Ionic solution and nanoparticle assisted MALDI-MS as bacterial biosensors for rapid analysis of yogurt

Chia-Hsun Lee, Judy Gopal, Hui-Fen Wu
Biosensors and Bioelectronics, Volume 31, Issue 1, January 2012
Abstract

Bacterial analysis from food samples is a highly challenging task because food samples contain intensive interferences from proteins and carbohydrates. Three different conditions of yogurt were analyzed: (1) the fresh yogurt immediately after purchasing, (2) the yogurt after expiry date stored in the refrigerator and (3) the yogurt left outside, without refrigeration. The shelf lives of both these yogurt was compared in terms of the decrease in bacterial signals. AB which initially contained 10⁹ cells/mL drastically reduced to 10⁷ cells/mL. However, Lin (Feng-Yin) yogurt which initially (fresh) had 10⁸ cells/mL, even after two weeks beyond the expiry period showed no marked drop in bacterial count. Conventional MALDI-MS analysis showed limited sensitivity for analysis of yogurt bacteria amidst the complex milk proteins present in yogurt. A cost effective ionic solution, CrO₄²⁻ solution was used to enable the successful detection of bacterial signals (40-fold increased in sensitivity) selectively without the interference of the milk proteins. 0.035 mg of Ag nanoparticles (NPs) were also found to improve the detection of bacteria 2–6 times in yogurt samples. The current approach can be further applied as a rapid, sensitive and effective platform for bacterial analysis from food.

Highlights

1. Bacteria analysis from food samples is a highly challenging task we demonstrate the use of MALDI-MS as bacterial sensor for detection of the bacteria in yogurt
2. Three different conditions of yogurt were analyzed: (1) the fresh yogurt immediately after purchasing, (2) the yogurt after expiry date stored in the refrigerator and (3) the yogurt left outside, without refrigeration.
3. Using bacteria as the markers we were able to assess the quality and shelf life of the yogurt using mass as the sensor.
4. A cost effective ionic solution, CrO42- solution and Ag NPs were used to enable the selective detection of bacterial signals in yogurt sample.

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