Dept. of Food Science, Nutrition and Health Promotion, Mississippi State Univ., Mississippi State, MS 39762, USA.
J Food Sci. 2011 Aug;76(6):M353-60. doi: 10.1111/j.1750-3841.2011.02209.x. Epub 2011 May 27.
Blueberries for the frozen market are washed but this process sometimes is not effective or further contaminates the berries. This study was designed to optimize conditions for hot water treatment (temperature, time, and antimicrobial concentration) to remove biofilm and decrease microbial load on blueberries. Scanning electron microscopy (SEM) image showed a well-developed microbial biofilm on blueberries dipped in room temperature water. The biofilm consisted of yeast and bacterial cells attached to the berry surface in the form of microcolonies, which produced exopolymer substances between or upon the cells. Berry exposure to 75 and 90 °C showed little to no microorganisms on the blueberry surface; however, the sensory quality (wax/bloom) of berries at those temperatures was unacceptable. Response surface plots showed that increasing temperature was a significant factor on reduction of aerobic plate counts (APCs) and yeast/mold counts (YMCs) while adding Boxyl® did not have significant effect on APC. Overlaid contour plots showed that treatments of 65 to 70 °C for 10 to 15 s showed maximum reductions of 1.5 and 2.0 log CFU/g on APCs and YMCs, respectively; with acceptable level of bloom/wax score on fresh blueberries. This study showed that SEM, response surface, and overlaid contour plots proved successful in arriving at optima to reduce microbial counts while maintaining bloom/wax on the surface of the blueberries.
Since chemical sanitizing treatments such as chlorine showed ineffectiveness to reduce microorganisms loaded on berry surface (Beuchat and others 2001, Sapers 2001), hot water treatment on fresh blueberries could maximize microbial reduction with acceptable quality of fresh blueberries.
用于冷冻市场的蓝莓经过清洗，但这一过程有时并不有效，甚至会进一步污染蓝莓。本研究旨在优化热水处理（温度、时间和抗菌剂浓度）条件，以去除蓝莓表面生物膜并减少微生物负荷。扫描电子显微镜（SEM）图像显示，蓝莓在室温水中浸泡后会形成发达的微生物生物膜。生物膜由附着在浆果表面的酵母和细菌细胞组成，这些细胞以微菌落的形式形成，细胞之间或之上产生了胞外聚合物物质。蓝莓暴露在 75 和 90°C 下，表面几乎没有微生物；然而，在这些温度下，蓝莓的感官品质（蜡质/光泽）是不可接受的。响应面图显示，提高温度是减少需氧平板计数（APCs）和酵母/霉菌计数（YMCs）的重要因素，而添加 Boxyl®对 APC 没有显著影响。叠加等高线图显示，在 65 至 70°C 下处理 10 至 15 秒，可分别使 APC 和 YMC 最大减少 1.5 和 2.0 个对数 CFU/g，同时保持新鲜蓝莓的可接受的蜡质/光泽评分。本研究表明，SEM、响应面和叠加等高线图成功地确定了最佳条件，以在保持蓝莓表面蜡质/光泽的同时降低微生物计数。
由于化学消毒剂处理（如氯）对减少负载在浆果表面的微生物效果不佳（Beuchat 等人，2001 年；Sapers，2001 年），因此，对新鲜蓝莓进行热水处理可以最大限度地减少微生物，同时保持新鲜蓝莓的品质。
