Rate Of Acid Development Research Articles

Influence of total solids contents of milk whey on the acidifying profile and viability of various lactic acid bacteria

The main objectives of the present study were (a) to study the effects of the different combinations of Lactobacillus delbrueckii subsp. bulgaricus (Lb), Lactobacillus acidophilus (La), Lactobacillus rhamnosus (Lr), and Bifidobacterium animalis subsp. lactis (Bl) in co-culture with Streptococcus thermophilus (St) on the rate of acid development in milk and milk-whey mixture, and (b) the effect of the level of the total solids of the different bases on the acidification profile and viability of potential health-promoting micro-organisms. The co-culture of St-Lr showed the lowest values V max in all bases; while the co-culture St-Bl had high t V max in milk and whey bases (12 and 10 g/100 g, respectively). Co-cultures St-La and St-Lb reached V max at pH 5.5, while St-Lr and St-Bl at pH 5.91. Fermentation time to reach pH 4.5 was longer when St-Lr co-culture was used, while St-Lb had the lowest value. All the products had slight development of acid during the storage period, and lowest values were observed when the St-Bl co-culture was employed. Lb, Bl and St cultures had high counts at pH 4.5 in the three bases. The total solids affected the viability of Lb and La. The technological interest of these combinations is discussed in this article.

EFFECT OF YOGHURT STARTER LACTIC ACID BACTERIA ON

The growth of lactic acid bacteria of yoghurt culture Str.salivarius sub-sp thermophilus (Str. thermophilus) and Lacto bacillus delrueckeii sub-sp bulgaricus (Lacto. bulgaricus)in milk inhibited the growth of vegetative cells of B .cereus and spores that resisted the high heat treatment which was isolated from raw milk and prevented the B .cereus from producing the enterotoxins in yoghurt . The B .cereus did not affect the growth of yoghurt starter culture, also the rate of acid development in yoghurt was not affected in the presence of B. cereus. The poisoning by this bacteria did not happen in dairy product when number decreased to less than 106 c.f.u. /ml .

A COMPARISON OF STIRRED CURD CHEESES MADE FROM NORMAL MILKS AND RECONSTITUTED NONFAT DRY MILK WITH VEGETABLE OILS

Cheeses made from 30% total solids (TS) mixtures of reconstituted nonfat dry milk and vegetable oils were compared with cheeses made from 12.5% TS mixtures and with cheeses made from normal milk. The 30% TS filled milks produced cheeses having firmer curd, lower moisture content and better body and texture characteristics than those made from 12.5% TS filled milks. The rate of acid development during cheese making was slower in filled milks than in normal milks. Filled cheeses were always graded lower than normal milk cheeses. The 30% TS filled milk cheeses were significantly harder than 12.5% TS filled milk cheeses and normal milk cheeses. Cheeses containing coconut oil were harder than those containing soybean oil.

Starters and Bacteriophages in Lactic Acid Casein Manufacture

A controlled starter system was used for the first time in commercial lactic acid casein manufacture in New Zealand. Multiple starters of up to four components were constructed from 18 recently derived Streptococcus cremoris isolates which were not lysed by any of the phages in the collection of the New Zealand Dairy Research Institute. During the first season of casein manufacture, phages attacking 17 isolates were detected in the casein whey. Of these, 12 prevented adequate acid production by the appropriate host even at levels below 1 phage per 10 to 1000 ml in the milk before starter addition. In contrast, the first detected phages attacking the other five isolates did not significantly influence the rate of acid development; use of these starters continued until phages which eliminated acid production appeared. An alternative starter system based on the continuous selection of “phage-tolerant” cultures was investigated. Regular addition of whey, from previous manufacture, to the individual mother cultures of each component permitted long-term use of the multiple starter. This procedure of continued selection for phage-tolerant organisms has been used successfully for a complete season in a major casein factory.

Proteolysis in Cheddar cheese: influence of the rate of acid production during manufacture

SummaryData are presented which show that the use of glucono-δ-lactone as a chemical acidulant in cheese manufacture results in a much more rapid decrease in pH than that occurring in biologically acidified cheese. One of the consequences of the excessive early acid development was a very marked increase in the level of proteolysis during cheese-manufacturing operations. Consequently, chemically acidified cheese, as manufactured by the technique of Mabbitt, Chapman & Berridge (1955) (expt 17), does not appear to be a suitable ‘reference cheese’, especially for studies in which proteolysis during ripening is under investigation. The technique of Mabbitt et al. Avas modified to simulate the pH development pattern of starter cheese more closely; the level of proteolysis in curd made by the modified method was approximately equal to that in starter curd.An attempt was made to link the propensity to develop bitterness of cheese made with fast acid-producing cultures with excessive early proteolysis in such cheese. The results show that fast- and slow-culture strains differed significantly in their acid-producing capability only after the cooking stage and consequently such cheeses differed little with respect to early proteolysis. Further, cheeses made with 0·5, 1·0, 2·0 or 4·0% of ML8 culture which differed considerably in rate of acid development and consequently in the level of early proteolysis did not develop bitterness, even when 4·0% starter was used.It is concluded that gross proteolysis and bitterness are not correlated.

Shortening Dariworld Process of Making Cheese

The time required to make cheese by the Dariworld process from addition of 1% starter to hooping is about six hours. By using 2.5 or 4% starter, and adding rennet immediately after the starter, the total making time can be reduced 16 or 25%. The usual acidity of about pH 6.0 at dipping and pH 5.4 at second heating are observed. Curd making, cheese composition, and grades are not significantly altered by increased starter and rate of acid development.

Interrelationships of Flavor and Chemical Changes in Cheese

A review of selected studies of Cheddar and Swiss cheese, emphasizing certain factors which appear to be involved with the flavor balance, flavor formation, and flavor stability of cheese. Free fatty acids and hydrogen sulfide are important ripening products in Cheddar cheese. Desirable flavor occurs only when these compounds are present in definite interdependent concentrations. Furthermore, the formation of active sulfhydryl (-SH) groups in Cheddar and Swiss cheese during curing may be the key to the development of characteristic cheese flavor. For Cheddar cheese, the formation of active -SH groups is impaired by heat treatment of the milk, relatively high redox potentials of the cheese, and the presence of copper. In contrast, the concentrations of active -SH groups in Swiss cheese appear to be unaffected by redox potential and copper content but may be affected by the rate of acid development during manufacturing.Consumer-packaging of cheese generally results in loss of flavor quality. Primarily, the flavor change appears to be a function of the redox stability of the cheese, and the change may be retarded by the exclusion of air from the cut cheese surface. The need for processes which will result in accelerated cheese ripening and which will provide maximum control over flavor quality and flavor stability is discussed.

Factors Affecting the pH of Skimmilk Coagulation by Lactic Culture

Summary The A-C (acid-coagulation) test measures the stage of gel formation in acidcoagulated skimmilk at which the gel will first shrink and expel whey when cut with a knife. This test was chosen to study certain factors influencing the pH of coagulation of skimmilk by action of lactic culture. The rate of acid development and the use of different commercial lactic cultures did not affect the pH at the A-C end-point. Increased amounts of rennet added early in the fermentation process caused the skimmilk to coagulate at progressively higher pH values, but very small additions had little or no effect. Different skimmilks did not respond alike to variations of rennet. Additions of chloride of calcium and sodium decreased the pH at the A-C end-point more than did monosodium phosphate or a mixture of salts when all were added to increase the ionic strength by 0.10 at pH 4.70. The pH at which the A-C end-point occurred decreased as the total solids in reconstituted nonfat dry milk increased, probably because of the greater ionic strength of milk in reconstituted nonfat dry milk with high total solids. Heat treatments of skimmilk which denatured whey proteins resulted in an increase in the pH at which the A-C end-point occurred.

Manufacture and Technology of Swiss Cheese

Summary The successful outcome of Swiss cheese manufacture is dependent on a number of factors. Acid-forming and eye-forming bacteria have to be selected and properly taken care of by frequent propagations. Every step involved in the manufacturing procedure must be applied in a manner which will insure a proper rate and amount of acid development. During curing, degradation of the constituents of the cheese occurs. Fatty acids and amino acids are liberated. Certain compounds important in intermediate bacterial metabolism also are formed. Characteristic flavor and body and texture development of Swiss cheese appear to be dependent on a proper balance of products of metabolism. Poor milk, improper rate of acid development, and adverse curing-room conditions are some of the causes of low-quality Swiss cheese. Certain theories are advanced regarding flavor development and the role of copper in Swiss cheese.

478. Hard cheese made from Egyptian cows' and buffaloes' milks

1. Hard cheese of Cheddar, Derby and Manfis types was made from cows' milk and from buffaloes' milk. Buffaloes' milk curd of the Derby type was also milled at different acidities.2. Initial acidity was higher and rate of acid development was greater in cows' milk and curd, whilst loss of fat in the whey was lower.3. Cows' milk cheese contained more moisture, more total, soluble, and non-protein nitrogen, but less fat than buffaloes' milk cheese.4. During ripening, the rate of acid development and protein degradation was greater in cows' milk cheese, whilst loss of moisture was usually smaller.5. Buffaloes' milk cheese was inferior in grading quality to cows' milk cheese.6. Attempts to improve the quality of buffaloes' milk cheese were made by altering the Derby cheese-making process as follows:(a) ripening milk longer before renneting;(b) modification of the milk casein/fat ratio;(c) combining (a) and (b);(d) modification of the casein/fat ratio plus scalding of the curd at a lower temperature and for a shorter time.7. The last treatment (d) proved most effective and yielded cheese of very similar chemical composition and grading quality to that obtained from cows' milk.

Influence of the Frequency of Transfer of Lactic Starters upon Rate of Acid Development and Quality of Cheddar Cheese

Summary When lactic starters were inoculated every day or every third day and carried under excellent conditions, their quality was identical as judged by appearance, flavor, and acid development. When incubated in milk at temperatures used in cheese making, there were slight differences in the starters. When incubated at 86° F. acid development was rapid and the same for both starters; at 100° F. acid development was very slow; and at 86° F. for 2 hours followed by 100° F. for 6 hours the acid development was good and the same for both starters. When the freshly coagulated starters were used in cheese making the results were not identical to those secured in milk. The greatest difference was that in the cheese making process the starter transferred every third day gave slower acid development in the curd. When inoculated and set in milk at 100° F. the acid development was almost arrested in the curd and both starters gave comparable results. Cooling the cooked curd back to 86° F. did not affect the rate of increase in acid. An initial incubation of the cultures at 86° F. in the cheese milk was very important in securing the desired increase of acid in the curd at higher temperatures. Aging starters generally slowed the increases in acidity. Cheese manufactured with starters transferred daily developed more flavor of better quality in less time than when made with starters transferred every third day. This was true even though the starters appeared to be of equal quality. The old starters produced unclean flavors in the cheese. However, the cheeses that developed flavor sooner also over-ripened in less time so that they should be put in cold storage earlier to maintain their fine flavor. The data show that transfer of lactic cultures every third day as compared with daily transfer reduced the acid produced during the Cheddar cheese, making process, and incubation at 86° F. in the cheese milk increased, the production of acid at the cooking temperature.

311. The influence of bacteriophage on the cheese-making process

The presence, in the cheese milk, of phage active against the organisms of the ‘singlestrain ’ culture in use as starter leads to its multiplication during the cheese-making process. The extent to which the presence of phage is made evident in the vat depends largely upon the amount of initial infection. A heavy infection permits sufficient multiplication of the phage to cause lysis of the organisms and consequent cessation of acid development before the manufacturing process is completed. A light infection may have no noticeable influence upon the performance of the starter in the vat. Intermediate amounts have an effect on the rate of acid development in the later stages of the process, but within certain limits there is little adverse influence on the quality of the cheese produced.

The Heat Resistance of Streptococcus Thermophilus Grown in Mixed Culture with Caseolytic Bacteria

The increased heat resistance of Streptococcus thermophilus and Lactobacillus helveticus grown in mixed culture with Candida krusei, a film-forming yeast, has been observed by Peppler and Frazier (1). The beneficial effect of the film yeast on the bacteria was greatest near the surface of the medium where the yeast grew abundantly. The influence of the yeast was attributable to the combined effect of reduced oxygen tension, reduced acidity, and accessory substances formed during the association with the lactic acid bacteria. It was suggested that other microorganism grown with acid-forming bacteria may increase the activity of the lactic acid bacteria after severe temperature exposures. The present study is a preliminary report of data showing the effect of different caseolytic bacteria on the heat resistance of lactic acid organisms grown in mixed culture in milk. The addition of peptones and malt extract to a reconstituted skimmilk medium is known to increase the rate of acid development and heat resistance of Lad,tobacillus helveticus (2) and Streptococcus thermophilus (3). It is probable that certain proteolytic bacteria grown in whey can produce protein derivatives more available to pure cultures of the acid-forming bacteria than the proteins of milk. Therefore the enrichment of ordinary skimmilk media with small amounts of heat-killed whey cultures of caseolytic bacteria should increase the heat resistance of S. thermophilus and L. helveticus. The following experiments indicate the extent to which such enrichments of milk are a useful method of preparing heat resistant lactic acid bacteria.

The Effect of Temperature and Time of Storage of Cream on the Rate and Type of Deterioration

Summary The results may be summarized as follows: 1. When cream was held at 50° F. it changed from first to second grade in from 11 to 16 or more days. At 70° F. it changed in from 3 to 10 days, and at 90° F. in from 1 to 4 days. The time required for the cream to change from first to third grade varied from 4 to more than 16 days as the temperature was varied by 5° intervals between 50 and 90° F. 2. The cream soured in from 1 to 6 days, souring more rapidly as the storage temperature increased. Stale flavors were most prevalent at low storage temperatures after several days (4–14) holding. Putrid flavors were detected at high or low temperatures but not at intermediate temperatures (60–75° F.). Bitter flavor varied widely in time of appearance (1–14 days) but apparently was retarded at low temperatures. Unclean flavor appeared early. Rancidity was not detected in cream stored at 50 to 55° F. but appeared in from 3 to 9 days at other storage temperatures. With one exception cheesy flavor appeared only at temperatures of 65° F. or above. Yeastiness appeared in from 4 to 5 days at temperatures of 85 and 90° F., but as storage temperatures were reduced development of this flavor was retarded. 3. At the lower storage temperatures (50 and 60° F.) the cream was regarded as second grade at lower levels of acidity than when the cream was stored at higher temperatures. At 60° F. the acidity of poor cream increased only slightly faster than that of good cream, the maximum being 0.7 per cent in 4 days and remained the same thereafter. At 70 and 90° F. the rate of acid development in the poor cream was much greater than in the good cream, the rate of acid development being dependent on the storage temperature. Addition of starter to poor cream increased the rate of acidity development at all temperatures, being greatest at the higher temperature. 4. The hydrogen-ion concentration of the cream decreased rapidly during the first 2 days to a value of pH 4.6, after which the rate of decrease was less. The pH values revealed little information not indicated by tests for total acidity. 5. Formol titrations of cream held at 60° P. indicated that protein decomposition was less in good cream than in poor cream. At higher storage temperatures proteolysis was accelerated, but the difference between the rate in poor and good cream was more marked at lower temperatures. Addition of starter to poor cream caused an increase in the formol titration at all temperatures. Data presented raises a question regarding the validity of the formol titration as an index of undesirable conditions. 6. Practically no yeasts or molds developed in cream held for 16 days at 50° F. At temperatures of 70° F. or above mold and yeast development increased rapidly.

153. Studies on the chemistry of Cheddar cheese making. VI. Factors affecting the relation between lactic acid and titratable acidity in wheys

The experiments described above have shown that on the whole there is a close relationship between titratable acidity and lactic acid concentration in wheys obtained under various conditions of cheese-making. Variations in the rate of acid development or in the lactose content of the cheese milk have no significant effect on the relationship. Variations in the mineral content of the curd brought about by differences in the composition of the milk or by different acidities up to the running stage do have a certain effect. In curd with a lower mineral content there is a less complete neutralization of lactic acid and the wheys show a higher titratable acidity for the same lactate content. The differences, however, are small and affect only the wheys coming off late in the cheese-making process.

New universal indicator

The results may be summarized as follows:1.When cream was held at 50° F. it changed from first to second grade in from 11 to 16 or more days. At 70° F. it changed in from 3 to 10 days, and at 90° F. in from 1 to 4 days. The time required for the cream to change from first to third grade varied from 4 to more than 16 days as the temperature was varied by 5° intervals between 50 and 90° F.2.The cream soured in from 1 to 6 days, souring more rapidly as the storage temperature increased. Stale flavors were most prevalent at low storage temperatures after several days (4–14) holding. Putrid flavors were detected at high or low temperatures but not at intermediate temperatures (60–75° F.). Bitter flavor varied widely in time of appearance (1–14 days) but apparently was retarded at low temperatures. Unclean flavor appeared early. Rancidity was not detected in cream stored at 50 to 55° F. but appeared in from 3 to 9 days at other storage temperatures. With one exception cheesy flavor appeared only at temperatures of 65° F. or above. Yeastiness appeared in from 4 to 5 days at temperatures of 85 and 90° F., but as storage temperatures were reduced development of this flavor was retarded.3.At the lower storage temperatures (50 and 60° F.) the cream was regarded as second grade at lower levels of acidity than when the cream was stored at higher temperatures. At 60° F. the acidity of poor cream increased only slightly faster than that of good cream, the maximum being 0.7 per cent in 4 days and remained the same thereafter. At 70 and 90° F. the rate of acid development in the poor cream was much greater than in the good cream, the rate of acid development being dependent on the storage temperature. Addition of starter to poor cream increased the rate of acidity development at all temperatures, being greatest at the higher temperature.4.The hydrogen-ion concentration of the cream decreased rapidly during the first 2 days to a value of pH 4.6, after which the rate of decrease was less. The pH values revealed little information not indicated by tests for total acidity.5.Formol titrations of cream held at 60° P. indicated that protein decomposition was less in good cream than in poor cream. At higher storage temperatures proteolysis was accelerated, but the difference between the rate in poor and good cream was more marked at lower temperatures. Addition of starter to poor cream caused an increase in the formol titration at all temperatures. Data presented raises a question regarding the validity of the formol titration as an index of undesirable conditions.6.Practically no yeasts or molds developed in cream held for 16 days at 50° F. At temperatures of 70° F. or above mold and yeast development increased rapidly.

The tide at tahiti

The results may be summarized as follows:1.When cream was held at 50° F. it changed from first to second grade in from 11 to 16 or more days. At 70° F. it changed in from 3 to 10 days, and at 90° F. in from 1 to 4 days. The time required for the cream to change from first to third grade varied from 4 to more than 16 days as the temperature was varied by 5° intervals between 50 and 90° F.2.The cream soured in from 1 to 6 days, souring more rapidly as the storage temperature increased. Stale flavors were most prevalent at low storage temperatures after several days (4–14) holding. Putrid flavors were detected at high or low temperatures but not at intermediate temperatures (60–75° F.). Bitter flavor varied widely in time of appearance (1–14 days) but apparently was retarded at low temperatures. Unclean flavor appeared early. Rancidity was not detected in cream stored at 50 to 55° F. but appeared in from 3 to 9 days at other storage temperatures. With one exception cheesy flavor appeared only at temperatures of 65° F. or above. Yeastiness appeared in from 4 to 5 days at temperatures of 85 and 90° F., but as storage temperatures were reduced development of this flavor was retarded.3.At the lower storage temperatures (50 and 60° F.) the cream was regarded as second grade at lower levels of acidity than when the cream was stored at higher temperatures. At 60° F. the acidity of poor cream increased only slightly faster than that of good cream, the maximum being 0.7 per cent in 4 days and remained the same thereafter. At 70 and 90° F. the rate of acid development in the poor cream was much greater than in the good cream, the rate of acid development being dependent on the storage temperature. Addition of starter to poor cream increased the rate of acidity development at all temperatures, being greatest at the higher temperature.4.The hydrogen-ion concentration of the cream decreased rapidly during the first 2 days to a value of pH 4.6, after which the rate of decrease was less. The pH values revealed little information not indicated by tests for total acidity.5.Formol titrations of cream held at 60° P. indicated that protein decomposition was less in good cream than in poor cream. At higher storage temperatures proteolysis was accelerated, but the difference between the rate in poor and good cream was more marked at lower temperatures. Addition of starter to poor cream caused an increase in the formol titration at all temperatures. Data presented raises a question regarding the validity of the formol titration as an index of undesirable conditions.6.Practically no yeasts or molds developed in cream held for 16 days at 50° F. At temperatures of 70° F. or above mold and yeast development increased rapidly.