Department of Food Science and Technology, Pharmaceutical Sciences Branch, Islamic Azad University, Tehran, Iran.
Plasma Physics Research Center, Science and Research Branch, Islamic Azad University, Tehran, Iran.
Int J Food Microbiol. 2019 Sep 2;304:39-48. doi: 10.1016/j.ijfoodmicro.2019.05.015. Epub 2019 May 25.
A novel and facile method is developed for rapid estimation of lactic acid bacterial concentration in fermented milk. Growth of bacteria in a liquid changes physicochemical property of the medium and its behavior at solid-liquid interface. Wettability determines characteristic of solid-liquid interface. Nano-rod, helical tetragonal and L-shaped morphologies were designed and fabricated. Hydrophobicity and zeta potential were measured for dried surfaces of 5 dairy bacterial strains. Relationship between microbial population and changes in solid-liquid interface was studied by wettability and surface free energy measurements. Due to hydrophobic surface property of conventional dairy strains, they strongly affect solid-liquid and liquid-vapor surface tensions when dispersed in a liquid, which are dependent on the bacterial concentration. Response surface methodology results showed that type and concentration of bacteria, droplet volume and solid-surface morphology affect wettability significantly. Higher hydrophobicity resulted in higher ∆θ (absolute value of the difference between the pure physiological saline and the bacterial suspension contact angles) dependence on the bacterial concentration. Probiotic bacteria concentration in fermented milk was estimated using the proposed method. A direct relationship was obtained between milk contact angle and bacterial concentration. Results show that this physical method can be applied for rapid estimation of bacterial concentration.
一种新颖且简便的方法被开发出来，用于快速估计发酵乳中的乳酸菌浓度。细菌在液体中的生长改变了介质的物理化学性质及其在固液界面上的行为。润湿性决定了固液界面的特性。设计并制造了纳米棒、螺旋四方和 L 形形态。测量了 5 种乳细菌菌株干燥表面的疏水性和动电电势。通过润湿性和表面自由能测量研究了微生物种群与固液界面变化之间的关系。由于传统乳制品菌株具有疏水性表面特性，因此当它们在液体中分散时，它们会强烈影响固液和液气表面张力，这取决于细菌浓度。响应面法结果表明，细菌的类型和浓度、液滴体积和固体表面形态对润湿性有显著影响。较高的疏水性导致∆θ（生理盐水和细菌悬浮液接触角之间的差值的绝对值）对细菌浓度的依赖性更高。使用所提出的方法估计发酵乳中的益生菌浓度。获得了牛奶接触角与细菌浓度之间的直接关系。结果表明，这种物理方法可用于快速估计细菌浓度。
