No abstract

No abstract

Although the action of the lactic acid bacteria on carbohydrates has been the subject of many investigations, comparatively little attention has been paid to their proteolytic activity. Kulp and Rettger (1924) found that from 2 to 6 per cent of the proteins i milk were broken down by L. acidophilus and L. bulgaricus.Oila-Jensen (1919) studied the proteolytic action of a large number of lactic acid bacteria on the proteins of milk and Witte's peptone broth. In milk from 0 to 22.7 per cent of the total nitrogen was changed into soluble forms and in Witte's peptone the amino nitrogen produced varied from 0.5 to 33.9 per cent of the total. Ammonia nitrogen generally amounted to less than 2 per cent of the total nitrogen. Itano (1916) in studying the influence of hydrogen ion concentration upon the proteolytic activity of S. lacticus obtained an increase of 8.7 to 33.5 per cent in the amount of amino nitrogen. Sears (1916) reported that B. acidi-lactici produced much more ammomna and amino nitrogen when glucose was left out of the medium than when it was included.Various criteria have been used by different investigators as indexes of proteolysis. The early investigators, Smith (1897) and Peckham (1897), took putrefactive products as a test, Heller (1921) employed pH changes, Hall (1922) used liquefaction of coagulated proteins and gelatin as standards, Kendall and Walker 1 This work was supported in part by a grant from the special research fund of the University of Wisconsin. The authors are indebted to Miss Katherine M. Bolliger for assistance in the analytical work.

Lactic acid has been made from such materials as corn, potatoes, molasses, sugar beets, glucose, and whey by fermentation with Lactobacillus casei, Lactobacillus bulgaricus, Streptococcus lactis, Laotobacillus detbriickii, or other organisms (See references at end of paper). The manufacturer's choice of raw material depends upon his location, equipment, the price of the carbohydrate, and the quality of the product desired. Choice of culture depends upon the raw material and the conditions of fermentation selected.Of the widely available, directly fermentable raw materials, molasses is cheap, and L. delbrickii is perhaps the most useful culture for the transformation of its sugar to lactic acid. We have chosen this combination and determined the conditions producing the largest yield in the shortest time. EXPERIMENTAL PROCEDUREThe cultures, obtained from distiller's malt, were maintained on a 10 per cent malt mash, with transfers made every three or four days. Titratable acidity of this seed mash should be the equivalent of at least 15 cc. of 0.1 N acid per 10 cc. Crude cultures appeared to give as good results as pure cultures.The inoculant for the final mashes was grown for 24 hours in molasses mash containing 5 per cent sugar, with half the usual CaCO3 and a slight excess of nutrients over those of the final mashes. The latter were seeded with 3 per cent of the inoculant.Eight liters of final mash was fermented in a 9.5 liter Pyrex 149 H. R. STILES AND L. M. PRUESS bottle equipped with a mechanical agitator, and also with a tube for moderate aeration of the fermenting mash. The theoretical amount of calcium carbonate for the complete neutralization of a 95 per cent yield of lactic acid was added at the time the mash was made up. AUl mashes were-steamed for 90 minutes.It was found that an incubation temperature of 5052oC. was as high as could be used for good yields. There was no apparent trouble with infection in this range. ANALYTICAL METHODSAcids were determined by acidifying 300 cc. of the fermented mash with 10 cc. of concentrated sulfuric acid. After the sample had cooled and the calcium sulfate had settled, a 5-cc. clear, top sample was taken and continuously extracted with ethyl ether for 5 to 7 hours. This extraction removed both the lactic and volatile acids, which were titrated with 0.

No abstract