In this study, the feasibility of improving the extraction yield of green tea antioxidant polyphenols by the combination of ultrasound-assisted extraction (UAE) and deep eutectic solvents (DESs) was investigated. Choline chloride (ChCl)-glycerol was selected as the best DES among 12 ChCl-based DESs to extract tea antioxidant polyphenols. Subsequently, the influences of extraction parameters on total phenolic content (TPC) values were investigated, and liquid/solid ratio, ultrasonic power, and ultrasonic time were optimized based on the response surface methodology. The optimal extraction conditions were a liquid to solid ratio of 36:1 (mL/g), ultrasonic power of 461.5 W, and ultrasonic time of 21 min, with the highest TPC value of 243 ± 7 mg gallic acid equivalent (mg GAE)/g dry weight (DW), which was 13% higher than that before optimization. In addition, under the optimal extraction conditions, tea polyphenolic extract exhibited higher antioxidant activity compared with conventional extraction methods. Four major catechins in the green tea extracts, including (−)-epicatechin (EC), (−)-epigallocatechin (EGC), (−)-epicatechin gallate (ECG) and (−)-epigallocatechin gallate (EGCG) were identified and quantified by high-performance liquid chromatography. In addition, scanning electron microscopy (SEM) analysis revealed that UAE-DES effectively disrupted the green tea leaf cells, thereby improving tea polyphenol yield. In summary, UAE-DES is an ideal green extraction method for the extraction of tea antioxidant polyphenols.

Riboflavin, also known as vitamin B2, plays an important role in human cell metabolism and participates in various redox reactions and in energy utilization. In this study, 90 riboflavin-producing lactic acid bacteria (LAB) were screened out from pickle juices. The yields of riboflavin in these LAB were about 0.096–0.700 mg/L, and one strain, Lactobacillus plantarum RYG-YYG-9049, was found to produce the highest riboflavin content. Next, roseoflavin was used to induce the spontaneous mutation of RYG-YYG-9049, and selected roseoflavin-resistant colonies generally produced higher riboflavin contents, ranging from 1.013 to 2.332 mg/L. The No. 10 mutant, L. plantarum RYG-YYG-9049-M10, had the highest riboflavin content. Next, the molecular mechanism of enhancing riboflavin production in RYG-YYG-9049-M10 was explored, leading to the finding that roseoflavin treatment did not change the rib operons including the ribA, ribB, ribC, ribH, and ribG genes. Unexpectedly, however, this mechanism did induce an insertion of a 1059-bp DNA fragment in the upstream regulatory region of the rib operon, as compared to the wild-type RYG-YYG-9049. To the best of our knowledge, this is the first report that roseoflavin could induce an insertion of DNA fragment in LAB to increase riboflavin content, representing a new mutation type that is induced by roseoflavin. Finally, in order to fortify riboflavin content in soymilk, RYG-YYG-9049 and RYG-YYG-9049-M10 were used to ferment soymilk, and several fermentation parameters were optimized to obtain the fermented soymilk with riboflavin contents of up to 2.920 mg/L. In general, roseoflavin induction is an economical and feasible biotechnological strategy to induce riboflavin-overproducing LAB, and this strategy can be used to develop LAB-fermented functional foods that are rich in riboflavin.

In this study, the efficiency of microwave-assisted hydro-distillation (MAHD) to extract essential oil from Cinnamomum camphora leaf, and the recovery of polyphenols from extract fluid were investigated. The effects of microwave power, liquid-to-material ratio, and extraction time on the extraction efficiency were studied by a single factor test as well as the response surface methodology (RSM) based on the central composite design method. The optimal extraction conditions were a microwave power of 786.27 W, liquid-to-material ratio of 7.47:1 mL/g, and extraction time of 35.57 min. The yield of essential oil was 3.26 ± 0.05% (w/w), and the recovery of polyphenols was 4.97 ± 0.02 mg gallic acid equivalent/g dry weight under the optimal conditions. Furthermore, the comprehensive two-dimensional gas chromatography-time-of-flight mass spectrometry (GC×GC-TOFMS) was used to characterize the essential oils of fresh and fallen leaves, and 159 individual compounds were tentatively identified, accounting for more than 89.68 and 87.88% of the total contents, respectively. The main ingredients include sabinene, l-β-pinene, β-myrcene, α-terpineol, 3-heptanone, and β-thujene, as well as δ-terpineol and 3-heptanone, which were first identified in C. camphora essential oil. In conclusion, the MAHD method could extract essential oil from C. camphora with high efficiency, and the polyphenols could be obtained from the extract fluid at the same time, improving the utilization of C. camphora leaf.

An ultrasonic-assisted extraction (UAE) method was adopted to extract natural antioxidants from edible Gordonia axillaris fruit. Single-factor experiments and response surface methodology were conducted to investigate the influences of five different parameters on antioxidant capacity. The optimal conditions of the UAE were 39.78% ethanol, 30.94 mL/g solvent/material ratio, 59.47 min extraction time, 40 °C temperature, and 400 W ultrasonication power. The antioxidant capacity was 525.05 ± 14.34 µmol Trolox/g DW under the optimal conditions, which was in agreement with the predicted one (531.71 µmol Trolox/g DW). Additionally, in comparison with two traditional methods (maceration and Soxhlet extraction), the established UAE method greatly improved the yield of antioxidants and significantly reduced the extraction time. Besides, nine phenolic compounds were identified and quantified in the extract of Gordonia axillaris fruits by ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS), including rutin, gallic acid, protocatechuic acid, epicatechin, 2-hydrocinnamic acid, p-coumaric acid, quercetin, epicatechin gallate, and ferulic acid. The richness of phenolic compounds in the Gordonia axillaris fruits indicated its potential health benefits, and its extract rich in antioxidants could be developed into functional food or nutraceuticals with the potential to prevent certain diseases induced by oxidative stress, such as cardiovascular diseases and cancers. This study also provided a way to enhance the economic values of Gordonia axillaris fruits compared to raw fruits.