| Pomegranate is mainly cultivated in California for production in the U.S. In California alone, about 20.5 thousand tons of pomegranate fruits are produced each year. Pomegranate fruits are consumed as fresh or processed juice and wine, etc. The industrialized production of pomegranate fruits creates a large amount of pomegranate marc as a by-product, which not only results in serious resource waste but also enviromental problems. It has been reported that pomegranate fruits are rich in polyphenol antioxidants and the most of polyphenol antioxidants consist in peel and seed. Therefore, further researches in pomegranate marc are important and meaningful. Conventional extraction methods have many disadvantages such as low extraction efficiency and yield, as well as undesirable effects on bioactive component activities. Thus new technologies need to be developed for solving these problems, and at the same time, related theory development need to be studied. Therefore, this research has good practice guidance with value in theory.The objectives of this study were to determine the polyphenol content in pomegranate marc, evaluate the conventional and ultrasound-assisted extractions of pomegranate peel polyphenol and their kinetics, and examine the feasibility of converting pomegranate residue into biogas energy. By producing value-added products and extending industrial chain, this research will improve the availability of pomegranate marc resource, and bring economic benefits to pomegranate marc production.The polyphenol and oil were extracted from Madera pomegranate marc. The determined results showed that pomegranate seed was rich in oil with plentiful unsaturated fatty acids and its oil yield was 13.8%d.b.. In addition, pomegranate peel was abundant in polyphenol with high yield of 10.6%d.b. and antioxidant activity (expressed as the DPPH scavenging activity per gram of polyphenol) of 6.6 g g~-1, respectively. Furthermore, pomegranate peel polyphenol had good thermal stability for drying treatment.The conventional extraction and its kinetics of pomegranate peel polyphenol were systemically studied. The determined optimum condition of conventional extraction was peel particle size of 0.2 mm, water to pomegranate peel ratio of 50:1 (w/w), temperature of 25℃and time of 2 min. Under this optimum condition, the polyphenol yield and DPPH scavenging activity were 11.5%d.b. and 6.2 g g~-1, respectively. The mathematical kinetic models were successfully developed for simulating the conventional extraction processes of pomegranate peel polyphenol.The ultrasound technology was used to increase the polyphenol yield or shorten the extraction time. Under the extraction condition at peel particle size of 1.4 mm, water to pomegranate peel ratio of 50:1 (w/w) and temperature of 25℃, and the continuous ultrasound condition at intensity level of 59.2 W cm~-2, the polyphenol yield was increased by 24%and the extraction time was decreased by 90%compared to the conventional extraction. Under the same extraction condition, and the pulsed ultrasound condition at intensity level of 59.2 W cm~-2 and pulsed duration and interval ratio of 5s/5s, the polyphenol yield was increased by 22%and the extraction time was decreased by 87%compared to the conventional extraction. However, the pulsed ultrasound-assisted extraction, saved 50%of electrical energy compared to the continuous ultrasound-assisted extraction, was superior for producing pomegranate peel polyphenol. Under this condition of pulsed ultrasound-assisted extraction, the polyphenol yield and DPPH scavenging activity were 14.5%d.b. and 5.8 g g~-1, respectively. A second-order kinetic model was successfully developed for describing the ultrasound-assisted extraction process of pomegranate peel polyphenol.A new High Performance Liquid Chromatography (HPLC) analytical method was established, which can simultaneously determine the punicalagin A, punicalagin B, gallic acid and ellagic acid in pomegranate peel polyphenol, and distinguish true from false in commercial pomegranate juice drinks. The built HPLC analytical method had low limit of detection and limit of quantitation, high recovery rate and daily reproducibility, dramatically reduced retention time and increased detection efficiency.The pomegranate peel polyphenol, produced at peel particle size of 0.2 mm, water to pomegranate peel ratio of 50:1 (w/w), temperature of 25℃and time of 2 min, was autoclaved at 121℃for 10 s. The results showed that the pomegranate peel polyphenol had good thermal stability for sterilization treatment. Subsequently, the autoclaved pomegranate peel polyphenol were stored at different pH, temperature and packaging method. The results showed that the pomegranate peel polyphenol remained good storage stability under the storage condition at pH value of 3.5, temperature of 4℃, time of 30 day and with packaging treatment. Under this storage condition, pomegranate peel polyphenol had good industrial, color and spectral characteristics stabilities, high polyphenol concentration and DPPH scavenging activity (2.2x10~3 mg L~-1 and 5.1 g g~-1, respectively), and high gallic acid, punicalagin A, punicalagin B and ellagic acid concentrations (20.8,160.8,181.8 and 85.2 mg L~-1, respectively).The anaerobic digestion method was used to produce biogas with high methane content from pomegranate residue after extracting polyphenol or oil. The determined optimum condition of anaerobic digestion was temperature of 35℃, substrate to mesophilic inoculum ratio of 1:2 (w/w), reactor working volume of 500 mL, initial organic loading of 5.0 gVS L~-1 and time of 20 day. Under this optimum condition, the biogas yield and methane content were 292 mL gVS~-1 and 61.2%, respectively. The results showed that the integrated process of extraction followed by anaerobic digestion for recovery of nutraceuticals and natural biogas energy from pomegranate marc was a feasibly value-added utilization project. A modified Gompertz kinetic model was successfully developed for predicting the biogas production potential of pomegranate residue. |
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