Title: Freezing lactic starter cultures
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Permanent Link: http://ufdc.ufl.edu/UF00091688/00001
 Material Information
Title: Freezing lactic starter cultures
Physical Description: Book
Creator: Liska, Bernard Joseph,
Publisher: Florida Agricultural Experiment Station, Department of Dairy Science,
Copyright Date: 1959
 Record Information
Bibliographic ID: UF00091688
Volume ID: VID00001
Source Institution: University of Florida
Holding Location: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: 312494767 - OCLC

Full Text

Department of Dairy Science
Gainesville, Florida

Dairy Science Mimeo 59-2
January 5, 1959

Freezing Lactic Starter Cultures

B. J. Liska

Having a sufficient supply ef active lactic starter culture is a problem

in many dairy plants producing fermented milk products. Lactic cultures can be

obtained from commercial supply houses in liquid or freeze dried forms. Freeze

dried cultures will remain active at refrigerator temperatures for a year or more

bt* liquid cultures must be kept frozen if held for longer than one week.

A ripened culture loses activity rapidly in frozen storage. Research

has shown that by reducing the acidity of a ripened culture with alkali before

freezing, the culture remained active for longer periods of time in frozen storage.

Instead of using alkali to reduce the acid, attempts were made in this study

to reduce the acidity by dilution with sterile skimmilk. Cultures were ripened to

an acidity of 0.80 0.95% and diluted 1-10 with sterile skimmilk. Ten ml.

portions of these diluted cultures were placed in sterile test tubes and stored at

-10 to -150F. The viability of the cultures was checked by making plate counts

and actual transfers to determine speed of acid production a2ter 1, 15, 30, 60,

90, 120 and 150 days storage. The results for one culture appear in Table 1.

Other cultures reacted in a similar manner. After 150 days storage the

cultures used in this study had lost only 10% of their original activity. After

the second transfer, activity and flavor production of the thawed cultures were

equal to the original unfrozen cultures in most cases, LM-.=


Table 1. Viability of H 4 Frozen Lactic Culture Diluted 1-10 with 12.5% Sterile
Reconstituted NDM Before Freezing. (a, b)




% Acidity of 1st Transfer
ime in Bacterial Count (c) After 16 Hours at
storage (days) Millions/ml. 700 F.
40 0.85
30 0.83
5 -- 0.84
0 23.5 0.84
0 -- 0.82
0 18.1 0.81
20 -- 0.80
50 8.5 0.76

a) Samples were stored at --100 to --150 F.
b) Samples were thawed in water bath at 400 F.
c) Bacterial counts on samples immediately after thawing.

Two additional factors studied were thawing temperature and percent solids

in the sterile skimmilk used for dilution of cultures prior to freezing. The

percentages of solids of the skimmilk (from 10% to 15%) had no noticeable effect

on survival of cultures. Therefore heated skimmilk containing 10% solids will

serve the purpose well. Tharing frozen cultures at 400 F. gave better results

than temperatures of 600 F. to 700 F.

Keeping good cultures in a frozen state can be helpful in several ways:

(1) additional cultures can be kept on hand for emergency use, (2) a plant can

dispense with caring for mother cultures over weekends and during periods of

slack operations, (3) a particularly good culture can be preserved for later

use, and (4) sufficient st-rter can be frozen at one time for use in making

small quantities of fermented products over a period of time.

- 3 -


Mixed strain lactic starter cultures can be stored in frozen state for

several months with only a minor loss of activity. These cultures should

be handled as follows: (1) transfer a culture several times to determine activity,

flavor and aroma and freedom from contamination, (2) on the last transfer make

sufficient starter for freezing and ripen it to 0.80 to 0.85% acidity, (3) dilute

the starter 1-10 with 10% reconstituted NDM which has been steamed for one hour,

or preferably autoclaved at 1210 C. for 10 minutes, (4) place in suitable closed

sterile containers, freeze and store at -100F. to -150 F; (5) thaw these samples

in water at 400 F, (6) either use the diluted tha-ed culture and inoculate at ten

times the usual rate (equivalent to the undiluted culture) or incubate the thawed

culture until the desired acidity is reached and then use it as undiluted starter,

at the normal rate depending on the fermented product being produced.

300 copies

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