Microwave treatment, proteins

Finally, many of the newer fixation methods incorporate microwave treatments, either for the fixation itself or to speed fixation of other reagents (6). Direct microwave fixation is probably fixation due to heat, and is primarily a coagulation of the proteins. In conjunction with fixatives, microwaving probably speeds the reaction by heating the solution. It also perhaps speeds the penetration of the solution due to the relaxing of the cell structure. 

Samples used for analyses of functional properties were the redissolved protein fractions (RDP) from the unheated, the 60 sec microwave treatment and from the hot water treatments that had subsequently been freeze-dried, a procedure reported to result in minimum denaturation (7.) - At least six determinations were done for each test. 

Table II gives the results of residual trypsin inhibitor levels for the various soymilk preparations. The 90 and 120 sec microwave treatments were the most effective in inactivating the trypsin inhibitor complex while hot water treated and unheated samples showed the highest levels. It is not surprising to find that microwave processing is more efficient than hot water in suppressing trypsin inhibitor considering the rapid penetration of food material by microwaves and the susceptibility of protein action to small heat induced changes in tertiary structure. Hence, Collins and McCarty (12) found microwaves produced a more rapid destruction of endogenous potato enzymes (polyphenol oxidase and peroxidase) than hot water heating.

Although the soybeans used in this study were soaked prior to microwave treatment, this may not he necessary. It has been observed (Pour-El, personal communication) that irradiation of soybeans containing only innate moisture (6-7 ) for a period comparable to those used in this work reduced trypsin inhibitor levels by 90%. Allowing the microenvironmental water of the protein to be the energy transmitter reduced the time needed for inactivation. It was postulated that adding moisture actually reduced the process efficiency because of the energy required to heat the additional water. 

It will be noted that the two proteins, trypsin inhibitor and lipoxidase, are apparently influenced differently by the microwave treatment. While microwave heating is more effective than hot water in destroying trypsin inhibitors (Table II) the reverse is true for lipoxidases(Table III). 

Before applications are dealt with, the main variables governing microwave-assisted processes and the parameters characterizing specific microwave treatments are examined. The applications discussed include not only microwave-assisted digestion and extraction — which are the two most widely implemented and hence those with the highest potential interest to readers — but also others of special significance to solid sample treatment such as microwave-assisted drying, distillation and protein hydrolysis. Finally, some safety recommendations on the use of microwave equipment are made. 

The pH change could have a significant effect on dielectric properties of a material. In the case of SPl, it was observed that the e value increased at pH 4.5 and 10. However, there were not any significant differences in e at pH 4.5 and 10 as compared to the value at the neutral pH. The penetration depth varied significantly with pH, temperature, and frequency. As microwave treatment time progresses, an increase in binding and redistribution of water around protein molecules was observed. This effect could be attributed to the transformation of macromolecules due to heating (Ahmed et al., 2008). 

The synthesis of benzo[Z>]furan derivatives has become a very active field because these molecules have been recently identified as having a variety of biological activities. For example, they can function as inhibitors of protein tyrosine phosphatase IB with antihyperglycemic properties <00JMC1293>, as well as potent and short-acting p-blockers in the treatment of various cardiovascular diseases . An inexpensive, reusable clay has been utilized to catalyze a facile cyclodehydration under microwave without solvent to form 3-substituted benzo[2>]furans from substituted a-phenoxy acetophenones 104. One of the important features of this procedure is that all the selected cyclodehydration reactions are complete in less than 10 minutes <00SL1273>. 

Figure 6. Scanning electron micrographs of freeze-dried protein fractions from soy milk (a, b, c) untreated, (d, e, f) 60-sec microwave, (g, h, i) hot water treatment. Note relative size of pores (arrows). (0—0) Unheated (B-B) 60-sec microwave (A—A) hot water.

In the case of protein, heat treatment of pork does not greatly affect retention as long as the critical temperature or time is not greatly exceeded according to Sebranek (1988). This has been suggested to be about 100°C and less than 1 hr, respectively. Heating methods (microwave, steam, infra-... 

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