Division of Animal and Nutritional Sciences, West Virginia University, Morgantown, West Virginia 26506, USA.
J Food Prot. 2011 Aug;74(8):1348-52. doi: 10.4315/0362-028X.JFP-10-543.
During mechanical fish processing, a substantial amount of protein is discarded as by-products. Isoelectric solubilization and precipitation (ISP) is a process that uses extreme pH shifts to solubilize and precipitate protein from by-products to recover previously discarded protein. Typically, strong acids are used for pH reduction, but these acids do not have a pasteurization effect (6 log reduction) on bacterial load; therefore, organic acids were used during ISP processing to test the impact on Listeria innocua concentrations. Headed and gutted rainbow trout (Oncorhynchus mykiss) were inoculated with L. innocua, homogenized, and brought to the target pH with granular citric acid (pH 2.0 and 2.5) or glacial acetic acid (pH 3.0 and 3.5). Proteins were solubilized for 10 min at 4°C, and insoluble components (e.g., skin and insoluble protein) were removed by centrifugation. The remaining solution was pH shifted to the protein isoelectric point (pH 5.5) with sodium hydroxide, and precipitated protein was separated from the water. Microbial cells for each component (proteins, insolubles, and water) were enumerated on modified Oxford agar (MOX) and tryptic soy agar with 6% yeast extract (TSAYE). The sums of the surviving cells from each component were compared with the initial inoculum levels. No significant differences were observed between results obtained from TSAYE and from MOX (P > 0.05). Significant reductions in microbial populations were detected, regardless of pH or acid type (P < 0.05). The greatest reduction was at pH 3.0 with glacial acetic acid, resulting in a mean reduction of 6.41 log CFU/g in the recovered protein and 5.88 log CFU/g in the combined components. These results demonstrate the antimicrobial potential of organic acids in ISP processing.
在机械鱼类加工过程中，会产生大量的蛋白质作为副产品被丢弃。等电溶解沉淀（ISP）是一种利用极端 pH 值变化来溶解和沉淀副产品中的蛋白质以回收先前丢弃的蛋白质的过程。通常，使用强酸来降低 pH 值，但这些酸对细菌负荷没有巴氏杀菌效果（6 个对数减少）；因此，在 ISP 处理过程中使用有机酸来测试其对无害李斯特菌浓度的影响。将头和内脏的虹鳟（Oncorhynchus mykiss）接种无害李斯特菌，均质化，并使用颗粒柠檬酸（pH 2.0 和 2.5）或冰醋酸（pH 3.0 和 3.5）将其 pH 值调至目标 pH 值。蛋白质在 4°C 下溶解 10 分钟，然后通过离心去除不溶性成分（例如，皮肤和不溶性蛋白质）。将剩余的溶液 pH 值调至蛋白质等电点（pH 5.5），用氢氧化钠沉淀蛋白质，并将其与水分离。用改良牛津琼脂（MOX）和含 6%酵母提取物的胰蛋白酶大豆琼脂（TSAYE）对每个成分（蛋白质、不溶性物和水）中的微生物细胞进行计数。将每个成分中存活细胞的总和与初始接种物水平进行比较。在 MOX 和 TSAYE 获得的结果之间未观察到显著差异（P > 0.05）。无论 pH 值或酸类型如何，都检测到微生物种群的显著减少（P < 0.05）。在 pH 3.0 时使用冰醋酸的减少幅度最大，导致回收蛋白质中的平均减少 6.41 log CFU/g，组合成分中的平均减少 5.88 log CFU/g。这些结果表明，有机酸在 ISP 处理中具有抗菌潜力。
