College of Food Science and Engineering, Northwest A&F University, Yangling, Shaanxi, 712100, China.
College of Food Science and Engineering, Northwest A&F University, Yangling, Shaanxi, 712100, China.
Food Microbiol. 2021 Apr;94:103657. doi: 10.1016/j.fm.2020.103657. Epub 2020 Oct 5.
Alicyclobacillus acidoterrestris has unique thermo-acidophilic properties and is the main cause of fruit juice deterioration. Given the acidic environment and thermal treatment during juice processing, the effects of acid adaptation (pH 3.5, 3.2, and 3.0) on the resistance of A. acidoterrestris to heat (65 °C, 5 min) and acid (pH = 2.2, 1 h) stresses were investigated for the first time. The results showed that acid adaptation induced cross-protection against heat stress of A. acidoterrestris and acid tolerance response, and the extent of induced tolerance was increased with the decrease of adaptive pH values. Acid adaptation treatments did not disrupt the membrane potential stability and intracellular pH homeostasis, but reduced intracellular ATP concentration, increased cyclic fatty acids content, and changed the acquired Fourier transform infrared spectra. Transcription levels of stress-inducible (dnaK, grpE, clpP, ctsR) genes and genes related to spore formation (spo0A, ctoX) were up-regulated after acid adaptation, and spore formation was observed by scanning electron microscopy. This study revealed that the intracellular microenvironment homeostasis, expression of chaperones and proteases, and spore formation played a coordinated role in acid stress adaptive responses, with implications for applications in fruit juice processing.
嗜酸耐热菌具有独特的嗜热嗜酸特性，是导致果汁变质的主要原因。鉴于果汁加工过程中的酸性环境和热处理，首次研究了酸适应（pH 值 3.5、3.2 和 3.0）对嗜酸耐热菌耐热（65°C，5 分钟）和耐酸（pH=2.2，1 小时）应激的影响。结果表明，酸适应诱导了嗜酸耐热菌对热应激的交叉保护和酸耐受反应，诱导的耐受程度随适应 pH 值的降低而增加。酸适应处理不会破坏膜电位稳定性和细胞内 pH 稳态，但会降低细胞内 ATP 浓度，增加环状脂肪酸含量，并改变获得的傅里叶变换红外光谱。酸适应后，应激诱导基因（dnaK、grpE、clpP、ctsR）和与孢子形成相关的基因（spo0A、ctoX）的转录水平上调，并通过扫描电子显微镜观察到孢子形成。本研究揭示了细胞内微环境稳态、伴侣蛋白和蛋白酶的表达以及孢子形成在酸应激适应反应中发挥了协同作用，这对果汁加工应用具有重要意义。
