Lactic acid fermentative production

Fermented milks are cultured dairy products manufactured from whole, partly skimmed, skim, or slightly concentrated milk. Specific lactic acid bacteria or food-grade acids are required to develop the characteristic flavor and texture of these beverages. Fermented milks are either fluid or semifluid in consistency, with various proportions of lactic acid. Fermented products are regulated by federal standards in the United States, as stated in Table 2.2. Other fermented milks without established federal standards are regulated by state standards. Compositional standards for fermented milks have been proposed by the International Dairy Federation (Hargrove and Alford 1974). Typical analyses of various fermented milks, as well as of their condensed and dried counterparts, are given in Table 2.4. 

Table 22.2 Raw materials for lactic acid fermented products in Europe...

Biacetyl is produced by the dehydrogenation of 2,3-butanediol with a copper catalyst (290,291). Prior to the availabiUty of 2,3-butanediol, biacetyl was prepared by the nitrosation of methyl ethyl ketone and the hydrolysis of the resultant oxime. Other commercial routes include passing vinylacetylene into a solution of mercuric sulfate in sulfuric acid and decomposing the insoluble product with dilute hydrochloric acid (292), by the reaction of acetal with formaldehyde (293), by the acid-cataly2ed condensation of 1-hydroxyacetone with formaldehyde (294), and by fermentation of lactic acid bacterium (295—297). Acetoin [513-86-0] (3-hydroxy-2-butanone) is also coproduced in lactic acid fermentation. 

Uneviscerated salted mullet fish was a source of the outbreak (type E) in Egypt (Weber et ah, 1993). The level of carbohydrates in such products is usually too low for lactic acid fermentation. If the pH of the product is not low enough, it will not protect against the outgrowth of C. botulinum. 

Modern methods of livestock production are intensive and the environmental conditions stress the animals. The use of antibiotics promotes growth and protects the animals from otherwise certain infection under these conditions. Antibiotic-like compounds formed in lactic acid fermentations prevent proliferation of spoilage and pathogenic microorganisms and increase the shelf life of the products. Nisin is a antimicrobial produced by a lactic acid bacterium and is used in some countries as a food preservative. Some lactic acid bacteria are capable of favorably influencing the fecal flora in man and animals. 

Differentiation has been based on the main products of the fermentation. Generally, fermentation does not yield homogeneous products. For example, butyric acid is practically always accompanied by other fatty acids, both lower and higher in the series, as well as by alcohols, especially butanol, and by lactic acid. It may be noted that, according to Kempner and Kubowitz, fermentation can be transformed into lactic acid fermentation if the fermentation is carried out in an atmosphere of carbon monoxide. 

Having determined the effect of temperature and NaCl on koji autolysis, the next step in finding an optimal protocol for the rapid production of soy sauce with high flavor quality was to examine die effect of independent and combined effect of lactic acid fermentation and alcohol on koji autolysis. 

A new method for the preparation of soy sauce has been developed. The new scaled-up method divides the moromi process into two processes autolysis and fermentation. Because of the utilization of high temperatures, the new process permits the production of a NaCl free autolyzate from koji. Division of the fermentation process into two separated processes permit better control of lactic acid fermentation and alcohol fermentation processed which used to require great skill. The new scale-up procedure for soy sauce production yields a product in half the time required by the traditional (conventional) method and still produces a soy sauce with high levels of the desirable Bavor component, glutamic acid. Utilization of this protocol by the soy sauce producing industry should have significant economic impact to bo producers and consumers. 

Hydroxy-2-butanone (acetoin) is a characteristic constituent of butter flavour used for flavouring margarine and can be obtained as a by-product of molasses-based and lactic acid fermentations [49, 71]. The closely related 2,3-butanedione (diacetyl) has a much lower organoleptic threshold than acetoin and is an important strongly butter-like flavour compound in butter and other dairy products [72] in buttermilk, for instance, the diacetyl concentration is only about 2-4 mg [73]. a-Acetolactate (a-AL) is an intermediate of lactic acid bacteria mainly produced from pyruvate by a-acetolactate synthase. In most lactic acid bacteria, a-AL is decarboxylated to the metabolic end product acetoin by a-AL decarboxylase (ALDB) [71] (Scheme 23.5). 

The product of this metabolic sequence, pyruvate, is a metabolite of caitral importance. Its fate depends upon the conditions within a cell and upon the type of cell. When oxygen is plentiful pyruvate is usually converted to acetyl-coenzyme A, but under anaerobic conditions it may be reduced by NADH + H+ to the alcohol lactic acid (Fig. 10-3, step h). This reduction exactly balances the previous oxidation step, that is, the oxidation of glycer-aldehyde 3-phosphate to 3-phospho-glycerate (steps a and b). With a balanced sequence of an oxidation reaction, followed by a reduction reaction, glucose can be converted to lactate in the absence of oxygen, a fermentation process. The lactic acid fermentation occurs not only in certain bacteria but also in our own muscles under conditions of extremely vigorous exercise. It also occurs continuously in some tissues, e.g., the transparent lens and cornea of the eye. 

Luedeking and Piret<56) proposed that the formation of microbial products could be described by a two parameter model. This was based on their studies of lactic acid fermentation using Lactobacillus delbruekii in which the accumulation of the acid is not directly linked to the growth rate. The function used was ... 

In general, there is a low risk of high amounts of BAs in vegetables and root crops, where BAs are produced as a result of lactic acid fermentation (81,82). Furthermore, the His contents reported in sauerkraut (83,84), cucumbers (85), and green table olives (86) are far below the level of 100 mg per 100 g that has been associated with outbreaks of food poisoning. Nevertheless, a safe evaluation of the products of natural lactic fermentation should take into account other amines, because Tyr, Put, and Cad can also be produced during sauerkraut fermentation (87). Moreover, certain strains of lactobacilli and cocci have been associated with the presence of these compounds in fermented products (82) and synthetic broth (88). 

Combined use of lactate fermentation and ED separation has been proposed to overcome the main drawbacks of this fermentation process, that is, low microbial acidic productivity and expensive downstream processing of lactic acid fermentation broths (Boyaval et al., 1987 Hongo et al., 1986 ... 

Simultaneous L-lactic acid fermentation (by Rhizopus oryzae immobilized in calcium alginate beads) and separation was carried out using a three-phase fluidized-bed bioreactor as a fermenter (F), an external electrodialyzer as a separator, and a pump to recycle the fermentation broth between the bioreactor and the separator. In this way, the experimental specific lactate productivity and yield practically coincided with those obtained in the CaC03-buffered fermentation process (Xuemei et al., 1999), thus confirming the capability of the combined system to alleviate product inhibition without any addition of alkali or alkali salts. It was also shown that the adoption of ED-F for the production of inoculum reduced variability in inoculum quality, thus shortening the length of the lag phase of L-lactate production practically to zero as compared to that observed using an inoculum... 

Boyaval, P., Corre, C., and Terre, S. 1987. Continuous lactic acid fermentation with concentrated product recovery by ultrafiltration and electrodialysis. Biotechnol. Lett. 9(3), 207-212. 

Lactic acid fermentation occurs when lactate is the end product of fermentation. Coupled with glycolysis, lactic acid fermentation can generate ATP from ADP and provide energy for cellular processes. The fermentation step in lactic acid fermentation generates NAD+ from NADH + H+, and the NAD+ cycles back to the glycolysis process. The lactic acid fermentation cycle is illustrated in Figure 4.10. 

Alcoholic fermentation occurs when the end product is ethanol, as shown in Figure 4.11. In this process the pyruvate is first converted enzymatically to acetaldehyde. The conversion of acetaldehyde to ethanol produces NAD+ from NADH + H+, and the NAD+ is cycled through the glycolysis process. As with lactic acid fermentation, the glycolysis process produces usable energy contained in two molecules of ATP produced for each molecule of glucose metabolized. 

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