Abstract
Extension of shelf life and preservation of products are both very important for the food industry. However, just as with other processes, speed and higher manufacturing performance are also beneficial. Although microwave heating is utilized in a number of industrial processes, there are many unanswered questions about its effects on foods. Here we analyze whether the effects of microwave heating with continuous flow are equivalent to those of traditional heat transfer methods. In our study, the effects of heating of liquid foods by conventional and continuous flow microwave heating were studied. Among other properties, we compared the stability of the liquid foods between the two heat treatments. Our goal was to determine whether the continuous flow microwave heating and the conventional heating methods have the same effects on the liquid foods, and, therefore, whether microwave heat treatment can effectively replace conventional heat treatments. We have compared the colour, separation phenomena of the samples treated by different methods. For milk, we also monitored the total viable cell count, for orange juice, vitamin C contents in addition to the taste of the product by sensory analysis. The majority of the results indicate that the circulating coil microwave method used here is equivalent to the conventional heating method based on thermal conduction and convection. However, some results in the analysis of the milk samples show clear differences between heat transfer methods. According to our results, the colour parameters (lightness, red-green and blue-yellow values) of the microwave treated samples differed not only from the untreated control, but also from the traditional heat treated samples. The differences are visually undetectable, however, they become evident through analytical measurement with spectrophotometer. This finding suggests that besides thermal effects, microwave-based food treatment can alter product properties in other ways as well.
Highlights
Microwave heat treatment of food products results in both thermal and non-thermal effects
There is no difference between the Beneficial Effects of Microwave and Traditional Heat Treatment on the Shelf Life, the Sedimentation of Fractions and the Generation of CO2 During the Storage of Orange Juice
The results clearly indicated that neither the microwave, nor the traditional heat treatment method caused significant decrease in vitamin C content compared to the control group (Figure 7)
Summary
Microwave heat treatment of food products results in both thermal and non-thermal effects. The non-thermal effects are reactions and processes, during which the physical, chemical or biological conditions of the product change without an increase in its temperature. The application of well-known heat transfer mechanisms (conduction, convection, radiation) and - by another classification - direct and indirect heating methods offer a number of possibilities for heat treatments of food products. For heat treatments of liquid food, the most frequently used methods are plate- or tube-based heat exchangers, where heat transfer is applied indirectly using water or steam. The higher speed of the internal heating - compared to that of the traditional methods based on external heat transfer and heat conduction - made microwave equipment popular for these applications. Additional advantages include energy savings, lower operating costs, fast processing and flexibility; all of which could make the use of microwave attractive in both industrial and small-scale applications [5], [6]
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