Acetic acid , dairy products

Enzymatic hydrolysis is a nondestructive alternative to saponification for removing triglycerides in vitamin K determinations. For the simultaneous determination of vitamins A, D, E, and K in milk- and soy-based infant formulas and dairy products fortified with these vitamins (81), an amount of sample containing approximately 3.5-4.0 g of fat was digested for 1 h with lipase at 37°C and at pH 7.7. This treatment effectively hydrolyzed the glycerides, but only partially converted retinyl palmitate and a-tocopheryl acetate to their alcohol forms vitamin D and phyllo-quinone were unaffected. The hydrolysate was made alkaline in order to precipitate the fatty acids as soaps and then diluted with ethanol and extracted with pentane. A final water wash yielded an organic phase containing primarily the fat-soluble vitamins and cholesterol. 

A simple isocratic technique was developed for the quantitative analysis of OAs in dairy products. An Aminex HPX-87 (300-mm X 7.8-mm ID) analytical column was eluted with 0.009 N H2S04 mobile phase UV detection at 220 and 275 nm was utilized. Lactic, citric, formic, acetic, propionic, and butyric acids were quantified for whole milk, skim milk powder,... 

The lactic acid accumulated during the production of fermented milks and cheeses, besides the related pH drop, represents the key component for the antimicrobial effect of dairy LAB against many spoilage and/or pathogenic bacteria. On the other hand, in some dairy products, and mainly in vegetable-based fermented foods or in intermediate food products such as sourdough, acetic acid released by facultatively or obli-gately heterofermentative LAB can account for an additive preservative effect related to fermentation. 

Carbonyl compounds make a particularly significant contribution to the flavor of fermented dairy products. Diacetyl, characterized as having a buttery, nut-like aroma, is one of the most important carbonyls to the flavor of these products. Diacetyl is produced via the fermentation of citrate. The most important citric acid fermenters are Leuconostoc citrovorum, L. creamoris, L. dextranicum, Streptococcus lactis subspecies diacetylactis, S. Thermophilus, and certain strains of Proprionibacterium shermani [90,91]. The metabolic pathway leading to the synthesis of diacetyl involves the degradation of citrate to acetate and oxaloacetate, and the oxaloacetate is then decarboxylated to form pyruvate (Figure 5.9) [92]. Pyruvate plus acetaldehyde forms a-acetolactate, and ultimately, diacetyl. Diacetyl is relatively nontoxic to the bacteria cell so excess pyruvate is channeled into diacetyl. 

Liquid-phase reductive extraction with zinc chloride in an acid medium was tested to extract K vitamers as acetonitrile soluble hydroquinones from dairy products [125,126]. Acid hydrolysis [125] proved advantageous in isolating long chain menaquinones from cheese, provided the digestion time (10 min) was short. Semipreparative LC [125,127,128] and SPE [126] have sometimes been employed as a cleanup and concentration step after solvent extraction. Matrix solid-phase dispersion (MSPD) followed by PLE wifh ethyl acetate at 50°C and 1500 psi [129] and SEE using carbon dioxide at 8000 psi and 60°C [130] are fast, alternative procedures for exfracfing phylloquinone. 

A carboxylic acid contains a carboxyl group, which is a hydroxyl group attached to a carbonyl group. Many carboxylic acids have common names, which are derived from their natural sources. Formic acid is injected under the skin from bee or red ant slings and other insect bites. Acetic acid is produced when ethanol in wines and apple cider reacts with the oxygen in the air. Propionic acid is obtained from the fats in dairy products. Butyric acid gives the foul odor to rancid butter (see Table 14.2). 

Characteristic flavouring substances of fermented dairy products are metabolites of lactic acid bacteria, especially biacetyl, acetaldehyde, dimethylsulfide, lactic and acetic acids, various aldehydes, ketones and esters. An important product is carbon dioxide. The acetaldehyde content in good quality yoghurts is 13-16 M-g/kg, while the biacetyl content is about four times higher. 

Benefat ) Science, USA 4 0, 18 0 intended for use in oven-baked French fries, baked and dairy products, dressings, dips, sauces, cocoa butter substitute, chocolate-flavored coatings of hydrogenated vegetable oils with triacylglycerols containing acetic and/or propionic and/or butyric acids... 

As can be expected, many aspects of the citric acid chemistry are linked with chemical analysis of citric acid or citrates in biological materials [169, 172, 179, 326-328], in fermentation media [179, 188, 192, 329-333], in foods [155, 334-340], in fraits [165, 177, 341-347], in tomato-based products [348-350], in musts, wines and beers [155, 174, 351-363], in soft drinks and fruit juices [155, 165, 177, 361, 364-377], in milk and dairy products [155,170,173,176,378-386], in honey [387, 388], in pharmaceutical formulations [361, 389-391], in medical tests (blood, se-ram, mine, pancreatic juice and other physiological flttids) [162, 183, 187, 193-195,392-400], and in mixtures with other caiboxyhc acids (formic, acetic, tartaric, malic, oxalic, isocitric, succinic, lactic, pyruvic, oxalacetic and others) [160, 184, 211,265,401-409]. 

Mixed cultures of a broad variety of microorganisms, especially of bacteria and yeasts in particular have been used for millenia to produce dairy products, bread, and alcoholic beverages. The foundations for a scientific approach, however, were laid by L. Pasteur [1] in 1862 by using a pme culture of Bacterium xylinum to transform [2] ethanol into acetic acid. In 1874, Dumas [3] reported the reduction of sulfur to hydrogen sulfide by fermenting yeast, Sacdiaromyces ceremsiae. The first reduction ("phytochemical reduction") of an organic molecule imder anaerobic conditions was performed by Windisch [4] in 1898, and fiufuryl alcohol 2 was obtained from furfural 1 (Figure 21.1). 

Microbial transformations, and yeast-mediated conversions in particular, have been widely used since the early days of mankind for the production of dairy products, bread, and alcoholic beverages. Whereas all of these early applications used mixed cultures of microorganisms it was the merit of Pasteur in 1862 [1] to lay a scientific foundation of one of these early applications, namely, the oxidation of alcohol to acetic acid by using a pure culture of Bacterium xylinium. All of these early biotechnological operations have been more or less directed in the areas of agricultural and humane nutrition the reduction of furfural to furfuryl alcohol under anaerobic conditions of fermentation, however, by means of living yeast [2,3] was the first phytochemical reduction of an organic molecule described in the literature. 

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