Abstract
This study optimized the headspace solid phase microextraction (HS-SPME) conditions for the analysis of the volatile flavor compounds of Chinese south stinky tofu brine by gas chromatography-mass spectrometry (GC-MS). The optimum HS-SPME conditions established were as follows: polar column CD-WAX, white 85 μm polyella extractor, extraction temperature 60 °C, equilibrium time 20 min, extraction time 40 min. Under these conditions, a total of 63 volatile flavor compounds in five stinky tofu brines were identified. The offensive odor of the stinky tofu may be derived from some of the volatile flavor compounds such as phenol, p-cresol, 3-methylindole, indole, acetic acid, propionic acid, isobutyric acid, n-butyric acid and 3-methylbutanoic acid. The volatile flavor substances data was examined by principal component analysis (PCA) to visualize the response patterns in the feature space of principal components (PC). PCA analysis results revealed that the Chengshifu brine (STB1) and Baise jingdian brine (STB4) are similar in PC 1, 2, and 3, and the two brines have a similar flavor. Results also indicate that the Huogongdian brine (STB2) and Wangcheng brine (STB3) can be grouped in the same class as they are similar in PC 3. However, PC 1, 2, and 3 of the Luojia brine (STB5) and other brands of brine are different as is the flavor.
Highlights
Stinky tofu, known as Oriental cheese, is one of the time-honored traditional snacks in China.According to the process technology, there are two kinds of stinky tofu: southern stinky tofu and northern stinky tofu
Stinky tofu brine is the key point in the process, which is made by a natural fermentation of soy sauce, mushroom, amaranth, and bamboo shoots mixed with water from several months to 1–2 years [5]
The volatile components of stinky tofu brine were separated by three chromatographic columns of different degrees of polarity
Summary
Known as Oriental cheese, is one of the time-honored traditional snacks in China. According to the process technology, there are two kinds of stinky tofu: southern stinky tofu and northern stinky tofu. As one of the famous southern stinky tofu, is a consumer favorite for its characteristics of being “black as ink,” “fragrant as alcohol,” “tender as crisp,” “soft as velvet” and “rich in nutrition” [1,2,3,4]. A delicious food, is first dipped into the fermented brine for several hours or days. Stinky tofu brine is the key point in the process, which is made by a natural fermentation of soy sauce, mushroom, amaranth, and bamboo shoots mixed with water from several months to 1–2 years [5]. The transfer of microorganisms, Molecules 2018, 23, 3155; doi:10.3390/molecules23123155 www.mdpi.com/journal/molecules
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