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In the present study, we aimed to investigate the effects of pH and sodium chloride (NaCl) concentration on the structure of β‐casein (β‐CN) purified from buffalo milk using circular dichroism (CD), intrinsic tryptophan, and anilino‐8‐naphthalene sulfonate (ANS) fluorescence spectroscopy. We found that NaCl concentration played a critical role in the stability of the secondary structure of β‐CN. The CD negative peak had a redshift as the NaCl concentration was increased and accompanied by a decrease of β‐sheet content and an increase of α‐helix content. ANS fluorescence spectroscopy also indicated that higher NaCl concentration and lower pH significantly affected the tertiary structure of β‐CN. Dynamic light scattering (DLS) results showed that the particle size of buffalo β‐CN had a blueshift, and then a redshift within the pH range of 5.0–7.5, and it showed a redshift when the NaCl concentration was increased., This study aimed to investigate the effects of pH and NaCl concentration on purified β‐casein structure from buffalo milk using circular dichroism (CD), intrinsic tryptophan and ANS fluorescence spectroscopic. It was found that NaCl concentration was a critical factor in affecting stability of the secondary structure of β‐casein.

In this work, an exploratory study was conducted to examine Gram staining based on the capillary tube. Each Gram staining step for all bacterial strains tested was completed in capillary tubes. The results showed that different Gram staining morphologies were clearly visible in the capillary tubes. The results presented here demonstrated that the improved method could effectively distinguish between Gram-positive and Gram-negative bacteria, and only small volumes of reagents were required in this method. Collectively, this efficient method could rapidly and accurately identify the types of bacteria. Therefore, our findings could be used as a useful reference study for other staining methods.