Physicochemical, microbial, and aroma characteristics of Chinese pickled red peppers (Capsicum annuum) with and without biofilm.

Qixian Zhang,Xinyi Tan,Qisheng Zhang,Yuanlong Chi,Yao Ren,Chuanjie Gong,Kai Yao,Feng Zhang

doi:10.1039/d0ra00490a

Abstract

Biofilm formation in the production of fermented vegetable might impact its quality and safety. In this study, physicochemical and microbial properties, volatile and aroma-active compounds between PRPs without biofilm (NPRP) and with biofilm (FPRP) were investigated by gas chromatography-mass spectrometry, gas chromatography-olfactometry, aroma extract dilution analysis, and spiking tests. The pH and titratable acidity were 3.66 ± 0.00 and 0.47 ± 0.08 g/100 g lactic acid in NPRP and 3.48 ± 0.01 and 0.87 ± 0.10 g/100 g lactic acid in FPRP, respectively. The nitrite level of the two PRPs was 1.87–1.92 mg kg−1, which was below the limited value (20 mg kg−1) of fermented vegetables regulated by the GB2760-2017. FPRP had relatively higher microbial and yeast numbers than NPRP, three common pathogens, namely, Salmonella spp., Staphylococcus aureus, and Shigella spp. were not detected. A total of 70 and 151 aroma compounds were detected in NPRP and FPRP, respectively, including 13 classes of compounds. The dominant aroma attributes of FPRP were sour, floral, mushroom-like, green, and smoky, while NPRP exhibits a mushroom-like flavor. Acetic acid, ethanol, α-terpineol, (E)-2-nonenal, 2-heptanol, phenylethyl alcohol, and linalool were potent key aroma-active compounds in NPRP and FPRP. Results of spiking tests showed that the addition of each substance not only increased its own odour, but also had significant effects on other smells. FPRP displayed richer varieties and contents of aroma profile than NPRP. However, some compounds, such as 4-ethylguaiacol and 4-vinylguaiacol, which were only detected in FPRP, had negative roles on the aroma attributes.

Highlights

Fermented foods, such as fermented sausage, yogurt, vinegar, wine, and fermented vegetables, produced or preserved by the action of microorganisms, are popular worldwide
A bio lm always appears on the surface of fermented foods and solutions
The indicators of pH and titratable acidity (TTA) are employed to evaluate the maturity of Chinese pickles, and the fermented vegetables were considered mature when pH was lower than 4 and TTA was higher than 0.3 g/100 g

Summary

Introduction

Fermented foods, such as fermented sausage, yogurt, vinegar, wine, and fermented vegetables, produced or preserved by the action of microorganisms, are popular worldwide. A bio lm always appears on the surface of fermented foods and solutions. Bio lm formation depends on genetic bases and their regulation, and on properties of the substratum and bacterial cells as well as environmental factors including pH, temperature and nutrient components.. Avor is an important index for the evaluation of fermented food. Bio lm helps convert substrates to acids and Fermented vegetables, as a common fermented food, are generally produced by immersing fresh vegetable in brine with certain salt concentration (4–15% w/w). Various fermented vegetables are found in different regions and countries, such as the fermented cucumbers in the USA, the fermented olives in the Mediterranean region, kimchi in Korea, and paocai in

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