Reference number  
DRS 49:2017  
© RSB 2017  
 
 
 RWANDA 
STANDARD  DRS 
49 
 
Second edition  
2017 -mm-dd 
 
Yoghurt — Specification  
 
  DRS 49:2017  
©RSB 2017 - All rights reserved                  ii 
 In order to match with technological development and to keep continuous progress in industries, 
standards are subject to periodic review. Users shall ascertain that they are in possession of the latest 
edition  
 
 
 
 
 
 
 
 
© RSB 2017  
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized 
in any form or by any means, electronic or mechanical, including photocopying and microfilm, without 
prior written permission from R SB. 
Requests for permission to reprodu ce this document should be addressed to : 
Rwanda Standards  Board  
P.O Box 7099 Kigali -Rwanda  
KK 15 Rd, 49  
Tel. +250 252 586103/ 582945  
Toll Free: 3250  
E-mail: info@rsb.gov.rw  
Website: www.rsb.gov.rw  DRS 49:2017  
iii                ©RSB 2017 - All rights reserved  
 Contents  Page 
1 Scope  ................................ ................................ ................................ ................................ ......................  1 
2 Normative references  ................................ ................................ ................................ ............................  1 
3 Term s and definitions  ................................ ................................ ................................ ...........................  2 
4 Requirements  ................................ ................................ ................................ ................................ .........  3 
4.1 Ingredients  ................................ ................................ ................................ ................................ .............  3 
4.1.1  Essential ingredients  ................................ ................................ ................................ ............................  3 
4.1.2  Optional ingredients  ................................ ................................ ................................ ..............................  4 
4.2 General requirements  ................................ ................................ ................................ ...........................  5 
4.3 Composition of Yoghurt  ................................ ................................ ................................ .......................  5 
4.3.1 Plain Yoghurt  ................................ ................................ ................................ ................................ .........  5 
4.3.2  Sweetened and flavoured Yoghurt  ................................ ................................ ................................ ...... 5 
4.3.3  Fruit Yoghurt  ................................ ................................ ................................ ................................ ..........  6 
4.3.4  Heat treated yoghurt  ................................ ................................ ................................ .............................  6 
4.4 Microbiological requirements  ................................ ................................ ................................ ..............  6 
5 Food additives  ................................ ................................ ................................ ................................ ....... 6 
6 Contaminants  ................................ ................................ ................................ ................................ .........  7 
6.1 Heavy meta ls ................................ ................................ ................................ ................................ ..........  7 
6.2 Pesticide and veterinary drug residues  ................................ ................................ ..............................  7 
6.3 Aflatoxins  ................................ ................................ ................................ ................................ ...............  7 
7 Hygiene  ................................ ................................ ................................ ................................ ...................  7 
8 Packaging  ................................ ................................ ................................ ................................ ...............  7 
9 Labelling  ................................ ................................ ................................ ................................ .................  7 
10 Sampling  ................................ ................................ ................................ ................................ ................  8 
Annex  A (normative )  Identification of Lactobacilus bulgaricus  and Streptococcus thermophiles   
as characteristic microorganisms in yoghurt  ................................ ................................ ....................  9 
A.1 Scope ................................ ................................ ................................ ................................ ......................  9 
A.2 Definition  ................................ ................................ ................................ ................................ ................  9 
A.3 Principle of the method ................................ ................................ ................................ .........................  9 
A.4 Isolation of colonies  ................................ ................................ ................................ ..............................  9 
A.5 Phenotypic characteristics required for proper identification of l. bulgaricus;  .............................  9 
A.5.1  Recommended culture media.  ................................ ................................ ................................ .............  9 
A.5.2  Characteristics to consider  ................................ ................................ ................................ ................  10 
A.6 Phenotypic characteristics required for a proper Ident ification of S.hermophilus . .....................  11 
A.6.1  Recommended culture media.  ................................ ................................ ................................ ...........  11 
A.6.2  Characteristics to consider:  ................................ ................................ ................................ ...............  11 
A.7 Expression of results  ................................ ................................ ................................ ..........................  12 
A.7.1  Recommended culture media.  ................................ ................................ ................................ ...........  12 
A.7.2  Characteristics to consider  ................................ ................................ ................................ ................  12 
A.8 Expression of results  ................................ ................................ ................................ ..........................  13 
 DRS 49:2017  
©RSB 2017 - All rights reserved                  iv 
 Foreword  
Rwanda Standard s are prepared  by Technical Committees and approved by R wanda Standards Board (RSB) 
Board  of Directors in accordance with the procedures of RSB, in compliance with Annex 3 of the WTO/TBT 
agreement on the preparation, adoption and application of standards.  
The ma in task of technical committees is to prepare national standards.  Final Draft Rwanda S tandards 
adopted by Technical committ ees are ratified  by me mbers of RSB Board of Director s for publication and 
gazettment as Rwanda Standards.  
RS 49 was prepared by Techn ical Committee RSB/TC 004, Milk and milk products . 
In the preparation of this standard, reference was made to the following standard  (s): 
1) KS 05 -34, Yoghurt — Specification  
2) SAZS 792 , Yoghurt — Specification  
The assistance de rived from the above source is hereby acknowledged with thanks.  
This second  edition cancels and replaces the first  edition (RS  49:2012 ), which has been  technically revised.  
Committee membership  
The following organizations were represented on the Technical Committee on Milk and milk prod ucts (RSB/TC 
004) in the preparation of this standard.  
Enterprise Urwibutso   
Global Trading Impex Serena Nice Cream (GTI)  
Inyange Industries  
Laiterie Nyabisindu  
Ministry of Agriculture (MINAGRI/RALIS)  
Agashinguracumu Ltd  
Rwanda Consumer’s Rights Protection  Organization (ADECOR)  
Rwanda National Dairy Platform (RNDP)  DRS 49:2017  
v                ©RSB 2017 - All rights reserved  
 Rwanda  Standards Board (RSB) – Secretariat  
 DRS 49:2017  
1                ©RSB 2017 - All rights reserved  
 Yoghurt  — Specification  
1 Scope  
This standard specifies requirements, sampling and test  methods  for yoghurt.  
This standard  shall apply to different types of yoghurt  such as plain, sweetened, fruit, flavo ured, and heat 
treated.  
2 Normative references  
The following docum ents are referred to in the text in such a way that some or all of  their content constitutes 
requirements of this document.  For dated references, only the edition  cited applies. For undated references, 
the latest edition of the referenced document (includi ng any amendments) applies.  
CODEX STAN 193, Codex general standard for contaminants and toxins in foods  
ISO 14501 , Milk and milk powder -- Determination of aflatoxin M1 content -- Clean -up by immunoaffinity  
chromatography and determination by high -performance liquid chromatography  
ISO 8069,  Dried milk -- Determination of content of lactic acid and lactates  
ISO 9232 , Yogurt -- Identification of characteristic microorganisms (Lactobacillus delbrueckii subsp. bulgaricus 
and Streptococcus thermophilus)  
ISO/TS 11869, Fermented milks -- Determination of titratable acidity -- Potentiometric method  
RS CAC/RCP 1, General Principle for Food Hygiene.  
RS CODEX STAN 192 , Codex general standard for food additives  
RS CODEX  STAN 212 , Sugars –Specification   
RS EAS 38 , General standard for labelling of pre -packaged foods  
RS ISO 10560, Milk and milk products – Detection of Listeria monocytogenes  
RS ISO 11290 -2, Microbiology of food and animal feeding stuffs — Horizontal method for the detection and 
enumeration of Listeria monocytogenes —Part 2: Enumeration method  
RS ISO 11866 -2, Milk and milk Products -Enumeration of presumptive Escherichia coli -part 2: colony -count 
technique at 44oC using membranes  
RS ISO 2446, Milk — Determinat ion of fat content (Routine method)   
©RSB 2017 - All rights reserved                  2 
 RS ISO 3728, Ice-cream and milk ice -- Determination of total solids content (Reference method)  
RS ISO 6579 -1, Microbiology of the food chain -- Horizontal method for the detection, enumeration and 
serotyping of Salmonel la -- Part 1: Detection of Salmonella spp.  
RS ISO 6611, Milk and milk products - Methods of microbiological examination part 3: Enumeration of colony 
forming units of yeasts and/or moulds -colony -count technique at 25  degrees celcius   
RS ISO 707, Milk and milk products — Guidance on sampling  
3 Terms and definitions  
For the purposes of this standard, the follow ing terms and definitions apply.  
3.1 
yoghurt  
coagulated milk product obtained by lactic acid fermentation through the action of Lactobacillus bulgaricus  and 
Streptococcus thermophillus  and other suitable bacteria  from milk products which have been pasteurized prior 
to fermentation.  
Note: Other suitable bacteria may be other Lactobacilli  spp and Bifidobacteria  are also sometimes added during or after 
cultu ring yogurt.  
3.2  
plain Yoghurt  
yoghurt as defined in clause 3.1 to which no sugar and food additives have been added  
3.3  
fruit Yoghurt  
yoghurt as defined in clause 3.1 to which fruits have been added to characterize the flavour  
3.4  
flavoured Yoghurt  
yoghurt as defined in clause 3.1 to which flavouring essences, foods or ingredients have been added with or 
without added sugars and/or colouring substances to characterize the flavour  
3.5  
sweetened Yoghurt  
natural yoghurt as defined in clauses 3.1 to 3.4  which carbohydrate sugar has been added  DRS 49:2017  
3                ©RSB 2017 - All rights reserved  
 3.6  
heat-Treated Yoghurt  
yoghurt as defined in clauses 3.1. to 3.4 which has been subjected to heat treatment after fermentation. It may 
not contain viable and abundant micro -organisms  
3.7  
pasteurized yoghurt  
yogh urt which has been subjected to a pasteurization process for the purpose of destroying most of the micro -
organisms and extending the shelf life.  
3.8  
thermized yoghurt  
yoghurt that has been heat -treated aimed at reducing the number of viable organisms and prolonging shelf -
life. 
4 Requirements  
4.1 Ingredients  
All ingredients used for the manufacture of yoghurt shall be of good quality  and shall comply w ith the relevant 
standards.  
4.1.1  Essential ingredients  
All yoghurts shall be made from any of the following milk and milk products and essential additions. The basic 
mix ingredients shall be pasteurized before fermentation.  
4.1.1.1  Milk and milk products  
Those products include:  
a) pasteurized milk;  
b) evaporate or condensed milk;  
c) pasteurized partly skimmed milk;  
d) evaporated or condense d partly skimmed milk;  
e) pasteurized skimmed milk;  
f) evaporated or condensed skimmed milk;   
©RSB 2017 - All rights reserved                  4 
 g) pasteurized cream; and  
h) a mixture of two or more products.  
4.1.1.2  Yoghurt cultures  
The following cultures shall be added to all types of yoghurt:  
a)  Cultures of Lactobacillus b ulgaricus ; and  
b) Streptococcus thermophillus  
4.1.2  Optional ingredients  
The following ingredients may be added to all types of yoghurts. Those include but are not limited to:  
4.1.2.1 Milk products which shall have been pasteurized in their production : 
a) milk pow der; 
b) skimmed milk powder;  
c) unfermented buttermilk;  
d) concentrated whey;  
e) whey proteins;  
f) whey protein concentrates;  
g) water soluble milk proteins;  
h) edible casein; and  
i) caseinates.  
4.1.2.2 Other suitable lactic acid producing bacteria cultures in addition to those in 4.1.1.2  
4.1.2.3 Sugars (in sweetened types of yoghurt only), complying with RS CODEX STAN 212.  
4.1.2.4 Permitted flavours conforming to RS CODEX STAN 192  DRS 49:2017  
5                ©RSB 2017 - All rights reserved  
 4.2 General requirements  
Yoghurt shall : 
a) be free from off flavours and off odours  such as m etallic flavour or yeast flavour;  
b) be free from foreign matter ; 
c) have the cha racteristic taste and flavour o f the type of yoghurt;  
d) be free from bitterness;  and  
e) be free from coarseness due to over ripening . 
4.3 Composition of Yoghurt  
All types of yoghurt when tested acc ording to Annex A shall contain characteristic microorganisms of 
L.bulgaricus  and S. thermophilus.  Other compositional factors may vary depending on the milk fat content of 
the milk part of yoghurt.  
4.3.1  Plain Yoghurt  
When tested in accordance with appropriate test methods, plain yoghurt shall comply with the requirements 
specified in t able 1.  
Table 1 ▬ compositional requirements for plain yoghurt  
S/N  Characteristic  
 Whole milk 
Yoghurt  
 Partially  
skimmed milk  
yoghurt  Skimmed milk  
Yoghurt  
 High fat  
yoghurt  Test method  
i.  Milk fat % m/m  3.0- 7 >0.5 -<3 0.5(min)  7 (min)  RS ISO 2446  
ii.  Milk solids not fat % 
m/m ,min 8.5 8.5 8.5 8.5 RS ISO 3728  
iii.  Titratable acidity % 
lactic acid  0.6 – 1.2 0.6 – 1.2 0.6 – 1.2 0.6 – 1.2 ISO/TS 11869  
iv.  Lactobacillus 
Bulgaricus  and 
Streptococcus 
Thermophillus per g , 
min 107 107 107 107 Annex A / ISO 
9232  
4.3.2  Sweetened and flavoured Yoghurt  
When tested in accordance with appropriate test methods , sweetened and/or flavoured yoghurt shall comply 
with the compositional requirements in table  2.  
©RSB 2017 - All rights reserved                  6 
 Table 2 ▬ Compositional requirements for sweetened yoghurt.  
S/N  
 Characteristics  
 Sweetened 
Yoghurt  
 Partially 
skimmed milk 
sweetened 
yoghurt  
 Skimmed milk 
sweetened 
yoghurt  
 Test method  
I.  Milk fat %  2.25 (m in) >0.5 –1.25 (max)  0.5 (max)  RS ISO 2446  
II.  Milk solids not fat % 
m/m (min)  8.5 8.5 8.5 RS ISO 3728  
III.  Titratable acidity % 
lactic acid  0.6 – 1.2 0.6 – 1.2 0.6 – 1.2 ISO/TS 11869  
IV.  Lactobacillus 
bulgaricus  and 
Streptococcus 
thermopiles  per g 
(min)  107 107 107 Annex A  
4.3.3  Fruit Yoghurt  
The milk part of fruit yoghurt or yoghurt containing food materials shall comply with the requirements of 
sweetened yoghurt in table 2. The minimum amount of yoghurt in the final product shall be 70 % m/m.  
4.3.4  Heat treated yoghurt  
In addition to the compositional requirements in clause 4. 3.1, 4. 3.2 and 4. 3.3. Heat treated yoghurt may have 
no live micro -organisms.  
4.4 Microbiological requirements  
Yoghurt shall comply with the microbiological r equirements specified in Table 2 . 
Table 2 ▬ Microbiological requirements  
S/N  Microorganisms  Maximum limits (CFU per ml)  Test method  
i.  E.coli  CFU/ml  Absent  RS ISO 11866 -2 
ii.  Salmonella spp  in 25ml  Absent  RS ISO 6579 -1 
iii.  L monocytogenes , CFU/ml  Absent  RS ISO 10560  
iv.  Moulds, CFU/ml  10 RS ISO 6611  
v.  Yeasts , CFU/ml  10 
5 Food additives  
Food additives which may be  used shall comply with RS CODEX STAN 192.  DRS 49:2017  
7                ©RSB 2017 - All rights reserved  
 6 Contaminants  
6.1 Heavy metals  
The products covered by this standard shall comply with the maximum limits established by the Codex 
Alimentarius Commission.  
 
6.2 Pesticide and veterinary drug resi dues  
The products covered by this standard shall comply with the maximum residue limits for veterinary drug and 
pesticide residues established in Codex Standard Guide for Maximum Pesticide Limits in Foods.  
6.3 Aflatoxins  
When tested in accordance with ISO 1450 1, the level of Aflatoxin M1 shall not exceed 0.50 μg/l 
7 Hygiene  
The product covered by the provision s of this standard shall be prepared and handled in accordance with RS 
CAC/RCP 1 . 
8 Packaging  
Yoghurt shall be packaged in food grade containers which shall safeguard the quality of the product  
9 Labelling  
In addition to the requirements specified in RS EAS 38, the following requirements shall apply:  
a) name of the product as plain yoghurt, fruit yoghurt, flavoured  yoghurt or sweetened yoghurt.;  
b) name, address and physical location of the manufacturer;  
c) list of ingredients;  
d) lot number;  
e) date of manufacture;  
f) expiry date;  
g) Country of origin ;  
©RSB 2017 - All rights reserved                  8 
 h) Net contents in  volume;  
i) Storage conditions;  
j) Lot n umber ; 
k) Origin of milk used if different from cow’s milk ; 
l) Declaration of partly ski mmed milk yoghurt as fat reduced yoghurt ; 
m) For heat -treated yoghurt, declaration as either pasteurized or thermised ; 
n) Declaration of milk fat content as a percentage by mass ; and  
o) Declaration or products with a liquid consistency as ‘’drinking yoghurt’’.  
10 Sam pling  
Sampling shall be done in accordance with RS ISO 707.  DRS 49:2017  
9                ©RSB 2017 - All rights reserved  
 Annex  A 
(normative)  
 
Identification of Lactobacilus bulgaricus  and Streptococcus  
thermophiles   as characteristic microorganisms in yoghurt  
A.1 Scope  
A1.1  This method specifies the simplified methods using the cultural and physiological properties for 
identification of the characteristic micro -organisms.  
A1.2 Field of application : The method is applicable to the strains isolated from plain, flavoured, stirre d or 
unstirred yoghurt and fruit yoghurts, where both characteristic micro -organisms are viable and abundant.  
A.2 Definition  
For the purpose of this standard the following definitions shall apply: Characteristic micro -organisms: 
Lactobacillus bulgaricus  and Streptococcus thermophilus . 
A.3 Principle of the method  
a) Determination of morphological, cultural and biochemical characteristics for E. bulcaricus.  
b) Determination of morphological, cultural and biochemical characteristics for S. Thermophilus.  
A.4 Isolation of colonie s 
See A.6  
A.5 Phenotypic characteristics required for proper identification of l. bulgaricus;  
A.5.1  Recommended culture media.  
A.5.1.1  For routine cultures and physiological tests: autoclaved skimmed milk and Mrs. Broth.  
A.5.1.2  For special tests, for example fermen tation tests, use a basic medium (BM), similar to that of 
MRS* without glucose and meat extract, at pH 6.9 -7, which is supplied with the producer’s diagnostic kits.   
©RSB 2017 - All rights reserved                  10 
 A.5.2  Characteristics to consider  
A.5.2.1  Morphology  
Cultures on skimmed milk should be freshly made. Sme ars of cultures stained with methylene blue for few 
minutes. (Observe the presence of voluting grains after 24 hours incubation at 37°C in skimmed milk.)  
A.5.2.2  Catalase Activity  
Mix equal volumes of every broth culture with 1.5 % hydrogen peroxide in a test wit h a rubber. Invert the 
catalase tubes and observe for about 20 min at room temperature. Controls are prepared simultaneously. 
Under these conditions L. bulgaricus will not develop in oxygen.  
A.5.2.3  Growth on MRS.  
 Broth at 15 °C and 45 °C - inoculate one drop on a 18 – 24 h culture and observe for up to 7 days. No 
turbidity at 15° C: turbidity at 45 °C.  
A.5.2.4   Production of C02 from glucose:  
A.5.2.4.1  Culture medium.  
A.5.2.4.2  Composition  
BM (A5.1.2) per cent glucose.  
A.5.2.4.3  Preparation  
Dissolve and distribute 10 ml of culture medium (A5.2.4.1)  in tubes of 16 mm x 160 mm, and sterilize at 121 
°C for 15 min.  
A.5.2.4.4  White agar  
A.5.2.4.5  Composition  
Agar 20 g Distilled water 1 000 ml.  
A.5.2.4.6  Preparation  
Dissolve and distribute 10 m l of white agar in tubes of 16 mm x 160 mm and sterilize at 121 °C for 15 min.  
A.5.2.4.7  Procedure  
Inoculate culture medium with 1 per cent of the culture grown on MRS. Cover the surface to a depth of 1 cm 
white agar (avoid any trace on the interior surface of the tube). Incubate at 37 °C for 15 days. Presence of gas DRS 49:2017  
11                ©RSB 2017 - All rights reserved  
 is evident when the white agar layer  detaches itself from the underlying contents. In these conditions L. 
bulgaricus  does not produces gas.  
A.5.2.5  Fermentation of Sugars  
Table 1 indicates the important sugars to distinguish L. bulgaricus  from the taxonomically nearest group of 
thermo -bacteria.  
A.5.2.5.1  Culture medium  
A.5.2.5.2  BM plus diagnostic kit (clause 5.1.2) for lactobacillus.  
A.5.2.5.3  Procedure  
For preparation of the inoculums and reading of results see directions of the commercial micro methods.  
A.5.2.6  Determination of Lactic Acid Isomers in the Culture  
See ISO 8069: Interna tional standard for lactic acid and lactates content.  
A.6 Phenotypic characteristics required for a proper Identification of S.hermophilus . 
A.6.1  Recommended culture media.  
For routine cultures and physiological tests autoclaved litmus milk and M 17 broth.  
A.6.2  Characteristics to consider:  
A.6.2.1  Morphology  
Cultures on litmus ilk should be freshly made. Smears of cultures stained with methylene blue for a few 
minutes.  
A.6.2.2  Catalase Activity  
See A.5.2.2. Under these conditions S. thermophilus  will not develop oxygen.  
A.6.2.3  Growth on litmus milk at 10 °C and 45 °C  
For procedure see A.5.2.3 At 10 °C.S. thermophiles does not change litmus milk.  
A.6.2.4  Action on litmus milk (acidification, coagulation, and reduction)  
Litmus milk acidified by S.thermophilus turns pink and then coagulates, af ter coagulation the color remains 
pink due to incomplete reduction of litmus, with a more intensely coloured upper ring.   
©RSB 2017 - All rights reserved                  12 
 A.6.2.5  Growth with 6.5 % NaCI.  
A.6.2.6  Culture medium.  
A.6.2.6.1  Composition  
M 17 broth (A.6.1.1.) without B -glycerol phosphate NaCI 6.6 %.  
A.6.2.6.2  Preparation  
Dissol ve and distribute 10 ml aliquots of A6.2.6.1 in tubes of 16 mm x 160 mm and sterilize at 121°C for 15 
min. 
A.6.2.6.3  Procedure  
Inoculate the tubes with a drop of washed cells suspension of overnight M 17 broth culture of the strains to be 
tested. Incubate at 37 °C a nd observe the growth for up to 7 days. In these conditions S. thermophilus does 
not develop.  
A.7 Expression of results  
Compare the results of the tests of Clause 7 with main attributes Expressed on Table 1, for bulgaricus  and 
compare the results of the tests of Clause 8 with main attributes expressed in Table 2 for S. thermophilus.  
A.7.1  Recommended culture media.  
For routine cultures and physiological tests autoclaved litmus milk and M 17 broth.  
A.7.2  Characteristics to consider  
A.7.2.1 Morphology – Cultures on litmus ilk should be freshly made. Smears of cultures stained with 
methylene blue for a few minutes.  
A.7.2.2  Catalase Activity – See clause A5.2.2. Under these conditions S. thermophilus will not develop 
oxygen.  
A.7.2.3  Growth on litmus milk at 10°C and 45°C – For procedure see clause A5.2.3 At 10°C.S. thermophilus 
does not change litmus milk.  
A.7.2.4  Action on litmus milk (acidification, coagulation, and reduction) – Litmus milk acidified by S. 
thermophilus turns pink and then coagulates, after coagulation the co lor remains pink due to incomplete 
reduction of litmus, with a more intensely coloured upper ring.  
A.7.2.5  Growth with 6.5 per cent NaCI.  DRS 49:2017  
13                ©RSB 2017 - All rights reserved  
 A.7.2.6  Culture medium.  
A.7.2.6.1  Composition – M 17 broth (A6.1.1.) without B -glycerol phosphate NaCI 6.6 %.  
A.7.2.6. 2 Preparation – Dissolve and distribute 10 ml aliquots of A.7.2.6.1 in tubes of 16 mm x 160 mm and 
sterilize at 121°C for 15 min.  
A.7.2.6.3 Procedure – Inoculate the tubes with a drop of washed cells suspension of overnight M 17 broth 
culture of the strain s to be tested. Incubate at 37°C and observe the growth for up to 7 days. In these 
conditions S. thermophilus does not develop.  
A.8 Expression of results  
A.8.1  Compare the results of the tests of Clause 7 with main attributes Expressed on Table 1, for bulgaric us 
A.8.2  Compare the results of the tests of Clause 8 with main attributes expressed in Table 2 for S. 
thermophiles  
Table A.1 ▬ Main attributes of L. bulgaricus , L. lactis , L. Helveticas  
Attributes  L. bulgaricus  L. lactis  L. helveticsu  L. acidophilus  
Morphology  Rods with round 
variable according to 
age, medium, strain. 
Numerous 
metachromatic bodies 
of cells of old culture 
stained with 
methylene blue  As L; bulgaricus  Polymorphism of old 
culture not so marked 
as with L. Bulgaricus. 
No met achromatic 
bodies Rods with round end, 
singly, in pairs or 
short chains. No met 
achromatic bodies  
Catalase  - - - - 
Gas - - - - 
Production from 
glucose  No growth  No growth  No growth  No growth  
Growing temperature 
At 15°C -45°C  + + + + 
Fermented Sugars      
Fructose  + + ± + 
Galactose  ± + + + 
Glucose  + + + + 
Lactose  - + + + 
Maltose  + + + + 
Mannose  - + ± + 
Sucrose  - + - + 
Trehalose  - + ± + 
Gluconate  - - - - 
Cellobiose  - - - +  
©RSB 2017 - All rights reserved                  14 
 Esculine  - - - + 
Lactic acid isomer  D(-) D(-) DL DL 
NOTE 1 + = positive reaction for 90 % or more strains  
NOTE 2 - = negative reaction for 90 % or more strains.  
NOTE 3 ± = variable reaction, weak, slow or negative DRS 49:2017  
ICS 67.100.10  
 
 
©RSB 2017  - All right s reserved