Rose bengal agar

E. coli O157:H7, AMC, aerobic psychrotrophic count (APC), coliforms, and molds and yeasts (M&Y) were analyzed immediately after acid disinfection and at the end of the storage period (day 5). At the sampling points, 10 g was sampled and each piece was divided into four parts to ensure full contact with the NaCl solution. Next, 5 g of the sample was placed in an Erlenmeyer flask containing 70 mL of 8.5 g/L NaCl solution and shaken for 3 min at 260 rpm to prepare a 15-fold dilution, after which 6 mL of the suspension was added to 34 mL of 8.5 g/L NaCl solution to prepare a 100-fold dilution [2 (link)]. Other dilutions were prepared as needed. A 1 mL dilution was pour-plated onto (1) plate count agar (Hopebio) and incubated at 37 °C for 2 days for the measurement of AMC, as well as at 7 °C for 10 days for the measurement of APC and (2) violet red bile glucose agar (VRBGA; Hopebio) and incubated at 37 °C for 1 day for the measurement of coliforms. Moreover, a 0.1 mL dilution was surface-plated on (3) rose Bengal agar (Hopebio) and incubated at 30 °C for 3 days for the measurement of M&Y; (4) SMAC agar (Hopebio) and incubated at 37 °C for 1 day for the measurement of E. coli O157:H7; and (5) Listeria chromogenic agar (Land Bridge) and incubated at 37 °C for 1 day for the measurement of L. monocytogenes. The results are expressed as microbial reductions (log CFU g⁻¹).

After disinfection, the samples (15 g) were transferred to a sterilized stomacher bag, diluted 1:15 in 225 mL of sterilized 0.85% NaCl solution and homogenized in a stomacher for 90 s. For E. coli and L. monocytogenes, 0.1 mL of diluted bacterial suspension was surface-plated on SMAC agar and Listeria chromogenic agar, respectively, and microbial counts were obtained after a 24-h incubation period at 37 °C. For naturally present microbial taxa, 0.1 mL of the diluted bacterial suspension was surface-plated on rose Bengal agar (Hopebio) and incubated at 30 °C for three days to quantify molds and yeasts (M&Y). Additionally, 1 mL of the dilution was pour-plated onto plate count agar (Hopebio) and incubated at 37 °C for 2 days to obtain aerobic mesophilic counts (AMC) and at 7 °C for 10 days to obtain aerobic psychrotrophic counts (APC).

Samples were analyzed at 0, 3, and 7 days. A 25-g sample was homogenized with 225 mL sterile NaCl solution for 1.5 min in a stomacher bag. Then, the suspension was serially diluted. The suspension (0.1 mL) was surface-plated on modified sorbitol MacConkey agar (Hopebio), Listeria chromogenic agar (Land Bridge, Beijing, China), and xylose lysine deoxycholate agar (Hopebio) to analyze E. coli O157:H7, L. monocytogenes, and Salmonella Typhimurium, respectively, and incubated for 24 h at 37 °C. For naturally present microbes, 0.1 mL of the diluted bacterial suspension was surface-plated on Rose Bengal agar (Hopebio) and incubated at 30 °C for 3 days to quantify molds and yeasts (M&Y). In addition, 1 mL of the suspension was pour-plated onto plate count agar (Hopebio) and incubated at 7 °C for 10 days to obtain the aerobic psychrotrophic count (APC) and or at 37 °C for 2 days to obtain the aerobic mesophilic count (AMC). All results are expressed as log CFU/g.

Eight samples were randomly selected from the package, transferred to a sterile stomacher bag, diluted 1:9 (w/v) in sterile 0.85% NaCl solution, and homogenized in a stomacher for 2 min. Then, 1 mL of the diluted bacterial suspension was spread-plated on modified sorbitol MacConkey agar (Hopebio) and xylose lysine deoxycholate agar (Hopebio) and incubated for 24 h at 37 °C to analyze E. coli O157:H7 and S. Typhimurium, respectively. For naturally-present microbes, 1 mL of the bacterial suspension was pour-plated in plate count agar (Hopebio) and incubated at 37 °C for 2 d to obtain the AMC, and 1 mL was pour-plated in rose bengal agar (Hopebio) and incubated at 28 °C for 5 days to quantify the M&Y.

The sample and the sterilized 0.85% NaCl were added into a stomacher bag at a ratio of 1:9 (w/v) and homogenized for 2 min to obtain a bacterial suspension. The diluted bacterial suspension (1 mL) was pour-plated into plate count agar (Hopebio, Qingdao, China) and incubated for 2 days at 37 °C to analyze the aerobic mesophilic count (AMC). For molds and yeasts (M&Y), 1 mL diluted suspension was pour-plated into rose bengal agar (Hopebio) and incubated for 5 days at 28 °C. The results were expressed as log CFU/g.

Ten blueberries and 0.85% sterile NaCl solution at a ratio of 1:9 (w/v) were added to a stomacher bag and homogenized for 2 mins under 250 rpm. The bacterial suspensions were then serially diluted. The diluted suspension was surface-plated on modified sorbitol MacConkey agar (Hopebio) and xylose lysine deoxycholate agar (Hopebio) and incubated for 24 h at 37 °C to analyze E. coli O157:H7 and S. Typhimurium, respectively. For naturally present microbes, 1 mL of suspension was pour-plated on plate count agar (Hopebio) and incubated 48 h at 37 °C to analyze aerobic mesophilic counts (AMC). In addition, 1 mL suspension was pour-plated on Rose Bengal agar (Hopebio) and incubated for 5 days at 28 °C to quantify the amount of molds and yeast (M&Y).