plates for further
purication. The assessment of Gram–positive and catalase–
negative colonies was performed in a medium containing 6.5%
and 18% NaCl and at temperatures of 10 and 45°C, at pH 4.4
and pH 9.6. Furthermore, CO
2
production as a result of glucose
metabolism of the isolates and arrangement of cells (tetrad form,
chain form) was assessed. Gram–positive and catalase negative
pure isolates were selected from all cheese samples, and they were
stored at -20°C (Arçelik, 4252EY, Türkiye) with glycerol (Merck,
Darmstadt, Germany) stocks [7, 12, 13].
Extraction of bacterial DNA from pure isolates of cheese samples
Bacterial DNA from pure isolates was extracted using method
described in previous studies [7, 14, 15]. 2 mL overnight culture were
obtained for total DNA extraction. Microbial cells were centrifugated
(Hermle Z326K, Germany) for 5 min at 4,000 g at 4°C. Supernatant
was poured and then the pellets were resuspended in 500 μL of the
lysis buffer. After incubation (Nuve ES 120 cooled incubator, Türkiye)
for 10 min at 65°C, 150 μL potassium acetate was added. The mixture