Phenolic extraction parameters and effects of wet and dried pomegranate peel were studied, aiming to increase the extraction sustainability with reduced cost. The chemical characteristics of the extracted components were also evaluated. The study in Chapter 3 investigated the potential of developing functional food fortified with a value-added ingredient from pomegranate peel extract, specifically Greek Style Yogurt. Products with different levels of protein content and phenolic content were formulated to study the chemical and sensory properties, which provided solid guidance for future product development. In the research of Chapter 4, the hypolipidemic properties of pomegranate peel and extract were investigated in vivo using hamster models. Currently, no literature is available on the functionality of complete pomegranate peel and extract. In this study, dutch bucket for tomatoes it was found that the pomegranate peel and extract were effective in lowering blood cholesterol in hamsters fed with high-fat diets. The study in Chapter 5 studied the co-extraction mechanism of pectin and polyphenol for improved extract yield and phenolic stability.
Ultrasound extraction of pectin and polyphenol in citric acid from pomegranate peel was tested and the corresponding physicochemical properties were evaluated. Unlike most of the research using inorganic acid for extraction, this research utilized GRAS organic acid and provided functional ingredients from fruit by-products without safety concerns. Conclusions and future directions on reutilizing the pomegranate waste as food ingredients are detailed in Chapter 6.Pomegranate belongs to the family Punicaceae. It has been grown since ancient times for its delicious fruit and as an ornamental plant for its red, orange, or occasionally creamy yellow flowers. The estimated global cultivation area for pomegranate is about 300,000 ha, with fruit production of 3.0 million metric tons . Spanish missionaries brought pomegranate to the Americas in the 1500s . Wonderful, a primary cultivar in the U.S., was discovered in Florida and brought to California in 1896. Since then, pomegranate has been grown abundantly in California and Arizona, where mild winters enable the fruits to reach the quality necessary for successful commercial production. In 2015, about 282,000 tons of pomegranate fruit were grown in California, with an economic value of $115.4 million .
Pomegranate consists of three major parts , namely pomegranate peel , pomegranate seed , and pomegranate aril that is the flesh part for pomegranate juice production. Teh studied the different fruit part distribution of 5 pomegranate cultivars grown in California, observed a range of 38.33~50.38% PJ, 38.77~53.01% PP, and 7.71~12.10% PS. The study also determined the components of PP and PS through proximate analysis. The peel portion consisted of 90.6~91.9% carbohydrate as the principal constituent, followed by 3.1~3.9% protein, 1.3~2.3% fat, and 3.3~4.3% ash or minerals. The PS contained higher proportions of protein and fat and included 60.5~71.8% carbohydrate and 1.6~2.5% minerals. PJ consisted of 85% water, 10% total sugars, organic acids,amino acids, and phenolics. Pomegranate exhibits a sweet, sweet-sour, or sour taste, which color ranges from white to pink and red .Traditional processes in the pomegranate juice industry squeezed the whole pomegranate, which had low yield, impurity, and bitter taste due to non-edible parts. Nowadays, novel techniques introduced a deseeding step at the beginning. Then the seed, aril, and juice are separated from the peel and squeezed, while the peel and the remaining pulp are discarded as wastes in landfills or used as animal feed. The juice stream continues to go through the processes of pasteurization, centrifugation, membrane process, storage, and quality assessment. Other juice extraction methods and their features were also discussed by as shown in Figure 1.2. PJ processing generates two types of solid by-products: peel and seeds. PP is non-edible and comprised mainly of bio-active compounds, such as hydrolyzable tannins at concentrations ranging from 27 to 172 g kg-1 , flavonoids ,and complex polysaccharides .
Therefore, PP is an excellent source of phenolic compounds, tannins, flavonoids, sterols, fatty acids, dietary fiber, minerals, and vitamins.Fruit and vegetable pomace has a long history of simply being disposed of in landfills or underutilized as fertilizers and soil conditioners. Several studies investigated the health potential of supplementing PP into animal feed. Modaresi et al., added 12% pomegranate seed pulp into the goat diets and observed increased polyunsaturated and conjugated fatty acids in goat milk. A feed with 1-2% PP lowered cholesterol levels and improved oxidative stability in the harvested boiler chicken meats . Shabtay et al. supplemented PP in calves’ diets and observed a significant increase in weight gain and blood antioxidant contents in the ruminants. Therefore, pomegranate pomace demonstrated great potentials for nutritional feed with improved health benefits in ruminant and chicken feed. Due to the massive quantity of pomace, the convenience of disposal, and low realizable revenue from current waste utilization practices, processors and farmers have a low incentive to apply alternative waste management methods. With the pressure of climate change, energy shortage, and increasing nutritional needs, creating value-added products from the by-products would be an outstanding solution to incentivize novel waste practices. Food additives and packaging materials With an enormous amount and variety of polyphenols within the pomace, pomegranate by-products demonstrated great antioxidant and anti-microbial properties, which contributed to diverse application potentials as food additives and packaging materials. Lipid oxidation is the principal deteriorative reaction during food processing and storage. It sharply reduces the product shelf life, destroys essential nutritional components, and generates toxic compounds which pose hazards to human health . Synthetic antioxidants have been dominantly applied in the food industry to prevent oxidation, such as butylated hydroxytoluene and butylated hydroxyanisole . Natural antioxidants are gaining attention as consumers prefer safe and natural ingredients . Topuz et al. incorporated alcoholic extract of PP into anchovy fish oil and observed a dose-dependent inhibitory effect on lipid oxidation, especially at a concentration of 500–1000 ppm. The antioxidant capacity of 500 ppm of PP extract was comparable with that of 100 ppm of BHT, indicating that PPE could be applied as a potent antioxidant. Turgut et al., infused PPE into freshly minced beef at 5000/10000 ppm and compared it with 100 ppm BHT.Their results demonstrated a lower thiobarbituric acid reactive substances value, peroxide formation, and other parameters, suggesting promising oxidation retarding effect of lipid and protein in pomegranate extract. However, they also observed a potential negative change of sensory value after extract addition, which required further research to quantitatively investigate the effects. Similar research also proved the preservative effects of pomegranate extract in burgers and cheese . A more comprehensive review on the practical use of PP in meat products was reported by Smaoui et al., . PP may also prevent foodborne illness, which has been a worldwide safety concern. In the USA, there were millions of cases related to food contamination and foodborne outbreak each year, posing a severe threat to public health . Traditional synthetic antimicrobial agents may have potential side effects, are expensive, blueberry grow pot and could induce drug resistance of microorganisms as their indiscriminate killing effects . Natural anti-microbial agents are needed. Pomegranate is rich in polyphenols, which can inhibit bacterial growth by interacting with the sulfhydryl groups of bacterial cell wall proteins and forming complexes, and then induce lysis . More applications of pomegranate by-products as anti-microbial agents could be found in Singh et al. . Biotechnological products Biofuel is considered an ideal alternative to fossil fuel, as fossil fuels are experiencing a rapid depletion, uncertainty in the price, and contributing to significant environmental pollution .
Biofuel is produced from biomass via thermochemical processes, including gasification, carbonization, pyrolysis, and direct combustion. Among all the methods, pyrolysis is considered the most viable due to its simplicity, cost-effectiveness, and wide range of final products . Siddiqui et al. studied the optimizedprocess parameters for biochar production from PP. Results showed that, at a temperature of 300 °C, the pyrolysis reaction time of 20 min and the particle size of 3 mm, biochar could be produced at a yield of 54.9% with an improved higher heating value at 23.5 from 14.61 MJ/kg of parent biomass. Besides energy supply, PP-based biochar also demonstrated a desirable ability in eliminating inorganic compounds from water and CO2capture/storage . As for biofuel, Demiray et al. optimized bioethanol production from PP by Saccharomyces cerevisiae and Pichia stipites. They successfully increased the ethanol yield produced by S. cerevisiae up to 44.9%. Ethanol productivity and Ethanol yield of S. cerevisiae increased to 0.46 g/L/h and 0.43 g/g, respectively. These findings along with other similar research have demonstrated that PP is a promising biofuel source.Polyphenols, a family of molecules, are commonly found in fruits, vegetables, nuts, seeds, flowers, and tree bark. These components fundamentally are plant metabolites to attract pollinators, but research concluded multiple pharmaceutical effects, including antioxidant, antimicrobial, anti-cancer, etc . This family derives from a fundamental polyphenol group . The structure ranges from simple elementary substances to complex polymerized molecules , contributing to a diversified classification profile . Furthermore, sugar residues can conjugate with the hydroxylgroups of natural polyphenols through direct linkage of the sugar unit to an aromatic carbon, further diversifying the polyphenol structure . Based on the number of phenol rings and the binding components, polyphenols can be classified into the following 5 types of sub-groups: hydroxybenzoic acid, hydroxycinnamic acid, flavonoids, stilbenes, and lignans , as illustrated in Figure 1.3.According to Fischer et al., , PP is an ideal source for polyphenol, as 48 types of polyphenols were detected within, including 9 anthocyanins, 2 gallotannins, 22 ellagitannins , 2 gallagyl esters, 4 hydroxybenzoic acids, 7 hydroxycinnamic acids, and 1 dihydroflavonol. Among the polyphenols in pomegranate, punicalagin is the most abundant and unique water-soluble ellagitannin within. Besides PP and PJ, PUs are also commonly found in the leaves of Lafoensia pacari .The synthesis pathway of PU is shown in Figure 1.4. Phenolic acids including two gallic acids and ellagic acid are combined to form gallagic acid. With glucose addition, gallagic acid can form punicalin and be further transformed into PU by adding an EA. The difference in the glucose carbon-1 induces two isomers of PU . These features provided higher functionality with a large number of hydroxyl groups and a lower chance of degradation. A typical phenolic composition distribution in HPLC analysis is shown in Figure 1.5 .MAE is another common extraction method with reducing extraction time and solvent consumption. The heat and mass transfer processes take place at the same time and accelerate the overall extraction. Kaderides, Papaoikonomou, Serafim, & Goula compared the extraction performance of microwave-assisted extraction and the UAE. Results showed that the optimal MAE condition was using 60mL 50% aqueous ethanol per gram at 600 W power for 4 mins, with an extract yield of 199.4 mg/g GAE, PU yield of 143.64 mg/g, and radical scavenging activity of 94.91%. In contrast to 10 mins of UAE at 52 W power using 32.2mL water per gram peel at 35⁰C, MAE achieved 1.7 times higher extract yield in a shorter processing time , which was due to higher cell destruction but similar PU yield and scavenging activity. Limited research has focused on this topic so far. Researchers suggested a focus on the MAE-assisted process to achieve a high yield of polyphenols as well as extract with great polyphenol profile and quality.PU is sensitive to temperature and pH. Therefore, conventional hot acidic processing methods might increase the hydrolysis of PU and reduce its bio-activity. Alexandre et al. proposed that cellulase and pectinase degraded the cell wall and released the intact PU along with pectin. They compared extraction under 300/600 MPa high pressure with that using 4% cellulase and pectinase. As result, enzymatic extraction yielded 1481.29 μg/g TPC with 62.9% PU, significantly higher than extraction at 300MPa and slightly lower than 600 MPa . Talekar, Patti, Vijayraghavan, & Arora, applied 55 U/g cellulases at a solvent ratio of 15 mL/g for 4h with 20 min ultrasound treatment. As the results, 84.8 mg/g PU was recovered, accounting for 71.2% of its TPC and was superior to the ones recovered by a conventional method . This result demonstrated reduced hydrolysis of PU under mild enzymatic extraction. Since enzymes could be costly due to low recovery and reusability, biocatalyst became a more sustainable option. Biocatalyst immobilizes enzymes onto solid phase for selective enzyme recovery after the reaction. Talekar et al., experimented with extraction with magnetic nanocatalyst of FeSO47H2O and FeCl36H2O solutions, which yielded 64.2–66.5 mg/g PU . It was lower than their previous research using cellulase . However, the nanocatalysts are recyclable and could reduce the cost of cellulase.Compared to other processing methods, enzymatic extraction might have less TPC. On the other hand, it is desirable for PU retention.