A Study On Ohmic Heating Properties And Its Physical-Chemical Characters Of Fruit Juice With Fruit Particles

Ohmic heating calls resistance heating. Ohmic heating of food is a kind of technology to heat sterilization and processing, especially it is a kind of new method that process in succession to go on to viscidity or high food with particles. This technology has advantages such as supplies intensify fast, heating even, high utilization ratio and good processing food. This technology had already appeared more than one century ago, people does not deepen to their understanding and study in an all-round way enough, and its business application is less too. There are some similar studies in foreign countries, the relevant research and development in domestic have just started, and however the research of Ohmic heating of fruit juice with fruit particles has not appeared in the literature dish yet. So, this research is significant. This paper has carried on a deep and extensive research on Ohmic heating properties and impact on its physic-chemistry characters through the following several respects, and drawing the worthy conclusions: (1) Through studying the Ohmic heating properties of liquid food material such as the sodium chloride citric acid with different density and different kinds of fruit juice, the results are: ①The heating results are different in different heating devices: As the area of the polar plate increases and the distance between two polar plates reduces, heat time reduces, heat velocity increases and temperature distribution is even closely. Experimental study showing that: the heating effect is better if adopting the plastic heat sealing tube of long 113mm , internal diameter 75mm and thick of walls 5mm. ②Electric conductivity is the main factor to influence heating velocity of liquid food material, electric conductivity is great, heat time used to heat until 99 degrees Centigrade is little, namely heating velocity is fast; electric conductivity increases with the density of the liquid food material; as the pH value of liquid food material is reduced, the intensity of electrolyte ionization increases, electric conductivity increases, heat time used to heat until 99 degrees Centigrade is little, heating velocity is fast. ③Electric conductivity of the food material increases linearly with rising of temperature; with the rising of temperature, if initial electric conductivity value of material is great their increase range is yet great, namely as the initial value of electric conductivity increases, the slope of electric conductivity straight line increases. ④Laws of heating velocity and temperature changing over time are different because of the different material. Various fruit juice and other liquid food material with high salt, high acid are all fit for Ohmic heating, their heating velocity are relatively bigger. (2)Through studying the Ohmic heating properties of fruit juice with fruit particles, the results are: ①In Ohmic heating of apple juice with apple particles, when the densities and forms of apple particles that apple juice containing are the same, if apple particles are small in size, the time used to heat it until 99 degrees Centigrade is little, electric conductivities of apple juice and apple particles are great that heat in the course, and the heating curve presents the even trend. When the sizes and forms of apple particles that apple juice containing are the same, if apple particles are small in density, the time used to heat it until 99 degrees Centigrade is little, heating velocity is quick, electric conductivities of apple juice and apple particles are great that heat in the course. When the sizes and densities of apple particles that apple juice containing are the same, apple juice with Cube apple particles spends less time than one with spheroid apple particles, electric conductivity of one with cube particles is bigger, and the heating effect with cube particles is better. ②The size , density and form of apple particles in apple juice have plural linear return relation to heat time. The regression model is y? = 308.732+1.097z1 +2.1456z2+16.334z3+0.338z1z2. By statistical check, the equation plans to share well. Its significance level is 0. 01. Namely confidence degree of the equation is 99%. The three factors all have influence on Ohmic heating velocity, the size is the most influential factor, secondly it is density , and then form. ③In the course of Ohmic heating of apple juice with different density of citricacid, and the apple juice containing cube apple particles soaked with different density solution of citric acid, compared with not containing citric acid of apple juice, the laws of heating time and electric conductivity change that impacted by the size, density and form of apple particles is about the same as the aforesaid. But because apple particles have soaked with the citric acid solution and citric acid adding a certain amount in the apple juice, making the electric conductivity of the two increase, heating time is shorten greatly. With the increase of the contents of citric acid in apple juice and citric acid solution soaking apple particles, the electric conductivity increases, and heating time reduces, namely heat velocity accelerates. ④Heating effects are different with the different fruit kinds. The initial electric conductivity of the kiwi fruit is the highest, and its heating velocity is the quickest, secondly it is pine apple , strawberry , grape, the initial electric conductivity of crystal pear is the minimum, and heating velocity is the slowest. With the increase of the size of particle, the heating time to 99 degrees Centigrade increases, the electric conductivity is reduced. ⑤In Ohmic heating of all fruit juice with fruit particles, electric conductivity increases linear with rising of temperature. Besides of grape juice with grape particles that taking the cover, initial conductivity values of fruit particles are smaller than that of relevant fruit juice, however, they'll approximate to, equal or even go beyond that of fruit juice with fruit juice accompanying the climbing of heating temperature. ⑥Fruit juices with fruit particles are all fit to Ohmic heating. The fruit particles and fruit juice can reach and heat at the same time, it will not cause fruit juice processed excessively. The heating result to the fruit juice containing big particle is better . (3)Physical-chemical characters of fruit juice with fruit particles are examined through several heating method such as Ohmic heating from beginning to end, it is found that: ①After different kinds of fruit juices are treated by three kinds of heating methods such as Ohmic heating, microwave heating and traditional heating, the total sugar and total acid of the fruit juice do not change basically. Vc in kiwi juice and orange juice all reduce. Vc reduces least by Ohmic heating. Soluble solid slightly increases.