Pomegranate Peel as a Sustainable Additive for Baijiu Fermentation: Physicochemical and Flavor Analysis with Process Optimization

Rice hulls, a traditional ingredient in Chinese light-flavor Baijiu, contribute to bran and furfural flavors but may adversely affect the aroma and taste. This study explores fresh pomegranate peel as a sustainable alternative to rice hulls in Baijiu fermentation. The flavor profiles in jiupei and Baijiu were interpreted by employing head-space solid-phase microextraction coupled with gas chromatography-mass spectrometry (HS-SPME-GC-MS), while their physicochemical characteristics were systematically assessed. Statistical evaluations, such as correlation analysis and cluster analysis, were conducted to interpret the data. The results showed that compared with rice hull, pomegranate peel reduced furfural content in jiupei by 90%, increased the alcohol distillation rate (alcohol distillation rate: this refers to the weight percentage of 50% alcohol by volume (ABV) Baijiu produced from a unit amount of raw material under standard atmospheric pressure at 20 °C (also known as Baijiu yield)) by 30%, enhanced antioxidant capacity by 24.38%, and improved starch efficiency by 3%. Notably, the Baijiu complied with the premium Baijiu standards specified in the Chinese National Standard for light-flavor Baijiu. Additionally, under the experimental conditions of this study, the optimal Baijiu yield (optimal Baijiu yield: the maximum achievable Baijiu production under defined constraints (e.g., energy input, time, cost)) (48% ± 3.41%) correlated with the pomegranate peel particle size. This research highlights the viability of using pomegranate peel as a sustainable and environmentally friendly adjunct in the fermentation of light-flavor Baijiu, offering valuable perspectives for exploring alternative brewing ingredients.

Characterization of the content characteristics of pyrazines and volatile phenols in Chinese Baijiu Daqu by QuEChERS-UPLC-MS/MS approach

Based on QuEChERS dispersed purification and UPLC-MS/MS, a novel robust and sensitive approach for the detection of pyrazines and volatile phenols in Baijiu Daqu was established. Pyrazines and volatile phenols were purified by dispersion with primary secondary amine (PSA)/C18 and C18 respectively. Volatile phenols were analyzed by UPLC-MS/MS after being derivatized with dansyl chloride. The matrix effect value of the established method falls within the range 85.46 %-102.68 %. The method attains excellent extraction recoveries (78.32 %-109.45 %), demonstrating outstanding repeatability (precisions < 10 %). The limits of detection for pyrazines and volatile phenols are 0.09-1.54 μg/kg and 0.09-0.19 μg/kg, respectively. Through analysis of different quality levels of medium-high Daqu, it was found that in high-quality Daqu, 2-ethyl-3,5-dimethylpyrazine, vanillin and 4-vinylguaiacol are particularly prominent, with vanillin reaching concentrations as high as 2546.32 μg/kg in premium Daqu. In low grade Daqu, the levels of 2,3,5,6-tetramethylpyrazine, 2,3,5-trimethylpyrazine and p-Cresol are notably elevated. Analysis of different fermentation stages of Daqu reveals that pyrazines and volatile phenols are significantly synthesized in the late and middle stages of fermentation, respectively. This study offers an efficient approach for the quantitative assessment of Baijiu Daqu quality, as well as the control and improvement of medium-high Daqu quality.

Changes in Polyphenols and Antioxidant Activity in Fermentation Substrate during Maotai-Flavored Liquor Processing

To investigate the changes in phenols and antioxidant capacity in fermented grains during different stages of the fermentation process (Xiasha, Zaosha, and single-round stages) of Maotai-flavored liquor, the total phenolic contents of 61 samples, collected in different stages, were analyzed via the Folin-Ciocalteu method, and the phenolic compounds were then identified by high-performance liquid chromatography (HPLC). Subsequently, the antioxidant activities were determined using the DPPH free radical scavenging rate and ABTS and FRAP antioxidant capacities. The correlations among the total phenolic contents, individual phenolics, and three antioxidant activities of the samples were analyzed. The results show that the total phenolic contents of the fermented samples did not change significantly in the Xiasha and Zaosha stages but showed an upward trend in the single-round stage. A total of 12 phenol acids were identified in the fermented grains, including 5 phenolic acids (e.g., ferulic acid and caffeic acid), 4 flavonoids (e.g., luteolin and apigenin), and 3 proanthocyanidins (e.g., apigeninidin), for which the DPPH free radical scavenging rates and ABTS and FRAP antioxidant capacities of all of the fermented grain samples ranged from 78.91 ± 4.09 to 98.57 ± 1.52%, 3.23 ± 0.72 to 13.69 ± 1.40 mM Trolox, and 5.06 ± 0.36 to 14.10 ± 0.69 mM FeSO4, respectively. The total phenolic contents of the fermented grain samples were significantly and positively correlated with the ABTS and FRAP (p ≤ 0.05), while no significant correlations were found between total phenolic content and DPPH. In general, the total phenolic content, phenolic substances, and antioxidant capacity of the fermented grains exhibited changes during the fermentation process in liquor production, and the phenolic components contributed more to the antioxidant properties of the fermented grains. The present study provides a theoretical reference for analyzing the dynamic changes and antioxidant properties of functional phenolic components in fermented grains.

Investigation on fresh bamboo replacing rice husks for brewing light-aroma Baijiu

Husks are the main source of bran and furfural flavor in traditional Chinese light-aroma Baijiu, but they negatively affect its smell and taste. Here, bran husks were replaced with fresh bamboo to brew light-aroma Baijiu. Flavor components in Jiupei and Baijiu were detected through headspace solid-phase microextraction with gas chromatography-mass spectrometry, and physicochemical properties were assessed; flavor results were obtained from correlation, principal component, and cluster analyses. Starch and reducing sugar content in Jiupei negatively correlated with moisture, alcohol content, and acidity. Fresh bamboo reduced furfural from bran husks in Jiupei by 88.5% and increased alcohol distillation by 51%; it also improved starch efficiency (5%). Surprisingly, isovanillin was found to be present in Baijiu. Total Baijiu yield (57% ± 2.01%) was attained when crushed bamboo size was 1.5 cm × 0.3 cm × 0.3 cm. This study supports the use of fresh bamboo (an eco-friendly alternative for husks) in brewing light-aroma Baijiu. PRACTICAL APPLICATION: The use of fresh bamboo as a replacement for rice husks in brewing light-aroma Baijiu was investigated. It attenuated the chaff taste in light-aroma Baijiu and increased the liquor yield. Surprisingly, isovanillin was also present in the base Baijiu, and it added to the fragrance. This study not only supports the use of bamboo as an auxiliary material for brewing light-aroma Baijiu but also provides a reference for brewing light-aroma Baijiu with alternative auxiliary materials.

“Key Factor” for Baijiu Quality: Research Progress on Acid Substances in Baijiu

Baijiu is the national liquor of China, which has lasted in China for more than 2000 years. Abundant raw materials, multi-strain co-fermentation, and complex processes make the secrets of baijiu flavor and taste still not fully explored. Acid substances not only have a great influence on the flavor and taste of baijiu, but also have certain functions. Therefore, this paper provides a systematic review for the reported acid substances, especially for their contribution to the flavor and functional quality of baijiu. Based on previous studies, this paper puts forward a conjecture, a suggestion, and a point of view, namely: the conjecture of “whether acid substances can be used as ‘key factor’ for baijiu quality “; the suggestion of “the focus of research on acid substances in baijiu should be transferred to evaluating their contribution to the taste of baijiu”; and the view of “acid substances are ‘regulators’ in the fermentation process of baijiu”. It is worth thinking about whether acid substances can be used as the key factors of baijiu to be studied and confirmed by practice in the future. It is hoped that the systematic review of acid substances in baijiu in this paper can contribute to further in-depth and systematic research on baijiu by researchers in the future.