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Lactic Acid

(CAS#: 50-21-5)

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CH 3 CHOHCO 2 H, a colorless liquid organic acid. It is miscible with water or ethanol. Lactic acid is a fermentation product of lactose (milk sugar); it is present in sour milk, koumiss, leban, yogurt, and cottage cheese. The protein in milk is coagulated (curdled) by lactic acid. Lactic acid is produced in the muscles during intense activity. Calcium lactate, a soluble lactic acid salt, is used as a source of calcium in the diet. Lactic acid is produced commercially for use in pharmaceuticals and foods, in leather tanning and textile dyeing, and in making plastics, solvents, inks, and lacquers. Although it can be prepared by chemical synthesis, production of lactic acid by fermentation of glucose and other substances is a less expensive method. Chemically, lactic acid occurs as two optical isomers , a dextro and a levo form; only the levo form takes part in animal metabolism. The lactic acid of commerce is usually an optically inactive racemic mixture of the two isomers.

Lactic Acid and Performance

Lactic acid build up is most commonly associated with the intense burning pain felt in your muscles after an intense effort. Recently, a lot of attention has been focused on reducing lactic acid build so you can exercise at a higher intensity for a longer time and improving performance. In order to understand how to reduce the lactic acid build up in your muscles, you need to understand a bit about how it is developed in the first place.

During most exercise breathing rates increase and in turn increase the amount of oxygen traveling through the body. During aerobic exercise this increased oxygen is enough to meet your energy needs. During intense efforts, however, there isn't enough oxygen available to continue using the aerobic system to create energy. At this point you switch to anaerobic metabolism (glycolysis) to create energy. This system works without oxygen to supply energy to the muscles for a few minutes of high intensity effort. The downside is that you will soon feel burning muscles and have to decrease your intensity and return to the aerobic system.

What is lactic acid?
Lactic acid is a by-product of anaerobic glycolysis. If enough oxygen is not available, lactic acid is produced and begins to accumulate in the muscles. Lactic acid causes the "burning" sensation felt in muscles during high intensity exercise and also prevents muscles from working their best. This burning sensation is the result of a change in muscular acidity.

The point at which lactic acid begins to quickly accumulate in the blood is known as the anaerobic threshold or Lactic Threshold (LT). You can reduce the lactic acid build up faster if you perform light exercise after an intense effort. Continue moving slowly until your breathing rate slows.

How can I produce less lactic acid?
Through proper training. When your aerobic capacity is increased with training, you produce less lactic acid than you do when untrained. The closer you can get your anaerobic threshold to your Max VO2, the faster you will become. Simply having a high Max VO2 does not necessarily make you fast; but being able to sustain an effort close to your Max VO2 is what will determine how fast you can become.

Training will also make you better able to burn fat for fuel, a process that does not directly produce lactic acid. During maximum efforts, you will also be able to withstand higher lactic acid levels in the muscle, before they begin to fatigue.

Interval training is one key to reducing lactic acid buildup. Your training program should include interval training two to three days per week (include high intensity periods alternating with moderate intensity periods). Your body will learn how to handle lactic acid that is created during these high intensity workouts. This adaptation will gradually allow you to continue at a higher intensity for a longer time without feeling the burn of the lactic acid build up. In addition to interval training, you need to perform endurance training.

Lactic acid bacteria - their uses in food

Lactic acid bacteria have been used to ferment or culture foods for at least 4000 years. They are used in particular in fermented milk products from all over the world, including yoghurt, cheese, butter, buttermilk, kefir and koumiss.

Lactic acid bacteria refers to a large group of beneficial bacteria that have similar properties and all produce lactic acid as an end product of the fermentation process. They are widespread in nature and are also found in our digestive systems. Although they are best known for their role in the preparation of fermented dairy products, they are also used for pickling of vegetables, baking, winemaking, curing fish, meats and sausages.

Without understanding the scientific basis, people thousands of years ago used lactic acid bacteria to produce cultured foods with improved preservation properties and with characteristic flavours and textures different from the original food.

Similarly today, a wide variety of fermented milk products including liquid drinks such as kefir and semi-solid or firm products like yoghurt and cheese respectively, make good use of these illustrious microbial allies.

The manufacture involves a microbial process by which the milk sugar, lactose is converted to lactic acid. As the acid accumulates, the structure of the milk protein changes (curdling) and thus the texture of the product. Other variables such as temperature and the composition of the milk, also contribute to the particular features of different products.

Lactic acid also gives fermented milks their slightly tart taste. Additional characteristic flavours and aromas are often the result of other products of lactic acid bacteria. For example acetaldehyde, provides the characteristic aroma of yoghurt, while diacetyl imparts a buttery taste to other fermented milks. Additional micro-organisms such as yeasts can also be included in the culture to provide unique tastes. For example, alcohol and carbon dioxide produced by yeasts contribute to the refreshing, frothy taste of kefir, koumiss and leben. Other manufacturing techniques such as removing the whey or adding flavours, also contribute to the large variety of available products.

For yoghurt, the manufacture depends on a symbiotic relationship between two bacteria, Streptococcus thermophilus and Lactobacillus bulgaricus, where each species of bacterium stimulates the growth of the other. This interaction results in a shortened fermentation time and a product with different characteristics than one fermented with a single species.

With yoghurt and other fermented milks there are considerable opportunities for exploiting lactic acid bacteria as probiotic cultures. These supplement and help our normal gut bacteria to function more efficiently. The world-wide market for these products continues to increase in response to the demands of an increasingly health-conscious public.

Lactic acid bacteria are therefore excellent ambassadors for an often maligned microbial world. They are not only of major economic significance, but are also of value in maintaining and promoting human health.

Literature:

1. Modelling strategies for the industrial exploitation of lactic acid bacteria.------More information.

Lactic acid bacteria (LAB) have a long tradition of use in the food industry, and the number and diversity of their applications has increased considerably over the years. Traditionally, process optimization for these applications involved both strain selection and trial and error. More recently, metabolic engineering has emerged as a discipline that focuses on the rational improvement of industrially useful strains. In the post-genomic era, metabolic engineering increasingly benefits from systems biology, an approach that combines mathematical modelling techniques with functional-genomics data to build models for biological interpretation and - ultimately - prediction. In this review, the industrial applications of LAB are mapped onto available global, genome-scale metabolic modelling techniques to evaluate the extent to which functional genomics and systems biology can live up to their industrial promise.

2. Genome update: lactic acid bacteria genome sequencing is booming.----More information.

3.Differential real-time PCR assay for enumeration of lactic acid bacteria in wine.----More information.

Oenococcus oeni is often employed to perform the malolactic fermentation in wine production, while nonoenococcal lactic acid bacteria often contribute to wine spoilage. Two real-time PCR assays were developed to enumerate the total, and nonoenococcal, lactic acid bacterial populations in wine. Used together, these assays can assess the spoilage risk of juice or wine from lactic acid bacteria.