Enzyme in vegetables

Peroxidase, in combination with phenolic compounds, utilizes hydrogen peroxide to bring about oxidation. The enzymes do not act in intact fruits because of the physical separation of enzyme and substrate. Mechanical damage, rot, or senescence lead to cellular disorganization and initiate decomposition. Inhibition of the enzymes in vegetables is achieved by blanching with steam or by... 

Lipase and alkaline phosphatase in milk are ther-molabile (Fig. 2.37), whereas acid phosphatase is relatively stable. Therefore, alkaline phosphatase is used to distinguish raw from pasteurized milk because its activity is easier to determine than that of lipase. Of all the enzymes in the potato tuber (Fig. 2.38), peroxidase is the last one to be thermally inactivated. Such inactivation patterns are often found among enzymes in vegetables. In such cases, peroxidase is a suitable indicator for controlling the total inactivation of all the enzymes e. g., in assessing the adequacy of a blanching process. However, newer developments aim to limit the enzyme inactivation to... 

A continuous stirred tank reactor has been reported for the hydrolysis of the triglycerides existing in vegetable oil in the presence of the aqueous phase and for synthesis reactions (Table 5). A microfilter can be used to prevent the immobilized enzyme from leaving the reactor. Kawano et al. [115] investigated the hydrolysis of olive oil in octane with Candida cylindracea lipase in aqueous solution in a Vibro Mixer reactor containing vibration plates connected to the crankshaft of a motor and oscillated with fixed rates. 

Mayer AM, Harel E. Polyphenol oxidases and their significance in fruits and vegetables, in Enzymes in Foods, Elsevier, Amsterdam, The Netherlands, 1990. 

These enzymes are found in filamentous Cyanobacteria, e.g. Anabaena 7120 (Houchins and Burris 1981), Nostoc sp. strain PCC73102 (Oxelfelt et al. 1998) and Anabaena variabilis (Schmitz et al. 1995) where they occur in the heterocysts. They may also occur in vegetative Anabaena cells grown under microaerobic or anaerobic non-N2-fixing... 

Two broad areas of application for xylanolytic enzymes have been identified (1). The first involves the use of xylanases with other hydrolytic enzymes in the bioconversion of wastes such as those from the forest and agricultural industries, and in the clarification and liquification of juices, vegetables and fruits. For these purposes, the enzyme preparations need only to be filtered and concentrated as essentially no further purification is required. Several specific examples of applications involving crude xylanase preparations include bioconversion of cellulosic materials for subsequent fermentation (2) hydrolysis of pulp waste liquors and wood extractives to monomeric sugars for subsequent production of single cell protein (3-5). Xylose produced by the action of xylanases can be used for subsequent production of higher value compounds such as ethanol (6), xylulose (7) and xyIonic acid (8-9). 

Herrmann, K. Oxidative enzymes and phenolic substrate in vegetables and fruit. I. Hydroxycinnamic acids. Z Lebensm-Unters Forsch 1957 106 341-348. 

Glycerophospholipids contain a glycerol skeleton to which two fatty acids are esterified saturated fatty acids occupy mostly sn-position 1, whereas unsaturated fatty acids are mainly present on sn-position 2. The third hydroxyl is linked to a phosphate group to which an organic base is mostly esterified (Fig. 1). The most important components of soybean lecithin are phosphatidylcholine (PC), phosphatidylethanolamine (PE), and phosphatidylinositol (PI). Phosphatidic acid (PA) may become important due to the presence of phospholipase D this enzyme slowly converts PC into PA in vegetable lecithins. Phosphatidylserine (PS), phosphatidylglycerol (PG), and lyso-phosphatidylcholine (LPC) are known as minor components lysophospholipids contain only one acyl group per molecule. Besides, ether phospholipids occur in which one or both fatty acyl... 

As can be seen in Tables 17.2 and 17.4, a wide variety of different enzymes present in vegetable tissue or in the crude extracts have been immobilized onto Clark-type oxygen electrode membranes or in carbon paste electrodes. To facilitate understanding of the operation of electrode containing PPO or peroxidase in combination with amperometric biosensors a brief discussion is provided below. 

PPO and peroxidase are widely distributed in the plant kingdom and have been detected in most known fruits and vegetables. The concentration of these enzymes in plants depends on the species, cultivation, age and maturity [61-64]. 

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