8
STUDIES ON DAHI : I. INTRODUCTION
[Vol. XXII, Part I
variety for 20 days in sour milk. Mattick [1946] has made some interesting observa-
tions regarding the destruction of tubercle bacilli in sour milk. While further in-
vestigation in necessary for determining the bactericidal action of fermented milk
on specific pathogens, the concensus of opinion is in favour of regarding sour milk
as a poor culture medium for the growth of pathogens and as a much safer food pro-
duct to handle than sweet milk even where sanitary methods are not practised.
The food value of fermented milk is considered to be more or less similar to
that of milk from which it is prepared. The sugar content is slightly reduced due
to its fermentation into acid, alcohol or gas, while the casein is precipitated in a
readily digestible condition. The increased digestibility of fermented milk is attri-
buted to the finely divided state in which casein is available [Orla Jensen and Spur,
1924]. These milks are, therefore, frequently used in cases of gastric irritation when
it is difficult to find foods which can be retained by the stomach. The lactic acid
in these products is said to be completely metabolized to carbon dioxide and water
in man and is not excreted in the urine nor does it have any effect on the acid—base
balance in the system (White House Conference on Child Health and Protection,
1932). Davies [1940] has referred to two other possible advantages of drinking
fermented milks, namely, (a) the increased availability of calcium and phosphorus
from calcium precipitated in the lower intestines due to the acid condition brought
about by the lactic acid organisms, and (b) the increased efficiency of the body to
cope with comparatively large quantities of lactic acid entering the system. It has
also been shown [Wegner and associates, 1940 ; Welch and Wright, 1943] that some
of the organisms occurring in fermented milks are able to synthesize certain vitamins
and if such organisms are also present in the intestines they may play a significant
role in the synthesis of some of the vitamins required by the host. Gasser [1931]
has reported that Saya (a fermented milk of the East recently introduced on the
Continent) is rich in vitamins A, B, C, and D and is superior to Kefir, Yoghurt or
fresh milk. Chitre and Patwardhan [1945] found the riboflavin content of curd to
be greater than that of the milk from which it was made. There was no appreciable
change in thiamine, but nicotinic acid showed a slight decrease. Recent work on
these aspects has been reviewed by Kon and Henry [1949].
Composition of dahi
Dahi is a thick, sour, coagulated milk product bearing a close resemblance to
Yoghurt in many respects. It is prepared either from cow's or buffalo's milk, while
lassi is made from skim milk. Generally, cow's or buffalo's milk is boiled or sim-
mered for a long time to concentrate it, allowed to cool to body temperature and
then transferred to earthenware pots or pans. A small amount of the previous day's
curd is added as a starter and the inoculated milk is incubated at room temperature
or at a temperature of 30° to 37°C., according to convenience. The curd is usually
ready in 16 to 20 hours. Occasionally raw milk may be employed or heated milk
may be allowed to sour naturally without the addition of any starter.
Davies [1940] has discussed some of the factors involved in the manufacture of
dahi and lassi. The following ranges of composition for normal samples of dahi and
lassi have been reported by him in Table III.