射频加热杀灭浓缩苹果汁中鲁氏接合酵母的工艺优化

为研究射频对苹果汁中鲁氏接合酵母杀灭作用,该文以鲁氏接合酵母为试验菌株,通过单因素试验分析了射频加热时间、极板间距、果汁体积、果汁可溶性固形物对杀菌效果及果汁升温速度的影响。在固定果汁可溶性固形物为70%的条件下,通过响应面试验,建立了鲁氏接合酵母菌落总数降低对数值的二次多项数学模型,确定了在极板间距为110 mm、果汁体积40 m L、果汁可溶性固形物70%的条件下射频加热处理70 s,可以使果汁中鲁氏接合酵母菌落总数下降6个对数值以上。研究比较了相同样品经射频和传统水浴杀菌达到相同杀菌效果时,处理前后果汁理化指标及风味变化程度,结果表明,射频(70 s)比水浴(330 s)能更快达到杀菌目的,同时对果汁品质以及风味的影响(P0.01)小于水浴处理。研究结果为射频杀菌方面的深入研究及实际应用提供了参考。

Optimization of Zygosaccharomyces rouxii sterilization from concentrated apple juice by radio frequency heating

Abstract: As the production of concentrated apple juice becomes larger in recent years, the spoilage of osmotolerant yeasts is increasingly serious, and the safety and quality of concentrated apple juice in China has been under serious threat. Zygosaccharomyces rouxii (Z. rouxii) is a kind of osmotolerant yeast which possesses great resistance to osmosis, acid and preservative and might result in spoilage for concentrated apple juice. This is not only a risk to consumers'' health, but also bringing huge losses to the production enterprises. Therefore, it is necessary to seek a new sterilization method which can sterilize Z. rouxii quickly, as well as exert less impact on apple juice quality. Radio frequency (RF) heating sterilization is a novel dielectric heating sterilization method, by which the internal heating is rapidly generated as a result of molecular friction in response to an applied alternating electric ?eld with the frequency between 3 kHz and 300 MHz. This technology can offer the advantages of rapid heating, high penetration depth, heating homogeneity and so on. This article used Z. rouxii as model microorganism, and studied the influence of different factors on apple juice heating and Z. rouxii sterilization under the RF heating treatment. To achieve the goal, single-factor analysis was conducted to measure the effects of RF heating time, polar plates'' spacing, juice volume, juice concentration on the sterilization efficacy. Combining single-factor experiment results and practice, RF heating time, polar plates'' spacing and juice volume were further researched using a three-variable three-level Box-Benhnken design to optimize the sterilization conditions. A quadratic polynomial model for the logarithmic reduction of viable count for Z. rouxii was established, and the results indicated that the interaction effects of RF heating time and polar plates'' spacing, RF heating time and juice volume, and polar plates'' spacing and juice volume were extremely significant (P<0.01). Moreover, the order of significant degree of 3 factors was as follows: polar plates'' spacing > juice volume > RF heating time. When the concentration of apple juice was selected as 70%, the optimized parameters were determined by response surface experiment and they were as follows: polar plates'' spacing of 110 mm, juice volume of 45 mL and heating time of 70 s. Under this optimal condition, at least a reduction of logarithm value of 6 for viable count of Z. rouxii could be achieved. In addition, the verification test showed that there was a good fit between the experimental and the predicted values. Meanwhile, this study also compared the variations of juice physical indicators and juice flavor between RF heating and traditional water bath by electronic nose when achieving the same sterilizing effect. The results indicated that the sterilization rate of RF heating (70 s) was outstandingly faster than water bath (330 s), and furthermore, its impacts on the quality and flavor of apple juice were less than water bath treatment. Therefore, the results indicate that the method of RF heating can efficiently sterilize Z. rouxii in concentrated apple juice. The research provides a theoretical basis for further study on the RF heating sterilization and its application in sterilizing Z. rouxii in concentrated apple juice in industry.