Lactic acid bacteria acidification

An improvement of the productivity of the NF-based process to 7.1gl h is obtained by running the process semi-continuously [64]. Final lactic acid concentrations in the permeate can reach values between 10 and 60 g 1 . The higher values are at the lower limit of concentrations found in UF- and MF-based processes [60]. Based on these data, a three-step repetitive process has been proposed [64]. The first step is the cell multiplication step during which pH can be controlled, the second step is an acid production step, followed by NF. In this approach a constant pH is assumed during each separate process step. However, other strategies in the acidification stage, which make use of natural acidification by the lactic acid bacteria are also possible. 

For laboratory-scale production of casein, HC1 is usually used for acidification acetic or lactic acids are used less frequently. Industrially, HC1 is also usually used H2S04 is used occasionally but the resulting whey is not suitable for animal feeding (MgS04 is a laxative). Lactic acid produced in situ by a culture of lactic acid bacteria is also widely used, especially in New Zealand, the principal producer of casein. 

The contribution of these agents, individually or in various combinations, has been assessed in model cheese systems from which one or more of the agents was excluded or eliminated, e.g. by using an acidogen rather than starter for acidification or manufacturing cheese in a sterile environment to eliminate non-starter lactic acid bacteria (NSLAB). Such model systems have given very useful information on the biochemistry of ripening. 

Acidification to the isolectric pH of casein using lactic acid bacteria or food-grade acids/acidogens, at 20 40 C. and resultant slow quiescent aggregation of the sensitized casein micelles e.g., for cream cheese. [A combination of acidification and rennet-hydrolysis (a smaller quantity of rennet than for rennet-curd cheeses, e.g., 5-100 versus 900-1000 chymosin units per 100 L milk) is normally used for low-fat acid-curd cheeses such as Quark and related varieties (Schulz-Collins and Senge, 2004)]... 

By one definition, sourdough has been described as a dough made of cereal products (and other ingredients, if required), liquids, and microorganisms (such as lactic acid bacteria and yeasts) in an active state. Acidification... 

This is due to the nature of the sourdough system where the effects of acidification and the endogenous microbial and cereal proteases all contribute to a complex set of dynamics. It is further complicated by the fact that there may be divergence between studies in terms of the particular lactoba-cilli used given that proteolytic activity is strain dependent. The enhanced proteolysis seen during sourdough fermentation has been attributed to both the proteolytic activity of lactic acid bacteria and that of cereal proteases. 

Next the mash is cooled to about 55° and acidified by inoculation with pure cultures of lactic acid bacteria. The purpose of this acidification is to protect the mash from the action of putrefactive bacteria and at the same time to create a condition in the mash which hastens peptonization of the proteins. When the acidification of the mash has reached about 1.6% acid it is sterilized, filtered, cooled and passed into the yeast fermentation tank. 

Lactic acid bacteria are used primarily to accelerate and control the acidification of the sausage. Carbohydrates are metabolised via the homo-fermentative pathway (see Figure 1.1). The lactic acid that is produced results in the tangy taste characteristic of fermented sausages. 

In the northern part of Europe, the necessary acidification of dough for rye bread is often obtained by lactic acid bacteria fermentation. 

Vilhelm Storch (1837-1918), who graduated from the Polytechnical College in 1861, worked on the acidification of cream. He investigated those strains of lactic acid bacteria that gave particular qualities of taste and odour. This resulted in production of pure cultures of lactic acid bacteria from 1893. 

Thomsen MH, Kiel P (2008) Selection of lactic acid bacteria for acidification of brown juice (grass juice), with the aim of making a durable substrate for L-lysine fermentation. J Sci Food Agric 88(6) 976-983. doi 10.1002/jsfa.3176... 

Martinussen, J., Solem, C., Holm, A.K., and Jensen, RR. (2013) Engineering strategies aimed at control of acidification rate of lactic acid bacteria. Curr Opin Biotechnol 24,124—129. 

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