Coffee is one of the most widely consumed beverages worldwide, primarily due to the stimulating effects attributed to its caffeine content. However, excessive intake of caffeine results in negative effects, including palpitations, anxiety, and insomnia. Therefore, low-caffeine coffee has captivated growing consumer interest, highlighting its significant market potential. Traditional decaffeination methods often lead to non-selective extraction, resulting in a loss of desirable flavor compounds, thereby compromising coffee quality. In recent years, microbial fermentation has emerged as a promising, targeted, and safe approach for reducing caffeine content during processing. Additionally, mixed-culture fermentation further enhances coffee flavor and overcomes the drawbacks of monoculture fermentation, such as low efficiency and limited flavor profiles. Nonetheless, several challenges are yet to be resolved, including microbial tolerance to caffeine and related alkaloids, the safety of fermentation products, and elucidation of the underlying mechanisms behind microbial synergy in co-cultures. This review outlines the variety of microorganisms with the potential to degrade caffeine and the biochemical processes involved in this process. It explores how microbes tolerate caffeine, the safety of metabolites produced during fermentation, and the synergistic effects of mixed microbial cultures on the modulation of coffee flavor compounds, including esters and carbonyls. Future directions are discussed, including the screening of alkaloid-tolerant strains, constructing microbial consortia for simultaneous caffeine degradation for flavor enhancement, and developing high-quality low-caffeine coffee.

Coffee (Coffea sp.) bean variety and harvesting periods are factors that directly affect its overall quality. In this study, we investigated the effects of four different harvesting periods (December, January, February and March) on the physicochemical and sensory properties of two coffee bean Catimor varieties (7963 and T8667) planted in the same orchard. Physiological characteristics were significantly affected by the delay in harvest periods, specifically the physicochemical properties of each coffee bean variety between the periods. For the green 7963 variety, the defect rate decreased from 11.08% to 4.19% while chlorogenic acid content increased from 3.78% to 4.99% as the harvest period was delayed. The 7963 variety harvested in February and March and T8667 variety harvested in February had the best quality performance, and their cupping scores were significantly higher than those harvested in other periods. Furthermore, a high correlation was found between physical attributes (defect rate, thousand-grain weight, and green bean size), chemical components (lipids, proteins, chlorogenic acid, caffeine, and trigonelline) and cupping scores.

The quality of different coffee varieties varies, and the corresponding bioactive value of coffee processing byproducts is often overlooked. For that, we employed HPLC, GC-MS, and electronic sensory analyses to evaluate the key bioactive components, antioxidant potential, and flavor traits of green coffee bean and coffee processing byproducts of seven coffee varieties. The results showed that green coffee beans (Oe+Ie) and exocarp (Ep) possessed strong antioxidant activity and high total phenolic content (TPC), caffeine and trigonelline content. Among the varieties, DR390 contained higher levels of total phenols, caffeine, and trigonelline, whereas DR402 was rich in caffeine and chlorogenic acid. In addition, RY3 exhibited higher TPC, total flavonoid content (TFC), caffeine, and chlorogenic acid. The parchment (Pc) layer was rich in soluble sugars (1.83–5.43%), while the silverskin (Sk) contained relatively high levels of chlorogenic acid (3.58–4.69 mg/g). Flavor analysis identified eleven classes of volatile compounds in green coffee bean (Oe+Ie) and byproducts (Ep, Pc, Sk), with esters, ketones, alcohols, and aldehydes being the most prevalent. Seven key aroma compounds, including methyl salicylate, phenethyl alcohol, nonanal, and benzaldehyde, were identified across the various structural tissues of coffee fruit. Distinct flavor profiles were observed among the coffee fruit parts: green coffee bean (Oe+Ie) was nutty; the Ep showed fruity and cocoa-like aromas; the Pc and Sk exhibited papery and nutty aromas, respectively. Varieties DR397, DR402, and RY3 exhibited pronounced aroma profiles. Comprehensive analysis showed that DR402 and RY3 had higher overall scores for bioactive and flavor components than other varieties in their groups. In summary, green coffee bean (Oe+Ie) exhibited strong antioxidant activity and high levels of bioactive compounds. Coffee byproducts, such as the Ep, hold potential for extracting natural antioxidants and bioactive compounds to develop specialty products or for other high-value utilization.

This study focuses on the storage process of coffee beans, employing electron beam irradiation (EBI) to investigate the comprehensive effects of different irradiation doses on coffee beans and their storage process, including physicochemical indicators, microbial abundance, and flavor compounds. The results showed that a 2 kGy dose of EBI could effectively reduce the total number of bacteria, molds, and yeasts in green coffee beans (GCBs), while a dose of 4 kGy can completely inactivate the bacteria and maintain this effect for one month. Compared with the control sample that has not undergone processing by EBI (CK), the crude fat content of the irradiated samples decreased, accompanied by a significant increase in acid value. After 30 days of storage, compared with the CK-30 sample, EBI treatment significantly reduced both the moisture content and overall brightness value of GCB. The analysis of aroma compounds in roasted coffee beans (RCBs) revealed that substances related to Maillard reaction, caramelization reaction and sugar degradation, such as 2-Furanmethanol and acetic acid, changed in the irradiated samples, but had no significant effect on the characteristic components like caffeine and the aroma detected by the electronic nose. The obtained results provide a scientific basis for applying irradiation technology to the preservation of coffee beans.