Subramanian Anand, Ahn Juhee, Balasubramaniam V M, Rodriguez-Saona Luis
Department of Food Science and Technology, Ohio State University, 2015 Fyffe Court, Columbus, Ohio 43210, USA.
J Agric Food Chem. 2007 Oct 31;55(22):9311-7. doi: 10.1021/jf0708241. Epub 2007 Oct 2.
Pressure-assisted thermal processing (PATP) is being widely investigated for processing low acid foods. However, its microbial safety has not been well established and the mechanism of inactivation of pathogens and spores is not well understood. Fourier transform infrared (FT-IR) spectroscopy was used to study some of the biochemical changes in bacterial spores occurring during PATP and thermal processing (TP). Spore suspensions (approximately 10(9) CFU/mL of water) of Clostridium tyrobutyricum, Bacillus sphaericus, and three strains of Bacillus amyloliquefaciens were treated by PATP (121 degrees C and 700 MPa) for 0, 10, 20, and 30 s and TP (121 degrees C) for 0, 10, 20, and 30 s. Treated and untreated spore suspensions were analyzed using FT-IR in the mid-infrared region (4000-800 cm(-1)). Multivariate classification models based on soft independent modeling of class analogy (SIMCA) were developed using second derivative-transformed spectra. The spores could be differentiated up to the strain level due to differences in their biochemical composition, especially dipicolinic acid (DPA) and secondary structure of proteins. During PATP changes in alpha-helix and beta-sheets of secondary protein were evident in the spectral regions 1655 and 1626 cm(-1), respectively. Infrared absorption bands from DPA (1281, 1378, 1440, and 1568 cm(-1)) decreased significantly during the initial stages of PATP, indicating release of DPA. During TP changes were evident in the bands associated with secondary proteins. DPA bands showed little or no change during TP. A correlation was found between the spore's Ca-DPA content and its resistance to PATP. FT-IR spectroscopy could classify different strains of bacterial spores and determine some of the changes occurring during spore inactivation by PATP and TP. Furthermore, this technique shows great promise for rapid screening PATP-resistant bacterial spores.
压力辅助热加工（PATP）正在被广泛研究用于低酸性食品的加工。然而，其微生物安全性尚未得到充分确立，病原体和孢子的失活机制也尚未完全了解。傅里叶变换红外（FT-IR）光谱被用于研究在PATP和热加工（TP）过程中细菌孢子发生的一些生化变化。酪丁酸梭菌、球形芽孢杆菌和三株解淀粉芽孢杆菌的孢子悬浮液（约10⁹CFU/mL水）分别用PATP（121℃和700MPa）处理0、10、20和30秒，以及用TP（121℃）处理0、10、20和30秒。处理过和未处理的孢子悬浮液在中红外区域（4000 - 800cm⁻¹）使用FT-IR进行分析。基于类类比软独立建模（SIMCA）的多变量分类模型使用二阶导数变换光谱建立。由于其生化组成的差异，特别是吡啶二羧酸（DPA）和蛋白质二级结构的差异，孢子可以在菌株水平上被区分。在PATP过程中，蛋白质二级结构的α-螺旋和β-折叠变化分别在1655和1626cm⁻¹光谱区域明显可见。来自DPA的红外吸收带（1281、1378、1440和1568cm⁻¹）在PATP初始阶段显著下降，表明DPA的释放。在TP过程中，与二级蛋白质相关的谱带变化明显。DPA谱带在TP过程中几乎没有变化或没有变化。发现孢子的钙-DPA含量与其对PATP的抗性之间存在相关性。FT-IR光谱可以对不同菌株的细菌孢子进行分类，并确定在PATP和TP导致孢子失活过程中发生的一些变化。此外，这项技术在快速筛选抗PATP细菌孢子方面显示出巨大潜力。
