Eleek Eeae Peg Aada) MASTER of HOME ECONOMICS

Ele ek ee ae Peg aad a) MASTER OF HOME ECONOMICS BY LYDIA ZAE NORTHRUP i 1913 @ ; c 3 Lge 0 hae, KB AN ORE ORS isk Beas AM Ke Fo sry! a yn GS Oe on KOM ae, a = 5 “¢ ms SAP TND A ae NS? en OC aae YAR na Pies Hs TOY OO RNERG ate . >) > . RAN ey ry . ‘, ee ae, . see ot SAK a ah ay pt Abe net ed S86 935 nN 12 e 1) ee, 7 Ore 2) ‘5 Sort en ao Wert ap, ‘ i & Bh 1 Ree etd Raat OF £2 eS fs see RoR a aN BT ; 2 Oy: € wire * petto yen Vit LR uit . Pye ; Hic wi" ‘ ; 7,32 eaten IR USS 4 ey EN PORE SSN eh oe 2 ae Rishon sie FON COI Tel ROMA I Ae AGM OSE I eR AO ok ane ee SG %f ei Se Nimes 3s Se eh Re en ¢ rd ose oO ; ig 8 vs sn THO 4% c 3 ~ e AY I Ae ; Ke SCN Z ig ay ay Shan: ie ap ee, Ki br ars oe We aLeeae AYER @ Reh Yi YE i! OCR : CR Re toes : ar 2 5? ep . “ es pA role we das DAG ® A a ts s de THKH UTILITY OF LACTIC BACTERIA. Thesis for the derree of MASTER OF HOME EBFCOWOMICS . by Lydia zoe Northrup =a on ww we 4 oe OR 1913 THESIS THE UTILITY OF LACTIC BACTERIA. Pernaps no other single group of micro6r- ganisms has such a wide distribution in nature and in addition, such a range of usefulness sas has the group of lactic acid forming bacteria which sare re~ sponsible for the cheracteristic fermentative change in milk known as curdling. These bacteris are also responsible for the characteristic fermentation in other types of food as well, ssauer~ kraut and dill pickles being well known examples: ensilage also derives its peculiar odor and flavor from the growth of these micro6rganisms. The most common phenomenon produced by the lactic bacteria, the curdling of milk, has been recorded from time immemorisl. "Butter", the translation of the Hebrew word “hemah" given in the Fnglish authorized version of the Old Testament, means "curds" or curdled milk (9). In Genesis 18: 8, we ere told that Abraham placed curds before his guests (2250 = 2000 B.C.); in Deuteronomy 32: 14 (1750 B.C.), Moses told the Israelites that curdled milk was one of the blessings which Jeho- ve 103196 van had given to his chosen people (46). In Isaiah 7; 15 and 22, butter or curds is mentioned as one of the few foods left to the Judeans during their war with the Syrians and Ephraimites (735 B.C.) (10.). For centuries soured milk has been used as a food by the peoples of Eastern Europe, Western and Middle Asia and parts of Africa. Fermented milk, a soured milk beverage, has also been used from time immemorial by the wandering tribes of Arabia. Those of the ancient fermented milk bever-~ ages best known today are koumiss, kefir, leben, yoghurt and mazun, dadhi, gioddu, khilat, oxygala, chiston, rayet, huslanka and taettamoelk being less commonly known. Each of these milk drinks is the result of the concerted action of one or more species of lactic bacteria with other bacteria and yeasts. Koumiss (kumyss, kumiss, etc.) is a drink originally prepared from mare's milk by the Kumanes @ Russian trive which lived along the river Kuma. The milk of, the mare was placed in leather bags and a small amount of old koumiss added as a starter. This beverage is strongly effervescent, due to the evolution of gas (carbon dioxide) produced Curing the alcoholic fermentation by the yeasts present. Kefir (kephir, kepfir, kefyr, kefr, etc.), the fermented milk of goats, sheep or cows wes Oo- riginelly made end used by the inhabitents of the Caucasus Mountains and wos prepared by adding "“kefir grains" to the milk. The origin of these grains is unknown but the natives believe that they were the gift of Mahomet and are carefully preserved by them. The natives prepared this drink by placing the dried kefir grains in milk in a goat Bkin vag and vy shaking occasionally until fermentation commenced, when the grains were removed and dried, thus preserving them for future use. The fermentation was also often sterted by adding some of the freshly fermented kefir to a new lot of milk. In kefir, as with koumiss, alcoholic fermentetion with the accompanying effervescence is more desir-~ able than marked acid production. Four different organisms were found in the Kefir grains, yeasts and three different types of bacteria; the combined action of all four seem to be necessary to the pro- Guction of good kefir. Leben or leben raib is the name given by the Eeyptians to their fermented milk drink. This oo, ~4~ beverage which they have used for centuries, is prepared from the milk of cows, buffaloes and goats. The fermentation process is very similar to that of other fermented milk drinks. Yoghurt (yoghourt, yogurt, etc.) is a sim- ljlar fermented milk prepared by the Bulgarians. This differs from the preceding beverages in that the acid fermentation is allowed to predominate. It is made in skin bags in much the same way that the Russians prepare koumiss. Mazun (matzoon, matzun, madzoon, etc.) is an Armenian drink almost identical with yoghurt. Dadhi and khilat are fermented milks used in India, Calcutta and Bengal respectively, very similar to yoghurt, leben, etc.(17).* Gioddu is a Sardinian fermented milk and is produced by micro@8rganisms similar to those found in the more studied fermented-milk beverages.(31). The oxygala and chiston of Rome and Greece, the rayet of Algeria and the huslanka of the Ruth- enians are other known varieties of curdied milk drinks (17}( 44). * Chatterjee notes that the type of fermented milk "“khilat" used in Bengal alone, has no prototype to his knowledge. "The production of the curd depends on the action of the products of a bacillus and not on the living bacillus itself****there are very few Bengalee householcs in which food prepared from this curd is not in daily use ond 2 large trade is cerried on in curd" (17). There are two types of Tactic bvacteris which ore capable of producing the characteristic cos¢g- ulation of milk; these are for convenience often differentiated by the terms "short" and "long" lac-~ tic bacteria. The former is the type met with in ordinary sour milk, comprising over ninety nine ner cent of its microflora. These ordinary lactic bacteria, Bacterium lactis acidi, sre very small, being from 0.6 micron to 1 micron long and O.5 micron wide, are oval in form and from the fact that some of the shorter cells appear nearly spher- ical and of ten oceur in chains, hes led to the ap- plication of the name Streptococcus lacticus to the group. The “long” lactic bacteria present in the Eastern fermented milks, sare true lactic bacteria also as they produce almost exclusively lactic acid from the sugar fermented, only very small quantities of formic, acteic and propionic acids being formed. These differ sreatly from Bact. lactis acidi in size, being large rod-shaped forms ~ microns to 3 microns long and 0.5 micron to 0.75 , “~~? TT =a6G= micron wide. The bacteria belonging to this latter group are known as Bacterium bulgaricum, socalled because first isolated and studied from Bulgarian soured milk. Both types of organisms are alike in that they do not form spores and consequently are easi- ly killed by heat, have no organs of locomotion and form lactic acid from certain sugars as a main product of their metabolic activities. They differ physically however in their respective temperature requirements, Bact. lactis acidi requiring a temperature between 30° and 35°C. for its @pti- mum growth while that for Bact. bulgaricum is from 40° to 45°C; they also differ physiologically, in their acid production, Bact. lactis acidi producing in normal milk a maximum acidity of from 0.9 to 1.25 percent only while with the long lactic bacteria the maximum acidity varies from 1.25 to 4.0 percent. It is this physiological property, that of acid formation, /which depends the importance of these lactic bacteria in their many phases of usefulness. Milk does not lose any of its valuable properties by undergoing acid fermentation, in fact its benefits as a food are generally augmented a7 = by the presence of the acid produced by the activity of the lactic bacteria. The longevity of the Bastern peoples is attributed by Metchnikoff to the use of acid milk as their staple article of diet. He offers this explanation of its action: lactic bacteria when introduced into the intestine transform its carbohye drate contents into lactic acid; this acts as an intestinal antiseptic, destroying or inhibiting the putre- factive organisms (which work in an alkaline medi- um), thus preventing the formation and subsequent absorption of toxic substances which have a degen- erative influence on the body tissues. To Metchnikoff is due the great credit for having insisted on the importance of introducing these lactic bacteria into the intestines for the purpose of controlling the type of fermantation therein. As a result of his teachings many lead- ing physicians today are recommending acid milk Ber- erages for use in intestinal therapy, and several large laboratories have been organized solely for the preparation and distribution of concentrated forms of starter for these curdled milk drinks. Two of such are the “Pasteur Laboratories of Amer- ica" and the "Ferment Company" both located at New York City.

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