Association of Anoxybacillus sp. with acid off-flavor development in a spoiled, boiled, rice dish

• Published in: International journal of food microbiology 2018-12, Vol.286, p.111-119
• Main Authors: Suzuki, Yasunori, Kobayashi, Makiko, Saito, Ikue, Igarashi, Tsuyoshi, Kubota, Hiroaki, Kato, Rei, Suzuki, Jun, Hirai, Akihiko, Sadamasu, Kenji
• Format: Article
• Language: English
• Subjects: Acetic acid; Acetic Acid - metabolism; Acids; Anoxybacillus; Anoxybacillus - genetics; Anoxybacillus - isolation & purification; Anoxybacillus - metabolism; Bacteria; Base Sequence; Carbohydrate metabolism; Carbohydrate Metabolism - physiology; Carbohydrates; Condensation; Contamination; Flavors; Food contamination; Food contamination & poisoning; Food Microbiology; Gene expression; Gene sequencing; Genetic testing; Genome, Bacterial - genetics; Genomes; Ipomoea batatas - microbiology; Metabolism; Next-generation sequencing; Odor thresholds; Odors; Off flavor; Oryza - microbiology; Phylogeny; Polymerase chain reaction; Potatoes; Reverse transcription; Ribonucleic acid; RNA; RNA, Ribosomal, 16S - genetics; RNA-seq; Starch; Sweet potatoes; Temperature; Whole Genome Sequencing
• ISSN: 0168-1605; 1879-3460
• DOI: 10.1016/j.ijfoodmicro.2018.07.025

Off-flavor is one of the most common food complaints. In this study, we demonstrated that acetic acid produced by Anoxybacillus sp. contamination of takikomi-gohan (boiled rice with sweet potato mixed in advance) was considered the causative agent of acid off-flavor development. First, we conducted whole genome sequencing of the bacterial strain (S1674) isolated from the remains of the contaminated takikomi-gohan, and phylogenetic analysis of k-mer diversity demonstrated that S1674 belongs to the Anoxybacillus genus. Gene expression analysis of S1674 RNA sequencing (RNA-seq) and quantitative reverse transcription polymerase chain reaction (qRT-PCR) indicated that the genes encoding enzymes responsible for acetic acid formation, namely ackA1, eutD, pflA, pflB, and pykA, were upregulated in high-temperature cultures in Thermus medium supplemented with soluble starch. Additionally, we succeeded in reproducing the acid off-flavor by adding S1674 to boiled rice stored at 37 °C, 45 °C, and 60 °C. The most strongly detected organic acid was acetic acid, at the odor threshold value or more in both the air and condensation samples. Our findings suggest that some Anoxybacillus sp. produce acetic acid as a byproduct of carbohydrate metabolism, potentially causing the complaint of acid off-flavor even under high-temperature conditions in which other bacteria cannot survive. •Acetic acid produced by Anoxybacillus S1674 causes a complaint of off-flavor.•S1674 expresses the genes for acetic acid formation in the presence of soluble starch.•Acetic acid is detected from boiled rice inoculated with S1674 over an odor threshold.