Sterilizing Effect Of Ohmic Heating On Alicyclobacillus Acidoterrestris In Apple Juice

There are many quality-problems in the apple juice concentrate (AJC) industry, such as Alicyclobacillus acidoterrestris, and et al. They have strongly restrained the development of the fruit juice industry in China, Alicyclobacillus acidoterrestris is one of the most serious quality problems in the AJC industry, and it is also the major technical barriers of China's fruit juice industry nowadays.Alicyclobacillus spp. is currently one of the microorganisms of concern in the fruit juice industry. Especially the Alicyclobacillus acidoterrestris(AAT)-often called as thermophic acidophlic bacterium(TAB), is an important target microorganism in quality control of AJC. The spores of A. acidoterrestris are relatively heat resistant and can survive the commercial pasteurization process applied to AJC, and produce an off flavor in the apple juice. Researches indicate that the concentrate of 1CFU A. acidoterrestris /10g AJC will cause such a spoilage.Nowadays, people pay more and more attention to the Ohmic heating processing method, ohmic heating is based on passing an alternating electrical current (at 50 or 60 Hz) through a food sample, this results in internal energy generation in foods. This produces an inside-out heating pattern, since the food will present an electrical resistance to the current, then it will be heated rapidly. Ohmic Heating technology has both thermal effect and non-thermal effect on the microbes, it destroys the cell membrane and results in the death of the microbes, so it can reduce the sterilizing temperature and has great potentiality.The thesis studies the ohmic heating behavior of apple juice and its sterilizing effect on Alicyclobacillus acidoterrestris, it also studies the mechanism of ohmic heating on microbes and its influence on apple juice quality. The contents are as following:Firstly, ohmic heating behavior of apple juice was studied, Secondly, the sterilizing effect of ohmic heating on Alicyclobacillus acidoterrestris was studied, Thirdly, the non-thermal effect verification of ohmic heating on the microbe by bio-microscope and environmental scanning electron microscope (ESEM), and using conductomcter and ultraviolet spectrophotometer to detect the leakage of the intracellular contents Fourly,it studies the influence of ohmic heating on apple juice quality.And the results showed the conclusions as following:(l)The ohmic heating behavior of apple juice showed that the electrical conductivity of apple juice increased with temperature. The electrical conductivity and heating rate increased with soluble solid content when it was less than 26°Brix, but they would reduced when the soluble solid content was more than 26°Brix;the heating rate increased with electrical field strength and deduced with pH value, and at the same electrical field strength, the volume had no influence on the heating rate.(2) Ohmic heating can destroy the Alicyclobacillus acidoterrestris efficiently, the sterilizing effect on Alicyclobacillus acidoterrestris was increased with temperature, voltage and volume, decreased with pH value, increased with soluble solid content when it was less than 18°Brix, but they would reduced when the soluble solid content was more than 18°Brix;and the time had no influence on the sterilizing effect, considering to keep nutrition and save energy, the optimal temperature is 70°C,and the influential factors in turn are pH value, temperature, voltage , volume and soluble solid content then we get the optimal condition A2B4C1D4E3: the temperature is 70°C, the voltage is 250V, the pH value is 3.5, the volume is 10cm and the soluble solid content is 18°Brix.(3) The sterilization of Alicyclobacillus acidoterrestris with ohmic heating was thought to be electroporation. ESEM photographs of untreated and treated Alicyclobacillus acidoterrestris showed that crushed and destroyed microbe resulted from the combined effects, the increase of the electrical conductivity and the OD value indicate the leakage of the intracellular contents.(4) Ohmic heating has both thermal effect and non-thermal effect on Alicyclobacillus acidoterrestris, and has no negative influences on apple juice quality, it has a little influences on color value, absorbance and transparence, and has no influences on soluble solid content, pH value and turbidity. It could reduce the pasteurization condition and is favorable to keep the nutrition of the apple juice. Therefore ohmic heating technology has great development prospect.