Safety evaluation and application of lactic acid bacteria and yeast strains isolated from Sichuan broad bean paste

Abstract

Broad bean paste is one of the most popular characteristic traditional fermented bean products in China, which is prepared by mixed fermentation of a variety of microorganisms, among which lactic acid bacteria and yeast played an important role in the improvement of the fermented broad bean paste quality. However, the traditional open-air fermentation of broad bean paste brought some risks of harmful microorganisms. In this study, the safety and fermentation ability of lactic acid bacteria and yeast strains isolated from traditional broad bean paste was evaluated. The results showed that the protease activity of the strain Lactobacillus plantarum DPUL-J5 (366.73 ± 9.00 U/L) and Pichia kudriavzevii DPUY-J5 (237.18 ± 10.93 U/L) were the highest. Both strains produced little biogenic amines, and did not exhibit α-hemolytic activity or antibiotic resistance for some of the antibiotics most used in human medicine. Furthermore, the broad bean paste fermentation involving DPUL-J5 and DPUY-J5 was beneficial for accumulating higher total acid (1.69 ± 0.01 g/100 g), amino-acid nitrogen (0.85 ± 0.03 g/100 g), and more volatile flavor compounds, meanwhile, reducing the levels of biogenic amines and aflatoxin B1. Therefore, this study provided a new strategy to improve the safety and quality of traditional broad bean paste.

Keywords: broad bean paste; fermentation; lactic acid bacteria; safety evaluation; yeast.

FIGURE 1

The procedures to prepare broad bean paste. (AB) Inoculated with Bacillus subtilis DPUL‐J2 in broad bean koji. (ABL) Inoculated with Bacillus subtilis DPUL‐J2 and Lactobacillus plantarum DPUL‐J5 in broad bean koji. (ABP) Inoculated with Bacillus subtilis DPUL‐J2 and Pichia kudriavzevii in broad bean koji. (ABLP) Inoculated with Bacillus subtilis DPUL‐J2, lactobacillus plantarum DPUL‐J5, and Pichia kudriavzevii in broad bean koji. Aspergillus flavus DPUM‐J1 was used to prepare koji. The material‐to‐liquid ratio was 1:1 (w/v) and submerged into a brine solution (16% w/v, NaCl). The suspension concentration of strain was 10⁸–10⁹ CFU/ml, and the inoculation amount was 2% (v/v)

FIGURE 2

Phylogenetic tree of Lactobacillus plantarum DPUL‐J5 and Pichia kudriavzevii DPUY‐J5

FIGURE 3

Hemolytic activity of Lactobacillus plantarum DPUL‐J5 and Pichia kudriavzevii DPUL‐J5. (a) α‐Hemolytic for Listeria monocytogenes (Positive control); (b) Pichia kudriavzevii DPUL‐J5; and (c) Lactobacillus plantarum DPUL‐J5

FIGURE 4

Physicochemical parameters in fermented broad bean paste with different fermation time. (a) pH; (b) total acid; (c) reducing sugar; and (d) amino‐acid nitrogen. (AB) Lines with solid square marks(■) representing inoculated with Bacillus subtilis DPUL‐J2; (ABL) lines with solid circle marks(●) representing inoculated with Bacillus subtilis DPUL‐J2 and lactobacillus plantarum DPUL‐J5; (ABP) lines with solid upward triangle marks(▲) representing inoculated with Bacillus subtilis DPUL‐J2 and Pichia kudriavzevii DPUL‐J5; (ABLP) lines with solid downward triangle marks(▼) representing coculture with Bacillus subtilis DPUL‐J2, lactobacillus plantarum DPUL‐J5, and Pichia kudriavzevii DPUY‐J5 (p < .05)

FIGURE 5

The contents of biogenic amines in fermented broad bean paste with different fermentation time. (AB) Lines with solid square marks(■) representing inoculated with Bacillus subtilis DPUL‐J2; (ABL) lines with solid circle marks(●) representing inoculated with Bacillus subtilis DPUL‐J2 and lactobacillus plantarum DPUL‐J5; (ABP) lines with solid upward triangle marks(▲) representing inoculated with Bacillus subtilis DPUL‐J2 and Pichia kudriavzevii DPUL‐J5; (ABLP) lines with solid downward triangle marks(▼) representing coculture with Bacillus subtilis DPUL‐J2, lactobacillus plantarum DPUL‐J5, and Pichia kudriavzevii DPUY‐J5 (p < .05)

FIGURE 6

The concentration of AFB1 in fermented broad bean paste (p < .05)